bpf-helpers(7) — Linux manual page

NAME | DESCRIPTION | HELPERS | EXAMPLES | LICENSE | IMPLEMENTATION | SEE ALSO | COLOPHON

BPF-HELPERS(7)                                            BPF-HELPERS(7)

NAME         top

       BPF-HELPERS - list of eBPF helper functions

DESCRIPTION         top

       The extended Berkeley Packet Filter (eBPF) subsystem consists in
       programs written in a pseudo-assembly language, then attached to
       one of the several kernel hooks and run in reaction of specific
       events. This framework differs from the older, "classic" BPF (or
       "cBPF") in several aspects, one of them being the ability to call
       special functions (or "helpers") from within a program.  These
       functions are restricted to a white-list of helpers defined in
       the kernel.

       These helpers are used by eBPF programs to interact with the
       system, or with the context in which they work. For instance,
       they can be used to print debugging messages, to get the time
       since the system was booted, to interact with eBPF maps, or to
       manipulate network packets. Since there are several eBPF program
       types, and that they do not run in the same context, each program
       type can only call a subset of those helpers.

       Due to eBPF conventions, a helper can not have more than five
       arguments.

       Internally, eBPF programs call directly into the compiled helper
       functions without requiring any foreign-function interface. As a
       result, calling helpers introduces no overhead, thus offering
       excellent performance.

       This document is an attempt to list and document the helpers
       available to eBPF developers. They are sorted by chronological
       order (the oldest helpers in the kernel at the top).

HELPERS         top

       void *bpf_map_lookup_elem(struct bpf_map *map, const void *key)

              Description
                     Perform a lookup in map for an entry associated to
                     key.

              Return Map value associated to key, or NULL if no entry
                     was found.

       long bpf_map_update_elem(struct bpf_map *map, const void *key,
       const void *value, u64 flags)

              Description
                     Add or update the value of the entry associated to
                     key in map with value. flags is one of:

                     BPF_NOEXIST
                            The entry for key must not exist in the map.

                     BPF_EXIST
                            The entry for key must already exist in the
                            map.

                     BPF_ANY
                            No condition on the existence of the entry
                            for key.

                     Flag value BPF_NOEXIST cannot be used for maps of
                     types BPF_MAP_TYPE_ARRAY or
                     BPF_MAP_TYPE_PERCPU_ARRAY  (all elements always
                     exist), the helper would return an error.

              Return 0 on success, or a negative error in case of
                     failure.

       long bpf_map_delete_elem(struct bpf_map *map, const void *key)

              Description
                     Delete entry with key from map.

              Return 0 on success, or a negative error in case of
                     failure.

       long bpf_probe_read(void *dst, u32 size, const void *unsafe_ptr)

              Description
                     For tracing programs, safely attempt to read size
                     bytes from kernel space address unsafe_ptr and
                     store the data in dst.

                     Generally, use bpf_probe_read_user() or
                     bpf_probe_read_kernel() instead.

              Return 0 on success, or a negative error in case of
                     failure.

       u64 bpf_ktime_get_ns(void)

              Description
                     Return the time elapsed since system boot, in
                     nanoseconds.  Does not include time the system was
                     suspended.  See: clock_gettime(CLOCK_MONOTONIC)

              Return Current ktime.

       long bpf_trace_printk(const char *fmt, u32 fmt_size, ...)

              Description
                     This helper is a "printk()-like" facility for
                     debugging. It prints a message defined by format
                     fmt (of size fmt_size) to file
                     /sys/kernel/debug/tracing/trace from DebugFS, if
                     available. It can take up to three additional u64
                     arguments (as an eBPF helpers, the total number of
                     arguments is limited to five).

                     Each time the helper is called, it appends a line
                     to the trace.  Lines are discarded while
                     /sys/kernel/debug/tracing/trace is open, use
                     /sys/kernel/debug/tracing/trace_pipe to avoid this.
                     The format of the trace is customizable, and the
                     exact output one will get depends on the options
                     set in /sys/kernel/debug/tracing/trace_options (see
                     also the README file under the same directory).
                     However, it usually defaults to something like:

                        telnet-470   [001] .N.. 419421.045894: 0x00000001: <formatted msg>

                     In the above:

                        • telnet is the name of the current task.

                        • 470 is the PID of the current task.

                        • 001 is the CPU number on which the task is
                          running.

                        • In .N.., each character refers to a set of
                          options (whether irqs are enabled, scheduling
                          options, whether hard/softirqs are running,
                          level of preempt_disabled respectively). N
                          means that TIF_NEED_RESCHED and
                          PREEMPT_NEED_RESCHED are set.

                        • 419421.045894 is a timestamp.

                        • 0x00000001 is a fake value used by BPF for the
                          instruction pointer register.

                        • <formatted msg> is the message formatted with
                          fmt.

                     The conversion specifiers supported by fmt are
                     similar, but more limited than for printk(). They
                     are %d, %i, %u, %x, %ld, %li, %lu, %lx, %lld, %lli,
                     %llu, %llx, %p, %s. No modifier (size of field,
                     padding with zeroes, etc.) is available, and the
                     helper will return -EINVAL (but print nothing) if
                     it encounters an unknown specifier.

                     Also, note that bpf_trace_printk() is slow, and
                     should only be used for debugging purposes. For
                     this reason, a notice block (spanning several
                     lines) is printed to kernel logs and states that
                     the helper should not be used "for production use"
                     the first time this helper is used (or more
                     precisely, when trace_printk() buffers are
                     allocated). For passing values to user space, perf
                     events should be preferred.

              Return The number of bytes written to the buffer, or a
                     negative error in case of failure.

       u32 bpf_get_prandom_u32(void)

              Description
                     Get a pseudo-random number.

                     From a security point of view, this helper uses its
                     own pseudo-random internal state, and cannot be
                     used to infer the seed of other random functions in
                     the kernel. However, it is essential to note that
                     the generator used by the helper is not
                     cryptographically secure.

              Return A random 32-bit unsigned value.

       u32 bpf_get_smp_processor_id(void)

              Description
                     Get the SMP (symmetric multiprocessing) processor
                     id. Note that all programs run with preemption
                     disabled, which means that the SMP processor id is
                     stable during all the execution of the program.

              Return The SMP id of the processor running the program.

       long bpf_skb_store_bytes(struct sk_buff *skb, u32 offset, const
       void *from, u32 len, u64 flags)

              Description
                     Store len bytes from address from into the packet
                     associated to skb, at offset. flags are a
                     combination of BPF_F_RECOMPUTE_CSUM (automatically
                     recompute the checksum for the packet after storing
                     the bytes) and BPF_F_INVALIDATE_HASH (set
                     skb->hash, skb->swhash and skb->l4hash to 0).

                     A call to this helper is susceptible to change the
                     underlying packet buffer. Therefore, at load time,
                     all checks on pointers previously done by the
                     verifier are invalidated and must be performed
                     again, if the helper is used in combination with
                     direct packet access.

              Return 0 on success, or a negative error in case of
                     failure.

       long bpf_l3_csum_replace(struct sk_buff *skb, u32 offset, u64
       from, u64 to, u64 size)

              Description
                     Recompute the layer 3 (e.g. IP) checksum for the
                     packet associated to skb. Computation is
                     incremental, so the helper must know the former
                     value of the header field that was modified (from),
                     the new value of this field (to), and the number of
                     bytes (2 or 4) for this field, stored in size.
                     Alternatively, it is possible to store the
                     difference between the previous and the new values
                     of the header field in to, by setting from and size
                     to 0. For both methods, offset indicates the
                     location of the IP checksum within the packet.

                     This helper works in combination with
                     bpf_csum_diff(), which does not update the checksum
                     in-place, but offers more flexibility and can
                     handle sizes larger than 2 or 4 for the checksum to
                     update.

                     A call to this helper is susceptible to change the
                     underlying packet buffer. Therefore, at load time,
                     all checks on pointers previously done by the
                     verifier are invalidated and must be performed
                     again, if the helper is used in combination with
                     direct packet access.

              Return 0 on success, or a negative error in case of
                     failure.

       long bpf_l4_csum_replace(struct sk_buff *skb, u32 offset, u64
       from, u64 to, u64 flags)

              Description
                     Recompute the layer 4 (e.g. TCP, UDP or ICMP)
                     checksum for the packet associated to skb.
                     Computation is incremental, so the helper must know
                     the former value of the header field that was
                     modified (from), the new value of this field (to),
                     and the number of bytes (2 or 4) for this field,
                     stored on the lowest four bits of flags.
                     Alternatively, it is possible to store the
                     difference between the previous and the new values
                     of the header field in to, by setting from and the
                     four lowest bits of flags to 0. For both methods,
                     offset indicates the location of the IP checksum
                     within the packet. In addition to the size of the
                     field, flags can be added (bitwise OR) actual
                     flags. With BPF_F_MARK_MANGLED_0, a null checksum
                     is left untouched (unless BPF_F_MARK_ENFORCE is
                     added as well), and for updates resulting in a null
                     checksum the value is set to CSUM_MANGLED_0
                     instead. Flag BPF_F_PSEUDO_HDR indicates the
                     checksum is to be computed against a pseudo-header.

                     This helper works in combination with
                     bpf_csum_diff(), which does not update the checksum
                     in-place, but offers more flexibility and can
                     handle sizes larger than 2 or 4 for the checksum to
                     update.

                     A call to this helper is susceptible to change the
                     underlying packet buffer. Therefore, at load time,
                     all checks on pointers previously done by the
                     verifier are invalidated and must be performed
                     again, if the helper is used in combination with
                     direct packet access.

              Return 0 on success, or a negative error in case of
                     failure.

       long bpf_tail_call(void *ctx, struct bpf_map *prog_array_map, u32
       index)

              Description
                     This special helper is used to trigger a "tail
                     call", or in other words, to jump into another eBPF
                     program. The same stack frame is used (but values
                     on stack and in registers for the caller are not
                     accessible to the callee). This mechanism allows
                     for program chaining, either for raising the
                     maximum number of available eBPF instructions, or
                     to execute given programs in conditional blocks.
                     For security reasons, there is an upper limit to
                     the number of successive tail calls that can be
                     performed.

                     Upon call of this helper, the program attempts to
                     jump into a program referenced at index index in
                     prog_array_map, a special map of type
                     BPF_MAP_TYPE_PROG_ARRAY, and passes ctx, a pointer
                     to the context.

                     If the call succeeds, the kernel immediately runs
                     the first instruction of the new program. This is
                     not a function call, and it never returns to the
                     previous program. If the call fails, then the
                     helper has no effect, and the caller continues to
                     run its subsequent instructions. A call can fail if
                     the destination program for the jump does not exist
                     (i.e. index is superior to the number of entries in
                     prog_array_map), or if the maximum number of tail
                     calls has been reached for this chain of programs.
                     This limit is defined in the kernel by the macro
                     MAX_TAIL_CALL_CNT (not accessible to user space),
                     which is currently set to 32.

              Return 0 on success, or a negative error in case of
                     failure.

       long bpf_clone_redirect(struct sk_buff *skb, u32 ifindex, u64
       flags)

              Description
                     Clone and redirect the packet associated to skb to
                     another net device of index ifindex. Both ingress
                     and egress interfaces can be used for redirection.
                     The BPF_F_INGRESS value in flags is used to make
                     the distinction (ingress path is selected if the
                     flag is present, egress path otherwise).  This is
                     the only flag supported for now.

                     In comparison with bpf_redirect() helper,
                     bpf_clone_redirect() has the associated cost of
                     duplicating the packet buffer, but this can be
                     executed out of the eBPF program. Conversely,
                     bpf_redirect() is more efficient, but it is handled
                     through an action code where the redirection
                     happens only after the eBPF program has returned.

                     A call to this helper is susceptible to change the
                     underlying packet buffer. Therefore, at load time,
                     all checks on pointers previously done by the
                     verifier are invalidated and must be performed
                     again, if the helper is used in combination with
                     direct packet access.

              Return 0 on success, or a negative error in case of
                     failure.

       u64 bpf_get_current_pid_tgid(void)

              Return A 64-bit integer containing the current tgid and
                     pid, and created as such: current_task->tgid << 32
                     | current_task->pid.

       u64 bpf_get_current_uid_gid(void)

              Return A 64-bit integer containing the current GID and
                     UID, and created as such: current_gid << 32 |
                     current_uid.

       long bpf_get_current_comm(void *buf, u32 size_of_buf)

              Description
                     Copy the comm attribute of the current task into
                     buf of size_of_buf. The comm attribute contains the
                     name of the executable (excluding the path) for the
                     current task. The size_of_buf must be strictly
                     positive. On success, the helper makes sure that
                     the buf is NUL-terminated. On failure, it is filled
                     with zeroes.

              Return 0 on success, or a negative error in case of
                     failure.

       u32 bpf_get_cgroup_classid(struct sk_buff *skb)

              Description
                     Retrieve the classid for the current task, i.e. for
                     the net_cls cgroup to which skb belongs.

                     This helper can be used on TC egress path, but not
                     on ingress.

                     The net_cls cgroup provides an interface to tag
                     network packets based on a user-provided identifier
                     for all traffic coming from the tasks belonging to
                     the related cgroup. See also the related kernel
                     documentation, available from the Linux sources in
                     file
                     Documentation/admin-guide/cgroup-v1/net_cls.rst.

                     The Linux kernel has two versions for cgroups:
                     there are cgroups v1 and cgroups v2. Both are
                     available to users, who can use a mixture of them,
                     but note that the net_cls cgroup is for cgroup v1
                     only. This makes it incompatible with BPF programs
                     run on cgroups, which is a cgroup-v2-only feature
                     (a socket can only hold data for one version of
                     cgroups at a time).

                     This helper is only available is the kernel was
                     compiled with the CONFIG_CGROUP_NET_CLASSID
                     configuration option set to "y" or to "m".

              Return The classid, or 0 for the default unconfigured
                     classid.

       long bpf_skb_vlan_push(struct sk_buff *skb, __be16 vlan_proto,
       u16 vlan_tci)

              Description
                     Push a vlan_tci (VLAN tag control information) of
                     protocol vlan_proto to the packet associated to
                     skb, then update the checksum. Note that if
                     vlan_proto is different from ETH_P_8021Q and
                     ETH_P_8021AD, it is considered to be ETH_P_8021Q.

                     A call to this helper is susceptible to change the
                     underlying packet buffer. Therefore, at load time,
                     all checks on pointers previously done by the
                     verifier are invalidated and must be performed
                     again, if the helper is used in combination with
                     direct packet access.

              Return 0 on success, or a negative error in case of
                     failure.

       long bpf_skb_vlan_pop(struct sk_buff *skb)

              Description
                     Pop a VLAN header from the packet associated to
                     skb.

                     A call to this helper is susceptible to change the
                     underlying packet buffer. Therefore, at load time,
                     all checks on pointers previously done by the
                     verifier are invalidated and must be performed
                     again, if the helper is used in combination with
                     direct packet access.

              Return 0 on success, or a negative error in case of
                     failure.

       long bpf_skb_get_tunnel_key(struct sk_buff *skb, struct
       bpf_tunnel_key *key, u32 size, u64 flags)

              Description
                     Get tunnel metadata. This helper takes a pointer
                     key to an empty struct bpf_tunnel_key of size, that
                     will be filled with tunnel metadata for the packet
                     associated to skb.  The flags can be set to
                     BPF_F_TUNINFO_IPV6, which indicates that the tunnel
                     is based on IPv6 protocol instead of IPv4.

                     The struct bpf_tunnel_key is an object that
                     generalizes the principal parameters used by
                     various tunneling protocols into a single struct.
                     This way, it can be used to easily make a decision
                     based on the contents of the encapsulation header,
                     "summarized" in this struct. In particular, it
                     holds the IP address of the remote end (IPv4 or
                     IPv6, depending on the case) in key->remote_ipv4 or
                     key->remote_ipv6. Also, this struct exposes the
                     key->tunnel_id, which is generally mapped to a VNI
                     (Virtual Network Identifier), making it
                     programmable together with the
                     bpf_skb_set_tunnel_key() helper.

                     Let's imagine that the following code is part of a
                     program attached to the TC ingress interface, on
                     one end of a GRE tunnel, and is supposed to filter
                     out all messages coming from remote ends with IPv4
                     address other than 10.0.0.1:

                        int ret;
                        struct bpf_tunnel_key key = {};

                        ret = bpf_skb_get_tunnel_key(skb, &key, sizeof(key), 0);
                        if (ret < 0)
                                return TC_ACT_SHOT;     // drop packet

                        if (key.remote_ipv4 != 0x0a000001)
                                return TC_ACT_SHOT;     // drop packet

                        return TC_ACT_OK;               // accept packet

                     This interface can also be used with all
                     encapsulation devices that can operate in "collect
                     metadata" mode: instead of having one network
                     device per specific configuration, the "collect
                     metadata" mode only requires a single device where
                     the configuration can be extracted from this
                     helper.

                     This can be used together with various tunnels such
                     as VXLan, Geneve, GRE or IP in IP (IPIP).

              Return 0 on success, or a negative error in case of
                     failure.

       long bpf_skb_set_tunnel_key(struct sk_buff *skb, struct
       bpf_tunnel_key *key, u32 size, u64 flags)

              Description
                     Populate tunnel metadata for packet associated to
                     skb. The tunnel metadata is set to the contents of
                     key, of size. The flags can be set to a combination
                     of the following values:

                     BPF_F_TUNINFO_IPV6
                            Indicate that the tunnel is based on IPv6
                            protocol instead of IPv4.

                     BPF_F_ZERO_CSUM_TX
                            For IPv4 packets, add a flag to tunnel
                            metadata indicating that checksum
                            computation should be skipped and checksum
                            set to zeroes.

                     BPF_F_DONT_FRAGMENT
                            Add a flag to tunnel metadata indicating
                            that the packet should not be fragmented.

                     BPF_F_SEQ_NUMBER
                            Add a flag to tunnel metadata indicating
                            that a sequence number should be added to
                            tunnel header before sending the packet.
                            This flag was added for GRE encapsulation,
                            but might be used with other protocols as
                            well in the future.

                     Here is a typical usage on the transmit path:

                        struct bpf_tunnel_key key;
                             populate key ...
                        bpf_skb_set_tunnel_key(skb, &key, sizeof(key), 0);
                        bpf_clone_redirect(skb, vxlan_dev_ifindex, 0);

                     See also the description of the
                     bpf_skb_get_tunnel_key() helper for additional
                     information.

              Return 0 on success, or a negative error in case of
                     failure.

       u64 bpf_perf_event_read(struct bpf_map *map, u64 flags)

              Description
                     Read the value of a perf event counter. This helper
                     relies on a map of type
                     BPF_MAP_TYPE_PERF_EVENT_ARRAY. The nature of the
                     perf event counter is selected when map is updated
                     with perf event file descriptors. The map is an
                     array whose size is the number of available CPUs,
                     and each cell contains a value relative to one CPU.
                     The value to retrieve is indicated by flags, that
                     contains the index of the CPU to look up, masked
                     with BPF_F_INDEX_MASK. Alternatively, flags can be
                     set to BPF_F_CURRENT_CPU to indicate that the value
                     for the current CPU should be retrieved.

                     Note that before Linux 4.13, only hardware perf
                     event can be retrieved.

                     Also, be aware that the newer helper
                     bpf_perf_event_read_value() is recommended over
                     bpf_perf_event_read() in general. The latter has
                     some ABI quirks where error and counter value are
                     used as a return code (which is wrong to do since
                     ranges may overlap). This issue is fixed with
                     bpf_perf_event_read_value(), which at the same time
                     provides more features over the
                     bpf_perf_event_read() interface. Please refer to
                     the description of bpf_perf_event_read_value() for
                     details.

              Return The value of the perf event counter read from the
                     map, or a negative error code in case of failure.

       long bpf_redirect(u32 ifindex, u64 flags)

              Description
                     Redirect the packet to another net device of index
                     ifindex.  This helper is somewhat similar to
                     bpf_clone_redirect(), except that the packet is not
                     cloned, which provides increased performance.

                     Except for XDP, both ingress and egress interfaces
                     can be used for redirection. The BPF_F_INGRESS
                     value in flags is used to make the distinction
                     (ingress path is selected if the flag is present,
                     egress path otherwise). Currently, XDP only
                     supports redirection to the egress interface, and
                     accepts no flag at all.

                     The same effect can also be attained with the more
                     generic bpf_redirect_map(), which uses a BPF map to
                     store the redirect target instead of providing it
                     directly to the helper.

              Return For XDP, the helper returns XDP_REDIRECT on success
                     or XDP_ABORTED on error. For other program types,
                     the values are TC_ACT_REDIRECT on success or
                     TC_ACT_SHOT on error.

       u32 bpf_get_route_realm(struct sk_buff *skb)

              Description
                     Retrieve the realm or the route, that is to say the
                     tclassid field of the destination for the skb. The
                     identifier retrieved is a user-provided tag,
                     similar to the one used with the net_cls cgroup
                     (see description for bpf_get_cgroup_classid()
                     helper), but here this tag is held by a route (a
                     destination entry), not by a task.

                     Retrieving this identifier works with the clsact TC
                     egress hook (see also tc-bpf(8)), or alternatively
                     on conventional classful egress qdiscs, but not on
                     TC ingress path. In case of clsact TC egress hook,
                     this has the advantage that, internally, the
                     destination entry has not been dropped yet in the
                     transmit path. Therefore, the destination entry
                     does not need to be artificially held via
                     netif_keep_dst() for a classful qdisc until the skb
                     is freed.

                     This helper is available only if the kernel was
                     compiled with CONFIG_IP_ROUTE_CLASSID configuration
                     option.

              Return The realm of the route for the packet associated to
                     skb, or 0 if none was found.

       long bpf_perf_event_output(void *ctx, struct bpf_map *map, u64
       flags, void *data, u64 size)

              Description
                     Write raw data blob into a special BPF perf event
                     held by map of type BPF_MAP_TYPE_PERF_EVENT_ARRAY.
                     This perf event must have the following attributes:
                     PERF_SAMPLE_RAW as sample_type, PERF_TYPE_SOFTWARE
                     as type, and PERF_COUNT_SW_BPF_OUTPUT as config.

                     The flags are used to indicate the index in map for
                     which the value must be put, masked with
                     BPF_F_INDEX_MASK.  Alternatively, flags can be set
                     to BPF_F_CURRENT_CPU to indicate that the index of
                     the current CPU core should be used.

                     The value to write, of size, is passed through eBPF
                     stack and pointed by data.

                     The context of the program ctx needs also be passed
                     to the helper.

                     On user space, a program willing to read the values
                     needs to call perf_event_open() on the perf event
                     (either for one or for all CPUs) and to store the
                     file descriptor into the map. This must be done
                     before the eBPF program can send data into it. An
                     example is available in file
                     samples/bpf/trace_output_user.c in the Linux kernel
                     source tree (the eBPF program counterpart is in
                     samples/bpf/trace_output_kern.c).

                     bpf_perf_event_output() achieves better performance
                     than bpf_trace_printk() for sharing data with user
                     space, and is much better suitable for streaming
                     data from eBPF programs.

                     Note that this helper is not restricted to tracing
                     use cases and can be used with programs attached to
                     TC or XDP as well, where it allows for passing data
                     to user space listeners. Data can be:

                     • Only custom structs,

                     • Only the packet payload, or

                     • A combination of both.

              Return 0 on success, or a negative error in case of
                     failure.

       long bpf_skb_load_bytes(const void *skb, u32 offset, void *to,
       u32 len)

              Description
                     This helper was provided as an easy way to load
                     data from a packet. It can be used to load len
                     bytes from offset from the packet associated to
                     skb, into the buffer pointed by to.

                     Since Linux 4.7, usage of this helper has mostly
                     been replaced by "direct packet access", enabling
                     packet data to be manipulated with skb->data and
                     skb->data_end pointing respectively to the first
                     byte of packet data and to the byte after the last
                     byte of packet data. However, it remains useful if
                     one wishes to read large quantities of data at once
                     from a packet into the eBPF stack.

              Return 0 on success, or a negative error in case of
                     failure.

       long bpf_get_stackid(void *ctx, struct bpf_map *map, u64 flags)

              Description
                     Walk a user or a kernel stack and return its id. To
                     achieve this, the helper needs ctx, which is a
                     pointer to the context on which the tracing program
                     is executed, and a pointer to a map of type
                     BPF_MAP_TYPE_STACK_TRACE.

                     The last argument, flags, holds the number of stack
                     frames to skip (from 0 to 255), masked with
                     BPF_F_SKIP_FIELD_MASK. The next bits can be used to
                     set a combination of the following flags:

                     BPF_F_USER_STACK
                            Collect a user space stack instead of a
                            kernel stack.

                     BPF_F_FAST_STACK_CMP
                            Compare stacks by hash only.

                     BPF_F_REUSE_STACKID
                            If two different stacks hash into the same
                            stackid, discard the old one.

                     The stack id retrieved is a 32 bit long integer
                     handle which can be further combined with other
                     data (including other stack ids) and used as a key
                     into maps. This can be useful for generating a
                     variety of graphs (such as flame graphs or off-cpu
                     graphs).

                     For walking a stack, this helper is an improvement
                     over bpf_probe_read(), which can be used with
                     unrolled loops but is not efficient and consumes a
                     lot of eBPF instructions.  Instead,
                     bpf_get_stackid() can collect up to
                     PERF_MAX_STACK_DEPTH both kernel and user frames.
                     Note that this limit can be controlled with the
                     sysctl program, and that it should be manually
                     increased in order to profile long user stacks
                     (such as stacks for Java programs). To do so, use:

                        # sysctl kernel.perf_event_max_stack=<new value>

              Return The positive or null stack id on success, or a
                     negative error in case of failure.

       s64 bpf_csum_diff(__be32 *from, u32 from_size, __be32 *to, u32
       to_size, __wsum seed)

              Description
                     Compute a checksum difference, from the raw buffer
                     pointed by from, of length from_size (that must be
                     a multiple of 4), towards the raw buffer pointed by
                     to, of size to_size (same remark). An optional seed
                     can be added to the value (this can be cascaded,
                     the seed may come from a previous call to the
                     helper).

                     This is flexible enough to be used in several ways:

                     • With from_size == 0, to_size > 0 and seed set to
                       checksum, it can be used when pushing new data.

                     • With from_size > 0, to_size == 0 and seed set to
                       checksum, it can be used when removing data from
                       a packet.

                     • With from_size > 0, to_size > 0 and seed set to
                       0, it can be used to compute a diff. Note that
                       from_size and to_size do not need to be equal.

                     This helper can be used in combination with
                     bpf_l3_csum_replace() and bpf_l4_csum_replace(), to
                     which one can feed in the difference computed with
                     bpf_csum_diff().

              Return The checksum result, or a negative error code in
                     case of failure.

       long bpf_skb_get_tunnel_opt(struct sk_buff *skb, void *opt, u32
       size)

              Description
                     Retrieve tunnel options metadata for the packet
                     associated to skb, and store the raw tunnel option
                     data to the buffer opt of size.

                     This helper can be used with encapsulation devices
                     that can operate in "collect metadata" mode (please
                     refer to the related note in the description of
                     bpf_skb_get_tunnel_key() for more details). A
                     particular example where this can be used is in
                     combination with the Geneve encapsulation protocol,
                     where it allows for pushing (with
                     bpf_skb_get_tunnel_opt() helper) and retrieving
                     arbitrary TLVs (Type-Length-Value headers) from the
                     eBPF program. This allows for full customization of
                     these headers.

              Return The size of the option data retrieved.

       long bpf_skb_set_tunnel_opt(struct sk_buff *skb, void *opt, u32
       size)

              Description
                     Set tunnel options metadata for the packet
                     associated to skb to the option data contained in
                     the raw buffer opt of size.

                     See also the description of the
                     bpf_skb_get_tunnel_opt() helper for additional
                     information.

              Return 0 on success, or a negative error in case of
                     failure.

       long bpf_skb_change_proto(struct sk_buff *skb, __be16 proto, u64
       flags)

              Description
                     Change the protocol of the skb to proto. Currently
                     supported are transition from IPv4 to IPv6, and
                     from IPv6 to IPv4. The helper takes care of the
                     groundwork for the transition, including resizing
                     the socket buffer. The eBPF program is expected to
                     fill the new headers, if any, via skb_store_bytes()
                     and to recompute the checksums with
                     bpf_l3_csum_replace() and bpf_l4_csum_replace().
                     The main case for this helper is to perform NAT64
                     operations out of an eBPF program.

                     Internally, the GSO type is marked as dodgy so that
                     headers are checked and segments are recalculated
                     by the GSO/GRO engine.  The size for GSO target is
                     adapted as well.

                     All values for flags are reserved for future usage,
                     and must be left at zero.

                     A call to this helper is susceptible to change the
                     underlying packet buffer. Therefore, at load time,
                     all checks on pointers previously done by the
                     verifier are invalidated and must be performed
                     again, if the helper is used in combination with
                     direct packet access.

              Return 0 on success, or a negative error in case of
                     failure.

       long bpf_skb_change_type(struct sk_buff *skb, u32 type)

              Description
                     Change the packet type for the packet associated to
                     skb. This comes down to setting skb->pkt_type to
                     type, except the eBPF program does not have a write
                     access to skb->pkt_type beside this helper. Using a
                     helper here allows for graceful handling of errors.

                     The major use case is to change incoming skb*s to
                     **PACKET_HOST* in a programmatic way instead of
                     having to recirculate via redirect(...,
                     BPF_F_INGRESS), for example.

                     Note that type only allows certain values. At this
                     time, they are:

                     PACKET_HOST
                            Packet is for us.

                     PACKET_BROADCAST
                            Send packet to all.

                     PACKET_MULTICAST
                            Send packet to group.

                     PACKET_OTHERHOST
                            Send packet to someone else.

              Return 0 on success, or a negative error in case of
                     failure.

       long bpf_skb_under_cgroup(struct sk_buff *skb, struct bpf_map
       *map, u32 index)

              Description
                     Check whether skb is a descendant of the cgroup2
                     held by map of type BPF_MAP_TYPE_CGROUP_ARRAY, at
                     index.

              Return The return value depends on the result of the test,
                     and can be:

                     • 0, if the skb failed the cgroup2 descendant test.

                     • 1, if the skb succeeded the cgroup2 descendant
                       test.

                     • A negative error code, if an error occurred.

       u32 bpf_get_hash_recalc(struct sk_buff *skb)

              Description
                     Retrieve the hash of the packet, skb->hash. If it
                     is not set, in particular if the hash was cleared
                     due to mangling, recompute this hash. Later
                     accesses to the hash can be done directly with
                     skb->hash.

                     Calling bpf_set_hash_invalid(), changing a packet
                     prototype with bpf_skb_change_proto(), or calling
                     bpf_skb_store_bytes() with the
                     BPF_F_INVALIDATE_HASH are actions susceptible to
                     clear the hash and to trigger a new computation for
                     the next call to bpf_get_hash_recalc().

              Return The 32-bit hash.

       u64 bpf_get_current_task(void)

              Return A pointer to the current task struct.

       long bpf_probe_write_user(void *dst, const void *src, u32 len)

              Description
                     Attempt in a safe way to write len bytes from the
                     buffer src to dst in memory. It only works for
                     threads that are in user context, and dst must be a
                     valid user space address.

                     This helper should not be used to implement any
                     kind of security mechanism because of TOC-TOU
                     attacks, but rather to debug, divert, and
                     manipulate execution of semi-cooperative processes.

                     Keep in mind that this feature is meant for
                     experiments, and it has a risk of crashing the
                     system and running programs.  Therefore, when an
                     eBPF program using this helper is attached, a
                     warning including PID and process name is printed
                     to kernel logs.

              Return 0 on success, or a negative error in case of
                     failure.

       long bpf_current_task_under_cgroup(struct bpf_map *map, u32
       index)

              Description
                     Check whether the probe is being run is the context
                     of a given subset of the cgroup2 hierarchy. The
                     cgroup2 to test is held by map of type
                     BPF_MAP_TYPE_CGROUP_ARRAY, at index.

              Return The return value depends on the result of the test,
                     and can be:

                     • 0, if the skb task belongs to the cgroup2.

                     • 1, if the skb task does not belong to the
                       cgroup2.

                     • A negative error code, if an error occurred.

       long bpf_skb_change_tail(struct sk_buff *skb, u32 len, u64 flags)

              Description
                     Resize (trim or grow) the packet associated to skb
                     to the new len. The flags are reserved for future
                     usage, and must be left at zero.

                     The basic idea is that the helper performs the
                     needed work to change the size of the packet, then
                     the eBPF program rewrites the rest via helpers like
                     bpf_skb_store_bytes(), bpf_l3_csum_replace(),
                     bpf_l3_csum_replace() and others. This helper is a
                     slow path utility intended for replies with control
                     messages. And because it is targeted for slow path,
                     the helper itself can afford to be slow: it
                     implicitly linearizes, unclones and drops offloads
                     from the skb.

                     A call to this helper is susceptible to change the
                     underlying packet buffer. Therefore, at load time,
                     all checks on pointers previously done by the
                     verifier are invalidated and must be performed
                     again, if the helper is used in combination with
                     direct packet access.

              Return 0 on success, or a negative error in case of
                     failure.

       long bpf_skb_pull_data(struct sk_buff *skb, u32 len)

              Description
                     Pull in non-linear data in case the skb is
                     non-linear and not all of len are part of the
                     linear section. Make len bytes from skb readable
                     and writable. If a zero value is passed for len,
                     then the whole length of the skb is pulled.

                     This helper is only needed for reading and writing
                     with direct packet access.

                     For direct packet access, testing that offsets to
                     access are within packet boundaries (test on
                     skb->data_end) is susceptible to fail if offsets
                     are invalid, or if the requested data is in
                     non-linear parts of the skb. On failure the program
                     can just bail out, or in the case of a non-linear
                     buffer, use a helper to make the data available.
                     The bpf_skb_load_bytes() helper is a first solution
                     to access the data. Another one consists in using
                     bpf_skb_pull_data to pull in once the non-linear
                     parts, then retesting and eventually access the
                     data.

                     At the same time, this also makes sure the skb is
                     uncloned, which is a necessary condition for direct
                     write. As this needs to be an invariant for the
                     write part only, the verifier detects writes and
                     adds a prologue that is calling bpf_skb_pull_data()
                     to effectively unclone the skb from the very
                     beginning in case it is indeed cloned.

                     A call to this helper is susceptible to change the
                     underlying packet buffer. Therefore, at load time,
                     all checks on pointers previously done by the
                     verifier are invalidated and must be performed
                     again, if the helper is used in combination with
                     direct packet access.

              Return 0 on success, or a negative error in case of
                     failure.

       s64 bpf_csum_update(struct sk_buff *skb, __wsum csum)

              Description
                     Add the checksum csum into skb->csum in case the
                     driver has supplied a checksum for the entire
                     packet into that field. Return an error otherwise.
                     This helper is intended to be used in combination
                     with bpf_csum_diff(), in particular when the
                     checksum needs to be updated after data has been
                     written into the packet through direct packet
                     access.

              Return The checksum on success, or a negative error code
                     in case of failure.

       void bpf_set_hash_invalid(struct sk_buff *skb)

              Description
                     Invalidate the current skb->hash. It can be used
                     after mangling on headers through direct packet
                     access, in order to indicate that the hash is
                     outdated and to trigger a recalculation the next
                     time the kernel tries to access this hash or when
                     the bpf_get_hash_recalc() helper is called.

       long bpf_get_numa_node_id(void)

              Description
                     Return the id of the current NUMA node. The primary
                     use case for this helper is the selection of
                     sockets for the local NUMA node, when the program
                     is attached to sockets using the
                     SO_ATTACH_REUSEPORT_EBPF option (see also
                     socket(7)), but the helper is also available to
                     other eBPF program types, similarly to
                     bpf_get_smp_processor_id().

              Return The id of current NUMA node.

       long bpf_skb_change_head(struct sk_buff *skb, u32 len, u64 flags)

              Description
                     Grows headroom of packet associated to skb and
                     adjusts the offset of the MAC header accordingly,
                     adding len bytes of space. It automatically extends
                     and reallocates memory as required.

                     This helper can be used on a layer 3 skb to push a
                     MAC header for redirection into a layer 2 device.

                     All values for flags are reserved for future usage,
                     and must be left at zero.

                     A call to this helper is susceptible to change the
                     underlying packet buffer. Therefore, at load time,
                     all checks on pointers previously done by the
                     verifier are invalidated and must be performed
                     again, if the helper is used in combination with
                     direct packet access.

              Return 0 on success, or a negative error in case of
                     failure.

       long bpf_xdp_adjust_head(struct xdp_buff *xdp_md, int delta)

              Description
                     Adjust (move) xdp_md->data by delta bytes. Note
                     that it is possible to use a negative value for
                     delta. This helper can be used to prepare the
                     packet for pushing or popping headers.

                     A call to this helper is susceptible to change the
                     underlying packet buffer. Therefore, at load time,
                     all checks on pointers previously done by the
                     verifier are invalidated and must be performed
                     again, if the helper is used in combination with
                     direct packet access.

              Return 0 on success, or a negative error in case of
                     failure.

       long bpf_probe_read_str(void *dst, u32 size, const void
       *unsafe_ptr)

              Description
                     Copy a NUL terminated string from an unsafe kernel
                     address unsafe_ptr to dst. See
                     bpf_probe_read_kernel_str() for more details.

                     Generally, use bpf_probe_read_user_str() or
                     bpf_probe_read_kernel_str() instead.

              Return On success, the strictly positive length of the
                     string, including the trailing NUL character. On
                     error, a negative value.

       u64 bpf_get_socket_cookie(struct sk_buff *skb)

              Description
                     If the struct sk_buff pointed by skb has a known
                     socket, retrieve the cookie (generated by the
                     kernel) of this socket.  If no cookie has been set
                     yet, generate a new cookie. Once generated, the
                     socket cookie remains stable for the life of the
                     socket. This helper can be useful for monitoring
                     per socket networking traffic statistics as it
                     provides a global socket identifier that can be
                     assumed unique.

              Return A 8-byte long non-decreasing number on success, or
                     0 if the socket field is missing inside skb.

       u64 bpf_get_socket_cookie(struct bpf_sock_addr *ctx)

              Description
                     Equivalent to bpf_get_socket_cookie() helper that
                     accepts skb, but gets socket from struct
                     bpf_sock_addr context.

              Return A 8-byte long non-decreasing number.

       u64 bpf_get_socket_cookie(struct bpf_sock_ops *ctx)

              Description
                     Equivalent to bpf_get_socket_cookie() helper that
                     accepts skb, but gets socket from struct
                     bpf_sock_ops context.

              Return A 8-byte long non-decreasing number.

       u32 bpf_get_socket_uid(struct sk_buff *skb)

              Return The owner UID of the socket associated to skb. If
                     the socket is NULL, or if it is not a full socket
                     (i.e. if it is a time-wait or a request socket
                     instead), overflowuid value is returned (note that
                     overflowuid might also be the actual UID value for
                     the socket).

       long bpf_set_hash(struct sk_buff *skb, u32 hash)

              Description
                     Set the full hash for skb (set the field skb->hash)
                     to value hash.

              Return 0

       long bpf_setsockopt(void *bpf_socket, int level, int optname,
       void *optval, int optlen)

              Description
                     Emulate a call to setsockopt() on the socket
                     associated to bpf_socket, which must be a full
                     socket. The level at which the option resides and
                     the name optname of the option must be specified,
                     see setsockopt(2) for more information.  The option
                     value of length optlen is pointed by optval.

                     bpf_socket should be one of the following:

                     • struct bpf_sock_ops for BPF_PROG_TYPE_SOCK_OPS.

                     • struct bpf_sock_addr for BPF_CGROUP_INET4_CONNECT
                       and BPF_CGROUP_INET6_CONNECT.

                     This helper actually implements a subset of
                     setsockopt().  It supports the following levels:

                     • SOL_SOCKET, which supports the following
                       optnames: SO_RCVBUF, SO_SNDBUF,
                       SO_MAX_PACING_RATE, SO_PRIORITY, SO_RCVLOWAT,
                       SO_MARK, SO_BINDTODEVICE, SO_KEEPALIVE.

                     • IPPROTO_TCP, which supports the following
                       optnames: TCP_CONGESTION, TCP_BPF_IW,
                       TCP_BPF_SNDCWND_CLAMP, TCP_SAVE_SYN,
                       TCP_KEEPIDLE, TCP_KEEPINTVL, TCP_KEEPCNT,
                       TCP_SYNCNT, TCP_USER_TIMEOUT.

                     • IPPROTO_IP, which supports optname IP_TOS.

                     • IPPROTO_IPV6, which supports optname IPV6_TCLASS.

              Return 0 on success, or a negative error in case of
                     failure.

       long bpf_skb_adjust_room(struct sk_buff *skb, s32 len_diff, u32
       mode, u64 flags)

              Description
                     Grow or shrink the room for data in the packet
                     associated to skb by len_diff, and according to the
                     selected mode.

                     By default, the helper will reset any offloaded
                     checksum indicator of the skb to CHECKSUM_NONE.
                     This can be avoided by the following flag:

                     • BPF_F_ADJ_ROOM_NO_CSUM_RESET: Do not reset
                       offloaded checksum data of the skb to
                       CHECKSUM_NONE.

                     There are two supported modes at this time:

                     • BPF_ADJ_ROOM_MAC: Adjust room at the mac layer
                       (room space is added or removed below the layer 2
                       header).

                     • BPF_ADJ_ROOM_NET: Adjust room at the network
                       layer (room space is added or removed below the
                       layer 3 header).

                     The following flags are supported at this time:

                     • BPF_F_ADJ_ROOM_FIXED_GSO: Do not adjust gso_size.
                       Adjusting mss in this way is not allowed for
                       datagrams.

                     • BPF_F_ADJ_ROOM_ENCAP_L3_IPV4,
                       BPF_F_ADJ_ROOM_ENCAP_L3_IPV6: Any new space is
                       reserved to hold a tunnel header.  Configure skb
                       offsets and other fields accordingly.

                     • BPF_F_ADJ_ROOM_ENCAP_L4_GRE,
                       BPF_F_ADJ_ROOM_ENCAP_L4_UDP: Use with ENCAP_L3
                       flags to further specify the tunnel type.

                     • BPF_F_ADJ_ROOM_ENCAP_L2(len): Use with
                       ENCAP_L3/L4 flags to further specify the tunnel
                       type; len is the length of the inner MAC header.

                     A call to this helper is susceptible to change the
                     underlying packet buffer. Therefore, at load time,
                     all checks on pointers previously done by the
                     verifier are invalidated and must be performed
                     again, if the helper is used in combination with
                     direct packet access.

              Return 0 on success, or a negative error in case of
                     failure.

       long bpf_redirect_map(struct bpf_map *map, u32 key, u64 flags)

              Description
                     Redirect the packet to the endpoint referenced by
                     map at index key. Depending on its type, this map
                     can contain references to net devices (for
                     forwarding packets through other ports), or to CPUs
                     (for redirecting XDP frames to another CPU; but
                     this is only implemented for native XDP (with
                     driver support) as of this writing).

                     The lower two bits of flags are used as the return
                     code if the map lookup fails. This is so that the
                     return value can be one of the XDP program return
                     codes up to XDP_TX, as chosen by the caller. Any
                     higher bits in the flags argument must be unset.

                     See also bpf_redirect(), which only supports
                     redirecting to an ifindex, but doesn't require a
                     map to do so.

              Return XDP_REDIRECT on success, or the value of the two
                     lower bits of the flags argument on error.

       long bpf_sk_redirect_map(struct sk_buff *skb, struct bpf_map
       *map, u32 key, u64 flags)

              Description
                     Redirect the packet to the socket referenced by map
                     (of type BPF_MAP_TYPE_SOCKMAP) at index key. Both
                     ingress and egress interfaces can be used for
                     redirection. The BPF_F_INGRESS value in flags is
                     used to make the distinction (ingress path is
                     selected if the flag is present, egress path
                     otherwise). This is the only flag supported for
                     now.

              Return SK_PASS on success, or SK_DROP on error.

       long bpf_sock_map_update(struct bpf_sock_ops *skops, struct
       bpf_map *map, void *key, u64 flags)

              Description
                     Add an entry to, or update a map referencing
                     sockets. The skops is used as a new value for the
                     entry associated to key. flags is one of:

                     BPF_NOEXIST
                            The entry for key must not exist in the map.

                     BPF_EXIST
                            The entry for key must already exist in the
                            map.

                     BPF_ANY
                            No condition on the existence of the entry
                            for key.

                     If the map has eBPF programs (parser and verdict),
                     those will be inherited by the socket being added.
                     If the socket is already attached to eBPF programs,
                     this results in an error.

              Return 0 on success, or a negative error in case of
                     failure.

       long bpf_xdp_adjust_meta(struct xdp_buff *xdp_md, int delta)

              Description
                     Adjust the address pointed by xdp_md->data_meta by
                     delta (which can be positive or negative). Note
                     that this operation modifies the address stored in
                     xdp_md->data, so the latter must be loaded only
                     after the helper has been called.

                     The use of xdp_md->data_meta is optional and
                     programs are not required to use it. The rationale
                     is that when the packet is processed with XDP (e.g.
                     as DoS filter), it is possible to push further meta
                     data along with it before passing to the stack, and
                     to give the guarantee that an ingress eBPF program
                     attached as a TC classifier on the same device can
                     pick this up for further post-processing. Since TC
                     works with socket buffers, it remains possible to
                     set from XDP the mark or priority pointers, or
                     other pointers for the socket buffer.  Having this
                     scratch space generic and programmable allows for
                     more flexibility as the user is free to store
                     whatever meta data they need.

                     A call to this helper is susceptible to change the
                     underlying packet buffer. Therefore, at load time,
                     all checks on pointers previously done by the
                     verifier are invalidated and must be performed
                     again, if the helper is used in combination with
                     direct packet access.

              Return 0 on success, or a negative error in case of
                     failure.

       long bpf_perf_event_read_value(struct bpf_map *map, u64 flags,
       struct bpf_perf_event_value *buf, u32 buf_size)

              Description
                     Read the value of a perf event counter, and store
                     it into buf of size buf_size. This helper relies on
                     a map of type BPF_MAP_TYPE_PERF_EVENT_ARRAY. The
                     nature of the perf event counter is selected when
                     map is updated with perf event file descriptors.
                     The map is an array whose size is the number of
                     available CPUs, and each cell contains a value
                     relative to one CPU. The value to retrieve is
                     indicated by flags, that contains the index of the
                     CPU to look up, masked with BPF_F_INDEX_MASK.
                     Alternatively, flags can be set to
                     BPF_F_CURRENT_CPU to indicate that the value for
                     the current CPU should be retrieved.

                     This helper behaves in a way close to
                     bpf_perf_event_read() helper, save that instead of
                     just returning the value observed, it fills the buf
                     structure. This allows for additional data to be
                     retrieved: in particular, the enabled and running
                     times (in buf->enabled and buf->running,
                     respectively) are copied. In general,
                     bpf_perf_event_read_value() is recommended over
                     bpf_perf_event_read(), which has some ABI issues
                     and provides fewer functionalities.

                     These values are interesting, because hardware PMU
                     (Performance Monitoring Unit) counters are limited
                     resources. When there are more PMU based perf
                     events opened than available counters, kernel will
                     multiplex these events so each event gets certain
                     percentage (but not all) of the PMU time. In case
                     that multiplexing happens, the number of samples or
                     counter value will not reflect the case compared to
                     when no multiplexing occurs. This makes comparison
                     between different runs difficult.  Typically, the
                     counter value should be normalized before comparing
                     to other experiments. The usual normalization is
                     done as follows.

                        normalized_counter = counter * t_enabled / t_running

                     Where t_enabled is the time enabled for event and
                     t_running is the time running for event since last
                     normalization. The enabled and running times are
                     accumulated since the perf event open. To achieve
                     scaling factor between two invocations of an eBPF
                     program, users can use CPU id as the key (which is
                     typical for perf array usage model) to remember the
                     previous value and do the calculation inside the
                     eBPF program.

              Return 0 on success, or a negative error in case of
                     failure.

       long bpf_perf_prog_read_value(struct bpf_perf_event_data *ctx,
       struct bpf_perf_event_value *buf, u32 buf_size)

              Description
                     For en eBPF program attached to a perf event,
                     retrieve the value of the event counter associated
                     to ctx and store it in the structure pointed by buf
                     and of size buf_size. Enabled and running times are
                     also stored in the structure (see description of
                     helper bpf_perf_event_read_value() for more
                     details).

              Return 0 on success, or a negative error in case of
                     failure.

       long bpf_getsockopt(void *bpf_socket, int level, int optname,
       void *optval, int optlen)

              Description
                     Emulate a call to getsockopt() on the socket
                     associated to bpf_socket, which must be a full
                     socket. The level at which the option resides and
                     the name optname of the option must be specified,
                     see getsockopt(2) for more information.  The
                     retrieved value is stored in the structure pointed
                     by opval and of length optlen.

                     bpf_socket should be one of the following:

                     • struct bpf_sock_ops for BPF_PROG_TYPE_SOCK_OPS.

                     • struct bpf_sock_addr for BPF_CGROUP_INET4_CONNECT
                       and BPF_CGROUP_INET6_CONNECT.

                     This helper actually implements a subset of
                     getsockopt().  It supports the following levels:

                     • IPPROTO_TCP, which supports optname
                       TCP_CONGESTION.

                     • IPPROTO_IP, which supports optname IP_TOS.

                     • IPPROTO_IPV6, which supports optname IPV6_TCLASS.

              Return 0 on success, or a negative error in case of
                     failure.

       long bpf_override_return(struct pt_regs *regs, u64 rc)

              Description
                     Used for error injection, this helper uses kprobes
                     to override the return value of the probed
                     function, and to set it to rc.  The first argument
                     is the context regs on which the kprobe works.

                     This helper works by setting the PC (program
                     counter) to an override function which is run in
                     place of the original probed function. This means
                     the probed function is not run at all. The
                     replacement function just returns with the required
                     value.

                     This helper has security implications, and thus is
                     subject to restrictions. It is only available if
                     the kernel was compiled with the
                     CONFIG_BPF_KPROBE_OVERRIDE configuration option,
                     and in this case it only works on functions tagged
                     with ALLOW_ERROR_INJECTION in the kernel code.

                     Also, the helper is only available for the
                     architectures having the
                     CONFIG_FUNCTION_ERROR_INJECTION option. As of this
                     writing, x86 architecture is the only one to
                     support this feature.

              Return 0

       long bpf_sock_ops_cb_flags_set(struct bpf_sock_ops *bpf_sock, int
       argval)

              Description
                     Attempt to set the value of the
                     bpf_sock_ops_cb_flags field for the full TCP socket
                     associated to bpf_sock_ops to argval.

                     The primary use of this field is to determine if
                     there should be calls to eBPF programs of type
                     BPF_PROG_TYPE_SOCK_OPS at various points in the TCP
                     code. A program of the same type can change its
                     value, per connection and as necessary, when the
                     connection is established. This field is directly
                     accessible for reading, but this helper must be
                     used for updates in order to return an error if an
                     eBPF program tries to set a callback that is not
                     supported in the current kernel.

                     argval is a flag array which can combine these
                     flags:

                     • BPF_SOCK_OPS_RTO_CB_FLAG (retransmission time
                       out)

                     • BPF_SOCK_OPS_RETRANS_CB_FLAG (retransmission)

                     • BPF_SOCK_OPS_STATE_CB_FLAG (TCP state change)

                     • BPF_SOCK_OPS_RTT_CB_FLAG (every RTT)

                     Therefore, this function can be used to clear a
                     callback flag by setting the appropriate bit to
                     zero. e.g. to disable the RTO callback:

                     bpf_sock_ops_cb_flags_set(bpf_sock,
                            bpf_sock->bpf_sock_ops_cb_flags &
                            ~BPF_SOCK_OPS_RTO_CB_FLAG)

                     Here are some examples of where one could call such
                     eBPF program:

                     • When RTO fires.

                     • When a packet is retransmitted.

                     • When the connection terminates.

                     • When a packet is sent.

                     • When a packet is received.

              Return Code -EINVAL if the socket is not a full TCP
                     socket; otherwise, a positive number containing the
                     bits that could not be set is returned (which comes
                     down to 0 if all bits were set as required).

       long bpf_msg_redirect_map(struct sk_msg_buff *msg, struct bpf_map
       *map, u32 key, u64 flags)

              Description
                     This helper is used in programs implementing
                     policies at the socket level. If the message msg is
                     allowed to pass (i.e. if the verdict eBPF program
                     returns SK_PASS), redirect it to the socket
                     referenced by map (of type BPF_MAP_TYPE_SOCKMAP) at
                     index key. Both ingress and egress interfaces can
                     be used for redirection. The BPF_F_INGRESS value in
                     flags is used to make the distinction (ingress path
                     is selected if the flag is present, egress path
                     otherwise). This is the only flag supported for
                     now.

              Return SK_PASS on success, or SK_DROP on error.

       long bpf_msg_apply_bytes(struct sk_msg_buff *msg, u32 bytes)

              Description
                     For socket policies, apply the verdict of the eBPF
                     program to the next bytes (number of bytes) of
                     message msg.

                     For example, this helper can be used in the
                     following cases:

                     • A single sendmsg() or sendfile() system call
                       contains multiple logical messages that the eBPF
                       program is supposed to read and for which it
                       should apply a verdict.

                     • An eBPF program only cares to read the first
                       bytes of a msg. If the message has a large
                       payload, then setting up and calling the eBPF
                       program repeatedly for all bytes, even though the
                       verdict is already known, would create
                       unnecessary overhead.

                     When called from within an eBPF program, the helper
                     sets a counter internal to the BPF infrastructure,
                     that is used to apply the last verdict to the next
                     bytes. If bytes is smaller than the current data
                     being processed from a sendmsg() or sendfile()
                     system call, the first bytes will be sent and the
                     eBPF program will be re-run with the pointer for
                     start of data pointing to byte number bytes + 1. If
                     bytes is larger than the current data being
                     processed, then the eBPF verdict will be applied to
                     multiple sendmsg() or sendfile() calls until bytes
                     are consumed.

                     Note that if a socket closes with the internal
                     counter holding a non-zero value, this is not a
                     problem because data is not being buffered for
                     bytes and is sent as it is received.

              Return 0

       long bpf_msg_cork_bytes(struct sk_msg_buff *msg, u32 bytes)

              Description
                     For socket policies, prevent the execution of the
                     verdict eBPF program for message msg until bytes
                     (byte number) have been accumulated.

                     This can be used when one needs a specific number
                     of bytes before a verdict can be assigned, even if
                     the data spans multiple sendmsg() or sendfile()
                     calls. The extreme case would be a user calling
                     sendmsg() repeatedly with 1-byte long message
                     segments. Obviously, this is bad for performance,
                     but it is still valid. If the eBPF program needs
                     bytes bytes to validate a header, this helper can
                     be used to prevent the eBPF program to be called
                     again until bytes have been accumulated.

              Return 0

       long bpf_msg_pull_data(struct sk_msg_buff *msg, u32 start, u32
       end, u64 flags)

              Description
                     For socket policies, pull in non-linear data from
                     user space for msg and set pointers msg->data and
                     msg->data_end to start and end bytes offsets into
                     msg, respectively.

                     If a program of type BPF_PROG_TYPE_SK_MSG is run on
                     a msg it can only parse data that the (data,
                     data_end) pointers have already consumed. For
                     sendmsg() hooks this is likely the first
                     scatterlist element. But for calls relying on the
                     sendpage handler (e.g. sendfile()) this will be the
                     range (0, 0) because the data is shared with user
                     space and by default the objective is to avoid
                     allowing user space to modify data while (or after)
                     eBPF verdict is being decided. This helper can be
                     used to pull in data and to set the start and end
                     pointer to given values. Data will be copied if
                     necessary (i.e. if data was not linear and if start
                     and end pointers do not point to the same chunk).

                     A call to this helper is susceptible to change the
                     underlying packet buffer. Therefore, at load time,
                     all checks on pointers previously done by the
                     verifier are invalidated and must be performed
                     again, if the helper is used in combination with
                     direct packet access.

                     All values for flags are reserved for future usage,
                     and must be left at zero.

              Return 0 on success, or a negative error in case of
                     failure.

       long bpf_bind(struct bpf_sock_addr *ctx, struct sockaddr *addr,
       int addr_len)

              Description
                     Bind the socket associated to ctx to the address
                     pointed by addr, of length addr_len. This allows
                     for making outgoing connection from the desired IP
                     address, which can be useful for example when all
                     processes inside a cgroup should use one single IP
                     address on a host that has multiple IP configured.

                     This helper works for IPv4 and IPv6, TCP and UDP
                     sockets. The domain (addr->sa_family) must be
                     AF_INET (or AF_INET6). It's advised to pass zero
                     port (sin_port or sin6_port) which triggers
                     IP_BIND_ADDRESS_NO_PORT-like behavior and lets the
                     kernel efficiently pick up an unused port as long
                     as 4-tuple is unique. Passing non-zero port might
                     lead to degraded performance.

              Return 0 on success, or a negative error in case of
                     failure.

       long bpf_xdp_adjust_tail(struct xdp_buff *xdp_md, int delta)

              Description
                     Adjust (move) xdp_md->data_end by delta bytes. It
                     is possible to both shrink and grow the packet
                     tail.  Shrink done via delta being a negative
                     integer.

                     A call to this helper is susceptible to change the
                     underlying packet buffer. Therefore, at load time,
                     all checks on pointers previously done by the
                     verifier are invalidated and must be performed
                     again, if the helper is used in combination with
                     direct packet access.

              Return 0 on success, or a negative error in case of
                     failure.

       long bpf_skb_get_xfrm_state(struct sk_buff *skb, u32 index,
       struct bpf_xfrm_state *xfrm_state, u32 size, u64 flags)

              Description
                     Retrieve the XFRM state (IP transform framework,
                     see also ip-xfrm(8)) at index in XFRM "security
                     path" for skb.

                     The retrieved value is stored in the struct
                     bpf_xfrm_state pointed by xfrm_state and of length
                     size.

                     All values for flags are reserved for future usage,
                     and must be left at zero.

                     This helper is available only if the kernel was
                     compiled with CONFIG_XFRM configuration option.

              Return 0 on success, or a negative error in case of
                     failure.

       long bpf_get_stack(void *ctx, void *buf, u32 size, u64 flags)

              Description
                     Return a user or a kernel stack in bpf program
                     provided buffer.  To achieve this, the helper needs
                     ctx, which is a pointer to the context on which the
                     tracing program is executed.  To store the
                     stacktrace, the bpf program provides buf with a
                     nonnegative size.

                     The last argument, flags, holds the number of stack
                     frames to skip (from 0 to 255), masked with
                     BPF_F_SKIP_FIELD_MASK. The next bits can be used to
                     set the following flags:

                     BPF_F_USER_STACK
                            Collect a user space stack instead of a
                            kernel stack.

                     BPF_F_USER_BUILD_ID
                            Collect buildid+offset instead of ips for
                            user stack, only valid if BPF_F_USER_STACK
                            is also specified.

                     bpf_get_stack() can collect up to
                     PERF_MAX_STACK_DEPTH both kernel and user frames,
                     subject to sufficient large buffer size. Note that
                     this limit can be controlled with the sysctl
                     program, and that it should be manually increased
                     in order to profile long user stacks (such as
                     stacks for Java programs). To do so, use:

                        # sysctl kernel.perf_event_max_stack=<new value>

              Return A non-negative value equal to or less than size on
                     success, or a negative error in case of failure.

       long bpf_skb_load_bytes_relative(const void *skb, u32 offset,
       void *to, u32 len, u32 start_header)

              Description
                     This helper is similar to bpf_skb_load_bytes() in
                     that it provides an easy way to load len bytes from
                     offset from the packet associated to skb, into the
                     buffer pointed by to. The difference to
                     bpf_skb_load_bytes() is that a fifth argument
                     start_header exists in order to select a base
                     offset to start from. start_header can be one of:

                     BPF_HDR_START_MAC
                            Base offset to load data from is skb's mac
                            header.

                     BPF_HDR_START_NET
                            Base offset to load data from is skb's
                            network header.

                     In general, "direct packet access" is the preferred
                     method to access packet data, however, this helper
                     is in particular useful in socket filters where
                     skb->data does not always point to the start of the
                     mac header and where "direct packet access" is not
                     available.

              Return 0 on success, or a negative error in case of
                     failure.

       long bpf_fib_lookup(void *ctx, struct bpf_fib_lookup *params, int
       plen, u32 flags)

              Description
                     Do FIB lookup in kernel tables using parameters in
                     params.  If lookup is successful and result shows
                     packet is to be forwarded, the neighbor tables are
                     searched for the nexthop.  If successful (ie., FIB
                     lookup shows forwarding and nexthop is resolved),
                     the nexthop address is returned in ipv4_dst or
                     ipv6_dst based on family, smac is set to mac
                     address of egress device, dmac is set to nexthop
                     mac address, rt_metric is set to metric from route
                     (IPv4/IPv6 only), and ifindex is set to the device
                     index of the nexthop from the FIB lookup.

                     plen argument is the size of the passed in struct.
                     flags argument can be a combination of one or more
                     of the following values:

                     BPF_FIB_LOOKUP_DIRECT
                            Do a direct table lookup vs full lookup
                            using FIB rules.

                     BPF_FIB_LOOKUP_OUTPUT
                            Perform lookup from an egress perspective
                            (default is ingress).

                     ctx is either struct xdp_md for XDP programs or
                     struct sk_buff tc cls_act programs.

              Return

                     • < 0 if any input argument is invalid

                     • 0 on success (packet is forwarded, nexthop
                       neighbor exists)

                     • > 0 one of BPF_FIB_LKUP_RET_ codes explaining why
                       the packet is not forwarded or needs assist from
                       full stack

       long bpf_sock_hash_update(struct bpf_sock_ops *skops, struct
       bpf_map *map, void *key, u64 flags)

              Description
                     Add an entry to, or update a sockhash map
                     referencing sockets.  The skops is used as a new
                     value for the entry associated to key. flags is one
                     of:

                     BPF_NOEXIST
                            The entry for key must not exist in the map.

                     BPF_EXIST
                            The entry for key must already exist in the
                            map.

                     BPF_ANY
                            No condition on the existence of the entry
                            for key.

                     If the map has eBPF programs (parser and verdict),
                     those will be inherited by the socket being added.
                     If the socket is already attached to eBPF programs,
                     this results in an error.

              Return 0 on success, or a negative error in case of
                     failure.

       long bpf_msg_redirect_hash(struct sk_msg_buff *msg, struct
       bpf_map *map, void *key, u64 flags)

              Description
                     This helper is used in programs implementing
                     policies at the socket level. If the message msg is
                     allowed to pass (i.e. if the verdict eBPF program
                     returns SK_PASS), redirect it to the socket
                     referenced by map (of type BPF_MAP_TYPE_SOCKHASH)
                     using hash key. Both ingress and egress interfaces
                     can be used for redirection. The BPF_F_INGRESS
                     value in flags is used to make the distinction
                     (ingress path is selected if the flag is present,
                     egress path otherwise). This is the only flag
                     supported for now.

              Return SK_PASS on success, or SK_DROP on error.

       long bpf_sk_redirect_hash(struct sk_buff *skb, struct bpf_map
       *map, void *key, u64 flags)

              Description
                     This helper is used in programs implementing
                     policies at the skb socket level. If the sk_buff
                     skb is allowed to pass (i.e.  if the verdict eBPF
                     program returns SK_PASS), redirect it to the socket
                     referenced by map (of type BPF_MAP_TYPE_SOCKHASH)
                     using hash key. Both ingress and egress interfaces
                     can be used for redirection. The BPF_F_INGRESS
                     value in flags is used to make the distinction
                     (ingress path is selected if the flag is present,
                     egress otherwise). This is the only flag supported
                     for now.

              Return SK_PASS on success, or SK_DROP on error.

       long bpf_lwt_push_encap(struct sk_buff *skb, u32 type, void *hdr,
       u32 len)

              Description
                     Encapsulate the packet associated to skb within a
                     Layer 3 protocol header. This header is provided in
                     the buffer at address hdr, with len its size in
                     bytes. type indicates the protocol of the header
                     and can be one of:

                     BPF_LWT_ENCAP_SEG6
                            IPv6 encapsulation with Segment Routing
                            Header (struct ipv6_sr_hdr). hdr only
                            contains the SRH, the IPv6 header is
                            computed by the kernel.

                     BPF_LWT_ENCAP_SEG6_INLINE
                            Only works if skb contains an IPv6 packet.
                            Insert a Segment Routing Header (struct
                            ipv6_sr_hdr) inside the IPv6 header.

                     BPF_LWT_ENCAP_IP
                            IP encapsulation (GRE/GUE/IPIP/etc). The
                            outer header must be IPv4 or IPv6, followed
                            by zero or more additional headers, up to
                            LWT_BPF_MAX_HEADROOM total bytes in all
                            prepended headers. Please note that if
                            skb_is_gso(skb) is true, no more than two
                            headers can be prepended, and the inner
                            header, if present, should be either GRE or
                            UDP/GUE.

                     BPF_LWT_ENCAP_SEG6* types can be called by BPF
                     programs of type BPF_PROG_TYPE_LWT_IN;
                     BPF_LWT_ENCAP_IP type can be called by bpf programs
                     of types BPF_PROG_TYPE_LWT_IN and
                     BPF_PROG_TYPE_LWT_XMIT.

                     A call to this helper is susceptible to change the
                     underlying packet buffer. Therefore, at load time,
                     all checks on pointers previously done by the
                     verifier are invalidated and must be performed
                     again, if the helper is used in combination with
                     direct packet access.

              Return 0 on success, or a negative error in case of
                     failure.

       long bpf_lwt_seg6_store_bytes(struct sk_buff *skb, u32 offset,
       const void *from, u32 len)

              Description
                     Store len bytes from address from into the packet
                     associated to skb, at offset. Only the flags, tag
                     and TLVs inside the outermost IPv6 Segment Routing
                     Header can be modified through this helper.

                     A call to this helper is susceptible to change the
                     underlying packet buffer. Therefore, at load time,
                     all checks on pointers previously done by the
                     verifier are invalidated and must be performed
                     again, if the helper is used in combination with
                     direct packet access.

              Return 0 on success, or a negative error in case of
                     failure.

       long bpf_lwt_seg6_adjust_srh(struct sk_buff *skb, u32 offset, s32
       delta)

              Description
                     Adjust the size allocated to TLVs in the outermost
                     IPv6 Segment Routing Header contained in the packet
                     associated to skb, at position offset by delta
                     bytes. Only offsets after the segments are
                     accepted. delta can be as well positive (growing)
                     as negative (shrinking).

                     A call to this helper is susceptible to change the
                     underlying packet buffer. Therefore, at load time,
                     all checks on pointers previously done by the
                     verifier are invalidated and must be performed
                     again, if the helper is used in combination with
                     direct packet access.

              Return 0 on success, or a negative error in case of
                     failure.

       long bpf_lwt_seg6_action(struct sk_buff *skb, u32 action, void
       *param, u32 param_len)

              Description
                     Apply an IPv6 Segment Routing action of type action
                     to the packet associated to skb. Each action takes
                     a parameter contained at address param, and of
                     length param_len bytes.  action can be one of:

                     SEG6_LOCAL_ACTION_END_X
                            End.X action: Endpoint with Layer-3
                            cross-connect.  Type of param: struct
                            in6_addr.

                     SEG6_LOCAL_ACTION_END_T
                            End.T action: Endpoint with specific IPv6
                            table lookup.  Type of param: int.

                     SEG6_LOCAL_ACTION_END_B6
                            End.B6 action: Endpoint bound to an SRv6
                            policy.  Type of param: struct ipv6_sr_hdr.

                     SEG6_LOCAL_ACTION_END_B6_ENCAP
                            End.B6.Encap action: Endpoint bound to an
                            SRv6 encapsulation policy.  Type of param:
                            struct ipv6_sr_hdr.

                     A call to this helper is susceptible to change the
                     underlying packet buffer. Therefore, at load time,
                     all checks on pointers previously done by the
                     verifier are invalidated and must be performed
                     again, if the helper is used in combination with
                     direct packet access.

              Return 0 on success, or a negative error in case of
                     failure.

       long bpf_rc_repeat(void *ctx)

              Description
                     This helper is used in programs implementing IR
                     decoding, to report a successfully decoded repeat
                     key message. This delays the generation of a key up
                     event for previously generated key down event.

                     Some IR protocols like NEC have a special IR
                     message for repeating last button, for when a
                     button is held down.

                     The ctx should point to the lirc sample as passed
                     into the program.

                     This helper is only available is the kernel was
                     compiled with the CONFIG_BPF_LIRC_MODE2
                     configuration option set to "y".

              Return 0

       long bpf_rc_keydown(void *ctx, u32 protocol, u64 scancode, u32
       toggle)

              Description
                     This helper is used in programs implementing IR
                     decoding, to report a successfully decoded key
                     press with scancode, toggle value in the given
                     protocol. The scancode will be translated to a
                     keycode using the rc keymap, and reported as an
                     input key down event. After a period a key up event
                     is generated. This period can be extended by
                     calling either bpf_rc_keydown() again with the same
                     values, or calling bpf_rc_repeat().

                     Some protocols include a toggle bit, in case the
                     button was released and pressed again between
                     consecutive scancodes.

                     The ctx should point to the lirc sample as passed
                     into the program.

                     The protocol is the decoded protocol number (see
                     enum rc_proto for some predefined values).

                     This helper is only available is the kernel was
                     compiled with the CONFIG_BPF_LIRC_MODE2
                     configuration option set to "y".

              Return 0

       u64 bpf_skb_cgroup_id(struct sk_buff *skb)

              Description
                     Return the cgroup v2 id of the socket associated
                     with the skb.  This is roughly similar to the
                     bpf_get_cgroup_classid() helper for cgroup v1 by
                     providing a tag resp. identifier that can be
                     matched on or used for map lookups e.g. to
                     implement policy. The cgroup v2 id of a given path
                     in the hierarchy is exposed in user space through
                     the f_handle API in order to get to the same 64-bit
                     id.

                     This helper can be used on TC egress path, but not
                     on ingress, and is available only if the kernel was
                     compiled with the CONFIG_SOCK_CGROUP_DATA
                     configuration option.

              Return The id is returned or 0 in case the id could not be
                     retrieved.

       u64 bpf_get_current_cgroup_id(void)

              Return A 64-bit integer containing the current cgroup id
                     based on the cgroup within which the current task
                     is running.

       void *bpf_get_local_storage(void *map, u64 flags)

              Description
                     Get the pointer to the local storage area.  The
                     type and the size of the local storage is defined
                     by the map argument.  The flags meaning is specific
                     for each map type, and has to be 0 for cgroup local
                     storage.

                     Depending on the BPF program type, a local storage
                     area can be shared between multiple instances of
                     the BPF program, running simultaneously.

                     A user should care about the synchronization by
                     himself.  For example, by using the BPF_STX_XADD
                     instruction to alter the shared data.

              Return A pointer to the local storage area.

       long bpf_sk_select_reuseport(struct sk_reuseport_md *reuse,
       struct bpf_map *map, void *key, u64 flags)

              Description
                     Select a SO_REUSEPORT socket from a
                     BPF_MAP_TYPE_REUSEPORT_ARRAY map.  It checks the
                     selected socket is matching the incoming request in
                     the socket buffer.

              Return 0 on success, or a negative error in case of
                     failure.

       u64 bpf_skb_ancestor_cgroup_id(struct sk_buff *skb, int
       ancestor_level)

              Description
                     Return id of cgroup v2 that is ancestor of cgroup
                     associated with the skb at the ancestor_level.  The
                     root cgroup is at ancestor_level zero and each step
                     down the hierarchy increments the level. If
                     ancestor_level == level of cgroup associated with
                     skb, then return value will be same as that of
                     bpf_skb_cgroup_id().

                     The helper is useful to implement policies based on
                     cgroups that are upper in hierarchy than immediate
                     cgroup associated with skb.

                     The format of returned id and helper limitations
                     are same as in bpf_skb_cgroup_id().

              Return The id is returned or 0 in case the id could not be
                     retrieved.

       struct bpf_sock *bpf_sk_lookup_tcp(void *ctx, struct
       bpf_sock_tuple *tuple, u32 tuple_size, u64 netns, u64 flags)

              Description
                     Look for TCP socket matching tuple, optionally in a
                     child network namespace netns. The return value
                     must be checked, and if non-NULL, released via
                     bpf_sk_release().

                     The ctx should point to the context of the program,
                     such as the skb or socket (depending on the hook in
                     use). This is used to determine the base network
                     namespace for the lookup.

                     tuple_size must be one of:

                     sizeof(tuple->ipv4)
                            Look for an IPv4 socket.

                     sizeof(tuple->ipv6)
                            Look for an IPv6 socket.

                     If the netns is a negative signed 32-bit integer,
                     then the socket lookup table in the netns
                     associated with the ctx will be used. For the TC
                     hooks, this is the netns of the device in the skb.
                     For socket hooks, this is the netns of the socket.
                     If netns is any other signed 32-bit value greater
                     than or equal to zero then it specifies the ID of
                     the netns relative to the netns associated with the
                     ctx. netns values beyond the range of 32-bit
                     integers are reserved for future use.

                     All values for flags are reserved for future usage,
                     and must be left at zero.

                     This helper is available only if the kernel was
                     compiled with CONFIG_NET configuration option.

              Return Pointer to struct bpf_sock, or NULL in case of
                     failure.  For sockets with reuseport option, the
                     struct bpf_sock result is from reuse->socks[] using
                     the hash of the tuple.

       struct bpf_sock *bpf_sk_lookup_udp(void *ctx, struct
       bpf_sock_tuple *tuple, u32 tuple_size, u64 netns, u64 flags)

              Description
                     Look for UDP socket matching tuple, optionally in a
                     child network namespace netns. The return value
                     must be checked, and if non-NULL, released via
                     bpf_sk_release().

                     The ctx should point to the context of the program,
                     such as the skb or socket (depending on the hook in
                     use). This is used to determine the base network
                     namespace for the lookup.

                     tuple_size must be one of:

                     sizeof(tuple->ipv4)
                            Look for an IPv4 socket.

                     sizeof(tuple->ipv6)
                            Look for an IPv6 socket.

                     If the netns is a negative signed 32-bit integer,
                     then the socket lookup table in the netns
                     associated with the ctx will be used. For the TC
                     hooks, this is the netns of the device in the skb.
                     For socket hooks, this is the netns of the socket.
                     If netns is any other signed 32-bit value greater
                     than or equal to zero then it specifies the ID of
                     the netns relative to the netns associated with the
                     ctx. netns values beyond the range of 32-bit
                     integers are reserved for future use.

                     All values for flags are reserved for future usage,
                     and must be left at zero.

                     This helper is available only if the kernel was
                     compiled with CONFIG_NET configuration option.

              Return Pointer to struct bpf_sock, or NULL in case of
                     failure.  For sockets with reuseport option, the
                     struct bpf_sock result is from reuse->socks[] using
                     the hash of the tuple.

       long bpf_sk_release(struct bpf_sock *sock)

              Description
                     Release the reference held by sock. sock must be a
                     non-NULL pointer that was returned from
                     bpf_sk_lookup_xxx().

              Return 0 on success, or a negative error in case of
                     failure.

       long bpf_map_push_elem(struct bpf_map *map, const void *value,
       u64 flags)

              Description
                     Push an element value in map. flags is one of:

                     BPF_EXIST
                            If the queue/stack is full, the oldest
                            element is removed to make room for this.

              Return 0 on success, or a negative error in case of
                     failure.

       long bpf_map_pop_elem(struct bpf_map *map, void *value)

              Description
                     Pop an element from map.

              Return 0 on success, or a negative error in case of
                     failure.

       long bpf_map_peek_elem(struct bpf_map *map, void *value)

              Description
                     Get an element from map without removing it.

              Return 0 on success, or a negative error in case of
                     failure.

       long bpf_msg_push_data(struct sk_msg_buff *msg, u32 start, u32
       len, u64 flags)

              Description
                     For socket policies, insert len bytes into msg at
                     offset start.

                     If a program of type BPF_PROG_TYPE_SK_MSG is run on
                     a msg it may want to insert metadata or options
                     into the msg.  This can later be read and used by
                     any of the lower layer BPF hooks.

                     This helper may fail if under memory pressure (a
                     malloc fails) in these cases BPF programs will get
                     an appropriate error and BPF programs will need to
                     handle them.

              Return 0 on success, or a negative error in case of
                     failure.

       long bpf_msg_pop_data(struct sk_msg_buff *msg, u32 start, u32
       len, u64 flags)

              Description
                     Will remove len bytes from a msg starting at byte
                     start.  This may result in ENOMEM errors under
                     certain situations if an allocation and copy are
                     required due to a full ring buffer.  However, the
                     helper will try to avoid doing the allocation if
                     possible. Other errors can occur if input
                     parameters are invalid either due to start byte not
                     being valid part of msg payload and/or pop value
                     being to large.

              Return 0 on success, or a negative error in case of
                     failure.

       long bpf_rc_pointer_rel(void *ctx, s32 rel_x, s32 rel_y)

              Description
                     This helper is used in programs implementing IR
                     decoding, to report a successfully decoded pointer
                     movement.

                     The ctx should point to the lirc sample as passed
                     into the program.

                     This helper is only available is the kernel was
                     compiled with the CONFIG_BPF_LIRC_MODE2
                     configuration option set to "y".

              Return 0

       long bpf_spin_lock(struct bpf_spin_lock *lock)

              Description
                     Acquire a spinlock represented by the pointer lock,
                     which is stored as part of a value of a map. Taking
                     the lock allows to safely update the rest of the
                     fields in that value. The spinlock can (and must)
                     later be released with a call to
                     bpf_spin_unlock(lock).

                     Spinlocks in BPF programs come with a number of
                     restrictions and constraints:

                     • bpf_spin_lock objects are only allowed inside
                       maps of types BPF_MAP_TYPE_HASH and
                       BPF_MAP_TYPE_ARRAY (this list could be extended
                       in the future).

                     • BTF description of the map is mandatory.

                     • The BPF program can take ONE lock at a time,
                       since taking two or more could cause dead locks.

                     • Only one struct bpf_spin_lock is allowed per map
                       element.

                     • When the lock is taken, calls (either BPF to BPF
                       or helpers) are not allowed.

                     • The BPF_LD_ABS and BPF_LD_IND instructions are
                       not allowed inside a spinlock-ed region.

                     • The BPF program MUST call bpf_spin_unlock() to
                       release the lock, on all execution paths, before
                       it returns.

                     • The BPF program can access struct bpf_spin_lock
                       only via the bpf_spin_lock() and
                       bpf_spin_unlock() helpers. Loading or storing
                       data into the struct bpf_spin_lock lock; field of
                       a map is not allowed.

                     • To use the bpf_spin_lock() helper, the BTF
                       description of the map value must be a struct and
                       have struct bpf_spin_lock anyname; field at the
                       top level.  Nested lock inside another struct is
                       not allowed.

                     • The struct bpf_spin_lock lock field in a map
                       value must be aligned on a multiple of 4 bytes in
                       that value.

                     • Syscall with command BPF_MAP_LOOKUP_ELEM does not
                       copy the bpf_spin_lock field to user space.

                     • Syscall with command BPF_MAP_UPDATE_ELEM, or
                       update from a BPF program, do not update the
                       bpf_spin_lock field.

                     • bpf_spin_lock cannot be on the stack or inside a
                       networking packet (it can only be inside of a map
                       values).

                     • bpf_spin_lock is available to root only.

                     • Tracing programs and socket filter programs
                       cannot use bpf_spin_lock() due to insufficient
                       preemption checks (but this may change in the
                       future).

                     • bpf_spin_lock is not allowed in inner maps of
                       map-in-map.

              Return 0

       long bpf_spin_unlock(struct bpf_spin_lock *lock)

              Description
                     Release the lock previously locked by a call to
                     bpf_spin_lock(lock).

              Return 0

       struct bpf_sock *bpf_sk_fullsock(struct bpf_sock *sk)

              Description
                     This helper gets a struct bpf_sock pointer such
                     that all the fields in this bpf_sock can be
                     accessed.

              Return A struct bpf_sock pointer on success, or NULL in
                     case of failure.

       struct bpf_tcp_sock *bpf_tcp_sock(struct bpf_sock *sk)

              Description
                     This helper gets a struct bpf_tcp_sock pointer from
                     a struct bpf_sock pointer.

              Return A struct bpf_tcp_sock pointer on success, or NULL
                     in case of failure.

       long bpf_skb_ecn_set_ce(struct sk_buff *skb)

              Description
                     Set ECN (Explicit Congestion Notification) field of
                     IP header to CE (Congestion Encountered) if current
                     value is ECT (ECN Capable Transport). Otherwise, do
                     nothing. Works with IPv6 and IPv4.

              Return 1 if the CE flag is set (either by the current
                     helper call or because it was already present), 0
                     if it is not set.

       struct bpf_sock *bpf_get_listener_sock(struct bpf_sock *sk)

              Description
                     Return a struct bpf_sock pointer in TCP_LISTEN
                     state.  bpf_sk_release() is unnecessary and not
                     allowed.

              Return A struct bpf_sock pointer on success, or NULL in
                     case of failure.

       struct bpf_sock *bpf_skc_lookup_tcp(void *ctx, struct
       bpf_sock_tuple *tuple, u32 tuple_size, u64 netns, u64 flags)

              Description
                     Look for TCP socket matching tuple, optionally in a
                     child network namespace netns. The return value
                     must be checked, and if non-NULL, released via
                     bpf_sk_release().

                     This function is identical to bpf_sk_lookup_tcp(),
                     except that it also returns timewait or request
                     sockets. Use bpf_sk_fullsock() or bpf_tcp_sock() to
                     access the full structure.

                     This helper is available only if the kernel was
                     compiled with CONFIG_NET configuration option.

              Return Pointer to struct bpf_sock, or NULL in case of
                     failure.  For sockets with reuseport option, the
                     struct bpf_sock result is from reuse->socks[] using
                     the hash of the tuple.

       long bpf_tcp_check_syncookie(struct bpf_sock *sk, void *iph, u32
       iph_len, struct tcphdr *th, u32 th_len)

              Description
                     Check whether iph and th contain a valid SYN cookie
                     ACK for the listening socket in sk.

                     iph points to the start of the IPv4 or IPv6 header,
                     while iph_len contains sizeof(struct iphdr) or
                     sizeof(struct ip6hdr).

                     th points to the start of the TCP header, while
                     th_len contains sizeof(struct tcphdr).

              Return 0 if iph and th are a valid SYN cookie ACK, or a
                     negative error otherwise.

       long bpf_sysctl_get_name(struct bpf_sysctl *ctx, char *buf,
       size_t buf_len, u64 flags)

              Description
                     Get name of sysctl in /proc/sys/ and copy it into
                     provided by program buffer buf of size buf_len.

                     The buffer is always NUL terminated, unless it's
                     zero-sized.

                     If flags is zero, full name (e.g.
                     "net/ipv4/tcp_mem") is copied. Use
                     BPF_F_SYSCTL_BASE_NAME flag to copy base name only
                     (e.g. "tcp_mem").

              Return Number of character copied (not including the
                     trailing NUL).

                     -E2BIG if the buffer wasn't big enough (buf will
                     contain truncated name in this case).

       long bpf_sysctl_get_current_value(struct bpf_sysctl *ctx, char
       *buf, size_t buf_len)

              Description
                     Get current value of sysctl as it is presented in
                     /proc/sys (incl. newline, etc), and copy it as a
                     string into provided by program buffer buf of size
                     buf_len.

                     The whole value is copied, no matter what file
                     position user space issued e.g. sys_read at.

                     The buffer is always NUL terminated, unless it's
                     zero-sized.

              Return Number of character copied (not including the
                     trailing NUL).

                     -E2BIG if the buffer wasn't big enough (buf will
                     contain truncated name in this case).

                     -EINVAL if current value was unavailable, e.g.
                     because sysctl is uninitialized and read returns
                     -EIO for it.

       long bpf_sysctl_get_new_value(struct bpf_sysctl *ctx, char *buf,
       size_t buf_len)

              Description
                     Get new value being written by user space to sysctl
                     (before the actual write happens) and copy it as a
                     string into provided by program buffer buf of size
                     buf_len.

                     User space may write new value at file position >
                     0.

                     The buffer is always NUL terminated, unless it's
                     zero-sized.

              Return Number of character copied (not including the
                     trailing NUL).

                     -E2BIG if the buffer wasn't big enough (buf will
                     contain truncated name in this case).

                     -EINVAL if sysctl is being read.

       long bpf_sysctl_set_new_value(struct bpf_sysctl *ctx, const char
       *buf, size_t buf_len)

              Description
                     Override new value being written by user space to
                     sysctl with value provided by program in buffer buf
                     of size buf_len.

                     buf should contain a string in same form as
                     provided by user space on sysctl write.

                     User space may write new value at file position >
                     0. To override the whole sysctl value file position
                     should be set to zero.

              Return 0 on success.

                     -E2BIG if the buf_len is too big.

                     -EINVAL if sysctl is being read.

       long bpf_strtol(const char *buf, size_t buf_len, u64 flags, long
       *res)

              Description
                     Convert the initial part of the string from buffer
                     buf of size buf_len to a long integer according to
                     the given base and save the result in res.

                     The string may begin with an arbitrary amount of
                     white space (as determined by isspace(3)) followed
                     by a single optional '-' sign.

                     Five least significant bits of flags encode base,
                     other bits are currently unused.

                     Base must be either 8, 10, 16 or 0 to detect it
                     automatically similar to user space strtol(3).

              Return Number of characters consumed on success. Must be
                     positive but no more than buf_len.

                     -EINVAL if no valid digits were found or
                     unsupported base was provided.

                     -ERANGE if resulting value was out of range.

       long bpf_strtoul(const char *buf, size_t buf_len, u64 flags,
       unsigned long *res)

              Description
                     Convert the initial part of the string from buffer
                     buf of size buf_len to an unsigned long integer
                     according to the given base and save the result in
                     res.

                     The string may begin with an arbitrary amount of
                     white space (as determined by isspace(3)).

                     Five least significant bits of flags encode base,
                     other bits are currently unused.

                     Base must be either 8, 10, 16 or 0 to detect it
                     automatically similar to user space strtoul(3).

              Return Number of characters consumed on success. Must be
                     positive but no more than buf_len.

                     -EINVAL if no valid digits were found or
                     unsupported base was provided.

                     -ERANGE if resulting value was out of range.

       void *bpf_sk_storage_get(struct bpf_map *map, struct bpf_sock
       *sk, void *value, u64 flags)

              Description
                     Get a bpf-local-storage from a sk.

                     Logically, it could be thought of getting the value
                     from a map with sk as the key.  From this
                     perspective,  the usage is not much different from
                     bpf_map_lookup_elem(map, &sk) except this helper
                     enforces the key must be a full socket and the map
                     must be a BPF_MAP_TYPE_SK_STORAGE also.

                     Underneath, the value is stored locally at sk
                     instead of the map.  The map is used as the
                     bpf-local-storage "type". The bpf-local-storage
                     "type" (i.e. the map) is searched against all
                     bpf-local-storages residing at sk.

                     An optional flags (BPF_SK_STORAGE_GET_F_CREATE) can
                     be used such that a new bpf-local-storage will be
                     created if one does not exist.  value can be used
                     together with BPF_SK_STORAGE_GET_F_CREATE to
                     specify the initial value of a bpf-local-storage.
                     If value is NULL, the new bpf-local-storage will be
                     zero initialized.

              Return A bpf-local-storage pointer is returned on success.

                     NULL if not found or there was an error in adding a
                     new bpf-local-storage.

       long bpf_sk_storage_delete(struct bpf_map *map, struct bpf_sock
       *sk)

              Description
                     Delete a bpf-local-storage from a sk.

              Return 0 on success.

                     -ENOENT if the bpf-local-storage cannot be found.

       long bpf_send_signal(u32 sig)

              Description
                     Send signal sig to the process of the current task.
                     The signal may be delivered to any of this
                     process's threads.

              Return 0 on success or successfully queued.

                     -EBUSY if work queue under nmi is full.

                     -EINVAL if sig is invalid.

                     -EPERM if no permission to send the sig.

                     -EAGAIN if bpf program can try again.

       s64 bpf_tcp_gen_syncookie(struct bpf_sock *sk, void *iph, u32
       iph_len, struct tcphdr *th, u32 th_len)

              Description
                     Try to issue a SYN cookie for the packet with
                     corresponding IP/TCP headers, iph and th, on the
                     listening socket in sk.

                     iph points to the start of the IPv4 or IPv6 header,
                     while iph_len contains sizeof(struct iphdr) or
                     sizeof(struct ip6hdr).

                     th points to the start of the TCP header, while
                     th_len contains the length of the TCP header.

              Return On success, lower 32 bits hold the generated SYN
                     cookie in followed by 16 bits which hold the MSS
                     value for that cookie, and the top 16 bits are
                     unused.

                     On failure, the returned value is one of the
                     following:

                     -EINVAL SYN cookie cannot be issued due to error

                     -ENOENT SYN cookie should not be issued (no SYN
                     flood)

                     -EOPNOTSUPP kernel configuration does not enable
                     SYN cookies

                     -EPROTONOSUPPORT IP packet version is not 4 or 6

       long bpf_skb_output(void *ctx, struct bpf_map *map, u64 flags,
       void *data, u64 size)

              Description
                     Write raw data blob into a special BPF perf event
                     held by map of type BPF_MAP_TYPE_PERF_EVENT_ARRAY.
                     This perf event must have the following attributes:
                     PERF_SAMPLE_RAW as sample_type, PERF_TYPE_SOFTWARE
                     as type, and PERF_COUNT_SW_BPF_OUTPUT as config.

                     The flags are used to indicate the index in map for
                     which the value must be put, masked with
                     BPF_F_INDEX_MASK.  Alternatively, flags can be set
                     to BPF_F_CURRENT_CPU to indicate that the index of
                     the current CPU core should be used.

                     The value to write, of size, is passed through eBPF
                     stack and pointed by data.

                     ctx is a pointer to in-kernel struct sk_buff.

                     This helper is similar to bpf_perf_event_output()
                     but restricted to raw_tracepoint bpf programs.

              Return 0 on success, or a negative error in case of
                     failure.

       long bpf_probe_read_user(void *dst, u32 size, const void
       *unsafe_ptr)

              Description
                     Safely attempt to read size bytes from user space
                     address unsafe_ptr and store the data in dst.

              Return 0 on success, or a negative error in case of
                     failure.

       long bpf_probe_read_kernel(void *dst, u32 size, const void
       *unsafe_ptr)

              Description
                     Safely attempt to read size bytes from kernel space
                     address unsafe_ptr and store the data in dst.

              Return 0 on success, or a negative error in case of
                     failure.

       long bpf_probe_read_user_str(void *dst, u32 size, const void
       *unsafe_ptr)

              Description
                     Copy a NUL terminated string from an unsafe user
                     address unsafe_ptr to dst. The size should include
                     the terminating NUL byte. In case the string length
                     is smaller than size, the target is not padded with
                     further NUL bytes. If the string length is larger
                     than size, just size-1 bytes are copied and the
                     last byte is set to NUL.

                     On success, the length of the copied string is
                     returned. This makes this helper useful in tracing
                     programs for reading strings, and more importantly
                     to get its length at runtime. See the following
                     snippet:

                        SEC("kprobe/sys_open")
                        void bpf_sys_open(struct pt_regs *ctx)
                        {
                                char buf[PATHLEN]; // PATHLEN is defined to 256
                                int res = bpf_probe_read_user_str(buf, sizeof(buf),
                                                                  ctx->di);

                                // Consume buf, for example push it to
                                // userspace via bpf_perf_event_output(); we
                                // can use res (the string length) as event
                                // size, after checking its boundaries.
                        }

                     In comparison, using bpf_probe_read_user() helper
                     here instead to read the string would require to
                     estimate the length at compile time, and would
                     often result in copying more memory than necessary.

                     Another useful use case is when parsing individual
                     process arguments or individual environment
                     variables navigating current->mm->arg_start and
                     current->mm->env_start: using this helper and the
                     return value, one can quickly iterate at the right
                     offset of the memory area.

              Return On success, the strictly positive length of the
                     string, including the trailing NUL character. On
                     error, a negative value.

       long bpf_probe_read_kernel_str(void *dst, u32 size, const void
       *unsafe_ptr)

              Description
                     Copy a NUL terminated string from an unsafe kernel
                     address unsafe_ptr to dst. Same semantics as with
                     bpf_probe_read_user_str() apply.

              Return On success, the strictly positive length of the
                     string, including the trailing NUL character. On
                     error, a negative value.

       long bpf_tcp_send_ack(void *tp, u32 rcv_nxt)

              Description
                     Send out a tcp-ack. tp is the in-kernel struct
                     tcp_sock.  rcv_nxt is the ack_seq to be sent out.

              Return 0 on success, or a negative error in case of
                     failure.

       long bpf_send_signal_thread(u32 sig)

              Description
                     Send signal sig to the thread corresponding to the
                     current task.

              Return 0 on success or successfully queued.

                     -EBUSY if work queue under nmi is full.

                     -EINVAL if sig is invalid.

                     -EPERM if no permission to send the sig.

                     -EAGAIN if bpf program can try again.

       u64 bpf_jiffies64(void)

              Description
                     Obtain the 64bit jiffies

              Return The 64 bit jiffies

       long bpf_read_branch_records(struct bpf_perf_event_data *ctx,
       void *buf, u32 size, u64 flags)

              Description
                     For an eBPF program attached to a perf event,
                     retrieve the branch records (struct
                     perf_branch_entry) associated to ctx and store it
                     in the buffer pointed by buf up to size size bytes.

              Return On success, number of bytes written to buf. On
                     error, a negative value.

                     The flags can be set to
                     BPF_F_GET_BRANCH_RECORDS_SIZE to instead return the
                     number of bytes required to store all the branch
                     entries. If this flag is set, buf may be NULL.

                     -EINVAL if arguments invalid or size not a multiple
                     of sizeof(struct perf_branch_entry).

                     -ENOENT if architecture does not support branch
                     records.

       long bpf_get_ns_current_pid_tgid(u64 dev, u64 ino, struct
       bpf_pidns_info *nsdata, u32 size)

              Description
                     Returns 0 on success, values for pid and tgid as
                     seen from the current namespace will be returned in
                     nsdata.

              Return 0 on success, or one of the following in case of
                     failure:

                     -EINVAL if dev and inum supplied don't match dev_t
                     and inode number with nsfs of current task, or if
                     dev conversion to dev_t lost high bits.

                     -ENOENT if pidns does not exists for the current
                     task.

       long bpf_xdp_output(void *ctx, struct bpf_map *map, u64 flags,
       void *data, u64 size)

              Description
                     Write raw data blob into a special BPF perf event
                     held by map of type BPF_MAP_TYPE_PERF_EVENT_ARRAY.
                     This perf event must have the following attributes:
                     PERF_SAMPLE_RAW as sample_type, PERF_TYPE_SOFTWARE
                     as type, and PERF_COUNT_SW_BPF_OUTPUT as config.

                     The flags are used to indicate the index in map for
                     which the value must be put, masked with
                     BPF_F_INDEX_MASK.  Alternatively, flags can be set
                     to BPF_F_CURRENT_CPU to indicate that the index of
                     the current CPU core should be used.

                     The value to write, of size, is passed through eBPF
                     stack and pointed by data.

                     ctx is a pointer to in-kernel struct xdp_buff.

                     This helper is similar to bpf_perf_eventoutput()
                     but restricted to raw_tracepoint bpf programs.

              Return 0 on success, or a negative error in case of
                     failure.

       u64 bpf_get_netns_cookie(void *ctx)

              Description
                     Retrieve the cookie (generated by the kernel) of
                     the network namespace the input ctx is associated
                     with. The network namespace cookie remains stable
                     for its lifetime and provides a global identifier
                     that can be assumed unique. If ctx is NULL, then
                     the helper returns the cookie for the initial
                     network namespace. The cookie itself is very
                     similar to that of bpf_get_socket_cookie() helper,
                     but for network namespaces instead of sockets.

              Return A 8-byte long opaque number.

       u64 bpf_get_current_ancestor_cgroup_id(int ancestor_level)

              Description
                     Return id of cgroup v2 that is ancestor of the
                     cgroup associated with the current task at the
                     ancestor_level. The root cgroup is at
                     ancestor_level zero and each step down the
                     hierarchy increments the level. If ancestor_level
                     == level of cgroup associated with the current
                     task, then return value will be the same as that of
                     bpf_get_current_cgroup_id().

                     The helper is useful to implement policies based on
                     cgroups that are upper in hierarchy than immediate
                     cgroup associated with the current task.

                     The format of returned id and helper limitations
                     are same as in bpf_get_current_cgroup_id().

              Return The id is returned or 0 in case the id could not be
                     retrieved.

       long bpf_sk_assign(struct sk_buff *skb, struct bpf_sock *sk, u64
       flags)

              Description
                     Helper is overloaded depending on BPF program type.
                     This description applies to BPF_PROG_TYPE_SCHED_CLS
                     and BPF_PROG_TYPE_SCHED_ACT programs.

                     Assign the sk to the skb. When combined with
                     appropriate routing configuration to receive the
                     packet towards the socket, will cause skb to be
                     delivered to the specified socket.  Subsequent
                     redirection of skb via  bpf_redirect(),
                     bpf_clone_redirect() or other methods outside of
                     BPF may interfere with successful delivery to the
                     socket.

                     This operation is only valid from TC ingress path.

                     The flags argument must be zero.

              Return 0 on success, or a negative error in case of
                     failure:

                     -EINVAL if specified flags are not supported.

                     -ENOENT if the socket is unavailable for
                     assignment.

                     -ENETUNREACH if the socket is unreachable (wrong
                     netns).

                     -EOPNOTSUPP if the operation is not supported, for
                     example a call from outside of TC ingress.

                     -ESOCKTNOSUPPORT if the socket type is not
                     supported (reuseport).

       long bpf_sk_assign(struct bpf_sk_lookup *ctx, struct bpf_sock
       *sk, u64 flags)

              Description
                     Helper is overloaded depending on BPF program type.
                     This description applies to BPF_PROG_TYPE_SK_LOOKUP
                     programs.

                     Select the sk as a result of a socket lookup.

                     For the operation to succeed passed socket must be
                     compatible with the packet description provided by
                     the ctx object.

                     L4 protocol (IPPROTO_TCP or IPPROTO_UDP) must be an
                     exact match. While IP family (AF_INET or AF_INET6)
                     must be compatible, that is IPv6 sockets that are
                     not v6-only can be selected for IPv4 packets.

                     Only TCP listeners and UDP unconnected sockets can
                     be selected. sk can also be NULL to reset any
                     previous selection.

                     flags argument can combination of following values:

                     • BPF_SK_LOOKUP_F_REPLACE to override the previous
                       socket selection, potentially done by a BPF
                       program that ran before us.

                     • BPF_SK_LOOKUP_F_NO_REUSEPORT to skip
                       load-balancing within reuseport group for the
                       socket being selected.

                     On success ctx->sk will point to the selected
                     socket.

              Return 0 on success, or a negative errno in case of
                     failure.

                     • -EAFNOSUPPORT if socket family (sk->family) is
                       not compatible with packet family (ctx->family).

                     • -EEXIST if socket has been already selected,
                       potentially by another program, and
                       BPF_SK_LOOKUP_F_REPLACE flag was not specified.

                     • -EINVAL if unsupported flags were specified.

                     • -EPROTOTYPE if socket L4 protocol (sk->protocol)
                       doesn't match packet protocol (ctx->protocol).

                     • -ESOCKTNOSUPPORT if socket is not in allowed
                       state (TCP listening or UDP unconnected).

       u64 bpf_ktime_get_boot_ns(void)

              Description
                     Return the time elapsed since system boot, in
                     nanoseconds.  Does include the time the system was
                     suspended.  See: clock_gettime(CLOCK_BOOTTIME)

              Return Current ktime.

       long bpf_seq_printf(struct seq_file *m, const char *fmt, u32
       fmt_size, const void *data, u32 data_len)

              Description
                     bpf_seq_printf() uses seq_file seq_printf() to
                     print out the format string.  The m represents the
                     seq_file. The fmt and fmt_size are for the format
                     string itself. The data and data_len are format
                     string arguments. The data are a u64 array and
                     corresponding format string values are stored in
                     the array. For strings and pointers where pointees
                     are accessed, only the pointer values are stored in
                     the data array.  The data_len is the size of data
                     in bytes.

                     Formats %s, %p{i,I}{4,6} requires to read kernel
                     memory.  Reading kernel memory may fail due to
                     either invalid address or valid address but
                     requiring a major memory fault. If reading kernel
                     memory fails, the string for %s will be an empty
                     string, and the ip address for %p{i,I}{4,6} will be
                     0. Not returning error to bpf program is consistent
                     with what bpf_trace_printk() does for now.

              Return 0 on success, or a negative error in case of
                     failure:

                     -EBUSY if per-CPU memory copy buffer is busy, can
                     try again by returning 1 from bpf program.

                     -EINVAL if arguments are invalid, or if fmt is
                     invalid/unsupported.

                     -E2BIG if fmt contains too many format specifiers.

                     -EOVERFLOW if an overflow happened: The same object
                     will be tried again.

       long bpf_seq_write(struct seq_file *m, const void *data, u32 len)

              Description
                     bpf_seq_write() uses seq_file seq_write() to write
                     the data.  The m represents the seq_file. The data
                     and len represent the data to write in bytes.

              Return 0 on success, or a negative error in case of
                     failure:

                     -EOVERFLOW if an overflow happened: The same object
                     will be tried again.

       u64 bpf_sk_cgroup_id(struct bpf_sock *sk)

              Description
                     Return the cgroup v2 id of the socket sk.

                     sk must be a non-NULL pointer to a full socket,
                     e.g. one returned from bpf_sk_lookup_xxx(),
                     bpf_sk_fullsock(), etc. The format of returned id
                     is same as in bpf_skb_cgroup_id().

                     This helper is available only if the kernel was
                     compiled with the CONFIG_SOCK_CGROUP_DATA
                     configuration option.

              Return The id is returned or 0 in case the id could not be
                     retrieved.

       u64 bpf_sk_ancestor_cgroup_id(struct bpf_sock *sk, int
       ancestor_level)

              Description
                     Return id of cgroup v2 that is ancestor of cgroup
                     associated with the sk at the ancestor_level.  The
                     root cgroup is at ancestor_level zero and each step
                     down the hierarchy increments the level. If
                     ancestor_level == level of cgroup associated with
                     sk, then return value will be same as that of
                     bpf_sk_cgroup_id().

                     The helper is useful to implement policies based on
                     cgroups that are upper in hierarchy than immediate
                     cgroup associated with sk.

                     The format of returned id and helper limitations
                     are same as in bpf_sk_cgroup_id().

              Return The id is returned or 0 in case the id could not be
                     retrieved.

       long bpf_ringbuf_output(void *ringbuf, void *data, u64 size, u64
       flags)

              Description
                     Copy size bytes from data into a ring buffer
                     ringbuf.  If BPF_RB_NO_WAKEUP is specified in
                     flags, no notification of new data availability is
                     sent.  If BPF_RB_FORCE_WAKEUP is specified in
                     flags, notification of new data availability is
                     sent unconditionally.

              Return 0 on success, or a negative error in case of
                     failure.

       void *bpf_ringbuf_reserve(void *ringbuf, u64 size, u64 flags)

              Description
                     Reserve size bytes of payload in a ring buffer
                     ringbuf.

              Return Valid pointer with size bytes of memory available;
                     NULL, otherwise.

       void bpf_ringbuf_submit(void *data, u64 flags)

              Description
                     Submit reserved ring buffer sample, pointed to by
                     data.  If BPF_RB_NO_WAKEUP is specified in flags,
                     no notification of new data availability is sent.
                     If BPF_RB_FORCE_WAKEUP is specified in flags,
                     notification of new data availability is sent
                     unconditionally.

              Return Nothing. Always succeeds.

       void bpf_ringbuf_discard(void *data, u64 flags)

              Description
                     Discard reserved ring buffer sample, pointed to by
                     data.  If BPF_RB_NO_WAKEUP is specified in flags,
                     no notification of new data availability is sent.
                     If BPF_RB_FORCE_WAKEUP is specified in flags,
                     notification of new data availability is sent
                     unconditionally.

              Return Nothing. Always succeeds.

       u64 bpf_ringbuf_query(void *ringbuf, u64 flags)

              Description
                     Query various characteristics of provided ring
                     buffer. What exactly is queries is determined by
                     flags:

                     • BPF_RB_AVAIL_DATA: Amount of data not yet
                       consumed.

                     • BPF_RB_RING_SIZE: The size of ring buffer.

                     • BPF_RB_CONS_POS: Consumer position (can wrap
                       around).

                     • BPF_RB_PROD_POS: Producer(s) position (can wrap
                       around).

                     Data returned is just a momentary snapshot of
                     actual values and could be inaccurate, so this
                     facility should be used to power heuristics and for
                     reporting, not to make 100% correct calculation.

              Return Requested value, or 0, if flags are not recognized.

       long bpf_csum_level(struct sk_buff *skb, u64 level)

              Description
                     Change the skbs checksum level by one layer up or
                     down, or reset it entirely to none in order to have
                     the stack perform checksum validation. The level is
                     applicable to the following protocols: TCP, UDP,
                     GRE, SCTP, FCOE. For example, a decap of | ETH | IP
                     | UDP | GUE | IP | TCP | into | ETH | IP | TCP |
                     through bpf_skb_adjust_room() helper with passing
                     in BPF_F_ADJ_ROOM_NO_CSUM_RESET flag would require
                     one call to bpf_csum_level() with
                     BPF_CSUM_LEVEL_DEC since the UDP header is removed.
                     Similarly, an encap of the latter into the former
                     could be accompanied by a helper call to
                     bpf_csum_level() with BPF_CSUM_LEVEL_INC if the skb
                     is still intended to be processed in higher layers
                     of the stack instead of just egressing at tc.

                     There are three supported level settings at this
                     time:

                     • BPF_CSUM_LEVEL_INC: Increases skb->csum_level for
                       skbs with CHECKSUM_UNNECESSARY.

                     • BPF_CSUM_LEVEL_DEC: Decreases skb->csum_level for
                       skbs with CHECKSUM_UNNECESSARY.

                     • BPF_CSUM_LEVEL_RESET: Resets skb->csum_level to 0
                       and sets CHECKSUM_NONE to force checksum
                       validation by the stack.

                     • BPF_CSUM_LEVEL_QUERY: No-op, returns the current
                       skb->csum_level.

              Return 0 on success, or a negative error in case of
                     failure. In the case of BPF_CSUM_LEVEL_QUERY, the
                     current skb->csum_level is returned or the error
                     code -EACCES in case the skb is not subject to
                     CHECKSUM_UNNECESSARY.

       struct tcp6_sock *bpf_skc_to_tcp6_sock(void *sk)

              Description
                     Dynamically cast a sk pointer to a tcp6_sock
                     pointer.

              Return sk if casting is valid, or NULL otherwise.

       struct tcp_sock *bpf_skc_to_tcp_sock(void *sk)

              Description
                     Dynamically cast a sk pointer to a tcp_sock
                     pointer.

              Return sk if casting is valid, or NULL otherwise.

       struct tcp_timewait_sock *bpf_skc_to_tcp_timewait_sock(void *sk)

              Description
                     Dynamically cast a sk pointer to a
                     tcp_timewait_sock pointer.

              Return sk if casting is valid, or NULL otherwise.

       struct tcp_request_sock *bpf_skc_to_tcp_request_sock(void *sk)

              Description
                     Dynamically cast a sk pointer to a tcp_request_sock
                     pointer.

              Return sk if casting is valid, or NULL otherwise.

       struct udp6_sock *bpf_skc_to_udp6_sock(void *sk)

              Description
                     Dynamically cast a sk pointer to a udp6_sock
                     pointer.

              Return sk if casting is valid, or NULL otherwise.

       long bpf_get_task_stack(struct task_struct *task, void *buf, u32
       size, u64 flags)

              Description
                     Return a user or a kernel stack in bpf program
                     provided buffer.  To achieve this, the helper needs
                     task, which is a valid pointer to struct
                     task_struct. To store the stacktrace, the bpf
                     program provides buf with a nonnegative size.

                     The last argument, flags, holds the number of stack
                     frames to skip (from 0 to 255), masked with
                     BPF_F_SKIP_FIELD_MASK. The next bits can be used to
                     set the following flags:

                     BPF_F_USER_STACK
                            Collect a user space stack instead of a
                            kernel stack.

                     BPF_F_USER_BUILD_ID
                            Collect buildid+offset instead of ips for
                            user stack, only valid if BPF_F_USER_STACK
                            is also specified.

                     bpf_get_task_stack() can collect up to
                     PERF_MAX_STACK_DEPTH both kernel and user frames,
                     subject to sufficient large buffer size. Note that
                     this limit can be controlled with the sysctl
                     program, and that it should be manually increased
                     in order to profile long user stacks (such as
                     stacks for Java programs). To do so, use:

                        # sysctl kernel.perf_event_max_stack=<new value>

              Return A non-negative value equal to or less than size on
                     success, or a negative error in case of failure.

EXAMPLES         top

       Example usage for most of the eBPF helpers listed in this manual
       page are available within the Linux kernel sources, at the
       following locations:

       • samples/bpf/tools/testing/selftests/bpf/

LICENSE         top

       eBPF programs can have an associated license, passed along with
       the bytecode instructions to the kernel when the programs are
       loaded. The format for that string is identical to the one in use
       for kernel modules (Dual licenses, such as "Dual BSD/GPL", may be
       used). Some helper functions are only accessible to programs that
       are compatible with the GNU Privacy License (GPL).

       In order to use such helpers, the eBPF program must be loaded
       with the correct license string passed (via attr) to the bpf()
       system call, and this generally translates into the C source code
       of the program containing a line similar to the following:

          char ____license[] __attribute__((section("license"), used)) = "GPL";

IMPLEMENTATION         top

       This manual page is an effort to document the existing eBPF
       helper functions.  But as of this writing, the BPF sub-system is
       under heavy development. New eBPF program or map types are added,
       along with new helper functions. Some helpers are occasionally
       made available for additional program types. So in spite of the
       efforts of the community, this page might not be up-to-date. If
       you want to check by yourself what helper functions exist in your
       kernel, or what types of programs they can support, here are some
       files among the kernel tree that you may be interested in:

       • include/uapi/linux/bpf.h is the main BPF header. It contains
         the full list of all helper functions, as well as many other
         BPF definitions including most of the flags, structs or
         constants used by the helpers.

       • net/core/filter.c contains the definition of most
         network-related helper functions, and the list of program types
         from which they can be used.

       • kernel/trace/bpf_trace.c is the equivalent for most tracing
         program-related helpers.

       • kernel/bpf/verifier.c contains the functions used to check that
         valid types of eBPF maps are used with a given helper function.

       • kernel/bpf/ directory contains other files in which additional
         helpers are defined (for cgroups, sockmaps, etc.).

       • The bpftool utility can be used to probe the availability of
         helper functions on the system (as well as supported program
         and map types, and a number of other parameters). To do so, run
         bpftool feature probe (see bpftool-feature(8) for details). Add
         the unprivileged keyword to list features available to
         unprivileged users.

       Compatibility between helper functions and program types can
       generally be found in the files where helper functions are
       defined. Look for the struct bpf_func_proto objects and for
       functions returning them: these functions contain a list of
       helpers that a given program type can call. Note that the
       default: label of the switch ... case used to filter helpers can
       call other functions, themselves allowing access to additional
       helpers. The requirement for GPL license is also in those struct
       bpf_func_proto.

       Compatibility between helper functions and map types can be found
       in the check_map_func_compatibility() function in file
       kernel/bpf/verifier.c.

       Helper functions that invalidate the checks on data and data_end
       pointers for network processing are listed in function
       bpf_helper_changes_pkt_data() in file net/core/filter.c.

SEE ALSO         top

       bpf(2), bpftool(8), cgroups(7), ip(8), perf_event_open(2),
       sendmsg(2), socket(7), tc-bpf(8)

COLOPHON         top

       This page is part of release 5.10 of the Linux man-pages project.
       A description of the project, information about reporting bugs,
       and the latest version of this page, can be found at
       https://www.kernel.org/doc/man-pages/.

                                                          BPF-HELPERS(7)

Pages that refer to this page: bpf(2)capabilities(7)