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EPOLL_CTL(2) Linux Programmer's Manual EPOLL_CTL(2)
epoll_ctl - control interface for an epoll descriptor
#include <sys/epoll.h>
int epoll_ctl(int epfd, int op, int fd, struct epoll_event *event);
This system call performs control operations on the epoll(7) instance
referred to by the file descriptor epfd. It requests that the
operation op be performed for the target file descriptor, fd.
Valid values for the op argument are :
EPOLL_CTL_ADD
Register the target file descriptor fd on the epoll instance
referred to by the file descriptor epfd and associate the
event event with the internal file linked to fd.
EPOLL_CTL_MOD
Change the event event associated with the target file
descriptor fd.
EPOLL_CTL_DEL
Remove (deregister) the target file descriptor fd from the
epoll instance referred to by epfd. The event is ignored and
can be NULL (but see BUGS below).
The event argument describes the object linked to the file descriptor
fd. The struct epoll_event is defined as :
typedef union epoll_data {
void *ptr;
int fd;
uint32_t u32;
uint64_t u64;
} epoll_data_t;
struct epoll_event {
uint32_t events; /* Epoll events */
epoll_data_t data; /* User data variable */
};
The events member is a bit set composed using the following available
event types:
EPOLLIN
The associated file is available for read(2) operations.
EPOLLOUT
The associated file is available for write(2) operations.
EPOLLRDHUP (since Linux 2.6.17)
Stream socket peer closed connection, or shut down writing
half of connection. (This flag is especially useful for
writing simple code to detect peer shutdown when using Edge
Triggered monitoring.)
EPOLLPRI
There is urgent data available for read(2) operations.
EPOLLERR
Error condition happened on the associated file descriptor.
epoll_wait(2) will always wait for this event; it is not
necessary to set it in events.
EPOLLHUP
Hang up happened on the associated file descriptor.
epoll_wait(2) will always wait for this event; it is not
necessary to set it in events.
EPOLLET
Sets the Edge Triggered behavior for the associated file
descriptor. The default behavior for epoll is Level
Triggered. See epoll(7) for more detailed information about
Edge and Level Triggered event distribution architectures.
EPOLLONESHOT (since Linux 2.6.2)
Sets the one-shot behavior for the associated file descriptor.
This means that after an event is pulled out with
epoll_wait(2) the associated file descriptor is internally
disabled and no other events will be reported by the epoll
interface. The user must call epoll_ctl() with EPOLL_CTL_MOD
to rearm the file descriptor with a new event mask.
When successful, epoll_ctl() returns zero. When an error occurs,
epoll_ctl() returns -1 and errno is set appropriately.
EBADF epfd or fd is not a valid file descriptor.
EEXIST op was EPOLL_CTL_ADD, and the supplied file descriptor fd is
already registered with this epoll instance.
EINVAL epfd is not an epoll file descriptor, or fd is the same as
epfd, or the requested operation op is not supported by this
interface.
ENOENT op was EPOLL_CTL_MOD or EPOLL_CTL_DEL, and fd is not
registered with this epoll instance.
ENOMEM There was insufficient memory to handle the requested op
control operation.
ENOSPC The limit imposed by /proc/sys/fs/epoll/max_user_watches was
encountered while trying to register (EPOLL_CTL_ADD) a new
file descriptor on an epoll instance. See epoll(7) for
further details.
EPERM The target file fd does not support epoll.
epoll_ctl() was added to the kernel in version 2.6.
epoll_ctl() is Linux-specific. Library support is provided in glibc
starting with version 2.3.2.
The epoll interface supports all file descriptors that support
poll(2).
In kernel versions before 2.6.9, the EPOLL_CTL_DEL operation required
a non-NULL pointer in event, even though this argument is ignored.
Since Linux 2.6.9, event can be specified as NULL when using
EPOLL_CTL_DEL. Applications that need to be portable to kernels
before 2.6.9 should specify a non-NULL pointer in event.
epoll_create(2), epoll_wait(2), poll(2), epoll(7)
This page is part of release 3.51 of the Linux man-pages project. A
description of the project, and information about reporting bugs, can
be found at http://www.kernel.org/doc/man-pages/.
Linux 2012-04-15 EPOLL_CTL(2)
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