sd_bus_negotiate_fds() controls whether file descriptor passing shall
be negotiated for the specified bus connection. It takes a bus object
and a boolean, which, when true, enables file descriptor passing,
and, when false, disables it. Note that not all transports and
servers support file descriptor passing. In particular, networked
transports generally do not support file descriptor passing. To find
out whether file descriptor passing is available after negotiation,
use sd_bus_can_send(3) and pass SD_BUS_TYPE_UNIX_FD. Note that file
descriptor passing is always enabled for both sending and receiving
or for neither, but never only in one direction. By default, file
descriptor passing is negotiated for all connections.
Note that when bus activation is used, it is highly recommended to
set the AcceptFileDescriptors= setting in the .busname unit file to
the same setting as negotiated by the program ultimately activated.
By default, file descriptor passing is enabled for both.
sd_bus_negotiate_timestamp() controls whether implicit sender
timestamps shall be attached automatically to all incoming messages.
Takes a bus object and a boolean, which, when true, enables
timestamping, and, when false, disables it. Use
sd_bus_message_get_realtime_usec(3), sd_bus_message_get_seqnum(3) to
query the timestamps of incoming messages. If negotiation is disabled
or not supported, these calls will fail with -ENODATA. Note that
currently no transports support timestamping of messages. By default,
message timestamping is not negotiated for connections.
sd_bus_negotiate_creds() controls whether and which implicit sender
credentials shall be attached automatically to all incoming messages.
Takes a bus object and a boolean indicating whether to enable or
disable the credential parts encoded in the bit mask value argument.
Note that not all transports support attaching sender credentials to
messages, or do not support all types of sender credential
parameters, or might suppress them under certain circumstances for
individual messages. Specifically, dbus1 only supports
SD_BUS_CREDS_UNIQUE_NAME. The sender credentials are suitable for
authorization decisions. By default, only
SD_BUS_CREDS_WELL_KNOWN_NAMES and SD_BUS_CREDS_UNIQUE_NAME are
enabled. In fact, these two credential fields are always sent along
and cannot be turned off.
The sd_bus_negotiate_fds() function may be called only before the
connection has been started with sd_bus_start(3). Both
sd_bus_negotiate_timestamp() and sd_bus_negotiate_creds() may also be
called after a connection has been set up. Note that, when operating
on a connection that is shared between multiple components of the
same program (for example via sd_bus_default(3)), it is highly
recommended to only enable additional per message metadata fields,
but never disable them again, in order not to disable functionality
needed by other components.
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report for this manual page, see
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systemd 233 SD_BUS_NEGOTIATE_FDS(3)