sd_bus_negotiate_fds, sd_bus_negotiate_timestamp, sd_bus_negotiate_creds, sd_bus_get_creds_mask — Control feature negotiation on bus connections
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_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.
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
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
enabled. In fact, these two credential fields are always sent along and cannot be turned off.
sd_bus_get_creds_mask() returns the set of sender credentials that was
negotiated to be attached to all incoming messages in
mask. This value is an
upper boundary only. Hence, always make sure to explicitly check which credentials are attached to a
specific message before using it.
sd_bus_negotiate_fds() function may be called only before the connection
has been started with
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
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.
On success, these functions return a non-negative integer. On failure, they return a negative errno-style error code.
Functions described here are available as a shared
library, which can be compiled against and linked to with the
The code described here uses
which is declared to be not multi-thread-safe. This means that the code calling the functions described
here must not call
from a parallel thread. It is recommended to only do calls to
from an early phase of the program when no other threads have been started.