sd_bus_negotiate_fds

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## Name

sd_bus_negotiate_fds, sd_bus_negotiate_timestamps, sd_bus_negotiate_creds — Control feature negotiation on bus connections

## Synopsis

    #include <systemd/sd-bus.h>

`int sd_bus_negotiate_fds(` | sd_bus *bus,
| int b`)`;

`int sd_bus_negotiate_timestamp(` | sd_bus *bus,
| int b`)`;

`int sd_bus_negotiate_creds(` | sd_bus *bus,
| int b`)`;

## Description

`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. 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_timestamps()` 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. If this is disabled, sd_bus_message_get_monotonic_usec(3), sd_bus_message_get_realtime_usec(3), sd_bus_message_get_seqno(3) fail with `-ENODATA` on incoming messages. Note that not all transports support timestamping of messages. On local transports, the timestamping is applied by the kernel and cannot be manipulated by userspace.

`sd_bus_negotiate_creds()` controls whether implicit sender credentials shall be attached automatically to all incoming messages. Takes a bus object and a bit mask value, which controls which credential parameters are attached. If this is not used, sd_bus_message_get_creds(3) fails with `-ENODATA` on incoming messages. Note that not all transports support attaching sender credentials to messages, or do not support all types of sender credential parameters. On local transports, the sender credentials are attached by the kernel and cannot be manipulated by userspace. By default, no sender credentials are attached.

These functions may be called only before the connection has been started with sd_bus_start(3).

## Return Value

On success, these functions returns 0 or a positive integer. On failure, they return a negative errno-style error code.

## Errors

Returned errors may indicate the following problems:

`-EPERM`

  The bus connection has already been started.

## Notes

`sd_bus_negotiate_fs()` and the other functions described here are available as a shared library, which can be compiled and linked to with the `libsystemd` pkg-config(1) file.

## See Also

systemd(1), sd-bus(3), sd_bus_start(3), sd_bus_message_can_send(3), sd_bus_message_get_monotonic_usec(3), sd_bus_message_get_creds(3)