Ubuntu Manpage: sd_bus_negotiate_fds, sd_bus_negotiate_timestamp, sd_bus_negotiate_creds

Provided by: libsystemd-dev_229-4ubuntu21.31_amd64

NAME

       sd_bus_negotiate_fds, sd_bus_negotiate_timestamp, 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, uint64_t mask);

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. 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_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. Use
sd_bus_message_get_monotonic_usec(3), 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 not all
transports support timestamping of messages. Specifically, timestamping is only available
on the kdbus transport, but not on dbus1. The timestamping is applied by the kernel and
cannot be manipulated by userspace. 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, implicit sender credentials
on messages are only fully supported on kdbus transports, and dbus1 only supports
SD_BUS_CREDS_UNIQUE_NAME. The sender credentials are attached by the kernel and cannot be
manipulated by userspace, and are thus 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.

RETURN VALUE

       On success, these functions return 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