Ubuntu Manpage: sd_bus_message_get_monotonic_usec, sd_bus_message_get_realtime_usec, sd_bus_message_get_seqnum

Provided by: libsystemd-dev_255.4-1ubuntu8.5_amd64

NAME

       sd_bus_message_get_monotonic_usec, sd_bus_message_get_realtime_usec, sd_bus_message_get_seqnum - Retrieve
       the sender timestamps and sequence number of a message

SYNOPSIS

       #include <systemd/sd-bus.h>

       int sd_bus_message_get_monotonic_usec(sd_bus_message *message, uint64_t *usec);

       int sd_bus_message_get_realtime_usec(sd_bus_message *message, uint64_t *usec);

       int sd_bus_message_get_seqnum(sd_bus_message *message, uint64_t *seqnum);

DESCRIPTION

sd_bus_message_get_monotonic_usec() returns the monotonic timestamp of the time the message was sent.
This value is in microseconds since the CLOCK_MONOTONIC epoch, see clock_gettime(2) for details.

Similarly, sd_bus_message_get_realtime_usec() returns the realtime (wallclock) timestamp of the time the
message was sent. This value is in microseconds since Jan 1st, 1970, i.e. in the CLOCK_REALTIME clock.

sd_bus_message_get_seqnum() returns the kernel-assigned sequence number of the message. The kernel
assigns a global, monotonically increasing sequence number to all messages transmitted on the local
system, at the time the message was sent. This sequence number is useful for determining message send
order, even across different buses of the local system. The sequence number combined with the boot ID of
the system (as returned by sd_id128_get_boot(3)) is a suitable globally unique identifier for bus
messages.

Note that the sending order and receiving order of messages might differ, in particular for broadcast
messages. This means that the sequence number and the timestamps of messages a client reads are not
necessarily monotonically increasing.

These timestamps and the sequence number are attached to each message by the kernel and cannot be
manipulated by the sender.

Note that these timestamps are only available on some bus transports, and only after support for them has
been negotiated with the sd_bus_negotiate_timestamp(3) call.

RETURN VALUE

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

       On success, the timestamp or sequence number is returned in the specified 64-bit unsigned integer
       variable.

   Errors
       Returned errors may indicate the following problems:

       -EINVAL
           A specified parameter is invalid.

       -ENODATA
           No timestamp or sequence number information is attached to the passed message. This error is returned
           if the underlying transport does not support timestamping or assigning of sequence numbers, or if
           this feature has not been negotiated with sd_bus_negotiate_timestamp(3).

NOTES

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

       The code described here uses getenv(3), which is declared to be not multi-thread-safe. This means that
       the code calling the functions described here must not call setenv(3) from a parallel thread. It is
       recommended to only do calls to setenv() from an early phase of the program when no other threads have
       been started.

HISTORY