SD_BUS_GET_FD(3)                 sd_bus_get_fd                SD_BUS_GET_FD(3)

NAME
       sd_bus_get_fd, sd_bus_get_events, sd_bus_get_timeout - Get the file
       descriptor, I/O events and timeout to wait for from a message bus
       object

SYNOPSIS
       #include <systemd/sd-bus.h>

       int sd_bus_get_fd(sd_bus *bus);

       int sd_bus_get_events(sd_bus *bus);

       int sd_bus_get_timeout(sd_bus *bus, uint64_t *timeout_usec);

DESCRIPTION
       sd_bus_get_fd() returns the file descriptor used to communicate from a
       message bus object. This descriptor can be used with poll(3) or a
       similar function to wait for I/O events on the specified bus connection
       object. If the bus object was configured with the sd_bus_set_fd()
       function, then the input_fd file descriptor used in that call is
       returned.

       sd_bus_get_events() returns the I/O events to wait for, suitable for
       passing to poll() or a similar call. Returns a combination of POLLIN,
       POLLOUT, ... events, or negative on error.

       sd_bus_get_timeout() returns the timeout in <micro>s to pass to poll()
       or a similar call when waiting for events on the specified bus
       connection. The returned timeout may be zero, in which case a
       subsequent I/O polling call should be invoked in non-blocking mode. The
       returned timeout may be UINT64_MAX in which case the I/O polling call
       may block indefinitely, without any applied timeout. Note that the
       returned timeout should be considered only a maximum sleeping time. It
       is permissible (and even expected) that shorter timeouts are used by
       the calling program, in case other event sources are polled in the same
       event loop. Note that the returned time-value is absolute, based of
       CLOCK_MONOTONIC and specified in microseconds. When converting this
       value in order to pass it as third argument to poll() (which expects
       relative milliseconds), care should be taken to convert to a relative
       time and use a division that rounds up to ensure the I/O polling
       operation doesn't sleep for shorter than necessary, which might result
       in unintended busy looping (alternatively, use ppoll(2) instead of
       plain poll(), which understands timeouts with nano-second granularity).

       These three functions are useful to hook up a bus connection object
       with an external or manual event loop involving poll() or a similar I/O
       polling call. Before each invocation of the I/O polling call, all three
       functions should be invoked: the file descriptor returned by
       sd_bus_get_fd() should be polled for the events indicated by
       sd_bus_get_events(), and the I/O call should block for that up to the
       timeout returned by sd_bus_get_timeout(). After each I/O polling call
       the bus connection needs to process incoming or outgoing data, by
       invoking sd_bus_process(3).

       Note that these functions are only one of three supported ways to
       implement I/O event handling for bus connections. Alternatively use
       sd_bus_attach_event(3) to attach a bus connection to an sd-event(3)
       event loop. Or use sd_bus_wait(3) as a simple synchronous, blocking I/O
       waiting call.

RETURN VALUE
       On success, sd_bus_get_fd() returns the file descriptor used for
       communication. On failure, it returns a negative errno-style error
       code.

       On success, sd_bus_get_events() returns the I/O event mask to use for
       I/O event watching. On failure, it returns a negative errno-style error
       code.

       On success, sd_bus_get_timeout() returns a non-negative integer. On
       failure, it returns a negative errno-style error code.

   Errors
       Returned errors may indicate the following problems:

       -EINVAL
           An invalid bus object was passed.

       -ECHILD
           The bus connection was allocated in a parent process and is being
           reused in a child process after fork().

       -ENOTCONN
           The bus connection has been terminated.

       -EPERM
           Two distinct file descriptors were passed for input and output
           using sd_bus_set_fd(), which sd_bus_get_fd() cannot return.

       -ENOPKG
           The bus cannot be resolved.

NOTES
       These APIs are implemented 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_process(3), sd_bus_attach_event(3),
       sd_bus_wait(3), sd_bus_set_fd(3), poll(3)

systemd 252                                                   SD_BUS_GET_FD(3)

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