systemd sd_bus_get_fd 3 sd_bus_get_fd sd_bus_get_events sd_bus_get_timeout Get the file descriptor, I/O events and time-out to wait for from a message bus object #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 sd_bus_get_fd() returns the file descriptor used to communicate from a message bus object. This descriptor can be used with poll3 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_fd3 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 time-out in µs to pass to to poll() or a similar call when waiting for events on the specified bus connection. The returned time-out 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 time-out. Note that the returned time-out should be considered only a maximum sleeping time. It is permissible (and even expected) that shorter time-outs 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 relative and specified in microseconds. When converting this value in order to pass it as third argument to poll() (which expects milliseconds), care should be taken to 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 ppoll3 instead of plain poll(), which understands time-outs 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 time-out 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_process3. Note that these function are only one of three supported ways to implement I/O event handling for bus connections. Alternatively use sd_bus_attach_event3 to attach a bus connection to an sd-event3 event loop. Or use sd_bus_wait3 as a simple synchronous, blocking I/O waiting call. sd_bus_get_fd() returns the file descriptor used for communication, or a negative errno-style error code on error. sd_bus_get_events() returns the I/O event mask to use for I/O event watching, or a negative errno-style error code on error. sd_bus_get_timeout() returns zero or positive on success, or a negative errno-style error code on error. 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. systemd1, sd-bus3, sd_bus_set_fd3, sd_bus_process3, sd_bus_attach_event3, sd_bus_wait3, poll3