sd_bus_get_fd(3)

1SD_BUS_GET_FD(3)                 sd_bus_get_fd                SD_BUS_GET_FD(3)
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NAME

6       sd_bus_get_fd, sd_bus_get_events, sd_bus_get_timeout - Get the file
7       descriptor, I/O events and timeout to wait for from a message bus
8       object
9

SYNOPSIS

11       #include <systemd/sd-bus.h>
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13       int sd_bus_get_fd(sd_bus *bus);
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15       int sd_bus_get_events(sd_bus *bus);
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17       int sd_bus_get_timeout(sd_bus *bus, uint64_t *timeout_usec);
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DESCRIPTION

20       sd_bus_get_fd() returns the file descriptor used to communicate from a
21       message bus object. This descriptor can be used with poll(3) or a
22       similar function to wait for I/O events on the specified bus connection
23       object. If the bus object was configured with the sd_bus_set_fd()
24       function, then the input_fd file descriptor used in that call is
25       returned.
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27       sd_bus_get_events() returns the I/O events to wait for, suitable for
28       passing to poll() or a similar call. Returns a combination of POLLIN,
29       POLLOUT, ... events, or negative on error.
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31       sd_bus_get_timeout() returns the timeout in µs to pass to poll() or a
32       similar call when waiting for events on the specified bus connection.
33       The returned timeout may be zero, in which case a subsequent I/O
34       polling call should be invoked in non-blocking mode. The returned
35       timeout may be UINT64_MAX in which case the I/O polling call may block
36       indefinitely, without any applied timeout. Note that the returned
37       timeout should be considered only a maximum sleeping time. It is
38       permissible (and even expected) that shorter timeouts are used by the
39       calling program, in case other event sources are polled in the same
40       event loop. Note that the returned time-value is relative and specified
41       in microseconds. When converting this value in order to pass it as
42       third argument to poll() (which expects milliseconds), care should be
43       taken to use a division that rounds up to ensure the I/O polling
44       operation doesn't sleep for shorter than necessary, which might result
45       in unintended busy looping (alternatively, use ppoll(2) instead of
46       plain poll(), which understands timeouts with nano-second granularity).
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48       These three functions are useful to hook up a bus connection object
49       with an external or manual event loop involving poll() or a similar I/O
50       polling call. Before each invocation of the I/O polling call, all three
51       functions should be invoked: the file descriptor returned by
52       sd_bus_get_fd() should be polled for the events indicated by
53       sd_bus_get_events(), and the I/O call should block for that up to the
54       timeout returned by sd_bus_get_timeout(). After each I/O polling call
55       the bus connection needs to process incoming or outgoing data, by
56       invoking sd_bus_process(3).
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58       Note that these functions are only one of three supported ways to
59       implement I/O event handling for bus connections. Alternatively use
60       sd_bus_attach_event(3) to attach a bus connection to an sd-event(3)
61       event loop. Or use sd_bus_wait(3) as a simple synchronous, blocking I/O
62       waiting call.
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RETURN VALUE

65       On success, sd_bus_get_fd() returns the file descriptor used for
66       communication. On failure, it returns a negative errno-style error
67       code.
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69       On success, sd_bus_get_events() returns the I/O event mask to use for
70       I/O event watching. On failure, it returns a negative errno-style error
71       code.
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73       On success, sd_bus_get_timeout() returns a non-negative integer. On
74       failure, it returns a negative errno-style error code.
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76   Errors
77       Returned errors may indicate the following problems:
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79       -EINVAL
80           An invalid bus object was passed.
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82       -ECHILD
83           The bus connection was allocated in a parent process and is being
84           reused in a child process after fork().
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86       -ENOTCONN
87           The bus connection has been terminated.
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89       -EPERM
90           Two distinct file descriptors were passed for input and output
91           using sd_bus_set_fd(), which sd_bus_get_fd() cannot return.
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93       -ENOPKG
94           The bus cannot be resolved.
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NOTES

97       These APIs are implemented as a shared library, which can be compiled
98       and linked to with the libsystemd pkg-config(1) file.
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NAME

SYNOPSIS

DESCRIPTION

RETURN VALUE

NOTES

SEE ALSO