1 .. SPDX-License-Identifier: GPL-2.0 OR GFDL-1. 1 .. SPDX-License-Identifier: GPL-2.0 OR GFDL-1.1-no-invariants-or-later
2 .. c:namespace:: MC 2 .. c:namespace:: MC
3 3
4 .. _request-func-poll: 4 .. _request-func-poll:
5 5
6 ************** 6 **************
7 request poll() 7 request poll()
8 ************** 8 **************
9 9
10 Name 10 Name
11 ==== 11 ====
12 12
13 request-poll - Wait for some event on a file d 13 request-poll - Wait for some event on a file descriptor
14 14
15 Synopsis 15 Synopsis
16 ======== 16 ========
17 17
18 .. code-block:: c 18 .. code-block:: c
19 19
20 #include <sys/poll.h> 20 #include <sys/poll.h>
21 21
22 .. c:function:: int poll( struct pollfd *ufds, 22 .. c:function:: int poll( struct pollfd *ufds, unsigned int nfds, int timeout )
23 23
24 Arguments 24 Arguments
25 ========= 25 =========
26 26
27 ``ufds`` 27 ``ufds``
28 List of file descriptor events to be watche 28 List of file descriptor events to be watched
29 29
30 ``nfds`` 30 ``nfds``
31 Number of file descriptor events at the \*u 31 Number of file descriptor events at the \*ufds array
32 32
33 ``timeout`` 33 ``timeout``
34 Timeout to wait for events 34 Timeout to wait for events
35 35
36 Description 36 Description
37 =========== 37 ===========
38 38
39 With the :c:func:`poll()` function application 39 With the :c:func:`poll()` function applications can wait
40 for a request to complete. 40 for a request to complete.
41 41
42 On success :c:func:`poll()` returns the number 42 On success :c:func:`poll()` returns the number of file
43 descriptors that have been selected (that is, 43 descriptors that have been selected (that is, file descriptors for which the
44 ``revents`` field of the respective struct :c: 44 ``revents`` field of the respective struct :c:type:`pollfd`
45 is non-zero). Request file descriptor set the 45 is non-zero). Request file descriptor set the ``POLLPRI`` flag in ``revents``
46 when the request was completed. When the func 46 when the request was completed. When the function times out it returns
47 a value of zero, on failure it returns -1 and 47 a value of zero, on failure it returns -1 and the ``errno`` variable is
48 set appropriately. 48 set appropriately.
49 49
50 Attempting to poll for a request that is not y 50 Attempting to poll for a request that is not yet queued will
51 set the ``POLLERR`` flag in ``revents``. 51 set the ``POLLERR`` flag in ``revents``.
52 52
53 Return Value 53 Return Value
54 ============ 54 ============
55 55
56 On success, :c:func:`poll()` returns the numbe 56 On success, :c:func:`poll()` returns the number of
57 structures which have non-zero ``revents`` fie 57 structures which have non-zero ``revents`` fields, or zero if the call
58 timed out. On error -1 is returned, and the `` 58 timed out. On error -1 is returned, and the ``errno`` variable is set
59 appropriately: 59 appropriately:
60 60
61 ``EBADF`` 61 ``EBADF``
62 One or more of the ``ufds`` members specif 62 One or more of the ``ufds`` members specify an invalid file
63 descriptor. 63 descriptor.
64 64
65 ``EFAULT`` 65 ``EFAULT``
66 ``ufds`` references an inaccessible memory 66 ``ufds`` references an inaccessible memory area.
67 67
68 ``EINTR`` 68 ``EINTR``
69 The call was interrupted by a signal. 69 The call was interrupted by a signal.
70 70
71 ``EINVAL`` 71 ``EINVAL``
72 The ``nfds`` value exceeds the ``RLIMIT_NO 72 The ``nfds`` value exceeds the ``RLIMIT_NOFILE`` value. Use
73 ``getrlimit()`` to obtain this value. 73 ``getrlimit()`` to obtain this value.
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