0001 .. SPDX-License-Identifier: GPL-2.0 OR GFDL-1.1-no-invariants-or-later
0002 .. c:namespace:: MC
0003
0004 .. _request-func-poll:
0005
0006 **************
0007 request poll()
0008 **************
0009
0010 Name
0011 ====
0012
0013 request-poll - Wait for some event on a file descriptor
0014
0015 Synopsis
0016 ========
0017
0018 .. code-block:: c
0019
0020 #include <sys/poll.h>
0021
0022 .. c:function:: int poll( struct pollfd *ufds, unsigned int nfds, int timeout )
0023
0024 Arguments
0025 =========
0026
0027 ``ufds``
0028 List of file descriptor events to be watched
0029
0030 ``nfds``
0031 Number of file descriptor events at the \*ufds array
0032
0033 ``timeout``
0034 Timeout to wait for events
0035
0036 Description
0037 ===========
0038
0039 With the :c:func:`poll()` function applications can wait
0040 for a request to complete.
0041
0042 On success :c:func:`poll()` returns the number of file
0043 descriptors that have been selected (that is, file descriptors for which the
0044 ``revents`` field of the respective struct :c:type:`pollfd`
0045 is non-zero). Request file descriptor set the ``POLLPRI`` flag in ``revents``
0046 when the request was completed. When the function times out it returns
0047 a value of zero, on failure it returns -1 and the ``errno`` variable is
0048 set appropriately.
0049
0050 Attempting to poll for a request that is not yet queued will
0051 set the ``POLLERR`` flag in ``revents``.
0052
0053 Return Value
0054 ============
0055
0056 On success, :c:func:`poll()` returns the number of
0057 structures which have non-zero ``revents`` fields, or zero if the call
0058 timed out. On error -1 is returned, and the ``errno`` variable is set
0059 appropriately:
0060
0061 ``EBADF``
0062 One or more of the ``ufds`` members specify an invalid file
0063 descriptor.
0064
0065 ``EFAULT``
0066 ``ufds`` references an inaccessible memory area.
0067
0068 ``EINTR``
0069 The call was interrupted by a signal.
0070
0071 ``EINVAL``
0072 The ``nfds`` value exceeds the ``RLIMIT_NOFILE`` value. Use
0073 ``getrlimit()`` to obtain this value.
