request-func-poll.rst (1772B)
1.. SPDX-License-Identifier: GPL-2.0 OR GFDL-1.1-no-invariants-or-later 2.. c:namespace:: MC 3 4.. _request-func-poll: 5 6************** 7request poll() 8************** 9 10Name 11==== 12 13request-poll - Wait for some event on a file descriptor 14 15Synopsis 16======== 17 18.. code-block:: c 19 20 #include <sys/poll.h> 21 22.. c:function:: int poll( struct pollfd *ufds, unsigned int nfds, int timeout ) 23 24Arguments 25========= 26 27``ufds`` 28 List of file descriptor events to be watched 29 30``nfds`` 31 Number of file descriptor events at the \*ufds array 32 33``timeout`` 34 Timeout to wait for events 35 36Description 37=========== 38 39With the :c:func:`poll()` function applications can wait 40for a request to complete. 41 42On success :c:func:`poll()` returns the number of file 43descriptors that have been selected (that is, file descriptors for which the 44``revents`` field of the respective struct :c:type:`pollfd` 45is non-zero). Request file descriptor set the ``POLLPRI`` flag in ``revents`` 46when the request was completed. When the function times out it returns 47a value of zero, on failure it returns -1 and the ``errno`` variable is 48set appropriately. 49 50Attempting to poll for a request that is not yet queued will 51set the ``POLLERR`` flag in ``revents``. 52 53Return Value 54============ 55 56On success, :c:func:`poll()` returns the number of 57structures which have non-zero ``revents`` fields, or zero if the call 58timed out. On error -1 is returned, and the ``errno`` variable is set 59appropriately: 60 61``EBADF`` 62 One or more of the ``ufds`` members specify an invalid file 63 descriptor. 64 65``EFAULT`` 66 ``ufds`` references an inaccessible memory area. 67 68``EINTR`` 69 The call was interrupted by a signal. 70 71``EINVAL`` 72 The ``nfds`` value exceeds the ``RLIMIT_NOFILE`` value. Use 73 ``getrlimit()`` to obtain this value.