1.. SPDX-License-Identifier: GPL-2.0 OR GFDL-1.1-no-invariants-or-later 2 3.. _request-func-poll: 4 5************** 6request poll() 7************** 8 9Name 10==== 11 12request-poll - Wait for some event on a file descriptor 13 14 15Synopsis 16======== 17 18.. code-block:: c 19 20 #include <sys/poll.h> 21 22 23.. c:function:: int poll( struct pollfd *ufds, unsigned int nfds, int timeout ) 24 :name: request-poll 25 26Arguments 27========= 28 29``ufds`` 30 List of file descriptor events to be watched 31 32``nfds`` 33 Number of file descriptor events at the \*ufds array 34 35``timeout`` 36 Timeout to wait for events 37 38 39Description 40=========== 41 42With the :c:func:`poll() <request-func-poll>` function applications can wait 43for a request to complete. 44 45On success :c:func:`poll() <request-func-poll>` returns the number of file 46descriptors that have been selected (that is, file descriptors for which the 47``revents`` field of the respective struct :c:type:`pollfd` 48is non-zero). Request file descriptor set the ``POLLPRI`` flag in ``revents`` 49when the request was completed. When the function times out it returns 50a value of zero, on failure it returns -1 and the ``errno`` variable is 51set appropriately. 52 53Attempting to poll for a request that is not yet queued will 54set the ``POLLERR`` flag in ``revents``. 55 56 57Return Value 58============ 59 60On success, :c:func:`poll() <request-func-poll>` returns the number of 61structures which have non-zero ``revents`` fields, or zero if the call 62timed out. On error -1 is returned, and the ``errno`` variable is set 63appropriately: 64 65``EBADF`` 66 One or more of the ``ufds`` members specify an invalid file 67 descriptor. 68 69``EFAULT`` 70 ``ufds`` references an inaccessible memory area. 71 72``EINTR`` 73 The call was interrupted by a signal. 74 75``EINVAL`` 76 The ``nfds`` value exceeds the ``RLIMIT_NOFILE`` value. Use 77 ``getrlimit()`` to obtain this value. 78