.. Permission is granted to copy, distribute and/or modify this
.. document under the terms of the GNU Free Documentation License,
.. Version 1.1 or any later version published by the Free Software
.. Foundation, with no Invariant Sections, no Front-Cover Texts
.. and no Back-Cover Texts. A copy of the license is included at
.. Documentation/userspace-api/media/fdl-appendix.rst.
..
.. TODO: replace it to GFDL-1.1-or-later WITH no-invariant-sections

.. _cec-func-poll:

**********
cec poll()
**********

Name
====

cec-poll - Wait for some event on a file descriptor


Synopsis
========

.. code-block:: c

    #include <sys/poll.h>


.. c:function:: int poll( struct pollfd *ufds, unsigned int nfds, int timeout )
   :name: cec-poll

Arguments
=========

``ufds``
   List of FD events to be watched

``nfds``
   Number of FD events at the \*ufds array

``timeout``
   Timeout to wait for events


Description
===========

With the :c:func:`poll() <cec-poll>` function applications can wait for CEC
events.

On success :c:func:`poll() <cec-poll>` returns the number of file descriptors
that have been selected (that is, file descriptors for which the
``revents`` field of the respective struct :c:type:`pollfd`
is non-zero). CEC devices set the ``POLLIN`` and ``POLLRDNORM`` flags in
the ``revents`` field if there are messages in the receive queue. If the
transmit queue has room for new messages, the ``POLLOUT`` and
``POLLWRNORM`` flags are set. If there are events in the event queue,
then the ``POLLPRI`` flag is set. When the function times out it returns
a value of zero, on failure it returns -1 and the ``errno`` variable is
set appropriately.

For more details see the :c:func:`poll() <cec-poll>` manual page.


Return Value
============

On success, :c:func:`poll() <cec-poll>` returns the number structures which have
non-zero ``revents`` fields, or zero if the call timed out. On error -1
is returned, and the ``errno`` variable is set appropriately:

``EBADF``
    One or more of the ``ufds`` members specify an invalid file
    descriptor.

``EFAULT``
    ``ufds`` references an inaccessible memory area.

``EINTR``
    The call was interrupted by a signal.

``EINVAL``
    The ``nfds`` value exceeds the ``RLIMIT_NOFILE`` value. Use
    ``getrlimit()`` to obtain this value.
