.. SPDX-License-Identifier: GPL-2.0 OR GFDL-1.1-no-invariants-or-later
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.. c:namespace:: MC
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.. _request-func-poll:
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**************
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request poll()
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**************
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Name
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====
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request-poll - Wait for some event on a file descriptor
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Synopsis
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========
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.. code-block:: c
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#include <sys/poll.h>
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.. c:function:: int poll( struct pollfd *ufds, unsigned int nfds, int timeout )
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Arguments
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=========
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``ufds``
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List of file descriptor events to be watched
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``nfds``
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Number of file descriptor events at the \*ufds array
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``timeout``
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Timeout to wait for events
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Description
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===========
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With the :c:func:`poll()` function applications can wait
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for a request to complete.
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On success :c:func:`poll()` returns the number of file
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descriptors that have been selected (that is, file descriptors for which the
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``revents`` field of the respective struct :c:type:`pollfd`
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is non-zero). Request file descriptor set the ``POLLPRI`` flag in ``revents``
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when the request was completed. When the function times out it returns
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a value of zero, on failure it returns -1 and the ``errno`` variable is
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set appropriately.
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Attempting to poll for a request that is not yet queued will
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set the ``POLLERR`` flag in ``revents``.
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Return Value
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============
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On success, :c:func:`poll()` returns the number of
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structures which have non-zero ``revents`` fields, or zero if the call
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timed out. On error -1 is returned, and the ``errno`` variable is set
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appropriately:
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``EBADF``
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One or more of the ``ufds`` members specify an invalid file
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descriptor.
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``EFAULT``
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``ufds`` references an inaccessible memory area.
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``EINTR``
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The call was interrupted by a signal.
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``EINVAL``
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The ``nfds`` value exceeds the ``RLIMIT_NOFILE`` value. Use
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``getrlimit()`` to obtain this value.
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