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Diffstat (limited to 'Documentation/userspace-api/media/v4l/func-select.rst')
| -rw-r--r-- | Documentation/userspace-api/media/v4l/func-select.rst | 42 |
1 files changed, 19 insertions, 23 deletions
diff --git a/Documentation/userspace-api/media/v4l/func-select.rst b/Documentation/userspace-api/media/v4l/func-select.rst index 6715d5efcc27..ba1879c728f0 100644 --- a/Documentation/userspace-api/media/v4l/func-select.rst +++ b/Documentation/userspace-api/media/v4l/func-select.rst @@ -1,4 +1,5 @@ .. SPDX-License-Identifier: GFDL-1.1-no-invariants-or-later +.. c:namespace:: V4L .. _func-select: @@ -11,7 +12,6 @@ Name v4l2-select - Synchronous I/O multiplexing - Synopsis ======== @@ -21,9 +21,7 @@ Synopsis #include <sys/types.h> #include <unistd.h> - .. c:function:: int select( int nfds, fd_set *readfds, fd_set *writefds, fd_set *exceptfds, struct timeval *timeout ) - :name: v4l2-select Arguments ========= @@ -43,11 +41,10 @@ Arguments ``timeout`` Maximum time to wait. - Description =========== -With the :ref:`select() <func-select>` function applications can suspend +With the :c:func:`select()` function applications can suspend execution until the driver has captured data or is ready to accept data for output. @@ -56,40 +53,39 @@ buffer has been filled or displayed and can be dequeued with the :ref:`VIDIOC_DQBUF <VIDIOC_QBUF>` ioctl. When buffers are already in the outgoing queue of the driver the function returns immediately. -On success :ref:`select() <func-select>` returns the total number of bits set in -:c:func:`struct fd_set`. When the function timed out it returns +On success :c:func:`select()` returns the total number of bits set in +``fd_set``. When the function timed out it returns a value of zero. On failure it returns -1 and the ``errno`` variable is set appropriately. When the application did not call :ref:`VIDIOC_QBUF` or -:ref:`VIDIOC_STREAMON` yet the :ref:`select() <func-select>` +:ref:`VIDIOC_STREAMON` yet the :c:func:`select()` function succeeds, setting the bit of the file descriptor in ``readfds`` or ``writefds``, but subsequent :ref:`VIDIOC_DQBUF <VIDIOC_QBUF>` calls will fail. [#f1]_ -When use of the :ref:`read() <func-read>` function has been negotiated and the -driver does not capture yet, the :ref:`select() <func-select>` function starts -capturing. When that fails, :ref:`select() <func-select>` returns successful and -a subsequent :ref:`read() <func-read>` call, which also attempts to start +When use of the :c:func:`read()` function has been negotiated and the +driver does not capture yet, the :c:func:`select()` function starts +capturing. When that fails, :c:func:`select()` returns successful and +a subsequent :c:func:`read()` call, which also attempts to start capturing, will return an appropriate error code. When the driver captures continuously (as opposed to, for example, still images) and -data is already available the :ref:`select() <func-select>` function returns +data is already available the :c:func:`select()` function returns immediately. -When use of the :ref:`write() <func-write>` function has been negotiated the -:ref:`select() <func-select>` function just waits until the driver is ready for a -non-blocking :ref:`write() <func-write>` call. +When use of the :c:func:`write()` function has been negotiated the +:c:func:`select()` function just waits until the driver is ready for a +non-blocking :c:func:`write()` call. -All drivers implementing the :ref:`read() <func-read>` or :ref:`write() <func-write>` -function or streaming I/O must also support the :ref:`select() <func-select>` +All drivers implementing the :c:func:`read()` or :c:func:`write()` +function or streaming I/O must also support the :c:func:`select()` function. -For more details see the :ref:`select() <func-select>` manual page. - +For more details see the :c:func:`select()` manual page. Return Value ============ -On success, :ref:`select() <func-select>` returns the number of descriptors +On success, :c:func:`select()` returns the number of descriptors contained in the three returned descriptor sets, which will be zero if the timeout expired. On error -1 is returned, and the ``errno`` variable is set appropriately; the sets and ``timeout`` are undefined. Possible @@ -115,6 +111,6 @@ EINVAL ``FD_SETSIZE``. .. [#f1] - The Linux kernel implements :ref:`select() <func-select>` like the - :ref:`poll() <func-poll>` function, but :ref:`select() <func-select>` cannot + The Linux kernel implements :c:func:`select()` like the + :c:func:`poll()` function, but :c:func:`select()` cannot return a ``POLLERR``. |