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author | Daniel Baumann <daniel.baumann@progress-linux.org> | 2024-04-27 10:05:51 +0000 |
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committer | Daniel Baumann <daniel.baumann@progress-linux.org> | 2024-04-27 10:05:51 +0000 |
commit | 5d1646d90e1f2cceb9f0828f4b28318cd0ec7744 (patch) | |
tree | a94efe259b9009378be6d90eb30d2b019d95c194 /Documentation/userspace-api/media/v4l/func-open.rst | |
parent | Initial commit. (diff) | |
download | linux-upstream/5.10.209.tar.xz linux-upstream/5.10.209.zip |
Adding upstream version 5.10.209.upstream/5.10.209upstream
Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>
Diffstat (limited to '')
-rw-r--r-- | Documentation/userspace-api/media/v4l/func-open.rst | 79 |
1 files changed, 79 insertions, 0 deletions
diff --git a/Documentation/userspace-api/media/v4l/func-open.rst b/Documentation/userspace-api/media/v4l/func-open.rst new file mode 100644 index 000000000..ba23ff1e4 --- /dev/null +++ b/Documentation/userspace-api/media/v4l/func-open.rst @@ -0,0 +1,79 @@ +.. SPDX-License-Identifier: GFDL-1.1-no-invariants-or-later +.. c:namespace:: V4L + +.. _func-open: + +*********** +V4L2 open() +*********** + +Name +==== + +v4l2-open - Open a V4L2 device + +Synopsis +======== + +.. code-block:: c + + #include <fcntl.h> + +.. c:function:: int open( const char *device_name, int flags ) + +Arguments +========= + +``device_name`` + Device to be opened. + +``flags`` + Open flags. Access mode must be ``O_RDWR``. This is just a + technicality, input devices still support only reading and output + devices only writing. + + When the ``O_NONBLOCK`` flag is given, the :c:func:`read()` + function and the :ref:`VIDIOC_DQBUF <VIDIOC_QBUF>` ioctl will + return the ``EAGAIN`` error code when no data is available or no + buffer is in the driver outgoing queue, otherwise these functions + block until data becomes available. All V4L2 drivers exchanging data + with applications must support the ``O_NONBLOCK`` flag. + + Other flags have no effect. + +Description +=========== + +To open a V4L2 device applications call :c:func:`open()` with the +desired device name. This function has no side effects; all data format +parameters, current input or output, control values or other properties +remain unchanged. At the first :c:func:`open()` call after loading the +driver they will be reset to default values, drivers are never in an +undefined state. + +Return Value +============ + +On success :c:func:`open()` returns the new file descriptor. On error +-1 is returned, and the ``errno`` variable is set appropriately. +Possible error codes are: + +EACCES + The caller has no permission to access the device. + +EBUSY + The driver does not support multiple opens and the device is already + in use. + +ENXIO + No device corresponding to this device special file exists. + +ENOMEM + Not enough kernel memory was available to complete the request. + +EMFILE + The process already has the maximum number of files open. + +ENFILE + The limit on the total number of files open on the system has been + reached. |