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author | Mauro Carvalho Chehab <mchehab+huawei@kernel.org> | 2020-03-04 10:21:39 +0100 |
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committer | Mauro Carvalho Chehab <mchehab+huawei@kernel.org> | 2020-04-14 10:31:49 +0200 |
commit | 54f38fcae536ea202ce7d6a359521492fba30c1f (patch) | |
tree | dd1a2b36d8de0b13702f2716526ad3b91650e090 /Documentation/userspace-api/media/v4l/func-open.rst | |
parent | 5dfb8db56b273740a76e8687ee7efb4b2c0ec83b (diff) | |
download | linux-stable-54f38fcae536ea202ce7d6a359521492fba30c1f.tar.gz linux-stable-54f38fcae536ea202ce7d6a359521492fba30c1f.tar.bz2 linux-stable-54f38fcae536ea202ce7d6a359521492fba30c1f.zip |
media: docs: move uAPI book to userspace-api/media
Since 2017, there is an space reserved for userspace API,
created by changeset 1d596dee3862 ("docs: Create a user-space API guide").
As the media subsystem was one of the first subsystems to use
Sphinx, until this patch, we were keeping things on a separate
place.
Let's just use the new location, as having all uAPI altogether
will likely make things easier for developers.
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Diffstat (limited to 'Documentation/userspace-api/media/v4l/func-open.rst')
-rw-r--r-- | Documentation/userspace-api/media/v4l/func-open.rst | 90 |
1 files changed, 90 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 000000000000..8bcdec8ab387 --- /dev/null +++ b/Documentation/userspace-api/media/v4l/func-open.rst @@ -0,0 +1,90 @@ +.. 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 + +.. _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 ) + :name: v4l2-open + +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 :ref:`read() <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 :ref:`open() <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 :ref:`open() <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 :ref:`open() <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. |