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author | André Fabian Silva Delgado <emulatorman@parabola.nu> | 2016-10-20 00:10:27 -0300 |
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committer | André Fabian Silva Delgado <emulatorman@parabola.nu> | 2016-10-20 00:10:27 -0300 |
commit | d0b2f91bede3bd5e3d24dd6803e56eee959c1797 (patch) | |
tree | 7fee4ab0509879c373c4f2cbd5b8a5be5b4041ee /Documentation/media/uapi/v4l/func-open.rst | |
parent | e914f8eb445e8f74b00303c19c2ffceaedd16a05 (diff) |
Linux-libre 4.8.2-gnupck-4.8.2-gnu
Diffstat (limited to 'Documentation/media/uapi/v4l/func-open.rst')
-rw-r--r-- | Documentation/media/uapi/v4l/func-open.rst | 83 |
1 files changed, 83 insertions, 0 deletions
diff --git a/Documentation/media/uapi/v4l/func-open.rst b/Documentation/media/uapi/v4l/func-open.rst new file mode 100644 index 000000000..06bcadc26 --- /dev/null +++ b/Documentation/media/uapi/v4l/func-open.rst @@ -0,0 +1,83 @@ +.. -*- coding: utf-8; mode: rst -*- + +.. _func-open: + +*********** +V4L2 open() +*********** + +Name +==== + +v4l2-open - Open a V4L2 device + + +Synopsis +======== + +.. code-block:: c + + #include <fcntl.h> + + +.. cpp: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 :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. |