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79 lines
2.0 KiB
79 lines
2.0 KiB
.. SPDX-License-Identifier: GFDL-1.1-no-invariants-or-later |
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.. c:namespace:: V4L |
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.. _func-open: |
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*********** |
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V4L2 open() |
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*********** |
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Name |
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==== |
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v4l2-open - Open a V4L2 device |
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Synopsis |
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======== |
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.. code-block:: c |
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#include <fcntl.h> |
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.. c:function:: int open( const char *device_name, int flags ) |
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Arguments |
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========= |
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``device_name`` |
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Device to be opened. |
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``flags`` |
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Open flags. Access mode must be ``O_RDWR``. This is just a |
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technicality, input devices still support only reading and output |
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devices only writing. |
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When the ``O_NONBLOCK`` flag is given, the :c:func:`read()` |
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function and the :ref:`VIDIOC_DQBUF <VIDIOC_QBUF>` ioctl will |
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return the ``EAGAIN`` error code when no data is available or no |
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buffer is in the driver outgoing queue, otherwise these functions |
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block until data becomes available. All V4L2 drivers exchanging data |
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with applications must support the ``O_NONBLOCK`` flag. |
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Other flags have no effect. |
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Description |
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=========== |
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To open a V4L2 device applications call :c:func:`open()` with the |
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desired device name. This function has no side effects; all data format |
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parameters, current input or output, control values or other properties |
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remain unchanged. At the first :c:func:`open()` call after loading the |
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driver they will be reset to default values, drivers are never in an |
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undefined state. |
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Return Value |
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============ |
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On success :c:func:`open()` returns the new file descriptor. On error |
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-1 is returned, and the ``errno`` variable is set appropriately. |
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Possible error codes are: |
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EACCES |
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The caller has no permission to access the device. |
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EBUSY |
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The driver does not support multiple opens and the device is already |
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in use. |
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ENXIO |
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No device corresponding to this device special file exists. |
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ENOMEM |
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Not enough kernel memory was available to complete the request. |
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EMFILE |
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The process already has the maximum number of files open. |
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ENFILE |
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The limit on the total number of files open on the system has been |
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reached.
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