| Olivier Deprez | 157378f | 2022-04-04 15:47:50 +0200 | [diff] [blame^] | 1 | .. SPDX-License-Identifier: GFDL-1.1-no-invariants-or-later |
| 2 | .. c:namespace:: V4L |
| 3 | |
| 4 | .. _func-open: |
| 5 | |
| 6 | *********** |
| 7 | V4L2 open() |
| 8 | *********** |
| 9 | |
| 10 | Name |
| 11 | ==== |
| 12 | |
| 13 | v4l2-open - Open a V4L2 device |
| 14 | |
| 15 | Synopsis |
| 16 | ======== |
| 17 | |
| 18 | .. code-block:: c |
| 19 | |
| 20 | #include <fcntl.h> |
| 21 | |
| 22 | .. c:function:: int open( const char *device_name, int flags ) |
| 23 | |
| 24 | Arguments |
| 25 | ========= |
| 26 | |
| 27 | ``device_name`` |
| 28 | Device to be opened. |
| 29 | |
| 30 | ``flags`` |
| 31 | Open flags. Access mode must be ``O_RDWR``. This is just a |
| 32 | technicality, input devices still support only reading and output |
| 33 | devices only writing. |
| 34 | |
| 35 | When the ``O_NONBLOCK`` flag is given, the :c:func:`read()` |
| 36 | function and the :ref:`VIDIOC_DQBUF <VIDIOC_QBUF>` ioctl will |
| 37 | return the ``EAGAIN`` error code when no data is available or no |
| 38 | buffer is in the driver outgoing queue, otherwise these functions |
| 39 | block until data becomes available. All V4L2 drivers exchanging data |
| 40 | with applications must support the ``O_NONBLOCK`` flag. |
| 41 | |
| 42 | Other flags have no effect. |
| 43 | |
| 44 | Description |
| 45 | =========== |
| 46 | |
| 47 | To open a V4L2 device applications call :c:func:`open()` with the |
| 48 | desired device name. This function has no side effects; all data format |
| 49 | parameters, current input or output, control values or other properties |
| 50 | remain unchanged. At the first :c:func:`open()` call after loading the |
| 51 | driver they will be reset to default values, drivers are never in an |
| 52 | undefined state. |
| 53 | |
| 54 | Return Value |
| 55 | ============ |
| 56 | |
| 57 | On success :c:func:`open()` returns the new file descriptor. On error |
| 58 | -1 is returned, and the ``errno`` variable is set appropriately. |
| 59 | Possible error codes are: |
| 60 | |
| 61 | EACCES |
| 62 | The caller has no permission to access the device. |
| 63 | |
| 64 | EBUSY |
| 65 | The driver does not support multiple opens and the device is already |
| 66 | in use. |
| 67 | |
| 68 | ENXIO |
| 69 | No device corresponding to this device special file exists. |
| 70 | |
| 71 | ENOMEM |
| 72 | Not enough kernel memory was available to complete the request. |
| 73 | |
| 74 | EMFILE |
| 75 | The process already has the maximum number of files open. |
| 76 | |
| 77 | ENFILE |
| 78 | The limit on the total number of files open on the system has been |
| 79 | reached. |