| b.liu | e958203 | 2025-04-17 19:18:16 +0800 | [diff] [blame^] | 1 | .. Permission is granted to copy, distribute and/or modify this |
| 2 | .. document under the terms of the GNU Free Documentation License, |
| 3 | .. Version 1.1 or any later version published by the Free Software |
| 4 | .. Foundation, with no Invariant Sections, no Front-Cover Texts |
| 5 | .. and no Back-Cover Texts. A copy of the license is included at |
| 6 | .. Documentation/media/uapi/fdl-appendix.rst. |
| 7 | .. |
| 8 | .. TODO: replace it to GFDL-1.1-or-later WITH no-invariant-sections |
| 9 | |
| 10 | .. _func-write: |
| 11 | |
| 12 | ************ |
| 13 | V4L2 write() |
| 14 | ************ |
| 15 | |
| 16 | Name |
| 17 | ==== |
| 18 | |
| 19 | v4l2-write - Write to a V4L2 device |
| 20 | |
| 21 | |
| 22 | Synopsis |
| 23 | ======== |
| 24 | |
| 25 | .. code-block:: c |
| 26 | |
| 27 | #include <unistd.h> |
| 28 | |
| 29 | |
| 30 | .. c:function:: ssize_t write( int fd, void *buf, size_t count ) |
| 31 | :name: v4l2-write |
| 32 | |
| 33 | Arguments |
| 34 | ========= |
| 35 | |
| 36 | ``fd`` |
| 37 | File descriptor returned by :ref:`open() <func-open>`. |
| 38 | |
| 39 | ``buf`` |
| 40 | Buffer with data to be written |
| 41 | |
| 42 | ``count`` |
| 43 | Number of bytes at the buffer |
| 44 | |
| 45 | Description |
| 46 | =========== |
| 47 | |
| 48 | :ref:`write() <func-write>` writes up to ``count`` bytes to the device |
| 49 | referenced by the file descriptor ``fd`` from the buffer starting at |
| 50 | ``buf``. When the hardware outputs are not active yet, this function |
| 51 | enables them. When ``count`` is zero, :ref:`write() <func-write>` returns 0 |
| 52 | without any other effect. |
| 53 | |
| 54 | When the application does not provide more data in time, the previous |
| 55 | video frame, raw VBI image, sliced VPS or WSS data is displayed again. |
| 56 | Sliced Teletext or Closed Caption data is not repeated, the driver |
| 57 | inserts a blank line instead. |
| 58 | |
| 59 | |
| 60 | Return Value |
| 61 | ============ |
| 62 | |
| 63 | On success, the number of bytes written are returned. Zero indicates |
| 64 | nothing was written. On error, -1 is returned, and the ``errno`` |
| 65 | variable is set appropriately. In this case the next write will start at |
| 66 | the beginning of a new frame. Possible error codes are: |
| 67 | |
| 68 | EAGAIN |
| 69 | Non-blocking I/O has been selected using the |
| 70 | :ref:`O_NONBLOCK <func-open>` flag and no buffer space was |
| 71 | available to write the data immediately. |
| 72 | |
| 73 | EBADF |
| 74 | ``fd`` is not a valid file descriptor or is not open for writing. |
| 75 | |
| 76 | EBUSY |
| 77 | The driver does not support multiple write streams and the device is |
| 78 | already in use. |
| 79 | |
| 80 | EFAULT |
| 81 | ``buf`` references an inaccessible memory area. |
| 82 | |
| 83 | EINTR |
| 84 | The call was interrupted by a signal before any data was written. |
| 85 | |
| 86 | EIO |
| 87 | I/O error. This indicates some hardware problem. |
| 88 | |
| 89 | EINVAL |
| 90 | The :ref:`write() <func-write>` function is not supported by this driver, |
| 91 | not on this device, or generally not on this type of device. |