1.. SPDX-License-Identifier: GFDL-1.1-no-invariants-or-later 2.. c:namespace:: V4L 3 4.. _func-write: 5 6************ 7V4L2 write() 8************ 9 10Name 11==== 12 13v4l2-write - Write to a V4L2 device 14 15Synopsis 16======== 17 18.. code-block:: c 19 20 #include <unistd.h> 21 22.. c:function:: ssize_t write( int fd, void *buf, size_t count ) 23 24Arguments 25========= 26 27``fd`` 28 File descriptor returned by :c:func:`open()`. 29 30``buf`` 31 Buffer with data to be written 32 33``count`` 34 Number of bytes at the buffer 35 36Description 37=========== 38 39:c:func:`write()` writes up to ``count`` bytes to the device 40referenced by the file descriptor ``fd`` from the buffer starting at 41``buf``. When the hardware outputs are not active yet, this function 42enables them. When ``count`` is zero, :c:func:`write()` returns 0 43without any other effect. 44 45When the application does not provide more data in time, the previous 46video frame, raw VBI image, sliced VPS or WSS data is displayed again. 47Sliced Teletext or Closed Caption data is not repeated, the driver 48inserts a blank line instead. 49 50Return Value 51============ 52 53On success, the number of bytes written are returned. Zero indicates 54nothing was written. On error, -1 is returned, and the ``errno`` 55variable is set appropriately. In this case the next write will start at 56the beginning of a new frame. Possible error codes are: 57 58EAGAIN 59 Non-blocking I/O has been selected using the 60 :ref:`O_NONBLOCK <func-open>` flag and no buffer space was 61 available to write the data immediately. 62 63EBADF 64 ``fd`` is not a valid file descriptor or is not open for writing. 65 66EBUSY 67 The driver does not support multiple write streams and the device is 68 already in use. 69 70EFAULT 71 ``buf`` references an inaccessible memory area. 72 73EINTR 74 The call was interrupted by a signal before any data was written. 75 76EIO 77 I/O error. This indicates some hardware problem. 78 79EINVAL 80 The :c:func:`write()` function is not supported by this driver, 81 not on this device, or generally not on this type of device. 82