V4L2 write()
&manvol;

# v4l2-write

Write to a V4L2 device

          #include <unistd.h>

    	ssize_t write
    	int fd
    	void *buf
    	size_t count

## Arguments

`fd`

  &fd;

`buf`

`count`

## Description

`write()` writes up to `count` bytes to the device referenced by the file descriptor `fd` from the buffer starting at `buf`. When the hardware outputs are not active yet, this function enables them. When `count` is zero, `write()` returns 0 without any other effect.

When the application does not provide more data in time, the previous video frame, raw VBI image, sliced VPS or WSS data is displayed again. Sliced Teletext or Closed Caption data is not repeated, the driver inserts a blank line instead.

## Return Value

On success, the number of bytes written are returned. Zero indicates nothing was written. On error, -1 is returned, and the `errno` variable is set appropriately. In this case the next write will start at the beginning of a new frame. Possible error codes are:

EAGAIN

  Non-blocking I/O has been selected using the `O_NONBLOCK` flag and no buffer space was available to write the data immediately.

EBADF

  `fd` is not a valid file descriptor or is not open for writing.

EBUSY

  The driver does not support multiple write streams and the device is already in use.

EFAULT

  `buf` references an inaccessible memory area.

EINTR

  The call was interrupted by a signal before any data was written.

EIO

  I/O error. This indicates some hardware problem.

EINVAL

  The `write()` function is not supported by this driver, not on this device, or generally not on this type of device.