7.73. V4L2 write()

7.73.1. Name

v4l2-write - Write to a V4L2 device

7.73.2. Synopsis

#include <unistd.h>

ssize_t write(int fd, void *buf, size_t count)

7.73.3. Arguments

fd

File descriptor returned by open().

buf

Buffer with data to be written

count

Number of bytes at the buffer

7.73.4. 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.

7.73.5. 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.