7.69. V4L2 write()¶

7.69.1. Name¶

v4l2-write - Write to a V4L2 device

7.69.2. Synopsis¶

#include <unistd.h>

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

7.69.3. Arguments¶

fd: File descriptor returned by open().
buf: Buffer with data to be written
count: Number of bytes at the buffer

7.69.4. 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.

7.69.5. 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.