7.45. ioctl VIDIOC_PREPARE_BUF

7.45.1. Name

VIDIOC_PREPARE_BUF - Prepare a buffer for I/O

7.45.2. Synopsis

int ioctl(int fd, VIDIOC_PREPARE_BUF, struct v4l2_buffer *argp)

7.45.3. Arguments

fd

File descriptor returned by open().

argp

Pointer to struct v4l2_buffer.

7.45.4. Description

Applications can optionally call the ioctl VIDIOC_PREPARE_BUF ioctl to pass ownership of the buffer to the driver before actually enqueuing it, using the ioctl VIDIOC_QBUF, VIDIOC_DQBUF ioctl, and to prepare it for future I/O. Such preparations may include cache invalidation or cleaning. Performing them in advance saves time during the actual I/O. In case such cache operations are not required, the application can use one of V4L2_BUF_FLAG_NO_CACHE_INVALIDATE and V4L2_BUF_FLAG_NO_CACHE_CLEAN flags to skip the respective step.

The struct v4l2_buffer structure is specified in Buffers.

7.45.5. Return Value

On success 0 is returned, on error -1 and the errno variable is set appropriately. The generic error codes are described at the Generic Error Codes chapter.

EBUSY

File I/O is in progress.

EINVAL

The buffer type is not supported, or the index is out of bounds, or no buffers have been allocated yet, or the userptr or length are invalid.