6.9. ioctl MEDIA_IOC_REQUEST_ALLOC¶
6.9.1. Name¶
MEDIA_IOC_REQUEST_ALLOC - Allocate a request
6.9.2. Synopsis¶
-
int
ioctl(int fd, MEDIA_IOC_REQUEST_ALLOC, int *argp)¶
6.9.4. Description¶
If the media device supports requests, then
this ioctl can be used to allocate a request. If it is not supported, then
errno is set to ENOTTY. A request is accessed through a file descriptor
that is returned in *argp.
If the request was successfully allocated, then the request file descriptor can be passed to the VIDIOC_QBUF, VIDIOC_G_EXT_CTRLS, VIDIOC_S_EXT_CTRLS and VIDIOC_TRY_EXT_CTRLS ioctls.
In addition, the request can be queued by calling ioctl MEDIA_REQUEST_IOC_QUEUE and re-initialized by calling ioctl MEDIA_REQUEST_IOC_REINIT.
Finally, the file descriptor can be polled to wait for the request to complete.
The request will remain allocated until all the file descriptors associated with it are closed by close() and the driver no longer uses the request internally. See also here for more information.
6.9.5. 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.
- ENOTTY
The driver has no support for requests.