5.13. ioctl MEDIA_REQUEST_IOC_QUEUE¶
MEDIA_REQUEST_IOC_QUEUE - Queue a request
ioctl(int request_fd, MEDIA_REQUEST_IOC_QUEUE)¶
- File descriptor returned by ioctl MEDIA_IOC_REQUEST_ALLOC.
If the media device supports requests, then this request ioctl can be used to queue a previously allocated request.
If the request was successfully queued, then the file descriptor can be polled to wait for the request to complete.
If the request was already queued before, then
EBUSY is returned.
Other errors can be returned if the contents of the request contained
invalid or inconsistent data, see the next section for a list of
common error codes. On error both the request and driver state are unchanged.
Once a request is queued, then the driver is required to gracefully handle
errors that occur when the request is applied to the hardware. The
exception is the
EIO error which signals a fatal error that requires
the application to stop streaming to reset the hardware state.
It is not allowed to mix queuing requests with queuing buffers directly
(without a request).
EBUSY will be returned if the first buffer was
queued directly and you next try to queue a request, or vice versa.
A request must contain at least one buffer, otherwise this ioctl will
5.13.5. 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.
- The request was already queued or the application queued the first buffer directly, but later attempted to use a request. It is not permitted to mix the two APIs.
- The request did not contain any buffers. All requests are required to have at least one buffer. This can also be returned if some required configuration is missing in the request.
- Out of memory when allocating internal data structures for this request.
- The request has invalid data.
- The hardware is in a bad state. To recover, the application needs to stop streaming to reset the hardware state and then try to restart streaming.