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.. SPDX-License-Identifier: GPL-2.0 OR GFDL-1.1-or-later WITH no-invariant-sections
.. _media_request_ioc_queue:
*****************************
ioctl MEDIA_REQUEST_IOC_QUEUE
*****************************
Name
====
MEDIA_REQUEST_IOC_QUEUE - Queue a request
Synopsis
========
.. c:function:: int ioctl( int request_fd, MEDIA_REQUEST_IOC_QUEUE )
:name: MEDIA_REQUEST_IOC_QUEUE
Arguments
=========
``request_fd``
File descriptor returned by :ref:`MEDIA_IOC_REQUEST_ALLOC`.
Description
===========
If the media device supports :ref:`requests <media-request-api>`, 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
:ref:`polled <request-func-poll>` 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.
Typically if you get an error here, then that means that the application
did something wrong and you have to fix the application.
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). ``EPERM`` 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
return an ``ENOENT`` error.
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
:ref:`Generic Error Codes <gen-errors>` chapter.
EBUSY
The request was already queued.
EPERM
The application queued the first buffer directly, but later attempted
to use a request. It is not permitted to mix the two APIs.
ENOENT
The request did not contain any buffers. All requests are required
to have at least one buffer. This can also be returned if required
controls are missing.
ENOMEM
Out of memory when allocating internal data structures for this
request.
EINVAL
The request has invalid data.
EIO
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.
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