86 lines
2.5 KiB
ReStructuredText
86 lines
2.5 KiB
ReStructuredText
|
.. SPDX-License-Identifier: GFDL-1.1-no-invariants-or-later
|
||
|
|
.. c:namespace:: DTV.dmx
|
||
|
|
|
||
|
|
.. _DMX_QBUF:
|
||
|
|
|
||
|
|
*************************
|
||
|
|
ioctl DMX_QBUF, DMX_DQBUF
|
||
|
|
*************************
|
||
|
|
|
||
|
|
Name
|
||
|
|
====
|
||
|
|
|
||
|
|
DMX_QBUF - DMX_DQBUF - Exchange a buffer with the driver
|
||
|
|
|
||
|
|
.. warning:: this API is still experimental
|
||
|
|
|
||
|
|
Synopsis
|
||
|
|
========
|
||
|
|
|
||
|
|
.. c:macro:: DMX_QBUF
|
||
|
|
|
||
|
|
``int ioctl(int fd, DMX_QBUF, struct dmx_buffer *argp)``
|
||
|
|
|
||
|
|
.. c:macro:: DMX_DQBUF
|
||
|
|
|
||
|
|
``int ioctl(int fd, DMX_DQBUF, struct dmx_buffer *argp)``
|
||
|
|
|
||
|
|
Arguments
|
||
|
|
=========
|
||
|
|
|
||
|
|
``fd``
|
||
|
|
File descriptor returned by :c:func:`open()`.
|
||
|
|
|
||
|
|
``argp``
|
||
|
|
Pointer to struct :c:type:`dmx_buffer`.
|
||
|
|
|
||
|
|
Description
|
||
|
|
===========
|
||
|
|
|
||
|
|
Applications call the ``DMX_QBUF`` ioctl to enqueue an empty
|
||
|
|
(capturing) or filled (output) buffer in the driver's incoming queue.
|
||
|
|
The semantics depend on the selected I/O method.
|
||
|
|
|
||
|
|
To enqueue a buffer applications set the ``index`` field. Valid index
|
||
|
|
numbers range from zero to the number of buffers allocated with
|
||
|
|
:ref:`DMX_REQBUFS` (struct :c:type:`dmx_requestbuffers` ``count``) minus
|
||
|
|
one. The contents of the struct :c:type:`dmx_buffer` returned
|
||
|
|
by a :ref:`DMX_QUERYBUF` ioctl will do as well.
|
||
|
|
|
||
|
|
When ``DMX_QBUF`` is called with a pointer to this structure, it locks the
|
||
|
|
memory pages of the buffer in physical memory, so they cannot be swapped
|
||
|
|
out to disk. Buffers remain locked until dequeued, until the
|
||
|
|
device is closed.
|
||
|
|
|
||
|
|
Applications call the ``DMX_DQBUF`` ioctl to dequeue a filled
|
||
|
|
(capturing) buffer from the driver's outgoing queue.
|
||
|
|
They just set the ``index`` field with the buffer ID to be queued.
|
||
|
|
When ``DMX_DQBUF`` is called with a pointer to struct :c:type:`dmx_buffer`,
|
||
|
|
the driver fills the remaining fields or returns an error code.
|
||
|
|
|
||
|
|
By default ``DMX_DQBUF`` blocks when no buffer is in the outgoing
|
||
|
|
queue. When the ``O_NONBLOCK`` flag was given to the
|
||
|
|
:c:func:`open()` function, ``DMX_DQBUF`` returns
|
||
|
|
immediately with an ``EAGAIN`` error code when no buffer is available.
|
||
|
|
|
||
|
|
The struct :c:type:`dmx_buffer` structure is specified in
|
||
|
|
:ref:`buffer`.
|
||
|
|
|
||
|
|
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.
|
||
|
|
|
||
|
|
EAGAIN
|
||
|
|
Non-blocking I/O has been selected using ``O_NONBLOCK`` and no
|
||
|
|
buffer was in the outgoing queue.
|
||
|
|
|
||
|
|
EINVAL
|
||
|
|
The ``index`` is out of bounds, or no buffers have been allocated yet.
|
||
|
|
|
||
|
|
EIO
|
||
|
|
``DMX_DQBUF`` failed due to an internal error. Can also indicate
|
||
|
|
temporary problems like signal loss or CRC errors.
|