Documentation/userspace-api/media/dvb/dmx-qbuf.rst
.. SPDX-License-Identifier: GFDL-1.1-no-invariants-or-later .. c:namespace:: DTV.dmx
.. _DMX_QBUF:
ioctl DMX_QBUF, DMX_DQBUF
DMX_QBUF - DMX_DQBUF - Exchange a buffer with the driver
.. warning:: this API is still experimental
.. 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)
fd
File descriptor returned by :c:func:open().
argp
Pointer to struct :c:type:dmx_buffer.
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.
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.