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.. _DMX_QUERYBUF:
******************
ioctl DMX_QUERYBUF
******************
Name
====
DMX_QUERYBUF - Query the status of a buffer
.. warning:: this API is still experimental
Synopsis
========
.. c:function:: int ioctl( int fd, DMX_QUERYBUF, struct dvb_buffer *argp )
:name: DMX_QUERYBUF
Arguments
=========
``fd``
File descriptor returned by :ref:`open() <dmx_fopen>`.
``argp``
Pointer to struct :c:type:`dvb_buffer`.
Description
===========
This ioctl is part of the mmap streaming I/O method. It can
be used to query the status of a buffer at any time after buffers have
been allocated with the :ref:`DMX_REQBUFS` ioctl.
Applications set the ``index`` field. Valid index numbers range from zero
to the number of buffers allocated with :ref:`DMX_REQBUFS`
(struct :c:type:`dvb_requestbuffers` ``count``) minus one.
After calling :ref:`DMX_QUERYBUF` with a pointer to this structure,
drivers return an error code or fill the rest of the structure.
On success, the ``offset`` will contain the offset of the buffer from the
start of the device memory, the ``length`` field its size, and the
``bytesused`` the number of bytes occupied by data in the buffer (payload).
Return Value
============
On success 0 is returned, the ``offset`` will contain the offset of the
buffer from the start of the device memory, the ``length`` field its size,
and the ``bytesused`` the number of bytes occupied by data in the buffer
(payload).
On error it returns -1 and the ``errno`` variable is set
appropriately. The generic error codes are described at the
:ref:`Generic Error Codes <gen-errors>` chapter.
EINVAL
The ``index`` is out of bounds.
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