1.. SPDX-License-Identifier: GFDL-1.1-no-invariants-or-later
2.. c:namespace:: DTV.dmx
3
4.. _DMX_QUERYBUF:
5
6******************
7ioctl DMX_QUERYBUF
8******************
9
10Name
11====
12
13DMX_QUERYBUF - Query the status of a buffer
14
15.. warning:: this API is still experimental
16
17Synopsis
18========
19
20.. c:macro:: DMX_QUERYBUF
21
22``int ioctl(int fd, DMX_QUERYBUF, struct dvb_buffer *argp)``
23
24Arguments
25=========
26
27``fd``
28    File descriptor returned by :c:func:`open()`.
29
30``argp``
31    Pointer to struct :c:type:`dvb_buffer`.
32
33Description
34===========
35
36This ioctl is part of the mmap streaming I/O method. It can
37be used to query the status of a buffer at any time after buffers have
38been allocated with the :ref:`DMX_REQBUFS` ioctl.
39
40Applications set the ``index`` field. Valid index numbers range from zero
41to the number of buffers allocated with :ref:`DMX_REQBUFS`
42(struct :c:type:`dvb_requestbuffers` ``count``) minus one.
43
44After calling :ref:`DMX_QUERYBUF` with a pointer to this structure,
45drivers return an error code or fill the rest of the structure.
46
47On success, the ``offset`` will contain the offset of the buffer from the
48start of the device memory, the ``length`` field its size, and the
49``bytesused`` the number of bytes occupied by data in the buffer (payload).
50
51Return Value
52============
53
54On success 0 is returned, the ``offset`` will contain the offset of the
55buffer from the start of the device memory, the ``length`` field its size,
56and the ``bytesused`` the number of bytes occupied by data in the buffer
57(payload).
58
59On error it returns -1 and the ``errno`` variable is set
60appropriately. The generic error codes are described at the
61:ref:`Generic Error Codes <gen-errors>` chapter.
62
63EINVAL
64    The ``index`` is out of bounds.
65