1.. SPDX-License-Identifier: GFDL-1.1-no-invariants-or-later
2.. c:namespace:: V4L
3
4.. _VIDIOC_QUERYBUF:
5
6*********************
7ioctl VIDIOC_QUERYBUF
8*********************
9
10Name
11====
12
13VIDIOC_QUERYBUF - Query the status of a buffer
14
15Synopsis
16========
17
18.. c:macro:: VIDIOC_QUERYBUF
19
20``int ioctl(int fd, VIDIOC_QUERYBUF, struct v4l2_buffer *argp)``
21
22Arguments
23=========
24
25``fd``
26    File descriptor returned by :c:func:`open()`.
27
28``argp``
29    Pointer to struct :c:type:`v4l2_buffer`.
30
31Description
32===========
33
34This ioctl is part of the :ref:`streaming <mmap>` I/O method. It can
35be used to query the status of a buffer at any time after buffers have
36been allocated with the :ref:`VIDIOC_REQBUFS` ioctl.
37
38Applications set the ``type`` field of a struct
39:c:type:`v4l2_buffer` to the same buffer type as was
40previously used with struct :c:type:`v4l2_format` ``type``
41and struct :c:type:`v4l2_requestbuffers` ``type``,
42and the ``index`` field. Valid index numbers range from zero to the
43number of buffers allocated with
44:ref:`VIDIOC_REQBUFS` (struct
45:c:type:`v4l2_requestbuffers` ``count``) minus
46one. The ``reserved`` and ``reserved2`` fields must be set to 0. When
47using the :ref:`multi-planar API <planar-apis>`, the ``m.planes``
48field must contain a userspace pointer to an array of struct
49:c:type:`v4l2_plane` and the ``length`` field has to be set
50to the number of elements in that array. After calling
51:ref:`VIDIOC_QUERYBUF` with a pointer to this structure drivers return an
52error code or fill the rest of the structure.
53
54In the ``flags`` field the ``V4L2_BUF_FLAG_MAPPED``,
55``V4L2_BUF_FLAG_PREPARED``, ``V4L2_BUF_FLAG_QUEUED`` and
56``V4L2_BUF_FLAG_DONE`` flags will be valid. The ``memory`` field will be
57set to the current I/O method. For the single-planar API, the
58``m.offset`` contains the offset of the buffer from the start of the
59device memory, the ``length`` field its size. For the multi-planar API,
60fields ``m.mem_offset`` and ``length`` in the ``m.planes`` array
61elements will be used instead and the ``length`` field of struct
62:c:type:`v4l2_buffer` is set to the number of filled-in
63array elements. The driver may or may not set the remaining fields and
64flags, they are meaningless in this context.
65
66The struct :c:type:`v4l2_buffer` structure is specified in
67:ref:`buffer`.
68
69Return Value
70============
71
72On success 0 is returned, on error -1 and the ``errno`` variable is set
73appropriately. The generic error codes are described at the
74:ref:`Generic Error Codes <gen-errors>` chapter.
75
76EINVAL
77    The buffer ``type`` is not supported, or the ``index`` is out of
78    bounds.
79