1 .. SPDX-License-Identifier: GFDL-1.1-no-invari
2 .. c:namespace:: V4L
3
4 .. _VIDIOC_QUERYBUF:
5
6 *********************
7 ioctl VIDIOC_QUERYBUF
8 *********************
9
10 Name
11 ====
12
13 VIDIOC_QUERYBUF - Query the status of a buffer
14
15 Synopsis
16 ========
17
18 .. c:macro:: VIDIOC_QUERYBUF
19
20 ``int ioctl(int fd, VIDIOC_QUERYBUF, struct v4
21
22 Arguments
23 =========
24
25 ``fd``
26 File descriptor returned by :c:func:`open(
27
28 ``argp``
29 Pointer to struct :c:type:`v4l2_buffer`.
30
31 Description
32 ===========
33
34 This ioctl is part of the :ref:`streaming <mma
35 be used to query the status of a buffer at any
36 been allocated with the :ref:`VIDIOC_REQBUFS`
37
38 Applications set the ``type`` field of a struc
39 :c:type:`v4l2_buffer` to the same buffer type
40 previously used with struct :c:type:`v4l2_form
41 and struct :c:type:`v4l2_requestbuffers` ``typ
42 and the ``index`` field. Valid index numbers r
43 number of buffers allocated with
44 :ref:`VIDIOC_REQBUFS` (struct
45 :c:type:`v4l2_requestbuffers` ``count``) minus
46 one. The ``reserved`` and ``reserved2`` fields
47 using the :ref:`multi-planar API <planar-apis>
48 field must contain a userspace pointer to an a
49 :c:type:`v4l2_plane` and the ``length`` field
50 to the number of elements in that array. After
51 :ref:`VIDIOC_QUERYBUF` with a pointer to this
52 error code or fill the rest of the structure.
53
54 In the ``flags`` field the ``V4L2_BUF_FLAG_MAP
55 ``V4L2_BUF_FLAG_PREPARED``, ``V4L2_BUF_FLAG_QU
56 ``V4L2_BUF_FLAG_DONE`` flags will be valid. Th
57 set to the current I/O method. For the single-
58 ``m.offset`` contains the offset of the buffer
59 device memory, the ``length`` field its size.
60 fields ``m.mem_offset`` and ``length`` in the
61 elements will be used instead and the ``length
62 :c:type:`v4l2_buffer` is set to the number of
63 array elements. The driver may or may not set
64 flags, they are meaningless in this context.
65
66 The struct :c:type:`v4l2_buffer` structure is
67 :ref:`buffer`.
68
69 Return Value
70 ============
71
72 On success 0 is returned, on error -1 and the
73 appropriately. The generic error codes are des
74 :ref:`Generic Error Codes <gen-errors>` chapte
75
76 EINVAL
77 The buffer ``type`` is not supported, or t
78 bounds.
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