1 .. SPDX-License-Identifier: GFDL-1.1-no-invari 1 .. SPDX-License-Identifier: GFDL-1.1-no-invariants-or-later
2 .. c:namespace:: V4L 2 .. c:namespace:: V4L
3 3
4 .. _VIDIOC_QUERYBUF: 4 .. _VIDIOC_QUERYBUF:
5 5
6 ********************* 6 *********************
7 ioctl VIDIOC_QUERYBUF 7 ioctl VIDIOC_QUERYBUF
8 ********************* 8 *********************
9 9
10 Name 10 Name
11 ==== 11 ====
12 12
13 VIDIOC_QUERYBUF - Query the status of a buffer 13 VIDIOC_QUERYBUF - Query the status of a buffer
14 14
15 Synopsis 15 Synopsis
16 ======== 16 ========
17 17
18 .. c:macro:: VIDIOC_QUERYBUF 18 .. c:macro:: VIDIOC_QUERYBUF
19 19
20 ``int ioctl(int fd, VIDIOC_QUERYBUF, struct v4 20 ``int ioctl(int fd, VIDIOC_QUERYBUF, struct v4l2_buffer *argp)``
21 21
22 Arguments 22 Arguments
23 ========= 23 =========
24 24
25 ``fd`` 25 ``fd``
26 File descriptor returned by :c:func:`open( 26 File descriptor returned by :c:func:`open()`.
27 27
28 ``argp`` 28 ``argp``
29 Pointer to struct :c:type:`v4l2_buffer`. 29 Pointer to struct :c:type:`v4l2_buffer`.
30 30
31 Description 31 Description
32 =========== 32 ===========
33 33
34 This ioctl is part of the :ref:`streaming <mma 34 This ioctl is part of the :ref:`streaming <mmap>` I/O method. It can
35 be used to query the status of a buffer at any 35 be used to query the status of a buffer at any time after buffers have
36 been allocated with the :ref:`VIDIOC_REQBUFS` 36 been allocated with the :ref:`VIDIOC_REQBUFS` ioctl.
37 37
38 Applications set the ``type`` field of a struc 38 Applications set the ``type`` field of a struct
39 :c:type:`v4l2_buffer` to the same buffer type 39 :c:type:`v4l2_buffer` to the same buffer type as was
40 previously used with struct :c:type:`v4l2_form 40 previously used with struct :c:type:`v4l2_format` ``type``
41 and struct :c:type:`v4l2_requestbuffers` ``typ 41 and struct :c:type:`v4l2_requestbuffers` ``type``,
42 and the ``index`` field. Valid index numbers r 42 and the ``index`` field. Valid index numbers range from zero to the
43 number of buffers allocated with 43 number of buffers allocated with
44 :ref:`VIDIOC_REQBUFS` (struct 44 :ref:`VIDIOC_REQBUFS` (struct
45 :c:type:`v4l2_requestbuffers` ``count``) minus 45 :c:type:`v4l2_requestbuffers` ``count``) minus
46 one. The ``reserved`` and ``reserved2`` fields 46 one. The ``reserved`` and ``reserved2`` fields must be set to 0. When
47 using the :ref:`multi-planar API <planar-apis> 47 using the :ref:`multi-planar API <planar-apis>`, the ``m.planes``
48 field must contain a userspace pointer to an a 48 field must contain a userspace pointer to an array of struct
49 :c:type:`v4l2_plane` and the ``length`` field 49 :c:type:`v4l2_plane` and the ``length`` field has to be set
50 to the number of elements in that array. After 50 to the number of elements in that array. After calling
51 :ref:`VIDIOC_QUERYBUF` with a pointer to this 51 :ref:`VIDIOC_QUERYBUF` with a pointer to this structure drivers return an
52 error code or fill the rest of the structure. 52 error code or fill the rest of the structure.
53 53
54 In the ``flags`` field the ``V4L2_BUF_FLAG_MAP 54 In the ``flags`` field the ``V4L2_BUF_FLAG_MAPPED``,
55 ``V4L2_BUF_FLAG_PREPARED``, ``V4L2_BUF_FLAG_QU 55 ``V4L2_BUF_FLAG_PREPARED``, ``V4L2_BUF_FLAG_QUEUED`` and
56 ``V4L2_BUF_FLAG_DONE`` flags will be valid. Th 56 ``V4L2_BUF_FLAG_DONE`` flags will be valid. The ``memory`` field will be
57 set to the current I/O method. For the single- 57 set to the current I/O method. For the single-planar API, the
58 ``m.offset`` contains the offset of the buffer 58 ``m.offset`` contains the offset of the buffer from the start of the
59 device memory, the ``length`` field its size. 59 device memory, the ``length`` field its size. For the multi-planar API,
60 fields ``m.mem_offset`` and ``length`` in the 60 fields ``m.mem_offset`` and ``length`` in the ``m.planes`` array
61 elements will be used instead and the ``length 61 elements will be used instead and the ``length`` field of struct
62 :c:type:`v4l2_buffer` is set to the number of 62 :c:type:`v4l2_buffer` is set to the number of filled-in
63 array elements. The driver may or may not set 63 array elements. The driver may or may not set the remaining fields and
64 flags, they are meaningless in this context. 64 flags, they are meaningless in this context.
65 65
66 The struct :c:type:`v4l2_buffer` structure is 66 The struct :c:type:`v4l2_buffer` structure is specified in
67 :ref:`buffer`. 67 :ref:`buffer`.
68 68
69 Return Value 69 Return Value
70 ============ 70 ============
71 71
72 On success 0 is returned, on error -1 and the 72 On success 0 is returned, on error -1 and the ``errno`` variable is set
73 appropriately. The generic error codes are des 73 appropriately. The generic error codes are described at the
74 :ref:`Generic Error Codes <gen-errors>` chapte 74 :ref:`Generic Error Codes <gen-errors>` chapter.
75 75
76 EINVAL 76 EINVAL
77 The buffer ``type`` is not supported, or t 77 The buffer ``type`` is not supported, or the ``index`` is out of
78 bounds. 78 bounds.
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