Commit | Line | Data |
---|---|---|
5377d91f MH |
1 | .. -*- coding: utf-8; mode: rst -*- |
2 | ||
af4a4d0d | 3 | .. _VIDIOC_QUERYBUF: |
5377d91f MH |
4 | |
5 | ********************* | |
6 | ioctl VIDIOC_QUERYBUF | |
7 | ********************* | |
8 | ||
9 | *man VIDIOC_QUERYBUF(2)* | |
10 | ||
11 | Query the status of a buffer | |
12 | ||
13 | ||
14 | Synopsis | |
15 | ======== | |
16 | ||
17 | .. c:function:: int ioctl( int fd, int request, struct v4l2_buffer *argp ) | |
18 | ||
19 | Arguments | |
20 | ========= | |
21 | ||
22 | ``fd`` | |
23 | File descriptor returned by :ref:`open() <func-open>`. | |
24 | ||
25 | ``request`` | |
26 | VIDIOC_QUERYBUF | |
27 | ||
28 | ``argp`` | |
29 | ||
30 | ||
31 | Description | |
32 | =========== | |
33 | ||
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 time after buffers have | |
7347081e | 36 | been allocated with the :ref:`VIDIOC_REQBUFS` ioctl. |
5377d91f MH |
37 | |
38 | Applications set the ``type`` field of a struct | |
39 | :ref:`v4l2_buffer <v4l2-buffer>` to the same buffer type as was | |
40 | previously used with struct :ref:`v4l2_format <v4l2-format>` ``type`` | |
41 | and struct :ref:`v4l2_requestbuffers <v4l2-requestbuffers>` ``type``, | |
42 | and the ``index`` field. Valid index numbers range from zero to the | |
43 | number of buffers allocated with | |
7347081e | 44 | :ref:`VIDIOC_REQBUFS` (struct |
5377d91f MH |
45 | :ref:`v4l2_requestbuffers <v4l2-requestbuffers>` ``count``) minus |
46 | one. The ``reserved`` and ``reserved2`` fields must be set to 0. When | |
47 | using the :ref:`multi-planar API <planar-apis>`, the ``m.planes`` | |
48 | field must contain a userspace pointer to an array of struct | |
49 | :ref:`v4l2_plane <v4l2-plane>` and the ``length`` field has to be set | |
50 | to the number of elements in that array. After calling | |
51 | ``VIDIOC_QUERYBUF`` with a pointer to this structure drivers return an | |
52 | error code or fill the rest of the structure. | |
53 | ||
54 | In 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 | |
57 | set 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 | |
59 | device memory, the ``length`` field its size. For the multi-planar API, | |
60 | fields ``m.mem_offset`` and ``length`` in the ``m.planes`` array | |
61 | elements will be used instead and the ``length`` field of struct | |
62 | :ref:`v4l2_buffer <v4l2-buffer>` is set to the number of filled-in | |
63 | array elements. The driver may or may not set the remaining fields and | |
64 | flags, they are meaningless in this context. | |
65 | ||
66 | The :c:type:`struct v4l2_buffer` structure is specified in | |
67 | :ref:`buffer`. | |
68 | ||
69 | ||
70 | Return Value | |
71 | ============ | |
72 | ||
73 | On success 0 is returned, on error -1 and the ``errno`` variable is set | |
74 | appropriately. The generic error codes are described at the | |
75 | :ref:`Generic Error Codes <gen-errors>` chapter. | |
76 | ||
77 | EINVAL | |
78 | The buffer ``type`` is not supported, or the ``index`` is out of | |
79 | bounds. | |
80 | ||
81 | ||
82 | .. ------------------------------------------------------------------------------ | |
83 | .. This file was automatically converted from DocBook-XML with the dbxml | |
84 | .. library (https://github.com/return42/sphkerneldoc). The origin XML comes | |
85 | .. from the linux kernel, refer to: | |
86 | .. | |
87 | .. * https://github.com/torvalds/linux/tree/master/Documentation/DocBook | |
88 | .. ------------------------------------------------------------------------------ |