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1 | .. -*- coding: utf-8; mode: rst -*- |
2 | ||
af4a4d0d | 3 | .. _VIDIOC_QUERYBUF: |
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4 | |
5 | ********************* | |
6 | ioctl VIDIOC_QUERYBUF | |
7 | ********************* | |
8 | ||
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9 | NAME |
10 | ==== | |
5377d91f | 11 | |
586027ce | 12 | VIDIOC_QUERYBUF - Query the status of a buffer |
5377d91f | 13 | |
586027ce | 14 | SYNOPSIS |
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15 | ======== |
16 | ||
b7e67f6c | 17 | .. cpp:function:: int ioctl( int fd, int request, struct v4l2_buffer *argp ) |
5377d91f | 18 | |
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19 | |
20 | ARGUMENTS | |
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21 | ========= |
22 | ||
23 | ``fd`` | |
24 | File descriptor returned by :ref:`open() <func-open>`. | |
25 | ||
26 | ``request`` | |
27 | VIDIOC_QUERYBUF | |
28 | ||
29 | ``argp`` | |
30 | ||
31 | ||
586027ce | 32 | DESCRIPTION |
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33 | =========== |
34 | ||
35 | This ioctl is part of the :ref:`streaming <mmap>` I/O method. It can | |
36 | be used to query the status of a buffer at any time after buffers have | |
7347081e | 37 | been allocated with the :ref:`VIDIOC_REQBUFS` ioctl. |
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38 | |
39 | Applications set the ``type`` field of a struct | |
40 | :ref:`v4l2_buffer <v4l2-buffer>` to the same buffer type as was | |
41 | previously used with struct :ref:`v4l2_format <v4l2-format>` ``type`` | |
42 | and struct :ref:`v4l2_requestbuffers <v4l2-requestbuffers>` ``type``, | |
43 | and the ``index`` field. Valid index numbers range from zero to the | |
44 | number of buffers allocated with | |
7347081e | 45 | :ref:`VIDIOC_REQBUFS` (struct |
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46 | :ref:`v4l2_requestbuffers <v4l2-requestbuffers>` ``count``) minus |
47 | one. The ``reserved`` and ``reserved2`` fields must be set to 0. When | |
48 | using the :ref:`multi-planar API <planar-apis>`, the ``m.planes`` | |
49 | field must contain a userspace pointer to an array of struct | |
50 | :ref:`v4l2_plane <v4l2-plane>` and the ``length`` field has to be set | |
51 | to the number of elements in that array. After calling | |
2212ff25 | 52 | :ref:`VIDIOC_QUERYBUF` with a pointer to this structure drivers return an |
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53 | error code or fill the rest of the structure. |
54 | ||
55 | In the ``flags`` field the ``V4L2_BUF_FLAG_MAPPED``, | |
56 | ``V4L2_BUF_FLAG_PREPARED``, ``V4L2_BUF_FLAG_QUEUED`` and | |
57 | ``V4L2_BUF_FLAG_DONE`` flags will be valid. The ``memory`` field will be | |
58 | set to the current I/O method. For the single-planar API, the | |
59 | ``m.offset`` contains the offset of the buffer from the start of the | |
60 | device memory, the ``length`` field its size. For the multi-planar API, | |
61 | fields ``m.mem_offset`` and ``length`` in the ``m.planes`` array | |
62 | elements will be used instead and the ``length`` field of struct | |
63 | :ref:`v4l2_buffer <v4l2-buffer>` is set to the number of filled-in | |
64 | array elements. The driver may or may not set the remaining fields and | |
65 | flags, they are meaningless in this context. | |
66 | ||
acf309a2 | 67 | The :ref:`struct v4l2_buffer <v4l2-buffer>` structure is specified in |
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68 | :ref:`buffer`. |
69 | ||
70 | ||
586027ce | 71 | RETURN VALUE |
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72 | ============ |
73 | ||
74 | On success 0 is returned, on error -1 and the ``errno`` variable is set | |
75 | appropriately. The generic error codes are described at the | |
76 | :ref:`Generic Error Codes <gen-errors>` chapter. | |
77 | ||
78 | EINVAL | |
79 | The buffer ``type`` is not supported, or the ``index`` is out of | |
80 | bounds. |