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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 | ||
15e7d615 | 9 | Name |
586027ce | 10 | ==== |
5377d91f | 11 | |
586027ce | 12 | VIDIOC_QUERYBUF - Query the status of a buffer |
5377d91f | 13 | |
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14 | |
15 | Synopsis | |
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16 | ======== |
17 | ||
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18 | .. c:function:: int ioctl( int fd, VIDIOC_QUERYBUF, struct v4l2_buffer *argp ) |
19 | :name: VIDIOC_QUERYBUF | |
5377d91f | 20 | |
586027ce | 21 | |
15e7d615 | 22 | Arguments |
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23 | ========= |
24 | ||
25 | ``fd`` | |
26 | File descriptor returned by :ref:`open() <func-open>`. | |
27 | ||
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28 | ``argp`` |
29 | ||
30 | ||
15e7d615 | 31 | Description |
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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. |
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37 | |
38 | Applications set the ``type`` field of a struct | |
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39 | :c:type:`v4l2_buffer` to the same buffer type as was |
40 | previously used with struct :c:type:`v4l2_format` ``type`` | |
41 | and struct :c:type:`v4l2_requestbuffers` ``type``, | |
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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 |
e8be7e97 | 45 | :c:type:`v4l2_requestbuffers` ``count``) minus |
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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 | |
e8be7e97 | 49 | :c:type:`v4l2_plane` and the ``length`` field has to be set |
5377d91f | 50 | to the number of elements in that array. After calling |
2212ff25 | 51 | :ref:`VIDIOC_QUERYBUF` with a pointer to this structure drivers return an |
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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 | |
e8be7e97 | 62 | :c:type:`v4l2_buffer` is set to the number of filled-in |
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63 | array elements. The driver may or may not set the remaining fields and |
64 | flags, they are meaningless in this context. | |
65 | ||
fc78c7c7 | 66 | The struct :c:type:`v4l2_buffer` structure is specified in |
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67 | :ref:`buffer`. |
68 | ||
69 | ||
15e7d615 | 70 | Return Value |
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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. |