| Andrew Scull | b4b6d4a | 2019-01-02 15:54:55 +0000 | [diff] [blame] | 1 | .. -*- coding: utf-8; mode: rst -*- |
| 2 | |
| 3 | .. _VIDIOC_QUERYBUF: |
| 4 | |
| 5 | ********************* |
| 6 | ioctl VIDIOC_QUERYBUF |
| 7 | ********************* |
| 8 | |
| 9 | Name |
| 10 | ==== |
| 11 | |
| 12 | VIDIOC_QUERYBUF - Query the status of a buffer |
| 13 | |
| 14 | |
| 15 | Synopsis |
| 16 | ======== |
| 17 | |
| 18 | .. c:function:: int ioctl( int fd, VIDIOC_QUERYBUF, struct v4l2_buffer *argp ) |
| 19 | :name: VIDIOC_QUERYBUF |
| 20 | |
| 21 | |
| 22 | Arguments |
| 23 | ========= |
| 24 | |
| 25 | ``fd`` |
| 26 | File descriptor returned by :ref:`open() <func-open>`. |
| 27 | |
| 28 | ``argp`` |
| 29 | Pointer to struct :c:type:`v4l2_buffer`. |
| 30 | |
| 31 | |
| 32 | Description |
| 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 |
| 37 | been allocated with the :ref:`VIDIOC_REQBUFS` ioctl. |
| 38 | |
| 39 | Applications set the ``type`` field of a struct |
| 40 | :c:type:`v4l2_buffer` to the same buffer type as was |
| 41 | previously used with struct :c:type:`v4l2_format` ``type`` |
| 42 | and struct :c:type:`v4l2_requestbuffers` ``type``, |
| 43 | and the ``index`` field. Valid index numbers range from zero to the |
| 44 | number of buffers allocated with |
| 45 | :ref:`VIDIOC_REQBUFS` (struct |
| 46 | :c:type:`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 | :c:type:`v4l2_plane` and the ``length`` field has to be set |
| 51 | to the number of elements in that array. After calling |
| 52 | :ref:`VIDIOC_QUERYBUF` with a pointer to this structure drivers return an |
| 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 | :c:type:`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 | |
| 67 | The struct :c:type:`v4l2_buffer` structure is specified in |
| 68 | :ref:`buffer`. |
| 69 | |
| 70 | |
| 71 | Return Value |
| 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. |