1 .. SPDX-License-Identifier: GFDL-1.1-no-invariants-or-later 2 .. c:namespace:: V4L 3 4 .. _VIDIOC_QUERYBUF: 5 6 ********************* 7 ioctl VIDIOC_QUERYBUF 8 ********************* 9 10 Name 11 ==== 12 13 VIDIOC_QUERYBUF - Query the status of a buffer 14 15 Synopsis 16 ======== 17 18 .. c:macro:: VIDIOC_QUERYBUF 19 20 ``int ioctl(int fd, VIDIOC_QUERYBUF, struct v4l2_buffer *argp)`` 21 22 Arguments 23 ========= 24 25 ``fd`` 26 File descriptor returned by :c:func:`open()`. 27 28 ``argp`` 29 Pointer to struct :c:type:`v4l2_buffer`. 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 36 been allocated with the :ref:`VIDIOC_REQBUFS` ioctl. 37 38 Applications set the ``type`` field of a struct 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``, 42 and the ``index`` field. Valid index numbers range from zero to the 43 number of buffers allocated with 44 :ref:`VIDIOC_REQBUFS` (struct 45 :c:type:`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 :c:type:`v4l2_plane` and the ``length`` field has to be set 50 to the number of elements in that array. After calling 51 :ref:`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 :c:type:`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 struct :c:type:`v4l2_buffer` structure is specified in 67 :ref:`buffer`. 68 69 Return Value 70 ============ 71 72 On success 0 is returned, on error -1 and the ``errno`` variable is set 73 appropriately. The generic error codes are described at the 74 :ref:`Generic Error Codes <gen-errors>` chapter. 75 76 EINVAL 77 The buffer ``type`` is not supported, or the ``index`` is out of 78 bounds.
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