1.. -*- coding: utf-8; mode: rst -*- 2 3.. _VIDIOC_QUERYBUF: 4 5********************* 6ioctl VIDIOC_QUERYBUF 7********************* 8 9Name 10==== 11 12VIDIOC_QUERYBUF - Query the status of a buffer 13 14 15Synopsis 16======== 17 18.. c:function:: int ioctl( int fd, VIDIOC_QUERYBUF, struct v4l2_buffer *argp ) 19 :name: VIDIOC_QUERYBUF 20 21 22Arguments 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 32Description 33=========== 34 35This ioctl is part of the :ref:`streaming <mmap>` I/O method. It can 36be used to query the status of a buffer at any time after buffers have 37been allocated with the :ref:`VIDIOC_REQBUFS` ioctl. 38 39Applications set the ``type`` field of a struct 40:c:type:`v4l2_buffer` to the same buffer type as was 41previously used with struct :c:type:`v4l2_format` ``type`` 42and struct :c:type:`v4l2_requestbuffers` ``type``, 43and the ``index`` field. Valid index numbers range from zero to the 44number of buffers allocated with 45:ref:`VIDIOC_REQBUFS` (struct 46:c:type:`v4l2_requestbuffers` ``count``) minus 47one. The ``reserved`` and ``reserved2`` fields must be set to 0. When 48using the :ref:`multi-planar API <planar-apis>`, the ``m.planes`` 49field must contain a userspace pointer to an array of struct 50:c:type:`v4l2_plane` and the ``length`` field has to be set 51to the number of elements in that array. After calling 52:ref:`VIDIOC_QUERYBUF` with a pointer to this structure drivers return an 53error code or fill the rest of the structure. 54 55In 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 58set 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 60device memory, the ``length`` field its size. For the multi-planar API, 61fields ``m.mem_offset`` and ``length`` in the ``m.planes`` array 62elements will be used instead and the ``length`` field of struct 63:c:type:`v4l2_buffer` is set to the number of filled-in 64array elements. The driver may or may not set the remaining fields and 65flags, they are meaningless in this context. 66 67The struct :c:type:`v4l2_buffer` structure is specified in 68:ref:`buffer`. 69 70 71Return Value 72============ 73 74On success 0 is returned, on error -1 and the ``errno`` variable is set 75appropriately. The generic error codes are described at the 76:ref:`Generic Error Codes <gen-errors>` chapter. 77 78EINVAL 79 The buffer ``type`` is not supported, or the ``index`` is out of 80 bounds. 81