vidioc-querybuf.rst (2581B)
1.. SPDX-License-Identifier: GFDL-1.1-no-invariants-or-later 2.. c:namespace:: V4L 3 4.. _VIDIOC_QUERYBUF: 5 6********************* 7ioctl VIDIOC_QUERYBUF 8********************* 9 10Name 11==== 12 13VIDIOC_QUERYBUF - Query the status of a buffer 14 15Synopsis 16======== 17 18.. c:macro:: VIDIOC_QUERYBUF 19 20``int ioctl(int fd, VIDIOC_QUERYBUF, struct v4l2_buffer *argp)`` 21 22Arguments 23========= 24 25``fd`` 26 File descriptor returned by :c:func:`open()`. 27 28``argp`` 29 Pointer to struct :c:type:`v4l2_buffer`. 30 31Description 32=========== 33 34This ioctl is part of the :ref:`streaming <mmap>` I/O method. It can 35be used to query the status of a buffer at any time after buffers have 36been allocated with the :ref:`VIDIOC_REQBUFS` ioctl. 37 38Applications set the ``type`` field of a struct 39:c:type:`v4l2_buffer` to the same buffer type as was 40previously used with struct :c:type:`v4l2_format` ``type`` 41and struct :c:type:`v4l2_requestbuffers` ``type``, 42and the ``index`` field. Valid index numbers range from zero to the 43number of buffers allocated with 44:ref:`VIDIOC_REQBUFS` (struct 45:c:type:`v4l2_requestbuffers` ``count``) minus 46one. The ``reserved`` and ``reserved2`` fields must be set to 0. When 47using the :ref:`multi-planar API <planar-apis>`, the ``m.planes`` 48field must contain a userspace pointer to an array of struct 49:c:type:`v4l2_plane` and the ``length`` field has to be set 50to the number of elements in that array. After calling 51:ref:`VIDIOC_QUERYBUF` with a pointer to this structure drivers return an 52error code or fill the rest of the structure. 53 54In 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 57set 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 59device memory, the ``length`` field its size. For the multi-planar API, 60fields ``m.mem_offset`` and ``length`` in the ``m.planes`` array 61elements will be used instead and the ``length`` field of struct 62:c:type:`v4l2_buffer` is set to the number of filled-in 63array elements. The driver may or may not set the remaining fields and 64flags, they are meaningless in this context. 65 66The struct :c:type:`v4l2_buffer` structure is specified in 67:ref:`buffer`. 68 69Return Value 70============ 71 72On success 0 is returned, on error -1 and the ``errno`` variable is set 73appropriately. The generic error codes are described at the 74:ref:`Generic Error Codes <gen-errors>` chapter. 75 76EINVAL 77 The buffer ``type`` is not supported, or the ``index`` is out of 78 bounds.