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1.. SPDX-License-Identifier: GFDL-1.1-no-invariants-or-later2.. c:namespace:: V4L3 4.. _VIDIOC_QUERYBUF:5 6*********************7ioctl VIDIOC_QUERYBUF8*********************9 10Name11====12 13VIDIOC_QUERYBUF - Query the status of a buffer14 15Synopsis16========17 18.. c:macro:: VIDIOC_QUERYBUF19 20``int ioctl(int fd, VIDIOC_QUERYBUF, struct v4l2_buffer *argp)``21 22Arguments23=========24 25``fd``26 File descriptor returned by :c:func:`open()`.27 28``argp``29 Pointer to struct :c:type:`v4l2_buffer`.30 31Description32===========33 34This ioctl is part of the :ref:`streaming <mmap>` I/O method. It can35be used to query the status of a buffer at any time after buffers have36been allocated with the :ref:`VIDIOC_REQBUFS` ioctl.37 38Applications set the ``type`` field of a struct39:c:type:`v4l2_buffer` to the same buffer type as was40previously 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 the43number of buffers allocated with44:ref:`VIDIOC_REQBUFS` (struct45:c:type:`v4l2_requestbuffers` ``count``) minus46one. The ``reserved`` and ``reserved2`` fields must be set to 0. When47using the :ref:`multi-planar API <planar-apis>`, the ``m.planes``48field must contain a userspace pointer to an array of struct49:c:type:`v4l2_plane` and the ``length`` field has to be set50to the number of elements in that array. After calling51:ref:`VIDIOC_QUERYBUF` with a pointer to this structure drivers return an52error 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`` and56``V4L2_BUF_FLAG_DONE`` flags will be valid. The ``memory`` field will be57set to the current I/O method. For the single-planar API, the58``m.offset`` contains the offset of the buffer from the start of the59device memory, the ``length`` field its size. For the multi-planar API,60fields ``m.mem_offset`` and ``length`` in the ``m.planes`` array61elements will be used instead and the ``length`` field of struct62:c:type:`v4l2_buffer` is set to the number of filled-in63array elements. The driver may or may not set the remaining fields and64flags, they are meaningless in this context.65 66The struct :c:type:`v4l2_buffer` structure is specified in67:ref:`buffer`.68 69Return Value70============71 72On success 0 is returned, on error -1 and the ``errno`` variable is set73appropriately. The generic error codes are described at the74:ref:`Generic Error Codes <gen-errors>` chapter.75 76EINVAL77 The buffer ``type`` is not supported, or the ``index`` is out of78 bounds.79