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+.. -*- coding: utf-8; mode: rst -*-
+
+.. _vidioc-querybuf:
+
+*********************
+ioctl VIDIOC_QUERYBUF
+*********************
+
+*man VIDIOC_QUERYBUF(2)*
+
+Query the status of a buffer
+
+
+Synopsis
+========
+
+.. c:function:: int ioctl( int fd, int request, struct v4l2_buffer *argp )
+
+Arguments
+=========
+
+``fd``
+    File descriptor returned by :ref:`open() <func-open>`.
+
+``request``
+    VIDIOC_QUERYBUF
+
+``argp``
+
+
+Description
+===========
+
+This ioctl is part of the :ref:`streaming <mmap>` I/O method. It can
+be used to query the status of a buffer at any time after buffers have
+been allocated with the :ref:`VIDIOC_REQBUFS <vidioc-reqbufs>` ioctl.
+
+Applications set the ``type`` field of a struct
+:ref:`v4l2_buffer <v4l2-buffer>` to the same buffer type as was
+previously used with struct :ref:`v4l2_format <v4l2-format>` ``type``
+and struct :ref:`v4l2_requestbuffers <v4l2-requestbuffers>` ``type``,
+and the ``index`` field. Valid index numbers range from zero to the
+number of buffers allocated with
+:ref:`VIDIOC_REQBUFS <vidioc-reqbufs>` (struct
+:ref:`v4l2_requestbuffers <v4l2-requestbuffers>` ``count``) minus
+one. The ``reserved`` and ``reserved2`` fields must be set to 0. When
+using the :ref:`multi-planar API <planar-apis>`, the ``m.planes``
+field must contain a userspace pointer to an array of struct
+:ref:`v4l2_plane <v4l2-plane>` and the ``length`` field has to be set
+to the number of elements in that array. After calling
+``VIDIOC_QUERYBUF`` with a pointer to this structure drivers return an
+error code or fill the rest of the structure.
+
+In the ``flags`` field the ``V4L2_BUF_FLAG_MAPPED``,
+``V4L2_BUF_FLAG_PREPARED``, ``V4L2_BUF_FLAG_QUEUED`` and
+``V4L2_BUF_FLAG_DONE`` flags will be valid. The ``memory`` field will be
+set to the current I/O method. For the single-planar API, the
+``m.offset`` contains the offset of the buffer from the start of the
+device memory, the ``length`` field its size. For the multi-planar API,
+fields ``m.mem_offset`` and ``length`` in the ``m.planes`` array
+elements will be used instead and the ``length`` field of struct
+:ref:`v4l2_buffer <v4l2-buffer>` is set to the number of filled-in
+array elements. The driver may or may not set the remaining fields and
+flags, they are meaningless in this context.
+
+The :c:type:`struct v4l2_buffer` structure is specified in
+:ref:`buffer`.
+
+
+Return Value
+============
+
+On success 0 is returned, on error -1 and the ``errno`` variable is set
+appropriately. The generic error codes are described at the
+:ref:`Generic Error Codes <gen-errors>` chapter.
+
+EINVAL
+    The buffer ``type`` is not supported, or the ``index`` is out of
+    bounds.
+
+
+.. ------------------------------------------------------------------------------
+.. This file was automatically converted from DocBook-XML with the dbxml
+.. library (https://github.com/return42/sphkerneldoc). The origin XML comes
+.. from the linux kernel, refer to:
+..
+.. * https://github.com/torvalds/linux/tree/master/Documentation/DocBook
+.. ------------------------------------------------------------------------------