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+.. -*- coding: utf-8; mode: rst -*-
+
+.. _VIDIOC_REQBUFS:
+
+********************
+ioctl VIDIOC_REQBUFS
+********************
+
+Name
+====
+
+VIDIOC_REQBUFS - Initiate Memory Mapping or User Pointer I/O
+
+
+Synopsis
+========
+
+.. cpp:function:: int ioctl( int fd, int request, struct v4l2_requestbuffers *argp )
+
+
+Arguments
+=========
+
+``fd``
+    File descriptor returned by :ref:`open() <func-open>`.
+
+``request``
+    VIDIOC_REQBUFS
+
+``argp``
+
+
+Description
+===========
+
+This ioctl is used to initiate :ref:`memory mapped <mmap>`,
+:ref:`user pointer <userp>` or :ref:`DMABUF <dmabuf>` based I/O.
+Memory mapped buffers are located in device memory and must be allocated
+with this ioctl before they can be mapped into the application's address
+space. User buffers are allocated by applications themselves, and this
+ioctl is merely used to switch the driver into user pointer I/O mode and
+to setup some internal structures. Similarly, DMABUF buffers are
+allocated by applications through a device driver, and this ioctl only
+configures the driver into DMABUF I/O mode without performing any direct
+allocation.
+
+To allocate device buffers applications initialize all fields of the
+:ref:`struct v4l2_requestbuffers <v4l2-requestbuffers>` structure. They set the ``type``
+field to the respective stream or buffer type, the ``count`` field to
+the desired number of buffers, ``memory`` must be set to the requested
+I/O method and the ``reserved`` array must be zeroed. When the ioctl is
+called with a pointer to this structure the driver will attempt to
+allocate the requested number of buffers and it stores the actual number
+allocated in the ``count`` field. It can be smaller than the number
+requested, even zero, when the driver runs out of free memory. A larger
+number is also possible when the driver requires more buffers to
+function correctly. For example video output requires at least two
+buffers, one displayed and one filled by the application.
+
+When the I/O method is not supported the ioctl returns an ``EINVAL`` error
+code.
+
+Applications can call :ref:`VIDIOC_REQBUFS` again to change the number of
+buffers, however this cannot succeed when any buffers are still mapped.
+A ``count`` value of zero frees all buffers, after aborting or finishing
+any DMA in progress, an implicit
+:ref:`VIDIOC_STREAMOFF <VIDIOC_STREAMON>`.
+
+
+.. _v4l2-requestbuffers:
+
+.. flat-table:: struct v4l2_requestbuffers
+    :header-rows:  0
+    :stub-columns: 0
+    :widths:       1 1 2
+
+
+    -  .. row 1
+
+       -  __u32
+
+       -  ``count``
+
+       -  The number of buffers requested or granted.
+
+    -  .. row 2
+
+       -  __u32
+
+       -  ``type``
+
+       -  Type of the stream or buffers, this is the same as the struct
+	  :ref:`v4l2_format <v4l2-format>` ``type`` field. See
+	  :ref:`v4l2-buf-type` for valid values.
+
+    -  .. row 3
+
+       -  __u32
+
+       -  ``memory``
+
+       -  Applications set this field to ``V4L2_MEMORY_MMAP``,
+	  ``V4L2_MEMORY_DMABUF`` or ``V4L2_MEMORY_USERPTR``. See
+	  :ref:`v4l2-memory`.
+
+    -  .. row 4
+
+       -  __u32
+
+       -  ``reserved``\ [2]
+
+       -  A place holder for future extensions. Drivers and applications
+	  must set the array to zero.
+
+
+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 (``type`` field) or the requested I/O method
+    (``memory``) is not supported.