1.. SPDX-License-Identifier: GFDL-1.1-no-invariants-or-later 2.. c:namespace:: V4L 3 4.. _VIDIOC_REQBUFS: 5 6******************** 7ioctl VIDIOC_REQBUFS 8******************** 9 10Name 11==== 12 13VIDIOC_REQBUFS - Initiate Memory Mapping, User Pointer I/O or DMA buffer I/O 14 15Synopsis 16======== 17 18.. c:macro:: VIDIOC_REQBUFS 19 20``int ioctl(int fd, VIDIOC_REQBUFS, struct v4l2_requestbuffers *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_requestbuffers`. 30 31Description 32=========== 33 34This ioctl is used to initiate :ref:`memory mapped <mmap>`, 35:ref:`user pointer <userp>` or :ref:`DMABUF <dmabuf>` based I/O. 36Memory mapped buffers are located in device memory and must be allocated 37with this ioctl before they can be mapped into the application's address 38space. User buffers are allocated by applications themselves, and this 39ioctl is merely used to switch the driver into user pointer I/O mode and 40to setup some internal structures. Similarly, DMABUF buffers are 41allocated by applications through a device driver, and this ioctl only 42configures the driver into DMABUF I/O mode without performing any direct 43allocation. 44 45To allocate device buffers applications initialize all fields of the 46struct :c:type:`v4l2_requestbuffers` structure. They set the ``type`` 47field to the respective stream or buffer type, the ``count`` field to 48the desired number of buffers, ``memory`` must be set to the requested 49I/O method and the ``reserved`` array must be zeroed. When the ioctl is 50called with a pointer to this structure the driver will attempt to 51allocate the requested number of buffers and it stores the actual number 52allocated in the ``count`` field. It can be smaller than the number 53requested, even zero, when the driver runs out of free memory. A larger 54number is also possible when the driver requires more buffers to 55function correctly. For example video output requires at least two 56buffers, one displayed and one filled by the application. 57 58When the I/O method is not supported the ioctl returns an ``EINVAL`` error 59code. 60 61Applications can call :ref:`VIDIOC_REQBUFS` again to change the number of 62buffers. Note that if any buffers are still mapped or exported via DMABUF, 63then :ref:`VIDIOC_REQBUFS` can only succeed if the 64``V4L2_BUF_CAP_SUPPORTS_ORPHANED_BUFS`` capability is set. Otherwise 65:ref:`VIDIOC_REQBUFS` will return the ``EBUSY`` error code. 66If ``V4L2_BUF_CAP_SUPPORTS_ORPHANED_BUFS`` is set, then these buffers are 67orphaned and will be freed when they are unmapped or when the exported DMABUF 68fds are closed. A ``count`` value of zero frees or orphans all buffers, after 69aborting or finishing any DMA in progress, an implicit 70:ref:`VIDIOC_STREAMOFF <VIDIOC_STREAMON>`. 71 72.. c:type:: v4l2_requestbuffers 73 74.. tabularcolumns:: |p{4.4cm}|p{4.4cm}|p{8.5cm}| 75 76.. flat-table:: struct v4l2_requestbuffers 77 :header-rows: 0 78 :stub-columns: 0 79 :widths: 1 1 2 80 81 * - __u32 82 - ``count`` 83 - The number of buffers requested or granted. 84 * - __u32 85 - ``type`` 86 - Type of the stream or buffers, this is the same as the struct 87 :c:type:`v4l2_format` ``type`` field. See 88 :c:type:`v4l2_buf_type` for valid values. 89 * - __u32 90 - ``memory`` 91 - Applications set this field to ``V4L2_MEMORY_MMAP``, 92 ``V4L2_MEMORY_DMABUF`` or ``V4L2_MEMORY_USERPTR``. See 93 :c:type:`v4l2_memory`. 94 * - __u32 95 - ``capabilities`` 96 - Set by the driver. If 0, then the driver doesn't support 97 capabilities. In that case all you know is that the driver is 98 guaranteed to support ``V4L2_MEMORY_MMAP`` and *might* support 99 other :c:type:`v4l2_memory` types. It will not support any other 100 capabilities. 101 102 If you want to query the capabilities with a minimum of side-effects, 103 then this can be called with ``count`` set to 0, ``memory`` set to 104 ``V4L2_MEMORY_MMAP`` and ``type`` set to the buffer type. This will 105 free any previously allocated buffers, so this is typically something 106 that will be done at the start of the application. 107 * - __u8 108 - ``flags`` 109 - Specifies additional buffer management attributes. 110 See :ref:`memory-flags`. 111 * - __u8 112 - ``reserved``\ [3] 113 - Reserved for future extensions. 114 115.. _v4l2-buf-capabilities: 116.. _V4L2-BUF-CAP-SUPPORTS-MMAP: 117.. _V4L2-BUF-CAP-SUPPORTS-USERPTR: 118.. _V4L2-BUF-CAP-SUPPORTS-DMABUF: 119.. _V4L2-BUF-CAP-SUPPORTS-REQUESTS: 120.. _V4L2-BUF-CAP-SUPPORTS-ORPHANED-BUFS: 121.. _V4L2-BUF-CAP-SUPPORTS-M2M-HOLD-CAPTURE-BUF: 122.. _V4L2-BUF-CAP-SUPPORTS-MMAP-CACHE-HINTS: 123.. _V4L2-BUF-CAP-SUPPORTS-MAX-NUM-BUFFERS: 124 125.. raw:: latex 126 127 \footnotesize 128 129.. tabularcolumns:: |p{8.1cm}|p{2.2cm}|p{7.0cm}| 130 131.. cssclass:: longtable 132 133.. flat-table:: V4L2 Buffer Capabilities Flags 134 :header-rows: 0 135 :stub-columns: 0 136 :widths: 3 1 4 137 138 * - ``V4L2_BUF_CAP_SUPPORTS_MMAP`` 139 - 0x00000001 140 - This buffer type supports the ``V4L2_MEMORY_MMAP`` streaming mode. 141 * - ``V4L2_BUF_CAP_SUPPORTS_USERPTR`` 142 - 0x00000002 143 - This buffer type supports the ``V4L2_MEMORY_USERPTR`` streaming mode. 144 * - ``V4L2_BUF_CAP_SUPPORTS_DMABUF`` 145 - 0x00000004 146 - This buffer type supports the ``V4L2_MEMORY_DMABUF`` streaming mode. 147 * - ``V4L2_BUF_CAP_SUPPORTS_REQUESTS`` 148 - 0x00000008 149 - This buffer type supports :ref:`requests <media-request-api>`. 150 * - ``V4L2_BUF_CAP_SUPPORTS_ORPHANED_BUFS`` 151 - 0x00000010 152 - The kernel allows calling :ref:`VIDIOC_REQBUFS` while buffers are still 153 mapped or exported via DMABUF. These orphaned buffers will be freed 154 when they are unmapped or when the exported DMABUF fds are closed. 155 * - ``V4L2_BUF_CAP_SUPPORTS_M2M_HOLD_CAPTURE_BUF`` 156 - 0x00000020 157 - Only valid for stateless decoders. If set, then userspace can set the 158 ``V4L2_BUF_FLAG_M2M_HOLD_CAPTURE_BUF`` flag to hold off on returning the 159 capture buffer until the OUTPUT timestamp changes. 160 * - ``V4L2_BUF_CAP_SUPPORTS_MMAP_CACHE_HINTS`` 161 - 0x00000040 162 - This capability is set by the driver to indicate that the queue supports 163 cache and memory management hints. However, it's only valid when the 164 queue is used for :ref:`memory mapping <mmap>` streaming I/O. See 165 :ref:`V4L2_BUF_FLAG_NO_CACHE_INVALIDATE <V4L2-BUF-FLAG-NO-CACHE-INVALIDATE>`, 166 :ref:`V4L2_BUF_FLAG_NO_CACHE_CLEAN <V4L2-BUF-FLAG-NO-CACHE-CLEAN>` and 167 :ref:`V4L2_MEMORY_FLAG_NON_COHERENT <V4L2-MEMORY-FLAG-NON-COHERENT>`. 168 169.. raw:: latex 170 171 \normalsize 172 173Return Value 174============ 175 176On success 0 is returned, on error -1 and the ``errno`` variable is set 177appropriately. The generic error codes are described at the 178:ref:`Generic Error Codes <gen-errors>` chapter. 179 180EINVAL 181 The buffer type (``type`` field) or the requested I/O method 182 (``memory``) is not supported. 183