Commit | Line | Data |
---|---|---|
5377d91f MH |
1 | .. -*- coding: utf-8; mode: rst -*- |
2 | ||
af4a4d0d | 3 | .. _VIDIOC_REQBUFS: |
5377d91f MH |
4 | |
5 | ******************** | |
6 | ioctl VIDIOC_REQBUFS | |
7 | ******************** | |
8 | ||
15e7d615 | 9 | Name |
586027ce | 10 | ==== |
5377d91f | 11 | |
53ce5239 | 12 | VIDIOC_REQBUFS - Initiate Memory Mapping, User Pointer I/O or DMA buffer I/O |
5377d91f | 13 | |
15e7d615 MCC |
14 | |
15 | Synopsis | |
5377d91f MH |
16 | ======== |
17 | ||
41d80465 MCC |
18 | .. c:function:: int ioctl( int fd, VIDIOC_REQBUFS, struct v4l2_requestbuffers *argp ) |
19 | :name: VIDIOC_REQBUFS | |
5377d91f | 20 | |
586027ce | 21 | |
15e7d615 | 22 | Arguments |
5377d91f MH |
23 | ========= |
24 | ||
25 | ``fd`` | |
26 | File descriptor returned by :ref:`open() <func-open>`. | |
27 | ||
5377d91f MH |
28 | ``argp`` |
29 | ||
30 | ||
15e7d615 | 31 | Description |
5377d91f MH |
32 | =========== |
33 | ||
34 | This ioctl is used to initiate :ref:`memory mapped <mmap>`, | |
35 | :ref:`user pointer <userp>` or :ref:`DMABUF <dmabuf>` based I/O. | |
36 | Memory mapped buffers are located in device memory and must be allocated | |
37 | with this ioctl before they can be mapped into the application's address | |
38 | space. User buffers are allocated by applications themselves, and this | |
39 | ioctl is merely used to switch the driver into user pointer I/O mode and | |
40 | to setup some internal structures. Similarly, DMABUF buffers are | |
41 | allocated by applications through a device driver, and this ioctl only | |
42 | configures the driver into DMABUF I/O mode without performing any direct | |
43 | allocation. | |
44 | ||
45 | To allocate device buffers applications initialize all fields of the | |
fc78c7c7 | 46 | struct :c:type:`v4l2_requestbuffers` structure. They set the ``type`` |
5377d91f MH |
47 | field to the respective stream or buffer type, the ``count`` field to |
48 | the desired number of buffers, ``memory`` must be set to the requested | |
49 | I/O method and the ``reserved`` array must be zeroed. When the ioctl is | |
50 | called with a pointer to this structure the driver will attempt to | |
51 | allocate the requested number of buffers and it stores the actual number | |
52 | allocated in the ``count`` field. It can be smaller than the number | |
53 | requested, even zero, when the driver runs out of free memory. A larger | |
54 | number is also possible when the driver requires more buffers to | |
55 | function correctly. For example video output requires at least two | |
56 | buffers, one displayed and one filled by the application. | |
57 | ||
cdb4af0f | 58 | When the I/O method is not supported the ioctl returns an ``EINVAL`` error |
5377d91f MH |
59 | code. |
60 | ||
2212ff25 | 61 | Applications can call :ref:`VIDIOC_REQBUFS` again to change the number of |
5377d91f MH |
62 | buffers, however this cannot succeed when any buffers are still mapped. |
63 | A ``count`` value of zero frees all buffers, after aborting or finishing | |
64 | any DMA in progress, an implicit | |
af4a4d0d | 65 | :ref:`VIDIOC_STREAMOFF <VIDIOC_STREAMON>`. |
5377d91f MH |
66 | |
67 | ||
e8be7e97 | 68 | .. c:type:: v4l2_requestbuffers |
5377d91f | 69 | |
5bd4bb78 MCC |
70 | .. tabularcolumns:: |p{4.4cm}|p{4.4cm}|p{8.7cm}| |
71 | ||
5377d91f MH |
72 | .. flat-table:: struct v4l2_requestbuffers |
73 | :header-rows: 0 | |
74 | :stub-columns: 0 | |
75 | :widths: 1 1 2 | |
76 | ||
77 | ||
78 | - .. row 1 | |
79 | ||
80 | - __u32 | |
81 | ||
82 | - ``count`` | |
83 | ||
84 | - The number of buffers requested or granted. | |
85 | ||
86 | - .. row 2 | |
87 | ||
88 | - __u32 | |
89 | ||
90 | - ``type`` | |
91 | ||
92 | - Type of the stream or buffers, this is the same as the struct | |
e8be7e97 | 93 | :c:type:`v4l2_format` ``type`` field. See |
56683d7d | 94 | :c:type:`v4l2_buf_type` for valid values. |
5377d91f MH |
95 | |
96 | - .. row 3 | |
97 | ||
98 | - __u32 | |
99 | ||
100 | - ``memory`` | |
101 | ||
102 | - Applications set this field to ``V4L2_MEMORY_MMAP``, | |
0579e6e3 | 103 | ``V4L2_MEMORY_DMABUF`` or ``V4L2_MEMORY_USERPTR``. See |
56683d7d | 104 | :c:type:`v4l2_memory`. |
5377d91f MH |
105 | |
106 | - .. row 4 | |
107 | ||
108 | - __u32 | |
109 | ||
8968da9b | 110 | - ``reserved``\ [2] |
5377d91f MH |
111 | |
112 | - A place holder for future extensions. Drivers and applications | |
0579e6e3 | 113 | must set the array to zero. |
5377d91f MH |
114 | |
115 | ||
15e7d615 | 116 | Return Value |
5377d91f MH |
117 | ============ |
118 | ||
119 | On success 0 is returned, on error -1 and the ``errno`` variable is set | |
120 | appropriately. The generic error codes are described at the | |
121 | :ref:`Generic Error Codes <gen-errors>` chapter. | |
122 | ||
123 | EINVAL | |
124 | The buffer type (``type`` field) or the requested I/O method | |
125 | (``memory``) is not supported. |