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1 | .. -*- coding: utf-8; mode: rst -*- |
2 | ||
af4a4d0d | 3 | .. _VIDIOC_CREATE_BUFS: |
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4 | |
5 | ************************ | |
6 | ioctl VIDIOC_CREATE_BUFS | |
7 | ************************ | |
8 | ||
15e7d615 | 9 | Name |
586027ce | 10 | ==== |
5377d91f | 11 | |
586027ce | 12 | VIDIOC_CREATE_BUFS - Create buffers for Memory Mapped or User Pointer or DMA Buffer I/O |
5377d91f | 13 | |
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14 | |
15 | Synopsis | |
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16 | ======== |
17 | ||
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18 | .. c:function:: int ioctl( int fd, VIDIOC_CREATE_BUFS, struct v4l2_create_buffers *argp ) |
19 | :name: VIDIOC_CREATE_BUFS | |
5377d91f | 20 | |
586027ce | 21 | |
15e7d615 | 22 | Arguments |
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23 | ========= |
24 | ||
25 | ``fd`` | |
26 | File descriptor returned by :ref:`open() <func-open>`. | |
27 | ||
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28 | ``argp`` |
29 | ||
30 | ||
15e7d615 | 31 | Description |
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32 | =========== |
33 | ||
34 | This ioctl is used to create buffers for :ref:`memory mapped <mmap>` | |
35 | or :ref:`user pointer <userp>` or :ref:`DMA buffer <dmabuf>` I/O. It | |
36 | can be used as an alternative or in addition to the | |
7347081e | 37 | :ref:`VIDIOC_REQBUFS` ioctl, when a tighter control |
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38 | over buffers is required. This ioctl can be called multiple times to |
39 | create buffers of different sizes. | |
40 | ||
41 | To allocate the device buffers applications must initialize the relevant | |
acf309a2 | 42 | fields of the :ref:`struct v4l2_create_buffers <v4l2-create-buffers>` structure. The |
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43 | ``count`` field must be set to the number of requested buffers, the |
44 | ``memory`` field specifies the requested I/O method and the ``reserved`` | |
45 | array must be zeroed. | |
46 | ||
47 | The ``format`` field specifies the image format that the buffers must be | |
48 | able to handle. The application has to fill in this struct | |
49 | :ref:`v4l2_format <v4l2-format>`. Usually this will be done using the | |
af4a4d0d | 50 | :ref:`VIDIOC_TRY_FMT <VIDIOC_G_FMT>` or |
4e03cb76 | 51 | :ref:`VIDIOC_G_FMT <VIDIOC_G_FMT>` ioctls to ensure that the |
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52 | requested format is supported by the driver. Based on the format's |
53 | ``type`` field the requested buffer size (for single-planar) or plane | |
54 | sizes (for multi-planar formats) will be used for the allocated buffers. | |
55 | The driver may return an error if the size(s) are not supported by the | |
56 | hardware (usually because they are too small). | |
57 | ||
58 | The buffers created by this ioctl will have as minimum size the size | |
59 | defined by the ``format.pix.sizeimage`` field (or the corresponding | |
60 | fields for other format types). Usually if the ``format.pix.sizeimage`` | |
61 | field is less than the minimum required for the given format, then an | |
62 | error will be returned since drivers will typically not allow this. If | |
63 | it is larger, then the value will be used as-is. In other words, the | |
64 | driver may reject the requested size, but if it is accepted the driver | |
65 | will use it unchanged. | |
66 | ||
67 | When the ioctl is called with a pointer to this structure the driver | |
68 | will attempt to allocate up to the requested number of buffers and store | |
69 | the actual number allocated and the starting index in the ``count`` and | |
70 | the ``index`` fields respectively. On return ``count`` can be smaller | |
71 | than the number requested. | |
72 | ||
73 | ||
74 | .. _v4l2-create-buffers: | |
75 | ||
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76 | .. tabularcolumns:: |p{4.4cm}|p{4.4cm}|p{8.7cm}| |
77 | ||
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78 | .. flat-table:: struct v4l2_create_buffers |
79 | :header-rows: 0 | |
80 | :stub-columns: 0 | |
81 | :widths: 1 1 2 | |
82 | ||
83 | ||
84 | - .. row 1 | |
85 | ||
86 | - __u32 | |
87 | ||
88 | - ``index`` | |
89 | ||
90 | - The starting buffer index, returned by the driver. | |
91 | ||
92 | - .. row 2 | |
93 | ||
94 | - __u32 | |
95 | ||
96 | - ``count`` | |
97 | ||
98 | - The number of buffers requested or granted. If count == 0, then | |
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99 | :ref:`VIDIOC_CREATE_BUFS` will set ``index`` to the current number of |
100 | created buffers, and it will check the validity of ``memory`` and | |
101 | ``format.type``. If those are invalid -1 is returned and errno is | |
102 | set to ``EINVAL`` error code, otherwise :ref:`VIDIOC_CREATE_BUFS` returns | |
103 | 0. It will never set errno to ``EBUSY`` error code in this particular | |
104 | case. | |
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105 | |
106 | - .. row 3 | |
107 | ||
108 | - __u32 | |
109 | ||
110 | - ``memory`` | |
111 | ||
112 | - Applications set this field to ``V4L2_MEMORY_MMAP``, | |
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113 | ``V4L2_MEMORY_DMABUF`` or ``V4L2_MEMORY_USERPTR``. See |
114 | :ref:`v4l2-memory` | |
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115 | |
116 | - .. row 4 | |
117 | ||
118 | - struct :ref:`v4l2_format <v4l2-format>` | |
119 | ||
120 | - ``format`` | |
121 | ||
122 | - Filled in by the application, preserved by the driver. | |
123 | ||
124 | - .. row 5 | |
125 | ||
126 | - __u32 | |
127 | ||
8968da9b | 128 | - ``reserved``\ [8] |
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129 | |
130 | - A place holder for future extensions. Drivers and applications | |
0579e6e3 | 131 | must set the array to zero. |
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132 | |
133 | ||
15e7d615 | 134 | Return Value |
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135 | ============ |
136 | ||
137 | On success 0 is returned, on error -1 and the ``errno`` variable is set | |
138 | appropriately. The generic error codes are described at the | |
139 | :ref:`Generic Error Codes <gen-errors>` chapter. | |
140 | ||
141 | ENOMEM | |
142 | No memory to allocate buffers for :ref:`memory mapped <mmap>` I/O. | |
143 | ||
144 | EINVAL | |
145 | The buffer type (``format.type`` field), requested I/O method | |
146 | (``memory``) or format (``format`` field) is not valid. |