Commit | Line | Data |
---|---|---|
5377d91f MH |
1 | .. -*- coding: utf-8; mode: rst -*- |
2 | ||
af4a4d0d | 3 | .. _VIDIOC_CREATE_BUFS: |
5377d91f MH |
4 | |
5 | ************************ | |
6 | ioctl VIDIOC_CREATE_BUFS | |
7 | ************************ | |
8 | ||
9 | *man VIDIOC_CREATE_BUFS(2)* | |
10 | ||
11 | Create buffers for Memory Mapped or User Pointer or DMA Buffer I/O | |
12 | ||
13 | ||
14 | Synopsis | |
15 | ======== | |
16 | ||
b7e67f6c | 17 | .. cpp:function:: int ioctl( int fd, int request, struct v4l2_create_buffers *argp ) |
5377d91f MH |
18 | |
19 | Arguments | |
20 | ========= | |
21 | ||
22 | ``fd`` | |
23 | File descriptor returned by :ref:`open() <func-open>`. | |
24 | ||
25 | ``request`` | |
26 | VIDIOC_CREATE_BUFS | |
27 | ||
28 | ``argp`` | |
29 | ||
30 | ||
31 | Description | |
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 |
5377d91f MH |
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 |
5377d91f MH |
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 |
5377d91f MH |
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 | ||
76 | .. flat-table:: struct v4l2_create_buffers | |
77 | :header-rows: 0 | |
78 | :stub-columns: 0 | |
79 | :widths: 1 1 2 | |
80 | ||
81 | ||
82 | - .. row 1 | |
83 | ||
84 | - __u32 | |
85 | ||
86 | - ``index`` | |
87 | ||
88 | - The starting buffer index, returned by the driver. | |
89 | ||
90 | - .. row 2 | |
91 | ||
92 | - __u32 | |
93 | ||
94 | - ``count`` | |
95 | ||
96 | - The number of buffers requested or granted. If count == 0, then | |
2212ff25 | 97 | :ref:`VIDIOC_CREATE_BUFS` will set ``index`` to the current number of |
5377d91f MH |
98 | created buffers, and it will check the validity of ``memory`` and |
99 | ``format.type``. If those are invalid -1 is returned and errno is | |
cdb4af0f MCC |
100 | set to ``EINVAL`` error code, otherwise :ref:`VIDIOC_CREATE_BUFS` returns |
101 | 0. It will never set errno to ``EBUSY`` error code in this particular | |
5377d91f MH |
102 | case. |
103 | ||
104 | - .. row 3 | |
105 | ||
106 | - __u32 | |
107 | ||
108 | - ``memory`` | |
109 | ||
110 | - Applications set this field to ``V4L2_MEMORY_MMAP``, | |
111 | ``V4L2_MEMORY_DMABUF`` or ``V4L2_MEMORY_USERPTR``. See | |
112 | :ref:`v4l2-memory` | |
113 | ||
114 | - .. row 4 | |
115 | ||
116 | - struct :ref:`v4l2_format <v4l2-format>` | |
117 | ||
118 | - ``format`` | |
119 | ||
120 | - Filled in by the application, preserved by the driver. | |
121 | ||
122 | - .. row 5 | |
123 | ||
124 | - __u32 | |
125 | ||
126 | - ``reserved``\ [8] | |
127 | ||
128 | - A place holder for future extensions. Drivers and applications | |
129 | must set the array to zero. | |
130 | ||
131 | ||
132 | ||
133 | Return Value | |
134 | ============ | |
135 | ||
136 | On success 0 is returned, on error -1 and the ``errno`` variable is set | |
137 | appropriately. The generic error codes are described at the | |
138 | :ref:`Generic Error Codes <gen-errors>` chapter. | |
139 | ||
140 | ENOMEM | |
141 | No memory to allocate buffers for :ref:`memory mapped <mmap>` I/O. | |
142 | ||
143 | EINVAL | |
144 | The buffer type (``format.type`` field), requested I/O method | |
145 | (``memory``) or format (``format`` field) is not valid. |