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1<refentry id="vidioc-create-bufs">
2 <refmeta>
3 <refentrytitle>ioctl VIDIOC_CREATE_BUFS</refentrytitle>
4 &manvol;
5 </refmeta>
6
7 <refnamediv>
8 <refname>VIDIOC_CREATE_BUFS</refname>
9 <refpurpose>Create buffers for Memory Mapped or User Pointer or DMA Buffer
10 I/O</refpurpose>
11 </refnamediv>
12
13 <refsynopsisdiv>
14 <funcsynopsis>
15 <funcprototype>
16 <funcdef>int <function>ioctl</function></funcdef>
17 <paramdef>int <parameter>fd</parameter></paramdef>
18 <paramdef>int <parameter>request</parameter></paramdef>
19 <paramdef>struct v4l2_create_buffers *<parameter>argp</parameter></paramdef>
20 </funcprototype>
21 </funcsynopsis>
22 </refsynopsisdiv>
23
24 <refsect1>
25 <title>Arguments</title>
26
27 <variablelist>
28 <varlistentry>
29 <term><parameter>fd</parameter></term>
30 <listitem>
31 <para>&fd;</para>
32 </listitem>
33 </varlistentry>
34 <varlistentry>
35 <term><parameter>request</parameter></term>
36 <listitem>
37 <para>VIDIOC_CREATE_BUFS</para>
38 </listitem>
39 </varlistentry>
40 <varlistentry>
41 <term><parameter>argp</parameter></term>
42 <listitem>
43 <para></para>
44 </listitem>
45 </varlistentry>
46 </variablelist>
47 </refsect1>
48
49 <refsect1>
50 <title>Description</title>
51
52 <note>
53 <title>Experimental</title>
54 <para>This is an <link linkend="experimental"> experimental </link>
55 interface and may change in the future.</para>
56 </note>
57
58 <para>This ioctl is used to create buffers for <link linkend="mmap">memory
59mapped</link> or <link linkend="userp">user pointer</link> or <link
60linkend="dmabuf">DMA buffer</link> I/O. It can be used as an alternative or in
61addition to the <constant>VIDIOC_REQBUFS</constant> ioctl, when a tighter
62control over buffers is required. This ioctl can be called multiple times to
63create buffers of different sizes.</para>
64
65 <para>To allocate the device buffers applications must initialize the
66relevant fields of the <structname>v4l2_create_buffers</structname> structure.
67The <structfield>count</structfield> field must be set to the number of
68requested buffers, the <structfield>memory</structfield> field specifies the
69requested I/O method and the <structfield>reserved</structfield> array must be
70zeroed.</para>
71
72 <para>The <structfield>format</structfield> field specifies the image format
73that the buffers must be able to handle. The application has to fill in this
74&v4l2-format;. Usually this will be done using the
75<constant>VIDIOC_TRY_FMT</constant> or <constant>VIDIOC_G_FMT</constant> ioctl()
76to ensure that the requested format is supported by the driver. Unsupported
77formats will result in an error.</para>
78
79 <para>The buffers created by this ioctl will have as minimum size the size
80defined by the <structfield>format.pix.sizeimage</structfield> field. If the
81<structfield>format.pix.sizeimage</structfield> field is less than the minimum
82required for the given format, then <structfield>sizeimage</structfield> will be
83increased by the driver to that minimum to allocate the buffers. If it is
84larger, then the value will be used as-is. The same applies to the
85<structfield>sizeimage</structfield> field of the
86<structname>v4l2_plane_pix_format</structname> structure in the case of
87multiplanar formats.</para>
88
89 <para>When the ioctl is called with a pointer to this structure the driver
90will attempt to allocate up to the requested number of buffers and store the
91actual number allocated and the starting index in the
92<structfield>count</structfield> and the <structfield>index</structfield> fields
93respectively. On return <structfield>count</structfield> can be smaller than
94the number requested. The driver may also increase buffer sizes if required,
95however, it will not update <structfield>sizeimage</structfield> field values.
96The user has to use <constant>VIDIOC_QUERYBUF</constant> to retrieve that
97information.</para>
98
99 <table pgwide="1" frame="none" id="v4l2-create-buffers">
100 <title>struct <structname>v4l2_create_buffers</structname></title>
101 <tgroup cols="3">
102 &cs-str;
103 <tbody valign="top">
104 <row>
105 <entry>__u32</entry>
106 <entry><structfield>index</structfield></entry>
107 <entry>The starting buffer index, returned by the driver.</entry>
108 </row>
109 <row>
110 <entry>__u32</entry>
111 <entry><structfield>count</structfield></entry>
112 <entry>The number of buffers requested or granted. If count == 0, then
113 <constant>VIDIOC_CREATE_BUFS</constant> will set <structfield>index</structfield>
114 to the current number of created buffers, and it will check the validity of
115 <structfield>memory</structfield> and <structfield>format.type</structfield>.
116 If those are invalid -1 is returned and errno is set to &EINVAL;,
117 otherwise <constant>VIDIOC_CREATE_BUFS</constant> returns 0. It will
118 never set errno to &EBUSY; in this particular case.</entry>
119 </row>
120 <row>
121 <entry>__u32</entry>
122 <entry><structfield>memory</structfield></entry>
123 <entry>Applications set this field to
124<constant>V4L2_MEMORY_MMAP</constant>,
125<constant>V4L2_MEMORY_DMABUF</constant> or
126<constant>V4L2_MEMORY_USERPTR</constant>. See <xref linkend="v4l2-memory"
127/></entry>
128 </row>
129 <row>
130 <entry>&v4l2-format;</entry>
131 <entry><structfield>format</structfield></entry>
132 <entry>Filled in by the application, preserved by the driver.</entry>
133 </row>
134 <row>
135 <entry>__u32</entry>
136 <entry><structfield>reserved</structfield>[8]</entry>
137 <entry>A place holder for future extensions.</entry>
138 </row>
139 </tbody>
140 </tgroup>
141 </table>
142 </refsect1>
143
144 <refsect1>
145 &return-value;
146
147 <variablelist>
148 <varlistentry>
149 <term><errorcode>ENOMEM</errorcode></term>
150 <listitem>
151 <para>No memory to allocate buffers for <link linkend="mmap">memory
152mapped</link> I/O.</para>
153 </listitem>
154 </varlistentry>
155 <varlistentry>
156 <term><errorcode>EINVAL</errorcode></term>
157 <listitem>
158 <para>The buffer type (<structfield>format.type</structfield> field),
159requested I/O method (<structfield>memory</structfield>) or format
160(<structfield>format</structfield> field) is not valid.</para>
161 </listitem>
162 </varlistentry>
163 </variablelist>
164 </refsect1>
165</refentry>