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. Drivers and applications
138must set the array to zero.</entry>
139	  </row>
140	</tbody>
141      </tgroup>
142    </table>
143  </refsect1>
144
145  <refsect1>
146    &return-value;
147
148    <variablelist>
149      <varlistentry>
150	<term><errorcode>ENOMEM</errorcode></term>
151	<listitem>
152	  <para>No memory to allocate buffers for <link linkend="mmap">memory
153mapped</link> I/O.</para>
154	</listitem>
155      </varlistentry>
156      <varlistentry>
157	<term><errorcode>EINVAL</errorcode></term>
158	<listitem>
159	  <para>The buffer type (<structfield>format.type</structfield> field),
160requested I/O method (<structfield>memory</structfield>) or format
161(<structfield>format</structfield> field) is not valid.</para>
162	</listitem>
163      </varlistentry>
164    </variablelist>
165  </refsect1>
166</refentry>
167