Re: [Linaro-mm-sig] [PATCHv8 17/26] Documentation: media: description of DMABUF exporting in V4L2

On Tue August 14 2012 17:34:47 Tomasz Stanislawski wrote:

This patch adds description and usage examples for exporting DMABUF file descriptor in V4L2.

Signed-off-by: Tomasz Stanislawski t.stanislaws@samsung.com Signed-off-by: Kyungmin Park kyungmin.park@samsung.com CC: linux-doc@vger.kernel.org

---

Documentation/DocBook/media/v4l/compat.xml | 3 + Documentation/DocBook/media/v4l/io.xml | 3 + Documentation/DocBook/media/v4l/v4l2.xml | 1 + Documentation/DocBook/media/v4l/vidioc-expbuf.xml | 223 +++++++++++++++++++++ 4 files changed, 230 insertions(+) create mode 100644 Documentation/DocBook/media/v4l/vidioc-expbuf.xml

diff --git a/Documentation/DocBook/media/v4l/compat.xml b/Documentation/DocBook/media/v4l/compat.xml index ff45330..802c1ab 100644 --- a/Documentation/DocBook/media/v4l/compat.xml +++ b/Documentation/DocBook/media/v4l/compat.xml @@ -2609,6 +2609,9 @@ ioctls.</para> <para>Importing DMABUF file descriptors as a new IO method described in <xref linkend="dmabuf" />.</para> </listitem>

•    <listitem>
  

•  <para>Exporting DMABUF files using &VIDIOC-EXPBUF; ioctl.</para>
  

•    </listitem>
   </itemizedlist>
  

  </section>

diff --git a/Documentation/DocBook/media/v4l/io.xml b/Documentation/DocBook/media/v4l/io.xml index 98253ee..c27e59b 100644 --- a/Documentation/DocBook/media/v4l/io.xml +++ b/Documentation/DocBook/media/v4l/io.xml @@ -488,6 +488,9 @@ buffer from userspace using a file descriptor previously exported for a different or the same device (known as the importer role), or both. This section describes the DMABUF importer role API in V4L2.</para>

• <para>Refer to <link linked="vidioc-expbuf"> DMABUF exporting </link> for

+details about exporting a V4L2 buffers as DMABUF file descriptors.</para>

<para>Input and output devices support the streaming I/O method when the <constant>V4L2_CAP_STREAMING</constant> flag in the <structfield>capabilities</structfield> field of &v4l2-capability; returned by diff --git a/Documentation/DocBook/media/v4l/v4l2.xml b/Documentation/DocBook/media/v4l/v4l2.xml index 0292ed1..874c085 100644 --- a/Documentation/DocBook/media/v4l/v4l2.xml +++ b/Documentation/DocBook/media/v4l/v4l2.xml @@ -568,6 +568,7 @@ and discussions on the V4L mailing list.</revremark> &sub-overlay; &sub-prepare-buf; &sub-qbuf;

• &sub-expbuf;

This list is sorted alphabetically, so sub-expbuf should go after sub-enumstd.

 &sub-querybuf;
 &sub-querycap;
 &sub-queryctrl;

diff --git a/Documentation/DocBook/media/v4l/vidioc-expbuf.xml b/Documentation/DocBook/media/v4l/vidioc-expbuf.xml new file mode 100644 index 0000000..30ebf67 --- /dev/null +++ b/Documentation/DocBook/media/v4l/vidioc-expbuf.xml @@ -0,0 +1,223 @@ +<refentry id="vidioc-expbuf">

• <refmeta>

• <refentrytitle>ioctl VIDIOC_EXPBUF</refentrytitle>
• &manvol;

• </refmeta>

• <refnamediv>

• <refname>VIDIOC_EXPBUF</refname>
• <refpurpose>Export a buffer as a DMABUF file descriptor.</refpurpose>

• </refnamediv>

• <refsynopsisdiv>

• <funcsynopsis>

•  <funcprototype>
  

• <funcdef>int <function>ioctl</function></funcdef>
• <paramdef>int <parameter>fd</parameter></paramdef>
• <paramdef>int <parameter>request</parameter></paramdef>
• <paramdef>struct v4l2_exportbuffer *<parameter>argp</parameter></paramdef>

•  </funcprototype>
  

• </funcsynopsis>

• </refsynopsisdiv>

• <refsect1>

• <title>Arguments</title>

• <variablelist>

•  <varlistentry>
  

• <term><parameter>fd</parameter></term>

• <listitem>

•  <para>&fd;</para>
  

• </listitem>

•  </varlistentry>
  

•  <varlistentry>
  

• <term><parameter>request</parameter></term>

• <listitem>

•  <para>VIDIOC_EXPBUF</para>
  

• </listitem>

•  </varlistentry>
  

•  <varlistentry>
  

• <term><parameter>argp</parameter></term>

• <listitem>

•  <para></para>
  

• </listitem>

•  </varlistentry>
  

• </variablelist>

• </refsect1>

• <refsect1>

• <title>Description</title>

• <note>

•  <title>Experimental</title>
  

•  <para>This is an <link linkend="experimental"> experimental </link>
  

•  interface and may change in the future.</para>
  

• </note>

+<para>This ioctl is an extension to the <link linkend="mmap">memory +mapping</link> I/O method therefore it is available only for +<constant>V4L2_MEMORY_MMAP</constant> buffers. It can be used to export a +buffer as DMABUF file at any time after buffers have been allocated with the +&VIDIOC-REQBUFS; ioctl.</para>

+<para>Prior to exporting an application calls <link +linkend="vidioc-querybuf">VIDIOC_QUERYBUF</link> to obtain memory offsets. When +using the <link linkend="planar-apis">multi-planar API</link> every plane has +own offset.</para>

+<para>To export a buffer, the application fills &v4l2-exportbuffer;. The +<structfield> mem_offset </structfield> field is set to the offset obtained +from <constant> VIDIOC_QUERYBUF </constant>. Additional flags may be posted in +the <structfield> flags </structfield> field. Refer to manual for open syscall

Better IMHO: 'Refer to the manual for open()'

+for details. Currently only O_CLOEXEC is guaranteed to be supported. All other +fields must be set to zero. In a case of multi-planar API, every plane is +exported separately using multiple <constant> VIDIOC_EXPBUF </constant> +calls.</para>

+<para> After calling <constant>VIDIOC_EXPBUF</constant> the <structfield> fd +</structfield> field will be set by a driver. This is a DMABUF file +descriptor. The application may pass it to other API. Refer to <link +linkend="dmabuf">DMABUF importing</link> for details about importing DMABUF +files into V4L2 nodes. A developer is encouraged to close a DMABUF file when it +is no longer used. </para>

Some explanation of why this is recommended would be useful.

• </refsect1>

• <refsect1>

• <section>

•  <title>Examples</title>
  

•  <example>
  

• <title>Exporting a buffer.</title>

• <programlisting>

+int buffer_export(int v4lfd, &v4l2-buf-type; bt, int index, int *dmafd) +{

• &v4l2-buffer; buf;
• &v4l2-exportbuffer; expbuf;
• memset(&amp;buf, 0, sizeof buf);
• buf.type = bt;
• buf.memory = V4L2_MEMORY_MMAP;
• buf.index = index;
• if (ioctl (v4lfd, &VIDIOC-QUERYBUF;, &amp;buf) == -1) {

• perror ("VIDIOC_QUERYBUF");
  

• return -1;
  

• }
• memset(&amp;expbuf, 0, sizeof expbuf);
• expbuf.mem_offset = buf.m.offset;
• if (ioctl (v4lfd, &VIDIOC-EXPBUF;, &amp;expbuf) == -1) {

• perror ("VIDIOC_EXPBUF");
  

• return -1;
  

• }

Same as in the review of the previous documentation patch: use the kernel coding style in these examples, so no space before '('.

• *dmafd = expbuf.fd;
• return 0;

+}

•    </programlisting>
  

•  </example>
  

•  <example>
  

• <title>Exporting a buffer using multi plane API.</title>

• <programlisting>

+int buffer_export_mp(int v4lfd, &v4l2-buf-type; bt, int index,

• int dmafd[], int n_planes)

+{

• &v4l2-buffer; buf;
• &v4l2-plane; planes[VIDEO_MAX_PLANES];
• int i;
• memset(&amp;buf, 0, sizeof buf);
• buf.type = bt;
• buf.memory = V4L2_MEMORY_MMAP;
• buf.index = index;
• buf.m.planes = planes;
• buf.length = n_planes;
• memset(&amp;planes, 0, sizeof planes);
• if (ioctl (v4lfd, &VIDIOC-QUERYBUF;, &amp;buf) == -1) {

• perror ("VIDIOC_QUERYBUF");
  

• return -1;
  

• }
• for (i = 0; i &lt; n_planes; ++i) {

• &v4l2-exportbuffer; expbuf;
  

• memset(&expbuf, 0, sizeof expbuf);
  

• expbuf.mem_offset = plane[i].m.offset;
  

• if (ioctl (v4lfd, &VIDIOC-EXPBUF;, &expbuf) == -1) {
  

• 	perror ("VIDIOC_EXPBUF");
  

• 	while (i)
  

• 		close(dmafd[--i]);
  

• 	return -1;
  

• }
  

• dmafd[i] = expbuf.fd;
  

• }
• return 0;

+}

•    </programlisting>
  

•  </example>
  

• </section>

• </refsect1>

• <refsect1>

• <table pgwide="1" frame="none" id="v4l2-exportbuffer">

•  <title>struct <structname>v4l2_exportbuffer</structname></title>
  

•  <tgroup cols="3">
  

• &cs-str;

• <tbody valign="top">

•  <row>
  

•    <entry>__u32</entry>
  

•    <entry><structfield>fd</structfield></entry>
  

•    <entry>The DMABUF file descriptor associated with a buffer. Set by
  

• a driver.</entry>
  

•  </row>
  

•  <row>
  

•    <entry>__u32</entry>
  

•    <entry><structfield>reserved0</structfield></entry>
  

•    <entry>Reserved field for future use. Must be set to zero.</entry>
  

•  </row>
  

•  <row>
  

•    <entry>__u32</entry>
  

•    <entry><structfield>mem_offset</structfield></entry>
  

•    <entry>Buffer memory offset as returned by <constant>
  

+VIDIOC_QUERYBUF </constant> in &v4l2-buffer;<structfield> ::m.offset +</structfield> (for single-plane formats) or &v4l2-plane;<structfield> +::m.offset </structfield> (for multi-planar formats)</entry>

•  </row>
  

•  <row>
  

•    <entry>__u32</entry>
  

•    <entry><structfield>flags</structfield></entry>
  

•    <entry>Flags for newly created file, currently only <constant>
  

+O_CLOEXEC </constant> is supported, refer to manual of open syscall for more

'to the manual of open() for more'

+details.</entry>

•  </row>
  

•  <row>
  

•    <entry>__u32</entry>
  

•    <entry><structfield>reserved[12]</structfield></entry>
  

•    <entry>Reserved field for future use. Must be set to zero.</entry>
  

•  </row>
  

• </tbody>

•  </tgroup>
  

• </table>

• </refsect1>

• <refsect1>

• &return-value;

• <variablelist>

•  <varlistentry>
  

• <term><errorcode>EINVAL</errorcode></term>

• <listitem>

•  <para>A queue is not in MMAP mode or DMABUF exporting is not
  

+supported or <structfield> flag </structfield> or <structfield> mem_offset

flag -> flags

+</structfield> fields are invalid.</para>

• </listitem>

•  </varlistentry>
  

• </variablelist>

• </refsect1>

+</refentry>

Regards,

Hans