This patch adds description and usage examples for exporting
DMABUF file descriptor in V4L2.
Signed-off-by: Tomasz Stanislawski <t.stanislaws@xxxxxxxxxxx>
Signed-off-by: Kyungmin Park <kyungmin.park@xxxxxxxxxxx>
CC: linux-doc@xxxxxxxxxxxxxxx
---
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 07a311f..7773450 100644
--- a/Documentation/DocBook/media/v4l/compat.xml
+++ b/Documentation/DocBook/media/v4l/compat.xml
@@ -2591,6 +2591,9 @@ 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 f55b0ab..7a0dfc9 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 015c561..8f650d2 100644
--- a/Documentation/DocBook/media/v4l/v4l2.xml
+++ b/Documentation/DocBook/media/v4l/v4l2.xml
@@ -561,6 +561,7 @@ and discussions on the V4L mailing list.</revremark>
&sub-log-status;
&sub-overlay;
&sub-qbuf;
+ &sub-expbuf;
&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
+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>
+
+ </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(&buf, 0, sizeof buf);
+ buf.type = bt;
+ buf.memory = V4L2_MEMORY_MMAP;
+ buf.index = index;
+
+ if (ioctl (v4lfd, &VIDIOC-QUERYBUF;, &buf) == -1) {
+ perror ("VIDIOC_QUERYBUF");
+ return -1;
+ }
+
+ memset(&expbuf, 0, sizeof expbuf);
+ expbuf.mem_offset = buf.m.offset;
+ if (ioctl (v4lfd, &VIDIOC-EXPBUF;, &expbuf) == -1) {
+ perror ("VIDIOC_EXPBUF");
+ return -1;
+ }
+
+ *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(&buf, 0, sizeof buf);
+ buf.type = bt;
+ buf.memory = V4L2_MEMORY_MMAP;
+ buf.index = index;
+ buf.m.planes = planes;
+ buf.length = n_planes;
+ memset(&planes, 0, sizeof planes);
+
+ if (ioctl (v4lfd, &VIDIOC-QUERYBUF;, &buf) == -1) {
+ perror ("VIDIOC_QUERYBUF");
+ return -1;
+ }
+
+ for (i = 0; i < 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
+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
+</structfield> fields are invalid.</para>
+ </listitem>
+ </varlistentry>
+ </variablelist>
+ </refsect1>
+
+</refentry>
--
1.7.9.5
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