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; &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>