This patch explicitly documents the relationship between bytesused and
data_offset.
But looking in the kernel there isn't a single driver that actually sets
data_offset.
Do such beasts exist? It's also annoying that there is no such equivalent for
the
single planar API, so it is asymmetrical. What was the reason that we never did
that
for single planar? Because existing applications wouldn't know what to do with
it?
Regards,
Hans
Signed-off-by: Hans Verkuil <hans.verk...@cisco.com>
diff --git a/Documentation/DocBook/media/v4l/io.xml
b/Documentation/DocBook/media/v4l/io.xml
index 8c4ee74..e5e8325 100644
--- a/Documentation/DocBook/media/v4l/io.xml
+++ b/Documentation/DocBook/media/v4l/io.xml
@@ -870,7 +870,8 @@ should set this to 0.</entry>
If the application sets this to 0 for an output stream, then
<structfield>bytesused</structfield> will be set to the size of
the
plane (see the <structfield>length</structfield> field of this
struct)
- by the driver.</entry>
+ by the driver. Note that the actual image data starts at
+ <structfield>data_offset</structfield> which may not be 0.</entry>
</row>
<row>
<entry>__u32</entry>
@@ -919,6 +920,10 @@ should set this to 0.</entry>
<entry>Offset in bytes to video data in the plane.
Drivers must set this field when <structfield>type</structfield>
refers to an input stream, applications when it refers to an
output stream.
+ Note that data_offset is included in
<structfield>bytesused</structfield>.
+ So the size of the image in the plane is
+
<structfield>bytesused</structfield>-<structfield>data_offset</structfield> at
+ offset <structfield>data_offset</structfield> from the start of
the plane.
</entry>
</row>
<row>
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