buffer. It depends on the negotiated data format and may change with
each buffer for compressed variable size data like JPEG images.
Drivers must set this field when <structfield>type</structfield>
-refers to an input stream, applications when it refers to an output stream.</entry>
+refers to an input stream, applications when it refers to an output stream.
+If the application sets this to 0 for an output stream, then
+<structfield>bytesused</structfield> will be set to the size of the
+buffer (see the <structfield>length</structfield> field of this struct) by
+the driver. For multiplanar formats this field is ignored and the
+<structfield>planes</structfield> pointer is used instead.</entry>
</row>
<row>
<entry>__u32</entry>
<entry></entry>
<entry>The number of bytes occupied by data in the plane
(its payload). Drivers must set this field when <structfield>type</structfield>
- refers to an input stream, applications when it refers to an output stream.</entry>
+ refers to an input stream, applications when it refers to an output stream.
+ 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>
</row>
<row>
<entry>__u32</entry>