Hi Laurent, Something that just caught my eye: On 06/24/2014 01:54 AM, Laurent Pinchart wrote: > The v4l2_pix_format structure has no reserved field. It is embedded in > the v4l2_framebuffer structure which has no reserved fields either, and > in the v4l2_format structure which has reserved fields that were not > previously required to be zeroed out by applications. > > To allow extending v4l2_pix_format, inline it in the v4l2_framebuffer > structure, and use the priv field as a magic value to indicate that the > application has set all v4l2_pix_format extended fields and zeroed all > reserved fields following the v4l2_pix_format field in the v4l2_format > structure. > > The availability of this API extension is reported to userspace through > the new V4L2_CAP_EXT_PIX_FORMAT capability flag. Just checking that the > priv field is still set to the magic value at [GS]_FMT return wouldn't > be enough, as older kernels don't zero the priv field on return. > > To simplify the internal API towards drivers zero the extended fields > and set the priv field to the magic value for applications not aware of > the extensions. > > Signed-off-by: Laurent Pinchart <laurent.pinchart+renesas@xxxxxxxxxxxxxxxx> > --- > > diff --git a/Documentation/DocBook/media/v4l/pixfmt.xml b/Documentation/DocBook/media/v4l/pixfmt.xml > index 91dcbc8..8c56cacd 100644 > --- a/Documentation/DocBook/media/v4l/pixfmt.xml > +++ b/Documentation/DocBook/media/v4l/pixfmt.xml > @@ -112,9 +112,28 @@ see <xref linkend="colorspaces" />.</entry> > <row> > <entry>__u32</entry> > <entry><structfield>priv</structfield></entry> > - <entry>Reserved for custom (driver defined) additional > -information about formats. When not used drivers and applications must > -set this field to zero.</entry> > + <entry><para>This field indicates whether the remaining fields of the > +<structname>v4l2_pix_format</structname> structure, also called the extended > +fields, are valid. When set to <constant>V4L2_PIX_FMT_PRIV_MAGIC</constant>, it > +indicates that the extended fields have been correctly initialized. When set to > +any other value it indicates that the extended fields contain undefined values. > +</para> > +<para>Applications that wish to use the pixel format extended fields must first > +ensure that the feature is supported by querying the device for the > +<link linkend="querycap"><constant>V4L2_CAP_EXT_PIX_FORMAT</constant></link> > +capability. If the capability isn't set the pixel format extended fields are not > +supported and using the extended fields will lead to undefined results.</para> > +<para>To use the extended fields, applications must set the > +<structfield>priv</structfield> field to > +<constant>V4L2_PIX_FMT_PRIV_MAGIC</constant>, initialize all the extended fields > +and zero the unused bytes of the <structname>v4l2_format</structname> > +<structfield>raw_data</structfield> field.</para> Easy to write, much harder to implement. You would end up with something like: memset(&fmt.fmt.pix.flags + sizeof(fmt.fmt.pix.flags), 0, sizeof(fmt.fmt.raw_data) - sizeof(fmt.fmt.pix)); Not user-friendly and error-prone. I would suggest adding a reserved array to pix_format instead, of at least size (10 + 2 * 7) / 4 = 6 __u32. So: __u32 reserved[6]. Better would be to go with 10 + 17 = 27 elements (same as the number of reserved elements in v4l2_pix_format_mplane and one struct v4l2_plane_pix_format). That will allow you to just say that the app should zero the reserved array. > +<para>When the <structfield>priv</structfield> field isn't set to > +<constant>V4L2_PIX_FMT_PRIV_MAGIC</constant> drivers must act as if all the > +extended fields were set to zero. On return drivers must set the > +<structfield>priv</structfield> field to > +<constant>V4L2_PIX_FMT_PRIV_MAGIC</constant> and all the extended field to > +applicable values.</para></entry> > </row> > </tbody> > </tgroup> Regards, Hans -- To unsubscribe from this list: send the line "unsubscribe linux-media" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
