Hi Hans,
On Monday 06 September 2010 18:51:59 Hans Verkuil wrote:
> On Wednesday, September 01, 2010 16:05:10 Laurent Pinchart wrote:
> > On Saturday 28 August 2010 13:02:22 Hans Verkuil wrote:
> > > On Friday, August 20, 2010 17:29:09 Laurent Pinchart wrote:
> > [snip]
> >
> > > > diff --git a/Documentation/media-framework.txt
> > > > b/Documentation/media-framework.txt index 66f7f6c..74a137d 100644
> > > > --- a/Documentation/media-framework.txt
> > > > +++ b/Documentation/media-framework.txt
> >
> > [snip]
> >
> > > > +The media_entity_desc structure is defined as
> > > > +
> > > > +- struct media_entity_desc
> > > > +
> > > > +__u32 id Entity id, set by the application. When the id is
> > > > + or'ed with MEDIA_ENTITY_ID_FLAG_NEXT, the driver
> > > > + clears the flag and returns the first entity with a
> > > > + larger id.
> > > > +char name[32] Entity name. UTF-8 NULL-terminated string.
> > >
> > > Why UTF-8 instead of ASCII?
> >
> > Because vendor-specific names could include non-ASCII characters (same
> > reason for the model name in the media_device structure, if we decice to
> > make the model name ASCII I'll make the entity name ASCII as well).
> >
> > [snip]
> >
> > > > +struct media_entity_desc {
> > > > + __u32 id;
> > > > + char name[32];
> > > > + __u32 type;
> > > > + __u32 revision;
> > > > + __u32 flags;
> > > > + __u32 group_id;
> > > > + __u16 pads;
> > > > + __u16 links;
> > > > +
> > > > + __u32 reserved[4];
> > > > +
> > > > + union {
> > > > + /* Node specifications */
> > > > + struct {
> > > > + __u32 major;
> > > > + __u32 minor;
> > > > + } v4l;
> > > > + struct {
> > > > + __u32 major;
> > > > + __u32 minor;
> > > > + } fb;
> > > > + int alsa;
> > > > + int dvb;
> > > > +
> > > > + /* Sub-device specifications */
> > > > + /* Nothing needed yet */
> > > > + __u8 raw[64];
> > > > + };
> > > > +};
> > >
> > > Should this be a packed struct?
> >
> > Why ? :-) Packed struct are most useful when they need to match hardware
> > structures or network protocols. Packing a structure can generate
> > unaligned fields, which are bad performance-wise.
>
> I'm thinking about preventing a compat32 mess as we have for v4l.
>
> It is my understanding that the only way to prevent different struct sizes
> between 32 and 64 bit is to use packed.
I don't think that's correct. Different struct sizes between 32bit and 64bit
are caused by variable-size fields, such as 'long' (32bit on 32bit
architectures, 64bit on 64bit architectures). I might be wrong though.
--
Regards,
Laurent Pinchart
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