Re: [RFC][PATCH resend 8/12] asm-generic: bitops: introduce le bitoffset macro

[Avi Kivity]

On 05/04/2010 06:03 PM, Arnd Bergmann wrote:
> On Tuesday 04 May 2010, Takuya Yoshikawa wrote:
>    
> > Although we can use *_le_bit() helpers to treat bitmaps le arranged,
> > having le bit offset calculation as a seperate macro gives us more freedom.
> >
> > For example, KVM has le arranged dirty bitmaps for VGA, live-migration
> > and they are used in user space too. To avoid bitmap copies between kernel
> > and user space, we want to update the bitmaps in user space directly.
> > To achive this, le bit offset with *_user() functions help us a lot.
> >
> > So let us use the le bit offset calculation part by defining it as a new
> > macro: generic_le_bit_offset() .
> >      
> Does this work correctly if your user space is 32 bits (i.e. unsigned long
> is different size in user space and kernel) in both big- and little-endian
> systems?
>
> I'm not sure about all the details, but I think you cannot in general share
> bitmaps between user space and kernel because of this.
>    

That's why the bitmaps are defined as little endian u64 aligned, even on 
big endian 32-bit systems.  Little endian bitmaps are wordsize agnostic, 
and u64 alignment ensures we can use long-sized bitops on mixed size 
systems.

--
error compiling committee.c: too many arguments to function

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/