Re: [Qemu-devel] buffer alignment for block backends

[Samuel Thibault <samuel.thibault@ens-lyon.org>]

Jamie Lokier, le Thu 09 Apr 2009 16:55:50 +0100, a écrit :
> Samuel Thibault wrote:
> > Gerd Hoffmann, le Thu 09 Apr 2009 15:54:34 +0200, a écrit :
> > > On 04/09/09 15:30, Stefano Stabellini wrote:
> > > >The userspace\kernelspace distinction does not make much sense in
> > > >minios, but yes it provides an interface to communicate with blkback in
> > > >dom0. This interface is used by block-vbd in qemu instead of
> > > >block-raw-posix when run in minios.
> > > 
> > > Sit back, look again.  Do you really need it being page-aligned?
> > 
> > Page aligned is an optimization which comes for free when you can
> > already choose the alignment.
> > 
> > > The xen block protocol can handle unaligned requests just fine.
> > 
> > Not completely arbitrarily aligned requests. They need to be
> > sector-aligned.
> 
> Thought about 4k sectors, to be found in new disks sometime soon?

Same wording: they will have to be sector-aligned (the blkback announces
the size of its sector).

Samuel