Re: [Qemu-devel] [Xen-devel] [PATCH] xen_disk: implement BLKIF_OP_FLUSH_DISKCACHE, remove BLKIF_OP_WRITE_BARRIER

[Ian Campbell]

On Wed, 2012-04-25 at 09:45 +0100, Christoph Hellwig wrote:
> > -    case BLKIF_OP_WRITE_BARRIER:
> > +    case BLKIF_OP_FLUSH_DISKCACHE:
> >          if (!ioreq->req.nr_segments) {
> >              ioreq->presync = 1;
> >              return 0;
> >          }
> > -        ioreq->presync = ioreq->postsync = 1;
> > +        ioreq->postsync = 1;
> >          /* fall through */
> 
> It might be worth documenting the semantics of BLKIF_OP_FLUSH_DISKCACHE
> in a comment here.  I haven't found any spec for the xen_disk protocol,

The blkif spec was recently much improved, you can find it at
http://xenbits.xen.org/docs/unstable/hypercall/include,public,io,blkif.h.html

TBH I'm not sure it actually answers your questions wrt
BLKIF_OP_FLUSH_DISKCACHE, if not please let us know and we can see about
improving it.

Ian