Re: [Xen-devel] [PATCH 1/3] qemu-xen-traditional: use O_DIRECT to open disk images for IDE

[Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>]

On Mon, 26 Mar 2012, Zhang, Yang Z wrote:
> > -----Original Message-----
> > From: xen-devel-bounces@xxxxxxxxxxxxx
> > [mailto:xen-devel-bounces@xxxxxxxxxxxxx] On Behalf Of Stefano Stabellini
> > Sent: Friday, March 23, 2012 10:51 PM
> > To: xen-devel@xxxxxxxxxxxxxxxxxxx
> > Cc: Ian.Jackson@xxxxxxxxxxxxx; Stefano Stabellini
> > Subject: [Xen-devel] [PATCH 1/3] qemu-xen-traditional: use O_DIRECT to open
> > disk images for IDE
> > 
> > Signed-off-by: Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>
> > ---
> >  xenstore.c |    2 +-
> >  1 files changed, 1 insertions(+), 1 deletions(-)
> > 
> > diff --git a/xenstore.c b/xenstore.c
> > index 4c483e2..ac90366 100644
> > --- a/xenstore.c
> > +++ b/xenstore.c
> > @@ -643,7 +643,7 @@ void xenstore_parse_domain_config(int hvm_domid)
> >         }
> >              pstrcpy(bs->filename, sizeof(bs->filename), params);
> > 
> > -            flags = BDRV_O_CACHE_WB; /* snapshot and write-back */
> > +            flags = BDRV_O_NOCACHE;
> >              is_readonly = 0;
> >              if (pasprintf(&buf, "%s/mode", bpath) == -1)
> >                  continue;
> Any reason for this change? 

performance and correctness: BDRV_O_NOCACHE in QEMU means opening the
disk image with O_DIRECT

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