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

[Ian Jackson <Ian.Jackson@xxxxxxxxxxxxx>]

Stefano Stabellini writes ("Re: [Xen-devel] [PATCH 1/3] qemu-xen-traditional: 
use O_DIRECT to open disk images for IDE"):
> On Thu, 29 Mar 2012, Ian Jackson wrote:
> > Ian Campbell writes ("Re: [Xen-devel] [PATCH 1/3] qemu-xen-traditional: use 
> > O_DIRECT to open disk images for IDE"):
> > So I think qemu-xen-unstable the use of write-back cacheing for
> > bdrv_write is correct.  (Apart from the wrinkle that the emulated
> > drive cache, write_cache, is enabled by default - but I wouldn't be
> > surprised if that accurately emulated the behaviour of real disks.)
> 
> You have missed my other emails on this thread about other disk formats
> and related bug reports.

I guess you mean this, which I had read:

Stefano Stabellini writes ("Re: [Xen-devel] [PATCH 1/3] qemu-xen-traditional: 
use O_DIRECT to open disk images for IDE"):
> On Wed, 28 Mar 2012, Ian Campbell wrote:
> > I think it is possible that we've incorrectly determined that
> > BDRV_O_CACHE has issues with correctness?
> 
> Following the latest disk cache thread on qemu-devel
> (http://marc.info/?l=qemu-devel&m=127434799425483) it looks like some
> image formats are unsafe with BDRV_O_CACHE_WB:

I'm not convinced that this bug applies to the approach taken in
qemu-xen-unstable, because in qemu-xen-unstable we always call
bdrv_flush at an appropriate point, and bdrv_flush is plumbed through
by qcow_aio_flush to a flush of the underlying device.

Ian.

_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxx
http://lists.xen.org/xen-devel