Re: HVM disc corruption (was Re: Xen won't start its device backend?)

[Manuel Bouyer <bouyer%antioche.eu.org@localhost>]

On Tue, Jun 02, 2015 at 01:04:16PM +0200, Reinoud Zandijk wrote:
> Hi,
> 
> On Wed, May 27, 2015 at 09:39:19PM +0100, Roger Pau Monn? wrote:
> > El 27/05/15 a les 21.29, Reinoud Zandijk ha escrit:
> > > It then reads the disklabel fine. Inspecting the code it seems to open the
> > > disc with O_BINARY, with a possible O_DIRECT / O_DSYNC. Reading it seems
> > > to do on a 512 block boundary for files opened with O_DIRECT and it uses
> > > lseek() in combination with the qemu_read(fd, buf, cnt) function.
> > > 
> > > Is there any special behaviour on raw devices for such flags / functions
> > > that could trigger the bug?
> > 
> > FWIW I had to craft the following patch for FreeBSD:
> > 
> > http://git.qemu.org/?p=qemu.git;a=patch;h=3cad83075c7b847fe0eb6e61316fdf50984d4570
> 
> Do you have suggestions on how to debug this? Somehow i don't have a network
> connection yet :-/ With that i could just dump the devices and see what
> changes? Would that help?

Maybe you could ktrace the qemu-dm process and see if it's requesting
the right blocks, and getting the right data ?

-- 
Manuel Bouyer <bouyer%antioche.eu.org@localhost>
     NetBSD: 26 ans d'experience feront toujours la difference
--