Re: [PATCH] extend e2fsprogs functionality to add EXT2_FLAG_DIRECT option

Michal Novotny
2010-01-12T16:43:52Z

On 01/12/2010 05:38 PM, Christoph Hellwig wrote:
> Ok, I looked at the issue. The problem is that the Xen backend drivers
> are (as expected) utterly braindead and submit bios directly from the
> virtualization backed without using proper abstractions and thus
> bypassing all the cache coherency features in the fileystems (the block
> device nodes are just another mini-filesystem in that respect). So
> when you first have buffered access in the host pages may stay in cache
> and get overwritten directly on disk by a Xen guest, and once the guest
> is down the host may still use the now stale cached data.
>
> I would recommend to migrate your cutomers to KVM which uses the proper
> abtractions and thus doesn't have this problem. There's a reason after
> all why all the Xen dom0 mess never got merged to mainline.
>
So, do you think the problem is in the Xen backend drivers and to make
it working right in Xen the driver fix is needed?