[sheepdog] [PATCH v1, RFC] sheep: writeback cache semantics in backend store

[MORITA Kazutaka]

At Wed, 29 Aug 2012 13:38:18 +0900,
MORITA Kazutaka wrote:
> 
> At Wed, 29 Aug 2012 12:18:50 +0800,
> Liu Yuan wrote:
> > 
> > On 08/29/2012 12:10 PM, MORITA Kazutaka wrote:
> > > How about the following?
> > > 
> > >   -w object,disk    turn on both object cache and disk cache
> > >   -w object         turn on only object cache
> > >   -w disk           turn on only disk cache
> > 
> > Looks okay to me, seems that this require changes on QEMU and protocol
> > between QEMU and sheepdog.
> 
> Yes, because QEMU needs to let sheepdog know the using cache semantics
> (writeback or writethrough).  Perhaps, this patch should be postponed
> until Sheepdog 0.5.0 and QEMU 1.2 are released.

On second thought, we don't need to modify QEMU and protocol at all.
When writeback is enabled, QEMU sends I/O requests with a
SD_FLAG_CMD_CACHE flag.

Thanks,

Kazutaka