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

[MORITA Kazutaka]

At Thu, 30 Aug 2012 12:17:47 +0800,
Liu Yuan wrote:
> 
> On 08/30/2012 12:14 PM, MORITA Kazutaka wrote:
> > 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.
> 
> So all other request means writethrough?

Yes.

> But how does qemu to disable all cache then?

Do you mean "cache=none" and "cache=directsync" options?  Hmm, yes, to
support them, we need to modify QEMU and protocol.

But how about keeping it as future work (later QEMU 1.2), and cleaning
up the '-w' option with this patch for now?  I think it is easy to
disable a Sheepdog cache according to the qemu cache option later.

Thanks,

Kazutaka