Re: [Qemu-devel] [PATCH] sheepdog: implement SD_OP_FLUSH_VDI operation

[Christoph Hellwig]

On Fri, Apr 20, 2012 at 12:15:36PM -0700, MORITA Kazutaka wrote:
> His patch sets the SD_FLAG_CMD_CACHE flag for writes only when the
> user selects cache=writeback or cache=none.  If SD_FLAG_CMD_CACHE is
> not set in the request, Sheepdog servers are forced to flush the cache
> like FUA commands.

Ok, I missed that part and it thus seems ok.  What still sems missing
is error handling in case the sheepdog cluster doesn't actually support
the new flag.  What happens if cache=none is specified with a cluster
not actually supporting it?  Remember that cache=none is the default for
many management frontends to qemu.