Re: [Qemu-devel] [Nbd] Is NBD_CMD_FLAG_FUA valid during NBD_CMD_FLUSH?

[Kevin Wolf]

Am 05.04.2016 um 15:28 hat Paolo Bonzini geschrieben:
> On 05/04/2016 07:09, Kevin Wolf wrote:
> > > TRIM is an advisory operation, so it doesn't make sense to force access
> > > to the medium.
> > 
> > I think it does make sense. It means that on completion there is no
> > pending discard operation (i.e. either there wasn't a discard or if
> > there was, it has completed) and other readers will see the final state
> > of the blocks.
> 
> This is what already happens though, isn't it?

You mean because in practice discard requests aren't even cached, so we
always behave as if FUA were specified? That's probably right, but is
there a fundamental reason why some storage backend couldn't have a
writeback cache for discards?

It probably wouldn't make sense to introduce FUA for this if it didn't
already exist elsewhere, but now that we do have it, I'd allow it for
TRIM, too, for the sake of consistency and symmetry.

Kevin