[dm-devel] Re: Barriers still not passing on simple dm devices...

[Bodo Eggert]

Eric Sandeen <sandeen at redhat.com> wrote:

> I've noticed that on 2.6.29-rcX, with Andi's patch
> (ab4c1424882be9cd70b89abf2b484add355712fa, dm: support barriers on
> simple devices) barriers are still getting rejected on these simple devices.

> So what's the right way around this?  What should dm (or md for that
> matter) advertise on their queues about ordered-ness?  Should there be
> some sort of "QUEUE_ORDERED_PASSTHROUGH" or something to say "this level
> doesn't care, ask the next level" or somesuch?  Or should it inherit the
> flag from the next level down?  Ideas?

IMO each block device SHOULD provide barriers - either native or emulated,
and each meta device MUST provide emulated barriers if it provides dynamic
device binding and barriers.