[Cluster-devel] cluster4 gfs_controld

[David Teigland <teigland@redhat.com>]

On Thu, Oct 13, 2011 at 03:41:31PM +0100, Steven Whitehouse wrote:
> > cluster4
> > . jid from dlm-kernel "slots" which will be assigned similarly
> What is the actual algorithm used to assign these slots?

The same as picking jids: lowest unused id starting with 0.  As for
implementation, I'll add it to the current dlm recovery messages.

(Frankly, I'd really like to just set jid to nodeid-1.  Any support for
that?  It would obviously add a slight requirement to picking nodeid's,
which 99.9% of people already do.)

> > . first mounter using a dlm lock in lock_dlm
> > 
> That sounds good to me. The thing we need to resolve is how do we get
> from one to the other. We may have to introduce a new name for the lock
> protocol to avoid people accidentally using both schemes in the same
> cluster.

Compatibility rests on the fact that the new dlm kernel features will only
work when the cluster4 dlm_controld is used.

dlm_controld.v3 running: dlm_recover_register() returns an error, and
everything falls back to working as it does now, with gfs_controld.v3 etc.

dlm_controld.v4 running: dlm_recover_register() works, lock_dlm sets jid
and first.  (gfs_controld.v3 will fail to even run with dlm_controld.v4,
and other combinations of v3/v4 daemons will also fail to run together.)

> > cluster4
> > . coordination of dlm-kernel/gfs-kernel recovery is done
> >   directly in kernel using callbacks from dlm-kernel to gfs-kernel.
> > . gdlm_mount(struct gfs2_sbd *sdp, const char *table, int *first, int *jid)
> >   calls dlm_recover_register(dlm, &jid, &recover_callbacks)
> Can we not just pass the extra functions to dlm_create_lockspace? That
> seems a bit simpler than adding an extra function just to register the
> callbacks,

Yes we could; I may do that.  Returning the error mentioned above becomes
less direct.  I'd have to overload the jid arg, or add another to indicate
the callbacks are enabled.