[dm-devel] convert dm-thin to use dm-bufio
Mike Snitzer
snitzer at redhat.com
Fri Aug 19 09:46:04 UTC 2011
On Fri, Aug 19 2011 at 5:11am -0400,
Joe Thornber <thornber at redhat.com> wrote:
> On Fri, Aug 19, 2011 at 03:04:36AM -0400, Mike Snitzer wrote:
> > Question for Joe:
> > You're making conflicting changes quick enough that I wonder if you
> > and Mikulas will ever converge (e.g. why do multiple block managers need
> > to have access to the same metadata device!?).
>
> They don't; my issue is with getting an oops if they do through user
> error. I clearly said in the commit message that this was a hack to
> get round issues introduced by agk's move to a kmemcache. Cook
> something cleaner up between yourselves, or wait for me to look at it
> again once I've got through some more pressing issues.
OK, so this kmemcache problem will go away once you switch over to
bufio.
> An alternative would be to iterate through all the pools in the system
> check whether any of them already had the same metadata device open.
> Of course this doesn't catch the cases where the stacking is used and
> a metadata device eventually maps onto the same physical disk as an
> existing md area.
The lack of checking for a metadata or data device that is already in
use should probably be fixed.
As for stacking, can't we just read the superblock to check if a device
is already in use (would work metadata anyway)? No idea if that'd be
too costly -- probably not: read superblock and check if
THIN_SUPERBLOCK_MAGIC is set.
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