From mboxrd@z Thu Jan 1 00:00:00 1970 From: Mike Snitzer Subject: Re: convert dm-thin to use dm-bufio Date: Fri, 19 Aug 2011 05:46:04 -0400 Message-ID: <20110819094604.GA1059@redhat.com> References: <20110815090416.GE3159@ubuntu> <20110816091600.GA4284@ubuntu> <20110817082656.GA3267@ubuntu> <20110819070435.GA32300@redhat.com> <20110819091106.GA3193@ubuntu> Reply-To: device-mapper development Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: Content-Disposition: inline In-Reply-To: <20110819091106.GA3193@ubuntu> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: dm-devel-bounces@redhat.com Errors-To: dm-devel-bounces@redhat.com To: Joe Thornber Cc: dm-devel@redhat.com, Mikulas Patocka , "Alasdair G. Kergon" List-Id: dm-devel.ids On Fri, Aug 19 2011 at 5:11am -0400, Joe Thornber 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.