From: Alasdair G Kergon Subject: Re: Re: [PATCH 3/3] Add timeout feature Date: Tue, 1 Jul 2008 11:52:51 +0100 Message-ID: <20080701105251.GC22522@agk.fab.redhat.com> References: <20080630212450t-sato@mail.jp.nec.com> <20080701081026.GB16691@infradead.org> Reply-To: device-mapper development Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: axboe@kernel.dk, mtk.manpages@googlemail.com, "linux-kernel@vger.kernel.org" , "xfs@oss.sgi.com" , Christoph Hellwig , "dm-devel@redhat.com" , viro@ZenIV.linux.org.uk, "linux-fsdevel@vger.kernel.org" , akpm@linux-foundation.org, "linux-ext4@vger.kernel.org" To: Takashi Sato Return-path: Content-Disposition: inline In-Reply-To: <20080701081026.GB16691@infradead.org> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: dm-devel-bounces@redhat.com Errors-To: dm-devel-bounces@redhat.com List-Id: linux-ext4.vger.kernel.org On Tue, Jul 01, 2008 at 04:10:26AM -0400, Christoph Hellwig wrote: > I still disagree with this whole patch. Same here - if you want a timeout, what stops you from implementing it in a userspace process? If your concern is that the process might die without thawing the filesystem, take a look at the userspace LVM/multipath code for ideas - lock into memory, disable OOM killer, run from ramdisk etc. In practice, those techniques seem to be good enough. > call can hang and this would be theoretically useful is when the > filesystem is already frozen by someone else, but this should be fixed > by refusing to do the second freeze, as suggested in my comment to patch > 1. Similarly if a device-mapper device is involved, how should the following sequence behave - A, B or C? 1. dmsetup suspend (freezes) 2. FIFREEZE 3. FITHAW 4. dmsetup resume (thaws) A: 1 succeeds, freezes 2 succeeds, remains frozen 3 succeeds, remains frozen 4 succeeds, thaws B: 1 succeeds, freezes 2 fails, remains frozen 3 shouldn't be called because 2 failed but if it is: succeeds, thaws 4 succeeds (already thawed, but still does the device-mapper parts) C: 1 succeeds, freezes 2 fails, remains frozen 3 fails (because device-mapper owns the freeze/thaw), remains frozen 4 succeeds, thaws Alasdair -- agk@redhat.com