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Message-Id: <E1KGTmZ-0006oz-Qi@pomaz-ex.szeredi.hu> Date: Wed, 09 Jul 2008 09:08:07 +0200 From: Miklos Szeredi <miklos@...redi.hu> To: arjan@...radead.org CC: miklos@...redi.hu, miklos@...redi.hu, hch@...radead.org, tytso@....edu, pavel@...e.cz, t-sato@...jp.nec.com, akpm@...ux-foundation.org, viro@...IV.linux.org.uk, linux-ext4@...r.kernel.org, xfs@....sgi.com, dm-devel@...hat.com, linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org, axboe@...nel.dk, mtk.manpages@...glemail.com Subject: Re: [PATCH 3/3] Add timeout feature On Tue, 8 Jul 2008, Arjan van de Ven wrote: > I tihnk the idea there is > > freeze . do the snapshot op . unfreeze . make backup of snapshot Ah, so then my proposal would become run_frozen mountpoint do-snapshot do-backup release-snapshot and if they are afraid of deadlocks they can just implement the timeout in userspace: run_frozen -t timeout mountpoint do-snapshot 'run_frozen' can be a trivial 30 line app, that can be guaranteed not to deadlock. > one can argue about the need of doing the first 3 steps via a userland > loop; it sure sounds like one needs to be really careful to not do any > writes to the fs from the app that does snapshots (and that includes > doing any syscalls in the kernel that allocate memory.. just because > that already could cause unrelated data to be written from inside the > app. Not fun.) Userland always has to be careful when messing with raw devices. That alone is not a reason to put the snapshotting facility in kernel IMO. Miklos -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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