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 -- dm-devel mailing list dm-devel@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/dm-devel
