On Wed, May 06, 2009 at 12:37:29AM +0900, Ryusuke Konishi wrote: > Oh, meaning of the (b) was ambiguous. How about the following one? > > b) Remounting an ro-mount to read-only is possible only if the > checkpoint number of the target ro-mount is latest and there is no > existent rw-mount. > > c) Remounting a snapshot to a different checkpoint is not allowed. > Remounting a snapshot to an rw-mount is possible only if the > target snapshot equals to the latest checkpoint. That's really rather messy... Let's see if I've got it right: * r/w -> r/w. Allowed. * r/w -> r/o. Allowed. * r/w -> snapshot. Not allowed. * snapshot -> r/w. Allowed if it's the latest one and no r/w is there. * snapshot -> r/o. It remains a snapshot, but says it has succeeded. * snapshot -> snapshot. Only if it's the same. * r/o -> r/w. Allowed [1] * r/o -> r/o. Allowed. * r/o -> snapshot. Allowed only if the snapshot number is the latest. r/w can't coexist with r/o, but can coexist with any snapshots. Can't be remounted to a snapshot directly, but can go through r/w->r/o->latest snapshot in two mount -o remount. "r/o" in the above means "read-only, SNAPSHOT flag not set". What happens if you mount the thing r/w, remount it r/o and then try to mount the latest snapshot? Will that give two superblocks or will it reuse the r/o mount? OTOH, what will happen if you take r/w mount, mount the latest snapshot and then remount the r/w one to r/o? [1] there couldn't have been new r/w mount while r/o one existed, snapshot number couldn't have changed and the only possible transition *into* r/o is from r/w, so another r/w superblock couldn't have survived since before our superblock has become r/o. -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
