On Mon, Oct 10, 2011 at 09:09:37AM -0400, Theodore Tso wrote: > > On Oct 10, 2011, at 7:18 AM, David Sterba wrote: > > > "Resetting the UUID on btrfs isn't a quick-and-easy thing - you > > have to walk the entire tree and change every object. We've got > > a bad-hack in meego that uses btrfs-debug-tree and changes the > > UUID while it runs the entire tree, but it's ugly as hell." > > Changing the UUID is going to be harder for ext4 as well, once we > integrate metadata checksums.
And for XFS, we're modifying the on-disk format to encode the UUID into every single piece of metadata in the filesystem. Hence changing it entails a similar problem to btrfs - an entire filesystem metadata RMW cycle. > So while it makes sense to have > on-line ways of updating labels for mounted file systems it > probably makes muchness sense to support it for UUIDs. ^^^^ less Agreed. > I suspect what it means in practice is that it will be useful for > file systems to provide fs image copying tools that also generate > a new UUID while you're at it, for use by IT administrators and > embedded systems manufacturers. Yup. xfs_admin already provides an interface for offline modification of the UUID for XFS filesytems. I.e. clone the filesytem using xfs_copy, then run xfs_admin -U generate <clone> to generate a new uuid in the cloned copy before you mount the clone.... Cheers, Dave. -- Dave Chinner da...@fromorbit.com -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html