Marc MERLIN posted on Sat, 03 May 2014 17:52:57 -0700 as excerpted: > (more questions I'm asking myself while writing my talk slides) > > I know Suse uses btrfs to roll back filesystem changes. > > So I understand how you can take a snapshot before making a change, but > not how you revert to that snapshot without rebooting or using rsync, > > How do you do a pivot-root like mountpoint swap to an older snapshot, > especially if you have filehandles opened on the current snapshot? > > Is that what Suse manages, or are they doing something simpler? While I don't have any OpenSuSE specific knowledge on this, I strongly suspect their solution is more along the select-the-root-snapshot-to-roll- back-to-from-the-initramfs/initrd line. Consider, they do the snapshot, then the upgrade. In-use files won't be entirely removed and the upgrade actually activated for them until a reboot or at least an application restart[1] for all those running apps in ordered to free their in-use files, anyway. At that point, if the user finds something broke, they've just rebooted[1], so rebooting[1] to select the pre-upgrade rootfs snapshot won't be too big a deal, since they've already disrupted the normal high level session and have just attempted a reload in ordered to discover the breakage, in the first place. IOW, for the rootfs and main system, anyway, the rollback technology is a great step up from not having that snapshot to rollback to in the first place, but it's /not/ /magic/; if a rollback is needed, they almost certainly will need to reboot[1] and from there select the rootfs snapshot to rollback to, in ordered to mount it and accomplish that rollback. --- [1] Reboot: Or possibly dipped to single user mode, and/or to the initramfs, which they'd need to reload and switch-root into for the purpose, but systemd is doing just that sort of thing these days in ordered to properly unmount rootfs after upgrades before shutdown as it's a step safer than the old style remount read-only, and implementing a snapshot selector and remount of the rootfs in that initr* instead of dropping all the way to a full reboot is only a small step from there. -- Duncan - List replies preferred. No HTML msgs. "Every nonfree program has a lord, a master -- and if you use the program, he is your master." Richard Stallman -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
