Re: rootfs snapshots and rollback (i.e. testing updates)

[Chris Ball <cjb@laptop.org>]

Hi,

   > Is it possible, with current btrfs:

Yes, I think so.

   > - to take a rootfs snapshot (i.e. prior to a major update),

btrfsctl -s newsnap /

   > - do changes in the root filesystem (i.e. install major update),
   > 
   > - if we don't like what the major update did to the system
   > (rootfs), "rollback" the snapshot and make it the "original"
   > rootfs again (perhaps, with a reboot in between).

Before rebooting, edit whatever mounts your root partition (initrd,
fstab, kernel argument) to add a "subvol=newsnap" mount argument.

An obvious way to make this nicer would be to:
   * have the package manager create the snapshot before modifying the
     system, with a timestamp.
   * modify the bootloader to give a choice of snapshots at boot-time.

Note that you're rolling back *all* rootfs changes, not merely the
changes that the package manager made, so it wouldn't be correct to
think of this as a way to only rollback package manager transactions.

- Chris.
-- 
Chris Ball   <cjb@laptop.org>
One Laptop Per Child