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

[John Dong <jdong@ubuntu.com>]

On Nov 10, 2009, at 4:53 AM, Tomasz Chmielewski wrote:

> Chris Ball wrote:
>> 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.
> 
> So, if I understand it correctly, it's not really "rolling back".
> 
> Rather, with a "failed upgrade", we would mount a "newsnap" snapshot to use the old rootfs again.
> 
> 
> What's still left here would be:
> 
> - remove the "failed upgrade" "(sub)volume" (which is "/" now?)
> 
> - turn everything to such a state, so that you can mount the old/original rootfs without adding any "subvol=newsnap" mount arguments
> 
> 
> Correct me if I'm wrong.

You're right. What's needed is a way to set the new default subvol