On Mon, Aug 11, 2014 at 09:46:57PM +0400, Matwey V. Kornilov wrote:
2014-08-11 21:32 GMT+04:00 Matthias G. Eckermann <mge@suse.com>:
For "full system rollback" (or at least "close to full system rollback") you need initrd and kernel/vmlinuz to be _inside_ the snapshot.
In other words: once you are in the initrd, it's too late already.
Does that explain (a bit)?
Wait... I see that the grub2 snapshot entries looks for vmlinuz and initrd into /.snapshots/*. So, I think we really take the kernel and initrd from the snapshot. Until initrd mounts / we don't perform disc access, so here we can decide whether we need rw-clone the snapshot before the mounting.
Booting to btrfs snapshot is target to fulfill full system rollback requirement, you can consider it's implementation a necessary piece in full system rollback's bootloader integration. While booting to an arbitary ro snasphot as rw is possible, it's not implemented in initird and no effort was spent on it because that's currently not the goal of snapshoting booting. That's my understanding to this topic and hope it helpful. Thanks, Michael
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