Re: WAPBL and backwards compatibility

[Joerg Sonnenberger <joerg%britannica.bec.de@localhost>]

On Fri, Aug 01, 2008 at 05:22:09PM +1000, Simon Burge wrote:
>  - Currently an old fsck will not know of the existance of the journal.
>    If it sees a filesystem that wasn't unmounted cleanly with WAPBL
>    active it will just think it was a "normal" crash and repair it as it
>    normally would.  The problem is that next time you use a WAPBL-aware
>    kernel or fsck_ffs will see the untouched dirty journal and replay
>    it, possibly (probably?) causing damage.

I want to have another flag in the superblock that is a kind of
generation ID. Consider suspend-to-RAM or even suspend-to-disk.
You want to make sure that all currently active filesystems are
as clean as possible. Ideally, a reboot when crashing in resume won't
have to run fsck at all. Additionally you want to be able to detect if
something else has mounted the filesystem in between.

One easy approach is to write a random 64bit value in the superblock on
write mount and compare if it is same. It would need some support in
fsck, I guess.

Joerg