[PATCH FOR REVIEW] fsck_ffs: Recover from catastrophic damage

[Kostik Belousov]

On Wed, Feb 20, 2008 at 01:58:36AM -0800, Xin LI wrote:
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> Alexander Leidinger wrote:
> > Quoting Xin LI <delphij at delphij.net> (from Tue, 19 Feb 2008 23:36:04
> > -0800):
> > 
> >> Change summary:
> >>
> >> fsutil.c:
> >>  - Really update standard superblock.  fsck_ffs -b used to update the
> >> backup superblock which does not recover file systems which have bad
> >> master superblocks.
> >>  - Instead of coredump, zero out whole cg if its signature is bad.
> >>
> >> inode.c:
> >>  - Instead of coredump, zero out whole cg if its signature is bad.
> > 
> > Does this modify (zero out) on-disk blocks? If yes, shouldn't this ask
> > for confirmation?
> 
> My assumption is that if a cylinder group's magic number is damaged,
> then the whole stuff can not be trusted at all, but yes, I think this
> should come with a prompt, will add tomorrow.

I have some uneasy feeling about automatically zeroing a cg.
I think it would be safer to show the message there, and add the same
functionality to fsdb, something like clrcg command, analogous to clri.
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