Re: newfs and mount vs. half-baked disks
From: Peter Jeremy (PeterJeremy_at_optushome.com.au)
Date: 11/05/03
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Date: Wed, 5 Nov 2003 19:15:16 +1100 To: Wes Peters <wes@softweyr.com>
On Tue, Nov 04, 2003 at 07:57:10PM -0600, Dan Nelson wrote:
>In the last episode (Nov 04), Wes Peters said:
>> I emailed Kirk about this state of affairs and he confirmed that
>> newfs was developed with operator intervention in mind. He suggested
>> employing one of the unused flags in the filesystem header as a
>> 'consistent' flag, setting it to 'not consistent' at the beginning of
>> newfs, and then updating to 'is consistent' at the end. The
>> performance hit in updating all superblock copies at the end is small
>> but noticable (< 1s on a rather slow 6GB filesystem).
>
>Would writing a block of zeros to the first (or first n) superblock,
>newfs'ing, then rewriting the correct data do the same thing without
>affecting the filesystem itself? I'm thinking about 4.x and cross-OS
>portability here.
My suggestion would be to write a non-standard magic number to
fs_magic in the primary and first backup superblock (block 32) - I
believe these are the only ones fsck will automatically search. The
"invalid" magic number means that neither mount nor fsck will
recognize the partition. Those two blocks can be re-written at the
end - the additional time should be unnoticable. The remaining
superblocks would appear valid but if someone is silly enough to
manually specify a alternate superblock in an incompletely newfs'd
filesystem, they get a neat hole in their foot. (A known non-standard
magic number would also allow fsck to warn that the filesystem was
incompletely newfs'd).
I'm surprised that this bug hasn't been noticed previously.
Peter
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- Previous message: Garance A Drosihn: "Re: newfs and mount vs. half-baked disks"
- In reply to: Dan Nelson: "Re: newfs and mount vs. half-baked disks"
- Next in thread: Wes Peters: "Re: newfs and mount vs. half-baked disks"
- Reply: Wes Peters: "Re: newfs and mount vs. half-baked disks"
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