Re: Flavours of deceased bovine

From: Malcolm Beattie (mbeattie@sable.ox.ac.uk)
Date: Fri Sep 08 2000 - 04:33:52 EST


Keith Owens writes:
> Just had an ext2 filesystem on SCSI that was corrupt. The first two
> words of the group descriptor had been overwritten with 0xdeadbeef,
> 0x00000000. The filesystem is fixed now but trying to track down the
> problem is difficult, there are 50+ places in the kernel that use
> 0xdeadbeef.
>
> I strongly suggest that people use different variants of dead beef to
> make it easier to work out where any corruption is coming from.
> Perhaps change the last 2-3 digits so magic values would be 0xdeadb000
> to 0xdeadbfff, assuming it does not affect any other code.

Nah, choose new words which stand out. There are plenty of them and
it avoids the problem of a 0xdeadb001 being decremented before being
noticed and thus confused with a 0xdeadb000. Be inventive:
    egrep -x '[abcdefilos]{3,8}' /usr/dict/words
and make one up whenever needed. For example,
    0baff1ed
    acce55ed
    decea5ed
    d15ab1ed
    d15ea5ed
along with multiword ones like
    fee1dead
    dead1055
    badca5e5

--Malcolm

-- 
Malcolm Beattie <mbeattie@sable.ox.ac.uk>
Unix Systems Programmer
Oxford University Computing Services
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