dump/restore

[Karl Lehenbauer]

cpio is supposed to have a salvage mode in Bell Tech Sys V/386 3.1 and
presumably in others.  It would be relatively easy to read the tape
no-rewind-on-close, then after the error, read the tape until you saw
something that looked like a cpio header, then feed the rest back
to cpio.  I started writing something like this, then decided to hack
the PD cpio to do it instead, but then I saw that 3.1 had it anyway,
so I blew it off.  

Note that salvaging cpio archives is a potential avenue for Trojan Horses
as users could put fake tricked-up cpio entries in big files and hope
that they would be seen as valid entries after an error.  Note also that
cpio archives within cpio archives can screw up salvage mode -- it can 
see the embedded files, recover them, then see the trailer record of
the embedded file and exit, blowing off the rest of the archive.



-- 
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