Re: kern/38717: sysinst shouldn't create LFS file systems

[David Holland <dholland-bugs%netbsd.org@localhost>]

On Mon, Jun 02, 2008 at 08:53:10AM +0100, Alan Barrett wrote:
 > > > Twice recently I have noticed files that ended
 > > > up with random binary content (of exactly the same size as the original
 > > > file) after a crash.
 > > 
 > > That's expected behavior in ffs-without-softdep.
 > 
 > Maybe.  I had the impression that, after a crash, files would usually be
 > missing, or moved to lost+found, or still containing old content (or a
 > mixture of old and new content).

Well, what happens is that block pointers get updated synchronously
without the data they point to having been written out; so if you
crash you can get whatever crap was on the disk in that location
previously.

This has just come up on tech-kern, also.

 > >  > ffs with -o async [...]
 > > ... cannot reasonably be expected to work.
 > 
 > If what you mean is "there are known bugs in this area", OK; but if you
 > mean "crashing is not a bug" then I disagree. I expect the file system
 > to be left in a bad state if the machine crashes for some reason (due to
 > hardware failure or a kernel bug), but I do not expect the mere usage
 > of ffs-async to cause the machine to crash.

Crashing is a bug, yes. I read what you wrote as meaning that the fs
corruption after a crash was even worse, though; that is to be
expected. (IME, crashes with ffs -o async are often unrecoverable.)

-- 
David A. Holland
dholland%netbsd.org@localhost