Re: Libvolume incorrectly detects FAT32

[Kay Sievers <kay.sievers@vrfy.org>]

On Tue, Mar 07, 2006 at 06:01:17PM +0100, iSteve wrote:
> On Mon, 6 Mar 2006 23:37:20 +0100
> Kay Sievers <kay.sievers@vrfy.org> wrote:
> 
> > On Mon, Mar 06, 2006 at 10:59:31PM +0100, Michael Buesch wrote:
> > > Yes, I fear users of stupid digicams may get hit by this.
> > > The Formating option on cheap digicams may sometimes be buggy implemented.
> > > I think you should instead do a
> > > dd if=/dev/zero of=/dev/partition bsQ2 count=1
> > > and reformat your partition.
> > 
> > Yes, just use a sane formatting program like everything which is
> > libparted based. The usual Linux commandline formatters are horribly
> > broken and I gave up to talk to the ignorant maintainers. Just zero-out
> > the device at the beginning _and_ the end of the device if you reformat it
> > with a new filesystem type. Or use a libparted or similar based program.
> > 
> > Thanks,
> > Kay
> 
> I would have another suggestion then; how about a scoring system?
> 
> Probes would be given OPTIONAL scoring system, let's say in percents, eg. in
> case of fat, lack of magic would make it lose 20%; some other filesystem would
> return just 0 or 100% hit (ie. just like it is now). Then the probe with
> greatest score wins.
> 
> I understand this design is for working with semibroken partitions, and I fear
> it won't be welcome warmly; but I still got to propose it:)
> 
> I am willing to code it, I've written about ten probes for my own detection
> system until I noticed libvolumeid, but I want approval of design first.

I'm all for fixing the stupid formatters. Seems the problems are really
rare these days anyway, with Windows doing it right now and almost all
distros use HAL today which has the same code and we don't get a lot of
error reports anymore.

The right way I think, is to add more checks to the probing code, if the
filesytem that is recognized is actually "valid". But that is impossible
for some situations like mkswap (which is the silliest formatting tool on
earth that I've ever seen) on top of fat. You can even mount the
corrupted fat volume with the kernel and write to it.

So, I'm not sure if a score will give us something valuable. You basically
push the problem to the user of the lib, which is a slippery road. But if
we detect that we can't be sure what kind of filesystem we detect, we
could throw an error and don't return any type, that would be at least a
safe way to handle that and would fix the real problem, which are in
almost all cases the too simple and broken Linux command line tools.

Thanks,
Kay


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