Re: grub-probe detects ext4 wronly as ext2

[Robert Millan]

On Wed, Jul 02, 2008 at 01:28:47AM +0200, Javier Martín wrote:
> > A --ignore-incompatible flag doesn't sound like a nice thing to do;  it 
> > means
> > we're passing our own problem to the user instead of solving it.
> We don't have any "problem" to pass to users: ext4 is not supported

We don't have an urge to support ext4, but that doesn't mean we shouldn't
consider it a problem.

I think adding an interface for the user to choose in which way to deal with
our limitations is a nasty thing.  I strongly object to that.

> and
> thus we do the Right Thing (tm) in patching our ext2 driver so that it
> won't try to read a filesystem it cannot.

That makes sense, with some caveats (see below).

> However, given Pavel's and
> others' objections, I suggested the addition of an user override to it.
> Thus, the user will have to knowingly force the system to interpret the
> filesystem with its current code, and accept any failures he might get,
> instead of the current behaviour of having the FS mounted automatically
> without checking incompatibilities (and then getting the errors anyway).

I don't think this is necessary.  First, let's take for granted that our code
is in every situation smart enough not to crash when a filesystem isn't
readable (this should always be the case, since we might occasionaly be asked
to read corrupt filesystems).  Then, what do flags mean?

If a flag means "GRUB won't be able to access this filesystem at all", we could
explicitly refuse to probe it, but then again our code must be graceful enough
to cope with it without crashing anyway (see above), so maybe it's not worth to
(depends on the time/size trade-off).

If a flag means "access to the filesystem isn't deterministic, and grub-probe
might be able to do things that real GRUB won't", then we're in a situation in
which we'd like grub-probe to be conservative _but_ real GRUB to be
best-effort.  I think this means an internal switch to tell fs probes whether
to be conservative or not.  We could even use #ifdef GRUB_UTIL so the flag
checking stuff doesn't make real GRUB fatter.

-- 
Robert Millan

<GPLv2> I know my rights; I want my phone call!
<DRM> What good is a phone call… if you are unable to speak?
(as seen on /.)