Re: [PATCH] Refuse to install on XFS destroying its superblock

[Robert Millan]

On Fri, Oct 16, 2009 at 10:09:41PM +0200, Vladimir 'phcoder' Serbinenko wrote:
> Robert Millan wrote:
> > On Fri, Oct 16, 2009 at 06:01:56PM +0200, Jordi Mallach wrote:
> >   
> >> On Fri, Oct 16, 2009 at 04:03:01PM +0200, Vladimir 'phcoder' Serbinenko 
> >> wrote:
> >>     
> >>> +  if (memcmp (tmp_img, "XFSB", 4) == 0)
> >>> +    grub_util_error ("Can't install on XFS.");
> >>>       
> >> Can this error message give some more detail on what the problem is?
> >>     
> >
> > I suggest something like:
> >
> >   grub_util_warn ("Refusing to overwrite XFS meta-data.");
> >
> > This is more informative, and with grub_util_warn() user has an opportunity 
> > to
> > override it if she knows what she's doing.
> >
> >   
> Installing with blocklists/to partition is considered
> backward-compatibility feature. We never supported a config with XFS why
> we would want bw-compat for it?

Because we can't reliably tell if it's a config with XFS, only the user can.
This is an issue for both MBR or PBR installs.

Maybe "XFSB" is only a remnant from one of this disk / partition former
lifes.  Maybe it's a valid XFS but user no longer cares about it.  Or
maybe a DOS-style label was created on top of it, without overwriting the first
440 bytes.  Or maybe another filesystem had overwritten most XFS metadata
but preserved the first block (this is conceivable since other filesystems
tend to avoid using the first block).

If user has to workaround GRUB heuristics by dd'ing zeros into a partition
before running grub-install, this is a sign GRUB isn't doing the right thing.

-- 
Robert Millan

  The DRM opt-in fallacy: "Your data belongs to us. We will decide when (and
  how) you may access your data; but nobody's threatening your freedom: we
  still allow you to remove your data and not access it at all."