Re: Migrating to GRUB 2 in Debian (Re: Interesting GSoC project ideas for 09)

[Yoshinori K. Okuji]

On Sunday 22 March 2009 22:23:53 phcoder wrote:
> Yoshinori K. Okuji wrote:
> > On Sunday 22 March 2009 19:48:36 phcoder wrote:
> >> Hello, I agree that non-sector aligned writes should be handled
> >> correctly. However I disagree with removing of the magic number. I
> >> personally would prefer if this file would have magic number and
> >> checksum. AFAIK currently grub2 doesn't write to FS except in
> >> load_env/save_env so a bug in code calling the hook could easily be
> >> present. And I don't want grub2 to corrupt the filesystem because of any
> >> such mistakes
> >
> > For magic, alright. But I am not certain about the necessity of checksum.
> >
> > Bean's code re-reads blocks so as to ensure that blocklists are identical
> > to what a given filesystem driver reads. So the probability of accidental
> > writes has been reduced very much already. It is hard for me to imagine
> > the benefit of adding more overhead. With this condition, if a checksum
> > is invalid, the cause must be either of these:
> >
> > - that GRUB has a bug in a filesystem driver, so this has read wrong
> > sectors - that the content of grubenv has already been corrupted (e.g.
> > because the user modified it mistakenly)
> >
> > In the latter case, there is no problem in GRUB overwriting the data, so
> > we don't have to care. In the former, this means that GRUB cannot read
> > the filesystem correctly anyway, so the user cannot boot any OS reliably.
> > It is rather surprising that the user has successfully installed GRUB.
>
> This assumption doesn't hold true if developping new FS using grub-emu.
> Perhaps a configure parameter to disable all writes would be a good idea?

I think you can just avoid invoking save_env.

Regards,
Okuji