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Re: Migrating to GRUB 2 in Debian (Re: Interesting GSoC project ideas fo

From: phcoder
Subject: Re: Migrating to GRUB 2 in Debian (Re: Interesting GSoC project ideas for 09)
Date: Sun, 22 Mar 2009 14:23:53 +0100
User-agent: Thunderbird (X11/20090318)

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?


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