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Re: Some ideas about new features of grub

From: Vladimir 'phcoder' Serbinenko
Subject: Re: Some ideas about new features of grub
Date: Sun, 23 Aug 2009 18:58:43 +0200

>> But I know both Marco and Pavel feel strongly about this.  Please can you
>> comment?
> I am against a configure flag (if configure is the one from configure, make,
> make install) but a configure flag (as something specified in grub.cfg) is
> ok.

Writing to filesystems is dangerous. Currently only grub-setup and
save_env can potentially destroy data or metadata and this risk is
minimised by just overwriting relevant sectors. Would you trust with
your data to a write driver which hasn't been thoroughfully tested? I
wouldn't. In current ro drivers we regularly find mistakes. Writing
support makes driver more complex and so failure is more likely. Even
a slightest mistake like putting entry in a wrong place in btree can
have devastating effects (like OS not seeing half of the files).
Writing files is only marginally needed for non-essential features
which reduces the benefits and even decreases the chances of drivers
to be tested enough. Currently grub2 does well what's supposed to do -
boot OS. Making it write to FS makes it less reliable and worse at
what its primary goal.
How long is rw driver marked experimental in kernel? A year perhaps
and it's more likely to be good tested because it 5 minutes of its use
for root fs you do a lot of transactions. But grub, will you save
grub.cfg 100 times at row?
What are benefits?
Saving environement? It's done with save_env. Only problem are
checksumming FSes but 2 I'm aware about ZFS and btrfs reserve space
for booter so we can embed config. Or just ask to disable checksumming
on grubenv. THis can be done as a part of grubenv creation on such
Recovering OS? You should use recovery OS. You can put a kernel and
initrd together with your grub for emergency cases. If grub survives
disaster recovery kernel is likely to survive it too.
Installing OS? You really need an installer
Saving modifications done to configuration? It can be useful but it's
done rarely enough to repeat it from OS if needed. Especially that
grub would have trouble to modify config if script that generated is a
bit more difficult than just array of menuentries
I really don't want hundreds of reports "I wanted to save modified
entry but grub destroyed my FS".
Vladimir 'phcoder' Serbinenko

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