Re: [PATCH] Backup old boot sectors before installation

[Zhu Yi]

On Fri, 2009-12-25 at 05:21 +0800, Robert Millan wrote:
> I think making a backup is a fine idea, but I'd rather avoid the "option
> creep".  It doesn't hurt to simply dump the files in /boot/grub/.  If user
> later discovers that valuable data was overwritten, she can figure out
> how to call dd just as she can figure out the right parameters for
> grub-install.

OK. My only concern is the start position of grub core.img (as in disk
sectors) is a variable (see find_usable_region_xxx). This ends up the
backup file is not a simple dump. I used below format in my patch.

<512 bytes MBR> + <U64 start position> + <sizeof(core.img) old sectors>

Option 2 is to put the start position in a separated file.

Option 3 is to use the information in boot.img (as I used in my patch as
a verification method) to get the start position, i.e. `od -j92 -N8 -An
-td8 $grubdir/boot.img`.

Option 4 is to backup everything from MBR to the end of core.img
(including the holes in the middle). This ends up with a bigger image.

Option 1~3 requires the recover has the knowledge of the backup file
format somehow, but a simple dd is enough for option 4. What do you
think?

Thanks,
-yi