proposal for the backup & uninstall issue

[Yoshinori K. Okuji]

This is a proposal on how backup/uninstall should work.

I have considered the issue for a while. The issue consists of (1)
when a backup should be made, (2) when an uninstall operation should
be done, (3) if these should be automatic, and (4) how these should
work precisely.

Things are complicated, because the user may install GRUB multiple
times, even with different device maps, even into different
drives. You must not forget that the user may replace a drive with
another.

So I think it is the easiest to allow the user to have at most one
backup, and that uninstall and backup operations are done before
install automatically. Here is pseudo code:

        if backup is present
                do uninstall
                remove backup
        end
        
        do backup
        do install

The next question is what are required to ensure the integrity of the
uninstall operation. An original boot sector is essential,
naturally. The device map file used at the installtation time is also
required, because the user may modify the default device map file,
after installing GRUB. The information on the device into which GRUB
was installed is necessary.

I thought those three files were sufficient at first glance, but if
the user replaces the installed drive with another, what happens?
Thus, a check is required to make sure that the boot sector which is
about to be restored really contains the installed image. For example,
comparing the stage1 used at the installation time with the boot
sector.

Also, it is questionable if a backup should be made even for
floppies. I don't think it should, though.

The last question is how uninstall should work. A boot sector consists
of a BPB, code, a partition table and a signature, in brief. What
parts should be restored? I'm not sure. Since GRUB doesn't overwrite a
BPB and a partition table, they may not have to be restored. But GRUB
can modify a partition table, so the user might want to restore a
partition table as well.

In addition, we need to take it into account what should happen when
uninstall is impossible (e.g. when no device map file is found).

Any comments?

Okuji