Bug#1017750: multiboot friendly /boot/efi/EFI/debian/grub.cfg update

[Osamu Aoki]

Package: grub-efi-amd64
Version: 2.06-3
Severity: wishlist

Currently, if you have dual boot of 2 Debian system installations, every
time grub2 of one system runs postinst, it overwrites
/boot/efi/EFI/debian/grub.cfg file in ESP pointing search.fs_uuid
pointing to lead to /boot/grub/* by UUID.

It doesn't backup existing /boot/efi/EFI/debian/grub.cfg.

If you consider this to be the result of upstream feature of update-grub
then it will be tough to be fixed.

But can you think of updating Debian postinst script to check the
existence of the /boot/efi/EFI/debian/grub.cfg file first and back it
up?  This helps recovery of system and trivial to be implemented.

I prefer time-stamped string as suffix for the backup file but this can
be anything maintainer likes.

This way, we can easily select /boot/grub/* after crash without manually
typing UUID.  Having at least 2 or 3 stage backups is more friendly.


-- Package-specific info:

*********************** BEGIN /proc/mounts
/dev/nvme0n1p5 / btrfs rw,relatime,ssd,space_cache,subvolid=22924,subvol=/@rootfs 0 0   <--- This is my main @rootfs
/dev/nvme0n1p5 /btrfs/main btrfs rw,relatime,ssd,space_cache,subvolid=5,subvol=/ 0 0
/dev/nvme0n1p5 /home/osamu btrfs rw,relatime,ssd,space_cache,subvolid=596,subvol=/@osamu 0 0
/dev/nvme1n1p1 /btrfs/sub btrfs rw,relatime,ssd,space_cache,subvolid=5,subvol=/ 0 0     <--- This partition holds 2nd @rootfs
/dev/nvme0n1p1 /boot/efi vfat rw,relatime,fmask=0077,dmask=0077,codepage=437,iocharset=ascii,shortname=mixed,utf8,errors=remount-ro 0 0 <--- ESP
*********************** END /proc/mounts

*********************** BEGIN /boot/grub/grub.cfg
#
# DO NOT EDIT THIS FILE
#
# It is automatically generated by grub-mkconfig using templates

.... (snip uninteresting part)
.... Followings are my custom dual boot configuration 

### BEGIN /etc/grub.d/40_fixed_linux ###
# This file provides an easy way to add custom menu entries.  Simply type the
# menu entries you want to add after this comment.  Be careful not to change
# the 'exec tail' line above.
menuentry 'Debian GNU/Linux --- main SSD' --class debian --class gnu-linux --class gnu --class os $menuentry_id_option 'gnulinux-fixed-fe3e1db5-6454-46d6-a14c-071208ebe4b1' {
	load_video
	insmod gzio
	if [ x$grub_platform = xxen ]; then insmod xzio; insmod lzopio; fi
	insmod part_gpt
	insmod btrfs
	search --no-floppy --fs-uuid --set=root fe3e1db5-6454-46d6-a14c-071208ebe4b1
	echo	'Loading Linux from /dev/nvme0n1p5 ...'
	linux	/@rootfs/vmlinuz root=UUID=fe3e1db5-6454-46d6-a14c-071208ebe4b1 ro rootflags=subvol=@rootfs  quiet
	echo	'Loading initial ramdisk from /dev/nvme0n1p5 ...'
	initrd	/@rootfs/initrd.img
}
menuentry 'Debian GNU/Linux --- sub SSD' --class debian --class gnu-linux --class gnu --class os $menuentry_id_option 'gnulinux-fixed-51f9cd11-30b3-4d99-b2ed-fe411fa22ee6' {
	load_video
	insmod gzio
	if [ x$grub_platform = xxen ]; then insmod xzio; insmod lzopio; fi
	insmod part_gpt
	insmod btrfs
	search --no-floppy --fs-uuid --set=root 51f9cd11-30b3-4d99-b2ed-fe411fa22ee6
	echo	'Loading Linux from /dev/nvme1n1p1 ...'
	linux	/@rootfs/vmlinuz root=UUID=51f9cd11-30b3-4d99-b2ed-fe411fa22ee6 ro rootflags=subvol=@rootfs  quiet
	echo	'Loading initial ramdisk from /dev/nvme1n1p1 ...'
	initrd	/@rootfs/initrd.img
}
### END /etc/grub.d/40_fixed_linux ###

### BEGIN /etc/grub.d/41_custom ###
if [ -f  ${config_directory}/custom.cfg ]; then
  source ${config_directory}/custom.cfg
elif [ -z "${config_directory}" -a -f  $prefix/custom.cfg ]; then
  source $prefix/custom.cfg
fi
### END /etc/grub.d/41_custom ###
*********************** END /boot/grub/grub.cfg


-- System Information:
Debian Release: bookworm/sid
  APT prefers testing
  APT policy: (500, 'testing')
Architecture: amd64 (x86_64)

Kernel: Linux 5.18.0-4-amd64 (SMP w/12 CPU threads; PREEMPT)
Locale: LANG=en_US.UTF-8, LC_CTYPE=en_US.UTF-8 (charmap=UTF-8), LANGUAGE=en_US:en
Shell: /bin/sh linked to /usr/bin/dash
Init: systemd (via /run/systemd/system)
LSM: AppArmor: enabled

Versions of packages grub-efi-amd64 depends on:
ii  debconf [debconf-2.0]  1.5.79
ii  grub-common            2.06-3
ii  grub-efi-amd64-bin     2.06-3
ii  grub2-common           2.06-3
ii  ucf                    3.0043

grub-efi-amd64 recommends no packages.

grub-efi-amd64 suggests no packages.

-- debconf information:
  grub2/kfreebsd_cmdline:
* grub2/linux_cmdline:
* grub2/force_efi_extra_removable: false
* grub2/update_nvram: true
* grub2/linux_cmdline_default: quiet
  grub2/kfreebsd_cmdline_default: quiet