partman-efi "Fix detection of BIOS-bootable systems" provides a
significant improvement over previous behaviour. However I have a few
comments.
1a) The patch assumes that a GPT disk may be BIOS-bootable only if it
has a BIOS boot partition. But a GPT disk can be BIOS-bootable even
without a BIOS boot partition:
- GRUB may be installed without a BIOS boot partition if /boot is a
plain partition (using blocklists), even though it is less reliable so a
BIOS boot partition is strongly recommended.
- Other BIOS boot loaders such as syslinux/extlinux do not need or use a
BIOS boot partition.
1b) IIUC the patch fixes #1033913 because the disk selected for
installation has received a new GPT disklabel without a BIOS boot
partition, so further checking is skipped. But IMO the root cause of
#1033913 is that changes are not committed to disk after setting the
'boot' and 'esp' flags to the newly created ESP partition before
stopping parted_server.
This can be seen in /var/log/partman:
/bin/autopartition-lvm
NEW_LABEL sda gpt
NEW_PARTITION 1 sda ext2 538MB (future ESP)
NEW_PARTITION 2 sda ext2 512MB (future /boot)
NEW_PARTITION 3 sda ext3 159GB (future LVM)
SET_FLAGS sda3 lvm
(user prompt to write changes to the disk)
COMMIT sda
...
/lib/partman/update.d/21efi_sync_flag
SET_FLAGS sda1 boot esp
...
/bin/perform_recipe_by_lvm
QUIT <- esp and boot flags have not been committed yet so are lost
...
/lib/partman/init.d/50efi
GET_FLAGS sda1 -> none
2) The patch considers the 'esp' and 'boot' flags to be equal. But this
is true only with GPT. With MSDOS, they have totally different meanings:
- 'esp' means that the partition has the ESP type identifier.
- 'boot' means that the partition has the active/boot indicator set. The
UEFI specification says that this indicator is ignored by EFI boot.
3) The patch considers LVM and RAID partitions not bootable. But both
LVM and RAID superblocks can have a boot loader reserved area. Also,
GRUB may boot them directly without a /boot partition.
4) It appears that partman fails to detect the specially crafted
partition table on the installation media created with a debian image.
Is it intended or fortunately unintentional ? If partman could see the
EFI partition on the installation media, the detection of BIOS-bootable
systems would fail.
