grub-ieee1275 installs to an arbitrary PReP partition when more than one is available

[Paride Legovini]

When the grub-ieee1275 package is installed or upgraded the grub-ieee1275.postinst script uses the prep-bootdev helper to find a PReP partition to install grub to via grub-install. When there is a single PReP partition on the system this is fine, however when more than one is present it's difficult to tell which one prep-bootdev will pick, and if it will always pick the same one.

We hit this on a test system where the partition layout is the one in the attached file. As you can see there are two PReP partitions:

Device Start End Sectors Size Type
/dev/vda4 10487808 10504191 16384 8M PowerPC PReP boot

Device Start End Sectors Size Type
/dev/vde2 2099200 2115583 16384 8M PowerPC PReP boot

In this case prep-bootdev chose /dev/vde2 to install grub to. This was unexpected.

I don't have a sensible alternative to propose here, as we want to keep grub guessing what is reasonable to guess and we don't want to break existing systems or workflows. Still the current behavior is less than ideal.

[Paride Legovini (paride)]

Partition layout with two PReP partitions.