This is not a bug in GRUB2. In fact it's not really a bug at all, just an un-implemented feature in os-prober.
os-prober has no script to detect BSD filesystems. Even if it did all BSD filesystems are mounted without specifying the ufstype because blkid returns a very unhelpful TYPE parameter. Then either mount chooses the wrong ufstype or it just uses the default of oldufs. In either case the NetBSD partition is unreadable. If the correct ufstype (44bsd) is given to the mount command the partition is readable.
So if it's thought worthwhile I will see if I can come up with a change to 50mounted-tests to do a better job of choosing the correct ufstype for ufs ilesystems, and write a script to output the correct parameters for GRUB2 for these filesystems.
I've been poking about...
This is not a bug in GRUB2. In fact it's not really a bug at all, just an un-implemented feature in os-prober.
os-prober has no script to detect BSD filesystems. Even if it did all BSD filesystems are mounted without specifying the ufstype because blkid returns a very unhelpful TYPE parameter. Then either mount chooses the wrong ufstype or it just uses the default of oldufs. In either case the NetBSD partition is unreadable. If the correct ufstype (44bsd) is given to the mount command the partition is readable.
So if it's thought worthwhile I will see if I can come up with a change to 50mounted-tests to do a better job of choosing the correct ufstype for ufs ilesystems, and write a script to output the correct parameters for GRUB2 for these filesystems.
Pete