Colin Watson writes:
On Xen (I'm told), it's possible to assign disk images in the host to
things that are named rather like partitions in the guest (e.g.
/dev/sda1), but that don't have an associated disk (e.g. /dev/sda);
indeed, the latter device is nonexistent. This confuses
grub_util_biosdisk_get_grub_dev.
There's really no other situation in which I think it's terribly
plausible that you might have /dev/sda1 but not /dev/sda, so it seems to
me that in this case we can reasonably treat the apparent "partition" as
a disk in its own right.
Can we make some of these 'decisions' switchable on the command line?
I perform a lot of block device redirections (Xen, iSCSI, nbd, etc) or
work from live cd's (where / is merely rootfs+unionfs with no disk,
but /boot is a mounted disk), and grub-setup raises fatal objections
that I would like to override when _I_ know what devnodes the
bootblocks and the filesystems belong on.