boot device detection on cdboot

[Izumi Tsutsui <tsutsui%ceres.dti.ne.jp@localhost>]

Is there any good way to detect boot device on cdboot?

It will be useful on one CD system with cd9660 root file system
and working dirs on tmpfs/mfs, like restorecd for cobalt.
(recompiling a whole kernel only for "root on cd0a" is a bit pain)

Current arch/x86/x86/x86_autoconf.c:findroot() doesn't
check cd(4) for the booted device.

On the other hand, arch/i386/stand/lib/biosdisk_ll.c:set_geometry()
checks a number of BIOS disks via get_harddrives() and sets
BIOSDISK_TYPE_CD in struct biosdisk_extinfo.

Current struct btinfo_bootdisk in <x86/bootinfo.h> doesn't have
appropriate members to check the above BIOSDISK_TYPE_CD.

Is there any reasonable idea how to pass the info about cdboot
via bootinfo?
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Izumi Tsutsui