install from hard disk and /dev/root does not exist message

[Gianluca Cecchi]

Hello,
Having a laptop without cd and not connected to the internet I'm
testing replacing an existing f16 (no backup needed)

First attempt:
- put vmlinuz and initrd.img from dvd iso into the /boot directory of
f16 installation
- put dvd iso under an usb external disk (/f17 dir in its first
partition, formatted as ext4)
- add section to grub2.cfg with only

insmod ext2
linux /boot/vmlinuz.f17
initrd /boot/initrd.f17

(don't know if I have to put "set root" to anything...)

- reboot and select new entry.

Installer starts but then arrives at dracut debug shell with

 dracut Warning: unable to process initqueue
 dracut Warning: /dev/root does not exist

also tried putting repo in linux line.
Attempt several syntax eg

linux /boot/vmlinuz.f17 repo=hd:sdb1:/f17

linux /boot/vmlinuz.f17 repo=hd:/dev/sdb1:/f17

and with "inst.repo" instead of "repo"

Same result.
I saw these bugs that should be solved now.
https://bugzilla.redhat.com/show_bug.cgi?id=806867
https://bugzilla.redhat.com/show_bug.cgi?id=806966

Is my method supposed to work with f17? Any way/command to give in
dracut debug shell?
Thanks in advance,
Gianluca