kernel boot failure with ipxe on uefi mode

[aberdine]

Hi, I'm hitting a similar error here, but with CentOS 7 x86_64 under Hyper-V. I get the following:

List of all partitions:
No filesystem could mount root, tried:
Kernel panic - not syncing: VFS: Unable to mount root fs on unknown-block(0,0)
....

My ipxe.cfg is

#!ipxe
dhcp
initrd /initrd.img
kernel vmlinuz inst.repo=http://mirror.bytemark.co.uk/centos/7/os/x86_64/ initrd=initrd.img ro root=/dev/ram0 ip=dhcp
boot

I've extracted the initrd but I'm at a loss to understand what root= should really be. It looks like it's not seeing any disks at all?

From the RHEL 7 docs it says to use (with grub2 efi, shim.efi)

linuxefi uefi/vmlinuz ip=dhcp inst.repo=http://10.32.5.1/mnt/archive/RHEL-7/7.1/Server/x86_64/os/
initrdefi uefi/initrd.img

What am I missing, or where can I continue looking?