how to specify "disk=[....]" setting in "xl create" config?

[Yang <teddyyyy123@xxxxxxxxx>]

I'm following the wiki https://help.ubuntu.com/community/Xen#Manually_Create_a_PV_Guest_VM 

(section "

Set Up Initial Guest Configuration

")

I downloaded the netboot initrd.gz from https://mirror.arizona.edu/ubuntu//ubuntu/dists/bionic/main/installer-amd64/current/images/netboot/xen/

but in the .cfg , what should I specify for the "disk = " line? ---- my host box is not using LVM, so I'll have to use "file-backed storage" for PV disk image. (https://wiki.xenproject.org/wiki/Storage_options  , indeed this worked when I gave --dir= instead of --lvm= when running the xml-create command in https://wiki.xenproject.org/wiki/Xen_Project_Beginners_Guide )

here is my current config:

yy@yy-70A4000HUX:~/ub_xen$ cat ub_xen.cfg

name = "ubud1"

kernel = "/home/yy/ub_xen/vmlinuz"

ramdisk = "/home/yy/ub_xen/initrd.gz"

#bootloader = "/usr/lib/xen-4.4/bin/pygrub"

memory = 1024

vcpus = 1

# Custom option for Open vSwitch

vif = [ 'bridge=xenbr0' ]

disk = [ 'vdev=hda,target=/home/yy/ub_xen/images' ]

# You may also consider some other options

# [[http://xenbits.xen.org/docs/4.4-testing/man/xl.cfg.5.html]]

yy@yy-70A4000HUX:~/ub_xen$ 

I ran the command with sudo xl create -c ub_xen.cfg

this worked fine first, giving me the regular install process on console, pulling install files from remote archive, but when it comes to the step of disk paritioning, it's showing me a "SCSI" partitioning choice, with no volumes / partitions/disks to be chosen.

I guess this is because I'm not setting the right value for "disk = [ ]" option. what should I use here if I use file-backed storage for PV (just like VMware does)?

thanks a lot

Yang