Xen block device

While reading "The Book of Xen", I ran into a snag with attaching a block device in dom0

# xm block-attach 0 duncan. img /dev/xvda1 w 0

I am expecting /dev/xvda1 to show up now, but it doesn't. As suggested in the book, I try

# /mknod /dev/xvda b 220 0

Doesn't work (btw, the book has a typo, it should be 202 not 220)

Turns out, the xenblk kernel module was not loaded. Do this
# modprobe xenblk
# lsmod | grep xenblk

Now xm block-attach works like a charm