Xen 4.5 to 4.8 upgrade

[Dima Veselov <kab00m%lich.phys.spbu.ru@localhost>]

Greetings,

I have an issue updating Xen 4.5 to 4.8 about using 
block devices in virtual machines.

From the beginning I was using phy:/<block>,xvda,w notation,
which is now deprecated. It still works on Xen 4.5 on NetBSD 
7-STABLE with LVM on top. Also, I notice that VM start is 
fast, without any delay.

After upgrading to Xen 4.8 built from pkgsrc (1, Dec, 2017) this
do not work anymore, complaining:

[root@midgard ~]$ xl create -c /etc/xen/rpd 
Parsing config from /etc/xen/rpd
xenstore-read: not found
libxl: error: libxl_exec.c:118:libxl_report_child_exitstatus: /usr/pkg/etc/xen/scripts/block /local/domain/0/backend/vbd/1/51712 [733] exited with error status 127
libxl: error: libxl_create.c:1255:domcreate_launch_dm: unable to add disk devices

Experiments says that I may not use block devices anymore.
What I tried:
disk = [ 'phy:/dev/mapper/midgard-rpd,xvda,w' ]
disk = [ 'phy:/dev/midgard/rpd,xvda,w' ]
disk = [ '/dev/mapper/midgard-rpd,,xvda,rw' ] 
disk = [ '/dev/mapper/midgard-rpd,raw,xvda,rw' ]

I can use raw devices in any notation, but there is a delay on VM start,
and after start they stuck on XENBUS: Waiting for devices to initialise:
phase.

What is wrong in Xen 4.8 on NetBSD-7-STABLE (possibly with LVM).

Not tested on HVM VMs, only on PV.

Thanks in advance.

-- 
Sincerely yours