HEADS UP: Imported Xen 4.7: no blkback

Roger Pau Monné royger at FreeBSD.org
Thu Jun 9 08:03:50 UTC 2016

On Thu, Jun 09, 2016 at 12:16:59AM +0000, Marcin Cieslak wrote:
> On Fri, 3 Jun 2016, Roger Pau Monné wrote:
> > One of the more relevant changes in 4.7 regarding FreeBSD is the support for 
> > block hotplug scripts. This means that we now have the option to use 
> > backends different than simple block or regular files, provided that someone 
> > writes the proper hotplug scripts to attach them (I've heard there are some 
> > iSCSI hotplug scripts around). This however requires changes in blkback, so 
> > if you plan to use the Xen 4.7 port, please make sure that you are running a 
> > kernel that contains revision r301269 (or any later version). The same also 
> I am running it with r301685 and the HVM guests have some trouble with
> block devices.
> SeaBIOS does not find /dev/zvol/zroot/freebsd1,raw,xvda,w to boot FreeBSD
> from, after chaging to "hda" I get up to the kernel mountroot prompt
> (Xen block devices seem to be detected in dmesg).

Yes, this is intentional, see:


Have you checked if you need to change your /etc/fstab to correctly point 
to the new device? Does FreeBSD correctly list the disk(s) at the mountroot 
prompt when issuing a "?" command?

Also, can you paste the output of `xenstore-ls -fp` from Dom0 when this 
> What used to be Windows 2016 domU with /dev/zvol/zroot/windows0,raw,hda,w
> ends up in the Tianocore UEFI shell. Block devices seem to be available,
> I can even list the fs0: partition, but no booting further possible.

Hm, I've never used Tianocore myself, so I'm not sure what the issue could 
be here. Again, can you post the output of `xenstore-ls -fp` from Dom0 when 
this happens? At least this will show if the PV block device has been 
correctly attached.


More information about the freebsd-virtualization mailing list