Re: Important note for HVM guests backed with LVM

[Manuel Bouyer <bouyer%antioche.eu.org@localhost>]

On Fri, Jan 13, 2017 at 05:09:31PM +0000, Roy Marples wrote:
> Hi List!
> 
> My XEN NetBSD DomU has been chugging along really well and I'm very pleased
> with it so far.
> 
> So I tried to get FreeBSD and OpenBSD HVM guests running (as they don't have
> PV support like we do).
> However, all XEN documentation (theirs, ours) is utterly useless for trying
> to get this to work with LVM backing.
> Errors are FreeBSD installing fine, but is then presented with an unbootable
> disk.
> OpenBSD just reports errors talking to wd0 and refuses to install.
> If you're quick enough to attach a VNC console to the guest you can see QEMU
> reporting a disk size of 0.
> 
> Looking at the qemu log in the Dom0, I see this:
> Using file /dev/vg0/freebsd in read-write mode
> qemu: could not open vbd '/local/domain/0/backend/vbd/15/768/mode' or hard
> disk image '/dev/vg0/freebsd' (drv 'phy' format 'raw')
> 
> And here's my config:
> disk = [
>         'phy:/dev/vg0/freebsd,xvda,w',
> 'file:/home/roy/FreeBSD-11.0-RELEASE-amd64-disc1.iso,xvdc:cdrom,r'
> ]
> 
> That matches every piece of documentation I could find.
> THIS IS WRONG!!!!
> 
> Then, by a sheer fluke I found this thread:
> http://port-xen.netbsd.narkive.com/MF6vPA3P/xen-and-lvm-backed-domu-s
> https://mail-index.netbsd.org/port-xen/2010/03/12/msg005804.html
> 
> I said it worked fine, but note the slight difference in stating the device.
> So I changed my config to this:
> 
> disk = [
>         'phy:/dev/mapper/vg0-freebsd,xvda,w',
> 'file:/home/roy/FreeBSD-11.0-RELEASE-amd64-disc1.iso,xvdc:cdrom,r'
> ]
> 
> And OMG it works fine!
> So can someone please add this to our howto? I think it's quite important.
> 
> BTW, does anyone know what the difference is between xvda and ioemu:hda is?

With xvd you're using the PV backend, not the qemu-emulated one.

So if this works I guess freebsd has PV driver for devices at last :)

-- 
Manuel Bouyer <bouyer%antioche.eu.org@localhost>
     NetBSD: 26 ans d'experience feront toujours la difference
--