[CentOS-virt] CentOS 6 Xen 4.4.1 packages available on virt6-testing / libvirt blktap2 problems

Mon Jan 5 22:15:25 UTC 2015
Pasi Kärkkäinen <pasik at iki.fi>

On Tue, Dec 16, 2014 at 10:29:53PM +0200, Pasi Kärkkäinen wrote:
> > 
> > * xend is now disabled by default.  You can enable it by running
> > chkconfig.  xend has been removed from the tree entirely in Xen 4.5,
> > so this should (hopefully) serve as a "wake-up-call" for people to
> > begin the transition over to xend.
> > 
> > * A lot have things have changed -- please to test this so we can get
> > a good idea what may have broken.
> >
> 
> I'll test soon. Thanks a lot!
> 


Ok I just used a couple of hours testing Xen 4.4.1 rpms on CentOS 6.6 with Linux 3.10 dom0 kernel.
This session was all about xm/xend testing. I manually enabled xend first. 


What Works OK:
	- Manually creating/managing guests with xm and domU cfgfiles in /etc/xen and LVM volumes as storage (phy backend).
	- Manually creating/managing guests with xm and domU cfgfiles in /etc/xen and file images as storage (tap2:aio backend).
	- Using virt-install to install PV domUs using LVM volumes as storage (phy backend).
	- Using virt-manager to install PV domUs using LVM volumes as storage (phy backend).

What doesn't work:
	- Using virt-manager to install PV domUs using file images as storage (tap:aio backend).


This libvirt/blktap2 file images failure with Xen 4.4 rpms is a regression from Xen 4.2 rpms, where blktap2 works OK with libvirt/virt-install/virt-manager.

The problem is most probably the fact that we had custom patches included in the xen4c6 libvirt rpms that we shipped with the Xen 4.2 rpms. 
We had to add two patches, one patch to fix the blktap2 backend type in libvirt, and one patch to fix the blktap2 backend type in virt-install or virt-manager, i'm not totally sure which one it was. Those patches should be included in the earlier libvirt source rpms, so we can check there. Or I can search thru my emails, because I hunted that down earlier aswell.

It seems we still need those patches with the latest libvirt rpms too.

The actual problem is libvirt/virt-manager tries to configure tap:aio: backend, which won't work.
It needs to be tap2:aio.

I get the exactly same behaviour with xm/xend. "tap:aio" stalls and fails. "tap2:aio" works OK.


-- Pasi