[Pkg-xen-devel] Bug#658100: Bug#658100: xl: hangs in qemu-dm when trying to run PV domU

[Ian Campbell]

On Tue, 2012-01-31 at 18:41 +0100, Witold Baryluk wrote:
> On 01-31 16:51, Ian Campbell wrote:
> > On Tue, 2012-01-31 at 12:32 +0100, Witold Baryluk wrote:
> > > I found NetBSD user/developer had very similar problem (when using xl as TOOLSTACK,
> > > just like me!) about year ago (Mar 2011).
> > > 
> > > http://mail-index.netbsd.org/port-xen/2011/03/31/msg006552.html
> > > with some discussion, that NetBSD doesn't have gnttap implemented in kernel:
> > 
> > I think that is correct and I'm afraid this will prevent the use of
> > either vfb or qdisk (which is what file:// becomes in the absence of
> > blktap, which freebsd does not have) disk backends. Userspace PV device
> > backends simply cannot work without a gnttab device.
> > 
> > There has been some work on xen-unstable (by Roger Pau Monet) to make
> > file:// type disks use the in kernel vbd backend (which won't need vbd)
> > but this is still a work in progress and won't be in 4.1. Hopefully this
> > will be in in time for 4.2.
> > 
> > As a workaround in the meantime you can use the FreeBSD equivalent of
> > losetup (vnconfig?) to manually turn your file:/path/etc into a
> > phy:/dev/vndN which will use the in kernel vbd backend.
> > 
> > (I'm not a FreeBSD guy so I may have got some of the names above wrong)
> 
> 
> I do not know what you are talking about. Im using Debian's Xen and
> Debian/GNU Linux 3.2 kernel as dom0. The same happens with freebsd and linux
> kernels as domU. Clearly I expect Linux dom0 (and domU) to support
> gnttab. (btw. there is NO dom0 support in FreeBSD).

Your bug report said:
movax-dev:/etc/xen# dpkg -l | grep -- -image
ii  gnumach-image-1-xen-486              2:1.3.99.dfsg.git20111010-1  The GNU version of the Mach microkernel
ii  gnumach-image-1.3.99-xen-486         2:1.3.99.dfsg.git20111010-1  The GNU version of the Mach microkernel for Xen
ii  kfreebsd-image-9-xen                 9.0-1                        kernel of FreeBSD 9 image (meta-package)
ii  kfreebsd-image-9.0-1-xen             9.0-1                        kernel of FreeBSD 9.0 image
[...]

so I'm sure you can see where I got the idea you might be running
Debian/kfreebsd from.

[...]
> I think this is because /dev/xen/gntdev file was provided by xen-evtchn
> or xenfs module in previous kernels (like 2.6.32 in squeeze), but is now
> in separate module (xen-gntdev).
> 
> 
> I performed 'lsmod' after reboot, and there was NO single xen releated
> module loaded, even after 'xl create ...'. So clearly something is not doing
> its job. I guess, 'xl' tool should make sure proper modules are loaded,
> or /etc/init.d/xen(d) should modprobe them.

$ grep modprobe /etc/init.d/xen*
/etc/init.d/xend:	modprobe xenfs 2>/dev/null
/etc/init.d/xend:	modprobe xen-evtchn 2>/dev/null

so it is loading some things but clearly it needs to load some more,
like xen-gntdev and xen-*back.

> I loaded xen-gntdev xen-evtchn xen-blkback xen-netback (not in this
> order) manually, and now everything works.

Great.

Ian.

-- 
Ian Campbell


If the thunder don't get you, then the lightning will.