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Re: [Xen-devel] [RFC] tools: don't use qemu default config

On Fri, Mar 11, 2016 at 03:08:30PM -0700, Jim Fehlig wrote:
> I recently changed SUSE's Xen package to use the distro qemu instead of 
> building
> qemu-xen. This got some other eyes looking at Xen's use of qemu and it was
> noticed that libxl and xen-qemu-dom0-disk-backend.service do not include
> '-no-user-config' when invoking qemu. The latter also does not include
> '-nodefaults'. Commit 6ef823fd added '-nodefaults' to the qemu args created by
> libxl, but missed adding it to the qemu args in 
> xen-qemu-dom0-disk-backend.service.

Right. That's probably an oversight.

> I _think_ adding '-nodefaults' to the qemu args in the service file is
> non-controversial. What do folks think of also adding '-no-user-config'? It
> seems the global config in /etc/qemu/qemu.conf would end up being more
> problematic than helpful for Xen.
> As a side note, the libvirt qemu driver includes '-no-user-config -nodefaults'
> in all its qemu invocations to avoid configuration which it doesn't control.

I think this is also a sensible thing to do.

> WRT qemu args, another suggestion was to explicitly specify 'accel=xen' in the
> machine arg. Together, these changes would e.g. result in the service file 
> qemu
> args changing slightly to
>   -machine xenpv,accel=xen -xen-domid 0 -xen-attach -name dom0 \
>   -daemonize -no-user-config -nodefaults -display none \
>   -pidfile /var/run/xen/qemu-dom0.pid

As for accel=xen, that's not strictly necessary because that's the
default machine option for xenpv machine.

> If folks agree with these changes, I'll be happy to provide a patches for 
> libxl
> and the systemd service file. Thanks for your comments.
> Regards,
> Jim

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