[RFC] tools: don't use qemu default config

[RFC] tools: don't use qemu default config

[Jim Fehlig]

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.

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.

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

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

[Konrad Rzeszutek Wilk]

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.
> 
> 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.

Is there a description (or URL) of what one can jam in there?

> 
> 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.
> 
> 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
> 
> 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
> 
> _______________________________________________
> Xen-devel mailing list
> Xen-devel@lists.xen.org
> http://lists.xen.org/xen-devel

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

[Wei Liu]

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

[Jim Fehlig]

On 03/11/2016 03:28 PM, Konrad Rzeszutek Wilk wrote:
> 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.
>>
>> 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.
> Is there a description (or URL) of what one can jam in there?

I failed to find one. I asked a few SUSE qemu devs and they too had no
documentation hints, but noted "pretty much anything that fits in the command
line can go into the config file these days".

The user config files are .ini-style. Command line option  '-opt_a foo=1,bar=2'
becomes

  [opt_a]
    foo=1
    bar=2

Regards,
Jim


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