Re: [Xen-devel] [PATCH] Plumb through xen-platform device logging

[Anthony PERARD <anthony.perard@xxxxxxxxxx>]

On 11/07/13 13:50, Ian Campbell wrote:
> On Thu, 2013-07-11 at 13:07 +0100, Paul Durrant wrote:
> 
>>> > > Looking at http://wiki.qemu.org/Features/Tracing is the tracing
>>> > > interface really the right way to be logging this particular class of
>>> > > information? I'd have thought a simple logfile support in the platform
>>> > > device would be a much more natural fit.
>>> > > 
>> > 
>> > That makes sense to me, but whoever coded up the platform device
>> > obviously believed tracing to be the correct way to log. I don't know
>> > the history of that decision.
> I guess either Anthony or Stefano knows. Do you guys know why we log the
> platform device I/O port debug via the trace subsystems? It doesn't seem
> like a good fit.

It seams that I made this choice long time ago.
http://marc.info/?l=xen-devel&m=129864357001108&w=2

But I never try to use it, that was maybe not a great choice. After a
quick look into the qemu tree, using the trace thing those not seams bad
as well. There is just few step:

 - compile qemu with traces enable
 - adding to the vm-xl-config this:
device_model_args_hvm = [ '-trace', 'events=/tmp/traces' ]
(with "xen_platform_log" in /tmp/traces)


So, about the patch, I don't feel a good idea to have it enable all the
time for all the guest. Also, QEMU will refuse to start if it's compiled
without trace support.

> A better fit would be the qemu chr subsystem (I think that's the name, I
> mean the thing which lets you direct serial/parallel etc to
> file,tcp,sockets etc etc.)

This can maybe be done using a property, which could be set via the
command line by using the -device options.

-- 
Anthony PERARD

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