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

[Ian Campbell <ian.campbell@xxxxxxxxxx>]

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.

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.)

> It doesn't change the fact though that, currently, xen builds of QEMU
> don't configure any form of tracing backend at all which doesn't seem
> particularly helpful, and I did introduce platform logging as an
> example of an event to log so I think the patch is useful as far as it
> goes, but maybe another patch to the platform device in QEMU would
> also be considered a good idea.
> 
>   Paul
> 
> > > >         $(MAKE) all
> > > >
> > > > diff --git a/tools/libxl/libxl_dm.c b/tools/libxl/libxl_dm.c
> > > > index 2924298..35f71cc 100644
> > > > --- a/tools/libxl/libxl_dm.c
> > > > +++ b/tools/libxl/libxl_dm.c
> > > > @@ -370,6 +370,13 @@ static char **
> > > > libxl__build_device_model_args_new(libxl__gc *gc,
> > > >                        "-xen-domid",
> > > >                        libxl__sprintf(gc, "%d", guest_domid), NULL);
> > > >
> > > > +    flexarray_vappend(dm_args,
> > > > +                      "-trace",
> > > > +                      libxl__sprintf(gc,
> > > > +                                     "events=%s/qemu-trace-events",
> > > > +                                     libxl__xen_config_dir_path()),
> > > > +                      NULL);
> > 
> > Doesn't this end up logging to /etc/xen? Not what we want I think.
> > 
> > or maybe this is just the config file, which, apart from my comments
> > about the suitability of the interface above, makes me wonder where the
> > logs do go? Ideally they would go to /var/log/xen/qemu-blah-name.log not
> > to xl stdout.
> > 
> 



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