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

[Paul Durrant <Paul.Durrant@xxxxxxxxxx>]

> -----Original Message-----
> From: Anthony PERARD [mailto:anthony.perard@xxxxxxxxxx]
> Sent: 11 July 2013 14:54
> To: Ian Campbell
> Cc: Paul Durrant; xen-devel@xxxxxxxxxxxxx; Stefano Stabellini
> Subject: Re: [Xen-devel] [PATCH] Plumb through xen-platform device logging
> 
> 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)
>

Yeah, that's what I had before :-)

 > 
> 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.
> 

Thatâs a good point. Should probably just have a minimal patch to the xen build 
to enable a tracing backend (under config control) and leave the libxl stuff 
out.

  Paul

> > 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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