ioport 0x12 logfile writing

ioport 0x12 logfile writing

[James Harper]

Under xen 4.1 and the old qemu I could write to /var/log/xen/qemu-dm-<domu name>.log from inside the vm by writing to ioport 0x12. Is that functionality replaced in any way in qemu upstream? Does qemu have its own logging mechanism?

Thanks

James

Re: ioport 0x12 logfile writing

[Paul Durrant]

> -----Original Message-----
> From: xen-devel-bounces@lists.xen.org [mailto:xen-devel-
> bounces@lists.xen.org] On Behalf Of James Harper
> Sent: 24 December 2013 06:28
> To: xen-devel@lists.xenproject.org
> Subject: [Xen-devel] ioport 0x12 logfile writing
> 
> Under xen 4.1 and the old qemu I could write to /var/log/xen/qemu-dm-
> <domu name>.log from inside the vm by writing to ioport 0x12. Is that
> functionality replaced in any way in qemu upstream? Does qemu have its
> own logging mechanism?
> 

That logging mechanism (via qemu tracing: see http://repo.or.cz/w/qemu/stefanha.git/blob_plain/refs/heads/tracing:/docs/tracing.txt) is still there, but unfortunately off by default. I think recent xen builds now compile upstream qemu with a stderr trace backend by default at least so all you should need to do is create a events file by doing:

Echo xen_platform_log > /tmp/events

And then adding "-trace events=/tmp/events" to your qemu command line via your xl.cfg:

device_model_args = ['-trace', 'events=/tmp/events']

Port 0x12 logging should then appear as before.

  Paul

Re: ioport 0x12 logfile writing

[Don Slutz]

On 12/24/13 04:10, Paul Durrant wrote:
>> -----Original Message-----
>> From: xen-devel-bounces@lists.xen.org [mailto:xen-devel-
>> bounces@lists.xen.org] On Behalf Of James Harper
>> Sent: 24 December 2013 06:28
>> To: xen-devel@lists.xenproject.org
>> Subject: [Xen-devel] ioport 0x12 logfile writing
>>
>> Under xen 4.1 and the old qemu I could write to /var/log/xen/qemu-dm-
>> <domu name>.log from inside the vm by writing to ioport 0x12. Is that
>> functionality replaced in any way in qemu upstream? Does qemu have its
>> own logging mechanism?
>>
> That logging mechanism (via qemu tracing: see http://repo.or.cz/w/qemu/stefanha.git/blob_plain/refs/heads/tracing:/docs/tracing.txt) is still there, but unfortunately off by default. I think recent xen builds now compile upstream qemu with a stderr trace backend by default at least so all you should need to do is create a events file by doing:
>
> Echo xen_platform_log > /tmp/events
>
> And then adding "-trace events=/tmp/events" to your qemu command line via your xl.cfg:
>
> device_model_args = ['-trace', 'events=/tmp/events']
>
> Port 0x12 logging should then appear as before.
>
>    Paul

QEMU tracing is on only for "debug=y" builds (tools/Makefile):

ifeq ($(debug),y)
QEMU_XEN_ENABLE_DEBUG := --enable-debug --enable-trace-backend=stderr
else
QEMU_XEN_ENABLE_DEBUG :=
endif

    -Don Slutz

>
>
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