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Re: [Qemu-devel] [PATCH 6/9] log: log QMP commands and replies

From: Denis V. Lunev
Subject: Re: [Qemu-devel] [PATCH 6/9] log: log QMP commands and replies
Date: Mon, 14 Mar 2016 18:05:07 +0300
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.5.1

On 03/14/2016 05:38 PM, Daniel P. Berrange wrote:
On Mon, Mar 14, 2016 at 03:33:53PM +0100, Paolo Bonzini wrote:

On 14/03/2016 12:21, Denis V. Lunev wrote:
From: Pavel Butsykin <address@hidden>

This log would be very welcome for long-term diagnostics of the system
in the production. This log is at least necessary to understand what
has been happened on the system and to identify issues at higher-level
subsystems (libvirt, etc).

These messages will be quite useful to understand how things are going.
There is now a logging mechanism for qemu-char.c.  Have you looked into
making libvirt provide a QMP log based on it?

The timestamping of patch 9 could be useful for character devices as well.
libvirt QEMU driver already has logging support for recording all the data
it both sends and receives over QMP, which should be sufficient for any
day to day troubleshooting of QMP issues. So I doubt duplicating that
info from QEMU side too is really beneficial for debugging issues when
libvirt is in use.

In libvirtd set


and it'll capture everything on the QMP monitor in the default libvirtd
log file.

The QMP data is also fed into the libvirt tracing backend, so you can
write systemtap scripts that hook on any QMP message, reply or event.
We ship a sample monitoring script examples/systemtap/qemu-monitor.stp
for this too.

you definitely sold this to me :) Thank you for pointing this out.

There is the only differences in the approaches:
- for example you have 20-50 VMs on the node
- you have 1 problematic VM to be debugged by support (not development)

In this case with my approach the load to the host IO subsystem will
be less (logs from 1 VM will be written only).

I can drop patches 5-9 if this is not important :)


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