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Re: [Qemu-devel] [PATCH 0/6] Device state visualization reloaded

From: Michael S. Tsirkin
Subject: Re: [Qemu-devel] [PATCH 0/6] Device state visualization reloaded
Date: Tue, 6 Sep 2011 19:09:04 +0300
User-agent: Mutt/1.5.21 (2010-09-15)

On Tue, Sep 06, 2011 at 10:51:26AM -0500, Anthony Liguori wrote:
> On 09/06/2011 10:45 AM, Jan Kiszka wrote:
> >On 2011-09-06 16:48, Michael S. Tsirkin wrote:
> >>I'm afraid that won't be enough to stop people
> >>scripting this command - libvirt accessed
> >>HMP for years.
> >>
> >>On the other hand, no QMP command means e.g.
> >>libvirt users don't get any benefit from this.
> >>
> >>What I think will solve these problems, for both HMP and QMP,
> >>is an explicit 'debug_unstable' or 'debug_unsupported' command that will
> >>expose all kind of debugging functionality making it
> >>very explicit that it's an unsupported debugging utility.
> >>
> >>Proposed syntax:
> >>
> >>debug_unstable<subcommand>  <options>
> >>
> >>Example:
> >>
> >>debug_unstable device_show -all
> >
> >For HMP, this would needlessly complicate the user interface, nothing I
> >would support. People scripting things on top of HMP are generally doing
> >this on their own risk and cannot expect output stability.
> >
> >device_show is like info qtree: the output will naturally change as the
> >emulated hardware evolves, information is added/removed, or we simply
> >improve the layout. Recent changes on info network are an example for
> >the latter.
> Yeah, I'm not worried about stability.  HMP commands that aren't
> exposed as QMP commands are inherently unstable and should not be
> scripted to.

They are also not accessible when using libvirt, right?
Which means almost all cases I care about: debugging on my laptop
I can easily attach with gdb and inspect state.

> I'm still contemplating how we go about doing this.  This series
> introduces a couple new concepts like QMP class hinting anonymous
> IDs. I'm concerned that we'll further complicate the need to support
> backwards compatibility.

Dazed and confused. Above you stated these commands are
inherently unstable and no need to support?

> Would the command be useful if you couldn't address devices?  If it
> just dumped the full machine state all at once?  That would at least
> obviate the need to add anonymous IDs.
> Regards,
> Anthony Liguori
> >
> >Jan
> >

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