Re: [Qemu-devel] Re: [PATCH v2 12/15] monitor: Add basic device state visualization

[Avi Kivity <avi@redhat.com>]

On 05/24/2010 11:22 PM, Anthony Liguori wrote:
>> This converts the entire qdev tree into an undocumented stable 
>> protocol (the qdev paths were already in this state I believe).  This 
>> really worries me.
>
>
> N.B. the association with qdev is only in identifying the device.  The 
> contents of the device's state are not part of qdev but rather part of 
> vmstate.  vmstate is something that we already guarantee to be stable 
> since that's required for live migration compatibility.

That removes out ability to deprecate older vmstate as time passes.  Not 
a blocker but something to consider.

> I don't think that qdev device names and paths are something we have 
> to worry much about changing over time since they reflect logical bus 
> layout.  They should remain static provided the devices remain static.

Modulo mistakes.  We already saw one (lack of pci domains).  To reduce 
the possibility of mistakes, we need reviewable documentation.

Note sysfs had similar assumptions and problems.

> The qdev properties are a different matter entirely.  A command like 
> 'info qdm' would be potentially difficult to support as part of QMP 
> but the proposed command's output is actually already part of a 
> backward compatible interface (vmstate).

That's all good.  But documentation is critical for this.  Not only to 
improve quality, but also so that tool authors would have something to 
code against instead of trial and error (which invariably misses some 
corner cases).

-- 
error compiling committee.c: too many arguments to function