Re: qmp-shell for GSoC/Outreachy?

[Daniel P . Berrangé]

On Thu, Feb 06, 2020 at 01:11:58PM +0100, Markus Armbruster wrote:
> Daniel P. Berrangé <address@hidden> writes:
> 
> > On Thu, Feb 06, 2020 at 10:40:37AM +0100, Markus Armbruster wrote:
> >> > If the user screwsup, it should give an error that prompts the user
> >> > to the parameter they got wrong.
> >> >
> >> > Output from commands should normally be pretty formatted (with an option
> >> > to display raw json for those needing it).
> >> >   e.g. that 'query-version' should give either just the package
> >> >   version (as info version currently does) or:
> >> >       4.2.50  Package: v4.2.0-1188-gd95a3885a9
> >> >
> >> > We shouldn't lose any HMP commands that some people find useful
> >> >   Ditching HMP isn't an option until we've got almost all of it
> >> >   covered.
> >> 
> >> In particular, we currently use HMP for debugging and monitoring
> >> purposes, where we don't need or want QMP's rigor, neither its rigorous
> >> interface stability, nor its structured I/O.  We want the "whipuptitude"
> >> we get from monitor_printf().  This is actually a point David has made
> >> several times.
> >
> > I'd like to argue that this decision to keep these debugging/monitoring
> > things in HMP only was a mistake, because it ensures that QEMU internals
> > need to keep HMP related code forever.
> >
> > What we actually need is a part of QMP that does not have the long term
> > stability requirement, nor need for fully structured data. In fact this
> > pretty much already exists - we have declared the 'x-' prefix as a way
> > to model QMP commands which are experimental / suboptimal / subject
> > to change.
> >
> > I suggest that every HMP command which does not have a QMP equivalent
> > should be turned into a QMP command with an "x-" prefix, with no
> > extra modelling applied
> 
> Makes sense (see my point about "allowing some [whipuptitude] in QMP"),
> except I disagree with your example:
> 
> > Take "info block"
> >
> > (hmp) info block
> > ide1-cd0: [not inserted]
> >     Attached to:      /machine/unattached/device[23]
> >     Removable device: not locked, tray closed
> >
> > floppy0: [not inserted]
> >     Attached to:      /machine/unattached/device[16]
> >     Removable device: not locked, tray closed
> >
> > sd0: [not inserted]
> >     Removable device: not locked, tray closed
> >
> >
> > I suggest we support it as "x-query-block"
> >
> > (qmp) x-query-block
> > {
> >     "return": {
> >         "info": "ide1-cd0: [not inserted]
> >     Attached to:      /machine/unattached/device[23]
> >     Removable device: not locked, tray closed
> >
> > floppy0: [not inserted]
> >     Attached to:      /machine/unattached/device[16]
> >     Removable device: not locked, tray closed
> >
> > sd0: [not inserted]
> >     Removable device: not locked, tray closed"
> >     }
> > }
> 
> This commmand does have a QMP equivalent: query-block.

Doh, I should have actually checked before picking a random
example :-)

> 
> Hmm, no more.  It actually wraps around both query-block and
> query-named-block-nodes now.  I think that makes it an example of "go
> beyond 1:1".
> 
> A better example for "allowing whipuptitude" would be "info registers".

Yep, that's a classic that would be horribly painful to try to represent
as a fully structured set of arrays & dicts for all architectures.


Regards,
Daniel
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