Re: [Qemu-devel] [PATCH] full introspection support for QMP

[Kevin Wolf <kwolf@redhat.com>]

Am 02.07.2013 um 19:06 hat Anthony Liguori geschrieben:
> Eric Blake <eblake@redhat.com> writes:
> > On 07/02/2013 08:51 AM, Anthony Liguori wrote:
> >> Amos Kong <akong@redhat.com> writes:
> >> 
> >>> Introduces new monitor command to query QMP schema information,
> >>> the return data is a nested dict/list, it contains the useful
> >>> metadata.
> >>>
> >>> we can add events definations to qapi-schema.json, then it can
> >>> also be queried.
> >>>
> >>> Signed-off-by: Amos Kong <akong@redhat.com>
> >> 
> >> Maybe I'm being too meta here, but why not just return qapi-schema.json
> >> as a string and call it as day?

I know you don't agree with this, but as I mentioned several times
before, I think the schema as returned by the introspection functions
shouldn't contain what a qemu of this version _could_ in theory provide,
but what this specific build actually _does_ provide. It shouldn't
include things that are compiled out.

> > I've also been the one arguing that the additional complexity (an array of
> > {"name":"str","type":"str","optional":bool"}) is better for libvirt in
> > that the JSON is then well-suited for scanning (it is easier to scan
> > through an array where the key is a constant "name", and looking for the
> > value that we are interested in, than it is to scan through a dictionary
> > where the keys of the dictionary are the names we are interested in).
> > That is, the JSON in qapi-schema.json is a nice compact representation
> > that works for humans, but may be a bit TOO compact for handling via
> > machines.
> 
> But adding a bunch of code to do JSON translation just adds a bunch of
> additional complexity.
> 
> One reasonable compromise would be:
> 
> { "command": "foo", "arguments": { "name": "str", "id": "int" },
>                     "optional": { "bar": "bool" } }

This assumes that optional vs. mandatory is the only property we ever
want to describe for fields. Eric's approach is much more future-proof.
Let's keep the format of qapi-schema.json an implementation detail that
we can change and extend when necessary.

Kevin