Re: QMP netdev_add multiple dnssearch values

[Eric Blake]

On 11/27/19 7:30 AM, Markus Armbruster wrote:

> "Good enough" was true back then.  It wasn't true when we reused it for
> netdev_add: hostfwd and guestfwd are list-valued.
>
> We did define a QAPI schema a few months later (14aa0c2de0 "qapi schema:
> add Netdev types").  net_client_init() uses it to convert from QemuOpts
> to QAPI type Netdev.  This took us to the crazy pipeline we still use
> today:
>
>                              CLI, HMP
>                          (key=value,...)
>                                 |
>                                 v
>      QMP (JSON) -> QDict -> QemuOpts -> Netdev
>
> We should instead use:
>
>                            CLI, HMP
>                        (key=value,...)
>                               |
>                               v
>                            QemuOpts
>                               |
>                               v
>      QMP (JSON) -> QDict -> Netdev
>
> Back in 2016, Eric (cc'ed) posted patches to get us to this pipeline.
> They got stuck on backward compatibility worries: the old code accepts
> all parameters as JSON strings in addition to their proper type, the new
> code doesn't.  Undocumented misfeature, but we chickened out anyway.

That was before we had a deprecation process.  Now we do.  If we are 
still worried about it, then we should start the deprecation clock 
(squeezing it into 4.2-rc3 is risky, more likely is starting it in 5.0, 
so that we get rid of string support in 5.2).  If we are not worried 
about it, then we can just kill the misfeature in 5.0.

> Let's reconsider.  Eric's patches break interface misuse that may or may
> not exist in the field.  They fix a correct use of interface people want
> to use (or Alex wouldn't have reported this bug), and they make QMP
> introspection work for netdev_add.
>
> Eric, what do you think?

Yes, it's time to revive that work (I have no idea if my patches from 
back then will still rebase nicely, though).

--
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3226
Virtualization:  qemu.org | libvirt.org