Re: [PATCH 7/8] qmp: add filtering of statistics by name

[Paolo Bonzini]

On 4/27/22 14:01, Dr. David Alan Gilbert wrote:
> >      "providers": [
> >        { "provider": "kvm",
> >          "names": [ "l1d_flush", "exits" ] } } }
> That looks inconsistent to me; I realise that 'names' has to be a child
> of providers (since the names are only relevant to a given provider) but
> how about making the "target" work similarly:
>
> { "execute": "query-stats",
>    "arguments": {
>      "target": {
>        "vcpus": [ "/machine/unattached/device[2]",
>                   "/machine/unattached/device[4]" ] },

This would allow queries for different types of targets in a single 
command, but it would be harder for the client to do filtering:

* with something like "target": { "vcpus": [ array ] }, there is no way 
for the client to say "I want this one statistic, but for all the vCPUs"

* if target is optional, a client might expect relatively small output 
from today's QEMU, yet suddenly get hundreds of KB from targets other 
than VMs and vCPUs (e.g. block devices including all backing files in 
the chain, NIC backends, etc.).

>      "providers": [
>         { "provider": "kvm",
>           "names": [ "l1d_flush", "exits" ] } } }
>
> It's not clear to me whether the "target" should also be specific
> to a given provider.

No, the target is a QEMU concept, such as a CPU or a device backend.  It 
is identified by either a QOM path or a unique id.

Paolo