Re: [PATCH v3 00/30] qapi/qom: QAPIfy --object and object-add

[Peter Krempa]

On Wed, Mar 10, 2021 at 18:30:44 +0100, Kevin Wolf wrote:
> Am 10.03.2021 um 15:31 hat Paolo Bonzini geschrieben:
> > On 10/03/21 15:22, Peter Krempa wrote:

[...]

> The keyval parser would create a list if multiple values are given for
> the same key. Some care needs to be taken to avoid mixing the magic
> list feature with the normal indexed list options.
> 
> The QAPI schema would then use an alternate between 'int' and ['int'],
> with the the memory-backend-ram implementation changed accordingly.
> 
> We could consider immediately deprecating the syntax and printing a
> warning in the keyval parser when it automatically creates a list from
> two values for a key, so that users don't start using this syntax

By 'creating a list from two values for a key' you mean:

host-nodes=0,host-nodes=1

to be converted into [0, 1] ?

> instead of the normal list syntax in other places. We'd probably still
> leave the implementation around for -device and other users of the same
> magic.

There's three options actually that libvirt uses, visible in one our
test files [1]

For a single value we format:

-object 
memory-backend-ram,id=ram-node0,size=20971520,host-nodes=3,policy=preferred

For a contiguous list:

-object 
memory-backend-ram,id=ram-node1,size=676331520,host-nodes=0-7,policy=bind

And for an interleaved list:

-object 
memory-backend-ram,id=ram-node2,size=24578621440,host-nodes=1-2,host-nodes=5,host-nodes=7,policy=bind

If any of the above is to be deprecated we'll need to adjust our
JSON->commandline generator accordignly.

Luckily the 'host-nodes' is storeable as a bitmap and the generator is
actually modular to allow plugging an array interpretor which actually
does the above conversion from a JSON array.

So, what is the preferred syntax here? Additionally we might need a
witness property to detect when to use the new syntax if basing it on
the object-add qapification will not be enough.

[1] 
https://gitlab.com/libvirt/libvirt/-/blob/master/tests/qemuxml2argvdata/numatune-memnode.args