[Qemu-devel] Re: [PATCH 3/8] Add QBuffer

[Avi Kivity]

On 05/17/2010 10:40 AM, Jan Kiszka wrote:
> > The alternative is to have a schema.  Sun RPC/XDR doesn't carry any type
> > information (you can't even distinguish between a number and text) yet C
> > clients have to problem extracting typed information from it.
> >
> > Having __class__ everywhere means we're carrying the schema in every
> > message instead of just once.
> >      
> The device_show command is already an example where you don't have a
> predefined schema. It is derived from the data stream the encodes the
> vmstate fields. So far we have no collision between base64-encoded
> buffers and real strings, but this may actually change when we start
> annotating the fields with symbolic constants.
>    

What is the receiver to do with it?

If it doesn't know the schema (and there is no schema), then all it can 
do is display the key/values.  If it does know the schema, then 
__class__ is unnecessary.

My worry is that __class__ will make the protocol more ad-hoc.

> I really don't see the problem with __class__. Being a text protocol,
> JSON is already fairly verbose.
>    

The problem is not the verbosity, it's that information is carried too 
late.  Many clients want to know this information at compile time or 
initialization time, and we are providing it at object instantiating time.

--
Do not meddle in the internals of kernels, for they are subtle and quick to 
panic.