Re: [Qemu-devel] wiki summary

[Richard W.M. Jones]

On Thu, Nov 24, 2011 at 02:40:07PM +0200, Dor Laor wrote:
> Using QMP is an advantage, I agree.
> However it can be used by another option - move the QMP schema out
> of qemu.git so all projects like libvirt, agents, vdsm, etc will be
> able to consume it directly.
> 
> This way, adding a new (agent) command will immediately propagate to
> all of the stack instead of each component to implement it
> differently (while it would still be possible).
> That's what libguestfs scheme do today.

I think Dor CC'd me on this because we use aggressive code generation
in libguestfs to simplify creating new APIs.  For an example see:

http://fedorapeople.org/gitweb?p=rjones/public_git/libguestfs.git;a=commitdiff;h=cbd1c45d95c530c8d94103dcc2c521bf5501ef59

The patch is in three parts:

(1) C code to implement the new API.  Constructing the command line,
    parsing the output.

(2) Metadata in the generator to describe the new API (parameters,
    return, documentation, etc.)

  ==> From this part *everything* is generated <==

      - C header file
      - bindings in 8+ programming languages
      - documentation
      - RPC used over internal virtio-serial connection

(3) A test.

Intelligently generating code like this has been an enormous win.

Here are two slightly more complicated examples demonstrating the same
thing:

http://fedorapeople.org/gitweb?p=rjones/public_git/libguestfs.git;a=commitdiff;h=c4bd6bba8d88ecf1ebf4a9c2c80a407d9971aaf7
http://fedorapeople.org/gitweb?p=rjones/public_git/libguestfs.git;a=commitdiff;h=c11a92751e003b3d4bc3584b598afc9bd9d9e703

Rich.

-- 
Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones
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