Re: [Qemu-devel] [RfC PATCH 0/5] console: qom-ify & extent screendump monitor command

[Paolo Bonzini]

Il 22/04/2013 18:49, Anthony Liguori ha scritto:
>> We've been adding fields to types since 0.15, sometimes in the middle of
>> a struct (since 1.2).
> 
> You can safely add fields to the end of a struct. 

For QEMU->user structs it is.  For user->QEMU structs you need to add a
sizeof() at the beginning, or ensure that everything is heap-allocated
(and zero-initialized).

At that point you could also use structs to pass arguments to the
functions (in the C client API) that execute a QMP command.  That's
similar to having keyword arguments in C.

> Well this is all well and good in abstract, in practice, we want a new
> screendump command anyway.
> 
> It'd be *much* nicer to return the screenshot data via the QMP session
> instead of writing it to a file.  So let's take the opportunity to fix
> the command.

That's debatable... the "nicest" way could also be to pass a pipe fd and
retrieve the dump from that fd.  That's quite easy to do with fdsets.
The choice is between implementing SCM_RIGHTS sendfd and a base64 decoder.

> We can also introduce a "format" parameter to allow specifying formats
> othe than PPM.

True, but I'm not sure we want to go there.  We'd need to add support
for options like JPG quality factor etc.

Paolo