Re: [Qemu-devel] [PATCH 00/22] QAPI Round 1

[Anthony Liguori <anthony@codemonkey.ws>]

On 03/08/2011 07:45 AM, Avi Kivity wrote:
> On 03/08/2011 03:35 PM, Anthony Liguori wrote:
>> On 03/08/2011 05:12 AM, Avi Kivity wrote:
>>> On 03/07/2011 05:59 PM, Anthony Liguori wrote:
>>>>
>>>>> How do async commands work?  You mentioned them when talking about
>>>>> QAPI but it's not obvious to me that there is any "native" support 
>>>>> for
>>>>> async commands?
>>>>
>>>> Async commands are interesting..
>>>
>>> Would there be anything in them other than starting each command in 
>>> its own thread?  If it then drops the right locks it can execute in 
>>> parallel with other commands, if it doesn't, then it's synchronous 
>>> (and presumably doesn't depend on external or guest events).
>>
>> I've implemented them (for virt-agent) and I'll have it in v2 of 
>> round 1.
>>
>> I use callbacks.  If a function is marked to be async, it generates a 
>> signature like:
>>
>> typedef void (GuestViewFileCompletionFunc)(void *qmp__opaque, const 
>> char * qmp__retval, Error *qmp__err);
>> void qmp_guest_view_file(const char * filename, Error **err, 
>> GuestViewFileCompletionFunc *qmp__cc, void *qmp__opaque);
>>
>> The handler just needs to squirrel away qmp__cc and qmp__opaque and 
>> call it whenever the command completes.
>
> Okay.  My preference would be threads, but we can always start with 
> one model and use adapters to switch to another.
>
> (and instead of an opaque/func pair, I'd do
>
> typedef struct GuestViewFileCompletion {
>     void (*complete)(struct GuestViewFileCompletion *gvfc);
> } GuestViewFileCompletion;
>
> so there's less squirrelling and more type-safetying.
> )

The opaque is a bit nicer to use because instead of having to generate 
another structure with this embedded, I can just pass the command state 
directly.

That said, once I get this all working nicely, I'll take a look at using 
a structure and see whether it makes it uglier.  I do prefer the 
embedded struct.

> (and gah, do we really need a vfs/rpc in qemu?)

Fun, eh :-)  Unfortunately, our friends at VMware provide a 
VixVM_CopyFileFromGuestToHost API so there's an expectation that we 
provide a similar interface.

Regards,

Anthony Liguori