Re: [Qemu-devel] [PATCH 06/10] qapi: simplify qmp_input_next_list

[Anthony Liguori <anthony@codemonkey.ws>]

On 03/22/2012 04:24 PM, Paolo Bonzini wrote:
> Il 22/03/2012 21:22, Anthony Liguori ha scritto:
>>>
>>> Signed-off-by: Paolo Bonzini<pbonzini@redhat.com>
>>
>> I've been staring a this patch for the past 5 minutes and I can't figure
>> out what's going on here.
>>
>> Maybe the code was too obscure to begin with.  Could you enhance the
>> commit message a bit with what's going on here?
>
> There's three possible questions about what's going on:
>
> 1) What's going on before the patch with so->entry
>
> 2) What's going on after the patch with so->entry
>
> 3) What's going on with *list.  The patch doesn't change this, it just
> unties it with so->entry, but it's the most puzzling part so the
> question is a good one. :)
>
>
> First of all, so->entry here is advanced and also used to figure out
> whether we have a next element.  It is then accessed in qmp_input_get_obj.
>
> The caller must:
>
> * call start_list
>
> * call next_list for each element *including the first*
>
> * on the first call to next_list, the result is the head of the list
> (works for both input and output visitor).
>
> Before: so->entry is initialized to qlist_first on start_list.  The
> first call will have *list == NULL, so it skips the qlist_next.  The
> caller assigns the result and makes *list not NULL, so that the next
> iteration will advance so->entry and modify (*list)->next.
>
> After: so->entry is initialized to NULL on start_list.  The first call
> sees so->entry == NULL and does qlist_first; subsequent calls do
> qlist_next.  *list is handled same as above: assignment done by the
> caller on the first call, done by next_list on the next ones.
>
>
> Thanks for making me write all this down,

No problem :-)  I was really looking for the commit message breakdown.  I 
convinced myself that what you were doing was right but it took me sufficiently 
long that I thought it warranted a better commit message.

Regards,

Anthony Liguori