Re: [Qemu-devel] [PATCH 06/21] qmp: Drop duplicated QMP command object checks

[Markus Armbruster <armbru@redhat.com>]

Eric Blake <eblake@redhat.com> writes:

> On 02/23/2017 03:45 PM, Markus Armbruster wrote:
>> qmp_check_input_obj() duplicates qmp_dispatch_check_obj(), except the
>> latter screws up an error message.  handle_qmp_command() runs first
>> the former, then the latter via qmp_dispatch(), masking the screwup.
>> 
>> qemu-ga also masks the screwup, because it also duplicates checks,
>> just differently.
>
> Cleaning up the duplication is a win in my book.
>
>> 
>> qmp_check_input_obj() exists because handle_qmp_command() needs to
>> examine the command before dispatching it.  The previous commit got
>> rid of this need, except for a tracepoint, and a bit of "id" code that
>> relies on qdict not being null.
>> 
>> Fix up the error message in qmp_dispatch_check_obj(), drop
>> qmp_check_input_obj() and the tracepoint.  Protect the "id" code with
>> a conditional.
>> 
>> Signed-off-by: Markus Armbruster <armbru@redhat.com>
>> ---
>>  monitor.c           | 74 +++++------------------------------------------------
>>  qapi/qmp-dispatch.c |  3 +--
>>  trace-events        |  1 -
>>  3 files changed, 7 insertions(+), 71 deletions(-)
>> 
>> diff --git a/monitor.c b/monitor.c
>> index dcf2de7..d83888d 100644
>> --- a/monitor.c
>> +++ b/monitor.c
>> @@ -3697,67 +3697,10 @@ static int monitor_can_read(void *opaque)
>>      return (mon->suspend_cnt == 0) ? 1 : 0;
>>  }
>>  
>> -/*
>> - * Input object checking rules
>> - *
>> - * 1. Input object must be a dict
>> - * 2. The "execute" key must exist
>> - * 3. The "execute" key must be a string
>> - * 4. If the "arguments" key exists, it must be a dict
>> - * 5. If the "id" key exists, it can be anything (ie. json-value)
>> - * 6. Any argument not listed above is considered invalid
>
> You know, with just a little tweak, we could add something to the .json
> file, and let generated code do all the checks of even the top-level
> entities:
>
> { 'struct': 'WireCommand',
>   'data': { 'execute': 'str', '*arguments': 'dict', '*id': 'any' } }
>
> if we had a way to force 'dict' as a subset of 'any' but where it must
> be a QDict.  (If we had a 'dict' recognized by the QAPI code generators,
> we could probably also fix 'object-add' to use '*props':'dict' instead
> of its current use of 'any')
>
> But that sounds like a bit much to ask for in the 2.9 timeframe, so it
> doesn't hold up this patch.

The thought came to me, too, but I banished it due to time pressure
before it could take presentable form.

Valid point on object-add.  If we find more uses for "generic object",
we can explore a new built-in QAPI type.

> We lose a trace, but I don't think that's fatal.

If we need one, it should be added to qmp_dispatch(), where it's also
useful for qemu-ga.

> Reviewed-by: Eric Blake <eblake@redhat.com>

Thanks!