Re: [Qemu-devel] [PATCH RFC 0/2] QMP command qom-new

[Anthony Liguori <anthony@codemonkey.ws>]

On 05/24/2012 09:23 AM, Peter Maydell wrote:
> On 24 May 2012 15:10, Anthony Liguori<anthony@codemonkey.ws>  wrote:
>> On 05/24/2012 08:18 AM, Peter Maydell wrote:
>>> Last time I was trying to argue for keeping the "create, set properties,
>>> realize" interface for devices/objects as simple as possible you wanted
>>> it to have an error-return interface rather than asserting...
>>
>>
>> You need to be more specific than that I'm afraid..
>
> https://lists.gnu.org/archive/html/qemu-devel/2012-05/msg00079.html

Ah, okay.  So you're taking those comments a bit out of context.

The right way to use object_new() is:

Object *foo = object_new(TYPE_E1000);

If you mistype TYPE_E1000, you should get a compile failure.  There's basically 
no way that this is going to fail unless you do:

Object *foo = object_new("garbage");

There's no point in adding error handling here because if you make this much of 
a mistake, then you're likely not going to handle errors properly.  That's 
entirely different from:

connect(foo, "baz", bar, "caz");

It's extremely likely that you'll mistype one of the property names.  We have 
existence proofs in the three with qdev_prop_set*().  This can be deep within 
the bowels of device initialization and assert()'ing QEMU doing a device_add is 
a pretty nasty thing to do.  There's also type errors that can occur here that 
are even more likely to happen by accident.

Contrast that with:

foo->baz = &bar->caz;

If you mistype the property names or mess up the types, you will get a compile 
error.

Regards,

Anthony Liguori

>
> -- PMM