Re: [Qemu-devel] [RFC][PATCH 11/45] msi: Factor out delivery hook

[Jan Kiszka]

On 2011-10-18 14:38, Michael S. Tsirkin wrote:
> On Tue, Oct 18, 2011 at 02:23:29PM +0200, Jan Kiszka wrote:
>> On 2011-10-18 14:05, Michael S. Tsirkin wrote:
>>> On Mon, Oct 17, 2011 at 09:15:47PM +0200, Jan Kiszka wrote:
>>>> On 2011-10-17 15:43, Michael S. Tsirkin wrote:
>>>>> On Mon, Oct 17, 2011 at 11:27:45AM +0200, Jan Kiszka wrote:
>>>>>> diff --git a/hw/msi.c b/hw/msi.c
>>>>>> index 3c7ebc3..9055155 100644
>>>>>> --- a/hw/msi.c
>>>>>> +++ b/hw/msi.c
>>>>>> @@ -40,6 +40,14 @@
>>>>>>  /* Flag for interrupt controller to declare MSI/MSI-X support */
>>>>>>  bool msi_supported;
>>>>>>  
>>>>>> +static void msi_unsupported(MSIMessage *msg)
>>>>>> +{
>>>>>> +    /* If we get here, the board failed to register a delivery handler. 
>>>>>> */
>>>>>> +    abort();
>>>>>> +}
>>>>>> +
>>>>>> +void (*msi_deliver)(MSIMessage *msg) = msi_unsupported;
>>>>>> +
>>>>>
>>>>> How about we set this to NULL, and check it instead of the bool
>>>>> flag?
>>>>>
>>>>
>>>> Yeah. I will introduce
>>>>
>>>> bool msi_supported(void)
>>>> {
>>>>     return msi_deliver != msi_unsupported;
>>>> }
>>>>
>>>> OK?
>>>>
>>>> Jan
>>>>
>>>
>>> Looks a bit weird ...
>>> NULL is a pretty standard value for an invalid pointer, isn't it?
>>
>> Save us the runtime check and is equally expressive and readable IMHO.
>>
>> Jan
> 
> Do we need to check?
> NULL dereference leads to a crash just as surely...

There is no NULL state of msi_deliver. A) it would execute
msi_unsupported if all goes wrong (which will abort) and B)
msi_supported() is supposed to protect us in the absence of bugs from
ever executing msi_deliver() if it points to msi_unsupported.

Jan

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