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Subject: Re: [PATCH v2 03/24] virtio: allow __virtioXX, __leXX in config space
To:     "Michael S. Tsirkin" <mst@redhat.com>
Cc:     linux-kernel@vger.kernel.org,
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From:   Jason Wang <jasowang@redhat.com>
Message-ID: <a4ef115c-f005-fd09-a94f-5b2a004b672b@redhat.com>
Date:   Fri, 7 Aug 2020 11:26:55 +0800
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On 2020/8/6 下午1:58, Michael S. Tsirkin wrote:
> On Thu, Aug 06, 2020 at 11:37:38AM +0800, Jason Wang wrote:
>> On 2020/8/5 下午7:45, Michael S. Tsirkin wrote:
>>>>>     #define virtio_cread(vdev, structname, member, ptr)			\
>>>>>     	do {								\
>>>>>     		might_sleep();						\
>>>>>     		/* Must match the member's type, and be integer */	\
>>>>> -		if (!typecheck(typeof((((structname*)0)->member)), *(ptr))) \
>>>>> +		if (!__virtio_typecheck(structname, member, *(ptr)))	\
>>>>>     			(*ptr) = 1;					\
>>>> A silly question,  compare to using set()/get() directly, what's the value
>>>> of the accessors macro here?
>>>>
>>>> Thanks
>>> get/set don't convert to the native endian, I guess that's why
>>> drivers use cread/cwrite. It is also nice that there's type
>>> safety, checking the correct integer width is used.
>>
>> Yes, but this is simply because a macro is used here, how about just doing
>> things similar like virtio_cread_bytes():
>>
>> static inline void virtio_cread(struct virtio_device *vdev,
>>                        unsigned int offset,
>>                        void *buf, size_t len)
>>
>>
>> And do the endian conversion inside?
>>
>> Thanks
>>
> Then you lose type safety. It's very easy to have an le32 field
> and try to read it into a u16 by mistake.
>
> These macros are all about preventing bugs: and the whole patchset
> is about several bugs sparse found - that is what prompted me to make
> type checks more strict.


Yes, but we need to do the macro with compiler extensions. I wonder 
whether or not the kernel has already had something since this request 
here is pretty common?

Thanks


>
>