Linux Virtualization - Aug 2020 - [PATCH v2 03/24] virtio: allow __virtioXX, __leXX in config space

On 2020/8/5 ??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

>

On Thu, Aug 06, 2020 at 11:37:38AM +0800, Jason Wang
wrote:
> 
> On 2020/8/5 ??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.

> >

On 2020/8/6 ??1:58, Michael S. Tsirkin wrote:
> On Thu, Aug 06, 2020 at 11:37:38AM +0800, Jason Wang wrote:
>> On 2020/8/5 ??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

>
>