Re: [PATCH v2 03/24] virtio: allow __virtioXX, __leXX in config space

[Jason Wang]

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


>