linux-kernel - Re: [PATCH v2 03/24] virtio: allow __virtioXX, _

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Date:   Thu, 6 Aug 2020 01:58:26 -0400
From:   "Michael S. Tsirkin" <mst@...hat.com>
To:     Jason Wang <jasowang@...hat.com>
Cc:     linux-kernel@...r.kernel.org,
        virtualization@...ts.linux-foundation.org
Subject: Re: [PATCH v2 03/24] virtio: allow __virtioXX, __leXX in config space

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.


> >