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

From: Jason Wang
Date: Thu Aug 06 2020 - 23:27:07 EST

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?

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?


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?