Re: [PATCH -next 1/2] string.h: Introduce memset_range() for wiping members

[xiujianfeng]

在 2021/12/8 12:28, Andrew Morton 写道:
> On Wed, 8 Dec 2021 11:04:50 +0800 Xiu Jianfeng <xiujianfeng@xxxxxxxxxx> wrote:
>
> > Motivated by memset_after() and memset_startat(), introduce a new helper,
> > memset_range() that takes the target struct instance, the byte to write,
> > and two member names where zeroing should start and end.
> Is this likely to have more than a single call site?
There maybe more call site for this function, but I just use bpf as an 
example.
> > ...
> >
> > --- a/include/linux/string.h
> > +++ b/include/linux/string.h
> > @@ -291,6 +291,26 @@ void memcpy_and_pad(void *dest, size_t dest_len, const void *src, size_t count,
> >   	       sizeof(*(obj)) - offsetof(typeof(*(obj)), member));	\
> >   })
> >   
> > +/**
> > + * memset_range - Set a value ranging from member1 to member2, boundary included.
> I'm not sure what "boundary included" means.
I mean zeroing from member1 to member2(including position indicated by 
member1 and member2)
> > + *
> > + * @obj: Address of target struct instance
> > + * @v: Byte value to repeatedly write
> > + * @member1: struct member to start writing at
> > + * @member2: struct member where writing should stop
> Perhaps "struct member before which writing should stop"?
memset_range should include position indicated by member2 as well
> > + *
> > + */
> > +#define memset_range(obj, v, member_1, member_2)			\
> > +({									\
> > +	u8 *__ptr = (u8 *)(obj);					\
> > +	typeof(v) __val = (v);						\
> > +	BUILD_BUG_ON(offsetof(typeof(*(obj)), member_1) >		\
> > +		     offsetof(typeof(*(obj)), member_2));		\
> > +	memset(__ptr + offsetof(typeof(*(obj)), member_1), __val,	\
> > +	       offsetofend(typeof(*(obj)), member_2) -			\
> > +	       offsetof(typeof(*(obj)), member_1));			\
> > +})
> struct a {
> 	int b;
> 	int c;
> 	int d;
> };
>
> How do I zero out `c' and `d'?
if you want to zero out 'c' and 'd', you can use it like 
memset_range(a_ptr, c, d);
> .