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SubjectRe: [PATCH -next 1/2] string.h: Introduce memset_range() for wiping members
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在 2021/12/8 12:28, Andrew Morton 写道:
> On Wed, 8 Dec 2021 11:04:50 +0800 Xiu Jianfeng <xiujianfeng@huawei.com> 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);
>
>
> .

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