RE: [PATCH net-next] net: fix recent csum changes
flat view
From: David Laight <hidden>
Date: 2021-12-04 14:00:54
Also in:
oe-kbuild-all
From: Eric Dumazet
Sent: 04 December 2021 04:41 On Fri, Dec 3, 2021 at 7:34 PM kernel test robot [off-list ref] wrote:quoted
I love your patch! Perhaps something to improve:
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quoted hunk ↗ jump to hunk
Yes, keeping sparse happy with these checksum is not easy. I will add and use this helper, unless someone has a better idea.diff --git a/include/net/checksum.h b/include/net/checksum.h index 5b96d5bd6e54532a7a82511ff5d7d4c6f18982d5..5218041e5c8f93cd369a2a3a46add3e6a5e41af7100644--- a/include/net/checksum.h +++ b/include/net/checksum.h@@ -180,4 +180,8 @@ static inline void remcsum_unadjust(__sum16 *psum,__wsum delta) *psum = csum_fold(csum_sub(delta, (__force __wsum)*psum)); } +static inline __wsum wsum_negate(__wsum val) +{ + return (__force __wsum)-((__force u32)val); +} #endif
I was thinking that the expression also requires some comments. So maybe put a #define / static inline in checksum.h like: /* Subract the checksum of a buffer. * The domain is __wsum is [1..~0u] (ie excludes zero) * so ~csum_partial() cannot be used. * The two's compliment gives the right answer provided the old 'csum' * isn't zero - which it shouldn't be. */ #define csum_partial_sub(buf, len, csum) (-csum_partial(buf, len, -(csum)) and then add the annotations there to keep sparse happy there. will sparse accept '1 + ~csum' ? The compiler should use negate for it. It actually makes it slightly more obvious why the code is right. David - Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK Registration No: 1397386 (Wales)