netdev - Re: [PATCH 5/9 v2] net: Generalize checksum

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Message-ID: <1398548524.16049.6.camel@deadeye.wl.decadent.org.uk>
Date:	Sat, 26 Apr 2014 22:42:04 +0100
From:	Ben Hutchings <ben@...adent.org.uk>
To:	Tom Herbert <therbert@...gle.com>
Cc:	davem@...emloft.net, netdev@...r.kernel.org
Subject: Re: [PATCH 5/9 v2] net: Generalize checksum_init functions

On Sat, 2014-04-26 at 14:25 -0700, Tom Herbert wrote:
> Create a general __skb_checksum_validate function (actually a
> macro) to subsume the various checksum_init functions. This
> function can either init the checksum, or do the full validation
> (logically checksum_init+skb_check_complete)-- a flag specifies
> if full vaidation is performed. Also, there is a flag to the function
> to indicate that zero checksums are allowed (to support optional
> UDP checksums).
> 
> Added several stub functions for calling __skb_checksum_validate.
> 
> Signed-off-by: Tom Herbert <therbert@...gle.com>
> ---
>  include/linux/skbuff.h | 87 ++++++++++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 87 insertions(+)
> 
> diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
> index 08074a8..3b14acc 100644
> --- a/include/linux/skbuff.h
> +++ b/include/linux/skbuff.h
> @@ -2741,6 +2741,93 @@ static inline __sum16 skb_checksum_complete(struct sk_buff *skb)
>                0 : __skb_checksum_complete(skb);
>  }
>  
> +/*
> + * Try to validate checksum based on unnecessary or zero checksum
> + * received.
> + *
> + * Return values:
> + * 0: checksum unnecessary validated, no further checks needed
> + * 1: checksum complete needed
> + */
> +static inline __sum16 __skb_checksum_validate_unnecessary(struct sk_buff *skb,
> +                                                         bool zero_okay,
> +                                                         __sum16 check)
> +{
> +       if (skb_csum_unnecessary(skb)) {
> +               return 0;
> +       } else if (zero_okay && !check) {
> +               skb->ip_summed = CHECKSUM_UNNECESSARY;
> +               return 0;
> +       }
> +
> +       return 1;
> +}

Why is this returning __sum16 and not bool?

> +/*
> + * Validate (init) checksum based on checksum complete.
> + *
> + * Return values:
> + * 0: checksum is validated or try to in skb_checksum_complete
> + * non-zero: value of invalid computed checksum
> + */
> +static inline __sum16 __skb_checksum_validate_complete(struct sk_buff *skb,
> +                                                      bool complete,
> +                                                      __wsum psum)
> +{
> +       if (skb->ip_summed == CHECKSUM_COMPLETE) {
> +               if (!csum_fold(csum_add(psum, skb->csum))) {
> +                       skb->ip_summed = CHECKSUM_UNNECESSARY;
> +                       return 0;
> +               }
> +       }
> +
> +       skb->csum = psum;
> +
> +       if (complete || skb->len <= 76)
> +               return __skb_checksum_complete(skb);
> +
> +       return 0;
> +}
> +
> +static inline __wsum null_compute_pseudo(struct sk_buff *skb, int proto)
> +{
> +       return 0;
> +}
> +
> +/*
> + * Perform checksum validate (init). Note that this is a macro since we only
> + * want to calculate the pseudo header which is an input function if necessary.
> + * First we try to validate without any computation (checksum unnecessary) and
> + * then calculate based on checksum complete calling the function to compute
> + * pseudo header.
> + */
> +#define __skb_checksum_validate(skb, proto, complete,                  \
> +                               zero_okay, check, compute_pseudo)       \
> +({                                                                     \
> +       __sum16 __ret = __skb_checksum_validate_unnecessary(skb,        \
> +                               zero_okay, check);                      \
> +       if (__ret)                                                      \
> +               __ret = __skb_checksum_validate_complete(skb,           \
> +                               complete, compute_pseudo(skb, proto));  \
> +       __ret;                                                          \
> +})

This may or may not yield an actual checksum, which is not obvious from
the comment.

> +#define skb_checksum_init(skb, proto, compute_pseudo)                  \
> +       __skb_checksum_validate(skb, proto, false, false, 0, compute_pseudo)
> +
> +#define skb_checksum_init_zero_check(skb, proto, check, compute_pseudo)        \
> +       __skb_checksum_validate(skb, proto, false, true, check, compute_pseudo)
> +
> +#define skb_checksum_validate(skb, proto, compute_pseudo)              \
> +       __skb_checksum_validate(skb, proto, true, false, 0, compute_pseudo)
> +
> +#define skb_checksum_validate_zero_check(skb, proto, check,            \
> +                                        compute_pseudo)                \
> +       __skb_checksum_validate_(skb, proto, true, true, check, compute_pseudo)
> +
> +#define skb_checksum_simple_validate(skb)                              \
> +       __skb_checksum_validate(skb, 0, true, false, 0, null_compute_pseudo)

Don't these deserve comments too?

Ben.

>  #if defined(CONFIG_NF_CONNTRACK) || defined(CONFIG_NF_CONNTRACK_MODULE)
>  void nf_conntrack_destroy(struct nf_conntrack *nfct);
>  static inline void nf_conntrack_put(struct nf_conntrack *nfct)

-- 
Ben Hutchings
The most exhausting thing in life is being insincere. - Anne Morrow Lindberg

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