Tom Herbert <t...@herbertland.com> wrote:
> This is used to get the skb->hash and then perturb it for a local use.
>
> Signed-off-by: Tom Herbert <t...@herbertland.com>
> ---
> include/linux/skbuff.h | 15 +++++++++++++++
> 1 file changed, 15 insertions(+)
>
> diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
> index 66e374d..b706889 100644
> --- a/include/linux/skbuff.h
> +++ b/include/linux/skbuff.h
> @@ -17,6 +17,7 @@
> #include <linux/kernel.h>
> #include <linux/kmemcheck.h>
> #include <linux/compiler.h>
> +#include <linux/jhash.h>
> #include <linux/time.h>
> #include <linux/bug.h>
> #include <linux/cache.h>
> @@ -927,6 +928,20 @@ static inline __u32 skb_get_hash(struct sk_buff *skb)
> return skb->hash;
> }
>
> +static inline __u32 skb_get_hash_perturb(struct sk_buff *skb,
> + u32 perturb)
> +{
> + u32 hash = skb_get_hash(skb);
> +
> + if (likely(hash)) {
> + hash = jhash_1word((__force __u32) hash, perturb);
Whats this perturb for?
perturb is supposed to make sure that if you have
flow1, flow2 where hash(flow1, perturb) == hash(flow2, perturb)
the collision will be temporary and go away once perturb changes.
If you perturb after hashing, such collision is permanent.
So I think this either should flow_dissect + hash in software,
or just use skb_get_hash without perturb.
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