[PATCH nft 0/3] meta: random match for statistic sampling

[Florian Westphal <fw@strlen.de>]

Replacement for iptables -m statistic 'random' mode.
I added it to meta match even though its not directly related to an skb
member. We already have cpu match which isn't related to skb either and
adding a new expression just for this seemed overkill.

If you'd rather like a new prandom expression just let me know and
I can rework it.

There is also a libnftnl patch but its only so that debug output
displays 'meta prandom' rather than 'meta unknown'.

Result after several minutes of constant flooding:

counter packets 2961796882 bytes 248790938088
meta random <= 0.900000000 counter packets 2665649546 bytes 223914561864
meta random <= 0.500000000 counter packets 1480856860 bytes 124391976240
meta random <= 0.100000000 counter packets 296190072 bytes 24879966048
meta random <= 0.010000000 counter packets 29618610 bytes 2487963240
meta random <= 0.001000000 counter packets 2963660 bytes 248947440
meta random <= 0.000100000 counter packets 295486 bytes 24820824
meta random <= 0.000010000 counter packets 29450 bytes 2473800
meta random <= 0.000001000 counter packets 2911 bytes 244524
meta random <= 0.000000100 counter packets 267 bytes 22428
meta random <= 0.000000010 counter packets 26 bytes 2184
meta random <= 0.000000001 counter packets 4 bytes 336

... so it seems to work as intended.

Let me know if you spot any issues with current approach.

Kernel part only does '*dest = prandom_u32()', I'll submit it once
I know that this approach is deemed sane.

Thanks!