udp mpsafe

[Sepherosa Ziehau]

Hi all,

Please review the devel^2 ~ devel^5 (inclusive) at:
http://gitweb.dragonflybsd.org/~sephe/dragonfly.git/shortlog/refs/heads/devel

The modification/accessing to the udbinfo is protected by two mechanism:
1) netisr barrier, which prevents code running in netisr from
accessing udbinfo when the modification is going to happen
2) serializer, which prevents code not running in netisr (e.g. sysctl,
interface detaching) from accessing udbinfo when the modification is
going to happen

1) makes the udp input/output path lock free.

Best Regards,
sephe

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