yep, basically the sk_peer trick that AF_UNIX is already using.
it just seems rather more tricky in the 'real skb' localhost case
because there's no real established trust path we can pass this coupling
of the two sockets over. Netfilter might affect it and deny a localhost
connection. Lifetime rules seem rather tricky as well: either end of the
localhost connection can go away independently so a refcount to the
socket has to be kept. skb->sk might be something to use, but it looks
like a dangerous complication and it would burden the fastpath with an
extra sk reference inc/dec.
... so i'm not implying that any of this is an easy topic to solve (to
me at least :). But fact is that database connections over localhost are
very common on web apps and it is very convenient as well. I use it
myself - AF_UNIX transport is often non-existing in apps and libraries
or is often just an afterthought with limitations - apps tend to
gravitate towards a single API. So i dont think "use AF_UNIX" is an
acceptable answer in this case. I believe we should try to make
localhost transport comparably fast to AF_UNIX.
Ingo
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