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Keepalive question

Hello

I am bothered with very simple situaction. Lets say we have a TCP connection:

S1 <----> S2

Lets assume that this connection is using blocking sockets. and that
both hosts: s1 and s2 are using SO_KEEPALIVE. If they both are not
using this connection then the kernel? is sending packets with no data
to keep connection alive.

I have marked "the kernel?" because I am not sure who does this. I
think its the kernel but I am not sure.

What would happen if only one of them would use keepalive? Could that
empty packet break the loop inside of sk_busy_loop function and return
empty data to the application layer? Or would that while loop body
just re-run?

Hehe is the code (the while loop starts on 128 line)
http://lxr.oss.org.cn/source/include/net/busy_poll.h?a=arm#L95