setsockopt(fd, SOL_SOCKET, SO_SNDBUF.....) still takes no effect after connect() ?

tclwp · 04-16-2010, 06:06 AM

Hi,guys
Now I learned that on Solaris, we can set TCP_NODELAY,SO_RCVBUF, SO_SNDBUF by setsockopt() any time before or after calling connect() or listen() , if the buffer size we need is greater than default(or last) size，the setsockopt() will take affect .
But on LINUX, man 7 tcp tell us: On individual connections, the socket buffer size must be set prior to the listen(2) or connect(2) calls in order to have it take effect.
Does current newly LINUX kernel keeps this limitation as the manual said ?

tclwp · 04-17-2010, 03:32 AM

I have read some linux kernel source (net/ipv4/tcp_input.c) ,and determine that :
tcp_init_buffer_space()->tcp_fixup_sndbuf()

so , on newly linux kernel, you can call setsockopt(fd, SOL_SOCKET, SO_SNDBUF...) after the socket changed to ESTABLISHED state, and
sk->sk_sndbuf is modified by setsockopt() indeed, but tcp_fixup_sndbuf() was not called, so here setsockopt(fd, SOL_SOCKET, SO_SNDBUF...) takes no effect