TIME_WAIT sockets clog system (part 1)

[Steven M. SchultzY]

Subject: TIME_WAIT sockets clog system (part 1)
Index:	sys/netinet/tcp_subr.c 2.10BSD

Description:
	Sockets in a TIME_WAIT state can constipate the networking
	buffer memory when generated in rapid succession by, for
	example, an "mget" in an ftp session.  If more than a dozen
	or so small files are transferred in rapid succession over
	an ethernet, all the mbufs in the system will be taken up
	by sockets in a TIME_WAIT state (from the socket opened for
	each data transfer).

Repeat-By:
	ftp in to a 2.10.1BSD system, do an "mget *" in a largish
	directory.  note that the transfer will hang/develope problems
	after about a dozen to twenty files.  the 2.10.1BSD system
	has run out of mbufs and will recover in a minute or so (hopefully).

Fix:
	Apply this patch to netinet/tcp_subr.c, this fix implements
	a tcp_drain() function that actually does something (the 
	original 4.3BSD tcp_drain() was a null function).  The other
	half of this fix will follow shortly and consists of a small
	modification to uipc_mbuf to invoke the drain routine at the
	appropriate time.

	The comment in the function pretty much sums the situation up.

*** tcp_subr.c.old	Thu Apr 28 16:22:56 1988
--- tcp_subr.c	Fri Jun  9 13:57:29 1989
***************
*** 251,257 ****
--- 251,279 ----
  
  tcp_drain()
  {
+ 	register struct inpcb *ip, *ipnxt;
+ 	register struct tcpcb *tp;
+ 	int s = splimp();
  
+ 	/*
+ 	 * Search through tcb's and look for TIME_WAIT states to liberate,
+ 	 * these are due to go away soon anyhow and we're short of space or
+  	 * we wouldn't be here...
+ 	 */
+ 	ip = tcb.inp_next;
+ 	if (ip == 0) {
+ 		splx(s);
+ 		return;
+ 	}
+ 	for (; ip != &tcb; ip = ipnxt) {
+ 		ipnxt = ip->inp_next;
+ 		tp = intotcpcb(ip);
+ 		if (tp == 0)
+ 			continue;
+ 		if (tp->t_state == TCPS_TIME_WAIT)
+ 			tcp_close(tp);
+ 	}
+ 	splx(s);
  }
  
  /*