>	i am happy to remove "max_linkhdr + hdrlen + len <= MCLBYTES" line.
>	if the line gets removed the "always-copy" behavior will go away.

	and if you really want to make sure there'll be no copy in the function,
	you can get rid of "if (len <= M_TRAILINGSPACE)" case.
	my proposed diff attached.

itojun


Index: tcp_output.c
===================================================================
RCS file: /cvsroot/syssrc/sys/netinet/tcp_output.c,v
retrieving revision 1.78
diff -u -r1.78 tcp_output.c
--- tcp_output.c	2002/03/01 22:54:09	1.78
+++ tcp_output.c	2002/04/27 00:17:04
@@ -384,9 +384,7 @@
 	m->m_data -= hdrlen;
 #else
 	MGETHDR(m, M_DONTWAIT, MT_HEADER);
-	if (m != NULL &&
-	    (max_linkhdr + hdrlen > MHLEN ||
-	     max_linkhdr + hdrlen + len <= MCLBYTES)) {
+	if (m != NULL && max_linkhdr + hdrlen > MHLEN) {
 		MCLGET(m, M_DONTWAIT);
 		if ((m->m_flags & M_EXT) == 0) {
 			m_freem(m);
@@ -397,7 +395,7 @@
 		return (ENOBUFS);
 	m->m_data += max_linkhdr;
 	m->m_len = hdrlen;
-	if (len <= M_TRAILINGSPACE(m)) {
+	if (0) {
 		m_copydata(so->so_snd.sb_mb, off, (int) len,
 		    mtod(m, caddr_t) + hdrlen);
 		m->m_len += len;