From 0ce39dfb1b1eb601eab9b925dffcdef4dc14fa7d Mon Sep 17 00:00:00 2001
From: dlg <dlg@openbsd.org>
Date: Thu, 8 Oct 2015 11:36:15 +0000
Subject: [PATCH] steal some padding in mbuf pkthdrs to store a flow id.

the flowid roughly identifies a flow or connection that the mbuf
is a part of, and can be used instead of hashing contents of the
packet (like src+dst mac and ip addresses) to decide which path a
packet should take.

ok mpi@ mikeb@ sthen@
---
 share/man/man9/mbuf.9 | 21 ++++++++++++++++++---
 sys/sys/mbuf.h        |  8 ++++++--
 2 files changed, 24 insertions(+), 5 deletions(-)

diff --git a/share/man/man9/mbuf.9 b/share/man/man9/mbuf.9
index 9ea87e2672f..75cf89ecc14 100644
--- a/share/man/man9/mbuf.9
+++ b/share/man/man9/mbuf.9
@@ -1,4 +1,4 @@
-.\"     $OpenBSD: mbuf.9,v 1.89 2015/09/21 11:30:50 mpi Exp $
+.\"     $OpenBSD: mbuf.9,v 1.90 2015/10/08 11:36:15 dlg Exp $
 .\"
 .\" Copyright (c) 2001 Jean-Jacques Bernard-Gundol <jjbg@openbsd.org>
 .\" All rights reserved.
@@ -25,7 +25,7 @@
 .\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
 .\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 .\"
-.Dd $Mdocdate: September 21 2015 $
+.Dd $Mdocdate: October 8 2015 $
 .Dt MBUF 9
 .Os
 .Sh NAME
@@ -122,7 +122,7 @@ struct pkthdr {
 	SLIST_HEAD(packet_tags, m_tag) tags;
 	int			 len;
 	u_int16_t		 tagsset;
-	u_int16_t		 pad;
+	u_int16_t		 flowid;
 	u_int16_t		 csum_flags;
 	u_int16_t		 ether_vtag;
 	u_int			 ph_rtableid;
@@ -335,6 +335,21 @@ ICMP/ICMPv6 checksum verified.
 ICMP/ICMPv6 checksum bad.
 .El
 .Pp
+The
+.Fa m_pkthdr.flowid
+variable can contain a low resolution (15 bit) classification of a
+flow or connection that the current mbuf is part of.
+If the flowid is valid, it may be used as an alternative to hashing
+the packets content to pick between different paths for the traffic.
+The following masks can be ORed with the flowid:
+.Pp
+.Bl -tag -compact -offset indent -width XXXXXXXXXXXXXXXXXX
+.It Dv M_FLOWID_VALID
+The flow id has been set.
+.It Dv M_FLOWID_MASK
+The flow id.
+.El
+.Pp
 When only M_EXT flag is set, an external storage buffer is being used to
 hold the data, which is no longer stored in the mbuf.
 The data part of the mbuf has now the following elements:
diff --git a/sys/sys/mbuf.h b/sys/sys/mbuf.h
index dfca8c1b4cc..3d8082b35e1 100644
--- a/sys/sys/mbuf.h
+++ b/sys/sys/mbuf.h
@@ -1,4 +1,4 @@
-/*	$OpenBSD: mbuf.h,v 1.196 2015/08/14 05:25:29 dlg Exp $	*/
+/*	$OpenBSD: mbuf.h,v 1.197 2015/10/08 11:36:15 dlg Exp $	*/
 /*	$NetBSD: mbuf.h,v 1.19 1996/02/09 18:25:14 christos Exp $	*/
 
 /*
@@ -125,7 +125,7 @@ struct	pkthdr {
 	SLIST_HEAD(packet_tags, m_tag) tags;	/* list of packet tags */
 	int			 len;		/* total packet length */
 	u_int16_t		 tagsset;	/* mtags attached */
-	u_int16_t		 pad;
+	u_int16_t		 flowid;	/* pseudo unique flow id */
 	u_int16_t		 csum_flags;	/* checksum flags */
 	u_int16_t		 ether_vtag;	/* Ethernet 802.1p+Q vlan tag */
 	u_int			 ph_rtableid;	/* routing table id */
@@ -237,6 +237,10 @@ struct mbuf {
 #define	MT_CONTROL	6	/* extra-data protocol message */
 #define	MT_OOBDATA	7	/* expedited data  */
 
+/* flowid field */
+#define M_FLOWID_VALID	0x8000	/* is the flowid set */
+#define M_FLOWID_MASK	0x7fff	/* flow id to map to path */
+
 /* flags to m_get/MGET */
 #define	M_DONTWAIT	M_NOWAIT
 #define	M_WAIT		M_WAITOK
-- 
2.20.1