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@

diff --git a/share/man/man9/mbuf.9 b/share/man/man9/mbuf.9
index 9ea87e2..75cf89e 100644 (file)
--- 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 dfca8c1..3d8082b 100644 (file)
--- 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