It turns out that too many drivers are not only parsing the L2/3/4

headers for TSO but also for generic checksum offloading.  Ideally we
would only have one common function shared amongst all drivers, and
perhaps when updating them for IPv6 we should introduce that.
Eventually we should provide the meta information along with mbufs to
avoid (re-)parsing entirely.

To not break IPv6 (checksums and offload) and to be able to MFC the
changes without risking to hurt 3rd party drivers, duplicate the v4
framework, as other OSes have done as well.

Introduce interface capability flags for TX/RX checksum offload with
IPv6, to allow independent toggling (where possible).  Add CSUM_*_IPV6
flags for UDP/TCP over IPv6, and reserve further for SCTP, and IPv6
fragmentation.  Define CSUM_DELAY_DATA_IPV6 as we do for legacy IP and
add an alias for CSUM_DATA_VALID_IPV6.

This pretty much brings IPv6 handling in line with IPv4.
TSO is still handled in a different way and not via if_hwassist.

Update ifconfig to allow (un)setting of the new capability flags.
Update loopback to announce the new capabilities and if_hwassist flags.

Individual driver updates will have to follow, as will SCTP.

Reported by:	gallatin, dim, ..
Reviewed by:	gallatin (glanced at?)
MFC after:	3 days
X-MFC with:	r235961,235959,235958

2 files changed, 25 insertions, 6 deletions

diff --git a/sys/net/if.h b/sys/net/if.h
index 47292cb..05be58f 100644
--- a/sys/net/if.h
+++ b/sys/net/if.h
@@ -230,6 +230,10 @@ struct if_data {
 #define	IFCAP_VLAN_HWTSO	0x40000 /* can do IFCAP_TSO on VLANs */
 #define	IFCAP_LINKSTATE		0x80000 /* the runtime link state is dynamic */
 #define	IFCAP_NETMAP		0x100000 /* netmap mode supported/enabled */
+#define	IFCAP_RXCSUM_IPV6	0x200000  /* can offload checksum on IPv6 RX */
+#define	IFCAP_TXCSUM_IPV6	0x400000  /* can offload checksum on IPv6 TX */
+
+#define IFCAP_HWCSUM_IPV6	(IFCAP_RXCSUM_IPV6 | IFCAP_TXCSUM_IPV6)
 
 #define IFCAP_HWCSUM	(IFCAP_RXCSUM | IFCAP_TXCSUM)
 #define	IFCAP_TSO	(IFCAP_TSO4 | IFCAP_TSO6)
diff --git a/sys/net/if_loop.c b/sys/net/if_loop.c
index 80e0eea..23eb450 100644
--- a/sys/net/if_loop.c
+++ b/sys/net/if_loop.c
@@ -92,7 +92,9 @@
 #endif
 
 #define	LO_CSUM_FEATURES	(CSUM_IP | CSUM_TCP | CSUM_UDP | CSUM_SCTP)
-#define	LO_CSUM_SET		(CSUM_DATA_VALID | CSUM_PSEUDO_HDR | \
+#define	LO_CSUM_FEATURES6	(CSUM_TCP_IPV6 | CSUM_UDP_IPV6 | CSUM_SCTP)
+#define	LO_CSUM_SET		(CSUM_DATA_VALID | CSUM_DATA_VALID_IPV6 | \
+				    CSUM_PSEUDO_HDR | \
 				    CSUM_IP_CHECKED | CSUM_IP_VALID | \
 				    CSUM_SCTP_VALID)
 
@@ -143,8 +145,9 @@ lo_clone_create(struct if_clone *ifc, int unit, caddr_t params)
 	ifp->if_ioctl = loioctl;
 	ifp->if_output = looutput;
 	ifp->if_snd.ifq_maxlen = ifqmaxlen;
-	ifp->if_capabilities = ifp->if_capenable = IFCAP_HWCSUM;
-	ifp->if_hwassist = LO_CSUM_FEATURES;
+	ifp->if_capabilities = ifp->if_capenable =
+	    IFCAP_HWCSUM | IFCAP_HWCSUM_IPV6;
+	ifp->if_hwassist = LO_CSUM_FEATURES | LO_CSUM_FEATURES6;
 	if_attach(ifp);
 	bpfattach(ifp, DLT_NULL, sizeof(u_int32_t));
 	if (V_loif == NULL)
@@ -247,12 +250,19 @@ looutput(struct ifnet *ifp, struct mbuf *m, struct sockaddr *dst,
 #if 1	/* XXX */
 	switch (dst->sa_family) {
 	case AF_INET:
-	case AF_INET6:
 		if (ifp->if_capenable & IFCAP_RXCSUM) {
 			m->m_pkthdr.csum_data = 0xffff;
 			m->m_pkthdr.csum_flags = LO_CSUM_SET;
 		}
 		m->m_pkthdr.csum_flags &= ~LO_CSUM_FEATURES;
+		break;
+	case AF_INET6:
+		if (ifp->if_capenable & IFCAP_RXCSUM_IPV6) {
+			m->m_pkthdr.csum_data = 0xffff;
+			m->m_pkthdr.csum_flags = LO_CSUM_SET;
+		}
+		m->m_pkthdr.csum_flags &= ~LO_CSUM_FEATURES6;
+		break;
 	case AF_IPX:
 	case AF_APPLETALK:
 		break;
@@ -436,10 +446,15 @@ loioctl(struct ifnet *ifp, u_long cmd, caddr_t data)
 			ifp->if_capenable ^= IFCAP_RXCSUM;
 		if ((mask & IFCAP_TXCSUM) != 0)
 			ifp->if_capenable ^= IFCAP_TXCSUM;
+		if ((mask & IFCAP_RXCSUM_IPV6) != 0)
+			ifp->if_capenable ^= IFCAP_RXCSUM_IPV6;
+		if ((mask & IFCAP_TXCSUM_IPV6) != 0)
+			ifp->if_capenable ^= IFCAP_TXCSUM_IPV6;
+		ifp->if_hwassist = 0;
 		if (ifp->if_capenable & IFCAP_TXCSUM)
 			ifp->if_hwassist = LO_CSUM_FEATURES;
-		else
-			ifp->if_hwassist = 0;
+		if (ifp->if_capenable & IFCAP_TXCSUM_IPV6)
+			ifp->if_hwassist |= LO_CSUM_FEATURES6;
 		break;
 
 	default: