Hi,

In general hardware devices handle VLAN Tags and checksum/segmentation
offloading together with VLAN offloading.  But, some devices like
vio(4), do no provide the capability of assisted VLAN tag injection.

The following diff introduces a new IFCAP flag.  So, vlan(4) injects an
inline VLAN Tag, but also inherit the offloading capabilities of this
parent device.

bye,
Jan

Index: sbin/ifconfig/ifconfig.8
===================================================================
RCS file: /cvs/src/sbin/ifconfig/ifconfig.8,v
diff -u -p -r1.399 ifconfig.8
--- sbin/ifconfig/ifconfig.8	11 Jan 2024 17:22:04 -0000	1.399
+++ sbin/ifconfig/ifconfig.8	4 Jun 2024 21:22:11 -0000
@@ -294,6 +294,9 @@ tag.
 On transmit, the device can add the
 .Xr vlan 4
 tag.
+.It Sy VLAN_HWOFFLOAD
+On transmit, the device can handle checksum or TSO offload without
+.Sy VLAN_HWTAGGING .
 .It Sy WOL
 The device supports Wake on LAN (WoL).
 .It Sy hardmtu
Index: sbin/ifconfig/ifconfig.c
===================================================================
RCS file: /cvs/src/sbin/ifconfig/ifconfig.c,v
diff -u -p -r1.472 ifconfig.c
--- sbin/ifconfig/ifconfig.c	18 May 2024 02:44:22 -0000	1.472
+++ sbin/ifconfig/ifconfig.c	4 Jun 2024 21:22:11 -0000
@@ -125,7 +125,7 @@
 
 #define HWFEATURESBITS							\
 	"\024\1CSUM_IPv4\2CSUM_TCPv4\3CSUM_UDPv4"			\
-	"\5VLAN_MTU\6VLAN_HWTAGGING\10CSUM_TCPv6"			\
+	"\5VLAN_MTU\6VLAN_HWTAGGING\7VLAN_HWOFFLOAD\10CSUM_TCPv6"	\
 	"\11CSUM_UDPv6\15TSOv4\16TSOv6\17LRO\20WOL"
 
 struct ifencap {
Index: sys/dev/pv/if_vio.c
===================================================================
RCS file: /cvs/src/sys/dev/pv/if_vio.c,v
diff -u -p -r1.37 if_vio.c
--- sys/dev/pv/if_vio.c	4 Jun 2024 09:51:52 -0000	1.37
+++ sys/dev/pv/if_vio.c	4 Jun 2024 21:22:11 -0000
@@ -605,6 +605,7 @@ vio_attach(struct device *parent, struct
 	ifp->if_start = vio_start;
 	ifp->if_ioctl = vio_ioctl;
 	ifp->if_capabilities = IFCAP_VLAN_MTU;
+	ifp->if_capabilities = IFCAP_VLAN_HWOFFLOAD;
 	if (virtio_has_feature(vsc, VIRTIO_NET_F_CSUM))
 		ifp->if_capabilities |= IFCAP_CSUM_TCPv4|IFCAP_CSUM_UDPv4|
 		    IFCAP_CSUM_TCPv6|IFCAP_CSUM_UDPv6;
Index: sys/net/if.h
===================================================================
RCS file: /cvs/src/sys/net/if.h,v
diff -u -p -r1.216 if.h
--- sys/net/if.h	11 Apr 2024 15:08:18 -0000	1.216
+++ sys/net/if.h	4 Jun 2024 21:22:11 -0000
@@ -249,6 +249,7 @@ struct if_status_description {
 #define	IFCAP_CSUM_UDPv4	0x00000004	/* can do IPv4/UDP csum */
 #define	IFCAP_VLAN_MTU		0x00000010	/* VLAN-compatible MTU */
 #define	IFCAP_VLAN_HWTAGGING	0x00000020	/* hardware VLAN tag support */
+#define	IFCAP_VLAN_HWOFFLOAD	0x00000040	/* hw offload w/ inline tag */
 #define	IFCAP_CSUM_TCPv6	0x00000080	/* can do IPv6/TCP checksums */
 #define	IFCAP_CSUM_UDPv6	0x00000100	/* can do IPv6/UDP checksums */
 #define	IFCAP_TSOv4		0x00001000	/* IPv4/TCP segment offload */
Index: sys/net/if_vlan.c
===================================================================
RCS file: /cvs/src/sys/net/if_vlan.c,v
diff -u -p -r1.218 if_vlan.c
--- sys/net/if_vlan.c	23 Dec 2023 10:52:54 -0000	1.218
+++ sys/net/if_vlan.c	4 Jun 2024 21:22:11 -0000
@@ -523,7 +523,7 @@ vlan_up(struct vlan_softc *sc)
 	/*
 	 * Note: In cases like vio(4) and em(4) where the offsets of the
 	 * csum can be freely defined, we could actually do csum offload
-	 * for VLAN and QINQ packets.
+	 * for QINQ packets.
 	 */
 	if (sc->sc_type != ETHERTYPE_VLAN) {
 		/*
@@ -531,10 +531,14 @@ vlan_up(struct vlan_softc *sc)
 		 * ethernet type (0x8100).
 		 */
 		ifp->if_capabilities = 0;
-	} else if (ISSET(ifp0->if_capabilities, IFCAP_VLAN_HWTAGGING)) {
+	} else if (ISSET(ifp0->if_capabilities, IFCAP_VLAN_HWTAGGING) ||
+	    ISSET(ifp0->if_capabilities, IFCAP_VLAN_HWOFFLOAD)) {
 		/*
 		 * Chips that can do hardware-assisted VLAN encapsulation, can
 		 * calculate the correct checksum for VLAN tagged packets.
+		 *
+		 * Hardware which does checksum offloading, but not VLAN tag
+		 * injection, have to set IFCAP_VLAN_HWOFFLOAD.
 		 */
 		ifp->if_capabilities = ifp0->if_capabilities &
 		    (IFCAP_CSUM_MASK | IFCAP_TSOv4 | IFCAP_TSOv6);