From: Timo Mirau <tmirau@genua.de>
Subject: Re: bridge(4): use vlan hardware tagging
To: Jan Klemkow <jan@openbsd.org>
Cc: <tech@openbsd.org>
Date: Thu, 14 Aug 2025 12:20:53 +0200

Hello Jan,

Am Mon, Aug 04, 2025 at 12:02:30PM +0200 schrieb Jan Klemkow:
> This diff adds the use of VLAN hardware tagging in bridge(4) and
> vether(4) similar to veb(4).

I've had a look at your diff. I simplified it by calling bridge_offload
at the beginning of bridge_ifenqueue. I've tested this diff with vlan(4),
vether(4) and ix(4) interfaces. I disabled the IFCAP_VLAN_HWTAGGING flag
in the ix(4) source code to test the vlan inject call path. 
It worked as expected in my setup.

regards 
Timo

Index: net/if_bridge.c
===================================================================
RCS file: /cvs/src/sys/net/if_bridge.c,v
diff -u -p -r1.376 if_bridge.c
--- net/if_bridge.c	7 Jul 2025 02:28:50 -0000	1.376
+++ net/if_bridge.c	13 Aug 2025 12:44:19 -0000
@@ -798,6 +798,24 @@ bridge_stop(struct bridge_softc *sc)
 	bridge_rtflush(sc, IFBF_FLUSHDYN);
 }
 
+struct mbuf *
+bridge_offload(struct ifnet *ifp, struct mbuf *m)
+{
+#if NVLAN > 0
+	/*
+	 * If the underlying interface has no VLAN hardware tagging support,
+	 * inject one in software.
+	 */
+	if (ISSET(m->m_flags, M_VLANTAG) &&
+	    !ISSET(ifp->if_capabilities, IFCAP_VLAN_HWTAGGING)) {
+		m = vlan_inject(m, ETHERTYPE_VLAN, m->m_pkthdr.ether_vtag);
+		if (m == NULL)
+			return NULL;
+	}
+#endif
+	return m;
+}
+
 /*
  * Send output from the bridge.  The mbuf has the ethernet header
  * already attached.  We must enqueue or free the mbuf before exiting.
@@ -1170,18 +1188,6 @@ bridge_process(struct ifnet *ifp, struct
 	if (m->m_pkthdr.len < sizeof(*eh))
 		goto bad;
 
-#if NVLAN > 0
-	/*
-	 * If the underlying interface removed the VLAN header itself,
-	 * add it back.
-	 */
-	if (ISSET(m->m_flags, M_VLANTAG)) {
-		m = vlan_inject(m, ETHERTYPE_VLAN, m->m_pkthdr.ether_vtag);
-		if (m == NULL)
-			goto bad;
-	}
-#endif
-
 #if NBPFILTER > 0
 	if_bpf = brifp->if_bpf;
 	if (if_bpf)
@@ -1915,21 +1921,29 @@ bridge_ifenqueue(struct ifnet *brifp, st
 {
 	int error, len;
 
+	if ((m = bridge_offload(ifp, m)) == NULL) {
+		error = ENOBUFS;
+		goto err;
+	}
+
 	/* Loop prevention. */
 	m->m_flags |= M_PROTO1;
 
 	len = m->m_pkthdr.len;
 
 	error = if_enqueue(ifp, m);
-	if (error) {
-		brifp->if_oerrors++;
-		return (error);
-	}
+	if (error) 
+		goto err; 
+	
 
 	brifp->if_opackets++;
 	brifp->if_obytes += len;
 
 	return (0);
+
+ err:
+	brifp->if_oerrors++;
+	return (error);
 }
 
 void
Index: net/if_vether.c
===================================================================
RCS file: /cvs/src/sys/net/if_vether.c,v
diff -u -p -r1.37 if_vether.c
--- net/if_vether.c	7 Jul 2025 02:28:50 -0000	1.37
+++ net/if_vether.c	8 Aug 2025 14:11:52 -0000
@@ -27,6 +27,7 @@
 #include <netinet/in.h>
 #include <netinet/if_ether.h>
 
+#include "vlan.h"
 #include "bpfilter.h"
 #if NBPFILTER > 0
 #include <net/bpf.h>
@@ -85,6 +86,9 @@ vether_clone_create(struct if_clone *ifc
 
 	ifp->if_hardmtu = ETHER_MAX_HARDMTU_LEN;
 	ifp->if_capabilities = IFCAP_VLAN_MTU;
+#if NVLAN > 0
+	ifp->if_capabilities |= IFCAP_VLAN_HWTAGGING;
+#endif
 	ifp->if_xflags = IFXF_CLONED | IFXF_MPSAFE;
 
 	ifmedia_init(&sc->sc_media, 0, vether_media_change,