git: 3bb09e6b1930 - stable/14 - ethernet: Set maximum Ethernet header length based on the capability IFCAP_VLAN_MTU

The branch stable/14 has been updated by zlei:

URL: https://cgit.FreeBSD.org/src/commit/?id=3bb09e6b1930b58d9d92aa3f28515114631a1d6b

commit 3bb09e6b1930b58d9d92aa3f28515114631a1d6b
Author:     Zhenlei Huang <zlei@FreeBSD.org>
AuthorDate: 2025-06-21 15:12:29 +0000
Commit:     Zhenlei Huang <zlei@FreeBSD.org>
CommitDate: 2025-07-07 10:05:10 +0000

    ethernet: Set maximum Ethernet header length based on the capability IFCAP_VLAN_MTU
    
    Lots of Ethernet drivers fix the header length after ether_ifattach().
    Well since the net stack can conclude it based on the capability
    IFCAP_VLAN_MTU, let the net stack do it rather than individual drivers.
    
    Reviewed by:    markj, glebius
    MFC after:      2 weeks
    Differential Revision:  https://reviews.freebsd.org/D50846
    
    (cherry picked from commit 6ce8fd1978a9526ff0dc02ed98ef797f9154ec1f)
---
 sys/net/if_ethersubr.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/sys/net/if_ethersubr.c b/sys/net/if_ethersubr.c
index 9210f1378666..baf3a27c2e7e 100644
--- a/sys/net/if_ethersubr.c
+++ b/sys/net/if_ethersubr.c
@@ -997,7 +997,8 @@ ether_ifattach(struct ifnet *ifp, const u_int8_t *lla)
 	struct sockaddr_dl *sdl;
 
 	ifp->if_addrlen = ETHER_ADDR_LEN;
-	ifp->if_hdrlen = ETHER_HDR_LEN;
+	ifp->if_hdrlen = (ifp->if_capabilities & IFCAP_VLAN_MTU) != 0 ?
+	    ETHER_HDR_LEN + ETHER_VLAN_ENCAP_LEN : ETHER_HDR_LEN;
 	ifp->if_mtu = ETHERMTU;
 	if_attach(ifp);
 	ifp->if_output = ether_output;