git: 590493c14190 - main - if_epair(4): use ether_gen_addr(9) for stable MAC address

The branch main has been updated by ronald:

URL: https://cgit.FreeBSD.org/src/commit/?id=590493c1419092e98f7ad1dcadb886973502341e

commit 590493c1419092e98f7ad1dcadb886973502341e
Author:     Ronald Klop <ronald@FreeBSD.org>
AuthorDate: 2025-07-03 16:33:03 +0000
Commit:     Ronald Klop <ronald@FreeBSD.org>
CommitDate: 2025-08-05 14:53:04 +0000

    if_epair(4): use ether_gen_addr(9) for stable MAC address
    
    Before this change epair interfaces get a random MAC. This does
    not help dhcp/dyndns when an epair gets destroyed/recreated
    after restart of a jail.
    
    With this change:
    $ sysctl net.link.epair.ether_gen_addr=0
    $ ifconfig epair8 create > /dev/null; ifconfig epair8a | grep ether; ifconfig epair8b | grep ether; ifconfig epair8a destroy
            ether 02:cb:78:56:e4:0a
            ether 02:cb:78:56:e4:0b
    $ ifconfig epair8 create > /dev/null; ifconfig epair8a | grep ether; ifconfig epair8b | grep ether; ifconfig epair8a destroy
            ether 02:8b:9b:6a:8f:0a
            ether 02:8b:9b:6a:8f:0b
    
    $ sysctl net.link.epair.ether_gen_addr=1
    $ ifconfig epair8 create > /dev/null; ifconfig epair8a | grep ether; ifconfig epair8b | grep ether; ifconfig epair8a destroy
            ether 58:9c:fc:10:2b:b4
            ether 58:9c:fc:00:39:10
    $ ifconfig epair8 create > /dev/null; ifconfig epair8a | grep ether; ifconfig epair8b | grep ether; ifconfig epair8a destroy
            ether 58:9c:fc:10:2b:b4
            ether 58:9c:fc:00:39:10
    
    A follow up commit will change the default to 1 in main.
    
    Approved by:    bz,ivy,kp
    MFC after:      2 weeks
    Relnotes:       yes
    Differential Revision: https://reviews.freebsd.org/D51157
---
 sys/net/if_epair.c | 35 +++++++++++++++++++++++++++++++----
 1 file changed, 31 insertions(+), 4 deletions(-)

diff --git a/sys/net/if_epair.c b/sys/net/if_epair.c
index 7051e31565d4..4d35584925a1 100644
--- a/sys/net/if_epair.c
+++ b/sys/net/if_epair.c
@@ -58,6 +58,7 @@
 #include <sys/smp.h>
 #include <sys/socket.h>
 #include <sys/sockio.h>
+#include <sys/sysctl.h>
 #include <sys/taskqueue.h>
 
 #include <net/bpf.h>
@@ -97,6 +98,15 @@ static unsigned int next_index = 0;
 #define	EPAIR_LOCK()			mtx_lock(&epair_n_index_mtx)
 #define	EPAIR_UNLOCK()			mtx_unlock(&epair_n_index_mtx)
 
+SYSCTL_DECL(_net_link);
+static SYSCTL_NODE(_net_link, OID_AUTO, epair, CTLFLAG_RW | CTLFLAG_MPSAFE, 0,
+	"Pair of virtual cross-over connected Ethernet-like interfaces");
+
+static bool use_ether_gen_addr = false;
+SYSCTL_BOOL(_net_link_epair, OID_AUTO, ether_gen_addr, CTLFLAG_RWTUN,
+	&use_ether_gen_addr, false,
+	"Generate MAC with FreeBSD OUI using ether_gen_addr(9)");
+
 struct epair_softc;
 struct epair_queue {
 	struct mtx		 mtx;
@@ -495,6 +505,17 @@ epair_clone_match(struct if_clone *ifc, const char *name)
 	return (1);
 }
 
+static void
+epair_generate_mac_byname(struct epair_softc *sc, uint8_t eaddr[])
+{
+	struct ether_addr gen_eaddr;
+	int i;
+
+	ether_gen_addr_byname(if_name(sc->ifp), &gen_eaddr);
+	for (i = 0; i < ETHER_ADDR_LEN; i++)
+		eaddr[i] = gen_eaddr.octet[i];
+}
+
 static void
 epair_clone_add(struct if_clone *ifc, struct epair_softc *scb)
 {
@@ -502,9 +523,12 @@ epair_clone_add(struct if_clone *ifc, struct epair_softc *scb)
 	uint8_t eaddr[ETHER_ADDR_LEN];	/* 00:00:00:00:00:00 */
 
 	ifp = scb->ifp;
-	/* Copy epairNa etheraddr and change the last byte. */
-	memcpy(eaddr, scb->oifp->if_hw_addr, ETHER_ADDR_LEN);
-	eaddr[5] = 0x0b;
+	if (!use_ether_gen_addr) {
+		/* Copy epairNa etheraddr and change the last byte. */
+		memcpy(eaddr, scb->oifp->if_hw_addr, ETHER_ADDR_LEN);
+		eaddr[5] = 0x0b;
+	} else
+		epair_generate_mac_byname(scb, eaddr);
 	ether_ifattach(ifp, eaddr);
 
 	if_clone_addif(ifc, ifp);
@@ -719,7 +743,10 @@ epair_clone_create(struct if_clone *ifc, char *name, size_t len,
 	/* Finish initialization of interface <n>a. */
 	ifp = sca->ifp;
 	epair_setup_ifp(sca, name, unit);
-	epair_generate_mac(sca, eaddr);
+	if (!use_ether_gen_addr)
+		epair_generate_mac(sca, eaddr);
+	else
+		epair_generate_mac_byname(sca, eaddr);
 
 	ether_ifattach(ifp, eaddr);