ifnet/mbuf: provide KPI to serialize/restore m->m_pkthdr.rcvif

Supplement ifindex table with generation count and use it to
serialize & restore an ifnet pointer.

Reviewed by:		kp
Differential revision:	https://reviews.freebsd.org/D33266
Fun note:		git show e6abef09187a

(cherry picked from commit e1882428dcbbafd2814d7e17b977a8f686784b39)

1 files changed, 36 insertions, 13 deletions

diff --git a/sys/net/if.c b/sys/net/if.c
index 3b303fe42e99..ff7071cea364 100644
--- a/sys/net/if.c
+++ b/sys/net/if.c
@@ -313,7 +313,10 @@ VNET_DEFINE(struct ifgrouphead, ifg_head);
 /* Table of ifnet by index. */
 static int if_index;
 static int if_indexlim = 8;
-static struct ifnet **ifindex_table;
+static struct ifindex_entry {
+	struct ifnet	*ife_ifnet;
+	uint16_t	ife_gencnt;
+} *ifindex_table;
 
 SYSCTL_NODE(_net_link_generic, IFMIB_SYSTEM, system,
     CTLFLAG_RW | CTLFLAG_MPSAFE, 0,
@@ -325,8 +328,8 @@ sysctl_ifcount(SYSCTL_HANDLER_ARGS)
 
 	IFNET_RLOCK();
 	for (int i = 1; i <= if_index; i++)
-		if (ifindex_table[i] != NULL &&
-		    ifindex_table[i]->if_vnet == curvnet)
+		if (ifindex_table[i].ife_ifnet != NULL &&
+		    ifindex_table[i].ife_ifnet->if_vnet == curvnet)
 			rv = i;
 	IFNET_RUNLOCK();
 
@@ -370,7 +373,7 @@ ifnet_byindex(u_int idx)
 	if (__predict_false(idx > if_index))
 		return (NULL);
 
-	ifp = ck_pr_load_ptr(&ifindex_table[idx]);
+	ifp = ck_pr_load_ptr(&ifindex_table[idx].ife_ifnet);
 
 	if (curvnet != NULL && ifp != NULL && ifp->if_vnet != curvnet)
 		ifp = NULL;
@@ -391,6 +394,24 @@ ifnet_byindex_ref(u_int idx)
 	return (ifp);
 }
 
+struct ifnet *
+ifnet_byindexgen(uint16_t idx, uint16_t gen)
+{
+	struct ifnet *ifp;
+
+	NET_EPOCH_ASSERT();
+
+	if (__predict_false(idx > if_index))
+		return (NULL);
+
+	ifp = ck_pr_load_ptr(&ifindex_table[idx].ife_ifnet);
+
+	if (ifindex_table[idx].ife_gencnt == gen)
+		return (ifp);
+	else
+		return (NULL);
+}
+
 /*
  * Network interface utility routines.
  *
@@ -557,13 +578,13 @@ if_alloc_domain(u_char type, int numa_domain)
 	 * next slot.
 	 */
 	for (idx = 1; idx <= if_index; idx++) {
-		if (ifindex_table[idx] == NULL)
+		if (ifindex_table[idx].ife_ifnet == NULL)
 			break;
 	}
 
 	/* Catch if_index overflow. */
 	if (idx >= if_indexlim) {
-		struct ifnet **new, **old;
+		struct ifindex_entry *new, *old;
 		int newlim;
 
 		newlim = if_indexlim * 2;
@@ -579,7 +600,8 @@ if_alloc_domain(u_char type, int numa_domain)
 		if_index = idx;
 
 	ifp->if_index = idx;
-	ck_pr_store_ptr(&ifindex_table[idx], ifp);
+	ifp->if_idxgen = ifindex_table[idx].ife_gencnt;
+	ck_pr_store_ptr(&ifindex_table[idx].ife_ifnet, ifp);
 	IFNET_WUNLOCK();
 
 	return (ifp);
@@ -654,9 +676,10 @@ if_free(struct ifnet *ifp)
 	 * virtualized and interface would outlive the vnet.
 	 */
 	IFNET_WLOCK();
-	MPASS(ifindex_table[ifp->if_index] == ifp);
-	ck_pr_store_ptr(&ifindex_table[ifp->if_index], NULL);
-	while (if_index > 0 && ifindex_table[if_index] == NULL)
+	MPASS(ifindex_table[ifp->if_index].ife_ifnet == ifp);
+	ck_pr_store_ptr(&ifindex_table[ifp->if_index].ife_ifnet, NULL);
+	ifindex_table[ifp->if_index].ife_gencnt++;
+	while (if_index > 0 && ifindex_table[if_index].ife_ifnet == NULL)
 		if_index--;
 	IFNET_WUNLOCK();
 
@@ -805,7 +828,7 @@ if_attach_internal(struct ifnet *ifp, bool vmove)
 	struct sockaddr_dl *sdl;
 	struct ifaddr *ifa;
 
-	MPASS(ifindex_table[ifp->if_index] == ifp);
+	MPASS(ifindex_table[ifp->if_index].ife_ifnet == ifp);
 
 #ifdef VIMAGE
 	ifp->if_vnet = curvnet;
@@ -4494,8 +4517,8 @@ if_show_ifnet(struct ifnet *ifp)
 	IF_DB_PRINTF("%d", if_dunit);
 	IF_DB_PRINTF("%s", if_description);
 	IF_DB_PRINTF("%u", if_index);
+	IF_DB_PRINTF("%d", if_idxgen);
 	IF_DB_PRINTF("%u", if_refcount);
-	IF_DB_PRINTF("%d", if_index_reserved);
 	IF_DB_PRINTF("%p", if_softc);
 	IF_DB_PRINTF("%p", if_l2com);
 	IF_DB_PRINTF("%p", if_llsoftc);
@@ -4550,7 +4573,7 @@ DB_SHOW_ALL_COMMAND(ifnets, db_show_all_ifnets)
 	u_short idx;
 
 	for (idx = 1; idx <= if_index; idx++) {
-		ifp = ifindex_table[idx];
+		ifp = ifindex_table[idx].ife_ifnet;
 		if (ifp == NULL)
 			continue;
 		db_printf( "%20s ifp=%p\n", ifp->if_xname, ifp);