Add IFNET_HOLD reserved pointer value for the ifindex ifnet array,

which allows an index to be reserved for an ifnet without making
the ifnet available for management operations.  Use this in if_alloc()
while the ifnet lock is released between initial index allocation and
completion of ifnet initialization.

Add ifindex_free() to centralize the implementation of releasing an
ifindex value.  Use in if_free() and if_vmove(), as well as when
releasing a held index in if_alloc().

Reviewed by:	bz
MFC after:	3 days

1 files changed, 39 insertions, 13 deletions

diff --git a/sys/net/if.c b/sys/net/if.c
index f2f1c4f..36c0d03 100644
--- a/sys/net/if.c
+++ b/sys/net/if.c
@@ -175,6 +175,13 @@ int	ifqmaxlen = IFQ_MAXLEN;
 struct rwlock ifnet_rwlock;
 struct sx ifnet_sxlock;
 
+/*
+ * The allocation of network interfaces is a rather non-atomic affair; we
+ * need to select an index before we are ready to expose the interface for
+ * use, so will use this pointer value to indicate reservation.
+ */
+#define	IFNET_HOLD	(void *)(uintptr_t)(-1)
+
 static	if_com_alloc_t *if_com_alloc[256];
 static	if_com_free_t *if_com_free[256];
 
@@ -193,6 +200,8 @@ ifnet_byindex_locked(u_short idx)
 
 	if (idx > V_if_index)
 		return (NULL);
+	if (V_ifindex_table[idx].ife_ifnet == IFNET_HOLD)
+		return (NULL);
 	return (V_ifindex_table[idx].ife_ifnet);
 }
 
@@ -228,18 +237,18 @@ ifnet_byindex_ref(u_short idx)
  * failure.
  */
 static int
-ifindex_alloc(u_short *idxp)
+ifindex_alloc_locked(u_short *idxp)
 {
 	u_short idx;
 
 	IFNET_WLOCK_ASSERT();
 
 	/*
-	 * Try to find an empty slot below if_index.  If we fail, take the
+	 * Try to find an empty slot below V_if_index.  If we fail, take the
 	 * next slot.
 	 */
 	for (idx = 1; idx <= V_if_index; idx++) {
-		if (ifnet_byindex_locked(idx) == NULL)
+		if (V_ifindex_table[idx].ife_ifnet == NULL)
 			break;
 	}
 
@@ -255,6 +264,27 @@ ifindex_alloc(u_short *idxp)
 }
 
 static void
+ifindex_free_locked(u_short idx)
+{
+
+	IFNET_WLOCK_ASSERT();
+
+	V_ifindex_table[idx].ife_ifnet = NULL;
+	while (V_if_index > 0 &&
+	    V_ifindex_table[V_if_index].ife_ifnet == NULL)
+		V_if_index--;
+}
+
+static void
+ifindex_free(u_short idx)
+{
+
+	IFNET_WLOCK();
+	ifindex_free_locked(idx);
+	IFNET_WUNLOCK();
+}
+
+static void
 ifnet_setbyindex_locked(u_short idx, struct ifnet *ifp)
 {
 
@@ -370,11 +400,12 @@ if_alloc(u_char type)
 
 	ifp = malloc(sizeof(struct ifnet), M_IFNET, M_WAITOK|M_ZERO);
 	IFNET_WLOCK();
-	if (ifindex_alloc(&idx) != 0) {
+	if (ifindex_alloc_locked(&idx) != 0) {
 		IFNET_WUNLOCK();
 		free(ifp, M_IFNET);
 		return (NULL);
 	}
+	ifnet_setbyindex_locked(idx, IFNET_HOLD);
 	IFNET_WUNLOCK();
 	ifp->if_index = idx;
 	ifp->if_type = type;
@@ -383,6 +414,7 @@ if_alloc(u_char type)
 		ifp->if_l2com = if_com_alloc[type](type, ifp);
 		if (ifp->if_l2com == NULL) {
 			free(ifp, M_IFNET);
+			ifindex_free(idx);
 			return (NULL);
 		}
 	}
@@ -421,9 +453,7 @@ if_free_internal(struct ifnet *ifp)
 	KASSERT(ifp == ifnet_byindex_locked(ifp->if_index),
 	    ("%s: freeing unallocated ifnet", ifp->if_xname));
 
-	ifnet_setbyindex_locked(ifp->if_index, NULL);
-	while (V_if_index > 0 && ifnet_byindex_locked(V_if_index) == NULL)
-		V_if_index--;
+	ifindex_free_locked(ifp->if_index);
 	IFNET_WUNLOCK();
 
 	if (if_com_free[ifp->if_alloctype] != NULL)
@@ -916,18 +946,14 @@ if_vmove(struct ifnet *ifp, struct vnet *new_vnet)
 	 * or we'd lock on one vnet and unlock on another.
 	 */
 	IFNET_WLOCK();
-	ifnet_setbyindex_locked(ifp->if_index, NULL);
-	while (V_if_index > 0 && ifnet_byindex_locked(V_if_index) == NULL)
-		V_if_index--;
-	IFNET_WUNLOCK();
+	ifindex_free_locked(ifp->if_index);
 
 	/*
 	 * Switch to the context of the target vnet.
 	 */
 	CURVNET_SET_QUIET(new_vnet);
 
-	IFNET_WLOCK();
-	if (ifindex_alloc(&idx) != 0) {
+	if (ifindex_alloc_locked(&idx) != 0) {
 		IFNET_WUNLOCK();
 		panic("if_index overflow");
 	}