net: Document dst->obsolete better.

Add a big comment explaining how the field works, and use defines
instead of magic constants for the values assigned to it.

Suggested by Joe Perches.

Signed-off-by: David S. Miller <davem@davemloft.net>

7 files changed, 35 insertions, 21 deletions

diff --git a/include/net/dst.h b/include/net/dst.h
index 51610468c63d..0df661a0c295 100644
--- a/include/net/dst.h
+++ b/include/net/dst.h
@@ -65,7 +65,19 @@ struct dst_entry {
         unsigned short          pending_confirm;
 
         short                   error;
+
+        /* A non-zero value of dst->obsolete forces by-hand validation
+         * of the route entry.  Positive values are set by the generic
+         * dst layer to indicate that the entry has been forcefully
+         * destroyed.
+         *
+         * Negative values are used by the implementation layer code to
+         * force invocation of the dst_ops->check() method.
+         */
         short                   obsolete;
+#define DST_OBSOLETE_NONE       0
+#define DST_OBSOLETE_DEAD       2
+#define DST_OBSOLETE_FORCE_CHK  -1
         unsigned short          header_len;     /* more space at head required */
         unsigned short          trailer_len;    /* space to reserve at tail */
 #ifdef CONFIG_IP_ROUTE_CLASSID
@@ -359,7 +371,7 @@ extern struct dst_entry *dst_destroy(struct dst_entry *dst);
 
 static inline void dst_free(struct dst_entry *dst)
 {
-        if (dst->obsolete > 1)
+        if (dst->obsolete > 0)
                 return;
         if (!atomic_read(&dst->__refcnt)) {
                 dst = dst_destroy(dst);
diff --git a/net/core/dst.c b/net/core/dst.c
index 07bacff84aa4..069d51d29414 100644
--- a/net/core/dst.c
+++ b/net/core/dst.c
@@ -94,7 +94,7 @@ loop:
                          * But we do not have state "obsoleted, but
                          * referenced by parent", so it is right.
                          */
-                        if (dst->obsolete > 1)
+                        if (dst->obsolete > 0)
                                 continue;
 
                         ___dst_free(dst);
@@ -202,7 +202,7 @@ static void ___dst_free(struct dst_entry *dst)
          */
         if (dst->dev == NULL || !(dst->dev->flags&IFF_UP))
                 dst->input = dst->output = dst_discard;
-        dst->obsolete = 2;
+        dst->obsolete = DST_OBSOLETE_DEAD;
 }
 
 void __dst_free(struct dst_entry *dst)
diff --git a/net/decnet/dn_route.c b/net/decnet/dn_route.c
index 47de90d8fe94..23cc11dd4e40 100644
--- a/net/decnet/dn_route.c
+++ b/net/decnet/dn_route.c
@@ -1176,7 +1176,7 @@ make_route:
         if (dev_out->flags & IFF_LOOPBACK)
                 flags |= RTCF_LOCAL;
 
-        rt = dst_alloc(&dn_dst_ops, dev_out, 1, 0, DST_HOST);
+        rt = dst_alloc(&dn_dst_ops, dev_out, 1, DST_OBSOLETE_NONE, DST_HOST);
         if (rt == NULL)
                 goto e_nobufs;
 
@@ -1444,7 +1444,7 @@ static int dn_route_input_slow(struct sk_buff *skb)
         }
 
 make_route:
-        rt = dst_alloc(&dn_dst_ops, out_dev, 0, 0, DST_HOST);
+        rt = dst_alloc(&dn_dst_ops, out_dev, 0, DST_OBSOLETE_NONE, DST_HOST);
         if (rt == NULL)
                 goto e_nobufs;
 
diff --git a/net/ipv4/route.c b/net/ipv4/route.c
index d1d579638092..50d2498c9284 100644
--- a/net/ipv4/route.c
+++ b/net/ipv4/route.c
@@ -1221,7 +1221,7 @@ static void rt_set_nexthop(struct rtable *rt, const struct flowi4 *fl4,
 static struct rtable *rt_dst_alloc(struct net_device *dev,
                                    bool nopolicy, bool noxfrm)
 {
-        return dst_alloc(&ipv4_dst_ops, dev, 1, -1,
+        return dst_alloc(&ipv4_dst_ops, dev, 1, DST_OBSOLETE_FORCE_CHK,
                          DST_HOST | DST_NOCACHE |
                          (nopolicy ? DST_NOPOLICY : 0) |
                          (noxfrm ? DST_NOXFRM : 0));
@@ -1969,9 +1969,10 @@ static struct dst_ops ipv4_dst_blackhole_ops = {
 
 struct dst_entry *ipv4_blackhole_route(struct net *net, struct dst_entry *dst_orig)
 {
-        struct rtable *rt = dst_alloc(&ipv4_dst_blackhole_ops, NULL, 1, 0, 0);
         struct rtable *ort = (struct rtable *) dst_orig;
+        struct rtable *rt;
 
+        rt = dst_alloc(&ipv4_dst_blackhole_ops, NULL, 1, DST_OBSOLETE_NONE, 0);
         if (rt) {
                 struct dst_entry *new = &rt->dst;
 
diff --git a/net/ipv6/route.c b/net/ipv6/route.c
index 84f6564dd372..cf02cb97bbdd 100644
--- a/net/ipv6/route.c
+++ b/net/ipv6/route.c
@@ -281,7 +281,7 @@ static inline struct rt6_info *ip6_dst_alloc(struct net *net,
                                              struct fib6_table *table)
 {
         struct rt6_info *rt = dst_alloc(&net->ipv6.ip6_dst_ops, dev,
-                                        0, 0, flags);
+                                        0, DST_OBSOLETE_NONE, flags);
 
         if (rt) {
                 struct dst_entry *dst = &rt->dst;
@@ -985,7 +985,7 @@ struct dst_entry *ip6_blackhole_route(struct net *net, struct dst_entry *dst_ori
         struct rt6_info *rt, *ort = (struct rt6_info *) dst_orig;
         struct dst_entry *new = NULL;
 
-        rt = dst_alloc(&ip6_dst_blackhole_ops, ort->dst.dev, 1, 0, 0);
+        rt = dst_alloc(&ip6_dst_blackhole_ops, ort->dst.dev, 1, DST_OBSOLETE_NONE, 0);
         if (rt) {
                 new = &rt->dst;
 
diff --git a/net/sctp/transport.c b/net/sctp/transport.c
index a6b7ee9ce28a..ec3a12b9b802 100644
--- a/net/sctp/transport.c
+++ b/net/sctp/transport.c
@@ -216,7 +216,7 @@ void sctp_transport_set_owner(struct sctp_transport *transport,
 void sctp_transport_pmtu(struct sctp_transport *transport, struct sock *sk)
 {
         /* If we don't have a fresh route, look one up */
-        if (!transport->dst || transport->dst->obsolete > 1) {
+        if (!transport->dst || transport->dst->obsolete) {
                 dst_release(transport->dst);
                 transport->af_specific->get_dst(transport, &transport->saddr,
                                                 &transport->fl, sk);
diff --git a/net/xfrm/xfrm_policy.c b/net/xfrm/xfrm_policy.c
index 65bd1ca51517..c5a5165a5927 100644
--- a/net/xfrm/xfrm_policy.c
+++ b/net/xfrm/xfrm_policy.c
@@ -1350,7 +1350,7 @@ static inline struct xfrm_dst *xfrm_alloc_dst(struct net *net, int family)
         default:
                 BUG();
         }
-        xdst = dst_alloc(dst_ops, NULL, 0, 0, 0);
+        xdst = dst_alloc(dst_ops, NULL, 0, DST_OBSOLETE_NONE, 0);
 
         if (likely(xdst)) {
                 struct dst_entry *dst = &xdst->u.dst;
@@ -1477,7 +1477,7 @@ static struct dst_entry *xfrm_bundle_create(struct xfrm_policy *policy,
                 dst1->xfrm = xfrm[i];
                 xdst->xfrm_genid = xfrm[i]->genid;
 
-                dst1->obsolete = -1;
+                dst1->obsolete = DST_OBSOLETE_FORCE_CHK;
                 dst1->flags |= DST_HOST;
                 dst1->lastuse = now;
 
@@ -2219,12 +2219,13 @@ EXPORT_SYMBOL(__xfrm_route_forward);
 static struct dst_entry *xfrm_dst_check(struct dst_entry *dst, u32 cookie)
 {
         /* Code (such as __xfrm4_bundle_create()) sets dst->obsolete
-         * to "-1" to force all XFRM destinations to get validated by
-         * dst_ops->check on every use.  We do this because when a
-         * normal route referenced by an XFRM dst is obsoleted we do
-         * not go looking around for all parent referencing XFRM dsts
-         * so that we can invalidate them.  It is just too much work.
-         * Instead we make the checks here on every use.  For example:
+         * to DST_OBSOLETE_FORCE_CHK to force all XFRM destinations to
+         * get validated by dst_ops->check on every use.  We do this
+         * because when a normal route referenced by an XFRM dst is
+         * obsoleted we do not go looking around for all parent
+         * referencing XFRM dsts so that we can invalidate them.  It
+         * is just too much work.  Instead we make the checks here on
+         * every use.  For example:
          *
          *      XFRM dst A --> IPv4 dst X
          *
@@ -2234,9 +2235,9 @@ static struct dst_entry *xfrm_dst_check(struct dst_entry *dst, u32 cookie)
          * stale_bundle() check.
          *
          * When a policy's bundle is pruned, we dst_free() the XFRM
-         * dst which causes it's ->obsolete field to be set to a
-         * positive non-zero integer.  If an XFRM dst has been pruned
-         * like this, we want to force a new route lookup.
+         * dst which causes it's ->obsolete field to be set to
+         * DST_OBSOLETE_DEAD.  If an XFRM dst has been pruned like
+         * this, we want to force a new route lookup.
          */
         if (dst->obsolete < 0 && !stale_bundle(dst))
                 return dst;