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>

1 files changed, 12 insertions, 11 deletions

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;