[XFRM] Optimize policy dumping

This change optimizes the dumping of Security policies.

1) Before this change ..
speedopolis:~# time ./ip xf pol

real    0m22.274s
user    0m0.000s
sys     0m22.269s

2) Turn off sub-policies

speedopolis:~# ./ip xf pol

real    0m13.496s
user    0m0.000s
sys     0m13.493s

i suppose the above is to be expected

3) With this change ..
speedopolis:~# time ./ip x policy

real    0m7.901s
user    0m0.008s
sys     0m7.896s

1 files changed, 25 insertions, 30 deletions

diff --git a/net/xfrm/xfrm_policy.c b/net/xfrm/xfrm_policy.c
index f6c77bd36fdd..4f04222698d9 100644
--- a/net/xfrm/xfrm_policy.c
+++ b/net/xfrm/xfrm_policy.c
@@ -860,33 +860,12 @@ EXPORT_SYMBOL(xfrm_policy_flush);
 int xfrm_policy_walk(u8 type, int (*func)(struct xfrm_policy *, int, int, void*),
                      void *data)
 {
-        struct xfrm_policy *pol;
+        struct xfrm_policy *pol, *last = NULL;
         struct hlist_node *entry;
-        int dir, count, error;
+        int dir, last_dir = 0, count, error;
 
         read_lock_bh(&xfrm_policy_lock);
         count = 0;
-        for (dir = 0; dir < 2*XFRM_POLICY_MAX; dir++) {
-                struct hlist_head *table = xfrm_policy_bydst[dir].table;
-                int i;
-
-                hlist_for_each_entry(pol, entry,
-                                     &xfrm_policy_inexact[dir], bydst) {
-                        if (pol->type == type)
-                                count++;
-                }
-                for (i = xfrm_policy_bydst[dir].hmask; i >= 0; i--) {
-                        hlist_for_each_entry(pol, entry, table + i, bydst) {
-                                if (pol->type == type)
-                                        count++;
-                        }
-                }
-        }
-
-        if (count == 0) {
-                error = -ENOENT;
-                goto out;
-        }
 
         for (dir = 0; dir < 2*XFRM_POLICY_MAX; dir++) {
                 struct hlist_head *table = xfrm_policy_bydst[dir].table;
@@ -896,21 +875,37 @@ int xfrm_policy_walk(u8 type, int (*func)(struct xfrm_policy *, int, int, void*)
                                      &xfrm_policy_inexact[dir], bydst) {
                         if (pol->type != type)
                                 continue;
-                        error = func(pol, dir % XFRM_POLICY_MAX, --count, data);
-                        if (error)
-                                goto out;
+                        if (last) {
+                                error = func(last, last_dir % XFRM_POLICY_MAX,
+                                             count, data);
+                                if (error)
+                                        goto out;
+                        }
+                        last = pol;
+                        last_dir = dir;
+                        count++;
                 }
                 for (i = xfrm_policy_bydst[dir].hmask; i >= 0; i--) {
                         hlist_for_each_entry(pol, entry, table + i, bydst) {
                                 if (pol->type != type)
                                         continue;
-                                error = func(pol, dir % XFRM_POLICY_MAX, --count, data);
-                                if (error)
-                                        goto out;
+                                if (last) {
+                                        error = func(last, last_dir % XFRM_POLICY_MAX,
+                                                     count, data);
+                                        if (error)
+                                                goto out;
+                                }
+                                last = pol;
+                                last_dir = dir;
+                                count++;
                         }
                 }
         }
-        error = 0;
+        if (count == 0) {
+                error = -ENOENT;
+                goto out;
+        }
+        error = func(last, last_dir % XFRM_POLICY_MAX, 0, data);
 out:
         read_unlock_bh(&xfrm_policy_lock);
         return error;