r11643@Kushana: nickm | 2006-12-19 13:15:14 -0500

 Stop recommmending exits as guards when the exit bandwidth is less than a third of the total bandwidth.


svn:r9154

ChangeLog

@@ -23,6 +23,8 @@ Changes in version 0.1.2.5-xxxx - 200?-??-??
       options files.
     - Reject *:563 (NTTPS) in the default exit policy. We already reject
       NNTP by default, so this seems like a sensible addition.
+    - Authorities do not recommend exits as guards if this would shift excess
+      load to the exit nodes.
 
   o Security bugfixes:
     - Stop sending the HttpProxyAuthenticator string to directory

doc/TODO

@@ -28,7 +28,7 @@ Items for 0.1.2.x, real soon now:
 N - Test guard unreachable logic; make sure that we actually attempt to
     connect to guards that we think are unreachable from time to time.
     Make sure that we don't freak out when the network is down.
-N - Stop recommending exits as guards?
+  o Stop recommending exits as guards?
     look at the overall fraction of exits in the network. if the
     fraction is too small, none of them get to be guards.
 

src/or/dirserv.c

@@ -1293,6 +1293,8 @@ should_generate_v2_networkstatus(void)
 static uint32_t stable_uptime = 0; /* start at a safe value */
 static uint32_t fast_bandwidth = 0;
 static uint32_t guard_bandwidth = 0;
+static uint64_t total_bandwidth = 0;
+static uint64_t total_exit_bandwidth = 0;
 
 static INLINE int
 real_uptime(routerinfo_t *router, time_t now)
@@ -1331,15 +1333,20 @@ _compare_uint32(const void **a, const void **b)
   return 0;
 }
 
-/** Look through the routerlist, and assign the median uptime
- * of running valid servers to stable_uptime, and the relative bandwidth
- * capacities to fast_bandwidth and guard_bandwidth. */
+/** Look through the routerlist, and assign the median uptime of running valid
+ * servers to stable_uptime, and the relative bandwidth capacities to
+ * fast_bandwidth and guard_bandwidth.  Set total_bandwidth to the total
+ * capacity of all running valid servers and total_exit_bandwidth to the
+ * capacity of all running valid exits. */
 static void
 dirserv_compute_performance_thresholds(routerlist_t *rl)
 {
   smartlist_t *uptimes, *bandwidths;
   time_t now = time(NULL);
 
+  total_bandwidth = 0;
+  total_exit_bandwidth = 0;
+
   uptimes = smartlist_create();
   bandwidths = smartlist_create();
 
@@ -1350,6 +1357,8 @@ dirserv_compute_performance_thresholds(routerlist_t *rl)
       *up = (uint32_t) real_uptime(ri, now);
       smartlist_add(uptimes, up);
       *bw = router_get_advertised_bandwidth(ri);
+      total_bandwidth += *bw;
+      total_exit_bandwidth += *bw;
       smartlist_add(bandwidths, bw);
     }
   });
@@ -1417,6 +1426,7 @@ generate_v2_networkstatus(void)
   int naming = options->NamingAuthoritativeDir;
   int versioning = options->VersioningAuthoritativeDir;
   int listbadexits = options->AuthDirListBadExits;
+  int exits_can_be_guards;
   const char *contact;
 
   if (resolve_my_address(LOG_WARN, options, &addr, &hostname)<0) {
@@ -1485,6 +1495,8 @@ generate_v2_networkstatus(void)
 
   dirserv_compute_performance_thresholds(rl);
 
+  exits_can_be_guards = total_exit_bandwidth > (total_bandwidth / 3);
+
   SMARTLIST_FOREACH(rl->routers, routerinfo_t *, ri, {
     if (ri->cache_info.published_on >= cutoff) {
       int f_exit = exit_policy_is_general_exit(ri->exit_policy);
@@ -1504,7 +1516,8 @@ generate_v2_networkstatus(void)
       int f_named = naming && ri->is_named;
       int f_valid = ri->is_valid;
       int f_guard = f_fast && f_stable &&
-        router_get_advertised_bandwidth(ri) > guard_bandwidth;
+        router_get_advertised_bandwidth(ri) > guard_bandwidth &&
+        (!f_exit || exits_can_be_guards);
       int f_bad_exit = listbadexits && ri->is_bad_exit;
       /* 0.1.1.9-alpha is the first version to support fetch by descriptor
        * hash. */