Merge branch 'fewer-diffs' into maint-0.3.1

changes/bug22883-config

@@ -0,0 +1,7 @@
+  o Minor features (directory cache, consensus diff):
+    - Add a new MaxConsensusAgeForDiffs option to allow directory cache
+      operators with low-resource environments to adjust the number of
+      consensuses they'll store and generate diffs from. Most cache operators
+      should leave it unchanged. Helps to work around bug 22883.
+
+

doc/tor.1.txt

@@ -2072,6 +2072,16 @@ details.)
     because clients connect via the ORPort by default. Setting either DirPort
     or BridgeRelay and setting DirCache to 0 is not supported.  (Default: 1)
 
+[[MaxConsensusAgeForDiffs]] **MaxConsensusAgeForDiffs**  __N__ **minutes**|**hours**|**days**|**weeks**::
+    When this option is nonzero, Tor caches will not try to generate
+    consensus diffs for any consensus older than this amount of time.
+    If this option is set to zero, Tor will pick a reasonable default from
+    the current networkstatus document.  You should not set this
+    option unless your cache is severely low on disk space or CPU.
+    If you need to set it, keeping it above 3 or 4 hours will help clients
+    much more than setting it to zero.
+    (Default: 0)
+
 
 DIRECTORY AUTHORITY SERVER OPTIONS
 ----------------------------------

src/or/config.c

@@ -393,6 +393,7 @@ static config_var_t option_vars_[] = {
   V(MaxAdvertisedBandwidth,      MEMUNIT,  "1 GB"),
   V(MaxCircuitDirtiness,         INTERVAL, "10 minutes"),
   V(MaxClientCircuitsPending,    UINT,     "32"),
+  V(MaxConsensusAgeForDiffs,     INTERVAL, "0 seconds"),
   VAR("MaxMemInQueues",          MEMUNIT,   MaxMemInQueues_raw, "0"),
   OBSOLETE("MaxOnionsPending"),
   V(MaxOnionQueueDelay,          MSEC_INTERVAL, "1750 msec"),

src/or/consdiffmgr.c

@@ -14,6 +14,7 @@
 #define CONSDIFFMGR_PRIVATE
 
 #include "or.h"
+#include "config.h"
 #include "conscache.h"
 #include "consdiff.h"
 #include "consdiffmgr.h"
@@ -462,12 +463,22 @@ cdm_cache_lookup_consensus(consensus_flavor_t flavor, time_t valid_after)
 static int32_t
 get_max_age_to_cache(void)
 {
-  /* The parameter is in hours. */
   const int32_t DEFAULT_MAX_AGE_TO_CACHE = 8192;
   const int32_t MIN_MAX_AGE_TO_CACHE = 0;
   const int32_t MAX_MAX_AGE_TO_CACHE = 8192;
   const char MAX_AGE_TO_CACHE_NAME[] = "max-consensus-age-to-cache-for-diff";
 
+  const or_options_t *options = get_options();
+
+  if (options->MaxConsensusAgeForDiffs) {
+    const int v = options->MaxConsensusAgeForDiffs;
+    if (v >= MAX_MAX_AGE_TO_CACHE * 3600)
+      return MAX_MAX_AGE_TO_CACHE;
+    else
+      return v;
+  }
+
+  /* The parameter is in hours, so we multiply */
   return 3600 * networkstatus_get_param(NULL,
                                         MAX_AGE_TO_CACHE_NAME,
                                         DEFAULT_MAX_AGE_TO_CACHE,

src/or/or.h

@@ -4558,6 +4558,11 @@ typedef struct {
 
   /** Bool (default: 0): Tells if a %include was used on torrc */
   int IncludeUsed;
+
+  /** The seconds after expiration which we as a relay should keep old
+   * consensuses around so that we can generate diffs from them.  If 0,
+   * use the default. */
+  int MaxConsensusAgeForDiffs;
 } or_options_t;
 
 /** Persistent state for an onion router, as saved to disk. */