- Carlo Contavalli added support for the glibc "rotate" option, as documented

  in man resolv.conf:

  causes round robin selection of nameservers from among those listed.  This
  has the effect of spreading the query load among all listed servers, rather
  than having all clients try the first listed server first every time.

  You can enable it with ARES_OPT_ROTATE

diff --git a/ares/CHANGES b/ares/CHANGES
index dd9bac6c9a78d89231a0ce9174340b086075ea3a..c590079b4bb4d995fe73e7a82c4e784a0569c868 100644 (file)
--- a/ares/CHANGES
+++ b/ares/CHANGES
@@ -1,5 +1,15 @@
   Changelog for the c-ares project
 
+* Nov 1 2008 (Daniel Stenberg)
+- Carlo Contavalli added support for the glibc "rotate" option, as documented
+  in man resolv.conf: 
+
+  causes round robin selection of nameservers from among those listed.  This
+  has the effect of spreading the query load among all listed servers, rather
+  than having all clients try the first listed server first every time.
+
+  You can enable it with ARES_OPT_ROTATE
+
 * Oct 21 2008 (Yang Tse)
   Charles Hardin added handling of EINPROGRESS for UDP connects.
 

diff --git a/ares/ares.h b/ares/ares.h
index 3609f867647cb4d45a7112594f9ca1aa6f16fd1a..1507f41e9078a9f38ee65acb39c5b77fecd4fc2f 100644 (file)
--- a/ares/ares.h
+++ b/ares/ares.h
@@ -114,6 +114,7 @@ extern "C" {
 #define ARES_OPT_SOCK_SNDBUF    (1 << 11)
 #define ARES_OPT_SOCK_RCVBUF    (1 << 12)
 #define ARES_OPT_TIMEOUTMS      (1 << 13)
+#define ARES_OPT_ROTATE         (1 << 14)
 
 /* Nameinfo flag values */
 #define ARES_NI_NOFQDN                  (1 << 0)
@@ -184,6 +185,7 @@ struct ares_options {
   int timeout; /* in seconds or milliseconds, depending on options */
   int tries;
   int ndots;
+  int rotate;
   unsigned short udp_port;
   unsigned short tcp_port;
   int socket_send_buffer_size;

diff --git a/ares/ares_init.c b/ares/ares_init.c
index 4d4ba1ea54ec9c816c9a648a09240c4e898a8723..4a147fc42f6efe4b7b8915ffa641aaa6c1631e2c 100644 (file)
--- a/ares/ares_init.c
+++ b/ares/ares_init.c
@@ -144,6 +144,7 @@ int ares_init_options(ares_channel *channelptr, struct ares_options *options,
   channel->timeout = -1;
   channel->tries = -1;
   channel->ndots = -1;
+  channel->rotate = -1;
   channel->udp_port = -1;
   channel->tcp_port = -1;
   channel->socket_send_buffer_size = -1;
@@ -159,6 +160,7 @@ int ares_init_options(ares_channel *channelptr, struct ares_options *options,
   channel->sock_state_cb = NULL;
   channel->sock_state_cb_data = NULL;
 
+  channel->last_server = 0;
   channel->last_timeout_processed = (time_t)now.tv_sec;
 
   /* Initialize our lists of queries */
@@ -352,6 +354,8 @@ static int init_by_options(ares_channel channel,
     channel->tries = options->tries;
   if ((optmask & ARES_OPT_NDOTS) && channel->ndots == -1)
     channel->ndots = options->ndots;
+  if ((optmask & ARES_OPT_ROTATE) && channel->rotate == -1)
+    channel->rotate = options->rotate;
   if ((optmask & ARES_OPT_UDP_PORT) && channel->udp_port == -1)
     channel->udp_port = options->udp_port;
   if ((optmask & ARES_OPT_TCP_PORT) && channel->tcp_port == -1)
@@ -932,6 +936,8 @@ static int init_by_defaults(ares_channel channel)
     channel->tries = DEFAULT_TRIES;
   if (channel->ndots == -1)
     channel->ndots = 1;
+  if (channel->rotate == -1)
+    channel->rotate = 0;
   if (channel->udp_port == -1)
     channel->udp_port = htons(NAMESERVER_PORT);
   if (channel->tcp_port == -1)
@@ -1302,6 +1308,9 @@ static int set_options(ares_channel channel, const char *str)
       val = try_option(p, q, "retry:");
       if (val && channel->tries == -1)
         channel->tries = atoi(val);
+      val = try_option(p, q, "rotate");
+      if (val && channel->rotate == -1)
+        channel->rotate = 1;
       p = q;
       while (ISSPACE(*p))
         p++;
@@ -1374,7 +1383,7 @@ static char *try_config(char *s, const char *opt)
 static const char *try_option(const char *p, const char *q, const char *opt)
 {
   size_t len = strlen(opt);
-  return ((size_t)(q - p) > len && !strncmp(p, opt, len)) ? &p[len] : NULL;
+  return ((size_t)(q - p) >= len && !strncmp(p, opt, len)) ? &p[len] : NULL;
 }
 
 #ifndef WIN32

diff --git a/ares/ares_private.h b/ares/ares_private.h
index 0b4edf94e413587c45eeb9fce51c89bb0d9791af..976fa9f10b5057ab6c0dc02a4d8465ae393f239f 100644 (file)
--- a/ares/ares_private.h
+++ b/ares/ares_private.h
@@ -195,8 +195,8 @@ struct query {
   void *arg;
 
   /* Query status */
-  int try;
-  int server;
+  int try; /* Number of times we tried this query already. */
+  int server; /* Server this query has last been sent to. */
   struct query_server_info *server_info;   /* per-server state */
   int using_tcp;
   int error_status;
@@ -242,6 +242,7 @@ struct ares_channeldata {
   int timeout; /* in milliseconds */
   int tries;
   int ndots;
+  int rotate; /* if true, all servers specified are used */
   int udp_port;
   int tcp_port;
   int socket_send_buffer_size;
@@ -268,6 +269,9 @@ struct ares_channeldata {
      just to draw the line somewhere. */
   time_t last_timeout_processed;
 
+  /* Last server we sent a query to. */
+  int last_server;
+
   /* Circular, doubly-linked list of queries, bucketed various ways.... */
   /* All active queries in a single list: */
   struct list_node all_queries;

diff --git a/ares/ares_process.c b/ares/ares_process.c
index 675af489d81a0369ee97b95450dd27a71d271bbc..b7f375e1922e250027426951586887a805d6458f 100644 (file)
--- a/ares/ares_process.c
+++ b/ares/ares_process.c
@@ -670,30 +670,33 @@ static void skip_server(ares_channel channel, struct query *query,
 static void next_server(ares_channel channel, struct query *query,
                         struct timeval *now)
 {
-  /* Advance to the next server or try. */
-  query->server++;
-  for (; query->try < channel->tries; query->try++)
+  /* We need to try each server channel->tries times. We have channel->nservers
+   * servers to try. In total, we need to do channel->nservers * channel->tries
+   * attempts. Use query->try to remember how many times we already attempted
+   * this query. Use modular arithmetic to find the next server to try. */
+  while (++(query->try) < (channel->nservers * channel->tries))
     {
-      for (; query->server < channel->nservers; query->server++)
+      struct server_state *server;
+
+      /* Move on to the next server. */
+      query->server = (query->server + 1) % channel->nservers;
+      server = &channel->servers[query->server];
+
+      /* We don't want to use this server if (1) we decided this
+       * connection is broken, and thus about to be closed, (2)
+       * we've decided to skip this server because of earlier
+       * errors we encountered, or (3) we already sent this query
+       * over this exact connection.
+       */
+      if (!server->is_broken &&
+           !query->server_info[query->server].skip_server &&
+           !(query->using_tcp &&
+             (query->server_info[query->server].tcp_connection_generation ==
+              server->tcp_connection_generation)))
         {
-          struct server_state *server = &channel->servers[query->server];
-          /* We don't want to use this server if (1) we decided this
-           * connection is broken, and thus about to be closed, (2)
-           * we've decided to skip this server because of earlier
-           * errors we encountered, or (3) we already sent this query
-           * over this exact connection.
-           */
-          if (!server->is_broken &&
-               !query->server_info[query->server].skip_server &&
-               !(query->using_tcp &&
-                 (query->server_info[query->server].tcp_connection_generation ==
-                  server->tcp_connection_generation)))
-            {
-               ares__send_query(channel, query, now);
-               return;
-            }
+           ares__send_query(channel, query, now);
+           return;
         }
-      query->server = 0;
 
       /* You might think that with TCP we only need one try. However,
        * even when using TCP, servers can time-out our connection just
@@ -702,6 +705,8 @@ static void next_server(ares_channel channel, struct query *query,
        * tickle a bug that drops our request.
        */
     }
+
+  /* If we are here, all attempts to perform query failed. */
   end_query(channel, query, query->error_status, NULL, 0);
 }
 
@@ -775,8 +780,7 @@ void ares__send_query(ares_channel channel, struct query *query,
     }
     query->timeout = *now;
     ares__timeadd(&query->timeout,
-                  (query->try == 0) ? channel->timeout
-                  : channel->timeout << query->try / channel->nservers);
+                  channel->timeout << (query->try / channel->nservers));
     /* Keep track of queries bucketed by timeout, so we can process
      * timeout events quickly.
      */

diff --git a/ares/ares_send.c b/ares/ares_send.c
index a5811d36d15f5a7d245f2c245c5d463e87fd64c5..be5478df2d4ac6682378821e286f6cbabecfe8b4 100644 (file)
--- a/ares/ares_send.c
+++ b/ares/ares_send.c
@@ -95,7 +95,13 @@ void ares_send(ares_channel channel, const unsigned char *qbuf, int qlen,
 
   /* Initialize query status. */
   query->try = 0;
-  query->server = 0;
+
+  /* Choose the server to send the query to. If rotation is enabled, keep track
+   * of the next server we want to use. */
+  query->server = channel->last_server;
+  if (channel->rotate == 1)
+    channel->last_server = (channel->last_server + 1) % channel->nservers;
+
   for (i = 0; i < channel->nservers; i++)
     {
       query->server_info[i].skip_server = 0;