Add a maximum diff option

README

@@ -252,4 +252,7 @@ and 3334 in proxy mode.
 
 "startdiff" : Starting diff that new clients are given. Default 42
 
+"maxdiff" : Optional maximum diff that vardiff will clamp to where zero is no
+maximum.
+
 "logdir" : Which directory to store pool and client logs. Default "logs"

ckpool.conf

@@ -20,6 +20,7 @@
 "serverurl" : "ckpool.org:3333",
 "mindiff" : 1,
 "startdiff" : 42,
+"maxdiff" : 0,
 "logdir" : "logs"
 }
 Comments from here on are ignored.

ckproxy.conf

@@ -15,6 +15,7 @@
 "serverurl" : "192.168.1.100:3334",
 "mindiff" : 1,
 "startdiff" : 42,
+"maxdiff" : 0,
 "logdir" : "logs"
 }
 Comments from here on are ignored.

src/ckpool.c

@@ -983,6 +983,7 @@ static void parse_config(ckpool_t *ckp)
 	json_get_string(&ckp->serverurl, json_conf, "serverurl");
 	json_get_int64(&ckp->mindiff, json_conf, "mindiff");
 	json_get_int64(&ckp->startdiff, json_conf, "startdiff");
+	json_get_int64(&ckp->maxdiff, json_conf, "maxdiff");
 	json_get_string(&ckp->logdir, json_conf, "logdir");
 	arr_val = json_object_get(json_conf, "proxy");
 	if (arr_val && json_is_array(arr_val)) {

src/ckpool.h

@@ -150,6 +150,7 @@ struct ckpool_instance {
 	/* Difficulty settings */
 	int64_t mindiff; // Default 1
 	int64_t startdiff; // Default 42
+	int64_t maxdiff; // No default
 
 	/* Coinbase data */
 	char *btcaddress; // Address to mine to

src/stratifier.c

@@ -1838,6 +1838,8 @@ static void add_submit(ckpool_t *ckp, stratum_instance_t *client, int diff, bool
 			optimal = client->suggest_diff;
 	} else if (optimal < worker->mindiff)
 		optimal = worker->mindiff;
+	if (ckp->maxdiff && optimal > ckp->maxdiff)
+		optimal = ckp->maxdiff;
 	if (optimal > network_diff)
 		optimal = network_diff;
 	if (client->diff == optimal)