Fix mdb_reader_list() and its spec.

It and the MDB_msg_func can now return >= 0 for success.
Always return any MDB_msg_func() error result.

libraries/liblmdb/lmdb.h

@@ -1409,7 +1409,7 @@ int  mdb_dcmp(MDB_txn *txn, MDB_dbi dbi, const MDB_val *a, const MDB_val *b);
 	 *
 	 * @param[in] msg The string to be printed.
 	 * @param[in] ctx An arbitrary context pointer for the callback.
-	 * @return < 0 on failure, 0 on success.
+	 * @return < 0 on failure, >= 0 on success.
 	 */
 typedef int (MDB_msg_func)(const char *msg, void *ctx);
 
@@ -1418,7 +1418,7 @@ typedef int (MDB_msg_func)(const char *msg, void *ctx);
 	 * @param[in] env An environment handle returned by #mdb_env_create()
 	 * @param[in] func A #MDB_msg_func function
 	 * @param[in] ctx Anything the message function needs
-	 * @return < 0 on failure, 0 on success.
+	 * @return < 0 on failure, >= 0 on success.
 	 */
 int	mdb_reader_list(MDB_env *env, MDB_msg_func *func, void *ctx);
 

libraries/liblmdb/mdb.c

@@ -8299,7 +8299,7 @@ int mdb_reader_list(MDB_env *env, MDB_msg_func *func, void *ctx)
 	unsigned int i, rdrs;
 	MDB_reader *mr;
 	char buf[64];
-	int first = 1;
+	int rc = 0, first = 1;
 
 	if (!env || !func)
 		return -1;
@@ -8311,7 +8311,6 @@ int mdb_reader_list(MDB_env *env, MDB_msg_func *func, void *ctx)
 	for (i=0; i<rdrs; i++) {
 		if (mr[i].mr_pid) {
 			size_t tid;
-			int rc;
 			tid = mr[i].mr_tid;
 			if (mr[i].mr_txnid == (txnid_t)-1) {
 				sprintf(buf, "%10d %"Z"x -\n", mr[i].mr_pid, tid);
@@ -8320,17 +8319,19 @@ int mdb_reader_list(MDB_env *env, MDB_msg_func *func, void *ctx)
 			}
 			if (first) {
 				first = 0;
-				func("    pid     thread     txnid\n", ctx);
+				rc = func("    pid     thread     txnid\n", ctx);
+				if (rc < 0)
+					break;
 			}
 			rc = func(buf, ctx);
 			if (rc < 0)
-				return rc;
+				break;
 		}
 	}
 	if (first) {
-		func("(no active readers)\n", ctx);
+		rc = func("(no active readers)\n", ctx);
 	}
-	return 0;
+	return rc;
 }
 
 /** Insert pid into list if not already present.