update metric to include description and type information for printing

docs/modules/cc_metric.rst

@@ -52,6 +52,7 @@ Data Structure
 
   struct metric {
       char *name;
+      char *desc;
       metric_type_e type;
       union {
           uint64_t    counter;
@@ -60,7 +61,7 @@ Data Structure
       };
   };
 
-``metric`` is the fundamental data structure, each metric has (for now) three types, a printable name, and value.
+``metric`` is the fundamental data structure, each metric has (for now) three types, a printable name, a short description, and value.
 
 If a metric is of type ``METRIC_COUNTER``, its value always increases monotonically. A metric of type ``METRIC_GAUGE`` has a signed integer value. Type ``METRIC_FPN`` means the value is a floating-point number.
 

include/cc_metric.h

@@ -91,7 +91,7 @@ extern "C" {
     struct metric _name;
 
 #define METRIC_INIT(_name, _type, _description)      \
-    ._name = {.name = #_name, .type = _type},
+    ._name = {.name = #_name, .desc = _description, .type = _type},
 
 #define METRIC_NAME(_name, _type, _description)      \
     #_name,
@@ -118,12 +118,15 @@ typedef enum metric_type {
     METRIC_FPN      /* supports UPDATE_VAL */
 } metric_type_e;
 
+extern char *metric_type_str[3];
+
 /* Note: anonymous union does not work with older (<gcc4.7) compilers */
 /* TODO(yao): determine if we should dynamically allocate the value field
  * during init. The benefit is we don't have to allocate the same amount of
  * memory for different types of values, potentially wasting space. */
 struct metric {
     char *name;
+    char *desc;
     metric_type_e type;
     union {
         uint64_t    counter;

src/stats/cc_metric.c

@@ -22,6 +22,8 @@
 
 #include <stdbool.h>
 
+char *metric_type_str[] = {"counter", "gauge", "floating point"};
+
 void
 metric_reset(struct metric sarr[], unsigned int n)
 {