Add new global counter for stats channel

New symbol is added for each stats protocol channel, the symbol is accessed by
same name as the underlying channel. Symbols evaluate to the sum of all routes
exported from connected table with generation less than max generation of
particular channel. Default max generation is 16.

Beware you shouldn't make cyclic references as the behavior of such
configuration is not defined!

conf/conf.h

@@ -124,6 +124,7 @@ struct symbol {
     struct ea_class *attribute;		/* For SYM_ATTRIBUTE */
     struct f_val *val;			/* For SYM_CONSTANT */
     uint offset;			/* For SYM_VARIABLE */
+    struct channel_config *ch_config;	/* For SYM_COUNTER */
   };
 
   char name[0];
@@ -156,6 +157,7 @@ struct bytestring {
 #define SYM_FILTER 4
 #define SYM_TABLE 5
 #define SYM_ATTRIBUTE 6
+#define SYM_COUNTER 7
 
 #define SYM_VARIABLE 0x100	/* 0x100-0x1ff are variable types */
 #define SYM_VARIABLE_RANGE SYM_VARIABLE ... (SYM_VARIABLE | 0xff)

filter/config.Y

@@ -758,6 +758,9 @@ symbol_value: symbol_known
       case SYM_ATTRIBUTE:
 	$$ = f_new_inst(FI_EA_GET, $1->attribute);
 	break;
+      case SYM_COUNTER:
+	$$ = f_new_inst(FI_COUNTER, $1);
+	break;
       default:
 	cf_error("Can't get value of symbol %s", $1->name);
     }

filter/f-inst.c

@@ -473,6 +473,12 @@
     RESULT_VAL(fstk->vstk[curline.vbase + sym->offset]);
   }
 
+  INST(FI_COUNTER, 0, 1) {
+    SYMBOL;
+    NEVER_CONSTANT;
+    RESULT(T_INT, i, get_stats_sum(sym));
+  }
+
   INST(FI_CONSTANT, 0, 1) {
     FID_MEMBER(
       struct f_val,

filter/filter.c

@@ -43,6 +43,7 @@
 #include "filter/filter.h"
 #include "filter/f-inst.h"
 #include "filter/data.h"
+#include "proto/stats/stats.h"  /* provides function get_stats_sum used in f-inst.c */
 
 
 /* Exception bits */

proto/stats/config.Y

@@ -61,6 +61,9 @@ stats_channel_start: net_type symbol
 {
   this_channel = channel_config_get(&channel_stats, $2->name, $1, this_proto);
   STATS_CC->max_generation = 16;
+  /* from filter/config.Y:
+       cf_define_symbol($3, SYM_VARIABLE | $2, offset, $3->scope->slots++) */
+  $2 = cf_define_symbol($2, SYM_COUNTER, ch_config, this_channel);
 }
 
 stats_proto:

proto/stats/stats.h

@@ -35,6 +35,13 @@ struct stats_channel_config {
   u8 max_generation;
 };
 
-
+static inline int
+get_stats_sum(struct symbol *sym)
+{
+  if (sym->ch_config->channel)
+    return (int) ((struct stats_channel *) sym->ch_config->channel)->sum;
+  else
+    return 0;
+}
 
 #endif