MINOR: http/conf: store the use_backend configuration file and line for logs

The error log of the directive use_backend doesn't provide the
file and line containing the declaration. This patch stores
theses informations.

include/types/arg.h

@@ -77,6 +77,7 @@ enum {
 	ARGC_CAP,      /* capture rule */
 	ARGC_SRV,      /* server line */
 	ARGC_SPOE,     /* spoe message args */
+	ARGC_UBK,      /* use_backend message */
 };
 
 /* flags used when compiling and executing regex */

include/types/proxy.h

@@ -446,6 +446,8 @@ struct switching_rule {
 		char *name;			/* target backend name during config parsing */
 		struct list expr;		/* logformat expression to use for dynamic rules */
 	} be;
+	char *file;
+	int line;
 };
 
 struct server_rule {

src/cfgparse.c

@@ -4018,6 +4018,12 @@ int cfg_parse_listen(const char *file, int linenum, char **args, int kwm)
 		}
 		rule->cond = cond;
 		rule->be.name = strdup(args[1]);
+		rule->line = linenum;
+		rule->file = strdup(file);
+		if (!rule->file) {
+			Alert("Out of memory error.\n");
+			goto out;
+		}
 		LIST_INIT(&rule->list);
 		LIST_ADDQ(&curproxy->switching_rules, &rule->list);
 	}
@@ -7792,6 +7798,9 @@ int check_config_validity()
 			 */
 			pxname = rule->be.name;
 			LIST_INIT(&rule->be.expr);
+			curproxy->conf.args.ctx = ARGC_UBK;
+			curproxy->conf.args.file = rule->file;
+			curproxy->conf.args.line = rule->line;
 			if (!parse_logformat_string(pxname, curproxy, &rule->be.expr, 0, SMP_VAL_FE_HRQ_HDR)) {
 				cfgerr++;
 				continue;

src/haproxy.c

@@ -1482,6 +1482,7 @@ void deinit(void)
 			if (rule->cond) {
 				prune_acl_cond(rule->cond);
 				free(rule->cond);
+				free(rule->file);
 			}
 			free(rule);
 		}

src/log.c

@@ -269,6 +269,8 @@ static inline const char *fmt_directive(const struct proxy *curproxy)
 		return "server";
 	case ARGC_SPOE:
 		return "spoe-message";
+	case ARGC_UBK:
+		return "use_backend";
 	default:
 		return "undefined(please report this bug)"; /* must never happen */
 	}