fiber: Define constants for reserved fids

Opencoded constants are not good for long time
support, make it named one. Moreover there was
a typo in comment, fid = 0 is reserved as well.

src/lib/core/fiber.c

@@ -974,9 +974,9 @@ fiber_new_ex(const char *name, const struct fiber_attr *fiber_attr,
 	}
 
 	fiber->f = f;
-	/* fids from 0 to 100 are reserved */
-	if (++cord->max_fid < 100)
-		cord->max_fid = 101;
+	/* Excluding reserved range */
+	if (++cord->max_fid < FIBER_ID_MAX_RESERVED)
+		cord->max_fid = FIBER_ID_MAX_RESERVED + 1;
 	fiber->fid = cord->max_fid;
 	fiber_set_name(fiber, name);
 	register_fid(fiber);
@@ -1055,14 +1055,14 @@ cord_create(struct cord *cord, const char *name)
 	cord->fiber_registry = mh_i32ptr_new();
 
 	/* sched fiber is not present in alive/ready/dead list. */
-	cord->sched.fid = 1;
+	cord->sched.fid = FIBER_ID_SCHED;
 	fiber_reset(&cord->sched);
 	diag_create(&cord->sched.diag);
 	region_create(&cord->sched.gc, &cord->slabc);
 	fiber_set_name(&cord->sched, "sched");
 	cord->fiber = &cord->sched;
 
-	cord->max_fid = 100;
+	cord->max_fid = FIBER_ID_MAX_RESERVED;
 	/*
 	 * No need to start this event since it's only used for
 	 * ev_feed_event(). Saves a few cycles on every

src/lib/core/fiber.h

@@ -52,6 +52,14 @@ extern "C" {
 
 enum { FIBER_NAME_MAX = 32 };
 
+/**
+ * Fiber ids [0; 100] are reserved.
+ */
+enum {
+	FIBER_ID_SCHED		= 1,
+	FIBER_ID_MAX_RESERVED	= 100
+};
+
 enum {
 	/**
 	 * It's safe to resume (wakeup) this fiber
@@ -445,7 +453,7 @@ struct cord {
 	struct fiber *fiber;
 	struct ev_loop *loop;
 	/**
-	 * Every new fiber gets a new monotonic id. Ids 1-100 are
+	 * Every new fiber gets a new monotonic id. Ids 0 - 100 are
 	 * reserved.
 	 */
 	uint32_t max_fid;

src/lib/core/say.c

@@ -750,7 +750,7 @@ say_format_plain_tail(char *buf, int len, int level, const char *filename,
 	struct cord *cord = cord();
 	if (cord) {
 		SNPRINT(total, snprintf, buf, len, " %s", cord->name);
-		if (fiber() && fiber()->fid != 1) {
+		if (fiber() && fiber()->fid != FIBER_ID_SCHED) {
 			SNPRINT(total, snprintf, buf, len, "/%i/%s",
 				fiber()->fid, fiber_name(fiber()));
 		}
@@ -875,7 +875,7 @@ say_format_json(struct log *log, char *buf, int len, int level, const char *file
 		SNPRINT(total, snprintf, buf, len, ", \"cord_name\": \"");
 		SNPRINT(total, json_escape, buf, len, cord->name);
 		SNPRINT(total, snprintf, buf, len, "\"");
-		if (fiber() && fiber()->fid != 1) {
+		if (fiber() && fiber()->fid != FIBER_ID_SCHED) {
 			SNPRINT(total, snprintf, buf, len,
 				", \"fiber_id\": %i, ", fiber()->fid);
 			SNPRINT(total, snprintf, buf, len,