Convert bts->depends_on from bitmask to llist

The amount of dependencies on each BTS is usually zero or a small
number, hence the computation cost is mostly similar regardless of using
a llist or a bitmask buffer.

Right now, even if the dependency chains are (almost) empty, the
previous code allocated (N * 256/8) bytes, where N is the amount of bts
configured.

Since we are now planning to increase the amount of bts (N) from uint8_t to
uint16_t, that means with this change we will then avoid:
* Increasing memory use to O(N * 65536/8).
* Having to adapt code operating on bitmask (size)

Related: SYS#7062
Change-Id: I59e37d6baa020aeafdffc2c3538e988effd37620

include/osmocom/bsc/bts.h

@@ -326,6 +326,12 @@ struct gsm_gprs_cell {
 	struct gprs_rlc_cfg rlc_cfg;
 };
 
+/* See (struct gsm_bts *)->depends_on */
+struct bts_depends_on_entry {
+	struct llist_head list;
+	uint8_t bts_nr; /* See (struct gsm_bts *)->nr */
+};
+
 /* One BTS */
 struct gsm_bts {
 	/* list header in net->bts_list */
@@ -596,8 +602,8 @@ struct gsm_bts {
 	/* supported codecs beside FR */
 	struct bts_codec_conf codec;
 
-	/* BTS dependencies bit field */
-	uint32_t depends_on[256/(8*4)];
+	/* BTS dependencies bit field, list of "struct bts_depends_on_entry" */
+	struct llist_head depends_on;
 
 	/* full and half rate multirate config */
 	struct amr_multirate_conf mr_full;
@@ -830,10 +836,10 @@ static inline bool gsm_bts_features_negotiated(struct gsm_bts *bts)
 }
 
 /* dependency handling */
-void bts_depend_mark(struct gsm_bts *bts, int dep);
+int bts_depend_mark(struct gsm_bts *bts, int dep);
 void bts_depend_clear(struct gsm_bts *bts, int dep);
-int bts_depend_check(struct gsm_bts *bts);
-int bts_depend_is_depedency(struct gsm_bts *base, struct gsm_bts *other);
+bool bts_depend_check(struct gsm_bts *bts);
+bool bts_depend_is_depedency(struct gsm_bts *base, struct gsm_bts *other);
 
 int gsm_bts_get_radio_link_timeout(const struct gsm_bts *bts);
 void gsm_bts_set_radio_link_timeout(struct gsm_bts *bts, int value);

src/osmo-bsc/bts.c

@@ -343,6 +343,7 @@ struct gsm_bts *gsm_bts_alloc(struct gsm_network *net, struct gsm_bts_sm *bts_sm
 	INIT_LLIST_HEAD(&bts->neighbors);
 	INIT_LLIST_HEAD(&bts->oml_fail_rep);
 	INIT_LLIST_HEAD(&bts->chan_rqd_queue);
+	INIT_LLIST_HEAD(&bts->depends_on);
 
 	/* Don't pin the BTS to any MGW by default: */
 	bts->mgw_pool_target = -1;
@@ -869,37 +870,43 @@ void gsm_bts_mo_reset(struct gsm_bts *bts)
 	}
 }
 
-/* Assume there are only 256 possible bts */
-osmo_static_assert(sizeof(((struct gsm_bts *) 0)->nr) == 1, _bts_nr_is_256);
-static void depends_calc_index_bit(int bts_nr, int *idx, int *bit)
+int bts_depend_mark(struct gsm_bts *bts, int dep)
 {
-	*idx = bts_nr / (8 * 4);
-	*bit = bts_nr % (8 * 4);
+	struct bts_depends_on_entry *entry;
+	entry = talloc_zero(bts, struct bts_depends_on_entry);
+	if (!entry) {
+		LOG_BTS(bts, DNM, LOGL_ERROR, "Alloc of struct bts_depends_on_entry failed");
+		return -1;
+	}
+	entry->bts_nr = dep;
+	llist_add_tail(&entry->list, &bts->depends_on);
+	return 0;
 }
 
-void bts_depend_mark(struct gsm_bts *bts, int dep)
+static struct bts_depends_on_entry *bts_depend_find_entry(const struct gsm_bts *bts, int dep)
 {
-	int idx, bit;
-	depends_calc_index_bit(dep, &idx, &bit);
-
-	bts->depends_on[idx] |= 1U << bit;
+	struct bts_depends_on_entry *entry;
+	llist_for_each_entry(entry, &bts->trx_list, list) {
+		if (entry->bts_nr == dep)
+			return entry;
+	}
+	return NULL;
 }
 
 void bts_depend_clear(struct gsm_bts *bts, int dep)
 {
-	int idx, bit;
-	depends_calc_index_bit(dep, &idx, &bit);
-
-	bts->depends_on[idx] &= ~(1U << bit);
+	struct bts_depends_on_entry *entry;
+	entry = bts_depend_find_entry(bts, dep);
+	if (!entry)
+		return;
+	llist_del(&entry->list);
+	talloc_free(entry);
 }
 
-int bts_depend_is_depedency(struct gsm_bts *base, struct gsm_bts *other)
+bool bts_depend_is_depedency(struct gsm_bts *base, struct gsm_bts *other)
 {
-	int idx, bit;
-	depends_calc_index_bit(other->nr, &idx, &bit);
-
-	/* Check if there is a depends bit */
-	return (base->depends_on[idx] & (1U << bit)) > 0;
+	struct bts_depends_on_entry *entry = bts_depend_find_entry(base, other->nr);
+	return !!entry;
 }
 
 static bool bts_is_online(const struct gsm_bts *bts)
@@ -914,7 +921,7 @@ static bool bts_is_online(const struct gsm_bts *bts)
 	return bts->mo.nm_state.operational == NM_OPSTATE_ENABLED;
 }
 
-int bts_depend_check(struct gsm_bts *bts)
+bool bts_depend_check(struct gsm_bts *bts)
 {
 	struct gsm_bts *other_bts;
 
@@ -923,9 +930,9 @@ int bts_depend_check(struct gsm_bts *bts)
 			continue;
 		if (bts_is_online(other_bts))
 			continue;
-		return 0;
+		return false;
 	}
-	return 1;
+	return true;
 }
 
 /* get the radio link timeout (based on SACCH decode errors, according

src/osmo-bsc/bts_vty.c

@@ -2633,7 +2633,8 @@ DEFUN_ATTR(cfg_bts_depends_on, cfg_bts_depends_on_cmd,
 		return CMD_WARNING;
 	}
 
-	bts_depend_mark(bts, dep);
+	if (bts_depend_mark(bts, dep) < 0)
+		return CMD_WARNING;
 	return CMD_SUCCESS;
 }
 
@@ -4490,6 +4491,14 @@ static void config_write_bts_ncc_permitted(struct vty *vty, const char *prefix,
 	vty_out(vty, "%s", VTY_NEWLINE);
 }
 
+static void config_write_bts_depends_on(struct vty *vty, const char *prefix, const struct gsm_bts *bts)
+{
+	struct bts_depends_on_entry *entry;
+	llist_for_each_entry(entry, &bts->depends_on, list) {
+		vty_out(vty, "%sdepends-on-bts %u%s", prefix, entry->bts_nr, VTY_NEWLINE);
+	}
+}
+
 static void config_write_bts_single(struct vty *vty, struct gsm_bts *bts)
 {
 	int i;
@@ -4775,23 +4784,7 @@ static void config_write_bts_single(struct vty *vty, struct gsm_bts *bts)
 		vty_out(vty, "  %sforce-combined-si%s",
 			bts->force_combined_si ? "" : "no ", VTY_NEWLINE);
 
-	for (i = 0; i < ARRAY_SIZE(bts->depends_on); ++i) {
-		int j;
-
-		if (bts->depends_on[i] == 0)
-			continue;
-
-		for (j = 0; j < sizeof(bts->depends_on[i]) * 8; ++j) {
-			int bts_nr;
-
-			if ((bts->depends_on[i] & (1<<j)) == 0)
-				continue;
-
-			bts_nr = (i * sizeof(bts->depends_on[i]) * 8) + j;
-			vty_out(vty, "  depends-on-bts %d%s", bts_nr, VTY_NEWLINE);
-		}
-	}
-
+	config_write_bts_depends_on(vty, "  ", bts);
 	ho_vty_write_bts(vty, bts);
 
 	if (bts->top_acch_cap.overpower_db > 0) {