stat_item: make value ids item specific

Fix counting of values missed because of FIFO overflow in
osmo_stat_item_get_next(), by assigning a new item value id effectively
as item->value[n + 1].id = item->value[n].id + 1, instead of increasing
a global_value_id that is shared between all items and groups. With
global_value_id, the count of values missed was wrong for one item, as
soon as a new value was added to another item.

This partially reverts b27b352e ("stats: Use a global index for stat
item values") from 2015, right after stats was added to libosmocore. It
was supposed to make multiple readers (reporters) possible, which could
read independently from stat_item (and later added comments explain it
like that). But this remained unused, stats has implemented multiple
reporters by reading all stat_items once and sending the same data to
all enabled reporters. The patch caused last_value_index in struct
osmo_stat_item to always remain at -1.

Replace this unused last_value_index with stats_next_id, so stats can
store the item-specific next_id in the struct again. It appears that
stats is the only direct user of osmo_stat_item, but if there are
others, they can bring their own item-specific next_id: functions in
stat_item.c still accept a next_id argument.

Related: OS#5088
Change-Id: Ie65dcdf52c8fc3d916e20d7f0455f6223be6b64f

1 files changed, 8 insertions, 4 deletions

diff --git a/include/osmocom/core/stat_item.h b/include/osmocom/core/stat_item.h
index 4a19465f..29e35ef6 100644
--- a/include/osmocom/core/stat_item.h
+++ b/include/osmocom/core/stat_item.h
@@ -6,6 +6,7 @@
 
 #include <stdint.h>
 
+#include <osmocom/core/defs.h>
 #include <osmocom/core/linuxlist.h>
 
 struct osmo_stat_item_desc;
@@ -23,9 +24,11 @@ struct osmo_stat_item_value {
 struct osmo_stat_item {
 	/*! back-reference to the item description */
 	const struct osmo_stat_item_desc *desc;
-	/*! the index of the freshest value */
-	int32_t last_value_index;
-	/*! offset to the freshest value in the value FIFO */
+	/* internal use by stats API (stats.c): the id of the next value to
+	 * be read from the FIFO. If accessing osmo_stat_item directly, without
+	 * the stats API, store this value elsewhere. */
+	int32_t stats_next_id;
+	/*! the index of the last value written to the FIFO */
 	int16_t last_offs;
 	/*! value FIFO */
 	struct osmo_stat_item_value values[0];
@@ -98,7 +101,8 @@ static int32_t osmo_stat_item_get_last(const struct osmo_stat_item *item);
 
 int osmo_stat_item_discard(const struct osmo_stat_item *item, int32_t *next_id);
 
-int osmo_stat_item_discard_all(int32_t *next_id);
+int osmo_stat_item_discard_all(int32_t *next_id)
+	OSMO_DEPRECATED("Use osmo_stat_item_discard with item-specific next_id instead");
 
 typedef int (*osmo_stat_item_handler_t)(
 	struct osmo_stat_item_group *, struct osmo_stat_item *, void *);