stats: Add stat_item for value monitoring

This commit adds instrumentation function to gather measurement
and statistical values similar to counter groups.

Multiple values can be stored per item, which can be retrieved in
FIFO order. Getting values from the item does not modify its state to
allow for multiple independant backends (e.g. VTY and statd).

When a new value is set, the oldest value gets silently overwritten.
Lost values are skipped when getting values from the item.

Sponsored-by: On-Waves ehf

2 files changed, 105 insertions, 0 deletions

diff --git a/include/Makefile.am b/include/Makefile.am
index 52c6a38f..7f8dd777 100644
--- a/include/Makefile.am
+++ b/include/Makefile.am
@@ -28,6 +28,7 @@ nobase_include_HEADERS = \
                        osmocom/core/prim.h \
                        osmocom/core/process.h \
                        osmocom/core/rate_ctr.h \
+                       osmocom/core/stat_item.h \
                        osmocom/core/select.h \
                        osmocom/core/signal.h \
                        osmocom/core/socket.h \
diff --git a/include/osmocom/core/stat_item.h b/include/osmocom/core/stat_item.h
new file mode 100644
index 00000000..e166579f
--- /dev/null
+++ b/include/osmocom/core/stat_item.h
@@ -0,0 +1,104 @@
+#pragma once
+
+/*! \defgroup stat_item Statistics value item
+ *  @{
+ */
+
+/*! \file stat_item.h */
+
+#include <stdint.h>
+
+#include <osmocom/core/linuxlist.h>
+
+struct stat_item_desc;
+
+/*! \brief data we keep for each actual value */
+struct stat_item {
+	const struct stat_item_desc *desc;
+	/*! \brief the index of the freshest value */
+	int32_t last_value_index;
+	/*! \brief offset to the freshest value in the value fifo */
+	int16_t last_offs;
+	/*! \brief value fifo */
+	int32_t values[0];
+};
+
+/*! \brief statistics value description */
+struct stat_item_desc {
+	const char *name;	/*!< \brief name of the item */
+	const char *description;/*!< \brief description of the item */
+	const char *unit;	/*!< \brief unit of a value */
+	unsigned int num_values;/*!< \brief number of values to store */
+	int32_t default_value;
+};
+
+/*! \brief description of a statistics value group */
+struct stat_item_group_desc {
+	/*! \brief The prefix to the name of all values in this group */
+	const char *group_name_prefix;
+	/*! \brief The human-readable description of the group */
+	const char *group_description;
+	/*! \brief The number of values in this group */
+	const unsigned int num_items;
+	/*! \brief Pointer to array of value names */
+	const struct stat_item_desc *item_desc;
+};
+
+/*! \brief One instance of a counter group class */
+struct stat_item_group {
+	/*! \brief Linked list of all value groups in the system */
+	struct llist_head list;
+	/*! \brief Pointer to the counter group class */
+	const struct stat_item_group_desc *desc;
+	/*! \brief The index of this value group within its class */
+	unsigned int idx;
+	/*! \brief Actual counter structures below */
+	struct stat_item *items[0];
+};
+
+struct stat_item_group *stat_item_group_alloc(
+	void *ctx,
+	const struct stat_item_group_desc *desc,
+	unsigned int idx);
+
+void stat_item_group_free(struct stat_item_group *grp);
+
+void stat_item_set(struct stat_item *val, int32_t value);
+
+int stat_item_init(void *tall_ctx);
+
+struct stat_item_group *stat_item_get_group_by_name_idx(
+	const char *name, const unsigned int idx);
+
+const struct stat_item *stat_item_get_by_name(
+	const struct stat_item_group *valg, const char *name);
+
+/*! \brief Retrieve the next value from the stat_item object.
+ * If a new value has been set, it is returned. The idx is used to decide
+ * which value to return.
+ * On success, *idx is updated to refer to the next unread value. If
+ * values have been missed due to FIFO overflow, *idx is incremented by
+ * (1 + num_lost).
+ * This way, the stat_item object can be kept stateless from the reader's
+ * perspective and therefore be used by several backends simultaneously.
+ *
+ * \param val	the stat_item object
+ * \param idx	identifies the next value to be read
+ * \param value	a pointer to store the value
+ * \returns  the increment of the index (0: no value has been read,
+ *           1: one value has been taken,
+ *           (1+n): n values have been skipped, one has been taken)
+ */
+int stat_item_get_next(const struct stat_item *val, int32_t *idx, int32_t *value);
+
+/*! \brief Get the last (freshest) value */
+static int32_t stat_item_get_last(const struct stat_item *val);
+
+/*! \brief Skip all values of the item and update idx accordingly */
+int stat_item_discard(const struct stat_item *val, int32_t *idx);
+
+static inline int32_t stat_item_get_last(const struct stat_item *val)
+{
+	return val->values[val->last_offs];
+}
+/*! @} */