[PATCH v2 1/5] histograms: Initial histograms interface

[Stevie Alvarez <stevie.6strings@gmail.com>]

From: "Stevie Alvarez (Google)" <stevie.6strings@gmail.com>

Initial header file for libtraceeval's histogram API. The interface
provides a simple way of aggregating trace data and reading through said
data.

Signed-off-by: Stevie Alvarez (Google) <stevie.6strings@gmail.com>
---
 include/traceeval-hist.h | 128 +++++++++++++++++++++++++++++++++++++++
 1 file changed, 128 insertions(+)
 create mode 100644 include/traceeval-hist.h

diff --git a/include/traceeval-hist.h b/include/traceeval-hist.h
new file mode 100644
index 0000000..4664974
--- /dev/null
+++ b/include/traceeval-hist.h
@@ -0,0 +1,128 @@
+/* SPDX-License-Identifier: MIT */
+/*
+ * libtraceeval histogram interface.
+ *
+ * Copyright (C) 2023 Google Inc, Steven Rostedt <rostedt@goodmis.org>
+ * Copyright (C) 2023 Google Inc, Stevie Alvarez <stevie.6strings@gmail.com>
+ */
+#ifndef __LIBTRACEEVAL_HIST_H__
+#define __LIBTRACEEVAL_HIST_H__
+
+#include <stdlib.h>
+#include <stddef.h>
+#include <stdbool.h>
+
+/* Data definition interfaces */
+
+/* Field name/descriptor for number of hits */
+#define TRACEEVAL_VAL_HITS ((const char *)(-1UL))
+
+/* Data type distinguishers */
+enum traceeval_data_type {
+	TRACEEVAL_TYPE_NONE,
+	TRACEEVAL_TYPE_STRING,
+	TRACEEVAL_TYPE_NUMBER,
+	TRACEEVAL_TYPE_NUMBER_64,
+	TRACEEVAL_TYPE_NUMBER_32,
+	TRACEEVAL_TYPE_NUMBER_16,
+	TRACEEVAL_TYPE_NUMBER_8,
+	TRACEEVAL_TYPE_DYNAMIC
+};
+
+/* Statistics specification flags */
+enum traceeval_flags {
+	TRACEEVAL_FL_SIGNED		= (1 << 0),
+	TRACEEVAL_FL_TIMESTAMP		= (1 << 1),
+	TRACEEVAL_FL_STATS		= (1 << 2)
+};
+
+/*
+ * Trace data entry for a traceeval histogram
+ * Constitutes keys and values.
+ */
+union traceeval_data {
+	char				*string;
+	struct traceeval_dynamic	*dyn_data;
+	unsigned long long		number_64;
+	unsigned long			number;
+	unsigned int			number_32;
+	unsigned short			number_16;
+	unsigned char			number_8;
+};
+
+/*
+ * struct traceeval_dynamic - Storage for dynamic traceeval_types
+ * @size: The size of the dynamic type
+ * @data: The pointer to the data of the dynamic type
+ */
+struct traceeval_dynamic {
+	void		*data;
+	size_t		size;
+};
+
+/* struct traceeval_dynamic release function signature */
+typedef void (*traceeval_dyn_release_fn)(struct traceeval_dynamic *,
+		struct traceeval_type *);
+
+/* struct traceeval_dynamic compare function signature */
+typedef int (*traceeval_dyn_cmp_fn)(struct traceeval_dynamic *,
+		struct traceeval_dynamic *, struct traceeval_type *);
+
+/*
+ * struct traceeval_type - Describes the type of a traceevent_data instance
+ * @type: The enum type that describes the traceeval_data
+ * @name: The string name of the traceeval_data
+ * @flags: flags to describe the traceeval_data
+ * @id: User specified identifier
+ * @dyn_release: For dynamic types called on release (ignored for other types)
+ * @dyn_cmp: A way to compare dynamic types (ignored for other types)
+ *
+ * The traceeval_type structure defines expectations for a corresponding
+ * traceeval_data instance for a traceeval histogram instance. Used to
+ * describe both keys and values.
+ *
+ * The @id field is an optional value in case the user has multiple struct
+ * traceeval_type instances with @type fields set to TRACEEVAL_TYPE_DYNAMIC,
+ * which each relate to distinct user defined struct traceeval_dynamic
+ * 'sub-types'.
+ *
+ * For flexibility, @dyn_cmp() and @dyn_release() take a struct
+ * traceeval_type instance. This allows the user to distinguish between
+ * different sub-types of struct traceeval_dynamic within a single
+ * callback function by examining the @id field. This is not a required
+ * approach, merely one that is accommodated.
+ *
+ * @dyn_cmp() is used to compare two struct traceeval_dynamic instances when a
+ * corresponding struct traceeval_type is reached with its type field set to
+ * TRACEEVAL_TYPE_DYNAMIC. It should return 0 on equality, 1 if the first
+ * argument is greater than the second, -1 for the other way around, and -2 on
+ * error.
+ *
+ * dyn_release() is used during traceeval_release() to release a union
+ * traceeval_data's struct traceeval_dynamic field when the corresponding
+ * traceeval_type type is set to TRACEEVAL_TYPE_DYNAMIC.
+ */
+struct traceeval_type {
+	char				*name;
+	traceeval_dyn_release_fn	dyn_release;
+	traceeval_dyn_cmp_fn		dyn_cmp;
+	enum traceeval_data_type	type;
+	size_t				flags;
+	size_t				id;
+};
+
+/* Statistics about a given entry element */
+struct traceeval_stat {
+	unsigned long long	max;
+	unsigned long long	min;
+	unsigned long long	total;
+	unsigned long long	avg;
+	unsigned long long	std;
+};
+
+/* Iterator over aggregated data */
+struct traceeval_iterator;
+
+struct traceeval;
+
+#endif /* __LIBTRACEEVAL_HIST_H__ */
-- 
2.41.0