[RFC PATCH 1/4] libtracefs: Add new constructors for histograms

["Yordan Karadzhov (VMware)" <y.karadz@gmail.com>]

The current way to create an N-dimensional histogram is bit
counterintuitive. We first have to call tracefs_hist_alloc()
which is essentially a constructor of 1d histogram. Then we
have to call tracefs_hist_add_key() N-1 times in order to
increase the dimentions of the histogram. Here we transform
tracefs_hist_alloc() into a constructor of N-dimensional
histogram and we also add 2 helper constructors for 1d and
2d histograms.

Signed-off-by: Yordan Karadzhov (VMware) <y.karadz@gmail.com>
---
 include/tracefs.h  | 17 +++++++++-
 src/tracefs-hist.c | 82 ++++++++++++++++++++++++++++++++++++++--------
 2 files changed, 85 insertions(+), 14 deletions(-)

diff --git a/include/tracefs.h b/include/tracefs.h
index b4aa75d..64fbb3f 100644
--- a/include/tracefs.h
+++ b/include/tracefs.h
@@ -280,10 +280,25 @@ enum tracefs_hist_sort_direction {
 struct tracefs_hist;
 
 void tracefs_hist_free(struct tracefs_hist *hist);
+struct tracefs_hist *
+tracefs_hist1d_alloc(struct tracefs_instance * instance,
+		     const char *system, const char *event,
+		     const char *key, enum tracefs_hist_key_type type);
+struct tracefs_hist *
+tracefs_hist2d_alloc(struct tracefs_instance * instance,
+		     const char *system, const char *event,
+		     const char *key1, enum tracefs_hist_key_type type1,
+		     const char *key2, enum tracefs_hist_key_type type2);
+
+struct tracefs_hist_axis {
+	const char *key;
+	enum tracefs_hist_key_type type;
+};
+
 struct tracefs_hist *
 tracefs_hist_alloc(struct tracefs_instance * instance,
 		   const char *system, const char *event,
-		   const char *key, enum tracefs_hist_key_type type);
+		   struct tracefs_hist_axis *axes);
 int tracefs_hist_add_key(struct tracefs_hist *hist, const char *key,
 			 enum tracefs_hist_key_type type);
 int tracefs_hist_add_value(struct tracefs_hist *hist, const char *value);
diff --git a/src/tracefs-hist.c b/src/tracefs-hist.c
index 6519f7e..8501d64 100644
--- a/src/tracefs-hist.c
+++ b/src/tracefs-hist.c
@@ -141,7 +141,7 @@ void tracefs_hist_free(struct tracefs_hist *hist)
 }
 
 /**
- * tracefs_hist_alloc - Initialize a histogram
+ * tracefs_hist1d_alloc - Initialize one-dimensional histogram
  * @instance: The instance the histogram will be in (NULL for toplevel)
  * @system: The system the histogram event is in.
  * @event: The event that the histogram will be attached to.
@@ -157,14 +157,69 @@ void tracefs_hist_free(struct tracefs_hist *hist)
  * NULL on failure.
  */
 struct tracefs_hist *
+tracefs_hist1d_alloc(struct tracefs_instance * instance,
+		     const char *system, const char *event,
+		     const char *key, enum tracefs_hist_key_type type)
+{
+	struct tracefs_hist_axis axis[] = {{key, type}, {NULL, 0}};
+
+	return tracefs_hist_alloc(instance, system, event, axis);
+}
+
+/**
+ * tracefs_hist2d_alloc - Initialize two-dimensional histogram
+ * @instance: The instance the histogram will be in (NULL for toplevel)
+ * @system: The system the histogram event is in.
+ * @event: The event that the histogram will be attached to.
+ * @key1: The first primary key the histogram will use
+ * @type1: The format type of the first key.
+ * @key2: The second primary key the histogram will use
+ * @type2: The format type of the second key.
+ *
+ * Will initialize a histogram descriptor that will be attached to
+ * the @system/@event with the given @key1 and @key2 as the primaries.
+ * This only initializes the descriptor, it does not start the histogram
+ * in the kernel.
+ *
+ * Returns an initialized histogram on success.
+ * NULL on failure.
+ */
+struct tracefs_hist *
+tracefs_hist2d_alloc(struct tracefs_instance * instance,
+		     const char *system, const char *event,
+		     const char *key1, enum tracefs_hist_key_type type1,
+		     const char *key2, enum tracefs_hist_key_type type2)
+{
+	struct tracefs_hist_axis axis[] = {{key1, type1},
+					   {key2, type2},
+					   {NULL, 0}};
+
+	return tracefs_hist_alloc(instance, system, event, axis);
+}
+
+/**
+ * tracefs_hist_alloc - Initialize N-dimensional histogram
+ * @instance: The instance the histogram will be in (NULL for toplevel)
+ * @system: The system the histogram event is in
+ * @event: The event that the histogram will be attached to
+ * @axes: An array of histogram axes, terminated by a {NULL, 0} entry
+ *
+ * Will initialize a histogram descriptor that will be attached to
+ * the @system/@event. This only initializes the descriptor with the given
+ * @axes keys as primaries. This only initializes the descriptor, it does
+ * not start the histogram in the kernel.
+ *
+ * Returns an initialized histogram on success.
+ * NULL on failure.
+ */
+struct tracefs_hist *
 tracefs_hist_alloc(struct tracefs_instance * instance,
 		   const char *system, const char *event,
-		   const char *key, enum tracefs_hist_key_type type)
+		   struct tracefs_hist_axis *axes)
 {
 	struct tracefs_hist *hist;
-	int ret;
 
-	if (!system || !event || !key)
+	if (!system || !event)
 		return NULL;
 
 	if (!tracefs_event_file_exists(instance, system, event, HIST_FILE))
@@ -174,8 +229,7 @@ tracefs_hist_alloc(struct tracefs_instance * instance,
 	if (!hist)
 		return NULL;
 
-	ret = trace_get_instance(instance);
-	if (ret < 0) {
+	if (trace_get_instance(instance) < 0) {
 		free(hist);
 		return NULL;
 	}
@@ -184,16 +238,18 @@ tracefs_hist_alloc(struct tracefs_instance * instance,
 
 	hist->system = strdup(system);
 	hist->event = strdup(event);
+	if (!hist->system || !hist->event)
+		goto fail;
 
-	ret = tracefs_hist_add_key(hist, key, type);
-
-	if (!hist->system || !hist->event || ret < 0) {
-		tracefs_hist_free(hist);
-		return NULL;
-	}
-
+	for (; axes && axes->key; axes++)
+		if (tracefs_hist_add_key(hist, axes->key, axes->type) < 0)
+			goto fail;
 
 	return hist;
+
+ fail:
+	tracefs_hist_free(hist);
+	return NULL;
 }
 
 /**
-- 
2.30.2