From 5fe3e097f121a17b37c098f87cba2b4a51d6208b Mon Sep 17 00:00:00 2001
From: =?utf8?q?J=C3=A9r=C3=A9mie=20Galarneau?=
 <jeremie.galarneau@efficios.com>
Date: Fri, 19 Jun 2020 18:20:08 -0400
Subject: [PATCH] common: add lttng_dynamic_array_set_count()
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Add an lttng_dynamic_array_set_count() helper to resize a dynamic
array.

Signed-off-by: Jérémie Galarneau <jeremie.galarneau@efficios.com>
Change-Id: Ic38efdb9c2ee6a4176fcde93e4b0d45052d14799
---
 src/common/dynamic-array.c | 29 +++++++++++++++++++++++++++++
 src/common/dynamic-array.h | 19 +++++++++++++++++++
 2 files changed, 48 insertions(+)

diff --git a/src/common/dynamic-array.c b/src/common/dynamic-array.c
index 198df19bb..81c2c3efa 100644
--- a/src/common/dynamic-array.c
+++ b/src/common/dynamic-array.c
@@ -18,6 +18,35 @@ void lttng_dynamic_array_init(struct lttng_dynamic_array *array,
 	array->destructor = destructor;
 }
 
+LTTNG_HIDDEN
+int lttng_dynamic_array_set_count(struct lttng_dynamic_array *array,
+		size_t new_element_count)
+{
+	int ret;
+
+	if (!array) {
+		ret = -1;
+		goto end;
+	}
+
+	if (array->destructor) {
+		size_t i;
+
+		for (i = new_element_count; i < array->size; i++) {
+			void *element = lttng_dynamic_array_get_element(
+					array, i);
+
+			array->destructor(element);
+		}
+	}
+
+	array->size = new_element_count;
+	ret = lttng_dynamic_buffer_set_size(&array->buffer,
+			new_element_count * array->element_size);
+end:
+	return ret;
+}
+
 LTTNG_HIDDEN
 int lttng_dynamic_array_add_element(struct lttng_dynamic_array *array,
 		const void *element)
diff --git a/src/common/dynamic-array.h b/src/common/dynamic-array.h
index 208dd1956..0b488a39c 100644
--- a/src/common/dynamic-array.h
+++ b/src/common/dynamic-array.h
@@ -56,6 +56,25 @@ void *lttng_dynamic_array_get_element(const struct lttng_dynamic_array *array,
 	return array->buffer.data + (element_index * array->element_size);
 }
 
+/*
+ * Set the array's element count to new_element_count. Any added element will
+ * be zeroed.
+ *
+ * Be careful to expand the array's element count _before_ calling out external
+ * APIs (e.g. read(3)) which may populate the buffer as setting the element
+ * count after will zero-out the result of the operation.
+ *
+ * Shrinking an array does not zero the old content. If the buffer may contain
+ * sensititve information, it must be cleared manually _before_ changing the
+ * size.
+ *
+ * NOTE: It is striclty _invalid_ to access memory after _size_, regardless
+ *       of prior calls to set_capacity().
+ */
+LTTNG_HIDDEN
+int lttng_dynamic_array_set_count(struct lttng_dynamic_array *array,
+		size_t new_element_count);
+
 /*
  * Add an element to the end of a dynamic array. The array's element count is
  * increased by one and its underlying capacity is adjusted automatically.
-- 
2.34.1