common: add lttng_dynamic_array_set_count()

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

diff --git a/src/common/dynamic-array.c b/src/common/dynamic-array.c
index 198df19bbaa89d5bff75911fdf2d1b915b0cfd3e..81c2c3efa15ba1927a61ecc608ea07a9bd9b6f07 100644 (file)
--- 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 208dd1956b41263df7f8336605f22e082bff21ac..0b488a39cd52f95b785f2f3a52ee48f6c3e9cd0b 100644 (file)
--- 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.