From: Jérémie Galarneau <jeremie.galarneau@efficios.com>
Date: Sat, 27 May 2017 11:32:50 +0000 (-0400)
Subject: Docs: improve the documentation of the dynamic buffer interface
X-Git-Tag: v2.11.0-rc1~555
X-Git-Url: https://git.lttng.org./?a=commitdiff_plain;h=63557623eba8b58076e0454731a2d52e2ac5966b;p=lttng-tools.git

Docs: improve the documentation of the dynamic buffer interface

Signed-off-by: Jérémie Galarneau <jeremie.galarneau@efficios.com>
---

diff --git a/src/common/dynamic-buffer.c b/src/common/dynamic-buffer.c
index 05d3022af..4f1116213 100644
--- a/src/common/dynamic-buffer.c
+++ b/src/common/dynamic-buffer.c
@@ -59,11 +59,11 @@ int lttng_dynamic_buffer_append(struct lttng_dynamic_buffer *buffer,
 		goto end;
 	}
 
-	assert(buffer->capacity >= buffer->size);
-	if (buffer->capacity < (len + buffer->size)) {
+	assert(buffer->_capacity >= buffer->size);
+	if (buffer->_capacity < (len + buffer->size)) {
 		ret = lttng_dynamic_buffer_set_capacity(buffer,
-				buffer->capacity +
-				(len - (buffer->capacity - buffer->size)));
+				buffer->_capacity +
+				(len - (buffer->_capacity - buffer->size)));
 		if (ret) {
 			goto end;
 		}
@@ -104,9 +104,9 @@ int lttng_dynamic_buffer_set_size(struct lttng_dynamic_buffer *buffer,
 		goto end;
 	}
 
-	if (new_size > buffer->capacity) {
+	if (new_size > buffer->_capacity) {
 		size_t original_size = buffer->size;
-		size_t original_capacity = buffer->capacity;
+		size_t original_capacity = buffer->_capacity;
 
 		ret = lttng_dynamic_buffer_set_capacity(buffer, new_size);
 		if (ret) {
@@ -155,7 +155,7 @@ int lttng_dynamic_buffer_set_capacity(struct lttng_dynamic_buffer *buffer,
 		goto end;
 	}
 
-	if (new_capacity == buffer->capacity) {
+	if (new_capacity == buffer->_capacity) {
 		goto end;
 	}
 
@@ -166,7 +166,7 @@ int lttng_dynamic_buffer_set_capacity(struct lttng_dynamic_buffer *buffer,
 		goto end;
 	}
 	buffer->data = new_buf;
-	buffer->capacity = new_capacity;
+	buffer->_capacity = new_capacity;
 end:
 	return ret;
 }
@@ -178,6 +178,6 @@ void lttng_dynamic_buffer_reset(struct lttng_dynamic_buffer *buffer)
 		return;
 	}
 	buffer->size = 0;
-	buffer->capacity = 0;
+	buffer->_capacity = 0;
 	free(buffer->data);
 }
diff --git a/src/common/dynamic-buffer.h b/src/common/dynamic-buffer.h
index 19097f927..d05356b73 100644
--- a/src/common/dynamic-buffer.h
+++ b/src/common/dynamic-buffer.h
@@ -23,33 +23,61 @@
 
 struct lttng_dynamic_buffer {
 	char *data;
+	/* size is the buffer's currently used capacity. */
 	size_t size;
-	size_t capacity;
+	/*
+	 * capacity shall not be accessed by users directly, it is meant for
+	 * internal use only.
+	 */
+	size_t _capacity;
 };
 
+/*
+ * Initialize a dynamic buffer. This performs no allocation and is meant
+ * to be used instead of memset or explicit initialization of the buffer.
+ */
 void lttng_dynamic_buffer_init(struct lttng_dynamic_buffer *buffer);
 
+/*
+ * Append the content of a raw memory buffer to the end of a dynamic buffer
+ * (after its current "size"). The dynamic buffer's size is increased by
+ * "len", and its capacity is adjusted automatically.
+ */
 int lttng_dynamic_buffer_append(struct lttng_dynamic_buffer *buffer,
 		const void *buf, size_t len);
 
+/*
+ * Performs the same action as lttng_dynamic_buffer_append(), but using another
+ * dynamic buffer as the source buffer. The source buffer's size is used in lieu
+ * of "len".
+ */
 int lttng_dynamic_buffer_append_buffer(struct lttng_dynamic_buffer *dst_buffer,
 		struct lttng_dynamic_buffer *src_buffer);
 
 /*
  * Set the buffer's size to new_size. The capacity of the buffer will
  * be expanded (if necessary) to accomodate new_size. Areas acquired by
- * an enlarging new_size _will be zeroed_.
+ * a size increase will be zeroed.
  *
  * Be careful to expand the buffer's size _before_ calling out external
  * APIs (e.g. read(3)) which may populate the buffer as setting the size
- * _after_ will zero-out the result of the operation.
+ * after will zero-out the result of the operation.
+ *
+ * Shrinking a buffer 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().
  */
 int lttng_dynamic_buffer_set_size(struct lttng_dynamic_buffer *buffer,
 		size_t new_size);
 
 /*
  * Set the buffer's capacity to accomodate the new_capacity, allocating memory
- * as necessary. The buffer's content is preserved.
+ * as necessary. The buffer's content is preserved. Setting a buffer's capacity
+ * is meant as a _hint_ to the underlying buffer and is only optimization; no
+ * guarantee is offered that subsequent calls to append or set_size will succeed.
  *
  * If the current size > new_capacity, the operation will fail.
  */