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 05d3022af19d0e4e8ef9d0527a6069394131eb6b..4f1116213a55dce6ec54be42efec2519f35a280e 100644 (file)
--- 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 19097f927e219bdb4e7eb69defe1f4e12db1f447..d05356b73a2d8c2d002861011b1fb08d0dee4c6d 100644 (file)
--- 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.
  */