lib: data-stack - data_stack_last_buffer_reset(() - Add comments and an assert

This clarifies how the function is expected to work.

diff --git a/src/lib/data-stack.c b/src/lib/data-stack.c
index fe7361402cf5bfd01374750fcbaca45498d4a08f..59d268d91bacf2401206dfd84b234c18f4f09ded 100644 (file)
--- a/src/lib/data-stack.c
+++ b/src/lib/data-stack.c
@@ -113,6 +113,10 @@ static void data_stack_last_buffer_reset(bool preserve_data ATTR_UNUSED)
 #ifdef DEBUG
                unsigned char *last_alloc_end, *p, *pend;
 
+               /* We assume that this function gets called before
+                  current_block changes. */
+               i_assert(last_buffer_block == current_block);
+
                last_alloc_end = data_stack_after_last_alloc(current_block);
                p = last_alloc_end + MEM_ALIGN(sizeof(size_t)) + last_buffer_size;
                pend = last_alloc_end + ALLOC_SIZE(last_buffer_size);
@@ -125,6 +129,11 @@ static void data_stack_last_buffer_reset(bool preserve_data ATTR_UNUSED)
                last_buffer_block = NULL;
 
 #ifdef DEBUG
+               /* NOTE: If the below panic triggers, it may also be due to an
+                  internal bug in data-stack (since this is rather complex). While
+                  debugging whether that is the case, it's a good idea to change the
+                  i_panic() to abort(). Otherwise the i_panic() changes the
+                  data-stack's internal state and complicates debugging. */
                while (p < pend)
                        if (*p++ != CLEAR_CHR)
                                i_panic("t_buffer_get(): buffer overflow");