updated talloc guide for recent API changes

1 files changed, 54 insertions, 2 deletions

diff --git a/lib/talloc/talloc_guide.txt b/lib/talloc/talloc_guide.txt
index 3201fe6f0f..7890f9f265 100644
--- a/lib/talloc/talloc_guide.txt
+++ b/lib/talloc/talloc_guide.txt
@@ -4,10 +4,10 @@ Using talloc in Samba4
 .. contents::
 
 Andrew Tridgell
-September 2004
+August 2009
 
 The most current version of this document is available at
-   http://samba.org/ftp/unpacked/samba4/source/lib/talloc/talloc_guide.txt
+   http://samba.org/ftp/unpacked/talloc/talloc_guide.txt
 
 If you are used to the "old" talloc from Samba3 before 3.0.20 then please read
 this carefully, as talloc has changed a lot. With 3.0.20 (or 3.0.14?) the
@@ -131,6 +131,22 @@ For more control on which parent is removed, see talloc_unlink()
 
 talloc_free() operates recursively on its children.
 
+As a special case, talloc_free() is refused on pointers that have more
+than one parent, as talloc would have no way of knowing which parent
+should be removed. To free a pointer that has more than one parent
+please use talloc_unlink().
+
+To help you find problems in your code caused by this behaviour, if
+you do try and free a pointer with more than one parent then the
+talloc logging function will be called to give output like this:
+
+  ERROR: talloc_free with references at some_dir/source/foo.c:123
+  	reference at some_dir/source/other.c:325
+  	reference at some_dir/source/third.c:121
+
+Please see the documentation for talloc_set_log_fn() and
+talloc_set_log_stderr() for more information on talloc logging
+functions.
 
 =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-
 int talloc_free_children(void *ptr);
@@ -349,6 +365,42 @@ as to your sanity or the safety of your data if you do this.
 
 talloc_steal (new_ctx, NULL) will return NULL with no sideeffects.
 
+Note that if you try and call talloc_steal() on a pointer that has
+more than one parent then the result is ambiguous. Talloc will choose
+to remove the parent that is currently indicated by talloc_parent()
+and replace it with the chosen parent. You will also get a message
+like this via the talloc logging functions:
+
+  WARNING: talloc_steal with references at some_dir/source/foo.c:123
+  	reference at some_dir/source/other.c:325
+  	reference at some_dir/source/third.c:121
+
+To unambiguously change the parent of a pointer please see the
+function talloc_reparent(). See the talloc_set_log_fn() documentation
+for more information on talloc logging.
+
+=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-
+void *talloc_reparent(const void *old_parent, const void *new_parent, const void *ptr);
+
+The talloc_reparent() function changes the parent context of a talloc
+pointer. It is typically used when the context that the pointer is
+currently a child of is going to be freed and you wish to keep the
+memory for a longer time.
+
+The talloc_reparent() function returns the pointer that you pass it. It
+does not have any failure modes.
+
+The difference between talloc_reparent() and talloc_steal() is that
+talloc_reparent() can specify which parent you wish to change. This is
+useful when a pointer has multiple parents via references.
+
+=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-
+void *talloc_parent(const void *ptr);
+
+The talloc_parent() function returns the current talloc parent. This
+is usually the pointer under which this memory was originally created,
+but it may have changed due to a talloc_steal() or talloc_reparent()
+
 =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-
 size_t talloc_total_size(const void *ptr);