17.09.2020 19:32, Alberto Garcia wrote:
On Wed 09 Sep 2020 08:59:25 PM CEST, Vladimir Sementsov-Ogievskiy
<vsement...@virtuozzo.com> wrote:
+ * On success return true with bm_list set (probably to NULL, if no bitmaps),
" probably " ? :-)
I note this as "set to NULL" is not obvious thing (is it "unset" ? :).. And by "probably" I mean
"may be", i.e. NULL is just one of possible cases. Probably I use "probably" in a wrong way?
+ * on failure return false with errp set.
*/
-Qcow2BitmapInfoList *qcow2_get_bitmap_info_list(BlockDriverState *bs,
- Error **errp)
+bool qcow2_get_bitmap_info_list(BlockDriverState *bs,
+ Qcow2BitmapInfoList **info_list, Error **errp)
{
BDRVQcow2State *s = bs->opaque;
Qcow2BitmapList *bm_list;
Qcow2Bitmap *bm;
- Qcow2BitmapInfoList *list = NULL;
- Qcow2BitmapInfoList **plist = &list;
So here 'list' points at NULL and 'plist' at &list.
Hmm, to be precise, list _is_ NULL (and points nowhere), and plist points to
list.
- *plist = obj;
- plist = &obj->next;
In the original code 'plist' is updated when you add a new element, so
it always points at the end of the list. But 'list' is unchanged and it
still points at the first element.
So the caller receives a pointer to the first element.
+ *info_list = obj;
+ info_list = &obj->next;
But in the new code there is only one variable (passed by the caller),
which always points at the end of the list.
No: at first "*info_list = obj", we set the result which user will get, users
pointer now points to the first object in the list.
Then, at "info_list = &obj->next", we reassign info_list to another pointer: to "next"
field of first list item. So, all further "*info_list = obj" are note visible to the caller.
Actually, the logic is not changed, just instead of plist we use info_list, and instead of list - a variable which
should be defined in the caller. Look: in old code, first "*plist = obj" sets "list" variable, but
all further "*plist = obj" don't change "list" variable.
--
Best regards,
Vladimir
