Nouveau - Mar 2022 - [PATCH 2/6] treewide: remove using list iterator after loop body as a ptr

On Tue, Mar 1, 2022 at 2:58 PM David Laight <David.Laight at aculab.com>
wrote:
>
> Can it be resolved by making:
> #define list_entry_is_head(pos, head, member) ((pos) == NULL)
> and double-checking that it isn't used anywhere else (except in
> the list macros themselves).
Well, yes, except for the fact that then the name is entirely misleading...

And somebody possibly uses it together with list_first_entry() etc, so
it really is completely broken to mix that change with the list
traversal change.

             Linus

               Linus

From: Linus Torvalds
> Sent: 01 March 2022 23:03
> 
> On Tue, Mar 1, 2022 at 2:58 PM David Laight <David.Laight at
aculab.com> wrote:
> >
> > Can it be resolved by making:
> > #define list_entry_is_head(pos, head, member) ((pos) == NULL)
> > and double-checking that it isn't used anywhere else (except in
> > the list macros themselves).
> 
> Well, yes, except for the fact that then the name is entirely misleading...
> 
> And somebody possibly uses it together with list_first_entry() etc, so
> it really is completely broken to mix that change with the list
> traversal change.
Probably true :-(

Actually adding list_entry_not_found() as a synonym for
list_entry_is_head() and changing the 25ish places that
use it after a loop might work.

Once that is done the loop can be changed at the same time
as list_entry_not_found().
That won't affect the in-tree callers.
(and my out of tree modules don't use those lists - so I
don't care about that!)

Having said that there are so few users of list_entry_is_head()
it is reasonable to generate two new names.
One for use after list_for_each_entry() and one for list_next_entry().
Then the change all the call sites.
After that list_entry_is_head() can be deleted - breaking out of
tree compiles.
Finally list_for_each_entry() can be rewritten to set NULL
at the end of the list.

	David

-
Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT,
UK
Registration No: 1397386 (Wales)