Re: [PATCH] drivers/block/ub.c: use list_for_each_entry()

Pete Zaitcev
2007-05-30T23:32:21Z

On Wed, 30 May 2007 16:14:01 -0700, Roland Dreier <rdreier@cisco.com> wrote:

> > The negative is the sheer number of helper functions in list.h. Personally,
> > I find it difficult to retain a working knowledge of them. Iterators are
> > particularly nasty that way. I'm thinking about dropping all of these
> > list_for_each_with_murky_argument_requirements_and_odd_side_effects()
> > and use plain for(;;), as a courtesy to someone who has to read the
> > code years down the road.
>
> I think I disagree with this reasoning. If I'm reading your code and
> I see, say, list_for_each_entry_safe(), I can be pretty confident that
> your loop works correctly. If you write your own for loop, then I
> have to check that you actually got the linked list walking right.

You have to check that I used list_for_each_entry_safe correctly too,
which is harder. Are you aware that we had (and probably still have)
dozens of cases where the use of list_for_each_entry_safe was buggy?
Most of them involved IHV programmers being lured into false sense
of security by the _safe suffix and getting their locking wrong.

You could not find a better way to blow up your own argument
than to mention list_for_each_entry_safe(), which is anything but.
Matthias' use of list_for_each_entry() actually IS safe, which is
why I am not NAKing it. Andrew has accepted it already. I just
think we aren't winning squat here.

-- Pete