Re: [PATCH] linux/kernel.h: add container_from()

[Al Viro <viro@zeniv.linux.org.uk>]

On Thu, Aug 27, 2020 at 01:46:33PM -0700, Linus Torvalds wrote:

> You really have to pick some pretty excessive type names (or variable
> names) to get close to 80 characters. Again, to pick an example:
> 
>         struct timer_group_priv *priv = container_of(handle,
>                         struct timer_group_priv, timer[handle->num]);
> 
> ends up being long even if you were to split it, but that funky
> container_from() wouldn't have helped the real problem - the fact that
> the above is complex and nasty.
> 
> And I had to _search_ for that example. All the normal cases of
> split-line container-of's were due to doing it with the declaration,
> or beause the first argument ended up being an expression in itself
> and the nested expressions made it more complex.

Speaking of searching, this kind of typeof use is, IMO, actively
harmful - it makes finding the places where we might get from
e.g. linked list to containing objects much harder.  container_of
(unless combined with obfuscating use of typeof()) at least gives
you a chance to grep - struct foo *not* followed by '*' is a pattern
that doesn't give too many false positives.  This one, OTOH, is
essentially impossible to grep for.