linux-kernel - Re: [RFC PATCH 4/4] llist.h: Fix parentheses around macro pointer parameter use

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Date:   Fri, 5 May 2023 11:08:46 -0700
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
Cc:     "Huang, Ying" <ying.huang@...el.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        linux-kernel@...r.kernel.org, Peter Zijlstra <peterz@...radead.org>
Subject: Re: [RFC PATCH 4/4] llist.h: Fix parentheses around macro pointer
 parameter use

On Fri, May 5, 2023 at 7:23 AM Mathieu Desnoyers
<mathieu.desnoyers@...icios.com> wrote:
>
> Is a list iteration position absolutely required to be a local variable,
> or can it be a dereferenced pointer ?

Well, it was certainly the intention, but while the member name
obviously has to be a member name, the iterator *could* be any lvalue.

Many of the "foreach" kind of loops would actually prefer to have
entirely local variables, but C syntax rules didn't allow that (now
with C11 we can do that variable declaration in the for-loop itself,
but we're still limited to just _one_ variable which can be a
problem).

So if we had started with C11, that 'list_for_each()' wouldn't have
had an external 'pos' declaration at all, it would have done it
internally, but that's not the reality we're in today ;/

              Linus