linux-kernel - Re: [RFC][PATCH 1/2] locking: Introduce __cleanup_

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Date:   Fri, 26 May 2023 21:10:14 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     keescook@...omium.org, gregkh@...uxfoundation.org,
        pbonzini@...hat.com, linux-kernel@...r.kernel.org,
        ojeda@...nel.org, ndesaulniers@...gle.com, mingo@...hat.com,
        will@...nel.org, longman@...hat.com, boqun.feng@...il.com,
        juri.lelli@...hat.com, vincent.guittot@...aro.org,
        dietmar.eggemann@....com, rostedt@...dmis.org, bsegall@...gle.com,
        mgorman@...e.de, bristot@...hat.com, vschneid@...hat.com,
        paulmck@...nel.org, frederic@...nel.org, quic_neeraju@...cinc.com,
        joel@...lfernandes.org, josh@...htriplett.org,
        mathieu.desnoyers@...icios.com, jiangshanlai@...il.com,
        rcu@...r.kernel.org, tj@...nel.org, tglx@...utronix.de
Subject: Re: [RFC][PATCH 1/2] locking: Introduce __cleanup__ based guards

On Fri, May 26, 2023 at 11:22:36AM -0700, Linus Torvalds wrote:

> But you can actually do the 'bool done' using the exact same type you
> have for the guard - just make it a pointer instead, and use NULL for
> "not done" and non-NULL for "done". It ends up acting exactly like a
> boolean.

Damn; I've actually seen that and should've thought of it.

> IOW, something like this:
> 
>   #define variable_scope(type, enter, exit) \
>         for (type *_done = NULL, _scope __cleanup(exit) = enter;
> !_done; _done = (void *)8)
> 
>   #define scoped(type, init...) \
>         variable_scope(scope_##type##_t, scope_##type##_init(init),
> scope_##type##_cleanup)
> 

> I dunno. I didn't *test* the above. Maybe you already tried something
> like the above, and there's a reason why it doesn't work.

I have not; let me go try that. That does look *much* nicer.