linux-kernel - Re: [PATCH v2 1/2] locking: Introduce __cleanup_

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Message-ID: <20230526212454.GB4057254@hirez.programming.kicks-ass.net>
Date:   Fri, 26 May 2023 23:24:54 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     torvalds@...ux-foundation.org, keescook@...omium.org,
        gregkh@...uxfoundation.org, pbonzini@...hat.com
Cc:     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: [PATCH v2 1/2] locking: Introduce __cleanup__ based guards

On Fri, May 26, 2023 at 10:52:05PM +0200, Peter Zijlstra wrote:

> +++ b/include/linux/guards.h
> @@ -0,0 +1,142 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +#ifndef __LINUX_GUARDS_H
> +#define __LINUX_GUARDS_H
> +
> +#include <linux/compiler_attributes.h>
> +
> +/*
> + * Pointer Guards are special pointers (variables) with a scope bound cleanup
> + * function.
> + *
> + * Various guard types can be created using:
> + *
> + *   DEFINE_PTR_GUARD(guard_type, typename, cleanup-exp)
> + *
> + * After which they can be used like so:
> + *
> + *   ptr_guard(guard_type, name) = find_get_object(foo);
> + *
> + * Where the return type of find_get_object() should match the guard_type's
> + * 'typname *'. And when @name goes out of scope cleanup-exp is ran (inserted
> + * by the compiler) when !NULL at that time. Also see the __cleanup attribute.
> + */
> +
> +#define DEFINE_PTR_GUARD(_type, _Type, _Put)					\
> +typedef _Type *ptr_guard_##_type##_t;						\
> +										\
> +static inline void ptr_guard_##_type##_cleanup(_Type **_ptr)			\
> +{										\
> +	_Type *_G = *_ptr;							\
> +	if (_G)									\
> +		_Put(_G);							\
> +}
> +
> +#define ptr_guard(_type, _name)							\
> +	ptr_guard_##_type##_t _name __cleanup(ptr_guard_##_type##_cleanup)
> +

Ha, and then I wanted to create an fdput() guard... :/