linux-kernel - Re: [PATCH v2 0/2] Lock and Pointer guards

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Message-ID: <113b1654-9fc1-50c1-fdd0-cac9574420d9@prevas.dk>
Date:   Fri, 9 Jun 2023 10:27:54 +0200
From:   Rasmus Villemoes <rasmus.villemoes@...vas.dk>
To:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Peter Zijlstra <peterz@...radead.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,
        linux-toolchains@...r.kernel.org
Subject: Re: [PATCH v2 0/2] Lock and Pointer guards

On 08/06/2023 17.45, Linus Torvalds wrote:

> And no, I didn't think too much about those names. "__automatic_kfree"
> is too damn long to type, but you hated "auto". And "no_free_ptr()" is
> not wonderful name either. But I tried to make the naming at least be
> obvious, if not wonderful.

No opinion either way, just throwing a data point out there:

So the systemd codebase makes quite heavy use of this automatic cleanup
stuff. Their name for no_free_ptr is TAKE_PTR(), and the verb "take"
apparently comes from Rust:

//// src/fundamental/macro-fundamental.h

/* Takes inspiration from Rust's Option::take() method: reads and
returns a pointer, but at the same time
 * resets it to NULL. See:
https://doc.rust-lang.org/std/option/enum.Option.html#method.take */
#define TAKE_GENERIC(var, type, nullvalue)                       \
        ({                                                       \
                type *_pvar_ = &(var);                           \
                type _var_ = *_pvar_;                            \
                type _nullvalue_ = nullvalue;                    \
                *_pvar_ = _nullvalue_;                           \
                _var_;                                           \
        })
#define TAKE_PTR_TYPE(ptr, type) TAKE_GENERIC(ptr, type, NULL)
#define TAKE_PTR(ptr) TAKE_PTR_TYPE(ptr, typeof(ptr))
#define TAKE_STRUCT_TYPE(s, type) TAKE_GENERIC(s, type, {})
#define TAKE_STRUCT(s) TAKE_STRUCT_TYPE(s, typeof(s))


and then they also have a

/* Like TAKE_PTR() but for file descriptors, resetting them to -EBADF */
#define TAKE_FD(fd) TAKE_GENERIC(fd, int, -EBADF)

with their "auto-close fd" helper of course knowing to ignore any
negative value.

Rasmus