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Sender: Ingo Molnar <mingo.kernel.org@gmail.com>
Date:   Fri, 22 Sep 2023 11:35:03 +0200
From:   Ingo Molnar <mingo@kernel.org>
To:     peterz@infradead.org
Cc:     tglx@linutronix.de, axboe@kernel.dk, linux-kernel@vger.kernel.org,
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        linux-mm@kvack.org, linux-arch@vger.kernel.org,
        malteskarupke@web.de, Geert Uytterhoeven <geert@linux-m68k.org>
Subject: Re: [PATCH v3 10/15] futex: Add sys_futex_requeue()
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References: <20230921104505.717750284@noisy.programming.kicks-ass.net>
 <20230921105248.511860556@noisy.programming.kicks-ass.net>
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* peterz@infradead.org <peterz@infradead.org> wrote:

> --- linux-2.6.orig/kernel/futex/syscalls.c
> +++ linux-2.6/kernel/futex/syscalls.c
> @@ -396,6 +396,44 @@ SYSCALL_DEFINE6(futex_wait,
>  	return ret;
>  }
>  
> +/*
> + * sys_futex_requeue - Requeue a waiter from one futex to another
> + * @waiters:	array describing the source and destination futex
> + * @flags:	unused
> + * @nr_wake:	number of futexes to wake
> + * @nr_requeue:	number of futexes to requeue
> + *
> + * Identical to the traditional FUTEX_CMP_REQUEUE op, except it is part of the
> + * futex2 family of calls.
> + */
> +
> +SYSCALL_DEFINE4(futex_requeue,
> +		struct futex_waitv __user *, waiters,
> +		unsigned int, flags,
> +		int, nr_wake,
> +		int, nr_requeue)
> +{
> +	struct futex_vector futexes[2];
> +	u32 cmpval;
> +	int ret;
> +
> +	if (flags)
> +		return -EINVAL;

Small detail, but isn't -ENOSYS the canonical error code for functionality 
not yet implemented - which the unused 'flags' ABI is arguably?

-EINVAL is for recognized but incorrect parameters, such as:

> +	if (!waiters)
> +		return -EINVAL;

Thanks,

	Ingo