# Re: \[PATCH v2 09/14\] futex: Add sys\_futex\_requeue()

- From: Thomas Gleixner \<hidden\>
- Date: 2023-08-07 19:06:08 
- List: linux-api
- Page: https://ratatoskr.run/linux-api/2023/08/2294798
- Thread: https://ratatoskr.run/linux-api/2023/08/2294049/t.md

```text
On Mon, Aug 07 2023 at 14:18, Peter Zijlstra wrote:

> Finish of the 'simple' futex2 syscall group by adding

s/of/off/

> sys_futex_requeue(). Unlike sys_futex_{wait,wake}() its arguments are
> too numerous to fit into a regular syscall. As such, use struct
> futex_waitv to pass the 'source' and 'destination' futexes to the
> syscall.

...

> +/*
> + * 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

Tabular format please

> + *
> + * 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;
> +
> +	if (!waiters)
> +		return -EINVAL;
> +
> +	ret = futex_parse_waitv(futexes, waiters, 2);
> +	if (ret)
> +		return ret;
> +
> +	cmpval = futexes[0].w.val;
> +
> +	return futex_requeue(u64_to_user_ptr(futexes[0].w.uaddr), futexes[0].w.flags,
> +			     u64_to_user_ptr(futexes[1].w.uaddr), futexes[1].w.flags,
> +			     nr_wake, nr_requeue, &cmpval, 0);
> +}

Reviewed-by: Thomas Gleixner <redacted>
```