Re: [PATCH v3 10/15] futex: Add sys_futex_requeue()

Ingo Molnar
2023-09-22T09:35:16Z

* 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