linux-kernel - Re: [PATCH] cpumask: provide a dummy cpumask_next

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Date:   Mon, 13 Aug 2018 15:57:39 -0700 (PDT)
From:   David Miller <davem@...emloft.net>
To:     arnd@...db.de
Cc:     akpm@...ux-foundation.org, peterz@...radead.org,
        caraitto@...gle.com, willemb@...gle.com, adobriyan@...il.com,
        mingo@...nel.org, rakib.mullick@...il.com,
        amritha.nambiar@...el.com, mhkelley@...look.com,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] cpumask: provide a dummy cpumask_next_wrap

From: Arnd Bergmann <arnd@...db.de>
Date: Mon, 13 Aug 2018 23:55:16 +0200

> The virtio_net driver has become the first one to call cpumask_next_wrap()
> even if CONFIG_SMP is disabled, leading to a build error:
> 
> drivers/net/virtio_net.c: In function 'virtnet_set_affinity':
> drivers/net/virtio_net.c:1916:10: error: implicit declaration of function 'cpumask_next_wrap'; did you mean 'cpumask_next_and'? [-Werror=implicit-function-declaration]
>     cpu = cpumask_next_wrap(cpu, cpu_online_mask,
> 
> Add a stub function along the lines of cpumask_first(), cpumask_next() etc.
> I'm not entirely sure what should be returned in this case, but at
> least for virtio_net, anything should work.
> 
> Fixes: 2ca653d607ce ("virtio_net: Stripe queue affinities across cores.")
> Signed-off-by: Arnd Bergmann <arnd@...db.de>

This should already be fixed in my tree, and:

> +static inline int cpumask_next_wrap(int n, const struct cpumask *mask, int start, bool wrap)
> +{
> +	return n;
> +}

this doesn't handle the "n==0 && wrap" case properly, in that situation you should
return '1'.