linux-kernel - Re: [PATCH RESEND v2 2/2] virt: acrn: Make remove_cpu sysfs invisible with !CONFIG_HOTPLUG

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Message-ID: <20210223152530.y2qfyozdaowmfcat@e107158-lin>
Date:   Tue, 23 Feb 2021 15:25:30 +0000
From:   Qais Yousef <qais.yousef@....com>
To:     shuo.a.liu@...el.com
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-kernel@...r.kernel.org, linux-next@...r.kernel.org,
        Randy Dunlap <rdunlap@...radead.org>,
        Stephen Rothwell <sfr@...b.auug.org.au>,
        Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH RESEND v2 2/2] virt: acrn: Make remove_cpu sysfs
 invisible with !CONFIG_HOTPLUG_CPU

On 02/21/21 21:43, shuo.a.liu@...el.com wrote:
> From: Shuo Liu <shuo.a.liu@...el.com>
> 
> Without cpu hotplug support, vCPU cannot be removed from a Service VM.
> Don't expose remove_cpu sysfs when CONFIG_HOTPLUG_CPU disabled.
> 
> Signed-off-by: Shuo Liu <shuo.a.liu@...el.com>
> Acked-by: Randy Dunlap <rdunlap@...radead.org> # build-tested
> Cc: Stephen Rothwell <sfr@...b.auug.org.au>
> Cc: Thomas Gleixner <tglx@...utronix.de>
> Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
> Cc: Qais Yousef <qais.yousef@....com>
> ---
>  drivers/virt/acrn/hsm.c | 9 +++++++++
>  1 file changed, 9 insertions(+)
> 
> diff --git a/drivers/virt/acrn/hsm.c b/drivers/virt/acrn/hsm.c
> index 1f6b7c54a1a4..6996ea6219e5 100644
> --- a/drivers/virt/acrn/hsm.c
> +++ b/drivers/virt/acrn/hsm.c
> @@ -404,6 +404,14 @@ static ssize_t remove_cpu_store(struct device *dev,
>  }
>  static DEVICE_ATTR_WO(remove_cpu);
>  
> +static umode_t acrn_attr_visible(struct kobject *kobj, struct attribute *a, int n)
> +{
> +       if (a == &dev_attr_remove_cpu.attr)
> +               return IS_ENABLED(CONFIG_HOTPLUG_CPU) ? a->mode : 0;
> +
> +       return a->mode;
> +}
> +

I can't find this code in Linus' master. But this looks fine from my narrow
PoV. Protecting the attribute with ifdef CONFIG_HOTPLUG_CPU is easier to read
for me, but this doesn't mean this approach is not fine.

Thanks

--
Qais Yousef

>  static struct attribute *acrn_attrs[] = {
>  	&dev_attr_remove_cpu.attr,
>  	NULL
> @@ -411,6 +419,7 @@ static struct attribute *acrn_attrs[] = {
>  
>  static struct attribute_group acrn_attr_group = {
>  	.attrs = acrn_attrs,
> +	.is_visible = acrn_attr_visible,
>  };
>  
>  static const struct attribute_group *acrn_attr_groups[] = {
> -- 
> 2.28.0
>