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

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Date:   Wed, 24 Feb 2021 09:11:47 +0800
From:   Shuo A Liu <shuo.a.liu@...el.com>
To:     Qais Yousef <qais.yousef@....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

Hi,

On Tue 23.Feb'21 at 15:25:30 +0000, Qais Yousef wrote:
>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

Now, the code is still in linux-next tree only.

>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.

Just FYI, Greg prefers this solution.
https://lore.kernel.org/lkml/20210212045724.77846-1-shuo.a.liu@intel.com/

Thanks
shuo