linux-kernel - Re: [PATCH 05/17] virt: acrn: Introduce ACRN HSM basic driver

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Date:   Sun, 30 Aug 2020 16:16:15 +0800
From:   Shuo A Liu <shuo.a.liu@...el.com>
To:     Dave Hansen <dave.hansen@...el.com>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        <linux-kernel@...r.kernel.org>, "H . Peter Anvin" <hpa@...or.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        Yu Wang <yu1.wang@...el.com>,
        "Reinette Chatre" <reinette.chatre@...el.com>, <x86@...nel.org>,
        Zhi Wang <zhi.a.wang@...el.com>,
        Zhenyu Wang <zhenyuw@...ux.intel.com>
Subject: Re: [PATCH 05/17] virt: acrn: Introduce ACRN HSM basic driver

Hi Dave,

On Sat 29.Aug'20 at  9:12:22 -0700, Dave Hansen wrote:
>On 8/29/20 3:46 AM, Shuo A Liu wrote:
>> On Fri 28.Aug'20 at 12:25:59 +0200, Greg Kroah-Hartman wrote:
>>> On Tue, Aug 25, 2020 at 10:45:05AM +0800, shuo.a.liu@...el.com wrote:
>>>> +static long acrn_dev_ioctl(struct file *filp, unsigned int cmd,
>>>> +               unsigned long ioctl_param)
>>>> +{
>>>> +    if (cmd == ACRN_IOCTL_GET_API_VERSION) {
>>>> +        if (copy_to_user((void __user *)ioctl_param,
>>>> +                 &api_version, sizeof(api_version)))
>>>> +            return -EFAULT;
>>>
>>> Why are you versioning your api?  Shouldn't that not be a thing and you
>>> either support an ioctl or you do not?
>>
>> The API version here is more for the hypercalls.
>> The hypercalls might evolve later
>
>They might evolve, but the old ones must always keep working.  Right?

Yes, it's right.

>
>> and the version indicates which set of interfaces (include the
>> paramters' format) should be used by user space tools. Currently,
>> it's used rarely.
>Why do you need this when the core kernel doesn't?  We add syscalls,
>ioctl()s and prctl()s all the time, but nothing is versioned.

Indeed. It looks a bit odd.

>
>This sounds like something you need to remove from the series.

OK. I will remove the api version related code.

Thanks
shuo