linux-kernel - Re: [PATCH v4 1/1] virt: acrn: Mark the uuid field as unused

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Message-ID: <Y3Tlu0BjgMk3xNDQ@smile.fi.intel.com>
Date:   Wed, 16 Nov 2022 15:29:31 +0200
From:   Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     linux-kernel@...r.kernel.org, Fei Li <fei1.li@...el.com>,
        "Rafael J. Wysocki" <rafael@...nel.org>
Subject: Re: [PATCH v4 1/1] virt: acrn: Mark the uuid field as unused

On Wed, Nov 16, 2022 at 12:42:16PM +0100, Greg Kroah-Hartman wrote:
> On Wed, Nov 16, 2022 at 11:22:54AM +0200, Andy Shevchenko wrote:
> > After the commits for userspace (see Link tags below) the uuid field is
> > not being used in the ACRN code. Update kernel to reflect these changes.
> > I.e. we do the following:
> > - adding a comment explaining that it's not used anymore
> > - replacing the specific type by a raw buffer
> > - updating the example code accordingly
> > 
> > The advertised field confused users and actually never been used. So
> > the wrong part here is that kernel puts something which userspace never
> > used and hence this may confuse a reader of this code.

> > - * @uuid:		UUID of the VM. Pass to hypervisor directly.
> > + * @uuid:		Reserved (used to be UUID of the VM)
> 
> If it's reserved, then don't you need to check for 0?

Reserved in a way that it may content something we just don't care about.

...

> > +	__u8	uuid[16];
> 
> You just changed the type here, so what is that going to break in
> userspace that depended on this being of a structure type and now it's
> an array?

It's the same. The previous was hidden behind additional type level.

> And no other kernel changes needed?  Shouldn't you warn if this field is
> set?

No, as pointed out in the commit message kernel never ever used this.

-- 
With Best Regards,
Andy Shevchenko