linux-kernel - Re: [PATCH v1 1/1] virt: acrn: Drop internal kernel type from ABI

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Date:   Mon, 13 Dec 2021 22:18:16 +0200
From:   Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     Reinette Chatre <reinette.chatre@...el.com>,
        Shuo Liu <shuo.a.liu@...el.com>,
        Zhi Wang <zhi.a.wang@...el.com>, linux-kernel@...r.kernel.org,
        Fei Li <fei1.li@...el.com>
Subject: Re: [PATCH v1 1/1] virt: acrn: Drop internal kernel type from ABI

On Fri, Oct 01, 2021 at 05:10:10PM +0200, Greg Kroah-Hartman wrote:
> On Fri, Oct 01, 2021 at 05:58:49PM +0300, Andy Shevchenko wrote:
> > On Fri, Oct 01, 2021 at 04:01:41PM +0200, Greg Kroah-Hartman wrote:
> > > On Fri, Oct 01, 2021 at 04:56:44PM +0300, Andy Shevchenko wrote:
> > > > guid_t is internal type of the kernel which is mistakenly had been exposed
> > > > to the user space. Replace it with raw buffers.
> > > 
> > > Wait, why is it a mistake to expose it to userspace?  What does this
> > > conflict with?  Is it a namespace issue?  Or something else?
> > 
> > It is the type which is defined solely for kernel use and what user space
> > should do is to use types defined by respective libraries, such as libuuid.
> 
> But that does not work here.  We want to expose a common uuid type that
> userspace can use in these structures, as well as the kernel.  Do you
> really want to "open code" arrays all over the place?

It's not used "all over a place", the only code is recently added by this
driver.

> > If you read the commit message to the end, you will notice that I have
> > mentioned the possible scenario what happened here. They seems misusing
> > guid_t as uuid_t, but the latter is not available for the users from
> > the kernel headers (and this is good). So this is an exact example why
> > guid_t shouldn't be exposed.
> 
> Then we should create a type that we can use here.  The kernel can not
> use libuuid, so what is wrong with using the kernel variable type
> namespace for this?  __guid?  __uuid?

Why? "All over the place" except this code (okay and one more, i.e. MEI,
but this is another story) we use raw arrays in ABI. Why virt out of a
sudden need a special _kernel_ type for that? I think the author simply
missed this subtle detail that it's not supposed to be outside of the
kernel.

-- 
With Best Regards,
Andy Shevchenko