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Date:   Mon, 21 Mar 2022 11:01:25 +0100
From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     Miklos Szeredi <miklos@szeredi.hu>
Cc:     Carlos Llamas <cmllamas@google.com>,
        Alessio Balsini <balsini@android.com>,
        Masahiro Yamada <masahiroy@kernel.org>,
        Arnd Bergmann <arnd@arndb.de>,
        kernel-team <kernel-team@android.com>,
        linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] fuse: fix integer type usage in uapi header
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On Mon, Mar 21, 2022 at 10:36:20AM +0100, Miklos Szeredi wrote:
> On Mon, 21 Mar 2022 at 09:50, Greg Kroah-Hartman
> <gregkh@linuxfoundation.org> wrote:
> >
> > On Mon, Mar 21, 2022 at 09:40:56AM +0100, Miklos Szeredi wrote:
> > > On Mon, 21 Mar 2022 at 03:07, Carlos Llamas <cmllamas@google.com> wrote:
> > > >
> > > > On Fri, Mar 18, 2022 at 08:24:55PM +0100, Miklos Szeredi wrote:
> > > > > On Fri, 18 Mar 2022 at 18:14, Carlos Llamas <cmllamas@google.com> wrote:
> > > > > >
> > > > > > Kernel uapi headers are supposed to use __[us]{8,16,32,64} defined by
> > > > > > <linux/types.h> instead of 'uint32_t' and similar. This patch changes
> > > > > > all the definitions in this header to use the correct type. Previous
> > > > > > discussion of this topic can be found here:
> > > > > >
> > > > > >   https://lkml.org/lkml/2019/6/5/18
> > > > >
> > > > > This is effectively a revert of these two commits:
> > > > >
> > > > > 4c82456eeb4d ("fuse: fix type definitions in uapi header")
> > > > > 7e98d53086d1 ("Synchronize fuse header with one used in library")
> > > > >
> > > > > And so we've gone full circle and back to having to modify the header
> > > > > to be usable in the cross platform library...
> > > > >
> > > > > And also made lots of churn for what reason exactly?
> > > >
> > > > There are currently only two uapi headers making use of C99 types and
> > > > one is <linux/fuse.h>. This approach results in different typedefs being
> > > > selected when compiling for userspace vs the kernel.
> > >
> > > Why is this a problem if the size of the resulting types is the same?
> >
> > uint* are not "valid" variable types to cross the user/kernel boundary.
> > They are part of the userspace variable type namespace, not the kernel
> > variable type namespace.  Linus wrong a long post about this somewhere
> > in the past, I'm sure someone can dig it up...
> 
> Looking forward to the details.  I cannot imagine why this would matter...

Here's the huge thread on the issue:
	https://lore.kernel.org/all/19865.1101395592@redhat.com/
and specifically here's Linus's answer:
	https://lore.kernel.org/all/Pine.LNX.4.58.0411281710490.22796@ppc970.osdl.org/

The whole thread is actually relevant for this .h file as well.  Some
things never change :)

thanks,

greg k-h