linux-kernel - Re: [PATCH v2] fuse: uapi: use UAPI types

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Message-ID: <20260109103827.1dc704f2@pumpkin>
Date: Fri, 9 Jan 2026 10:38:27 +0000
From: David Laight <david.laight.linux@...il.com>
To: Thomas Weißschuh <thomas.weissschuh@...utronix.de>
Cc: Bernd Schubert <bernd@...ernd.com>, Arnd Bergmann <arnd@...db.de>,
 Miklos Szeredi <miklos@...redi.hu>, linux-fsdevel@...r.kernel.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] fuse: uapi: use UAPI types

On Fri, 9 Jan 2026 09:11:28 +0100
Thomas Weißschuh <thomas.weissschuh@...utronix.de> wrote:

> On Thu, Jan 08, 2026 at 11:12:29PM +0100, Bernd Schubert wrote:
> > 
> > 
> > On 1/5/26 13:09, Arnd Bergmann wrote:  
> > > On Mon, Jan 5, 2026, at 09:50, Bernd Schubert wrote:  
...
> > > I don't think we'll find a solution that won't break somewhere,
> > > and using the kernel-internal types at least makes it consistent
> > > with the rest of the kernel headers.
> > > 
> > > If we can rely on compiling with a modern compiler (any version of
> > > clang, or gcc-4.5+), it predefines a __UINT64_TYPE__ macro that
> > > could be used for custom typedef:
> > > 
> > > #ifdef __UINT64_TYPE__
> > > typedef __UINT64_TYPE__		fuse_u64;
> > > typedef __INT64_TYPE__		fuse_s64;
> > > typedef __UINT32_TYPE__		fuse_u32;
> > > typedef __INT32_TYPE__		fuse_s32;
> > > ...
> > > #else
> > > #include <stdint.h>
> > > typedef uint64_t		fuse_u64;
> > > typedef int64_t			fuse_s64;
> > > typedef uint32_t		fuse_u32;
> > > typedef int32_t			fuse_s32;
> > > ...
> > > #endif  
> > 
> > I personally like this version.  
> 
> Ack, I'll use this. Although I am not sure why uint64_t and __UINT64_TYPE__
> should be guaranteed to be identical.

Indeed, on 64bit the 64bit types could be 'long' or 'long long'.
You've still got the problem of the correct printf format specifier.
On 32bit the 32bit types could be 'int' or 'long'.

stdint.h 'solves' the printf issue with the (horrid) PRIu64 defines.
But I don't know how you find out what gcc's format checking uses.
So you might have to cast all the values to underlying C types in
order pass the printf format checks.
At which point you might as well have:
typedef unsigned int fuse_u32;
typedef unsigned long long fuse_u64;
_Static_assert(sizeof (fuse_u32) == 4 && sizeof (fuse_u64) == 8);
And then use %x and %llx in the format strings.

	David