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

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Message-ID: <b975404f-fd6d-42aa-9743-c11e0088596b@bsbernd.com>
Date: Sat, 3 Jan 2026 13:44:49 +0100
From: Bernd Schubert <bernd@...ernd.com>
To: Thomas Weißschuh <thomas.weissschuh@...utronix.de>,
 Miklos Szeredi <miklos@...redi.hu>
Cc: linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
 Arnd Bergmann <arnd@...db.de>
Subject: Re: [PATCH v2] fuse: uapi: use UAPI types



On 1/2/26 23:27, Bernd Schubert wrote:
> 
> 
> On 12/30/25 13:10, Thomas Weißschuh wrote:
>> Using libc types and headers from the UAPI headers is problematic as it
>> introduces a dependency on a full C toolchain.
>>
>> Use the fixed-width integer types provided by the UAPI headers instead.
>> To keep compatibility with non-Linux platforms, add a stdint.h fallback.
>>
>> Signed-off-by: Thomas Weißschuh <thomas.weissschuh@...utronix.de>
>> ---
>> Changes in v2:
>> - Fix structure member alignments
>> - Keep compatibility with non-Linux platforms
>> - Link to v1: https://lore.kernel.org/r/20251222-uapi-fuse-v1-1-85a61b87baa0@linutronix.de
>> ---
>>  include/uapi/linux/fuse.h | 626 +++++++++++++++++++++++-----------------------
>>  1 file changed, 319 insertions(+), 307 deletions(-)
> 
> I tested this and it breaks libfuse compilation
> 
> https://github.com/libfuse/libfuse/pull/1410
> 
> Any chance you could test libfuse compilation for v3? Easiest way is to
> copy it to <libfuse>/include/fuse_kernel.h and then create PR. That
> includes a BSD test.
> 
> 
> libfuse3.so.3.19.0.p/fuse_uring.c.o -c
> ../../../home/runner/work/libfuse/libfuse/lib/fuse_uring.c
> ../../../home/runner/work/libfuse/libfuse/lib/fuse_uring.c:197:5: error:
> format specifies type 'unsigned long' but the argument has type '__u64'
> (aka 'unsigned long long') [-Werror,-Wformat]
>   196 |                 fuse_log(FUSE_LOG_DEBUG, "    unique: %" PRIu64
> ", result=%d\n",
>       |                                                       ~~~~~~~~~
>   197 |                          out->unique, ent_in_out->payload_sz);
>       |                          ^~~~~~~~~~~
> 1 error generated.
> 
> 
> I can certainly work it around in libfuse by adding a cast, IMHO,
> PRIu64 is the right format.
> 

I think what would work is the attached version. Short interesting part

#if defined(__KERNEL__)
#include <linux/types.h>
typedef __u8	fuse_u8;
typedef __u16	fuse_u16;
typedef __u32	fuse_u32;
typedef __u64	fuse_u64;
typedef __s8	fuse_s8;
typedef __s16	fuse_s16;
typedef __s32	fuse_s32;
typedef __s64	fuse_s64;
#else
#include <stdint.h>
typedef uint8_t		fuse_u8;
typedef uint16_t	fuse_u16;
typedef uint32_t	fuse_u32;
typedef uint64_t	fuse_u64;
typedef int8_t		fuse_s8;
typedef int16_t		fuse_s16;
typedef int32_t		fuse_s32;
typedef int64_t		fuse_s64;
#endif


And then the rest of the file has to use the fuse_ types.


Thanks,
Bernd
View attachment "fuse_kernel.h" of type "text/x-chdr" (32322 bytes)