linux-kernel - Re: [PATCH v5 0/7] fs: introduce file_getattr and file

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Message-ID: <B17E8366-DB80-45E6-90D6-294824C40FD9@zytor.com>
Date: Wed, 14 May 2025 08:10:12 -0700
From: "H. Peter Anvin" <hpa@...or.com>
To: Arnd Bergmann <arnd@...db.de>, Andrey Albershteyn <aalbersh@...hat.com>,
        Richard Henderson <richard.henderson@...aro.org>,
        Matt Turner <mattst88@...il.com>, Russell King <linux@...linux.org.uk>,
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        Andrey Albershteyn <aalbersh@...nel.org>
Subject: Re: [PATCH v5 0/7] fs: introduce file_getattr and file_setattr syscalls

On May 13, 2025 2:53:23 AM PDT, Arnd Bergmann <arnd@...db.de> wrote:
>On Tue, May 13, 2025, at 11:17, Andrey Albershteyn wrote:
>
>>
>> 	long syscall(SYS_file_getattr, int dirfd, const char *pathname,
>> 		struct fsxattr *fsx, size_t size, unsigned int at_flags);
>> 	long syscall(SYS_file_setattr, int dirfd, const char *pathname,
>> 		struct fsxattr *fsx, size_t size, unsigned int at_flags);
>
>I don't think we can have both the "struct fsxattr" from the uapi
>headers, and a variable size as an additional argument. I would
>still prefer not having the extensible structure at all and just
>use fsxattr, but if you want to make it extensible in this way,
>it should use a different structure (name). Otherwise adding
>fields after fsx_pad[] would break the ioctl interface.
>
>I also find the bit confusing where the argument contains both
>"ignored but assumed zero" flags, and "required to be zero"
>flags depending on whether it's in the fsx_pad[] field or
>after it. This would be fine if it was better documented.
>
>
>> 		fsx.fsx_xflags |= FS_XFLAG_NODUMP;
>> 		error = syscall(468, dfd, "./foo", &fsx, 0);
>
>The example still uses the calling conventions from a previous
>version.
>
>       Arnd

Well, ioctls carry the structure size in the ioctl number, so changing the structure size would change the ioctl number with it.