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

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Message-Id: <399fdabb-74d3-4dd6-9eee-7884a986dab1@app.fastmail.com>
Date: Tue, 13 May 2025 11:53:23 +0200
From: "Arnd Bergmann" <arnd@...db.de>
To: "Andrey Albershteyn" <aalbersh@...hat.com>,
 "Richard Henderson" <richard.henderson@...aro.org>,
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 "Andrey Albershteyn" <aalbersh@...nel.org>
Subject: Re: [PATCH v5 0/7] fs: introduce file_getattr and file_setattr syscalls

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