linux-kernel - Re: [PATCH v6 6/6] fs: introduce file_getattr and file

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Message-ID: <CAOQ4uxjfs=YJmgj0CfJ1NxuPaHgh4B6Vou6jG-WBoi1hGdSDdQ@mail.gmail.com>
Date: Wed, 2 Jul 2025 11:13:48 +0200
From: Amir Goldstein <amir73il@...il.com>
To: Christian Brauner <brauner@...nel.org>
Cc: Andrey Albershteyn <aalbersh@...hat.com>, Arnd Bergmann <arnd@...db.de>, 
	Casey Schaufler <casey@...aufler-ca.com>, Jan Kara <jack@...e.cz>, Pali Rohár <pali@...nel.org>, 
	Paul Moore <paul@...l-moore.com>, linux-api@...r.kernel.org, 
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org, 
	linux-xfs@...r.kernel.org, selinux@...r.kernel.org, 
	Andrey Albershteyn <aalbersh@...nel.org>
Subject: Re: [PATCH v6 6/6] fs: introduce file_getattr and file_setattr syscalls

> > +/*
> > + * Variable size structure for file_[sg]et_attr().
> > + *
> > + * Note. This is alternative to the structure 'struct fileattr'/'struct fsxattr'.
> > + * As this structure is passed to/from userspace with its size, this can
> > + * be versioned based on the size.
> > + */
> > +struct fsx_fileattr {
> > +     __u32   fsx_xflags;     /* xflags field value (get/set) */
> > +     __u32   fsx_extsize;    /* extsize field value (get/set)*/
> > +     __u32   fsx_nextents;   /* nextents field value (get)   */
> > +     __u32   fsx_projid;     /* project identifier (get/set) */
> > +     __u32   fsx_cowextsize; /* CoW extsize field value (get/set) */
>
> This misses a:
>
> __u32 __spare;
>
> so there's no holes in the struct. :)

Adding __spare and not verifying that it is zeroed gets us to the
point that we are not able to replace __spare with a real field later.

I suggest to resolve this hole as Darrick and Pali suggested by making it
__u64 fsx_xflags

w.r.t Darrick's comment, I kind of like it that the name for the UAPI
struct (fsxattr)
differs from the name of the kernel internal representation (fileattr), but
I agree that fsx_fileattr does not give a good hint on what it is.

I think that renaming struct fsx_fileattr to struct fsxattr64 along
with changing the
width of fsx_xflags will help reduce the confusion of users.

What do you guys think?

Thanks,
Amir.