linux-kernel - Re: [PATCH v6 4/6] fs: make vfs_fileattr

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Message-ID: <20251007-talent-extern-cda07dfddd11@brauner>
Date: Tue, 7 Oct 2025 13:00:11 +0200
From: Christian Brauner <brauner@...nel.org>
To: Andrey Albershteyn <aalbersh@...hat.com>
Cc: Jan Kara <jack@...e.cz>, Jiri Slaby <jirislaby@...nel.org>, 
	Amir Goldstein <amir73il@...il.com>, Arnd Bergmann <arnd@...db.de>, 
	Casey Schaufler <casey@...aufler-ca.com>, 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 4/6] fs: make vfs_fileattr_[get|set] return -EOPNOSUPP

On Mon, Oct 06, 2025 at 08:52:32PM +0200, Andrey Albershteyn wrote:
> On 2025-10-06 17:39:46, Jan Kara wrote:
> > On Mon 06-10-25 13:09:05, Jiri Slaby wrote:
> > > On 30. 06. 25, 18:20, Andrey Albershteyn wrote:
> > > > Future patches will add new syscalls which use these functions. As
> > > > this interface won't be used for ioctls only, the EOPNOSUPP is more
> > > > appropriate return code.
> > > > 
> > > > This patch converts return code from ENOIOCTLCMD to EOPNOSUPP for
> > > > vfs_fileattr_get and vfs_fileattr_set. To save old behavior translate
> > > > EOPNOSUPP back for current users - overlayfs, encryptfs and fs/ioctl.c.
> > > > 
> > > > Signed-off-by: Andrey Albershteyn <aalbersh@...nel.org>
> > > ...
> > > > @@ -292,6 +294,8 @@ int ioctl_setflags(struct file *file, unsigned int __user *argp)
> > > >   			fileattr_fill_flags(&fa, flags);
> > > >   			err = vfs_fileattr_set(idmap, dentry, &fa);
> > > >   			mnt_drop_write_file(file);
> > > > +			if (err == -EOPNOTSUPP)
> > > > +				err = -ENOIOCTLCMD;
> > > 
> > > This breaks borg code (unit tests already) as it expects EOPNOTSUPP, not
> > > ENOIOCTLCMD/ENOTTY:
> > > https://github.com/borgbackup/borg/blob/1c6ef7a200c7f72f8d1204d727fea32168616ceb/src/borg/platform/linux.pyx#L147
> > > 
> > > I.e. setflags now returns ENOIOCTLCMD/ENOTTY for cases where 6.16 used to
> > > return EOPNOTSUPP.
> > > 
> > > This minimal testcase program doing ioctl(fd2, FS_IOC_SETFLAGS,
> > > &FS_NODUMP_FL):
> > > https://github.com/jirislaby/collected_sources/tree/master/ioctl_setflags
> > > 
> > > dumps in 6.16:
> > > sf: ioctl: Operation not supported
> > > 
> > > with the above patch:
> > > sf: ioctl: Inappropriate ioctl for device
> > > 
> > > Is this expected?

Nope, unintentional regression as Arnd noted.

> > 
> > No, that's a bug and a clear userspace regression so we need to fix it. I
> > think we need to revert this commit and instead convert ENOIOCTLCMD from
> > vfs_fileattr_get/set() to EOPNOTSUPP in appropriate places. Andrey?
> 
> I will prepare a patch soon

Thanks!