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

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Message-Id: <69094222-d918-4108-877c-51a666b53707@app.fastmail.com>
Date: Mon, 06 Oct 2025 13:43:46 +0200
From: "Arnd Bergmann" <arnd@...db.de>
To: "Jiri Slaby" <jirislaby@...nel.org>,
 "Andrey Albershteyn" <aalbersh@...hat.com>,
 "Amir Goldstein" <amir73il@...il.com>,
 "Casey Schaufler" <casey@...aufler-ca.com>,
 "Christian Brauner" <brauner@...nel.org>, "Jan Kara" <jack@...e.cz>,
 Pali Rohár <pali@...nel.org>,
 "Paul Moore" <paul@...l-moore.com>
Cc: 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 6, 2025, at 13:09, 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.
>> 
...
> dumps in 6.16:
> sf: ioctl: Operation not supported
>
> with the above patch:
> sf: ioctl: Inappropriate ioctl for device
>
>
> Is this expected?

This does look like an unintentional bug: As far as I can see, the
-ENOIOCTLCMD was previously used to indicate that a particular filesystem
does not have a fileattr_{get,set} callback at all, while individual
filesystems used EOPNOSUPP to indicate that a particular attribute
flag is unsupported. With the double conversion, both error codes
get turned into a single one.

     Arnd