Re: [PATCH 2/2] fs: return EOPNOTSUPP from file_setattr/file_getattr syscalls

[Christian Brauner <brauner@kernel.org>]

On Fri, Oct 10, 2025 at 12:05:04PM +0200, Andrey Albershteyn wrote:
> On 2025-10-09 10:20:41, Darrick J. Wong wrote:
> > On Wed, Oct 08, 2025 at 02:44:18PM +0200, Andrey Albershteyn wrote:
> > > These syscalls call to vfs_fileattr_get/set functions which return
> > > ENOIOCTLCMD if filesystem doesn't support setting file attribute on an
> > > inode. For syscalls EOPNOTSUPP would be more appropriate return error.
> > > 
> > > Signed-off-by: Andrey Albershteyn <aalbersh@kernel.org>
> > > ---
> > >  fs/file_attr.c | 4 ++++
> > >  1 file changed, 4 insertions(+)
> > > 
> > > diff --git a/fs/file_attr.c b/fs/file_attr.c
> > > index 460b2dd21a85..5e3e2aba97b5 100644
> > > --- a/fs/file_attr.c
> > > +++ b/fs/file_attr.c
> > > @@ -416,6 +416,8 @@ SYSCALL_DEFINE5(file_getattr, int, dfd, const char __user *, filename,
> > >  	}
> > >  
> > >  	error = vfs_fileattr_get(filepath.dentry, &fa);
> > > +	if (error == -ENOIOCTLCMD)
> > 
> > Hrm.  Back in 6.17, XFS would return ENOTTY if you called ->fileattr_get
> > on a special file:
> > 
> > int
> > xfs_fileattr_get(
> > 	struct dentry		*dentry,
> > 	struct file_kattr	*fa)
> > {
> > 	struct xfs_inode	*ip = XFS_I(d_inode(dentry));
> > 
> > 	if (d_is_special(dentry))
> > 		return -ENOTTY;
> > 	...
> > }
> > 
> > Given that there are other fileattr_[gs]et implementations out there
> > that might return ENOTTY (e.g. fuse servers and other externally
> > maintained filesystems), I think both syscall functions need to check
> > for that as well:
> > 
> > 	if (error == -ENOIOCTLCMD || error == -ENOTTY)
> > 		return -EOPNOTSUPP;
> 
> Make sense (looks like ubifs, jfs and gfs2 also return ENOTTY for
> special files), I haven't found ENOTTY being used for anything else
> there

I'm folding this in.