Re: [PATCH v9 02/17] fs: add generic FS_IOC_SHUTDOWN definitions

[Darrick J. Wong]

On Sat, Feb 21, 2026 at 03:17:30PM +0900, David Timber wrote:
> > +/*
> > + * Shutdown the filesystem.
> > + */
> > +#define FS_IOC_SHUTDOWN _IOR('X', 125, __u32)
> Should've been _IOW, not _IOR. This is rather unfortunate.

Yep, it's too bad that this has been encoded in XFS like this for
decades. :/

You /could/ send patches to add an _IOW definition and make
fstests/xfsprogs prefer the new ioctl number over the old one.

--D

> Documentation/userspace-api/ioctl/ioctl-number.rst:
> >     ====== ===========================
> >     macro  parameters
> >     ====== ===========================
> >     _IO    none
> >     _IOW   write (read from userspace)
> >     _IOR   read (write to userspace)
> >     _IOWR  write and read
> >     ====== ===========================
> >
> > 'Write' and 'read' are from the user's point of view, just like the
> > system calls 'write' and 'read'.  For example, a SET_FOO ioctl would
> > be _IOW, although the kernel would actually read data from user space;
> > a GET_FOO ioctl would be _IOR, although the kernel would actually write
> > data to user space.
> All the *_ioctl_shutdown() do get_user(..., arg).
>