Re: [PATCH v1 3/4] xfs: add XFS_IOC_SETFSUUID ioctl

From: Amir Goldstein <amir73il@gmail.com>
To: Catherine Hoang <catherine.hoang@oracle.com>
Cc: linux-xfs@vger.kernel.org,
	linux-fsdevel <linux-fsdevel@vger.kernel.org>,
	Theodore Tso <tytso@mit.edu>
Subject: Re: [PATCH v1 3/4] xfs: add XFS_IOC_SETFSUUID ioctl
Date: Tue, 14 Mar 2023 07:50:55 +0200	[thread overview]
Message-ID: <CAOQ4uxiYVpF9gjt-kTVpnoVYboOFG-Fpfw=KMrM=-aEHod4vXw@mail.gmail.com> (raw)
In-Reply-To: <20230314042109.82161-4-catherine.hoang@oracle.com>

On Tue, Mar 14, 2023 at 6:27 AM Catherine Hoang
<catherine.hoang@oracle.com> wrote:
>
> Add a new ioctl to set the uuid of a mounted filesystem.
>
> Signed-off-by: Catherine Hoang <catherine.hoang@oracle.com>
> ---
>  fs/xfs/libxfs/xfs_fs.h |   1 +
>  fs/xfs/xfs_ioctl.c     | 107 +++++++++++++++++++++++++++++++++++++++++
>  fs/xfs/xfs_log.c       |  19 ++++++++
>  fs/xfs/xfs_log.h       |   2 +
>  4 files changed, 129 insertions(+)
>
> diff --git a/fs/xfs/libxfs/xfs_fs.h b/fs/xfs/libxfs/xfs_fs.h
> index 1cfd5bc6520a..a350966cce99 100644
> --- a/fs/xfs/libxfs/xfs_fs.h
> +++ b/fs/xfs/libxfs/xfs_fs.h
> @@ -831,6 +831,7 @@ struct xfs_scrub_metadata {
>  #define XFS_IOC_FSGEOMETRY          _IOR ('X', 126, struct xfs_fsop_geom)
>  #define XFS_IOC_BULKSTAT            _IOR ('X', 127, struct xfs_bulkstat_req)
>  #define XFS_IOC_INUMBERS            _IOR ('X', 128, struct xfs_inumbers_req)
> +#define XFS_IOC_SETFSUUID           _IOR ('X', 129, uuid_t)

Should be _IOW.

Would you consider defining that as FS_IOC_SETFSUUID in fs.h,
so that other fs could implement it later on, instead of hoisting it later?

It would be easy to add support for FS_IOC_SETFSUUID to ext4
by generalizing ext4_ioctl_setuuid().

Alternatively, we could hoist EXT4_IOC_SETFSUUID and struct fsuuid
to fs.h and use that ioctl also for xfs.

Using an extensible struct with flags for that ioctl may turn out to be useful,
for example, to verify that the new uuid is unique, despite the fact
that xfs was
mounted with -onouuid (useful IMO) or to explicitly request a restore of old
uuid that would fail if new_uuid != meta uuid.

Thanks,
Amir.