linux-ext4 - Re: [PATCH] fs: i_version mntopt gets visible through /proc/mounts

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Date:   Wed, 17 Jun 2020 21:30:26 -0400
From:   Masayoshi Mizuma <msys.mizuma@...il.com>
To:     "J. Bruce Fields" <bfields@...ldses.org>
Cc:     Eric Sandeen <sandeen@...deen.net>,
        "Darrick J. Wong" <darrick.wong@...cle.com>,
        Christoph Hellwig <hch@...radead.org>,
        Theodore Ts'o <tytso@....edu>,
        Andreas Dilger <adilger.kernel@...ger.ca>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Masayoshi Mizuma <m.mizuma@...fujitsu.com>,
        linux-ext4@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        linux-xfs <linux-xfs@...r.kernel.org>
Subject: Re: [PATCH] fs: i_version mntopt gets visible through /proc/mounts

On Wed, Jun 17, 2020 at 02:45:07PM -0400, J. Bruce Fields wrote:
> On Wed, Jun 17, 2020 at 01:28:11PM -0500, Eric Sandeen wrote:
> > but mount(8) has already exposed this interface:
> > 
> >        iversion
> >               Every time the inode is modified, the i_version field will be incremented.
> > 
> >        noiversion
> >               Do not increment the i_version inode field.
> > 
> > so now what?
> 
> It's not like anyone's actually depending on i_version *not* being
> incremented.  (Can you even observe it from userspace other than over
> NFS?)
> 
> So, just silently turn on the "iversion" behavior and ignore noiversion,
> and I doubt you're going to break any real application.

I suppose it's probably good to remain the options for user compatibility,
however, it seems that iversion and noiversiont are useful for
only ext4.
How about moving iversion and noiversion description on mount(8)
to ext4 specific option?

And fixing the remount issue for XFS (maybe btrfs has the same
issue as well)?
For XFS like as:

diff --git a/fs/xfs/xfs_super.c b/fs/xfs/xfs_super.c
index 379cbff438bc..2ddd634cfb0b 100644
--- a/fs/xfs/xfs_super.c
+++ b/fs/xfs/xfs_super.c
@@ -1748,6 +1748,9 @@ xfs_fc_reconfigure(
                        return error;
        }

+       if (XFS_SB_VERSION_NUM(&mp->m_sb) == XFS_SB_VERSION_5)
+               mp->m_super->s_flags |= SB_I_VERSION;
+
        return 0;
 }

Thanks,
Masa