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

From: "Darrick J. Wong" <darrick.wong@oracle.com>
To: Masayoshi Mizuma <msys.mizuma@gmail.com>
Cc: "J. Bruce Fields" <bfields@fieldses.org>,
	Eric Sandeen <sandeen@sandeen.net>,
	Christoph Hellwig <hch@infradead.org>,
	"Theodore Ts'o" <tytso@mit.edu>,
	Andreas Dilger <adilger.kernel@dilger.ca>,
	Alexander Viro <viro@zeniv.linux.org.uk>,
	Masayoshi Mizuma <m.mizuma@jp.fujitsu.com>,
	linux-ext4@vger.kernel.org, linux-fsdevel@vger.kernel.org,
	linux-xfs <linux-xfs@vger.kernel.org>
Subject: Re: [PATCH] fs: i_version mntopt gets visible through /proc/mounts
Date: Wed, 17 Jun 2020 18:44:29 -0700	[thread overview]
Message-ID: <20200618014429.GS11245@magnolia> (raw)
In-Reply-To: <20200618013026.ewnhvf64nb62k2yx@gabell>

On Wed, Jun 17, 2020 at 09:30:26PM -0400, Masayoshi Mizuma wrote:
> 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;
> +

I wonder, does this have to be done at the top of this function because
the vfs already removed S_I_VERSION from s_flags?

--D

>         return 0;
>  }
> 
> Thanks,
> Masa