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

From: Eric Sandeen <sandeen@sandeen.net>
To: "J. Bruce Fields" <bfields@fieldses.org>,
	Dave Chinner <david@fromorbit.com>
Cc: Masayoshi Mizuma <msys.mizuma@gmail.com>,
	"Darrick J. Wong" <darrick.wong@oracle.com>,
	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>,
	jlayton@redhat.com
Subject: Re: [PATCH] fs: i_version mntopt gets visible through /proc/mounts
Date: Sat, 20 Jun 2020 12:00:43 -0500	[thread overview]
Message-ID: <d6f9cac3-eec0-a88e-4eab-7673728db52c@sandeen.net> (raw)
In-Reply-To: <20200620015633.GA1516@fieldses.org>

On 6/19/20 8:56 PM, J. Bruce Fields wrote:
> On Sat, Jun 20, 2020 at 11:49:57AM +1000, Dave Chinner wrote:

...

>> However, other people have different opinions on this matter (and we
>> know that from the people who considered XFS v4 -> v5 going slower
>> because iversion a major regression), and so we must acknowledge
>> those opinions even if we don't agree with them.
> 
> Do you have any of those reports handy?  Were there numbers?

I can't answer that but did a little digging.  MS_I_VERSION as an option
appeared here:

commit 7a224228ed79d587ece2304869000aad1b8e97dd
Author: Jean Noel Cordenner <jean-noel.cordenner@bull.net>
Date:   Mon Jan 28 23:58:27 2008 -0500

    vfs: Add 64 bit i_version support

    The i_version field of the inode is changed to be a 64-bit counter that
    is set on every inode creation and that is incremented every time the
    inode data is modified (similarly to the "ctime" time-stamp).
    The aim is to fulfill a NFSv4 requirement for rfc3530.
    This first part concerns the vfs, it converts the 32-bit i_version in
    the generic inode to a 64-bit, a flag is added in the super block in
    order to check if the feature is enabled and the i_version is
    incremented in the vfs.

    Signed-off-by: Mingming Cao <cmm@us.ibm.com>
    Signed-off-by: Jean Noel Cordenner <jean-noel.cordenner@bull.net>
    Signed-off-by: Kalpak Shah <kalpak@clusterfs.com>

and ext4's Opt_i_version mount option appeared here:

commit 25ec56b518257a56d2ff41a941d288e4b5ff9488
Author: Jean Noel Cordenner <jean-noel.cordenner@bull.net>
Date:   Mon Jan 28 23:58:27 2008 -0500

    ext4: Add inode version support in ext4

    This patch adds 64-bit inode version support to ext4. The lower 32 bits
    are stored in the osd1.linux1.l_i_version field while the high 32 bits
    are stored in the i_version_hi field newly created in the ext4_inode.
    This field is incremented in case the ext4_inode is large enough. A
    i_version mount option has been added to enable the feature.

    Signed-off-by: Mingming Cao <cmm@us.ibm.com>
    Signed-off-by: Andreas Dilger <adilger@clusterfs.com>
    Signed-off-by: Kalpak Shah <kalpak@clusterfs.com>
    Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
    Signed-off-by: Jean Noel Cordenner <jean-noel.cordenner@bull.net>

so the optional enablement was there on day one, without any real explanation
of why.

-Eric