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

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Date:   Sat, 20 Jun 2020 12:00:43 -0500
From:   Eric Sandeen <sandeen@...deen.net>
To:     "J. Bruce Fields" <bfields@...ldses.org>,
        Dave Chinner <david@...morbit.com>
Cc:     Masayoshi Mizuma <msys.mizuma@...il.com>,
        "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>, jlayton@...hat.com
Subject: Re: [PATCH] fs: i_version mntopt gets visible through /proc/mounts

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@...l.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@...ibm.com>
    Signed-off-by: Jean Noel Cordenner <jean-noel.cordenner@...l.net>
    Signed-off-by: Kalpak Shah <kalpak@...sterfs.com>

and ext4's Opt_i_version mount option appeared here:

commit 25ec56b518257a56d2ff41a941d288e4b5ff9488
Author: Jean Noel Cordenner <jean-noel.cordenner@...l.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@...ibm.com>
    Signed-off-by: Andreas Dilger <adilger@...sterfs.com>
    Signed-off-by: Kalpak Shah <kalpak@...sterfs.com>
    Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@...ux.vnet.ibm.com>
    Signed-off-by: Jean Noel Cordenner <jean-noel.cordenner@...l.net>

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

-Eric