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

From: "J. Bruce Fields" <bfields@fieldses.org>
To: Dave Chinner <david@fromorbit.com>
Cc: Masayoshi Mizuma <msys.mizuma@gmail.com>,
	Eric Sandeen <sandeen@sandeen.net>,
	"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: Fri, 19 Jun 2020 16:40:33 -0400	[thread overview]
Message-ID: <20200619204033.GB1564@fieldses.org> (raw)
In-Reply-To: <20200619024455.GN2005@dread.disaster.area>

On Fri, Jun 19, 2020 at 12:44:55PM +1000, Dave Chinner wrote:
> On Thu, Jun 18, 2020 at 10:20:05PM -0400, J. Bruce Fields wrote:
> > My memory was that after Jeff Layton's i_version patches, there wasn't
> > really a significant performance hit any more, so the ability to turn it
> > off is no longer useful.
> 
> Yes, I completely agree with you here. However, with some
> filesystems allowing it to be turned off, we can't just wave our
> hands and force enable the option. Those filesystems - if the
> maintainers chose to always enable iversion - will have to go
> through a mount option deprecation period before permanently
> enabling it.

I don't understand why.

The filesystem can continue to let people set iversion or noiversion as
they like, while under the covers behaving as if iversion is always set.
I can't see how that would break any application.  (Or even how an
application would be able to detect that the filesystem was doing this.)

--b.

> 
> > But looking back through Jeff's postings, I don't see him claiming that;
> > e.g. in:
> > 
> > 	https://lore.kernel.org/lkml/20171222120556.7435-1-jlayton@kernel.org/
> > 	https://lore.kernel.org/linux-nfs/20180109141059.25929-1-jlayton@kernel.org/
> > 	https://lore.kernel.org/linux-nfs/1517228795.5965.24.camel@redhat.com/
> > 
> > he reports comparing old iversion behavior to new iversion behavior, but
> > not new iversion behavior to new noiversion behavior.
> 
> Yeah, it's had to compare noiversion behaviour on filesystems where
> it was understood that it couldn't actually be turned off. And,
> realistically, the comaprison to noiversion wasn't really relevant
> to the problem Jeff's patchset was addressing...
> 
> Cheers,
> 
> Dave.
> -- 
> Dave Chinner
> david@fromorbit.com