linux-ext4 - Re: [PATCH v4 2/9] fs: add infrastructure for multigrain inode i

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Date:   Wed, 14 Jun 2023 08:29:29 +0200
From:   Christian Brauner <brauner@...nel.org>
To:     Jeff Layton <jlayton@...nel.org>
Cc:     Jan Kara <jack@...e.cz>, Alexander Viro <viro@...iv.linux.org.uk>,
        "Darrick J. Wong" <djwong@...nel.org>,
        Hugh Dickins <hughd@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Dave Chinner <david@...morbit.com>,
        Chuck Lever <chuck.lever@...cle.com>,
        Amir Goldstein <amir73il@...il.com>,
        David Howells <dhowells@...hat.com>,
        Neil Brown <neilb@...e.de>,
        Matthew Wilcox <willy@...radead.org>,
        Andreas Dilger <adilger.kernel@...ger.ca>,
        Theodore T'so <tytso@....edu>, Chris Mason <clm@...com>,
        Josef Bacik <josef@...icpanda.com>,
        David Sterba <dsterba@...e.com>,
        Namjae Jeon <linkinjeon@...nel.org>,
        Steve French <sfrench@...ba.org>,
        Sergey Senozhatsky <senozhatsky@...omium.org>,
        Tom Talpey <tom@...pey.com>, linux-fsdevel@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-xfs@...r.kernel.org,
        linux-btrfs@...r.kernel.org, linux-ext4@...r.kernel.org,
        linux-mm@...ck.org, linux-nfs@...r.kernel.org,
        linux-cifs@...r.kernel.org
Subject: Re: [PATCH v4 2/9] fs: add infrastructure for multigrain inode
 i_m/ctime

On Tue, Jun 13, 2023 at 09:09:29AM -0400, Jeff Layton wrote:
> On Tue, 2023-05-23 at 14:46 +0200, Jan Kara wrote:
> > On Tue 23-05-23 06:40:08, Jeff Layton wrote:
> > > On Tue, 2023-05-23 at 12:02 +0200, Jan Kara wrote:
> > > > 
> > > > So there are two things I dislike about this series because I think they
> > > > are fragile:
> > > > 
> > > > 1) If we have a filesystem supporting multigrain ts and someone
> > > > accidentally directly uses the value of inode->i_ctime, he can get bogus
> > > > value (with QUERIED flag). This mistake is very easy to do. So I think we
> > > > should rename i_ctime to something like __i_ctime and always use accessor
> > > > function for it.
> > > > 
> > > 
> > > We could do this, but it'll be quite invasive. We'd have to change any
> > > place that touches i_ctime (and there are a lot of them), even on
> > > filesystems that are not being converted.
> > 
> > Yes, that's why I suggested Coccinelle to deal with this.
> 
> 
> I've done the work to convert all of the accesses of i_ctime into
> accessor functions in the kernel. The current state of it is here:
> 
>    
> https://git.kernel.org/pub/scm/linux/kernel/git/jlayton/linux.git/commit/?h=ctime
> 
> As expected, it touches a lot of code, all over the place. So far I have
> most of the conversion in one giant patch, and I need to split it up
> (probably per-subsystem).

Yeah, you have time since it'll be v6.6 material.

> 
> What's the best way to feed this change into mainline? Should I try to
> get subsystem maintainers to pick these up, or are we better off feeding
> this in via a separate branch?

I would prefer if we send them all through the vfs tree since trickle
down conversions are otherwise very painful and potentially very slow.