linux-ext4 - Re: [man-pages RFC PATCH v4] statx, inode: document the new STATX_INO

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Date:   Sat, 10 Sep 2022 20:46:57 +0100
From:   Al Viro <viro@...iv.linux.org.uk>
To:     NeilBrown <neilb@...e.de>
Cc:     Jeff Layton <jlayton@...nel.org>,
        Trond Myklebust <trondmy@...merspace.com>,
        "bfields@...ldses.org" <bfields@...ldses.org>,
        "zohar@...ux.ibm.com" <zohar@...ux.ibm.com>,
        "djwong@...nel.org" <djwong@...nel.org>,
        "xiubli@...hat.com" <xiubli@...hat.com>,
        "brauner@...nel.org" <brauner@...nel.org>,
        "linux-api@...r.kernel.org" <linux-api@...r.kernel.org>,
        "linux-xfs@...r.kernel.org" <linux-xfs@...r.kernel.org>,
        "david@...morbit.com" <david@...morbit.com>,
        "fweimer@...hat.com" <fweimer@...hat.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "chuck.lever@...cle.com" <chuck.lever@...cle.com>,
        "linux-man@...r.kernel.org" <linux-man@...r.kernel.org>,
        "linux-nfs@...r.kernel.org" <linux-nfs@...r.kernel.org>,
        "tytso@....edu" <tytso@....edu>, "jack@...e.cz" <jack@...e.cz>,
        "linux-ext4@...r.kernel.org" <linux-ext4@...r.kernel.org>,
        "linux-btrfs@...r.kernel.org" <linux-btrfs@...r.kernel.org>,
        "linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
        "lczerner@...hat.com" <lczerner@...hat.com>,
        "adilger.kernel@...ger.ca" <adilger.kernel@...ger.ca>,
        "ceph-devel@...r.kernel.org" <ceph-devel@...r.kernel.org>
Subject: Re: [man-pages RFC PATCH v4] statx, inode: document the new
 STATX_INO_VERSION field

On Thu, Sep 08, 2022 at 10:40:43AM +1000, NeilBrown wrote:

> We do hold i_rwsem today.  I'm working on changing that.  Preserving
> atomic directory changeinfo will be a challenge.  The only mechanism I
> can think if is to pass a "u64*" to all the directory modification ops,
> and they fill in the version number at the point where it is incremented
> (inode_maybe_inc_iversion_return()).  The (nfsd) caller assumes that
> "before" was one less than "after".  If you don't want to internally
> require single increments, then you would need to pass a 'u64 [2]' to
> get two iversions back.

Are you serious?  What kind of boilerplate would that inflict on the
filesystems not, er, opting in for that... scalability improvement
experiment?