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

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Date:   Fri, 09 Sep 2022 11:07:47 +1000
From:   "NeilBrown" <neilb@...e.de>
To:     "Trond Myklebust" <trondmy@...merspace.com>
Cc:     "jlayton@...nel.org" <jlayton@...nel.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>,
        "bfields@...ldses.org" <bfields@...ldses.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>,
        "viro@...iv.linux.org.uk" <viro@...iv.linux.org.uk>,
        "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>,
        "adilger.kernel@...ger.ca" <adilger.kernel@...ger.ca>,
        "lczerner@...hat.com" <lczerner@...hat.com>,
        "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 Fri, 09 Sep 2022, NeilBrown wrote:
> On Fri, 09 Sep 2022, Trond Myklebust wrote:
> 
> > 
> > IOW: the minimal condition needs to be that for all cases below, the
> > application reads 'state B' as having occurred if any data was
> > committed to disk before the crash.
> > 
> > Application				Filesystem
> > ===========				=========
> > read change attr <- 'state A'
> > read data <- 'state A'
> > 					write data -> 'state B'
> > 					<crash>+<reboot>
> > read change attr <- 'state B'
> 
> The important thing here is to not see 'state A'.  Seeing 'state C'
> should be acceptable.  Worst case we could merge in wall-clock time of
> system boot, but the filesystem should be able to be more helpful than
> that.
> 

Actually, without the crash+reboot it would still be acceptable to see
"state A" at the end there - but preferably not for long.
>From the NFS perspective, the changeid needs to update by the time of a
close or unlock (so it is visible to open or lock), but before that it
is just best-effort.

NeilBrown