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From:   "NeilBrown" <neilb@suse.de>
To:     "Trond Myklebust" <trondmy@hammerspace.com>
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Subject: Re: [man-pages RFC PATCH v4] statx, inode: document the new
 STATX_INO_VERSION field
In-reply-to: <166268467103.30452.1687952324107257676@noble.neil.brown.name>
References: <20220907111606.18831-1-jlayton@kernel.org>,
 <166255065346.30452.6121947305075322036@noble.neil.brown.name>,
 <79aaf122743a295ddab9525d9847ac767a3942aa.camel@kernel.org>,
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 <20220908083326.3xsanzk7hy3ff4qs@quack3>, <YxoIjV50xXKiLdL9@mit.edu>,
 <02928a8c5718590bea5739b13d6b6ebe66cac577.camel@kernel.org>,
 <166267775728.30452.17640919701924887771@noble.neil.brown.name>,
 <91e31d20d66d6f47fe12c80c34b1cffdfc202b6a.camel@hammerspace.com>,
 <166268467103.30452.1687952324107257676@noble.neil.brown.name>
Date:   Fri, 09 Sep 2022 11:07:47 +1000
Message-id: <166268566751.30452.13562507405746100242@noble.neil.brown.name>
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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