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From:   "NeilBrown" <neilb@suse.de>
To:     "Al Viro" <viro@zeniv.linux.org.uk>
Cc:     "Jeff Layton" <jlayton@kernel.org>,
        "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: <Yxzpsdn4S6mTToct@ZenIV>
References: <20220907111606.18831-1-jlayton@kernel.org>,
 <166255065346.30452.6121947305075322036@noble.neil.brown.name>,
 <79aaf122743a295ddab9525d9847ac767a3942aa.camel@kernel.org>,
 <20220907125211.GB17729@fieldses.org>,
 <771650a814ab1ff4dc5473d679936b747d9b6cf5.camel@kernel.org>,
 <8a71986b4fb61cd9b4adc8b4250118cbb19eec58.camel@hammerspace.com>,
 <c22baa64133a23be3aba81df23b4af866df51343.camel@kernel.org>,
 <166259764365.30452.5588074352157110414@noble.neil.brown.name>,
 <Yxzpsdn4S6mTToct@ZenIV>
Date:   Sun, 11 Sep 2022 09:00:10 +1000
Message-id: <166285081066.30452.6346804601094610224@noble.neil.brown.name>
Precedence: bulk

On Sun, 11 Sep 2022, Al Viro wrote:
> 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?
> 

Why would you think there would be any boiler plate?  Only filesystems
that opt in would need to do anything, and only when the caller asked
(by passing a non-NULL array pointer).

NeilBrown