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Re: [PATCH 09/18] nfsd: implement pNFS operations

To: Christoph Hellwig <hch@xxxxxx>
Subject: Re: [PATCH 09/18] nfsd: implement pNFS operations
From: Jeff Layton <jeff.layton@xxxxxxxxxxxxxxx>
Date: Fri, 9 Jan 2015 09:33:53 -0800
Cc: Jeff Layton <jeff.layton@xxxxxxxxxxxxxxx>, "J. Bruce Fields" <bfields@xxxxxxxxxxxx>, linux-nfs@xxxxxxxxxxxxxxx, linux-fsdevel@xxxxxxxxxxxxxxx, xfs@xxxxxxxxxxx, thomas.haynes@xxxxxxxxxxxxxxx, trond.myklebust@xxxxxxxxxxxxxxx, Sachin Bhamare <sachin.bhamare@xxxxxxxxxxxxxxx>
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On Fri, 9 Jan 2015 09:28:35 -0800
Jeff Layton <jlayton@xxxxxxxxxxxxxxx> wrote:

>  On Fri, 9 Jan 2015 18:16:41 +0100
> Christoph Hellwig <hch@xxxxxx> wrote:
> 
> > On Fri, Jan 09, 2015 at 08:51:30AM -0800, Jeff Layton wrote:
> > > Ok, it'd be good to document that in some comments then for the sake of
> > > posterity (maybe it is later in the set -- I haven't gotten to the end
> > > yet).
> > 
> > What kinds of comments do you expect?  Not implementing unused features
> > of a protocol should be the default for anything in Linux.
> > 
> 
> I was thinking just a comment saying that ROC is always true in this
> implementation, or maybe consider eliminating the lg_roc field in
> struct nfsd4_layoutget altogether since it's currently always "1".
> 
> It's a little confusing now since the encoder can handle the case where
> lg_roc is 0, but the rest of the code can't.
> 
> > > Now, that said...I think that your ROC semantics are wrong here. You
> > > also have to take delegations into account. [1]
> > > 
> > > Basically the semantics that you want are that nfsd should do all of
> > > the ROC stuff on last close iff there are no outstanding delegations or
> > > on delegreturn iff there are no opens.
> > > 
> > > What we ended up doing in the unreleased code we have was to create a
> > > new per-client and per-file object (that we creatively called an
> > > "odstate"). An open stateid and a delegation stateid would hold a
> > > reference to this object which is put when those stateids are freed.
> > > When its refcount goes to zero, then we'd free any outstanding layouts
> > > on the file for that client and free the object.
> > > 
> > > You probably want to do something similar here.
> > > 
> > > [1]: Tom and Trond mentioned that there's a RFC5661 errata pending for
> > >      this, but I don't see it right offhand.
> > 
> > It would be good to look at the errata.  While the idea of keeping
> > layouts around longer makes sense, I would only expect to do this
> > if they layout state was created based on a delegation stateid, not
> > a lock or open stateid.  In that case having the layouts hang off
> > the "parent" stateid might be another option.
> 
> I found it:
> 
>     http://www.rfc-editor.org/errata_search.php?rfc=5661&eid=3226
> 

Oh, hmm...except that doesn't seem to have been updated according to
the discussion from around a year ago. See the thread entitled:

    [nfsv4] NFSv4.1 errata id 3226 (the return of return-on-close layouts)

...on thee nfsv4@xxxxxxxx mailing list. Trond mentions it there.
Perhaps we need to revise that errata?

-- 
Jeff Layton <jlayton@xxxxxxxxxxxxxxx>

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