Subject: RE: [nfsv4] 2.9.4.1 Slot usage

From: "Noveck, Dave" <[email-masked]>
Date: Fri, 10 Nov 2006 14:39:10 -0500

> > be strengthened to "the requester MUST use the lowest" .. ?

> What would that mean?

I think it means the same as "is required to use the lowest" but it
adds the implication that using some other slot is violating the
protocol, as opposed to being a troublesome requester, let's say.

> Is the server going to reject the RPC call if the requester fails to
use
> the lowest slot? 

Clearly not, for two reasons.  One is that there is no error code
defined for this situation.  But the more definitive reason is that the
replier has no way of knowing whether the requestor is obeying this 
requirement.  All the replier knows is that he has made a given slot
free by sending a reply.  He doesn't know that the requester has 
received it until he gets a new request from the requester with that
slot number, but when he gets that new request that slot is no longer
free, so it is impossible for him to know that the slot number he
receives in a request is not the lowest.

I don't believe it is a requirement for making something a MUST, that
the other side be able to check for compliance.  Often, it goes the
other way.  When the server can check for the client's compliance we
no longer have to say MUST to the client.  Instead we can let the client
send whatever he wants, with the understanding the client will/MUST
reject it, if the specified rule is not followed.
 
> If so, what about races (slot n-1 becomes available
> just as I'm marshalling my XDR for slot n)?

Or after I've marshalled it but before my network stack sends it.

If we say "MUST" here, we wind up having to very precisely define the
instants when something becomes available and when we actually have
sent a given request.

I would change "is required" to "SHOULD".  I think that's more
consistent
with the logic of the requirement if "requirement" is the appropriate 
word for a SHOULD.

-----Original Message-----
From: Trond Myklebust [mailto:[email-masked]] 
Sent: Friday, November 10, 2006 2:07 PM
To: Robert Gordon
Cc: NFSv4
Subject: Re: [nfsv4] 2.9.4.1 Slot usage

On Fri, 2006-11-10 at 11:55 -0600, Robert Gordon wrote:
> In 2.9.4.1 Slot identifiers and reply cache we have this paragraph.
> 
> > In general, the receipt of a new sequenced request arriving on any
> > valid slot is an indication that the previous reply cache contents
> > of that slot may be discarded. In order to further assist the
replier
> > in slot management, the requester is required to use the lowest  
> > available
> > slot when issuing a new request. In this way, the replier may be  
> > able to
> > retire additional entries.
> 
> should the language that stipulates "the requester is required to use

> the lowest"
> 
> be strengthened to "the requester MUST use the lowest" .. ?

What would that mean?

Is the server going to reject the RPC call if the requester fails to use
the lowest slot? If so, what about races (slot n-1 becomes available
just as I'm marshalling my XDR for slot n)?

Cheers,
  Trond

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---

From: "James Yarbrough" <[email-masked]>
Date: Fri, 10 Nov 2006 12:04:32 -0800

> consistent with the logic of the requirement if "requirement" is
> the appropriate word for a SHOULD.

MUST and REQUIRED are equivalent according to RFC 2119.  They both
indicate an absolute requirement.  We don't seem to be talking about an
absolute requirement in this case.

---

From: Robert Gordon <[email-masked]>
Date: Fri, 10 Nov 2006 14:11:55 -0600

On Nov 10, 2006, at 1:39 PM, Noveck, Dave wrote:

> consistent with the logic of the requirement if "requirement"
> is the appropriate word for a SHOULD.

Okay, I think i was a little over zealous with MUST, [1]SHOULD
is the level of emphasizes that i believe is needed..

-- Robert

[1] SHOULD   This word, or the adjective "RECOMMENDED", mean that
there may exist valid reasons in particular circumstances to ignore
a particular item, but the full implications must be understood and
carefully weighed before choosing a different course.