Subject: Re: [nfsv4] pNFS: Open issues (from chapter 12 & 13 reviews)

From: Spencer Shepler <[email-masked]>
Date: Mon, 16 Jul 2007 16:13:49 -0500

On Jun 20, 2007, at 6:06 PM, Garth Goodson wrote:

> Pulled from meeting minutes thanks to Lisa and Sam.
>
> Chapter 12: Common pNFS
> -----------------------
>
> * Open Issue 1: Layout hint attribute on OPEN (or a later SETATTR)
>
>   (Line 12890 of draft 10)
>   - Dictates the use of a persistent reply cache if layout hints  
> are to
>     be used. General agreement that this is not good.
>   - SETATTR after an exclusive create may be a viable option (servers
>    may be fine with this)
>
> Noveck's proposed solution: Encourage, but not require a persistent  
> reply cache for layout_hint.  A client can do a layout_hint on  
> EXCLUSIVE CREATE, but the server may or may not be able to handle  
> it effectively.

I would like to clarify this a little to close on the issue.

I agree that if a client is attempting to combine the semantics of
OPEN with exclusive create and providing a layout_hint, that it
should be encouraged to use Sessions persistent reply cache.  This
would be embodied as a OPEN with createmode4 == GUARDED4.
This brings me to the clarification; the entire reason for this issue
is that with createmode4 == EXCLUSIVE4, the client is unable to
provide attributes for the create and then the second suggestion
that the server may or may not be able to "handle it" doesn't
make sense given that the OPEN call can not be encoded that way.

So, am I to assume that "EXCLUSIVE CREATE" be replaced with SETATTR  
or layout_hint?
This seems reasonable to me.  Should there be any additional guidance  
given
other than "may or may not be able to handle it"?  Should the server  
silently
ignore the attribute if not supported?  Is there a timeframe when a
server is most likely to be able to handle the hint? For example,  
before the
first read/write to the file?

Spencer

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---

From: "Noveck, Dave" <[email-masked]>
Date: Mon, 16 Jul 2007 17:43:45 -0400

> So, am I to assume that "EXCLUSIVE CREATE" be replaced 
> with SETATTR or layout_hint?

That's what I was assuming.

> This seems reasonable to me.  Should there be any additional 
> guidance given other than "may or may not be able to handle it"?  
> Should the server silently ignore the attribute if not supported?  

It is a hint so either the server would ignore it or the server
would return NOTSUPP and the client would ignore that.

> Is there a timeframe when a server is most likely to be able to 
> handle the hint? For example, before the first read/write to the 
> file?

I would go so far as to say the server SHOULD support setting this
at least once before the first IO to the newly created file. 

-----Original Message-----
From: Spencer Shepler [mailto:[email-masked]] 
Sent: Monday, July 16, 2007 5:14 PM
To: [email-masked]
Subject: Re: [nfsv4] pNFS: Open issues (from chapter 12 & 13 reviews)

On Jun 20, 2007, at 6:06 PM, Garth Goodson wrote:

>   - Dictates the use of a persistent reply cache if layout hints are 
> to
> EXCLUSIVE CREATE, but the server may or may not be able to handle it 
> effectively.

I agree that if a client is attempting to combine the semantics of OPEN
with exclusive create and providing a layout_hint, that it should be
encouraged to use Sessions persistent reply cache.  This would be
embodied as a OPEN with createmode4 == GUARDED4.
This brings me to the clarification; the entire reason for this issue is
that with createmode4 == EXCLUSIVE4, the client is unable to provide
attributes for the create and then the second suggestion that the server
may or may not be able to "handle it" doesn't make sense given that the
OPEN call can not be encoded that way.

So, am I to assume that "EXCLUSIVE CREATE" be replaced with SETATTR or
layout_hint?
This seems reasonable to me.  Should there be any additional guidance
given other than "may or may not be able to handle it"?  Should the
server silently ignore the attribute if not supported?  Is there a
timeframe when a server is most likely to be able to handle the hint?
For example, before the first read/write to the file?

Spencer

---

From: Spencer Shepler <[email-masked]>
Date: Mon, 16 Jul 2007 18:07:10 -0500

> at least once before the first IO to the newly created file.

Agreed.

Okay, I will work this into the next version of the I-D
presupposing no further comment.

Spencer

> OPEN

---

From: Benny Halevy <[email-masked]>
Date: Tue, 17 Jul 2007 15:20:36 +0300

>> That's what I was assuming.

Only if persistent sessions aren't supported by the server,
otherwise the client MUST still use GUARDED, right?

---

From: "Noveck, Dave" <[email-masked]>
Date: Tue, 17 Jul 2007 09:09:29 -0400

> otherwise the client MUST still use GUARDED, right?

The server MUST return NOTSUPP if EXCLUSIVE is done on a persistent
session.  If the client wants to get NOTSUPP, he MAY use EXCLUSIVE as
much as he wishes :-) 

-----Original Message-----
From: Benny Halevy [mailto:[email-masked]] 
Sent: Tuesday, July 17, 2007 8:21 AM
To: Spencer Shepler
Cc: Noveck, Dave; [email-masked]
Subject: Re: [nfsv4] pNFS: Open issues (from chapter 12 & 13 reviews)

>> So, am I to assume that "EXCLUSIVE CREATE" be replaced with SETATTR
or