[nfsv4] Re: OPEN_XOR_DELEGATION when there is existing OPEN stateid

[Rick Macklem <[e-mail]>]

On Thu, Oct 3, 2024 at 1:46 PM Rick Macklem <[e-mail]> wrote:
>
> On Thu, Oct 3, 2024 at 10:00 AM Thomas Haynes <[e-mail]> wrote:
> >
> >
> >
> > On Oct 3, 2024, at 8:12 AM, Rick Macklem <[e-mail]> wrote:
> >
> > On Thu, Oct 3, 2024 at 7:32 AM Rick Macklem <[e-mail]> wrote:
> >
> >
> > On Thu, Oct 3, 2024 at 3:21 AM Jeff Layton <[e-mail]> wrote:
> >
> >
> > On Wed, 2024-10-02 at 17:26 -0700, Rick Macklem wrote:
> >
> > On Wed, Oct 2, 2024 at 9:16 AM Thomas Haynes <[e-mail]> wrote:
> >
> >
> >
> >
> > On Oct 2, 2024, at 5:51 AM, Jeff Layton <[e-mail]> wrote:
> >
> > On Tue, 2024-10-01 at 22:24 -0700, Thomas Haynes wrote:
> >
> >
> > On Oct 1, 2024, at 6:11 AM, Jeff Layton <[e-mail]> wrote:
> >
> > Another delstid question. Consider the following situation. All opens
> > have WANT_OPEN_XOR_DELEGATION set:
> >
> > 1/ Client opens a file r/o. Server doesn't assign a delegation, so an
> > open stateid (with seq=1) is returned.
> >
> > 2/ Client opens the file again for r/w. Server assigns a delegation and
> > skips updating the OPEN stateid's seqid and sending the result back to
> > the client.
> >
> > Is that wrong behavior? It seems like that would morph the open stateid
> > for this openowner without updating the client as to the new stateid.
> > The delegation does cover it in that case, but it seems less than
> > optimal if the client ends up returning that delegation later.
> >
> > If the client already holds an open stateid, should we ignore
> > WANT_OPEN_XOR_DELEGATION?
> > --
> > Jeff Layton <[e-mail]>
> >
> >
> >
> > It seems to me we can’t break the upgrade, so we have to honor the WANT_OPEN_XOR_DELEGATION by returning an upgraded open stateid.
> >
> > I.e., if the client already has an open stateid and presents an WANT_OPEN_XOR_DELEGATION, then cannot return just a delegation. Either we just upgrade the existing open stateid or we upgrade it and also return the delegation.
> >
> > Likewise, if we had already returned a delegation stateid, we should just return a delegation stateid.
> >
> > Feel free to argue with me ….
> >
> >
> > No, that makes sense I think.
> >
> > Would it be OK to just ignore WANT_OPEN_XOR_DELEGATION in this case,
> > and return both an updated open stateid and the delegation stateid?
> > That's probably the more desirable outcome (regardless of the "XOR" in
> > the name).
> > --
> > Jeff Layton <[e-mail]>
> >
> >
> >
> > It is a hint, none of the language states it MUST return one or the other.
> >
> > The only bother is that you have to provide a reason for ignoring it.
> > Having said that, I doubt clients care what the reason is and I'll
> > note that a client is being "dumb" if it uses the
> > OPEN4_SHARE_ACCESS_WANT_OPEN_XOR_DELEGATION flag
> > in this case.
> >
> >
> > Do we need to provide a reason? I think we can just ignore this flag
> > and send both stateids in this case. We're not denying the delegation,
> > so there is no need to send a WND4_* status code.
> >
> > Oops, yes, you are correct. If you are replying with a delegation, you
> > don't need a "why I didn't" flag.  I was thinking that these had to be returned
> > whenever you ignored a WANT flag, but that is not what the RFC says.
> > (I now need to check the FreeBSD server to make sure I got that correct
> > when I implemented it.)
> >
> > However, for a typical XOR case (where the client does not have an Open
> > already) and choosing to not issue the delegation...
> > --> It is not 100% obvious if a WND4_* flag is required in the reply?
> > (I would say it is not required, because the server is satisfying the
> > request, but??)
> >
> > Hmm. Here's what RFC8881 says:
> >
> >   If the server supports the new _WANT_ flags and the client sends one
> >   or more of the new flags, then in the event the server does not
> >   return a delegation, it MUST return a delegation type of
> >   OPEN_DELEGATE_NONE_EXT.  The field ond_why in the reply indicates why
> >   no delegation was returned and will be one of:
> >
> > It sounds like it is clear, in that a WND4_* reply flag is needed if an Open
> > with OPEN4_SHARE_ACCESS_WANT_OPEN_XOR_DELEGATION does not
> > get a delegation in the reply.
> >
> > This brings me to something else that is not explicit in the draft...
> > --> OPEN4_SHARE_ACCESS_WANT_OPEN_XOR_DELEGATION only seems
> >      meaningful when it is combined with one of the other
> >      OPEN_SHARE_ACCESS_WANT_xxx flags.
> > Is this correct? Should this be explicit in the draft?
> >
> >
> > I was going to say yes, but now I believe not after reading RFC8881:
> >
> >    If (share_access & OPEN4_SHARE_ACCESS_WANT_DELEG_MASK) is not zero,
> >    then the client will have specified one and only one of:
> >
> >    OPEN4_SHARE_ACCESS_WANT_READ_DELEG
> >
> >    OPEN4_SHARE_ACCESS_WANT_WRITE_DELEG
> >
> >    OPEN4_SHARE_ACCESS_WANT_ANY_DELEG
> >
> >    OPEN4_SHARE_ACCESS_WANT_NO_DELEG
> >
> >    OPEN4_SHARE_ACCESS_WANT_CANCEL
> >
> >    Otherwise, the client is neither indicating a desire nor a non-desire
> >    for a delegation, and the server MAY or MAY not return a delegation
> >    in the OPEN response.
> >
> > I.e., if I set only OPEN4_SHARE_ACCESS_WANT_OPEN_XOR_DELEGATION, I am saying that I don’t care if you assign me a delegation, but if you do, only assign me one of a delegation or open stateid.
> Ok, I didn't notice that OPEN4_SHARE_ACCESS_WANT_OPEN_XOR_DELEGATION
> was not in OPEN4_SHARE_ACCESS_WANT_DELEG_MASK, so I suppose the above
> is correct.
>
> Btw, the draft has this...
>
> const OPEN4_SHARE_ACCESS_WANT_OPEN_XOR_DELEGATION = 0x200000;
>
> which appears to be a typo, since
> OPEN4_SHARE_ACCESS_WANT_PUSH_DELEG_WHEN_UNCONTENDED
> is defined as the same value in RFC8881.
Oops, again. I now see that they aren't the same 0x20000 vs 0x200000.
My old eyes
deceived me.

Sorry about that, rick

>
> rick
>
>
> >
> > Thoughts?
> >
> >
> >
> >
> > rick
> >
> >
> > rick
> >
> >
> > --
> > Jeff Layton <[e-mail]>
> >
> >