Re: [nfsv4] RFC: Is Open/Claim_Delegate_Prev done before/after Reclaim_complete?

[Trond Myklebust <[e-mail]>]

On Fri, 2024-04-05 at 16:13 -0700, Rick Macklem wrote:
> On Thu, Apr 4, 2024 at 9:18 PM Trond Myklebust
> <[e-mail]> wrote:
> > 
> > On Thu, 2024-04-04 at 16:23 -0700, Rick Macklem wrote:
> > > Hi,
> > > 
> > > I am in the process of implementing Open/Claim_Delegate_Prev and
> > > have
> > > run
> > > into a question I cannot seem to answer from reading RFC8881.
> > > 
> > > There is this snippet:
> > >    enum open_claim_type4 {
> > >            /*
> > >             * Not a reclaim.
> > >             */
> > >            CLAIM_NULL              = 0,
> > > 
> > >            CLAIM_PREVIOUS          = 1,
> > >            CLAIM_DELEGATE_CUR      = 2,
> > >            CLAIM_DELEGATE_PREV     = 3,
> > > 
> > >            /*
> > >             * Not a reclaim.
> > >             *
> > >             * Like CLAIM_NULL, but object identified
> > >             * by the current filehandle.
> > >             */
> > >            CLAIM_FH                = 4, /* new to v4.1 */
> > > The comments in the above seem to "hint" that CLAIM_DELEGATE_PREV
> > > is
> > > a
> > > reclaim type operation.
> > > If that is the case, I'd assume it/should be performed by the
> > > client
> > > before it does a
> > > Reclaim_Complete?
> > > 
> > > Then there is this snippet:
> > >    For OPEN requests that reach the server during the grace
> > > period,
> > > the
> > >    server returns an error of NFS4ERR_GRACE.  The following claim
> > > types
> > >    are exceptions:
> > > 
> > >    *  OPEN requests specifying the claim type CLAIM_PREVIOUS are
> > > devoted
> > >       to reclaiming opens after a server restart and are
> > > typically
> > > only
> > >       valid during the grace period.
> > > 
> > >    *  OPEN requests specifying the claim types CLAIM_DELEGATE_CUR
> > > and
> > >       CLAIM_DELEG_CUR_FH are valid both during and after the
> > > grace
> > >       period.  Since the granting of the delegation that they are
> > >       subordinate to assures that there is no conflict with locks
> > > to
> > > be
> > >       reclaimed by other clients, the server need not return
> > >       NFS4ERR_GRACE when these are received during the grace
> > > period.
> > > This clearly states that CLAIM_DELEGATE_PREV cannot be performed
> > > during the server's grace period.
> > > 
> > > The above two statements are not necessarily contradictory but it
> > > does seem
> > > that, if the server is in its grace period, the Reclaim_Complete
> > > needs to be
> > > done before any Open/Claim_Delegate_Prev, since Reclaim_Complete
> > > tells
> > > the server when to end its grace period.
> > > Note that, usually, a client would not be rebooting when a server
> > > is
> > > in its
> > > grace period, but that could happen.
> > > 
> > > Bottom line...
> > > Should a client perform Open/Claim_Delegate_Prev before or after
> > > Reclaim_Complete?
> > > And, if the answer is "after", how does the server know when a
> > > client
> > > is done recovering opens/delegations via
> > > Open/Claim_Delegate_Prev?
> > > 
> > > Thanks for any help with this, rick
> > 
> > CLAIM_DELEGATE_PREV has now survived at least 24 years as part of a
> > "standard" and has yet to be properly described. I can find
> > references
> > to it in RFC3010 and all NFSv4 descriptions since then, but I have
> > yet
> > to meet anybody who can claim to have implemented it in a product.
> > 
> > IMO, it is time to drop it, and start afresh with something that
> > has
> > actually been road tested before someone started putting pen to
> > paper.
> Well, I am going to respond to David's post in some more detail, but
> I will
> note here that, with the exception of whether to do it before or
> after
> Reclaim_complete,
> I have not found serious issues with it. (Btw, the FreeBSD server has
> had a "dormant"
> implementation for about 20years, although I am just now trying to
> use it by the
> FreeBSD client. I was wondering if I would find any other server
> implementation at
> the Bakeathon in a couple of weeks.)

I see. So how do you plan to deal with the case where the server denies
the request for a delegation? Will your client just toss away the dirty
data?

-- 
Trond Myklebust
Linux NFS client maintainer, Hammerspace
[e-mail]