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From:   Olga Kornievskaia <aglo@umich.edu>
Date:   Tue, 28 Apr 2020 19:02:46 -0400
Message-ID: <CAN-5tyGfCXVTz4dq3Qj2eXww8BNB_dT=0QwWteEGM93MZBJudw@mail.gmail.com>
Subject: Re: handling ERR_SERVERFAULT on RESTOREFH
To:     Trond Myklebust <trondmy@hammerspace.com>
Cc:     "linux-nfs@vger.kernel.org" <linux-nfs@vger.kernel.org>
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On Tue, Apr 28, 2020 at 5:32 PM Trond Myklebust <trondmy@hammerspace.com> wrote:
>
> On Tue, 2020-04-28 at 16:40 -0400, Olga Kornievskaia wrote:
> > On Tue, Apr 28, 2020 at 2:47 PM Trond Myklebust <
> > trondmy@hammerspace.com> wrote:
> > > Hi Olga,
> > >
> > > On Tue, 2020-04-28 at 14:14 -0400, Olga Kornievskaia wrote:
> > > > Hi folk,
> > > >
> > > > Looking for guidance on what folks think. A client is sending a
> > > > LINK
> > > > operation to the server. This compound after the LINK has
> > > > RESTOREFH
> > > > and GETATTR. Server returns SERVER_FAULT to on RESTOREFH. But
> > > > LINK is
> > > > done successfully. Client still fails the system call with EIO.
> > > > We
> > > > have a hardline and "ln" saying hardlink failed.
> > > >
> > > > Should the client not fail the system call in this case? The fact
> > > > that
> > > > we couldn't get up-to-date attributes don't seem like the reason
> > > > to
> > > > fail the system call?
> > > >
> > > > Thank you.
> > >
> > > I don't really see this as worth fixing on the client. It is very
> > > clearly a server bug.
> >
> > Why is that a server bug? A server can legitimately have an issue
> > trying to execute an operation (RESTOREFH) and legitimately returning
> > an error.
>
> If it is happening consistently on the server, then it is a bug, and it
> gets reported by the client in the same way we always report
> NFS4ERR_SERVERFAULT, by converting to an EREMOTEIO.

Yes but the client doesn't retry so it can't assess if it's
consistently happening or not. It can be a transient error (or ENOMEM)
that's later resolved.

> > NFS client also ignores errors of the returning GETATTR after the
> > RESTOREFH. So I'm not sure why we are then not ignoring errors (or
> > some errors) of the RESTOREFH.
>
> We do need to check the value of RESTOREFH in order to figure out if we
> can continue reading the XDR buffer to decode the file attributes. We
> want to read those file attributes because we do expect the change
> attribute, the ctime and the nlinks values to all change as a result of
> the operation.

I have nothing against decoding the error and using it in a decision
to keep decoding. But the client doesn't have to propagate the
RESTOREFH error to the application?

In all other non-idempotent operations that have other operations (ie
GETATTR) following them, the client ignores the errors. Btw I just
noticed that on OPEN compound, since we ignore decode error from the
GETATTR, it would continue decoding LAYOUTGET...

CREATE has problem if the following GETFH will return EDELAY. Client
doesn't deal with retrying a part of the compound. It retries the
whole compound. It leads to an error (since non-idempotent operation
is retried). But I guess that's a 2nd issue (or a 3rd if we could the
decoding layoutget)....

All this is under the umbrella of how to handle errors on
non-idempotent operations in a compound....


>
> Cheers
>   Trond
>
> --
> Trond Myklebust
> Linux NFS client maintainer, Hammerspace
> trond.myklebust@hammerspace.com
>
>