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From:   Olga Kornievskaia <aglo@umich.edu>
Date:   Thu, 30 May 2019 13:20:22 -0400
Message-ID: <CAN-5tyHUah=fAsiSLb=n__q5HxRy3qeS83evf-vB59r4cpYgsw@mail.gmail.com>
Subject: Re: [PATCH 0/9] Multiple network connections for a single NFS mount.
To:     Tom Talpey <tom@talpey.com>
Cc:     NeilBrown <neilb@suse.com>, Chuck Lever <chuck.lever@oracle.com>,
        Schumaker Anna <Anna.Schumaker@netapp.com>,
        Trond Myklebust <trondmy@hammerspace.com>,
        linux-nfs <linux-nfs@vger.kernel.org>
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On Thu, May 30, 2019 at 1:05 PM Tom Talpey <tom@talpey.com> wrote:
>
> On 5/29/2019 8:41 PM, NeilBrown wrote:
> > I've also re-arrange the patches a bit, merged two, and remove the
> > restriction to TCP and NFSV4.x,x>=1.  Discussions seemed to suggest
> > these restrictions were not needed, I can see no need.
>
> I believe the need is for the correctness of retries. Because NFSv2,
> NFSv3 and NFSv4.0 have no exactly-once semantics of their own, server
> duplicate request caches are important (although often imperfect).
> These caches use client XID's, source ports and addresses, sometimes
> in addition to other methods, to detect retry. Existing clients are
> careful to reconnect with the same source port, to ensure this. And
> existing servers won't change.

Retries are already bound to the same connection so there shouldn't be
an issue of a retransmission coming from a different source port.

> Multiple connections will result in multiple source ports, and possibly
> multiple source addresses, meaning retried client requests may be
> accepted as new, rather than having any chance of being recognized as
> retries.
>
> NFSv4.1+ don't have this issue, but removing the restrictions would
> seem to break the downlevel mounts.
>
> Tom.
>