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Date:   Thu, 4 Mar 2021 13:58:06 +0200
From:   Dan Aloni <dan@kernelim.com>
To:     Olga Kornievskaia <aglo@umich.edu>
Cc:     linux-nfs <linux-nfs@vger.kernel.org>,
        Anna Schumaker <anna.schumaker@netapp.com>,
        Trond Myklebust <trond.myklebust@hammerspace.com>
Subject: Re: [PATCH v1 0/8] sysfs files for multipath transport control
Message-ID: <20210304115806.rvoeju7gmqyd3v6i@gmail.com>
References: <20210215174002.2376333-1-dan@kernelim.com>
 <CAN-5tyGw3D-+emeQhu31agom9yuZ9=PL6YUVyEKiR-n2q9uE3A@mail.gmail.com>
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On Mon, Mar 01, 2021 at 10:56:22PM -0500, Olga Kornievskaia wrote:
> Hi Dan,
> 
> On Mon, Feb 15, 2021 at 12:43 PM Dan Aloni <dan@kernelim.com> wrote:
> >
> > Hi Anna,
> >
> > This patchset builds ontop v2 of your 'sysfs files for changing IP' changeset.
> >
> > - The patchset adds two more sysfs objects, for one for transport and another
> >   for multipath.
> > - Also, `net` renamed to `client`, and `client` now has symlink to its principal
> >   transport. A client also has a symlink to its `multipath` object.
> > - The transport interface lets you change `dstaddr` of individual transports,
> >   when `nconnect` is used (or if it wasn't used and these were added with the
> >   new interface).
> > - The interface to add a transport is using a single string written to 'add',
> >   for example:
> >
> >        echo 'dstaddr 192.168.40.8 kind rdma' \
> >                > /sys/kernel/sunrpc/client/0/multipath/add
> >
> > These changes are independent of the method used to obtain a sunrpc ID for a
> > mountpoint. For that I've sent a concept patch showing an fspick-based
> > implementation: https://marc.info/?l=linux-nfs&m=161332454821849&w=4
> 
> I'm confused: does this allow adding arbitrary connections between a
> client and some server IP to an existing RPC client? Given the above
> description, that's how it reads to me, can you clarify please. I
> thought it was something specifically for v3 (because it has no
> concept of trunking). As for NFSv4 there is a notion of getting server
> locations via FS_LOCATION and doing trunking (ie multipathing)? I
> don't see how this code restricts the addition of transports to v3.

Indeed, there's no restriction to NFSv3.

There can be potential uses for this for NFSv4 too. FS_LOCATIONS serving
as recommendation to which hosts the client can connect, while smart
load-balancing logic in userspace can determine to which subset of these
servers each client in a cluster should actually connect (a full mesh
is not always desired).

At any case, if this restriction is desired, we can add a new sunrpc
client flag for that and pass it only in NFSv3 client init.

-- 
Dan Aloni