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Subject: Re: [PATCH v1 4/4] xprtrdma: Plant XID in on-the-wire RDMA offset
 (FRWR)
From:   Chuck Lever <chuck.lever@oracle.com>
In-Reply-To: <CAN-5tyG26W+TjTsjpTVvF3RJOGCnD8L79dCbRqKTm5F1V3fuxw@mail.gmail.com>
Date:   Mon, 19 Nov 2018 12:58:55 -0500
Cc:     linux-rdma <linux-rdma@vger.kernel.org>,
        Linux NFS Mailing List <linux-nfs@vger.kernel.org>
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References: <20181119153707.10832.42881.stgit@manet.1015granger.net>
 <20181119154607.10832.92558.stgit@manet.1015granger.net>
 <CAN-5tyG26W+TjTsjpTVvF3RJOGCnD8L79dCbRqKTm5F1V3fuxw@mail.gmail.com>
To:     Olga Kornievskaia <aglo@umich.edu>
Sender: linux-nfs-owner@vger.kernel.org
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> On Nov 19, 2018, at 12:47 PM, Olga Kornievskaia <aglo@umich.edu> =
wrote:
>=20
> On Mon, Nov 19, 2018 at 10:46 AM Chuck Lever <chuck.lever@oracle.com> =
wrote:
>>=20
>> Place the associated RPC transaction's XID in the upper 32 bits of
>> each RDMA segment's rdma_offset field. These bits are currently
>> always zero.
>>=20
>> There are two reasons to do this:
>>=20
>> - The R_key only has 8 bits that are different from registration to
>>  registration. The XID adds more uniqueness to each RDMA segment to
>>  reduce the likelihood of a software bug on the server reading from
>>  or writing into memory it's not supposed to.
>>=20
>> - On-the-wire RDMA Read and Write operations do not otherwise carry
>>  any identifier that matches them up to an RPC. The XID in the
>>  upper 32 bits will act as an eye-catcher in network captures.
>=20
> Is this just an "eye-catcher" or do you have plans to use it in
> wireshark? If the latter, then can we really do that? while a linux
> implementation may do that, other (or even possibly future linux)
> implementation might not do this. Can we justify changing the
> wireshark logic for it?

No plans to change the wireshark RPC-over-RDMA dissector.
That would only be a valid thing to do if adding the XID
were made part of the RPC-over-RDMA protocol via an RFC.


--
Chuck Lever