On 2/24/2017 1:25 PM, Jeff Layton wrote:
v2: comment clarifications, and commit log cleanup. No functional changes.
RFC5661 says:
NFSv4.1 works over Remote Direct Memory Access (RDMA) and non-RDMA-
based transports with the following attributes:
o The transport supports reliable delivery of data, which NFSv4.1
requires but neither NFSv4.1 nor RPC has facilities for ensuring
[34].
o The transport delivers data in the order it was sent. Ordered
delivery simplifies detection of transmit errors, and simplifies
the sending of arbitrary sized requests and responses via the
record marking protocol [3].
...and then some hand-wavy stuff about congestion control. RFC7530
doesn't mention needing reliable and ordered delivery, but it does need
congestion control.
Snipping some stuff for a pedantic response :-)
There are several good reasons why RFC7530 does not specify reliable and
ordered. The most obvious being, it doesn't need them. Because it has
a session, it can handle out-of-order messages at its layer. This is in
fact critical to supporting trunking and multipathing. And with the
session comes the ability to detect replays, so reliability can be
obviated there too.
In fact, apart from congestion control, with the proper session support,
NFSv4.1 can run very nicely over an unreliable unordered transport.
Now, NFS4.0, and NFSv3 and NFSv2 before it, are another matter entirely.
Note that RDMA transports provide remote direct placement only in RC
(Reliable Connected) endpoints, which is why rpcrdma uses that mode.
Tom.
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