Subject: RE: [rdma] RE: [Tsvwg] RDMA over IP Requirements draft

From: [email-masked]
Date: Mon, 20 May 2002 13:55:18 -0400

> I agree with your points, but RDMA should introduce few requests
structures.
> If possible, making these structures compliant to an IDL would minimize a
> hardware requirement for those adapters that will also deal with other
> protocols.  I would see such a requirement more suitable if this
> requirements document was intended for DDP.  As RDMA is driving this
effort,
> perhaps the most that can be hoped for is a suggestion.

Let's take this down to brass tacks.  IDLs define things far more
complex than any RDMA request or command should ever use (e.g., if
an RDMA protocol structure needs a variable size string or array,
something is really wrong).  If one defines the data structures
involved as fixed size, follows some obvious alignment rules (entity
of size 2^n is aligned to the smaller of a 2^n or 32 bit boundary
in the structure), and always sends in network byte order, the result
is XDR (RFC 1832), except that use of 8-bit and 16-bit fields would
be prohibited.

I see no reason to a priori prohibit such fields (e.g., the SCTP
CHUNK header whose TLV structure Doug has recommended for this sort
of protocol design uses both 8 and 16 bit fields), and hence think
that following good design practices for size and alignment of
fields in data structures sent by RDMA is sufficient, and leads
to structures that will be easy to cope with in an implementation
that already handles XDR.

Thanks,
--David
---------------------------------------------------
David L. Black, Senior Technologist
EMC Corporation, 42 South St., Hopkinton, MA  01748
+1 (508) 249-6449 *NEW*      FAX: +1 (508) 497-8500
[email-masked]         Cell: +1 (978) 394-7754
---------------------------------------------------

_______________________________________________
tsvwg mailing list
[email-masked]
https://www1.ietf.org/mailman/listinfo/tsvwg

---

From: "Douglas Otis" <[email-masked]>
Date: Mon, 20 May 2002 13:42:51 -0700

David,

I have never seen an interface definition encompass transport headers.  Your
statement that an IDL consideration should not impact RDMA would seem to
remove a potential barrier.  Adding this feature as a recommended
consideration within the design process of request structures seems
innocuous.  I wonder what your concern is.  Would you consider a separate
requirements document for DDP?  Within this draft, an IDL recommendation
would not be out-of-line and may find consensus.

 -Doug

On May 20, 2002 10:55 AM David Black ([email-masked]) wrote:
>
> > I agree with your points, but RDMA should introduce few
> > requests structures.  If possible, making these structures
> > compliant to an IDL would minimize a hardware requirement for
> > those adapters that will also deal with other protocols.  I
> > would see such a requirement more suitable if this requirements
> > document was intended for DDP.  As RDMA is driving this effort,
> complex than any RDMA request or command should ever use (e.g.,
> if an RDMA protocol structure needs a variable size string or
> array, something is really wrong).  If one defines the data
> structures involved as fixed size, follows some obvious alignment
> rules (entity of size 2^n is aligned to the smaller of a 2^n or
> 32 bit boundary in the structure), and always sends in network
> byte order, the result is XDR (RFC 1832), except that use of 8-
> bit and 16-bit fields would be prohibited.
>
> CHUNK header whose TLV structure Doug has recommended for this
> sort of protocol design uses both 8 and 16 bit fields), and hence
> think that following good design practices for size and alignment
> of fields in data structures sent by RDMA is sufficient, and
> leads to structures that will be easy to cope with in an
> implementation that already handles XDR.
>
> Thanks,
> --David