[ofa-general] Re: [Query] ib add path record cache

[Sean Hefty]

>One could ask the IBTA for this if it is the right thing to do.

Checking with the IBTA makes sense.  Longer term, adding a distributed SA
application class, or expanding the existing SA class may be useful, if the IBTA
wants to define SA implementation at this level of detail.  However, I was
trying to focus on what could be done now.  If the IBTA would like to
standardize the communication, that'd be great.

One issue that isn't clear to me is what exactly is meant by the statement:
"Vendor-specific classes will never be used to define management operations that
are encompassed by the Infiniband Architecture."  For example, suppose that
there were a small number of SA caches available in the subnet.  Is it compliant
for a node to issue a PR query to one of the caches using a vendor-defined PR
query?  Or must this be done using an SA PR query with possible redirection?

>Are you saying to make the RMPP header as the first part of Data ?

Yes.

>Vendor class 1 are not RMPP MADs so I think this is nonconformant.

I didn't see any restriction on the vendor class 1 data - at least in section
16.5.  If I'm mistaken on this, then I agree that vendor class 2 seems to be our
only current option.

>That's one reason vendor class 2 was added. In addition, there is no way
>to detect one "vendor" from another "vendor" (which is why OUI was
>added) if the same class is used so these need to be unique across all
>vendors.

Yes - all vendor class 1 MADs suffer from this issue.  In practice, it seems
that there can only be a single vendor for a given class on a subnet.

>The only choice seems to me to be reformatting using vendor class 2 and
>dealing with the data copying.

>From an implementation viewpoint, this just seems less desirable.  Adding the
offset means that single-segment SA MAD may become our multi-segment vendor MAD,
and dealing with two MAD formats will be troublesome.  If we're only caching
PRs, this may not be a big deal, but if we ever want to create a truly
distributed SA, I think it will be.

- Sean