[openib-general] RFC: detecting duplicate MAD requests

[Michael S. Tsirkin]

Quoting r. Sean Hefty <sean.hefty at intel.com>:
> One of the ideas then, is for the kernel umad module to learn which MADs
> generate responses.  It would do this by updating an entry to a table whenever
> a response MAD is generated.  A received MAD would check against the table to
> see if a response is supposed to be generated.  If not, then the MAD would be
> freed after userspace claims it.  If a response is expected, then the MAD
> would not be freed until the response was generated.

Another concern with this approach: consider an application that accepts
incoming MAD requests and drops some of them.  With current code it can do this
safely and remote side will retry. With the duplicate tracking in umad module
that you propose, MAD will stay in the list forever, and application will never
again get called.

This kind of subtle behaviour change seems to me worse than outright ABI
breakage.

-- 
MST