[openib-general] [PATCH] [CM] add private data comparison to match REQs with listens

[Fab Tillier]

> From: Caitlin Bestler [mailto:caitlinb at broadcom.com]
> Sent: Friday, December 02, 2005 12:13 PM
> 
> Sean Hefty wrote:
> > Fab Tillier wrote:
> >>> Just listen on the Service ID / Port and let the ULP sort them out
> >>> by destination IP address.
> >>
> >> That only works if there is a single kernel module providing the
> >> extra checks. Multiple user-mode ULPs cannot do the checking in
> >> user-mode - the checking must be done in the kernel to figure out
> >> which user-mode client to hand the request to.
> >>
> >> I think putting in restrictions to the comparisons possible is fine,
> >> as the functionality of having the CM facilitate some sort of
> >> filtering is useful.
> >
> > My concern with pushing this to the ULP is that it requires
> > the ULP to track service IDs for reference counting purposes
> > and adds additional synchronization to the ULP that could have been
> > handled by the CM.
> >
> > I'm looking at what the full effect of implementing this in the ULP
> > would be.
> 
> I'm still missing something.
> 
> I don't see how filtering in the CM is of benefit in either case. The
> work either belongs in the Hypervisor or in the Daemon, not the CM.

Your focus is strictly on TCP socket semantics, but we're talking about IB CM
functionality - the IB CM does more than just provide TCP socket semantics.

Imagine a user-mode IB application (not virtualization mind you, but just an
app) that wants to listen on a given SID (because the SID defines the
application), but wants to discriminate incoming requests based on some content
in the private data.  Multiple instances of that application can only work
properly if the CM performs the private data comparison to properly dispatch the
incoming requests to the right user-mode process.

If the CM doesn't provide the private data compare functionality, then the app
developer needs to create a kernel agent to perform this functionality for the
app.  The functionality is simple enough, and has potential value to multiple
clients, that it makes sense to have the IB CM provide it.

- Fab