[openib-general] [RFC] [PATCH 2/7] ib_multicast 2.6.20: add ib_multicast module to track join requests from the same port

[Eitan Zahavi]

Sean Hefty wrote:
> Michael S. Tsirkin wrote:
>   
>> Why is this even a good idea?
>> If you are looking for reasons using mutlicast module in ipoib is good, I would
>> say blocking unpriviledged userspace from joining IPoIB GID and snoopig on all
>> mcast traffic sounds like a better idea.  BTW, Sean, I think this is something
>> we need for the ucma multicast part to go in. I would imagine kernel components
>> could set some kind of flag on mcast join to make them exclusive.
>> API currently does not allow for that.
>>     
>
> http://openib.org/pipermail/openib-general/2006-March/019147.html
>
> Why is it a bad idea?  The architecture allows this.  However, none of the 
> proposed patches allows a userspace app to join an ipoib multicast group.  And 
> an application that talks directly to the SA via MADs puts us no worse off than 
> before.
>
>   
This is incorrect. The SA can track requests from multiple different 
QPs. It could actually also enforce using QP1 for the requests. But it 
can not differentiate requests from same port different applications 
comming on QP1...
So if you did catch all QP1 traffic and refcount at that level you will 
be 100% clean.


>> And why the rush? Is the new module used at all yet?
>> Let's see it get some use before switching a basic component over.
>>     
>
> This module was added to svn in April.  The request was to begin the process for 
> queuing it to 2.6.20, which is likely 2-3 more months out.  I hardly call that a 
> rush.
>
>   
>> Finally, the patch in question also seems to introduce more cleanups and
>> such. It would be less controversial if it was just an API change.
>>     
>
> The cleanups are part of the change.  Once ib_join_multicast() has been invoked, 
> ib_free_multicast() must be called exactly once.  Proper state tracking for this 
> is required.
>
> - Sean
>
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