From mboxrd@z Thu Jan  1 00:00:00 1970
From: Roland Dreier <rdreier@cisco.com>
Subject: Re: IPoIB: Fix multicast packet drops before join is complete
Date: Tue, 09 Jun 2009 20:55:57 -0700
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To: David Miller <davem@davemloft.net>
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 > Block the process joining the multicast group, not the entire
 > interface.

Hmm... how do I do that?  The interface gets an skb that it sees should
be sent to a multicast group that it is not a member of yet, and so it
fires off a request to join that group (as a send-only member).  How
does a netdev block the process that queued up a given skb to send?
Couldn't the packet have come through a local software bridge or
something like that, so the original process is long since lost to the
network stack?

 - R.