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From: John Baldwin <jhb@freebsd.org>
To: Jack Vogel <jfvogel@gmail.com>
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	(bigwig.baldwin.cx); Mon, 17 Sep 2012 16:22:33 -0400 (EDT)
Cc: freebsd-net@freebsd.org, Adrian Chadd <adrian@freebsd.org>,
	Ryan Stone <rysto32@gmail.com>
Subject: Re: What's the latest on fixing IFF_DRV_OACTIVE/if_start/etc?
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On Monday, September 17, 2012 4:00:04 pm Jack Vogel wrote:
> So, you mean having them create their own buf ring I assume? Would be easy
> enough to hack some code and try it if someone is so inclined?

No, that would be backwards (back to giving them a queue).  Adrian's
suggestion is to provide a mechanism so that the "real" interface
(e.g. emX) can call back into the psuedo-interfaces on top of it
(vlanX or bridgeX) when a TX completion interrupt fires so that the
pseudo-interface would know to restart transmission.  However, I think
this is generally not ideal.  I don't think we want an additional queue
of pending packets in things like if_bridge(4) and vlan(4).  If the
underlying physical interface(s) are full, the packet should just get
dropped rather than queued.  Using if_transmit directly will do that while 
avoiding overhead.  Also, making the callback work would also be a bit 
ungainly.

-- 
John Baldwin