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From: Robert Watson <rwatson@FreeBSD.org>
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To: Rick Macklem <rmacklem@uoguelph.ca>
Subject: Re: svn commit: r271504 - in head/sys: dev/oce dev/vmware/vmxnet3
 dev/xen/netfront net netinet ofed/drivers/net/mlx4
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Cc: Hans Petter Selasky <hps@selasky.org>, svn-src-head@freebsd.org,
 svn-src-all@freebsd.org, src-committers@freebsd.org,
 Adrian Chadd <adrian@freebsd.org>
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On Sat, 13 Sep 2014, Rick Macklem wrote:

> Well, there are spare fields (if_ispare[4]) in struct ifnet that I believe 
> can be used for new u_ints when MFC'ng a patch that adds fields to struct 
> ifnet in head. (If I have this wrong, someone please correct me.)

In my notes from a few years ago on KBIs, it looked like we could potentially 
convert ifnet from "only use spares" to "OK to append to the structure in a 
stable branch".  It used to be that ifnet was embedded in driver softcs, and 
so ifnet changes broke compiled driver modules, but this is no longer the 
case.  A careful review might suggest to us that it's OK to simply add the new 
fields we want to the end, but need to do that review before assuming it.

Robert