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From:   James Prestwood <prestwoj@gmail.com>
To:     linux-wireless@vger.kernel.org
Cc:     James Prestwood <prestwoj@gmail.com>
Subject: [RFC 0/4] Allow live MAC address change
Date:   Wed,  4 Sep 2019 12:11:51 -0700
Message-Id: <20190904191155.28056-1-prestwoj@gmail.com>
Sender: linux-wireless-owner@vger.kernel.org
Precedence: bulk

This set enables userspace to change the devices MAC address via RTNL
or CMD_CONNECT/CMD_AUTHENTICATE without bringing the device down then
back up. This has several benefits:

 - Simplifies user space logic. No longer requires tracking multiple
   RTNL/netlink message transactions (down, change mac, up, connect).
 - Drastically speeds up connection times when changing MAC on a
   per-connect basis.
 - Eliminates potential race conditions in userspace. At any time
   during the down/change/up sequence the device could be hot
   unplugged or something could go wrong in the kernel leaving
   userspace in an unknown state.

A new extended feature was added,
NL80211_EXT_FEATURE_LIVE_ADDRESS_CHANGE which is set if the device
supports this feature. This feature is enabled by default for mac80211
based drivers.

A new NL80211 attribute was added, NL80211_ATTR_MAC_TO_CHANGE. This
attribute can be used with CMD_CONNECT/CMD_AUTHENTICATE to change the
MAC address automatically without having to go through RTNL.

I have taken some timings for all 3 ways of changing the MAC. Powered
change via RTNL, non powered via RTNL, and changing through
CMD_CONNECT. All times were taken in microseconds and tested on an
Intel 7260 PCI wireless adapter:

Powered via RTNL:

Average: 294508.9
Min: 284523
Max: 300345

==================================
Non-Powered via RTNL:

Average: 14824.7
Min: 11037
Max: 17812

Speedup from powered change: 19.87x (average)

==================================
via CMD_CONNECT:

Average: 11848.7
Min: 9748
Max: 17152

Speedup from powered change: 24.86x (average)

==================================

The speed increases between powered and non-powered are quite
impressive. Besides the obvious speedup, the amount of code requred
for userspace to take advantage of this feature is extremely small
(via CMD_CONNECT, essentially a feature check and an extra attribute).
In addition, the changes/complexity to the kernel is minimal.

James Prestwood (4):
  nl80211: Add LIVE_ADDR_CHANGE feature
  {nl|cfg}80211: Support mac change as part of SME Connect
  mac80211: Support LIVE_ADDRESS_CHANGE feature
  {nl,cfg}nl80211: Support mac change for mlme_authenticate

 include/net/cfg80211.h       |  1 +
 include/uapi/linux/nl80211.h | 10 +++++++
 net/mac80211/iface.c         | 51 ++++++++++++++++++++++++++++++++++--
 net/mac80211/main.c          |  1 +
 net/wireless/core.h          |  4 ++-
 net/wireless/mlme.c          |  9 ++++++-
 net/wireless/nl80211.c       | 18 ++++++++++++-
 net/wireless/sme.c           |  9 ++++++-
 net/wireless/util.c          | 11 ++++++++
 9 files changed, 108 insertions(+), 6 deletions(-)

-- 
2.17.1