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Subject: Re: [RFC 0/1] Allow MAC change on up interface
To:     Johannes Berg <johannes@sipsolutions.net>,
        James Prestwood <prestwoj@gmail.com>,
        linux-wireless@vger.kernel.org
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 <645af7dad899e8eb186b3fee0f8a8a151a408557.camel@sipsolutions.net>
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 <4848c3a9d0b330fab4442436244387a2c127fa03.camel@sipsolutions.net>
From:   Denis Kenzior <denkenz@gmail.com>
Message-ID: <1d975fec-a480-f40b-ff98-90d0e4852758@gmail.com>
Date:   Mon, 19 Aug 2019 15:58:16 -0500
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Hi Johannes,

> TBH, I'm not really sure I see any point in this to start with, many
> devices will give the address to the firmware when the interface is
> brought up (even iwlwifi does - I'm not sure we'd want to take your
> patch for iwlwifi even if that works today, nothing says the firmware
> might not change its mind on that), and so it's quite likely only going
> to be supported in few devices.

Hmm... I sense a pattern of you not seeing a point in doing many 
things... Do you actually use the stuff you maintain?

> 
> You've also not really explained what exactly is troubling you with
> changing the MAC address, you just mentioned some sort of "race
> condition"?

Well, one possible use case might be, oh something like this:

https://source.android.com/devices/tech/connect/wifi-mac-randomization

> 
> Now, one thing I can imagine would be that you'd want to optimize
> 
>   * ifdown
>     - remove iface from fw/hw
>     - stop fw/hw
>   * change MAC
>   * ifup
>     - start fw/hw
>     - add iface to fw/hw
> 
> to just
> 
>   * ifdown
>     - remove iface from fw/hw
>   * change MAC
>   * ifup
>     - add iface to fw/hw
> 

That would be a part of it...

> i.e. not restart the firmware (which takes time) for all this, but that
> seems much easier to solve by e.g. having a combined operation for all
> of this that gets handled in mac80211, or more generally by having a
> "please keep the firmware running" token that you can hold while you do
> the operation?

And also maybe a bunch of other optimizations like not flushing scan 
results?

> 
> Your changes are also a bit strange - you modified the "connect" path
> and iwlwifi, but the connect path is not usually (other than with iw or
> even iwconfig) taken for iwlwifi? And if you modify auth/assoc paths,
> you get into even weirder problems - what if you use different addresses
> for auth and assoc? What if the assoc (or even connect) really was a
> *re*assoc, and thus must have the same MAC address? To me, the whole
> thing seems like more of a problem than a solution.
> 

Okay, so there are some obstacles.  But can you get over the whole 
"Don't hold it like this" part and actually offer up something constructive?

Regards,
-Denis