svn commit: r346052 - head/sys/dev/usb/net

[John Baldwin]

On 4/9/19 9:59 AM, Ian Lepore wrote:
> On Tue, 2019-04-09 at 09:33 -0700, John Baldwin wrote:
>> On 4/9/19 9:17 AM, Ian Lepore wrote:
>>> On Tue, 2019-04-09 at 09:11 -0700, John Baldwin wrote:
>>>> On 4/9/19 6:54 AM, Ganbold Tsagaankhuu wrote:
>>>>> Author: ganbold
>>>>> Date: Tue Apr  9 13:54:08 2019
>>>>> New Revision: 346052
>>>>> URL: https://svnweb.freebsd.org/changeset/base/346052
>>>>>
>>>>> Log:
>>>>>   In some cases like NanoPI R1, its second USB ethernet
>>>>>   RTL8152 (chip version URE_CHIP_VER_4C10) doesn't
>>>>>   have hardwired MAC address, in other words, it is all zeros.
>>>>>   This commit fixes it by setting random MAC address
>>>>>   when MAC address is all zeros.
>>>>>   
>>>>>   Reviewed by:	kevlo
>>>>>   Differential Revision:	
>>>>> https://reviews.freebsd.org/D19856
>>>>
>>>> It would be best to not use a purely random mac address and to
>>>> use
>>>> the
>>>> function kevans@ added recently.  That function generates a MAC
>>>> address
>>>> from the FreeBSD OUI using a cryptographic hash so you get a
>>>> stable address across boots on a given host.
>>>>
>>>
>>> How could that possibly work?  If it's not random, you can't have
>>> two
>>> such devices on the same network.  If it is random, it's not stable
>>> from one boot to the next.
>>
>> It uses the UUID and interface name as input into the hash.  
> 
>> The UUID is per-host.
> 
> Oh, so it only works on x86 (or I guess any system that has something
> like a bios that can provide you with a uuid that doesn't change from
> one boot to the next).

The function is in one centralized place where you are free to add other
data as input into the hash.  We do always generate a uuid that we save
on boot if we aren't seeded with one by firmware, though that is probably
too late for this driver (so +1 may in fact be a better route).  It should
be fine for psuedo interfaces created post-boot though even on non-x86 due
to /etc/rc.d/hostid.  Pure random MAC's are not really great either.

-- 
John Baldwin