Date:	Thu, 4 Dec 2014 22:10:41 +0100
From:	Jiri Pirko <jiri@...nulli.us>
To:	"Eric W. Biederman" <ebiederm@...ssion.com>
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Subject: Re: [patch iproute2 1/6] iproute2: ipa: show switch id

Thu, Dec 04, 2014 at 09:55:07PM CET, ebiederm@...ssion.com wrote:
>Jiri Pirko <jiri@...nulli.us> writes:
>
>> Thu, Dec 04, 2014 at 09:06:14PM CET, ebiederm@...ssion.com wrote:
>>>ebiederm@...ssion.com (Eric W. Biederman) writes:
>>>
>>>> Jiri Pirko <jiri@...nulli.us> writes:
>>>>
>>>>>>So this id needs to be globally unique?
>>>>>
>>>>> No. It is enough to be unique within a single system. It serves for no
>>>>> more than to find out 2 ids are same or not, no other info value.
>>>>>
>>>>> So when the drivers uses sane ids (like mac for example, or in case of
>>>>> rocker an id which is passed by qemu command line), the chances of
>>>>> collision are very very close to none (never say never).
>>>
>>>Thinking about what you said a little more.
>>>
>>>Two different sources of persistent numbers picking numbers by
>>>completely different algorithms can give you no assurance that you don't
>>>produce conflicts.
>>>
>>>The switch id as desisgned can not work.
>>>
>>>There are expected to be between 2**36 to 2**40 devices in this world.
>>>Your first switch id is a 64it number.  At the very best by the birthday
>>>pardox predicts there will be a conflict ever 2**32 devices or between
>>>2**4 and 2**8 devices in the world with conflicts.  If the ids are not
>>>randomly distributed (which they won't be) things could easily be much
>>>much worse.
>>>
>>>That is just good enough the code could get out there and run for years
>>>before you have the nightmare of having to fix all of userspace.   That
>>>is a nightmare no one needs.
>>>
>>>So please remove this broken code, and this broken concept from the
>>>kernel and go back to the drawing board.
>>
>> In that case the phys port id is broken in the same way. Let's rather
>> think about how to avoid conflicts for both. Given the fact the
>> conflicts should be avoided only on a single baremetal, that should be
>> doable (for (bad) example using driver name mixed with driver created
>> id).
>
>No.  phys_port_id is not broken in the same way, and phys_port_id does
>not have the same set of properties.
>
>phys_port_id's in practice all have an IEEE prefix that identifies the
>manufacturer and a manufacture assigned serial number.  Aka a mac
>address or a EUID-64.  What the mlx4 ethernet driver is doing retunring
>a 64bit EUID-64 I don't know.  If there are problems in the worst
>case issues with phys_port_id are fixable by simple driver tweaks,
>because fundamentally we are working with globally uniuqe identifiers.
>Well globally unique baring manufacturing bugs in eeproms.

Well the fact that phys_post_id's are now implemented mostly by putting
mac into it does not mean that other drivers cannot do it differently.
So once again, phys_port_id and phys_switch_id are the same in this
matter.

>
>
>
>I agree with you that the switch id concept can be saved.  But I think
>we should fix switch id before we export it to userspace so we don't
>have to break userspace later.
>
>My intuition says we want something like ifindex, but I am not at all
>certain how switch id is planned to be used.  Given that it is single
>box I don't expect you are sending it out over the wire.

No, it is not to be send out.

>
>*shrug*
>
>Why does switch id need to be persistent?  Why can't switch id be
>property like ifindex?

Well I can imagine that multiple ports of the same switch chip could be
passed through to the virtual machines (similar to SR-IOV pf/vf).

>
>What are the actual requirements.


They are actually very similar to phys_port_id. Therefore I made that
the same.



>
>Eric
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