[systemd-devel] on the default for PredictableNetworkInterfaceNames

[Xen]

Greg KH schreef op 11-04-16 15:42:
> On Mon, Apr 11, 2016 at 11:56:00AM +0200, Xen wrote:
>> The predictability issue seems to be due to using a MAC address.
>>
>> AFAIK a reinstall will not change PCI bus devices etc.
> 
> No, PCI device numbers change all the time, they are not guaranteed to
> be stable at all.  Yes, lots of machines do not have them change, but a
> non-small number do.  Most of the time they change only if you have
> changed a PCI device (which includes thunderbolt and docking stations,
> quite common these days), or when you update your BIOS, but my favorite
> machine would renumber the whole bus every other boot for no good reason
> at all.
> 
> So don't think of PCI bus numbers as static, they aren't, sorry.

That implies that the whole PCI addressing is not something you can
depend on to begin with. I'm sorry, from their inclusion in the mapping
feature, I assumed that it would be something dependable. You basically
say that even on a single machine, that whole feature might not work
reliably, and hence should not be used.

However, this currently confuses me because my own ethernet device is
numbered by biosdev according to "PCI geographical location".

Maybe that is not a bus number, but:

[P<domain>]p<bus>s<slot>[f<function>][d<dev_port>]

My device is enp3s0, which implies 3rd bus number, which it indeed is:

E: ID_PATH=pci-0000:03:00.0

Are you telling me there are systems where this is not guaranteed to be
stable? Maybe these two numbers are coincidentally the same and not
related. It's an onboard chip (as most) and so not really geograpically
located.

In all of the examples though, this is not a coincidence and these
numbers are identical. This PCI path is used for the biosdev name.

You are saying it is not stable?

Regards.