Re: [PATCH] path_id: Re-introduce SAS phy enumeration of devices v2

[Hannes Reinecke <hare@suse.de>]

On 04/03/2012 08:24 PM, Kay Sievers wrote:
> On Tue, Apr 3, 2012 at 10:04, Nils Carlson <nils.carlson@ericsson.com> wrote:
> 
>> This patch reintroduces enumeration
>> of the form
>>
>> pci-0000:05:00.0-sas-phy0-0x500000e114de2b42:0-lun0
>>
>> where phy0 is the reintroduced substring where 0 corresponds
>> to the lowest phy identifier on the port to which the device
>> is connected.
> 
> Without having any real insight knowledge, a quick check:
> 
> We usually refuse any "find the lowest number approach" in new code,
> and require the kernel to export a stable instance number per parent
> device, which is entirely disconnected from any global device
> enumeration counter or prober ordering.
> 
> Almost all existing examples doing that are broken, and some even
> needed to be removed because they just blindly bet on luck that things
> are always in the same probe order.
> 
> Many device can individually unbound and rebound in the kernel, so
> after the rebind the same device will no longer have a smaller number
> like it had before. Kernel enumeration is only in a very few cases
> useful to build persistent paths.
> 
> The approach in this case is safe against individual pieces being
> unregistered and registered again?
> 
Note, this is just a first step towards real configuration.

This is the SAS PHY issue we've talked about earlier; eventually we'll
have to export paths for all phys.

I'm working on a patch (on top of this one), but it'll be quite a change
to path_id. So I've asked for this patch to be sent now, rather than
wait for the full blown solution.

Cheers,

Hannes
-- 
Dr. Hannes Reinecke		      zSeries & Storage
hare@suse.de			      +49 911 74053 688
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