Re: [RFC] Persistent naming of scsi devices

James Bottomley
2002-04-08T19:17:47Z

patmans@us.ibm.com said:
> We could have a set of interfaces to get a SCSI UUID, and then have
> hotplug tell us which interface (or module?) to use. That way we don't
> require sg.

I'm in two minds about this one. Deciding exactly what constitutes the UUID
for a particular device can be non trivial. Usually you have to probe for the
supported vital product pages, and if they have the WWN one use that otherwise
fall back to the (less guaranteed to be unique) SCSI-2 serial number page or
finally make something up dependent on what unique numbers you can get from
the device.

It makes sense to me that this type of complex rule (of thumb almost) based
lookup is best done from user level by doing the explicit SCSI commands if
necessary.

However, I'm biased. From a philosophical point of view, I like the hotplug
approach because it allows us to eject a lot of the use once initialisation
code into user space from the kernel.

> The device_list[] (black/white list) should also come from user land.
> Maybe hotplug could get the device_list[] characteristics, including
> the UUID method for the device.

> I'd also like a uuid stored in Scsi_Device for multi-path support in
> the mid-layer (independent of how it's set). This uuid could not be
> stored in the partition or as part of the file system.

If we can come up with a nice, general mechanism, there's no reason why it
cannot apply outside the SCSI system, so I wouldn't necessarily tie it to
Scsi_Devce. More likely (and actually what the persistent binding begins) is
to tie it to the concept of the Mochel internal device tree.

James