Subject: Re: A possible way of handling variant/common devices
To: Jonathan Stone <>
From: Chris G. Demetriou <>
List: tech-kern
Date: 03/28/1997 20:07:11
> Reordering SCSI devices on a bus doesn't change the user-level
> names.  Reordering cards on a PCI bus *does* change the user-level name.


unless you've hard-wired the config entries, yes, reordering SCSI
devices on a bus _does_ change the user-level names.  If you've got
sd* at scsibus ? ..., and your sd0 is normally at target 0 and sd1 is at
target 1, and you move the former disk to target 2, then _it_ will end
up as sd1 and the disk at target 1 will end up as sd0.

Reordering cards on a PCI bus has _exactly_ the same behaviour,
w.r.t. unit numbers, as reordering devices' SCSI target IDs, unless
you've explicitly hard-wired device units down to slots/targets.

> I just don't find the idea of having that happen on my firewall box
> acceptable.  Wearing my security-weenie hat, I don't even like the
> idea of having to get two levels of naming right (the pci-level, and
> lan* level) in order to tie specific IP addresses and filter rules to
> the right bulkhead ports.  It's just something else that might go
> wrong.

Yes, it's "something that might go wrong," and it's the same as for
SCSI devices.

It takes probably no more than 10 minutes, once (assuming you don't
radically change your config file, assuming you have some slight but
not great knowledge about kernel config files, and excluding kernel
build time), to configure a kernel to hard-wire devices.

If you _don't_ do that, then your SCSI devices might get renumbered if
one of them happens to go OTL or if you add one, or your network cards
might get renumbered in the same types of situation.