Review - 16718 Want mechanism to select smrt over cpqary3

Review - 16718 Want mechanism to select smrt over cpqary3

[Andy Fiddaman]

When the `smrt` driver was introduced, it was done so without defining any
PCI aliases to which it should attach since there is an overlap between it
and the extant `cpqary3`, and there is an obvious complication of changing
device paths on a running system which may have a root pool on a device using
one of these drivers.

Over the past five years, SmartOS has been assigning `smrt` to a range of newer
devices. Since the pools are imported fresh on each boot, this works fine.
https://github.com/TritonDataCenter/illumos-joyent/blob/93ed51f2345b1342f4659875b79cf853d1078f0a/usr/src/uts/intel/os/driver_aliases#L1589-L1625

I've raised the following change that allows systems which use IPS to easily
switch the overlapping aliases back and forth between the two drivers via a
new IPS variant. To make this seamless, I'm using a boolean variant and so this
depends on an IPS feature which was introduced in Oracle's IPS in 2016,
OpenIndiana's in 2019 and OmniOS' in 2023. Helios does not yet have this but
I am going to take care of that prior to integration, as well as send out a
heads-up for any other IPS-using distributions to check/update.

    23254680 'false' should be assumed for unknown variants
    https://github.com/oracle/solaris-ips/commit/b9f932cb82

In OmniOS we will start building installation media with the variant set to
true so that new installations use smrt for compatible devices.

With all that said, please can you review the following change?
I've put initial testing notes in the issue.

    16718 Want mechanism to select smrt over cpqary3
    https://www.illumos.org/issues/16718
    https://code.illumos.org/c/illumos-gate/+/3648

Thanks,

Andy