newbus: Create a preferred list of drivers

[imp]

Summary

When there is a tie for priority for a device, and the new driver is on
the preferred list, prefer it to the other driver. It's undefined what
happens if multiple drivers on the preferred list can claim a device.

Sponsored by: Netflix

Test Plan

Note: this needs a man page adjusted, but I'm at a loss for which one

[imp]

sys/kern/subr_bus.c

380

I should likely not delete this line... I'll fix locally, but not update the review unless other changes are needed since it's so trivial.

[jhb]

I guess this is ok (my only worry is we have to do something else in the future and have to maintain backwards compat for this and the other). It needs to be documented in some foo(4) manpage though?

sys/kern/subr_bus.c

264

I feel like using strsep would be slightly shorter as it would do the null terminate for you? I think there's even an example in the strsep() manpage that is kind of like this, something like:

memcpy(walk2, buffer, len);
for (int i = 0; i < npref; i++)
     preferred_drivers[i] = strsep(&walk2, ",");

2166

s/device/driver/? ("nvme" is a driver name, "nvme0" is a device name)

[imp]

In D34357#778242, @jhb wrote:

I guess this is ok (my only worry is we have to do something else in the future and have to maintain backwards compat for this and the other). It needs to be documented in some foo(4) manpage though?

which one though?

sys/kern/subr_bus.c

2166

sure.

[imp]

Fixed review comments