Should these debug prints be removed?

Yes. Of course. I have them as a separate commit I'll strip out before I push this upstream.

This is the only part I'm not sure of. Currently I don't think anything does a scan with this patch in place (e.g. if someone hotplugs a device during the window in rc.d/devmatch between freeze and thaw). I'm not sure what the right answer is. One might be to just let the NOMATCH events fire anyway. Another might be to queue them in the kernel and fire them during thaw (rechecking to see if a device is still unattached before firing the actual event though). You could use a similar 'DF_NOMATCHPENDING' flag here (which is always cleared if a device attaches) and then just walk all devices doing the NOMATCH bits for them during a thaw (or use a dedicated linked list instead of the flag if we think the list of devices is too long to walk)

I'd considered this when writing it, but was unsure. I've updated things, and it turns out to be easy and simplifies things a little (though we look at more devices, which isn't a huge burden). Let me know what you think of the NEEDNOMATCH flag.

I don't think this works? A driver link is just an instance of a parent devclass (e.g. "pci") to a set of driver methods (kobj class holding DEVMETHOD array). I think you'd have to have a separate loop after the outermost TAILQ_FOREACH completes that then iterates over all device_t's to handle this.

I think for now it might be simplest to just let NOMATCH events be (and let them fire during a freeze as it can't really hurt if the module is loaded multiple times during a freeze).

Doh! You're right. I misread the device definition. I'll update. It's easy enough to do.