geom_vinum: add gone_in deprecation notice

[emaste]

Summary

Fixes: b218441ac074 ("gvinum: add deprecation notice")

[emaste]

Followon to D29424

[emaste]

I'm not sure where the best place to put this is. At the end of gv_drive_tasted may be a bit spammy, but has a higher likelihood of being noticed when e.g. adding a disk etc. I could just put it in gv_init instead.

[jhb]

Have you tried testing it? Maybe try to 'gvinum create' across two memory disks or ZVOLs to see if the warning works? You could maybe then do 'gvinum detach' and 'gvinum attach' to replicate boot-time probing. That is what I did when testing deprecation warnings for GELI algorithms I deprecated for 13. I don't have a good opinion on where the warning should go, and if it works in testing I'm fine with whatever works.

[emaste]

I will make sure it works either way, but am unsure about the tradeoff between making sure the message is noticed and being overly spammy. At one end we can emit the message once during startup, at the other for every activity on a disk.

[jhb]

For GELI I took the strategy of spamming a message each time a new volume was created with a deprecated algorithm via geli init, and a message each time an existing volume created a new provider (so if you booted with 5 GELI volumes and each used a deprecated algorithm, you got 5 warnings IIRC). The geli changes for this were in R10:5c420aae3b18027809507dc9142182d4290897bf. Unlike some other warnings I added for IPsec, I didn't bother with rate limiting.