[Bug 235704] [net] [patch] tun(4) can't be destroyed on a VNET jail if it's renamed

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https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=235704

--- Comment #5 from genneko217 at gmail.com ---
Thank you for working on this issue.
I've briefly tested the patch and confirmed the reported issue was solved
with it.

I also confirmed that it changed the way unit numbers are assigned to if_tun.
While if_tun's unit numbers are assigned sequentially across a host and all
jails on it before the patch, it's now assigned independently so that vnet
jails and the host can have interfaces with the same name.

But now I began to wonder how the interfaces with the same name, say tun0,
are related to /dev/tun0 on the system.

When I did a quick testing with the following commands, the fourth command
removed tun0 interface from the host and also deleted /dev/tun0 while tun0
interface on the vnet jail "test" is still there. Then the fifth command
caused a kernel panic at destroy_devl in sys/kern/kern_conf.c.

# Assume there's no if_tun on the system.
jail -c -n test vnet persist
ifconfig tun create
jexec test ifconfig tun create
ifconfig tun0 destroy
jexec test ifconfig tun0 destroy

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