linsysfs(4): Refactor to avoid referencing an unstable interfaces

[dchagin]

Summary

Enter the net epoch when traversing a list of interfaces. For that
split the ifname_linux_to_bsd() function on two counterparts, where
the ifname_linux_to_ifp() intended to use in epoch, while the
ifname_linux_to_bsd() intended to be a self-contained.
Until the linux_ioctl_coket() function is refactored, the
ifname_linux_to_bsd() temporarily returns interface outside
of the epoch.

[melifaro]

sys/compat/linsysfs/linsysfs.c

214

Maybe the other way round? In that case, you don't need to have an additional epoch exit.

215

Nit: IIRC sbuf_printf() cannot sleep, so it's worth writing ifindex inside the epoch and avoid using a temporary variable.

233

Nit: same as previous one: do everything inside ifp != NULL condition

[dchagin]

done, btw, you are right, sbuf here don't sleep,
also vnet context stored as V_ifnet is not iniitalized without it