netlink: Don't directly access ifnet members

[jhibbits]

Summary

Remove the final direct access of struct ifnet members from netlink.
Since only the first address is used, create the iterator and then free,
without fully iterating.

[kp]

sys/netlink/route/iface.c

329

While it does nothing now I'd have to assume that there's some anticipated need for ifa_iter_finish() to either clean up the iterator or to release a lock (or epoch or ..).

Wouldn't it belong more after the ifa != NULL check and dump_sa() call?

[jhibbits]

sys/netlink/route/iface.c

329

I think ifa should survive until the epoch exits, ifa_iter_finish() is used to clean up the iterator itself. It's quite likely that I don't understand epoch, and I'm not opposed to moving it before the ifa_iter_finish() if that is the case.

That said, on second thought I do see a possibility where ifa might point to just a static internal buffer in the iterator, overwritten each time through the loop and cleaned up at the end.

[jhibbits]

Address @kp's feedback.

[glebius]

I don't understand the change. The epoch protection is already right here. We can safely use CK_STAILQ_FIRST.

[jhibbits]

In D42972#980127, @glebius wrote:

I don't understand the change. The epoch protection is already right here. We can safely use CK_STAILQ_FIRST.

It's not about safety, it's because netlink shouldn't know ifnet guts, it's a more generic interface. I'm trying to remove net/if_private.h from if_var.h as soon as possible, and this is the last netlink piece that touches directly.

[glebius]

Got it. Looks like there is also an assumption here that the first address is always the link level address. Maybe we just need to provide KPI if_getlladdr? May I ask to wait for Alexander melifaro@ to reappear before we proceed forward with that?

P.S. I'm also waiting for him on my netlink reviews.

[jhibbits]

In D42972#980139, @glebius wrote:

Got it. Looks like there is also an assumption here that the first address is always the link level address. Maybe we just need to provide KPI if_getlladdr? May I ask to wait for Alexander melifaro@ to reappear before we proceed forward with that?

P.S. I'm also waiting for him on my netlink reviews.

Looking, we do have if_getlladdr(). It looks like the correct fix in 7d482240 should have been to just wrap the existing call in the epoch. @bz?