netlink: Bypass refcounting when setting promiscuity

[obiwac]

Summary

When asking for IFF_PROMISC when modifying interfaces with netlink, set permanent flag instead (IFF_PPROMISC) as netlink interface modification has no way of doing promiscuity reference counting through ifpromisc(). We can't do reference counting because every netlink interface modification necessarily either sets or unsets IFF_PROMISC in ifi_flags, and ifi_change is usually set to 0xFFFFFFFF.

This logic was the same between this and SIOCSIFFLAGS, so factor out if_setppromisc() function.

Test Plan

will test this tomorrow, maybe add a set IFF_PROMISC, then 2* unset test to TestRtNlIface.

[saheed]

sys/net/if.c

4459

Shouldn't it be ((ifp->if_flags ^ new_flags) & IFF_PPROMISC)?

[obiwac]

sys/net/if.c

4459

yes you're right

[kp]

The commit message needs to answer the "Why?".
Why are we bypassing the reference counting?

I've not tested this, but it does look sane.

sys/net/if.c

4451

I'd use 'bool ppromisc' here. We're not passing flags, it's explicitly IFF_PPROMISC only.

sys/netlink/route/iface_drivers.c

99

I'd keep this out of this commit.

That's an unrelated 'Handle ifhwioct(SIOCSIFMTU) failure' change.

[obiwac]

Respond to review comments

[obiwac]

Remove failure handling change

[obiwac]

Thanks for your reviews @saheed and @kp, have updated my commit message :)

Set D52132 as parent because the error variable would be unused if we merged this first.

[saheed]

I tested it out, it works nicely :)

[mckusick]

Mentor approval - looks good to go.