zebra: ignore IFF_PROMISC message

[lsang6WIND]

Ignore netlink NEW_LINK message when the change is only IFF_PROMISC. This will avoid route updates when the interface enter/left promiscuous mode.

[donaldsharp]

I thought we went through this before. What guarantee do we have that only a promiscuous mode change is only that and nothing else on the interface?

[lsang6WIND]

I thought we went through this before. What guarantee do we have that only a promiscuous mode change is only that and nothing else on the interface?

Despite the Linux documentation on struct ifinfomsg:
if_flags contains the state of interface flags.
if_change indicate the state change (flag change(s)).

so if if_change have only the IFF_PROMISC bit set, we should have only interface enter/left promiscuous mode change.

However, this part is not mentionned by https://man7.org/linux/man-pages/man7/rtnetlink.7.html

[mjstapp]

even if this identifies the changed flags accurately, what about other changes to other interface attributes? I don't see how we can bail out at this point in the processing.

[mjstapp]

so in addition to the other comment I made, frankly: has someone done a survey of kernels, and identified the kernel versions where this statement is correct? is it always correct, for every kernel everywhere in use? if not, how will you adapt to the differences?

Despite the Linux documentation on struct ifinfomsg: if_flags contains the state of interface flags. if_change indicate the state change (flag change(s)).

so if if_change have only the IFF_PROMISC bit set, we should have only interface enter/left promiscuous mode change.

However, this part is not mentionned by https://man7.org/linux/man-pages/man7/rtnetlink.7.html

[lsang6WIND]

OK, close it.