netlink: store osreldate of the process in the netlink pcb

[glebius]

Summary

This will allow to provide backwards compatibility shims.

[emaste]

Do you have an example of the kind of backwards compat we'd provide?

[pouria]

In D56750#1313739, @emaste wrote:

Do you have an example of the kind of backwards compat we'd provide?

Hi,
This change was initially proposed to support my routing-stack changes (metric for example).
One of the cases is D57266.
My original approach used a 32-bit weight in the nexthop struct, but I rewrote the metric implementation and kept the 8-bit weight as-is in netlink.
The reason was BIRD, I saw @melifaro's commits on it and learned he wanted FreeBSD's netlink to remain as close to Linux's version as possible.

Please keep this review open if possible. the use case will come up soon, though I don't know exactly when or for what.

[bms]

In D56750#1313882, @pouria wrote:

The reason was BIRD, I saw @melifaro's commits on it and learned he wanted FreeBSD's netlink to remain as close to Linux's version as possible.
Please keep this review open if possible. the use case will come up soon, though I don't know exactly when or for what.

+1. Yes this sounds like the best approach to me. The netlink userland wrapper situation on Linux itself isn't ideal and I might even put in the cycles to port SNL to it if it comes to that. I might have other plans...