Investigate workaround in privileged tests for netlink.RuleAdd() returning EINVAL

[christarazi]

See #14337 (comment). For now the workaround is to shell out to ip rule add instead of using the netlink library.

[pchaigno]

For quicker future reference: we'd like to replace the tc call with the following (or similar):

c.Assert(netlink.RuleAdd(&netlink.Rule{
	Src:      &net.IPNet{IP: net.ParseIP("172.2.0.2"), Mask: net.CIDRMask(32, 32)},
	Priority: linux_defaults.RulePriorityEgress,
	Table:    dummy.Index,
}), IsNil)

[christarazi]

This can be useful to trace netlink requests to the kernel: https://github.com/socketpair/nltrace

[brb]

Alternatively, the recent enough strace version should help you to compare both netlink requests. If that doesn't work, then https://docs.pyroute2.org/debug.html might be useful.

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs.

[ti-mo]

@christarazi Turns out the default value of netlink.Rule cannot be used: #26486.