Commit 49ef064c8d attempts to handle
"stub loop" by switching to the next server *after the query has
been made*.
The approach may be good enough for link scopes. However, for the
manager / global scope, it is not. First of all, there are more than
one types (SYSTEM and FALLBACK) of servers it can use. Also, whether
those of type FALLBACK should be used depends.
Besides, dns_scope_good_domain() determines whether things should
be routed to a scope by checking whether the scope has a server.
The decision made would be incorrect if stubs were not filtered
beforehand.
Therefore, to avoid failing query unnecessarily, and to make sure
that extra stub listeners will not trigger unexpected and/or
inconsistent behavior, make manager_get_dns_server() do what it
should have done.
While we haven't implemented a key for users to set MACVLAN/MACVTAP flags,
we can at least allow them to make use of the Promiscuous= key of
the corresponding link to set the nopromisc flag.
As device units will be reloaded by systemd whenever the corresponding device generates a "changed" event, if the mount unit / cryptsetup service is wanted by its device unit, the former can be restarted by systemd unexpectedly after the user stopped them explicitly. It is not sensible at all and can be considered dangerous. Neither is the behaviour conventional (as `auto` in fstab should only affect behaviour on boot and `mount -a`) or ever documented at all (not even in systemd, see systemd.mount(5) and crypttab(5)).
For it's silly and unnecessary. Although it was apparently mandated by RFC 2462 in [5.5.2. Absence of Router Advertisements], that has been changed in the same section of RFC 4862, which obsoleted the former RFC.
dhcp6_request_address() was merely a function to switch the DHCPv6 client from "stateless" mode to "stateful" mode. It was also a one-way switch. Also, to (re)start the client, we would need to repeat separate function calls.
In this patch, dhcp6_request_address() is made a general starter/manager of the DHCPv6 client. It now takes an extra parameter so we will be specifying which mode the DHCPv6 client should be started in. Also it will keep track of the current mode and compare with the newly requested mode, and only restart the client in case there is a difference between them.
This also makes sure that the DHCPv6 client will be (re)started accordingly as per the Router Advertisement flags.
DHCPv6 requires an IPv6 link-local address to work. The client will not be started (even when enabled explicitly with `DHCP=`) if none is configured (either by autoconfiguration or manually). Therefore, disable IPv6 in such case.
Although networkd has option (LinkLocalAddressing=) to toggle IPv6LL autoconfiguration, when it is enabled, the address is autoconfigured by the kernel, but not networkd.
Therefore, we do not statically set IFLA_INET6_ADDR_GEN_MODE to IN6_ADDR_GEN_MODE_EUI64, but dynamically depending on whether stable_secret is set, just as what the kernel does by default.
Note that this does NOT affect the global addresses configured by networkd.
Starting the DHCP client doesn't seem like dhcp6_request_address()'s responsibility anyway. Whenever it's called, sd_dhcp6_client_start() is unconditionally called outside of it as well. See ndisc_router_handler() and ndisc_handler() in networkd-ndisc.c.
Tom Yan