While investigating https://github.com/systemd/systemd/issues/16356, I
discovered that networkd stops the radv service before adding or updating
prefixes and then starts it again. This causes networkd to send an RA with
a router lifetime of zero, causing the routes to flap on systems receiving
the RA for a fraction of a second before radv is started again and proper
RAs are sent. That has the potential to cause issues with latency-sensitive
traffic like gaming or VoIP. This patch adds a boolean argument to the
sd_radv_stop() function to control this behavior. The zero lifetime RA is
still sent whenever radv is actually being stopped, but when it is being
restarted for a prefix update (from networkd-dhcp6.c), the final RA is no
longer sent to avoid the route flapping.
This part of the copyright blurb stems from the GPL use recommendations:
https://www.gnu.org/licenses/gpl-howto.en.html
The concept appears to originate in times where version control was per
file, instead of per tree, and was a way to glue the files together.
Ultimately, we nowadays don't live in that world anymore, and this
information is entirely useless anyway, as people are very welcome to
copy these files into any projects they like, and they shouldn't have to
change bits that are part of our copyright header for that.
hence, let's just get rid of this old cruft, and shorten our codebase a
bit.
Let's add "const" where we don't change structures passed.
Also, we generally use "unsigned char" for IP prefix length values, do
so here too. Previously different parts of the sd-radv.h API used
different types for this.
As DHCPv6 leases may expire at some point, the delegated prefixes
have to be removed. Add a prefix removal function to the Router
Advertisement handling code.
Add a boolean that indicates whether the prefixes will always exist
or if they will time out after the assigned valid lifetime. In the
latter case calculate the expiry times for both preferred and valid
lifetimes for the prefixes, and decrease the remaining lifetimes
each time when a Router Advertisement is sent.
Should the prefix be updated, re-calculate the prefix lifetime. When
updating, update the existing entry, if any, with the lifetimes of
the added entry as the existing entry has its lifetimes set
according to its previously calculated expiry times.
When EmitDNS or EmitDomains is set, automatically look up values
for Router Advertisement DNS and DNS search domain options starting
with the values in the IPv6PrefixDelegationsection, if any. If none
are found, use the values set for the network, and as a last resort
try with the preferred upstream network.
The default DNS lifetime and therefore Router Advertisement interval
is added to the public sd_radv.h header as the DNS lifetime depends
on the maximum advertisement interval.
Add Router Advertisement DNS Search List option as specified
in RFC 8106. The search list option uses and identical option
header as the RDNSS option and therefore the option header
structure can be reused.
If systemd is compiled with IDNA support, internationalization
of the provided search domain is applied, after which the search
list is written in wire format into the DNSSL option.
Define Router Advertisement prefix structure. Add the Prefix
Information ICMPv6 option defined in RFC 4861 to the prefix
information structure, as it will simplify sending a Prefix
Information option later on. In order to handle endianness
correctly, the structure is redefined here instead of using
the one in netinet/icmp6.h.
Add functions to create and modify prefix information and set
default values as defined in RFC 4861, Section 6.2.1.
