The problem this is solving has a very long history. with a simple bugzilla search I found reports all the way back to 2012. The issue is that sometimes when a libvirt virtual network is started, it could be on exactly the same subnet as another interface already active on the host at libvirt install time (which was fixed long ago), or as another interface that isn't active in the install environment, but will be active when libvirt is actually started at a later time, possibly in a completely different environment than the install (this *wasn't* fixed. until now). At one point (which I've located in this bugzilla comment in 2014 - https://bugzilla.redhat.com/1146232#c17) I thought of having a config knob in virtual networks that would look for an unused network at runtime, and start the network with that subnet. Of course that would have solved the problem where the conflicting network was already active when libvirt started its networks, but wouldn't do anything about the case where the conflicting network was started *after* libvirt had started its networks. And anyway it would have required config settings in /etc/libvirt/network.conf which didn't exist at the time. Several years later (around 2020) I learned about NetworkManager dispatcher scripts, which are called any time NM brings an interface up or down, and wrote a python script that would use this to destroy any libvirt network that had a conflict with a newly activated NM interface. After sending it as an RFC patch, I promptly forgot about it (except for being on my "list of things I should get to someday"). A few weeks ago I realized that the "there is no network.conf to store config items" problem was recently solved (I had to add a network.conf file for the knob that selects nftables vs iptables), which prompted me to go back and find the branch with the NM dispatcher script, and *finally* implement the runtime auto address selection. Combining this with enhancing the NM dispatcher script to not only destroy conflicting networks, but to also then *restart* them if they have autoaddr set, gives what I think is finally a full solution to the problem - no matter what order interfaces are started vs. libvirt networks being started, a network with "autoaddr='yes'" set will *always* end up with all networks being usable. (Well, the one issue that still remains is that if there are already guests attached to the autoaddr='yes' network when its address is changed, those guests will then be disconnected, and once reconnected they will have stale IP addresses. That's another hill for another day though; I don't think anyone has complained about that. Yet.) I think this may break the record for "oldest bug to be fixed", which was previously set when danpb fixed the firewalling issue with guests on two different NATed networks being able to communicate with each other. :-) Laine Stump (7): conf: add XML config for autoaddr networks network: add configurable network autoaddr items to driver config network: reorganize the check for route collisions network: turn on autoaddr selection in bridge driver network: NetworkManager script to monitor/resolve conflicts with new interfaces network: turn on autoaddr in default network spec: stop trying to find unused network during deamon-network-config %post docs/formatnetwork.rst | 42 +++- libvirt.spec.in | 38 +--- meson.build | 14 +- meson_options.txt | 4 + src/conf/network_conf.c | 75 +++++-- src/conf/network_conf.h | 7 + src/conf/schemas/network.rng | 5 + src/network/bridge_driver.c | 201 +++++++++++++++++- src/network/bridge_driver_conf.c | 61 ++++++ src/network/bridge_driver_conf.h | 4 + src/network/bridge_driver_linux.c | 132 +++++++----- src/network/bridge_driver_nop.c | 22 +- src/network/bridge_driver_platform.h | 5 +- src/network/default.xml.in | 2 +- src/network/libvirtd_network.aug | 8 +- src/network/meson.build | 12 ++ src/network/network.conf.in | 11 + src/network/nm-dispatcher-check-nets.py | 196 +++++++++++++++++ src/network/test_libvirtd_network.aug.in | 3 + .../networkxml2xmlin/nat-network-autoaddr.xml | 11 + .../nat-network-autoaddr.xml | 11 + tests/networkxml2xmltest.c | 1 + 22 files changed, 744 insertions(+), 121 deletions(-) create mode 100755 src/network/nm-dispatcher-check-nets.py create mode 100644 tests/networkxml2xmlin/nat-network-autoaddr.xml create mode 100644 tests/networkxml2xmlout/nat-network-autoaddr.xml -- 2.45.2
