Re: [PATCH v3] network: introduce a "none" firewall backend type

There are two scenarios identified after the recent firewall backend selection was introduced, which result in libvirtd failing to startup due to an inability to find either iptables/nftables - On Linux if running unprivileged with $PATH lacking the dir containing iptables/nftables - On non-Linux where iptables/nftables never existed In the former case, it is preferrable to restore the behaviour whereby the driver starts successfully. Users will get an error reported when attempting to start any virtual network, due to the lack of permissions needed to create bridge devices. This makes the missing firewall backend irrelevant. In the latter case, the network driver calls the 'nop' platform implementation which does not attempt to implement any firewall logic, just allowing the network to start without firewall rules. To solve this are number of changes are required * Introduce VIR_FIREWALL_BACKEND_NONE, which does nothing except report a fatal error from virFirewallApply(). This code path is unreachable, since we'll never create a virFirewall object with with VIR_FIREWALL_BACKEND_NONE, so the error reporting is just a sanity check. * Ignore the compile time backend defaults and assume use of the 'none' backend if running unprivileged. This fixes the first regression, avoiding the failure to start libvirtd on Linux in unprivileged context, instead allowing use of the driver and expecting a permission denied when creating a bridge. * Reject the use of compile time backend defaults no non-Linux and hardcode the 'none' backend. The non-Linux platforms have no firewall implementation at all currently, so there's no reason to permit the use of 'firewall_backend_priority' meson option. This fixes the second regression, avoiding the failure to start libvirtd on non-Linux hosts due to non-existant Linux binaries. * Change the Linux platform backend to raise an error if the firewall backend is 'none'. Again this code path is unreachable by default since we'll fail to create the bridge before getting here, but if someone modified network.conf to request the 'none' backend, this will stop further progress. * Change the nop platform backend to raise an error if the firewall backend is 'iptables' or 'nftables'. Again this code path is unreachable, since we should already have failed to find the iptables/nftables binaries on non-Linux hosts, so this is just a sanity check. * 'none' is not permited as a value in 'firewall_backend_priority' meson option, since it is conceptually meaningless to ask for that on Linux. NB, 'firewall_backend_priority' allows repeated options temporarily, which we don't want. Meson intends to turn this into a hard error DEPRECATION: Duplicated values in array option is deprecated. This will become a hard error in the future. and we can live with the reduced error checking until that happens. Signed-off-by: Daniel P. Berrangé <berrange(a)redhat.com&gt; --- Changed in v3: - Fix various syntax-check errors - Added note about meson tightening up validation of duplicated choices meson.build | 26 +++++++++++++++++++------- meson_options.txt | 2 +- po/POTFILES | 1 + src/network/bridge_driver_conf.c | 19 ++++++++++++++----- src/network/bridge_driver_linux.c | 10 ++++++++++ src/network/bridge_driver_nop.c | 15 ++++++++++++++- src/util/virfirewall.c | 6 ++++++ src/util/virfirewall.h | 1 + 8 files changed, 66 insertions(+), 14 deletions(-)