lxd: Provide state for physical managed networks (#13965)

This PR adds support for providing state for physical managed networks.
When the parent of a physical managed network is available, we provide
this parent state. When the parent is not available, we provide a
response indicating that the state is `unavailable` and the type is
`unknown`.

Closes #13553.

lxd/network/driver_physical.go

@@ -9,6 +9,7 @@ import (
 	"github.com/canonical/lxd/lxd/cluster/request"
 	"github.com/canonical/lxd/lxd/db"
 	"github.com/canonical/lxd/lxd/ip"
+	"github.com/canonical/lxd/lxd/resources"
 	"github.com/canonical/lxd/shared"
 	"github.com/canonical/lxd/shared/api"
 	"github.com/canonical/lxd/shared/logger"
@@ -504,3 +505,26 @@ func (n *physical) DHCPv6Subnet() *net.IPNet {
 
 	return subnet
 }
+
+// State returns the api.NetworkState for the network.
+func (n *physical) State() (*api.NetworkState, error) {
+	if !n.IsManaged() {
+		return resources.GetNetworkState(n.name)
+	}
+
+	state, err := resources.GetNetworkState(GetHostDevice(n.config["parent"], n.config["vlan"]))
+	if err != nil {
+		// If the parent is not found, return a response indicating the network is unavailable.
+		if api.StatusErrorCheck(err, 404) {
+			return &api.NetworkState{
+				State: "unavailable",
+				Type:  "unknown",
+			}, nil
+		}
+
+		// In all other cases, return the original error.
+		return nil, err
+	}
+
+	return state, nil
+}

test/suites/network.sh

@@ -64,6 +64,22 @@ test_network() {
   lxc network create lxdt$$ ipv4.address=none ipv6.address=none
   lxc network delete lxdt$$
 
+  # Check that we can return state for physical networks
+  ip link add dummy0 type dummy
+  lxc network create lxdt$$ --type=physical parent=dummy0
+
+  expected_state=$(lxc network info dummy0 | grep -F "State:")
+  expected_type=$(lxc network info dummy0 | grep -F "Type:")
+  lxc network info lxdt$$ | grep -qF "${expected_state}"
+  lxc network info lxdt$$ | grep -qF "${expected_type}"
+
+  # Delete physical network and check for expected response
+  ip link delete dummy0
+  lxc network info lxdt$$ | grep -qF "State: unavailable"
+  lxc network info lxdt$$ | grep -qF "Type: unknown"
+
+  lxc network delete lxdt$$
+
   # Configured bridge with static assignment
   lxc network create lxdt$$ dns.domain=test dns.mode=managed ipv6.dhcp.stateful=true
   lxc network attach lxdt$$ nettest eth0