pasta: Create /etc/hosts entries for pods using pasta networking

For pods with bridged and slirp4netns networking we create /etc/hosts
entries to make it more convenient for the containers to address each
other.  We omitted to do this for pasta networking, however.  Add the
necessary code to do this.

Closes: https://github.com/containers/podman/issues/17922

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>

libpod/container_internal_common.go

@@ -2203,6 +2203,12 @@ func (c *Container) getHostsEntries() (etchosts.HostEntries, error) {
 	switch {
 	case c.config.NetMode.IsBridge():
 		entries = etchosts.GetNetworkHostEntries(c.state.NetworkStatus, names...)
+	case c.config.NetMode.IsPasta():
+		ip, err := getPastaIP(c.state)
+		if err != nil {
+			return nil, err
+		}
+		entries = etchosts.HostEntries{{IP: ip.String(), Names: names}}
 	case c.config.NetMode.IsSlirp4netns():
 		ip, err := getSlirp4netnsIP(c.slirp4netnsSubnet)
 		if err != nil {

libpod/networking_freebsd.go

@@ -271,3 +271,7 @@ func (c *Container) reloadRootlessRLKPortMapping() error {
 func (c *Container) setupRootlessNetwork() error {
 	return nil
 }
+
+func getPastaIP(state *ContainerState) (net.IP, error) {
+	return nil, fmt.Errorf("pasta networking is Linux only")
+}

libpod/networking_linux.go

@@ -19,6 +19,7 @@ import (
 	"github.com/containers/common/libnetwork/resolvconf"
 	"github.com/containers/common/libnetwork/slirp4netns"
 	"github.com/containers/common/libnetwork/types"
+	netUtil "github.com/containers/common/libnetwork/util"
 	"github.com/containers/common/pkg/netns"
 	"github.com/containers/common/pkg/util"
 	"github.com/containers/podman/v4/pkg/rootless"
@@ -757,3 +758,13 @@ func (c *Container) inspectJoinedNetworkNS(networkns string) (q types.StatusBloc
 	})
 	return result, err
 }
+
+func getPastaIP(state *ContainerState) (net.IP, error) {
+	var ip string
+	err := ns.WithNetNSPath(state.NetNS, func(_ ns.NetNS) error {
+		// get the first ip in the netns
+		ip = netUtil.GetLocalIP()
+		return nil
+	})
+	return net.ParseIP(ip), err
+}

test/system/505-networking-pasta.bats

@@ -235,6 +235,21 @@ function teardown() {
            "Container has IPv6 global address with IPv6 disabled"
 }
 
+@test "podman networking with pasta(1) - podman puts pasta IP in /etc/hosts" {
+    skip_if_no_ipv4 "IPv4 not routable on the host"
+
+    pname="p$(random_string 30)"
+    ip="$(default_addr 4)"
+
+    run_podman pod create --net=pasta --name "${pname}"
+    run_podman run --pod="${pname}" "${IMAGE}" getent hosts "${pname}"
+
+    assert "$(echo ${output} | cut -f1 -d' ')" = "${ip}" "Correct /etc/hsots entry missing"
+
+    run_podman pod rm "${pname}"
+    run_podman rmi $(pause_image)
+}
+
 ### Routes #####################################################################
 
 @test "podman networking with pasta(1) - IPv4 default route" {