enable dnsplugin for network create

when users create a new network and the dnsname plugin can be found by
podman, we will enable container name resolution on the new network.
there is an option to opt *out* as well.

tests cannot be added until we solve the packaging portion of the
dnsname plugin.

Signed-off-by: baude <bbaude@redhat.com>

pkg/network/config.go

@@ -14,6 +14,9 @@ const (
 	// CNIDeviceName is the default network device name and in
 	// reality should have an int appended to it (cni-podman4)
 	CNIDeviceName = "cni-podman"
+	// DefaultPodmanDomainName is used for the dnsname plugin to define
+	// a localized domain name for a created network
+	DefaultPodmanDomainName = "dns.podman"
 )
 
 // GetDefaultPodmanNetwork outputs the default network for podman
@@ -97,3 +100,14 @@ type FirewallConfig struct {
 func (f FirewallConfig) Bytes() ([]byte, error) {
 	return json.MarshalIndent(f, "", "\t")
 }
+
+// DNSNameConfig describes the dns container name resolution plugin config
+type DNSNameConfig struct {
+	PluginType string `json:"type"`
+	DomainName string `json:"domainName"`
+}
+
+// Bytes outputs the configuration as []byte
+func (d DNSNameConfig) Bytes() ([]byte, error) {
+	return json.MarshalIndent(d, "", "\t")
+}

pkg/network/netconflist.go

@@ -2,6 +2,8 @@ package network
 
 import (
 	"net"
+	"os"
+	"path/filepath"
 )
 
 // NcList describes a generic map
@@ -111,3 +113,22 @@ func NewFirewallPlugin() FirewallConfig {
 		Backend:    "iptables",
 	}
 }
+
+// NewDNSNamePlugin creates the dnsname config with a given
+// domainname
+func NewDNSNamePlugin(domainName string) DNSNameConfig {
+	return DNSNameConfig{
+		PluginType: "dnsname",
+		DomainName: domainName,
+	}
+}
+
+// HasDNSNamePlugin looks to see if the dnsname cni plugin is present
+func HasDNSNamePlugin(paths []string) bool {
+	for _, p := range paths {
+		if _, err := os.Stat(filepath.Join(p, "dnsname")); err == nil {
+			return true
+		}
+	}
+	return false
+}