allow switching of port-forward approaches in rootless/using slirp4netns

As of podman 1.8.0, because of commit da7595a, the default approach of providing
port-forwarding in rootless mode has switched (and been hard-coded) to rootlessport,
for the purpose of providing super performance. The side-effect of this switch is
source within the container to the port-forwarded service always appears to originate
from 127.0.0.1 (see issue #5138).

This commit allows a user to specify if they want to revert to the previous approach
of leveraging slirp4netns add_hostfwd() api which, although not as stellar performance,
restores usefulness of seeing incoming traffic origin IP addresses.

The change should be transparent; when not specified, rootlessport will continue to be
used, however if specifying --net slirp4netns:slirplisten the old approach will be used.

Note: the above may imply the restored port-forwarding via slirp4netns is not as
performant as the new rootlessport approach, however the figures shared in the original
commit that introduced rootlessport are as follows:
slirp4netns: 8.3 Gbps,
RootlessKit: 27.3 Gbps,
which are more than sufficient for many use cases where the origin of traffic is more
important than limits that cannot be reached due to bottlenecks elsewhere.

Signed-off-by: Aleks Mariusz <m.k@alek.cx>
Signed-off-by: Giuseppe Scrivano <gscrivan@redhat.com>

2 files changed, 26 insertions, 5 deletions

diff --git a/pkg/specgen/generate/namespaces.go b/pkg/specgen/generate/namespaces.go
index 09d6ba445..e038fc84e 100644
--- a/pkg/specgen/generate/namespaces.go
+++ b/pkg/specgen/generate/namespaces.go
@@ -2,6 +2,7 @@ package generate
 
 import (
 	"context"
+	"fmt"
 	"os"
 	"strings"
 
@@ -226,7 +227,11 @@ func namespaceOptions(ctx context.Context, s *specgen.SpecGenerator, rt *libpod.
 		if err != nil {
 			return nil, err
 		}
-		toReturn = append(toReturn, libpod.WithNetNS(portMappings, postConfigureNetNS, "slirp4netns", nil))
+		val := "slirp4netns"
+		if s.NetNS.Value != "" {
+			val = fmt.Sprintf("slirp4netns:%s", s.NetNS.Value)
+		}
+		toReturn = append(toReturn, libpod.WithNetNS(portMappings, postConfigureNetNS, val, nil))
 	case specgen.Bridge:
 		portMappings, err := createPortMappings(ctx, s, img)
 		if err != nil {
diff --git a/pkg/specgen/namespaces.go b/pkg/specgen/namespaces.go
index 5f56b242b..e62c8b709 100644
--- a/pkg/specgen/namespaces.go
+++ b/pkg/specgen/namespaces.go
@@ -108,7 +108,19 @@ func validateNetNS(n *Namespace) error {
 		return nil
 	}
 	switch n.NSMode {
-	case "", Default, Host, Path, FromContainer, FromPod, Private, NoNetwork, Bridge, Slirp:
+	case Slirp:
+		if n.Value != "" {
+			parts := strings.Split(n.Value, ",")
+			for _, p := range parts {
+				switch p {
+				case "port_handler=slirp4netns", "port_handler=rootlesskit":
+				default:
+					return errors.Errorf("invalid value for slirp %q", n.Value)
+				}
+			}
+		}
+		break
+	case "", Default, Host, Path, FromContainer, FromPod, Private, NoNetwork, Bridge:
 		break
 	default:
 		return errors.Errorf("invalid network %q", n.NSMode)
@@ -119,8 +131,8 @@ func validateNetNS(n *Namespace) error {
 		if len(n.Value) < 1 {
 			return errors.Errorf("namespace mode %s requires a value", n.NSMode)
 		}
-	} else {
-		// All others must NOT set a string value
+	} else if n.NSMode != Slirp {
+		// All others except must NOT set a string value
 		if len(n.Value) > 0 {
 			return errors.Errorf("namespace value %s cannot be provided with namespace mode %s", n.Value, n.NSMode)
 		}
@@ -250,8 +262,12 @@ func ParseNetworkNamespace(ns string) (Namespace, []string, error) {
 	var cniNetworks []string
 	// Net defaults to Slirp on rootless
 	switch {
-	case ns == "slirp4netns":
+	case ns == "slirp4netns", strings.HasPrefix(ns, "slirp4netns:"):
+		split := strings.SplitN(ns, ":", 2)
 		toReturn.NSMode = Slirp
+		if len(split) > 1 {
+			toReturn.Value = split[1]
+		}
 	case ns == "pod":
 		toReturn.NSMode = FromPod
 	case ns == "":