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>

1 files changed, 6 insertions, 1 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 {