rootless: support `podman network create` (CNI-in-slirp4netns)

Usage:
```
$ podman network create foo
$ podman run -d --name web --hostname web --network foo nginx:alpine
$ podman run --rm --network foo alpine wget -O - http://web.dns.podman
Connecting to web.dns.podman (10.88.4.6:80)
...
<h1>Welcome to nginx!</h1>
...
```

See contrib/rootless-cni-infra for the design.

Signed-off-by: Akihiro Suda <akihiro.suda.cz@hco.ntt.co.jp>

1 files changed, 11 insertions, 3 deletions

diff --git a/libpod/container_internal_linux.go b/libpod/container_internal_linux.go
index f789b0069..605b526a4 100644
--- a/libpod/container_internal_linux.go
+++ b/libpod/container_internal_linux.go
@@ -84,7 +84,11 @@ func (c *Container) prepare() error {
 		// Set up network namespace if not already set up
 		noNetNS := c.state.NetNS == nil
 		if c.config.CreateNetNS && noNetNS && !c.config.PostConfigureNetNS {
-			netNS, networkStatus, createNetNSErr = c.runtime.createNetNS(c)
+			if rootless.IsRootless() && len(c.config.Networks) > 0 {
+				netNS, networkStatus, createNetNSErr = AllocRootlessCNI(context.Background(), c)
+			} else {
+				netNS, networkStatus, createNetNSErr = c.runtime.createNetNS(c)
+			}
 			if createNetNSErr != nil {
 				return
 			}
@@ -98,8 +102,12 @@ func (c *Container) prepare() error {
 		}
 
 		// handle rootless network namespace setup
-		if noNetNS && c.config.NetMode.IsSlirp4netns() && !c.config.PostConfigureNetNS {
-			createNetNSErr = c.runtime.setupRootlessNetNS(c)
+		if noNetNS && !c.config.PostConfigureNetNS {
+			if rootless.IsRootless() {
+				createNetNSErr = c.runtime.setupRootlessNetNS(c)
+			} else if c.config.NetMode.IsSlirp4netns() {
+				createNetNSErr = c.runtime.setupSlirp4netns(c)
+			}
 		}
 	}()
 	// Mount storage if not mounted