libpod: fix c.Hostname() to respect the utsNsCtr

When we lookup the hostname for a given container we have to check if
the container is joined to another utsns and use this hostname then
instead.
This fixes a problem where the `hostname` command would use the correct
name but /etc/hostname would contain a different name.

Signed-off-by: Paul Holzinger <pholzing@redhat.com>

libpod/container.go

@@ -628,6 +628,15 @@ func (c *Container) RuntimeName() string {
 
 // Hostname gets the container's hostname
 func (c *Container) Hostname() string {
+	if c.config.UTSNsCtr != "" {
+		utsNsCtr, err := c.runtime.GetContainer(c.config.UTSNsCtr)
+		if err != nil {
+			// should we return an error here?
+			logrus.Errorf("unable to lookup uts namespace for container %s: %v", c.ID(), err)
+			return ""
+		}
+		return utsNsCtr.Hostname()
+	}
 	if c.config.Spec.Hostname != "" {
 		return c.config.Spec.Hostname
 	}

test/system/500-networking.bats

@@ -142,7 +142,7 @@ load helpers
     pid="$output"
     run_podman run --pod $pod_name --name $con1_name $IMAGE cat /etc/hosts
     is "$output" ".*\s$pod_name $infra_name.*" "Pod hostname in /etc/hosts"
-    is "$output" ".*127.0.0.1\s.*$con1_name.*" "Container1 name in /etc/hosts"
+    is "$output" ".*127.0.0.1\s$con1_name.*" "Container1 name in /etc/hosts"
     # get the length of the hosts file
     old_lines=${#lines[@]}
 
@@ -150,9 +150,13 @@ load helpers
     # new host entry and the old one should be removed (lines check)
     run_podman run --pod $pod_name --name $con2_name $IMAGE cat /etc/hosts
     is "$output" ".*\s$pod_name $infra_name.*" "Pod hostname in /etc/hosts"
-    is "$output" ".*127.0.0.1\s.*$con2_name.*" "Container2 name in /etc/hosts"
+    is "$output" ".*127.0.0.1\s$con2_name.*" "Container2 name in /etc/hosts"
     is "${#lines[@]}" "$old_lines" "Number of hosts lines is equal"
 
+    run_podman run --pod $pod_name  $IMAGE sh -c  "hostname && cat /etc/hostname"
+    is "${lines[0]}" "$pod_name" "hostname is the pod hostname"
+    is "${lines[1]}" "$pod_name" "/etc/hostname contains correct pod hostname"
+
     run_podman pod rm $pod_name
     is "$output" "$pid" "Only ID in output (no extra errors)"
 }