add domainname spec entity

add the domainname entity so that container runtimes can add special handling similar to hostname. The current workaround of adding a sysctl for kernel.domainname only works with rootful execution in most cases. This will allow for rootless execution.

Signed-off-by: Charlie Doern <cdoern@redhat.com>

config.md

@@ -355,6 +355,18 @@ For Windows based systems the user structure has the following fields:
 "hostname": "mrsdalloway"
 ```
 
+## <a name="configDomainname" />Domainname
+
+* **`domainname`** (string, OPTIONAL) specifies the container's domainname as seen by processes running inside the container.
+    On Linux, for example, this will change the domainname in the [container](glossary.md#container-namespace) [UTS namespace][uts-namespace.7].
+    Depending on your [namespace configuration](config-linux.md#namespaces), the container UTS namespace may be the [runtime](glossary.md#runtime-namespace) [UTS namespace][uts-namespace.7].
+
+### Example
+
+```json
+"domainname": "foobarbaz.test"
+```
+
 ## <a name="configPlatformSpecificConfiguration" />Platform-specific configuration
 
 * **`linux`** (object, OPTIONAL) [Linux-specific configuration](config-linux.md).

schema/test/config/good/spec-example.json

@@ -63,6 +63,7 @@
         "readonly": true
     },
     "hostname": "slartibartfast",
+    "domainname": "foobarbaz.test",
     "mounts": [
         {
             "destination": "/proc",

specs-go/config.go

@@ -12,6 +12,8 @@ type Spec struct {
 	Root *Root `json:"root,omitempty"`
 	// Hostname configures the container's hostname.
 	Hostname string `json:"hostname,omitempty"`
+	// Domainname configures the container's domainname.
+	Domainname string `json:"domainname,omitempty"`
 	// Mounts configures additional mounts (on top of Root).
 	Mounts []Mount `json:"mounts,omitempty"`
 	// Hooks configures callbacks for container lifecycle events.