config: Bump Hyper-V condition from root.path to root itself

Don't require users targetting Hyper-V to set an empty object ("root":
{}).  This also avoids confusion about whether you can set
root.readonly without setting root.path (you can't).

Move the relative, absolute, and rootfs bits into a POSIX paragraph,
because they don't apply to Windows where the value MUST be a volume
GUID path (since 2283e63, Windows: Remove Sandbox, additional tweaks,
2017-05-23, opencontainers#849).

We don't need the "for Windows Server containers" condition on volume
GUID paths, because with this commit that condition is already applied
at the 'root' level and the Hyper-V case has already been handled
there.

Signed-off-by: W. Trevor King <wking@tremily.us>

Author: wking

config.md

@@ -26,18 +26,22 @@ For all platform-specific configuration values, the scope defined below in the [
 
 ## <a name="configRoot" />Root
 
-**`root`** (object, REQUIRED) specifies the container's root filesystem.
+**`root`** (object, OPTIONAL) specifies the container's root filesystem.
+    On Windows, for Windows Server Containers, this field is REQUIRED.
+    For [Hyper-V Containers](config-windows.md#hyperv), this field MUST NOT be set.
 
-* **`path`** (string, OPTIONAL) Specifies the path to the root filesystem for the container.
-    The path is either an absolute path or a relative path to the bundle.
+    On all other platforms, this field is REQUIRED.
 
-    * On Windows, for Windows Server Containers, this field is REQUIRED and MUST be specified as a [volume GUID path][naming-a-volume].
-      For Hyper-V Containers, this field MUST be omitted.
-    * On all other platforms, this field is REQUIRED.
+* **`path`** (string, REQUIRED) Specifies the path to the root filesystem for the container.
+
+    * On Windows, `path` MUST be a [volume GUID path][naming-a-volume].
+
+    * On Linux and Solaris, `path` is either an absolute path or a relative path to the bundle.
+        For example, with a bundle at `/to/bundle` and a root filesystem at `/to/bundle/rootfs`, the `path` value can be either `/to/bundle/rootfs` or `rootfs`.
         The value SHOULD be the conventional `rootfs`.
-    * On Linux, for example, with a bundle at `/to/bundle` and a root filesystem at `/to/bundle/rootfs`, the `path` value can be either `/to/bundle/rootfs` or `rootfs`.
 
-    If defined, a directory MUST exist at the path declared by the field.
+    A directory MUST exist at the path declared by the field.
+
 * **`readonly`** (bool, OPTIONAL) If true then the root filesystem MUST be read-only inside the container, defaults to false.
     * On Windows, this field MUST be omitted or false.
 

schema/config-schema.json

@@ -59,6 +59,9 @@
             "description": "Configures the container's root filesystem.",
             "id": "https://opencontainers.org/schema/bundle/root",
             "type": "object",
+            "required": [
+                "path"
+            ],
             "properties": {
                 "path": {
                     "id": "https://opencontainers.org/schema/bundle/root/path",
@@ -233,7 +236,6 @@
     },
     "required": [
         "ociVersion",
-        "platform",
-        "root"
+        "platform"
     ]
 }

specs-go/config.go

@@ -11,7 +11,7 @@ type Spec struct {
 	// Process configures the container process.
 	Process *Process `json:"process,omitempty"`
 	// Root configures the container's root filesystem.
-	Root Root `json:"root"`
+	Root *Root `json:"root,omitempty"`
 	// Hostname configures the container's hostname.
 	Hostname string `json:"hostname,omitempty"`
 	// Mounts configures additional mounts (on top of Root).
@@ -96,7 +96,7 @@ type User struct {
 // Root contains information about the container's root filesystem on the host.
 type Root struct {
 	// Path is the absolute path to the container's root filesystem.
-	Path string `json:"path,omitempty"`
+	Path string `json:"path"`
 	// Readonly makes the root filesystem for the container readonly before the process is executed.
 	Readonly bool `json:"readonly,omitempty"`
 }