osbuild: introduce mount host service

Allows stages to access file systems provided by devices.
This makes mount handling transparent to the stages, i.e.
the individual stages do not need any code for different
file system types and the underlying devices.

schemas/osbuild2.json

@@ -61,6 +61,32 @@
       }
     },
 
+    "mounts": {
+      "title": "Collection of mount points for a stage",
+      "additionalProperties": {
+        "$ref": "#/definitions/mount"
+      }
+    },
+
+    "mount": {
+      "title": "Mount point for a stage",
+      "additionalProperties": false,
+      "required": ["type", "source", "target"],
+      "properties": {
+        "type": { "type": "string" },
+        "source": {
+          "type": "string"
+        },
+        "target": {
+          "type": "string"
+        },
+        "options": {
+          "type": "object",
+          "additionalProperties": true
+        }
+      }
+    },
+
     "pipelines": {
       "title": "Collection of pipelines to execute",
       "description": "Array of pipelines to execute one after another",
@@ -124,6 +150,7 @@
         "type": { "type": "string" },
         "devices": { "$ref": "#/definitions/devices" },
         "inputs": {"$ref": "#/definitions/inputs" },
+        "mounts": {"$ref": "#/definitions/mounts" },
         "options": {
           "type": "object",
           "additionalProperties": true