mounts: add new ostree.deployment service

Create a new OSTree deployment mount service that will set up bind
mounts inside the tree very much as it is done by OSTree in early
boot. This allows any stage to transparently work with OSTree
deployments.

mounts/org.osbuild.ostree.deployment

@@ -0,0 +1,122 @@
+#!/usr/bin/python3
+"""
+OSTree deployment mount service
+
+This mount service will setup all needed bind mounts so
+that a given `tree` will look like an active OSTree
+deployment, very much as OSTree does during early boot.
+
+More specifically it will:
+  - setup the sysroot bindmount to the deployment
+  - setup the shared var directory
+  - bind the boot directory into the deployment
+
+Host commands used: mount
+"""
+
+import os
+import sys
+import subprocess
+from typing import Dict
+
+from osbuild import mounts
+from osbuild.util import ostree
+
+
+SCHEMA_2 = """
+"additionalProperties": false,
+"required": ["name", "type"],
+"properties": {
+  "name": { "type": "string" },
+  "type": { "type": "string" },
+  "options": {
+    "type": "object",
+    "required": ["deployment"],
+    "properties": {
+      "deployment": {
+        "type": "object",
+        "additionalProperties": false,
+        "required": ["osname", "ref"],
+        "properties": {
+          "osname": {
+            "description": "Name of the stateroot to be used in the deployment",
+            "type": "string"
+          },
+          "ref": {
+            "description": "OStree ref to create and use for deployment",
+            "type": "string"
+          },
+          "serial": {
+            "description": "The deployment serial (usually '0')",
+            "type": "number",
+            "default": 0
+          }
+        }
+      }
+    }
+  }
+}
+"""
+
+
+class OSTreeDeploymentMount(mounts.MountService):
+
+    @staticmethod
+    def bind_mount(source, target):
+        subprocess.run([
+            "mount", "--bind", "--make-private", source, target,
+        ], check=True)
+
+    def mount(self, args: Dict):
+
+        tree = args["tree"]
+        options = args["options"]
+
+        deployment = options["deployment"]
+        osname = deployment["osname"]
+        ref = deployment["ref"]
+        serial = deployment.get("serial", 0)
+
+        root = ostree.deployment_path(tree, osname, ref, serial)
+
+        print(f"Deployment root at '{os.path.relpath(root, tree)}'")
+
+        var = os.path.join(tree, "ostree", "deploy", osname, "var")
+        boot = os.path.join(tree, "boot")
+
+        self.mountpoint = root
+        self.bind_mount(root, root)  # prepare to move it later
+
+        self.bind_mount(tree, os.path.join(root, "sysroot"))
+        self.bind_mount(var, os.path.join(root, "var"))
+        self.bind_mount(boot, os.path.join(root, "boot"))
+
+        subprocess.run([
+            "mount", "--move", root, tree,
+        ], check=True)
+
+        self.mountpoint = tree
+        self.check = True
+
+        return None
+
+    def umount(self):
+
+        if not self.mountpoint:
+            return
+
+        subprocess.run(["sync", "-f", self.mountpoint],
+                       check=self.check)
+
+        subprocess.run(["umount", "-R", self.mountpoint],
+                       check=self.check)
+        self.mountpoint = None
+
+
+def main():
+    service = OSTreeDeploymentMount.from_args(sys.argv[1:])
+    service.main()
+
+
+if __name__ == '__main__':
+    main()