utils/android: Restore adb root state when disconnecting

The current behavior is to issue "adb unroot" if the device needed to be
rooted upon connection. This breaks use of nested Targets, which LISA
requires as some target interaction needs to happen in a subprocess.

Fix that by restoring the same adb root state that there was when
creating the connection, rather than blindly unrooting the device upon
disconnection.

Author: douglas-raillard-arm

devlib/utils/android.py

@@ -305,13 +305,14 @@ def __init__(
         self.adb_server = adb_server
         self.adb_port = adb_port
         self.adb_as_root = adb_as_root
+        self._restore_to_adb_root = False
         lock, nr_active = AdbConnection.active_connections
         with lock:
             nr_active[self.device] += 1
 
         if self.adb_as_root:
             try:
-                self.adb_root(enable=True)
+                self._restore_to_adb_root = self._adb_root(enable=True)
             # Exception will be raised if we are not the only connection
             # active. adb_root() requires restarting the server, which is not
             # acceptable if other connections are active and can apparently
@@ -405,7 +406,7 @@ def _close(self):
 
         if disconnect:
             if self.adb_as_root:
-                self.adb_root(enable=False)
+                self.adb_root(enable=self._restore_to_adb_root)
             adb_disconnect(self.device, self.adb_server, self.adb_port)
 
     def cancel_running_command(self):
@@ -415,27 +416,34 @@ def cancel_running_command(self):
         pass
 
     def adb_root(self, enable=True):
+        self._adb_root(enable=enable)
+
+    def _adb_root(self, enable):
         lock, nr_active = AdbConnection.active_connections
         with lock:
             can_root = nr_active[self.device] <= 1
 
         if not can_root:
             raise AdbRootError('Can only restart adb server if no other connection is active')
 
+        def is_rooted(out):
+            return 'adbd is already running as root' in out
+
         cmd = 'root' if enable else 'unroot'
         try:
             output = adb_command(self.device, cmd, timeout=30, adb_server=self.adb_server, adb_port=self.adb_port)
         except subprocess.CalledProcessError as e:
+            was_rooted = is_rooted(e.output)
             # Ignore if we're already root
-            if 'adbd is already running as root' in e.output:
-                pass
-            else:
+            if not was_rooted:
                 raise AdbRootError(str(e)) from e
         else:
+            was_rooted = is_rooted(output)
             # Check separately as this does not cause a error exit code.
             if 'cannot run as root in production builds' in output:
                 raise AdbRootError(output)
         AdbConnection._connected_as_root[self.device] = enable
+        return was_rooted
 
     def wait_for_device(self, timeout=30):
         adb_command(self.device, 'wait-for-device', timeout, self.adb_server, self.adb_port)