test-driver.py: fix VM state directory deletion

The previous version of the code would only kick in if the state
directory path pointed at a *file*, which never occurs. Making that
codepath actually work reveals an ordering bug, which this patch fixes
as well.

It also replaces the confusing, imperative case log message "delete VM
state directory" with "deleting VM state directory".

Finally, we hint the user about how to prevent this deletion. IE. by
passing the --keep-vm-state flag.

Bug report:
https://github.com/NixOS/nixpkgs/pull/91046#issuecomment-685568750

Credit goes to Edef for the rebase on top of a recent nixpkgs commit
and for writing most of this commit message.

Co-authored-by: edef <edef@edef.eu>

1 files changed, 12 insertions, 9 deletions

diff --git a/nixos/lib/test-driver/test-driver.py b/nixos/lib/test-driver/test-driver.py
index 93f94587c0a50..5d3e632fac2c8 100644
--- a/nixos/lib/test-driver/test-driver.py
+++ b/nixos/lib/test-driver/test-driver.py
@@ -217,7 +217,7 @@ class Machine:
                 match = re.search("run-(.+)-vm$", cmd)
                 if match:
                     self.name = match.group(1)
-
+        self.logger = args["log"]
         self.script = args.get("startCommand", self.create_startcommand(args))
 
         tmp_dir = os.environ.get("TMPDIR", tempfile.gettempdir())
@@ -227,7 +227,10 @@ class Machine:
             os.makedirs(path, mode=0o700, exist_ok=True)
             return path
 
-        self.state_dir = create_dir("vm-state-{}".format(self.name))
+        self.state_dir = os.path.join(tmp_dir, f"vm-state-{self.name}")
+        if not args["keepVmState"]:
+            self.cleanup_statedir()
+        os.makedirs(self.state_dir, mode=0o700, exist_ok=True)
         self.shared_dir = create_dir("shared-xchg")
 
         self.booted = False
@@ -235,7 +238,6 @@ class Machine:
         self.pid: Optional[int] = None
         self.socket = None
         self.monitor: Optional[socket.socket] = None
-        self.logger: Logger = args["log"]
         self.allow_reboot = args.get("allowReboot", False)
 
     @staticmethod
@@ -780,9 +782,10 @@ class Machine:
         self.log("QEMU running (pid {})".format(self.pid))
 
     def cleanup_statedir(self) -> None:
-        self.log("delete the VM state directory")
-        if os.path.isfile(self.state_dir):
+        if os.path.isdir(self.state_dir):
             shutil.rmtree(self.state_dir)
+            self.logger.log(f"deleting VM state directory {self.state_dir}")
+            self.logger.log("if you want to keep the VM state, pass --keep-vm-state")
 
     def shutdown(self) -> None:
         if not self.booted:
@@ -940,10 +943,10 @@ if __name__ == "__main__":
     for nr, vde_socket, _, _ in vde_sockets:
         os.environ["QEMU_VDE_SOCKET_{}".format(nr)] = vde_socket
 
-    machines = [create_machine({"startCommand": s}) for s in vm_scripts]
-    for machine in machines:
-        if not cli_args.keep_vm_state:
-            machine.cleanup_statedir()
+    machines = [
+        create_machine({"startCommand": s, "keepVmState": cli_args.keep_vm_state})
+        for s in vm_scripts
+    ]
     machine_eval = [
         "{0} = machines[{1}]".format(m.name, idx) for idx, m in enumerate(machines)
     ]