generate: container: Enable usage of host files / directories as volumes

From podman-create(1):

	If a volume source is specified, it must be a path on the host or the
	name of a named volume. Host paths are allowed to be absolute or relative;
	relative paths are resolved relative to the directory Podman is run in.
	If the source does not exist, Podman returns an error. Users must pre-create
	the source files or directories. Any source that does not begin with
	a . or / is treated as the name of a named volume.

Implement this with the is_host_volume() check.

Signed-off-by: Enno Tensing <tenno@suij.in>

generate/container.py

@@ -63,12 +63,22 @@ class Volume:
             return None
         return [cls(key, value) for key, value in val.items()]
 
+    def is_host_volume(self) -> bool:
+        """Check if this Volume is a named or a host volume."""
+        return self.name.startswith("/") or self.name.startswith(".")
+
     def command(self) -> str:
         """Option for podman container create."""
         return f"--volume {self.name}:{self.path}"
 
     def create(self) -> str:
         """Create volume, if it does not exist."""
+        if self.is_host_volume():
+            # A HOST-DIR starting with a slash or dot is interpreted as a
+            # directory or file on the host machine. Since the script should
+            # not modify things outside its own tree, i.e.
+            # /var/lib/containerctl, ignore it.
+            return ""
         cmd = f"# Create volume {self.name}\n"
         cmd += f"if ! podman volume exists '{self.name}' 2> /dev/null\n"
         cmd += "then\n"
@@ -78,6 +88,9 @@ class Volume:
 
     def remove(self) -> str:
         """Remove volume if it exists."""
+        if self.is_host_volume():
+            # As with create, don't touch the host system
+            return ""
         cmd = f"# Remove volume {self.name}\n"
         cmd += f"if podman volume exists '{self.name}' 2> /dev/null\n"
         cmd += "then\n"