Include machine name in virtiofsd unit name

If the same directory is shared across multiple guests, we end up
with duplicate unit names even though we need separate virtiofsd
instances. Let's fix this by including the machine name in the
virtiofsd unit name so that the unit names will be unique across
guests.

mkosi/qemu.py

@@ -328,9 +328,6 @@ def start_virtiofsd(
     name: Optional[str] = None,
     selinux: bool = False,
 ) -> Iterator[Path]:
-    if name is None:
-        name = systemd_escape(config, directory, path=True)
-
     virtiofsd = find_virtiofsd(root=config.tools(), extra=config.extra_search_paths)
     if virtiofsd is None:
         die("virtiofsd must be installed to boot directory images or use RuntimeTrees= with mkosi qemu")
@@ -383,9 +380,13 @@ def start_virtiofsd(
         # We want RuntimeBuildSources= and RuntimeTrees= to do the right thing even when running mkosi qemu
         # as root without the source directories necessarily being owned by root. We achieve this by running
         # virtiofsd as the owner of the source directory and then mapping that uid to root.
+        if not name:
+            name = f"{config.machine_or_name()}-{systemd_escape(config, directory, path=True)}"
+        else:
+            name = systemd_escape(config, name)
 
         name = f"mkosi-virtiofsd-{name}"
-        description = f"virtiofsd for {directory}"
+        description = f"virtiofsd for machine {config.machine_or_name()} for {directory}"
         scope = []
         if st:
             scope = scope_cmd(name=name, description=description, user=st.st_uid, group=st.st_gid)