[PATCH v4 05/20] host/rootfs: Add helper program for per-VM services

[Demi Marie Obenour <demiobenour@gmail.com>]

The program handles cgroups and common substitutions.  This is better
than repeating the boilerplate multiple times.

Signed-off-by: Demi Marie Obenour <demiobenour@gmail.com>
---
 host/rootfs/file-list.mk                 |  1 +
 host/rootfs/image/usr/bin/vm-service-run | 34 ++++++++++++++++++++++++++++++++
 2 files changed, 35 insertions(+)

diff --git a/host/rootfs/file-list.mk b/host/rootfs/file-list.mk
index e1280ab56d8797e40b9b1c584ab0daef3cda41d7..c707c01179238231f70164ffda5b7c940b34192a 100644
--- a/host/rootfs/file-list.mk
+++ b/host/rootfs/file-list.mk
@@ -65,6 +65,7 @@ FILES = \
 	image/usr/bin/spectrum-update \
 	image/usr/bin/vm-console \
 	image/usr/bin/vm-import \
+	image/usr/bin/vm-service-run \
 	image/usr/bin/vm-start \
 	image/usr/bin/vm-stop \
 	image/usr/bin/xdg-open \
diff --git a/host/rootfs/image/usr/bin/vm-service-run b/host/rootfs/image/usr/bin/vm-service-run
new file mode 100755
index 0000000000000000000000000000000000000000..c788574cf95ec7fd0d93b656557f85fa80b31690
--- /dev/null
+++ b/host/rootfs/image/usr/bin/vm-service-run
@@ -0,0 +1,34 @@
+#!/usr/bin/execlineb -WS1
+# SPDX-License-Identifier: EUPL-1.2+
+# SPDX-FileCopyrightText: 2026 Demi Marie Obenour <demiobenour@gmail.com>
+
+# Substitute all of the needed environment variables
+# into both this script and its arguments
+# (the subsequent command to run).  This substitutes
+# the *caller*'s arguments.
+multisubstitute {
+  importas -iS VM
+  importas -iS "#"
+  importas -iS "1"
+  importas -iS WAYLAND_DISPLAY
+}
+
+# Check that the VM name and service are reasonable.
+# Then run the cgroup-setup program and the provided
+# command line.  Avoid premature substitution by
+# escaping ${#} and ${1} with backslashes.  Otherwise,
+# they would be values for this script, not for the caller.
+case -- "\\${#}@${VM}@\\${1}" {
+  # s6-supervise might start passing extra arguments in the future, but
+  # 0 arguments is not okay.
+  "[1-9][0-9]*@[A-Za-z0-9_][A-Za-z0-9_.-]*@[A-Za-z_][A-Za-z0-9_-]*" {
+    # The caller has been migrated from using -WS1 to using -Wp.
+    # Pop the environment to preserve the original behavior.
+    emptyenv -P cgroup-setup --leaf -- "\\${1}" $@
+  }
+}
+fdmove -c 1 2
+if { printf "Wrong VM name %s, \
+parent argument count %s, or parent argument %s\n"
+     $VM "\\$#" "\\${1}" }
+exit 100

-- 
2.55.0