binfmt_misc: example systemd service file

PACKAGING.md

@@ -46,3 +46,9 @@
   * `libwasmer-static`, containing `libwasmer.a`.
 
 The Wasmer distro packaging story is still in its infancy, so feedback is very welcome.
+
+## Miscellaneous: binfmt_misc
+
+Wasmer can be registered as a binfmt interpreter for wasm binaries.
+An example systemd [.service](./scripts/wasmer-binfmt.service.example) is included here.
+Please consider statically linking the wasmer binary so that this capability is also available in mount namespaces.

lib/cli/src/commands/binfmt.rs

@@ -19,6 +19,9 @@ enum Action {
 }
 
 /// Unregister and/or register wasmer as binfmt interpreter
+///
+/// Check the wasmer repository for a systemd service definition example
+/// to automate the process at start-up.
 #[derive(StructOpt)]
 pub struct Binfmt {
     // Might be better to traverse the mount list

scripts/wasmer-binfmt.service.example

@@ -0,0 +1,15 @@
+[Unit]
+Description=Set up wasmer to handle execution of wasm binaries
+DefaultDependencies=no
+Conflicts=shutdown.target
+After=proc-sys-fs-binfmt_misc.automount
+After=proc-sys-fs-binfmt_misc.mount
+Before=sysinit.target shutdown.target
+ConditionPathIsReadWrite=/proc/sys/
+
+[Service]
+Type=oneshot
+RemainAfterExit=yes
+ExecStart=/usr/bin/wasmer binfmt reregister
+ExecStop=/usr/bin/wasmer binfmt unregister
+TimeoutSec=10s