tools/oxenstored: Load the plugin for Xenctrl.domain_getinfo

Oxenstored dynamically loads the plugin provided in ocaml/libs/xsd_glue.
The plugin is verified to be providing the specified plugin_interface
during its loading.

If a V2 of the plugin is produced, V1 will still be present, and a new
version should only be loaded if it's verified to exist
(New oxenstored can run in an environment with only V1 of the plugin).

The plugin is not switched to as of yet, the old Xenctrl stubs are still
used.

Signed-off-by: Andrii Sultanov <andrii.sultanov@cloud.com>
Acked-by: Christian Lindig <christian.lindig@cloud.com>
Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>

tools/ocaml/xenstored/Makefile

@@ -15,7 +15,8 @@ OCAMLINCLUDE += \
 	-I $(OCAML_TOPLEVEL)/libs/xb \
 	-I $(OCAML_TOPLEVEL)/libs/mmap \
 	-I $(OCAML_TOPLEVEL)/libs/xc \
-	-I $(OCAML_TOPLEVEL)/libs/eventchn
+	-I $(OCAML_TOPLEVEL)/libs/eventchn \
+	-I $(OCAML_TOPLEVEL)/libs/xsd_glue
 
 LIBS = syslog.cma syslog.cmxa poll.cma poll.cmxa
 syslog_OBJS = syslog
@@ -59,6 +60,7 @@ INTF = symbol.cmi trie.cmi syslog.cmi systemd.cmi poll.cmi
 
 XENSTOREDLIBS = \
 	unix.cmxa \
+	dynlink.cmxa \
 	-ccopt -L -ccopt . syslog.cmxa \
 	-ccopt -L -ccopt . systemd.cmxa \
 	-ccopt -L -ccopt . poll.cmxa \
@@ -66,6 +68,7 @@ XENSTOREDLIBS = \
 	-ccopt -L -ccopt $(OCAML_TOPLEVEL)/libs/eventchn $(OCAML_TOPLEVEL)/libs/eventchn/xeneventchn.cmxa \
 	-ccopt -L -ccopt $(OCAML_TOPLEVEL)/libs/xc $(OCAML_TOPLEVEL)/libs/xc/xenctrl.cmxa \
 	-ccopt -L -ccopt $(OCAML_TOPLEVEL)/libs/xb $(OCAML_TOPLEVEL)/libs/xb/xenbus.cmxa \
+	-ccopt -L -ccopt $(OCAML_TOPLEVEL)/libs/xsd_glue $(OCAML_TOPLEVEL)/libs/xsd_glue/plugin_interface_v1.cmxa \
 	-ccopt -L -ccopt $(XEN_ROOT)/tools/libs/ctrl
 
 PROGRAMS = oxenstored

tools/ocaml/xenstored/domains.ml

@@ -20,6 +20,34 @@ let warn fmt  = Logging.warn  "domains" fmt
 
 let xc = Xenctrl.interface_open ()
 
+let load_plug fname =
+  let fail_with fmt = Printf.ksprintf failwith fmt in
+  let fname = Dynlink.adapt_filename fname in
+  if Sys.file_exists fname then
+    try Dynlink.loadfile fname with
+    | Dynlink.Error err as e ->
+      error "ERROR loading plugin '%s': %s\n%!" fname
+        (Dynlink.error_message err);
+      raise e
+    | _ -> fail_with "Unknown error while loading plugin"
+  else fail_with "Plugin file '%s' does not exist" fname
+
+let () =
+  let plugins_dir = Paths.libexec ^ "/ocaml/xsd_glue/xenctrl_plugin/" in
+  let filepath = plugins_dir ^ "domain_getinfo_v1.cmxs" in
+  debug "Trying to load plugin '%s'\n%!" filepath;
+  let list_files = Sys.readdir plugins_dir in
+  debug "Directory listing of '%s'\n%!" plugins_dir ;
+  Array.iter (fun x -> debug "\t%s\n%!" x) list_files;
+  Dynlink.allow_only [ "Plugin_interface_v1" ];
+  load_plug filepath
+
+module Plugin =
+  (val Plugin_interface_v1.get_plugin_v1 ()
+    : Plugin_interface_v1.Domain_getinfo_V1)
+
+let handle = Plugin.interface_open ()
+
 type domains = {
   eventchn: Event.t;
   table: (Xenctrl.domid, Domain.t) Hashtbl.t;

tools/ocaml/xenstored/paths.ml.in

@@ -2,3 +2,4 @@ let xen_log_dir = "@XEN_LOG_DIR@"
 let xen_config_dir = "@XEN_CONFIG_DIR@"
 let xen_run_dir = "@XEN_RUN_DIR@"
 let xen_run_stored = "@XEN_RUN_STORED@"
+let libexec = "@LIBEXEC@"