xapi_guest_agent: Update xenstore keys for Windows PV drivers versions (xapi-project#6432)

Windows PV drivers do not store their version information into
`drivers/{xeneventchn,xenvbd,xennet}` xenstore keys since 2015, see:

* PV drivers commit `784af16810d705ba2bc02bab6ac93b24119f886c (Publish
distribution information to xenstore)`
https://xenbits.xen.org/gitweb/?p=pvdrivers/win/xenbus.git;a=commit;h=784af16810d705ba2bc02bab6ac93b24119f886c

* Xen commit `71e64e163b2dae7d08f7d77ee942749663f484d5 (docs: Introduce
xenstore paths for PV driver information)`
https://xenbits.xen.org/gitweb/?p=xen.git;a=commit;h=71e64e163b2dae7d08f7d77ee942749663f484d5

Instead it is stored like this:
```
drivers/0 = "XenServer XENBUS 9.1.9.105 "
drivers/1 = "XenServer XENVBD 9.1.8.79 "
drivers/2 = "XenServer XENVIF 9.1.12.101 "
drivers/3 = "XenServer XENIFACE 9.1.10.87 "
drivers/4 = "XenServer XENNET 9.1.7.65 "
```

Modify `xapi_guest_agent` to list such entries under `drivers/` and
present version information for each driver.

Author: last-genius

ocaml/tests/test_guest_agent.ml

@@ -285,6 +285,7 @@ module Initial_guest_metrics = Generic.MakeStateless (struct
       Xapi_guest_agent.get_initial_guest_metrics (lookup tree) (list tree)
     in
     guest_metrics.Xapi_guest_agent.networks
+    @ guest_metrics.Xapi_guest_agent.pv_drivers_version
 
   let tests =
     `QuickAndAutoDocumented
@@ -465,6 +466,33 @@ module Initial_guest_metrics = Generic.MakeStateless (struct
           ]
         , []
         )
+      ; (* windows pv driver versions parsing *)
+        ( [
+            ("drivers/0", "XenServer XENBUS 9.1.9.105 ")
+          ; ("drivers/1", "XenServer XENVBD 9.1.8.79 ")
+          ; ("drivers/2", "XenServer XENVIF 9.1.12.101 ")
+          ; ("drivers/3", "XenServer XENIFACE 9.1.10.87 ")
+          ; ("drivers/4", "XenServer XENNET 9.1.7.65 ")
+          ]
+        , [
+            ("micro", "-1")
+          ; ("xennet", "XenServer 9.1.7.65 ")
+          ; ("xeniface", "XenServer 9.1.10.87 ")
+          ; ("xenvif", "XenServer 9.1.12.101 ")
+          ; ("xenvbd", "XenServer 9.1.8.79 ")
+          ; ("xenbus", "XenServer 9.1.9.105 ")
+          ]
+        )
+      ; ( [
+            ("drivers/0", "XenServer XENBUS 9.1.9.105 (DEBUG) (MOREDEBUG)")
+          ; ("drivers/2", "XCP_ng XENVIF 9.1.12.101 ")
+          ]
+        , [
+            ("micro", "-1")
+          ; ("xenvif", "XCP_ng 9.1.12.101 ")
+          ; ("xenbus", "XenServer 9.1.9.105 (DEBUG) (MOREDEBUG)")
+          ]
+        )
       ]
 end)
 

ocaml/xapi/xapi_guest_agent.ml

@@ -33,12 +33,6 @@ end)
    NB each key is annotated with whether it appears in windows and/or linux *)
 let pv_drivers_version =
   [
-    ("drivers/xenevtchn", "xenevtchn")
-  ; (* windows *)
-    ("drivers/xenvbd", "xenvbd")
-  ; (* windows *)
-    ("drivers/xennet", "xennet")
-  ; (* windows *)
     ("attr/PVAddons/MajorVersion", "major")
   ; (* linux + windows *)
     ("attr/PVAddons/MinorVersion", "minor")
@@ -294,7 +288,45 @@ let get_initial_guest_metrics (lookup : string -> string option)
     | None ->
         []
   in
-  let pv_drivers_version = to_map pv_drivers_version
+  (* enumerate all driver versions from xenstore, which are stored like
+     drivers/0 = "XenServer XENBUS 9.1.9.105 "
+     drivers/1 = "XenServer XENVBD 9.1.8.79 "
+     drivers/2 = "XenServer XENVIF 9.1.12.101 "
+     drivers/3 = "XenServer XENIFACE 9.1.10.87 "
+     drivers/4 = "XenServer XENNET 9.1.7.65 "
+
+     (see the format specified in xenstore-paths)
+  *)
+  let get_windows_driver_versions () =
+    (* Only look into directories that are numbers (indices) *)
+    let filter_dirs subdirs =
+      List.filter_map
+        (fun x ->
+          match int_of_string_opt x with
+          | Some _ ->
+              Some ("drivers/" ^ x, x)
+          | None ->
+              None
+        )
+        subdirs
+    in
+    let versions = list "drivers" |> filter_dirs |> to_map in
+    List.filter_map
+      (fun (_, version_string) ->
+        try
+          Scanf.sscanf version_string "%s@ %s@ %s@ %s@\n"
+            (fun vendor driver_name version attr ->
+              Some
+                ( String.lowercase_ascii driver_name
+                , String.concat " " [vendor; version; attr]
+                )
+          )
+        with _ -> None
+      )
+      versions
+  in
+  let pv_drivers_version =
+    to_map pv_drivers_version @ get_windows_driver_versions ()
   and os_version = to_map os_version
   and netbios_name =
     match to_map dns_domain with