CA-411477: Fix SM API version check failure

When shutdown a VM, xapi will check SM API version to decide if to
call `post_deactivate_hook`. But if the SR has already been unplugged,
the checking will fail.

Solution:
Check if the plugin of the SR still exists. If not, skip the SM API
checking.

Signed-off-by: Bengang Yuan <[email protected]>

Author: BengangY

ocaml/xapi/storage_mux.ml

@@ -652,8 +652,14 @@ module Mux = struct
         the SMAPI version of the SR, but as xapi-storage-script cannot call code
         xapi, and smapiv1_wrapper has state tracking logic, the hook has to be placed
         here for now. *)
-      if smapi_version_of_sr sr = SMAPIv3 then
-        Storage_migrate.post_deactivate_hook ~sr ~vdi ~dp
+      match find_plugin sr with
+      | Some _ when smapi_version_of_sr sr = SMAPIv3 ->
+          Storage_migrate.post_deactivate_hook ~sr ~vdi ~dp
+      | None ->
+          debug
+            "%s No plugin found for SR %s, the SR may be already destroyed, \
+             skip post_deactivate_hook"
+            __FUNCTION__ (s_of_sr sr)
 
     let detach () ~dbg ~dp ~sr ~vdi ~vm =
       with_dbg ~name:"VDI.detach" ~dbg @@ fun di ->

ocaml/xapi/storage_mux_reg.ml

@@ -69,6 +69,8 @@ let unregister sr =
         )
   )
 
+let find_plugin sr = with_lock m (fun () -> Hashtbl.find_opt plugins sr)
+
 let sr_has_capability sr capability =
   with_lock m (fun () ->
       match Hashtbl.find_opt plugins sr with

ocaml/xapi/storage_mux_reg.mli

@@ -36,6 +36,8 @@ val register :
 
 val unregister : Storage_interface.sr -> unit
 
+val find_plugin : Storage_interface.sr -> plugin option
+
 val sr_has_capability : Storage_interface.sr -> Smint.Feature.capability -> bool
 
 val of_sr : Storage_interface.sr -> processor