oxenstored: Factor out Process.do_reconnect()

The logic flow here is complicated.  In preparation to fix a bug, factor out
reconnecting a xenbus connection, and fold History.reconnect into it's single
caller.

No functional change.

This is part of XSA-512 / CVE-2026-79604.

Signed-off-by: Andrii Sultanov <andriy.sultanov@vates.tech>
Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: Andrii Sultanov <andriy.sultanov@vates.tech>

tools/ocaml/xenstored/history.ml

@@ -39,10 +39,6 @@ let end_transaction txn con tid commit =
   trim ~txn ();
   success
 
-let reconnect con =
-  trim ();
-  Connection.do_reconnect con
-
 let push (x: history_record) =
   let dom = x.con.Connection.dom in
   match dom with

tools/ocaml/xenstored/process.ml

@@ -350,6 +350,13 @@ let do_reset_watches con _t _domains cons _data =
   Connections.del_watches cons con;
   Connection.del_transactions con
 
+let do_reconnect cons con =
+  let domstr = Connection.get_domstr con in
+  info "%s requests a reconnect" domstr;
+  History.trim ();
+  Connection.do_reconnect con;
+  info "%s reconnection complete" domstr
+
 (* only in >= xen3.3                                                                                    *)
 let do_set_target con _t _domains cons data =
   if not (Connection.is_dom0 con)
@@ -735,9 +742,7 @@ let do_input store cons doms con =
       if Connection.can_input con then Connection.do_input con
       else None
     with Xenbus.Xb.Reconnect ->
-      info "%s requests a reconnect" (Connection.get_domstr con);
-      History.reconnect con;
-      info "%s reconnection complete" (Connection.get_domstr con);
+      do_reconnect cons con;
       None
        | Invalid_argument exp | Failure exp ->
          error "caught exception %s" exp;
@@ -760,7 +765,7 @@ let do_input store cons doms con =
     write_access_log ~ty ~tid ~con:(Connection.get_domstr con) ~data;
     Connection.incr_ops con
 
-let do_output _store _cons _doms con =
+let do_output _store cons _doms con =
   Connection.source_flush_watchevents con;
   if Connection.has_output con then (
     if Connection.has_new_output con then (
@@ -775,8 +780,6 @@ let do_output _store _cons _doms con =
     try
       ignore (Connection.do_output con)
     with Xenbus.Xb.Reconnect ->
-      info "%s requests a reconnect" (Connection.get_domstr con);
-      History.reconnect con;
-      info "%s reconnection complete" (Connection.get_domstr con)
+      do_reconnect cons con
   )