tools/oxenstored: Only quit on SIGTERM when a reload is possible

Currently when oxenstored receives SIGTERM it dumps its state and quits.  It
is possible to then restart it if --restart is given, however that is not
always safe:

* Domains could have active transactions, and after a restart they would
  either reuse transaction IDs of already open transactions, or get an error
  back that the transaction doesn't exist

* There could be pending data to send to a VM still in oxenstored's
  queue which would be lost

* There could be pending input to be processed from a VM in oxenstored's
  queue which would be lost

Prevent shutting down oxenstored via SIGTERM in the above situations.  Also
ignore domains marked as bad because oxenstored would never talk to them
again.

Signed-off-by: Edwin Török <edvin.torok@citrix.com>
Reviewed-by: Pau Ruiz Safont <pau.safont@citrix.com>
Reviewed-by: Christian Lindig <christian.lindig@citrix.com>

diff --git a/tools/ocaml/xenstored/connection.ml b/tools/ocaml/xenstored/connection.ml
index fa0d3c4d921c52c696d822f602a39c6bb642e561..bd02060cd0b9213522a50c4905aec1ef0ec9ee09 100644 (file)
--- a/tools/ocaml/xenstored/connection.ml
+++ b/tools/ocaml/xenstored/connection.ml
@@ -290,6 +290,41 @@ let has_new_output con = Xenbus.Xb.has_new_output con.xb
 let peek_output con = Xenbus.Xb.peek_output con.xb
 let do_output con = Xenbus.Xb.output con.xb
 
+let is_bad con = match con.dom with None -> false | Some dom -> Domain.is_bad_domain dom
+
+(* oxenstored currently only dumps limited information about its state.
+   A live update is only possible if any of the state that is not dumped would be empty.
+   Compared to https://xenbits.xen.org/docs/unstable/designs/xenstore-migration.html:
+     * GLOBAL_DATA: not strictly needed, systemd is giving the socket FDs to us
+     * CONNECTION_DATA: PARTIAL
+       * for domains: PARTIAL, see Connection.dump -> Domain.dump, only if data and tdomid is empty
+       * for sockets (Dom0 toolstack): NO
+     * WATCH_DATA: OK, see Connection.dump
+     * TRANSACTION_DATA: NO
+     * NODE_DATA: OK (except for transactions), see Store.dump_fct and DB.to_channel
+
+   Also xenstored will never talk to a Domain once it is marked as bad,
+   so treat it as idle for live-update.
+
+   Restrictions below can be relaxed once xenstored learns to dump more
+   of its live state in a safe way *)
+let has_extra_connection_data con =
+       let has_in = has_input con in
+       let has_out = has_output con in
+       let has_socket = con.dom = None in
+       let has_nondefault_perms = make_perm con.dom <> con.perm in
+       has_in || has_out
+       || has_socket (* dom0 sockets not dumped yet *)
+       || has_nondefault_perms (* set_target not dumped yet *)
+
+let has_transaction_data con =
+       let n = number_of_transactions con in
+       dbg "%s: number of transactions = %d" (get_domstr con) n;
+       n > 0
+
+let prevents_live_update con = not (is_bad con)
+       && (has_extra_connection_data con || has_transaction_data con)
+
 let has_more_work con =
        has_more_input con || not (has_old_output con) && has_new_output con
 

diff --git a/tools/ocaml/xenstored/connections.ml b/tools/ocaml/xenstored/connections.ml
index 6ee3552ec2d5af1415722b44519a313cb3d30363..82988f7e8dd304f66e4d7f5b5df73c73b90402e6 100644 (file)
--- a/tools/ocaml/xenstored/connections.ml
+++ b/tools/ocaml/xenstored/connections.ml
@@ -194,3 +194,11 @@ let debug cons =
        let anonymous = Hashtbl.fold (fun _ con accu -> Connection.debug con :: accu) cons.anonymous [] in
        let domains = Hashtbl.fold (fun _ con accu -> Connection.debug con :: accu) cons.domains [] in
        String.concat "" (domains @ anonymous)
+
+let filter ~f cons =
+       let fold _ v acc = if f v then v :: acc else acc in
+       []
+       |> Hashtbl.fold fold cons.anonymous
+       |> Hashtbl.fold fold cons.domains
+
+let prevents_quit cons = filter ~f:Connection.prevents_live_update cons

diff --git a/tools/ocaml/xenstored/xenstored.ml b/tools/ocaml/xenstored/xenstored.ml
index 39d6d767e4cfc230068d0216e5ea9fb8823da5d3..53d86618f2b8a517b40c69f939273da403eadcef 100644 (file)
--- a/tools/ocaml/xenstored/xenstored.ml
+++ b/tools/ocaml/xenstored/xenstored.ml
@@ -20,6 +20,7 @@ open Parse_arg
 open Stdext
 
 let error fmt = Logging.error "xenstored" fmt
+let warn fmt = Logging.warn "xenstored" fmt
 let debug fmt = Logging.debug "xenstored" fmt
 let info fmt = Logging.info "xenstored" fmt
 
@@ -312,7 +313,9 @@ let _ =
        );
 
        Sys.set_signal Sys.sighup (Sys.Signal_handle sighup_handler);
-       Sys.set_signal Sys.sigterm (Sys.Signal_handle (fun _ -> quit := true));
+       Sys.set_signal Sys.sigterm (Sys.Signal_handle (fun _ ->
+               info "Received SIGTERM";
+               quit := true));
        Sys.set_signal Sys.sigusr1 (Sys.Signal_handle (fun _ -> sigusr1_handler store));
        Sys.set_signal Sys.sigpipe Sys.Signal_ignore;
 
@@ -424,6 +427,12 @@ let _ =
                );
                let elapsed = Unix.gettimeofday () -. now in
                debug "periodic_ops took %F seconds." elapsed;
+               if !quit then (
+                       match Connections.prevents_quit cons with
+                       | [] -> ()
+                       | domains -> List.iter (fun con -> warn "%s prevents live update"
+                                                               (Connection.get_domstr con)) domains
+               );
                delay_next_frequent_ops_by elapsed
        in
 
@@ -475,7 +484,7 @@ let _ =
                in
 
        Systemd.sd_notify_ready ();
-       while not !quit
+       while not (!quit && Connections.prevents_quit cons = [])
        do
                try
                        main_loop ()