[xen master] tools/oxenstored: Only quit on SIGTERM when a reload is possible

[patchbot@xxxxxxx]

commit e663158bca89aa81ea567befc7c0f742568a6194
Author:     Edwin Török <edvin.torok@xxxxxxxxxx>
AuthorDate: Fri Jan 8 11:57:37 2021 +0000
Commit:     Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
CommitDate: Fri Jan 22 14:55:10 2021 +0000

    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@xxxxxxxxxx>
    Reviewed-by: Pau Ruiz Safont <pau.safont@xxxxxxxxxx>
    Reviewed-by: Christian Lindig <christian.lindig@xxxxxxxxxx>
---
 tools/ocaml/xenstored/connection.ml  | 35 +++++++++++++++++++++++++++++++++++
 tools/ocaml/xenstored/connections.ml |  8 ++++++++
 tools/ocaml/xenstored/xenstored.ml   | 13 +++++++++++--
 3 files changed, 54 insertions(+), 2 deletions(-)

diff --git a/tools/ocaml/xenstored/connection.ml 
b/tools/ocaml/xenstored/connection.ml
index fa0d3c4d92..bd02060cd0 100644
--- 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 6ee3552ec2..82988f7e8d 100644
--- 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 39d6d767e4..53d86618f2 100644
--- 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 ()
--
generated by git-patchbot for /home/xen/git/xen.git#master