[Xen-devel] [PATCH 1/7] oxenstored: refactor putting response on wire

[Jonathan Davies <jonathan.davies@xxxxxxxxxx>]

Previously, the functions reply_{ack,data,data_or_ack} and input_handle_error
put the response on the wire by invoking Connection.send_{ack,reply,error}.

Instead, these functions now return a value indicating what needs to be put on
the wire, and that action is done by a send_response function called
afterwards.

This refactoring gives us a chance to store the value of the response, useful
for replaying transactions.

Signed-off-by: Jonathan Davies <jonathan.davies@xxxxxxxxxx>
Reviewed-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
Reviewed-by: Jon Ludlam <jonathan.ludlam@xxxxxxxxxx>
Reviewed-by: Euan Harris <euan.harris@xxxxxxxxxx>
---
 tools/ocaml/xenstored/Makefile   |    1 +
 tools/ocaml/xenstored/process.ml |   34 ++++++++++++++++++++++++----------
 2 files changed, 25 insertions(+), 10 deletions(-)

diff --git a/tools/ocaml/xenstored/Makefile b/tools/ocaml/xenstored/Makefile
index 59875f7..dce9e70 100644
--- a/tools/ocaml/xenstored/Makefile
+++ b/tools/ocaml/xenstored/Makefile
@@ -36,6 +36,7 @@ OBJS = define \
        stdext \
        trie \
        config \
+       packet \
        logging \
        quota \
        perms \
diff --git a/tools/ocaml/xenstored/process.ml b/tools/ocaml/xenstored/process.ml
index e827678..3377966 100644
--- a/tools/ocaml/xenstored/process.ml
+++ b/tools/ocaml/xenstored/process.ml
@@ -126,8 +126,7 @@ let do_watch con t rid domains cons data =
                | _                   -> raise Invalid_Cmd_Args
                in
        let watch = Connections.add_watch cons con node token in
-       Connection.send_ack con (Transaction.get_id t) rid Xenbus.Xb.Op.Watch;
-       Connection.fire_single_watch watch
+       Packet.Ack (fun () -> Connection.fire_single_watch watch)
 
 let do_unwatch con t domains cons data =
        let (node, token) =
@@ -289,20 +288,32 @@ let do_set_target con t domains cons data =
                | _                           -> raise Invalid_Cmd_Args
 
 (*------------- Generic handling of ty ------------------*)
+let send_response ty con t rid response =
+       match response with
+       | Packet.Ack f ->
+               Connection.send_ack con (Transaction.get_id t) rid ty;
+               (* Now do any necessary follow-up actions *)
+               f ()
+       | Packet.Reply ret ->
+               Connection.send_reply con (Transaction.get_id t) rid ty ret
+       | Packet.Error e ->
+               Connection.send_error con (Transaction.get_id t) rid e
+
 let reply_ack fct ty con t rid doms cons data =
        fct con t doms cons data;
-       Connection.send_ack con (Transaction.get_id t) rid ty;
-       if Transaction.get_id t = Transaction.none then
-               process_watch (Transaction.get_ops t) cons
+       Packet.Ack (fun () ->
+               if Transaction.get_id t = Transaction.none then
+                       process_watch (Transaction.get_ops t) cons
+       )
 
 let reply_data fct ty con t rid doms cons data =
        let ret = fct con t doms cons data in
-       Connection.send_reply con (Transaction.get_id t) rid ty ret
+       Packet.Reply ret
 
 let reply_data_or_ack fct ty con t rid doms cons data =
        match fct con t doms cons data with
-               | Some ret -> Connection.send_reply con (Transaction.get_id t) 
rid ty ret
-               | None -> Connection.send_ack con (Transaction.get_id t) rid ty
+               | Some ret -> Packet.Reply ret
+               | None -> Packet.Ack (fun () -> ())
 
 let reply_none fct ty con t rid doms cons data =
        (* let the function reply *)
@@ -335,7 +346,7 @@ let function_of_type ty =
 
 let input_handle_error ~cons ~doms ~fct ~ty ~con ~t ~rid ~data =
        let reply_error e =
-               Connection.send_error con (Transaction.get_id t) rid e in
+               Packet.Error e in
        try
                fct ty con t rid doms cons data
        with
@@ -368,7 +379,10 @@ let process_packet ~store ~cons ~doms ~con ~tid ~rid ~ty 
~data =
                        else
                                Connection.get_transaction con tid
                        in
-               input_handle_error ~cons ~doms ~fct ~ty ~con ~t ~rid ~data;
+               let response = input_handle_error ~cons ~doms ~fct ~ty ~con ~t 
~rid ~data in
+
+               (* Put the response on the wire *)
+               send_response ty con t rid response
        with exn ->
                error "process packet: %s" (Printexc.to_string exn);
                Connection.send_error con tid rid "EIO"
-- 
1.7.10.4


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