oxenstored: keep track of each transaction's operations

A list of (request, response) pairs from the operations performed within the
transaction will be useful to support transaction replay.

Since this consumes memory, the number of requests per transaction must not be
left unbounded. Hence a new quota for this is introduced. This quota, configured
via the configuration key 'quota-maxrequests', limits the size of transactions
initiated by domUs.

After the maximum number of requests has been exhausted, any further requests
will result in EQUOTA errors. The client may then choose to end the transaction;
a successful commit will result in the retention of only the prior requests.

Reported-by: Juergen Gross <jgross@suse.com>
Signed-off-by: Jonathan Davies <jonathan.davies@citrix.com>
Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: Jon Ludlam <jonathan.ludlam@citrix.com>
Reviewed-by: Euan Harris <euan.harris@citrix.com>
Acked-by: David Scott <dave@recoil.org>

diff --git a/tools/ocaml/xenstored/define.ml b/tools/ocaml/xenstored/define.ml
index 89a6aacc88fcd829ee156bb3b4a441ba034cd44b..d60861ca34051d493fee870bfc2c484bc0d0452b 100644 (file)
--- a/tools/ocaml/xenstored/define.ml
+++ b/tools/ocaml/xenstored/define.ml
@@ -27,6 +27,7 @@ let default_config_dir = "/etc/xen"
 
 let maxwatch = ref (50)
 let maxtransaction = ref (20)
+let maxrequests = ref (-1)   (* maximum requests per transaction *)
 
 let domid_self = 0x7FF0
 

diff --git a/tools/ocaml/xenstored/oxenstored.conf b/tools/ocaml/xenstored/oxenstored.conf
index dd20eda14032e568794a7b47b70fadb425b828ae..ac60f49df8afc2f8fb725a145e6d5964d9b76af6 100644 (file)
--- a/tools/ocaml/xenstored/oxenstored.conf
+++ b/tools/ocaml/xenstored/oxenstored.conf
@@ -18,6 +18,7 @@ quota-maxentity = 1000
 quota-maxsize = 2048
 quota-maxwatch = 100
 quota-transaction = 10
+quota-maxrequests = 1024
 
 # Activate filed base backend
 persistent = false

diff --git a/tools/ocaml/xenstored/process.ml b/tools/ocaml/xenstored/process.ml
index 9d64e545a122ef4037471b750ebf14bac66be09b..53508ab42d48312d766cbf0a12d21a86bab1ac89 100644 (file)
--- a/tools/ocaml/xenstored/process.ml
+++ b/tools/ocaml/xenstored/process.ml
@@ -155,7 +155,7 @@ let do_transaction_end con t domains cons data =
        if not success then
                raise Transaction_again;
        if commit then
-               process_watch (List.rev (Transaction.get_ops t)) cons
+               process_watch (List.rev (Transaction.get_paths t)) cons
 
 let do_introduce con t domains cons data =
        if not (Connection.is_dom0 con)
@@ -298,7 +298,7 @@ let reply_ack fct con t doms cons data =
        fct con t doms cons data;
        Packet.Ack (fun () ->
                if Transaction.get_id t = Transaction.none then
-                       process_watch (Transaction.get_ops t) cons
+                       process_watch (Transaction.get_paths t) cons
        )
 
 let reply_data fct con t doms cons data =
@@ -378,6 +378,15 @@ let process_packet ~store ~cons ~doms ~con ~req =
                        in
                let response = input_handle_error ~cons ~doms ~fct ~con ~t ~req in
 
+               let response = try
+                       if tid <> Transaction.none then
+                               (* Remember the request and response for this operation in case we need to replay the transaction *)
+                               Transaction.add_operation ~perm:(Connection.get_perm con) t req response;
+                       response
+               with Quota.Limit_reached ->
+                       Packet.Error "EQUOTA"
+               in
+
                (* Put the response on the wire *)
                send_response ty con t rid response
        with exn ->

diff --git a/tools/ocaml/xenstored/transaction.ml b/tools/ocaml/xenstored/transaction.ml
index 77de4e8ac1726ac210cacf24201c2fe8df1ba064..6b37fc2ad0a459858aebddba450e91799f7d609e 100644 (file)
--- a/tools/ocaml/xenstored/transaction.ml
+++ b/tools/ocaml/xenstored/transaction.ml
@@ -75,7 +75,8 @@ type t = {
        ty: ty;
        store: Store.t;
        quota: Quota.t;
-       mutable ops: (Xenbus.Xb.Op.operation * Store.Path.t) list;
+       mutable paths: (Xenbus.Xb.Op.operation * Store.Path.t) list;
+       mutable operations: (Packet.request * Packet.response) list;
        mutable read_lowpath: Store.Path.t option;
        mutable write_lowpath: Store.Path.t option;
 }
@@ -86,16 +87,24 @@ let make id store =
                ty = ty;
                store = if id = none then store else Store.copy store;
                quota = Quota.copy store.Store.quota;
-               ops = [];
+               paths = [];
+               operations = [];
                read_lowpath = None;
                write_lowpath = None;
        }
 
 let get_id t = match t.ty with No -> none | Full (id, _, _) -> id
 let get_store t = t.store
-let get_ops t = t.ops
-
-let add_wop t ty path = t.ops <- (ty, path) :: t.ops
+let get_paths t = t.paths
+
+let add_wop t ty path = t.paths <- (ty, path) :: t.paths
+let add_operation ~perm t request response =
+       if !Define.maxrequests >= 0
+               && not (Perms.Connection.is_dom0 perm)
+               && List.length t.operations >= !Define.maxrequests
+               then raise Quota.Limit_reached;
+       t.operations <- (request, response) :: t.operations
+let get_operations t = List.rev t.operations
 let set_read_lowpath t path = t.read_lowpath <- get_lowest path t.read_lowpath
 let set_write_lowpath t path = t.write_lowpath <- get_lowest path t.write_lowpath
 
@@ -141,7 +150,7 @@ let getperms t perm path =
        r
 
 let commit ~con t =
-       let has_write_ops = List.length t.ops > 0 in
+       let has_write_ops = List.length t.paths > 0 in
        let has_coalesced = ref false in
        let has_commited =
        match t.ty with

diff --git a/tools/ocaml/xenstored/xenstored.ml b/tools/ocaml/xenstored/xenstored.ml
index bfe689b0f8ddc135e97e133ff573cbe73a938931..42c467b757e146be9b0cc207be14d9798f847dd1 100644 (file)
--- a/tools/ocaml/xenstored/xenstored.ml
+++ b/tools/ocaml/xenstored/xenstored.ml
@@ -95,6 +95,7 @@ let parse_config filename =
                ("quota-transaction", Config.Set_int Define.maxtransaction);
                ("quota-maxentity", Config.Set_int Quota.maxent);
                ("quota-maxsize", Config.Set_int Quota.maxsize);
+               ("quota-maxrequests", Config.Set_int Define.maxrequests);
                ("test-eagain", Config.Set_bool Transaction.test_eagain);
                ("persistent", Config.Set_bool Disk.enable);
                ("xenstored-log-file", Config.String Logging.set_xenstored_log_destination);