Test and fix acknowedge_watch from returning EINVAL.

Also ensure that daemon re-xmits event if they ack wrong thing
(otherwise confused clients get stuck, as we will send no more
data while awaiting ack).
Signed-off-by: Rusty Russel <rusty@rustcorp.com.au>
Signed-off-by: Christian Limpach <Christian.Limpach@cl.cam.ac.uk>

tools/xenstore/testsuite/13watch-ack.sh

@@ -0,0 +1,22 @@
+#! /bin/sh
+
+# This demonstrates a bug where an xs_acknowledge_watch returns
+# EINVAL, because the daemon doesn't track what watch event it sent
+# and relies on it being the "first" watch which has an event.
+# Watches firing after the first event is sent out will change this.
+
+# Create three things to watch.
+echo mkdir /test | ./xs_test
+echo mkdir /test/1 | ./xs_test
+echo mkdir /test/2 | ./xs_test
+echo mkdir /test/3 | ./xs_test
+
+# Watch all three, fire event on 2, read watch, fire event on 1 and 3, ack 2.
+[ "`echo '1 watch /test/1 token1 0
+1 watch /test/2 token2 0
+1 watch /test/3 token3 0
+2 write /test/2 create contents2
+1 waitwatch
+2 write /test/1 create contents1
+2 write /test/3 create contents3
+1 ackwatch token2' | ./xs_test 2>&1`" = "1:/test/2:token2" ]

tools/xenstore/xenstored_core.c

@@ -1166,7 +1166,7 @@ static void consider_message(struct connection *conn)
 	/* We might get a command while waiting for an ack: this means
 	 * the other end discarded it: we will re-transmit. */
 	if (type != XS_WATCH_ACK)
-		conn->waiting_for_ack = false;
+		conn->waiting_for_ack = NULL;
 
 	/* Careful: process_message may free connection.  We detach
 	 * "in" beforehand and allocate the new buffer to avoid

tools/xenstore/xenstored_core.h

@@ -64,7 +64,7 @@ struct connection
 	bool can_write;
 
 	/* Are we waiting for a watch event ack? */
-	bool waiting_for_ack;
+	struct watch *waiting_for_ack;
 
 	/* Buffered incoming data. */
 	struct buffered_data *in;

tools/xenstore/xenstored_watch.c

@@ -102,7 +102,7 @@ void queue_next_event(struct connection *conn)
 	if (conn->waiting_reply) {
 		conn->out = conn->waiting_reply;
 		conn->waiting_reply = NULL;
-		conn->waiting_for_ack = false;
+		conn->waiting_for_ack = NULL;
 		return;
 	}
 
@@ -115,7 +115,7 @@ void queue_next_event(struct connection *conn)
 		return;
 
 	/* If we decide to cancel, we will reset this. */
-	conn->waiting_for_ack = true;
+	conn->waiting_for_ack = event->watches[0];
 
 	/* If we deleted /foo and they're watching /foo/bar, that's what we
 	 * tell them has changed. */
@@ -348,12 +348,17 @@ bool do_watch_ack(struct connection *conn, const char *token)
 	if (!conn->waiting_for_ack)
 		return send_error(conn, ENOENT);
 
-	event = get_first_event(conn);
-	if (!streq(event->watches[0]->token, token))
+	event = list_top(&conn->waiting_for_ack->events,
+			 struct watch_event, list);
+	assert(event->watches[0] == conn->waiting_for_ack);
+	if (!streq(conn->waiting_for_ack->token, token)) {
+		/* They're confused: this will cause us to send event again */
+		conn->waiting_for_ack = NULL;
 		return send_error(conn, EINVAL);
+	}
 
 	move_event_onwards(event);
-	conn->waiting_for_ack = false;
+	conn->waiting_for_ack = NULL;
 	return send_ack(conn, XS_WATCH_ACK);
 }