tools/xenstore: allow live update only with no transaction active

In order to simplify live update state dumping only allow live update
to happen when no transaction is active.

A timeout is used to detect guests which have a transaction active for
longer periods of time. In case such a guest is detected when trying
to do a live update it will be reported and the update will fail.

The admin can then either use a longer timeout, or use the force flag
to just ignore the transactions of such a guest, or kill the guest
before retrying.

Signed-off-by: Juergen Gross <jgross@suse.com>
Acked-by: Wei Liu <wl@xen.org>

tools/xenstore/xenstored_control.c

@@ -312,12 +312,37 @@ static const char *lu_arch(const void *ctx, struct connection *conn,
 
 static bool lu_check_lu_allowed(void)
 {
-	return true;
+	struct connection *conn;
+	time_t now = time(NULL);
+	unsigned int ta_total = 0, ta_long = 0;
+
+	list_for_each_entry(conn, &connections, list) {
+		if (conn->ta_start_time) {
+			ta_total++;
+			if (conn->ta_start_time - now >= lu_status->timeout)
+				ta_long++;
+		}
+	}
+
+	return ta_total ? (lu_status->force && ta_long == ta_total) : true;
 }
 
 static const char *lu_reject_reason(const void *ctx)
 {
-	return "BUSY";
+	char *ret = NULL;
+	struct connection *conn;
+	time_t now = time(NULL);
+
+	list_for_each_entry(conn, &connections, list) {
+		if (conn->ta_start_time - now >= lu_status->timeout) {
+			ret = talloc_asprintf(ctx, "%s\nDomain %u: %ld s",
+					      ret ? : "Domains with long running transactions:",
+					      conn->id,
+					      conn->ta_start_time - now);
+		}
+	}
+
+	return ret ? (const char *)ret : "Overlapping transactions";
 }
 
 static const char *lu_dump_state(const void *ctx, struct connection *conn)

tools/xenstore/xenstored_core.h

@@ -107,6 +107,7 @@ struct connection
 	struct list_head transaction_list;
 	uint32_t next_transaction_id;
 	unsigned int transaction_started;
+	time_t ta_start_time;
 
 	/* List of delayed requests. */
 	struct list_head delayed;

tools/xenstore/xenstored_transaction.c

@@ -473,6 +473,8 @@ int do_transaction_start(struct connection *conn, struct buffered_data *in)
 	list_add_tail(&trans->list, &conn->transaction_list);
 	talloc_steal(conn, trans);
 	talloc_set_destructor(trans, destroy_transaction);
+	if (!conn->transaction_started)
+		conn->ta_start_time = time(NULL);
 	conn->transaction_started++;
 	wrl_ntransactions++;
 
@@ -511,6 +513,8 @@ int do_transaction_end(struct connection *conn, struct buffered_data *in)
 	conn->transaction = NULL;
 	list_del(&trans->list);
 	conn->transaction_started--;
+	if (!conn->transaction_started)
+		conn->ta_start_time = 0;
 
 	/* Attach transaction to in for auto-cleanup */
 	talloc_steal(in, trans);
@@ -589,6 +593,7 @@ void conn_delete_all_transactions(struct connection *conn)
 	assert(conn->transaction == NULL);
 
 	conn->transaction_started = 0;
+	conn->ta_start_time = 0;
 }
 
 int check_transactions(struct hashtable *hash)