Handle a failed disconnect correctly

If the sender disconnects its socket before sending the disconnect
message, the destination should restart the migration process.  This
patch makes sure that happens.

src/client.c

@@ -166,7 +166,7 @@ int fd_read_request( int fd, struct nbd_request_raw *out_request)
 
 /* Returns 1 if *request was filled with a valid request which we should
  * try to honour. 0 otherwise. */
-int client_read_request( struct client * client , struct nbd_request *out_request )
+int client_read_request( struct client * client , struct nbd_request *out_request, int * disconnected )
 {
 	NULLCHECK( client );
 	NULLCHECK( out_request );
@@ -199,6 +199,7 @@ int client_read_request( struct client * client , struct nbd_request *out_reques
 	}
 
 	if (fd_read_request(client->socket, &request_raw) == -1) {
+		*disconnected = 1;
 		switch( errno ){
 			case 0:
 				debug( "EOF while reading request" );
@@ -296,8 +297,7 @@ void client_write_init( struct client * client, uint64_t size )
  * DISCONNECT and any bad request.
  */
 int client_request_needs_reply( struct client * client, 
-		struct nbd_request request,
-		int *should_disconnect )
+		struct nbd_request request )
 {
 	debug("request type %d", request.type);
 	
@@ -323,7 +323,7 @@ int client_request_needs_reply( struct client * client,
 			  request.len
 			);
 			client_write_reply( client, &request, 1 );
-			*should_disconnect = 0;
+			client->disconnect = 0;
 			return 0;
 		}
 		break;
@@ -335,7 +335,7 @@ int client_request_needs_reply( struct client * client,
 		break;
 	case REQUEST_DISCONNECT:
 		debug("request disconnect");
-		*should_disconnect = 1;
+		client->disconnect = 1;
 		return 0;
 		
 	default:
@@ -434,12 +434,13 @@ void client_reply( struct client* client, struct nbd_request request )
 int client_serve_request(struct client* client)
 {
 	struct nbd_request    request;
-	int                   request_err;
 	int                   failure = 1;
+	int                   disconnected = 0;
 
-	if ( !client_read_request( client, &request ) ) { return failure; }
-	if ( !client_request_needs_reply( client, request, &request_err ) )  {
-		return request_err;
+	if ( !client_read_request( client, &request, &disconnected ) ) { return failure; }
+	if ( disconnected ) { return failure; }
+	if ( !client_request_needs_reply( client, request ) )  {
+		return client->disconnect;
 	} 
 
 	server_lock_io( client->serve );
@@ -501,9 +502,14 @@ void* client_serve(void* client_uncast)
 	debug("client: stopped serving requests");
 	client->stopped = 1;
 		
-	if ( client->entrusted ){
-		debug("client: control arrived" );
-		server_control_arrived( client->serve );
+	if ( client->entrusted ) {
+		if ( client->disconnect ){
+			debug("client: control arrived" );
+			server_control_arrived( client->serve );
+		}
+		else {
+			warn( "client: control transfer failed." );
+		}
 	}
 
 	FATAL_IF_NEGATIVE(

src/client.h

@@ -30,6 +30,9 @@ struct client {
 
 	/* Have we seen a REQUEST_ENTRUST message? */
 	int     entrusted;
+
+	/* Have we seen a REQUEST_DISCONNECT message? */
+	int     disconnect;
 };
 
 

tests/acceptance/fakes/dest/close_after_entrust_reply.rb

@@ -0,0 +1,36 @@
+#!/usr/bin/env ruby
+# encoding: utf-8
+
+# Receive a mirror, and disconnect after sending the entrust reply but
+# before it can send the disconnect signal.
+#
+# This test is currently unused: the sender can't detect that the
+# write failed.
+
+require 'flexnbd/fake_dest'
+include FlexNBD
+
+addr, port, src_pid = *ARGV
+server = FakeDest.new( addr, port )
+client = server.accept
+
+client.write_hello
+while (req = client.read_request; req[:type] == 1)
+  client.read_data( req[:len] )
+  client.write_reply( req[:handle] )
+end
+
+system "kill -STOP #{src_pid}"
+client.write_reply( req[:handle] )
+client.close
+system "kill -CONT #{src_pid}"
+
+sleep( 0.25 )
+client2 = server.accept( "Timed out waiting for a reconnection" )
+
+client2.close
+server.close
+
+$stderr.puts "done"
+exit(0)
+

tests/acceptance/fakes/dest/error_on_entrust.rb

@@ -0,0 +1,34 @@
+#!/usr/bin/env ruby
+# encoding: utf-8
+
+# Receive a mirror, but respond to the entrust with an error.  There's
+# currently no code path in flexnbd which can do this, but we could
+# add one.
+
+require 'flexnbd/fake_dest'
+include FlexNBD
+
+addr, port = *ARGV
+server = FakeDest.new( addr, port )
+client = server.accept
+
+client.write_hello
+loop do
+  req = client.read_request
+  if req[:type] == 1
+    client.read_data( req[:len] )
+    client.write_reply( req[:handle] )
+  else
+    client.write_reply( req[:handle], 1 )
+    break
+  end
+end
+
+client.close
+
+client2 = server.accept( "Timed out waiting for a reconnection" )
+
+client2.close
+server.close
+
+exit(0)

tests/acceptance/fakes/source/close_after_entrust_reply.rb

@@ -0,0 +1,32 @@
+#!/usr/bin/env ruby
+
+# Connect, send a migration, entrust then *immediately* disconnect.
+# This simulates a client which fails while the client is blocked.
+#
+# We attempt to reconnect immediately afterwards to prove that we can
+# retry the mirroring.
+
+require 'flexnbd/fake_source'
+include FlexNBD
+
+addr, port, srv_pid = *ARGV
+
+client = FakeSource.new( addr, port, "Timed out connecting" )
+client.read_hello
+client.write_write_request( 0, 8 )
+client.write_data( "12345678" )
+
+client.write_entrust_request
+client.read_response
+client.close
+
+sleep(0.25)
+
+client2 = FakeSource.new( addr, port, "Timed out reconnecting to mirror" )
+client2.send_mirror
+
+sleep(0.25)
+client3 = FakeSource.new( addr, port, "Timed out reconnecting to read" )
+client3.close
+
+exit(0)

tests/acceptance/flexnbd/fake_dest.rb

@@ -94,7 +94,7 @@ module FlexNBD
       end
 
 
-      def receive_mirror
+      def receive_mirror( opts = {} )
         write_hello()
         loop do
           req = read_request
@@ -103,7 +103,7 @@ module FlexNBD
             read_data( req[:len] )
             write_reply( req[:handle] )
           when 65536
-            write_reply( req[:handle] )
+            write_reply( req[:handle], opts[:err] == :entrust ? 1 : 0 )
             break
           else
             raise "Unexpected request: #{req.inspect}"

tests/acceptance/flexnbd/fake_source.rb

@@ -50,12 +50,27 @@ module FlexNBD
       send_request( 65536, handle )
     end
 
+    def write_disconnect_request( handle="myhandle" )
+      send_request( 2, handle )
+    end
+
 
     def write_data( data )
       @sock.write( data )
     end
 
 
+    def send_mirror
+      read_hello()
+      write_write_request( 0, 8 )
+      write_data( "12345678" )
+      read_response()
+      write_entrust_request()
+      read_response()
+      write_disconnect_request()
+      close()
+    end
+
 
     def read_response
       magic = @sock.read(4)

tests/acceptance/test_dest_error_handling.rb

@@ -66,6 +66,14 @@ class TestDestErrorHandling  < Test::Unit::TestCase
     run_fake( "source/close_after_write_data" )
   end
 
+
+  def test_disconnect_after_entrust_reply_causes_error
+    @env.nbd1.can_die(0)
+    # This fake runs a failed migration then a succeeding one, so we
+    # expect the destination to take control.
+    run_fake( "source/close_after_entrust_reply" )
+  end
+
   private
   def run_fake( name )
     @env.run_fake( name, @env.ip, @env.port1 )

tests/acceptance/test_source_error_handling.rb

@@ -85,6 +85,12 @@ class TestSourceErrorHandling < Test::Unit::TestCase
   end
 
 
+  def test_entrust_error_causes_retry
+    run_fake( "dest/error_on_entrust" )
+  end
+
+
+
   private
   def run_fake(name, opts = {})
     @env.run_fake( name, @env.ip, @env.port2 )