Enable writing after the 2G boundary

This patch fixes a bug in readwrite.c which truncated the 'from' field
in nbd requests.  It was casting them down from an off64_t to an int.

tests/acceptance/environment.rb

@@ -79,6 +79,10 @@ class Environment
   end
 
 
+  def truncate1( size )
+    system "truncate -s #{size} #{@filename1}"
+  end
+
 
   def listening_ports
     `netstat -ltn`.

tests/acceptance/test_happy_path.rb

@@ -81,4 +81,15 @@ class TestHappyPath < Test::Unit::TestCase
     assert @env.status2['has_control'], "destination didn't take control"
   end
 
+
+  def test_write_to_high_block
+    # Create a large file, then try to write to somewhere after the 2G boundary
+    @env.truncate1 "4G"
+    @env.serve1
+
+    @env.nbd1.write( 2**31+2**29, "12345678" )
+    sleep(1)
+    assert_equal "12345678", @env.nbd1.read( 2**31+2**29, 8 )
+  end
+
 end

tests/unit/check_nbdtypes.c

@@ -182,6 +182,24 @@ START_TEST(test_reply_handle)
 END_TEST
 
 
+START_TEST( test_convert_from )
+{
+	/* Check that we can correctly pull numbers out of an
+	 * nbd_request_raw */
+	struct nbd_request_raw request_raw;
+	struct nbd_request     request;
+	char readbuf[] = {0x80, 0, 0, 0, 0, 0, 0, 0};
+
+	memcpy( &request_raw.from, readbuf, 8 );
+
+	nbd_r2h_request( &request_raw, &request );
+
+	uint64_t target = 1;
+	target <<= 63;
+	fail_unless( target == request.from, "from was wrong" );
+}	
+END_TEST
+
 Suite *nbdtypes_suite(void) 
 {
 	Suite *s = suite_create( "nbdtypes" );
@@ -197,6 +215,7 @@ Suite *nbdtypes_suite(void)
 	tcase_add_test( tc_request, test_request_handle );
 	tcase_add_test( tc_request, test_request_from );
 	tcase_add_test( tc_request, test_request_len );
+	tcase_add_test( tc_request, test_convert_from );
 	tcase_add_test( tc_reply, test_reply_magic );
 	tcase_add_test( tc_reply, test_reply_error );
 	tcase_add_test( tc_reply, test_reply_handle );