Should raise SyscallError on IO#syswrite

instead of IOError

mrblib/io.rb

@@ -123,14 +123,9 @@ class IO
   def write(string)
     str = string.is_a?(String) ? string : string.to_s
     return str.size unless str.size > 0
-
     len = syswrite(str)
-    if len != -1
-      @pos += len
-      return len
-    end
-
-    raise IOError
+    @pos += len
+    len
   end
 
   def <<(str)

src/io.c

@@ -705,6 +705,9 @@ mrb_io_syswrite(mrb_state *mrb, mrb_value io)
     fd = fptr->fd2;
   }
   length = write(fd, RSTRING_PTR(buf), RSTRING_LEN(buf));
+  if (length == -1) {
+    mrb_sys_fail(mrb, 0);
+  }
 
   return mrb_fixnum_value(length);
 }