* io.c (ioctl_narg_len): don't use _IOC_SIZE macro on Linux.

  On Linux some constants for ioctl(2) doesn't include the size of
  its return value and 16bit value; for example FIONREAD 0x541B.
  Moreover the manual, ioctl_list(2),  says "Note  that  the  size
  bits  are  very unreliable: in lots of cases they are wrong,
  either because of buggy macros using sizeof(sizeof(struct)),
  or because of legacy values."
  So we shouldn't use it.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@33819 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

1 files changed, 9 insertions, 0 deletions

diff --git a/test/ruby/test_io.rb b/test/ruby/test_io.rb
index f1fc3233b6..d877f5e832 100644
--- a/test/ruby/test_io.rb
+++ b/test/ruby/test_io.rb
@@ -2112,5 +2112,14 @@ End
         f1.ioctl(0x80045200, entropy_count)
       }
     end
+
+    buf = ''
+    assert_nothing_raised do
+      fionread = 0x541B
+      File.open(__FILE__){|f1|
+        f1.ioctl(fionread, buf)
+      }
+    end
+    assert_equal(File.size(__FILE__), buf.unpack('i!')[0])
   end
 end