* 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

3 files changed, 20 insertions, 2 deletions

diff --git a/ChangeLog b/ChangeLog
index fa72628da5..84264a6cee 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,14 @@
+Wed Nov 23 20:03:43 2011  NARUSE, Yui  <naruse@ruby-lang.org>
+
+	* 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.
+
 Tue Nov 22 18:07:32 2011  NAKAMURA Usaku  <usa@ruby-lang.org>
 
 	* win32/win32.c (_pioinfo): need to declare _pioinfo() before using
diff --git a/io.c b/io.c
index 81da283384..0410e6339f 100644
--- a/io.c
+++ b/io.c
@@ -7956,8 +7956,6 @@ ioctl_narg_len(ioctl_req_t cmd)
 #endif
 #ifdef IOCPARM_LEN
     len = IOCPARM_LEN(cmd);	/* on BSDish systems we're safe */
-#elif defined(_IOC_SIZE)
-    len = _IOC_SIZE(cmd);
 #else
     len = 256;		/* otherwise guess at what's safe */
 #endif
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