Revert "Hide most of the implementation of `struct rb_io`. (#6511)"

This reverts commit 18e55fc1e1ec20e8f3166e3059e76c885fc9f8f2.

fix [Bug #19704]
https://bugs.ruby-lang.org/issues/19704
This breaks compatibility for extension libraries. Such changes
need a discussion.

1 files changed, 1 insertions, 1 deletions

diff --git a/debug.c b/debug.c
index b5cba590ba..d3f41f1a3a 100644
--- a/debug.c
+++ b/debug.c
@@ -70,7 +70,7 @@ const union {
         RUBY_FMODE_NOREVLOOKUP		= 0x00000100,
         RUBY_FMODE_TRUNC		= FMODE_TRUNC,
         RUBY_FMODE_TEXTMODE		= FMODE_TEXTMODE,
-        RUBY_FMODE_EXTERNAL		= 0x00010000,
+        RUBY_FMODE_PREP 		= 0x00010000,
         RUBY_FMODE_SETENC_BY_BOM	= FMODE_SETENC_BY_BOM,
         RUBY_FMODE_UNIX 		= 0x00200000,
         RUBY_FMODE_INET 		= 0x00400000,