[PATCH 1/2] Remove _IO_MTSAFE_IO from public headers.

[Zack Weinberg <zackw at panix dot com>]

_IO_MTSAFE_IO controls whether stdio is *built* with support for
multithreading.  In the distant past it might also have worked as a
feature selection macro, allowing library *users* to select
thread-safe or lock-free stdio at application build time, I haven't
done the archaeology.  Nowadays, defining _IO_MTSAFE_IO while using
the installed headers, or in _ISOMAC mode, will cause libio.h to throw
syntax errors.

This patch removes _IO_MTSAFE_IO from the public headers
(specifically, from libio/libio.h).  The internal-use-only macros
whose definitions were conditional on _IO_MTSAFE_IO are moved to
include/libio.h.  The other thing it controls is whether libio.h
defines _IO_lock_t itself or expects stdio-lock.h to have done it, and
we do still need a inter-header communication macro for that, because
stdio-lock.h can only define _IO_lock_t as a typedef.  I've invented
_IO_lock_t_defined, which is defined by both versions of stdio-lock.h.

I suspect that this entire mechanism is vestigial, and that glibc
won't build anymore if you *don't* define _IO_MTSAFE_IO, but that's
another patchset.  The bulk of libio.h is internal-use-only stuff that
no longer makes sense to expose (libstdc++ gave up on making a FILE
the same object as a C++ filebuf *decades* ago) but that, too, is
another patchset.

	* libio/libio.h: Condition dummy definition of _IO_lock_t on
	_IO_lock_t_defined, not _IO_MTSAFE_IO.	Move macro definitions
	conditioned on _IO_MTSAFE_IO ...
	* include/libio.h: ... here.

	* sysdeps/generic/stdio-lock.h, sysdeps/nptl/stdio-lock.h:
	Define _IO_lock_t_defined after defining _IO_lock_t.
---
 include/libio.h              | 31 +++++++++++++++++++++----------
 libio/libio.h                | 22 +++-------------------
 sysdeps/generic/stdio-lock.h |  1 +
 sysdeps/nptl/stdio-lock.h    |  1 +
 4 files changed, 26 insertions(+), 29 deletions(-)

diff --git a/include/libio.h b/include/libio.h
index 97fc5b548b..53321b669d 100644
--- a/include/libio.h
+++ b/include/libio.h
@@ -21,16 +21,27 @@ libc_hidden_proto (_IO_sgetn)
 libc_hidden_proto (_IO_vfprintf)
 libc_hidden_proto (_IO_vfscanf)
 
-#if defined _IO_MTSAFE_IO && _IO_lock_inexpensive
-# undef _IO_flockfile
-# define _IO_flockfile(_fp) \
-  if (((_fp)->_flags & _IO_USER_LOCK) == 0)				      \
-     _IO_lock_lock (*(_fp)->_lock)
-# undef _IO_funlockfile
-# define _IO_funlockfile(_fp) \
-  if (((_fp)->_flags & _IO_USER_LOCK) == 0)				      \
-    _IO_lock_unlock (*(_fp)->_lock)
-#endif
+#ifdef _IO_MTSAFE_IO
+# define _IO_peekc(_fp) _IO_peekc_locked (_fp)
+# if _IO_lock_inexpensive
+#  define _IO_flockfile(_fp) \
+  if (((_fp)->_flags & _IO_USER_LOCK) == 0) _IO_lock_lock (*(_fp)->_lock)
+#  define _IO_funlockfile(_fp) \
+  if (((_fp)->_flags & _IO_USER_LOCK) == 0) _IO_lock_unlock (*(_fp)->_lock)
+# else
+#  define _IO_flockfile(_fp) \
+  if (((_fp)->_flags & _IO_USER_LOCK) == 0) _IO_flockfile (_fp)
+#  define _IO_funlockfile(_fp) \
+  if (((_fp)->_flags & _IO_USER_LOCK) == 0) _IO_funlockfile (_fp)
+# endif
+#else
+# define _IO_peekc(_fp) _IO_peekc_unlocked (_fp)
+# define _IO_flockfile(_fp) /**/
+# define _IO_funlockfile(_fp) /**/
+# define _IO_ftrylockfile(_fp) /**/
+# define _IO_cleanup_region_start(_fct, _fp) /**/
+# define _IO_cleanup_region_end(_Doit) /**/
+#endif /* !_IO_MTSAFE_IO */
 
 #endif
 #endif
diff --git a/libio/libio.h b/libio/libio.h
index 2241c1471d..4fa9d74727 100644
--- a/libio/libio.h
+++ b/libio/libio.h
@@ -143,10 +143,9 @@
 
 struct _IO_jump_t;  struct _IO_FILE;
 
-/* Handle lock.  */
-#ifdef _IO_MTSAFE_IO
-/* _IO_lock_t defined in internal headers during the glibc build.  */
-#else
+/* During the build of glibc itself, _IO_lock_t will already have been
+   defined by internal headers.  */
+#ifndef _IO_lock_t_defined
 typedef void _IO_lock_t;
 #endif
 
@@ -441,21 +440,6 @@ extern void _IO_flockfile (_IO_FILE *) __THROW;
 extern void _IO_funlockfile (_IO_FILE *) __THROW;
 extern int _IO_ftrylockfile (_IO_FILE *) __THROW;
 
-#ifdef _IO_MTSAFE_IO
-# define _IO_peekc(_fp) _IO_peekc_locked (_fp)
-# define _IO_flockfile(_fp) \
-  if (((_fp)->_flags & _IO_USER_LOCK) == 0) _IO_flockfile (_fp)
-# define _IO_funlockfile(_fp) \
-  if (((_fp)->_flags & _IO_USER_LOCK) == 0) _IO_funlockfile (_fp)
-#else
-# define _IO_peekc(_fp) _IO_peekc_unlocked (_fp)
-# define _IO_flockfile(_fp) /**/
-# define _IO_funlockfile(_fp) /**/
-# define _IO_ftrylockfile(_fp) /**/
-# define _IO_cleanup_region_start(_fct, _fp) /**/
-# define _IO_cleanup_region_end(_Doit) /**/
-#endif /* !_IO_MTSAFE_IO */
-
 extern int _IO_vfscanf (_IO_FILE * __restrict, const char * __restrict,
 			_IO_va_list, int *__restrict);
 extern int _IO_vfprintf (_IO_FILE *__restrict, const char *__restrict,
diff --git a/sysdeps/generic/stdio-lock.h b/sysdeps/generic/stdio-lock.h
index 532bb5f23f..763c7d465a 100644
--- a/sysdeps/generic/stdio-lock.h
+++ b/sysdeps/generic/stdio-lock.h
@@ -22,6 +22,7 @@
 #include <libc-lock.h>
 
 __libc_lock_define_recursive (typedef, _IO_lock_t)
+#define _IO_lock_t_defined 1
 
 /* We need recursive (counting) mutexes.  */
 #ifdef _LIBC_LOCK_RECURSIVE_INITIALIZER
diff --git a/sysdeps/nptl/stdio-lock.h b/sysdeps/nptl/stdio-lock.h
index 35d6ce0a29..df749062ea 100644
--- a/sysdeps/nptl/stdio-lock.h
+++ b/sysdeps/nptl/stdio-lock.h
@@ -27,6 +27,7 @@
 #define _IO_lock_inexpensive	1
 
 typedef struct { int lock; int cnt; void *owner; } _IO_lock_t;
+#define _IO_lock_t_defined 1
 
 #define _IO_lock_initializer { LLL_LOCK_INITIALIZER, 0, NULL }
 
-- 
2.11.0