Remove _IO_MTSAFE_IO from public headers.

_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 most important thing it
controlled in there was 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.

_IO_MTSAFE_IO also controlled the definitions of a handful of macros
that _might_ count as part of the public libio.h interface.  They are
now unconditionally given their non-_IO_MTSAFE_IO definition in
libio/libio.h, and include/libio.h redefines them with the
_IO_MTSAFE_IO definition.  This should minimize the odds of breaking
old software that actually uses those macros.

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. Unconditionally use the
	non-_IO_MTSAFE_IO definitions for _IO_peekc, _IO_flockfile,
	_IO_funlockfile, and _IO_ftrylockfile.  Only define
	_IO_cleanup_region_start and _IO_cleanup_region_end if not
	already defined.
	* include/libio.h: If _IO_MTSAFE_IO is defined, redefine
        _IO_peekc, _IO_flockfile, _IO_funlockfile, and _IO_ftrylockfile
        appropriately.
	* sysdeps/generic/stdio-lock.h, sysdeps/nptl/stdio-lock.h:
	Define _IO_lock_t_defined after defining _IO_lock_t.

ChangeLog

@@ -1,3 +1,17 @@
+2017-05-11  Zack Weinberg  <zackw@panix.com>
+
+	* libio/libio.h: Condition dummy definition of _IO_lock_t on
+	_IO_lock_t_defined, not _IO_MTSAFE_IO. Unconditionally use the
+	non-_IO_MTSAFE_IO definitions for _IO_peekc, _IO_flockfile,
+	_IO_funlockfile, and _IO_ftrylockfile.  Only define
+	_IO_cleanup_region_start and _IO_cleanup_region_end if not
+	already defined.
+	* include/libio.h: If _IO_MTSAFE_IO is defined, redefine
+	_IO_peekc, _IO_flockfile, _IO_funlockfile, and _IO_ftrylockfile
+	appropriately.
+	* sysdeps/generic/stdio-lock.h, sysdeps/nptl/stdio-lock.h:
+	Define _IO_lock_t_defined after defining _IO_lock_t.
+
 2016-05-10  Adhemerval Zanella  <adhemerval.zanella@linaro.org>
 
 	* sysdeps/powerpc/powerpc32/backtrace.c (is_sigtramp_address): Use

include/libio.h

@@ -21,16 +21,25 @@ libc_hidden_proto (_IO_sgetn)
 libc_hidden_proto (_IO_vfprintf)
 libc_hidden_proto (_IO_vfscanf)
 
-#if defined _IO_MTSAFE_IO && _IO_lock_inexpensive
+#ifdef _IO_MTSAFE_IO
+# undef _IO_peekc
 # 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
+# undef _IO_ftrylockfile
+
+# 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
+#endif /* _IO_MTSAFE_IO */
 
 #endif
 #endif

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
 
@@ -441,20 +440,16 @@ 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 */
+#define _IO_peekc(_fp) _IO_peekc_unlocked (_fp)
+#define _IO_flockfile(_fp) /**/
+#define _IO_funlockfile(_fp) /**/
+#define _IO_ftrylockfile(_fp) /**/
+#ifndef _IO_cleanup_region_start
+#define _IO_cleanup_region_start(_fct, _fp) /**/
+#endif
+#ifndef _IO_cleanup_region_end
+#define _IO_cleanup_region_end(_Doit) /**/
+#endif
 
 extern int _IO_vfscanf (_IO_FILE * __restrict, const char * __restrict,
 			_IO_va_list, int *__restrict);

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

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 }