libio: Flush stream at freopen (BZ#21037)

As POSIX states [1] a freopen call should first flush the stream as if by a
call fflush.  C99 (n1256) and C11 (n1570) only states the function should
first close any file associated with the specific stream.  Although current
implementation only follow C specification, current BSD and other libc
implementation (musl) are in sync with POSIX and fflush the stream.

This patch change freopen{64} to fflush the stream before actually reopening
it (or returning if the stream does not support reopen).  It also changes the
Linux implementation to avoid a dynamic allocation on 'fd_to_filename'.

Checked on x86_64-linux-gnu.

	[BZ #21037]
	* libio/Makefile (tests): Add tst-memstream4 and tst-wmemstream4.
	* libio/freopen.c (freopen): Sync stream before reopen and adjust to
	new fd_to_filename interface.
	* libio/freopen64.c (freopen64): Likewise.
	* libio/tst-memstream.h: New file.
	* libio/tst-memstream4.c: Likewise.
	* libio/tst-wmemstream4.c: Likewise.
	* sysdeps/generic/fd_to_filename.h (fd_to_filename): Change signature.
	* sysdeps/unix/sysv/linux/fd_to_filename.h (fd_to_filename): Likewise
	and remove internal dynamic allocation.

[1] http://pubs.opengroup.org/onlinepubs/9699919799/

1 files changed, 68 insertions, 0 deletions

diff --git a/libio/tst-memstream.h b/libio/tst-memstream.h
new file mode 100644
index 0000000..b9b02bd
--- /dev/null
+++ b/libio/tst-memstream.h
@@ -0,0 +1,68 @@
+/* Common definitions for open_memstream tests.
+   Copyright (C) 2018 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <http://www.gnu.org/licenses/>.  */
+
+#include <mcheck.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <stdarg.h>
+#include <errno.h>
+
+#include <support/check.h>
+
+#ifdef TEST_WCHAR
+# include <wchar.h>
+
+/* Straighforward implementation so tst-memstream3 could use check
+   fwrite on open_memstream.  */
+static size_t __attribute__ ((used))
+fwwrite (const void *ptr, size_t size, size_t nmemb, FILE *arq)
+{
+  const wchar_t *wcs = (const wchar_t*) (ptr);
+  for (size_t s = 0; s < size; s++)
+    {
+      for (size_t n = 0; n < nmemb; n++)
+        if (fputwc (wcs[n], arq) == WEOF)
+          return n;
+    }
+  return size * nmemb;
+}
+
+# define CHAR_T wchar_t
+# define W(o) L##o
+# define OPEN_MEMSTREAM open_wmemstream
+# define PRINTF wprintf
+# define FWRITE fwwrite
+# define FPUTC  fputwc
+# define FPUTS  fputws
+# define STRCMP wcscmp
+# define STRLEN wcslen
+#else
+# define CHAR_T char
+# define W(o) o
+# define OPEN_MEMSTREAM open_memstream
+# define PRINTF printf
+# define FWRITE fwrite
+# define FPUTC fputc
+# define FPUTS  fputs
+# define STRCMP strcmp
+# define STRLEN strlen
+#endif
+
+#define S(s) S1 (s)
+#define S1(s) #s