[BZ 1190] Make EOF sticky in stdio.

C99 specifies that the EOF condition on a file is "sticky": once EOF
has been encountered, all subsequent reads should continue to return
EOF until the file is closed or something clears the "end-of-file
indicator" (e.g. fseek, clearerr).  This is arguably a change from
C89, where the wording was ambiguous; the BSDs always had sticky EOF,
but the System V lineage would attempt to read from the underlying fd
again.  GNU libc has followed System V for as long as we've been
using libio, but nowadays C99 conformance and BSD compatibility are
more important than System V compatibility.

You might wonder if changing the _underflow impls is sufficient to
apply the C99 semantics to all of the many stdio functions that
perform input.  It should be enough to cover all paths to _IO_SYSREAD,
and the only other functions that call _IO_SYSREAD are the _seekoff
impls, which is OK because seeking clears EOF, and the _xsgetn impls,
which, as far as I can tell, are unused within glibc.

The test programs in this patch use a pseudoterminal to set up the
necessary conditions.  To facilitate this I added a new test-support
function that sets up a pair of pty file descriptors for you; it's
almost the same as BSD openpty, the only differences are that it
allocates the optionally-returned tty pathname with malloc, and that
it crashes if anything goes wrong.

	[BZ #1190]
        [BZ #19476]
	* libio/fileops.c (_IO_new_file_underflow): Return EOF immediately
	if the _IO_EOF_SEEN bit is already set; update commentary.
	* libio/oldfileops.c (_IO_old_file_underflow): Likewise.
	* libio/wfileops.c (_IO_wfile_underflow): Likewise.

	* support/support_openpty.c, support/tty.h: New files.
	* support/Makefile (libsupport-routines): Add support_openpty.

	* libio/tst-fgetc-after-eof.c, wcsmbs/test-fgetwc-after-eof.c:
	New test cases.
	* libio/Makefile (tests): Add tst-fgetc-after-eof.
	* wcsmbs/Makefile (tests): Add tst-fgetwc-after-eof.

1 files changed, 109 insertions, 0 deletions

diff --git a/support/support_openpty.c b/support/support_openpty.c
new file mode 100644
index 0000000000..ac779ab91e
--- /dev/null
+++ b/support/support_openpty.c
@@ -0,0 +1,109 @@
+/* Open a pseudoterminal.
+   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 <support/tty.h>
+#include <support/check.h>
+#include <support/support.h>
+
+#include <errno.h>
+#include <stdlib.h>
+#include <string.h>
+
+#include <fcntl.h>
+#include <termios.h>
+#include <sys/ioctl.h>
+#include <unistd.h>
+
+/* As ptsname, but allocates space for an appropriately-sized string
+   using malloc.  */
+static char *
+xptsname (int fd)
+{
+  int rv;
+  size_t buf_len = 128;
+  char *buf = xmalloc (buf_len);
+  for (;;)
+    {
+      rv = ptsname_r (fd, buf, buf_len);
+      if (rv)
+        FAIL_EXIT1 ("ptsname_r: %s", strerror (errno));
+
+      if (memchr (buf, '\0', buf_len))
+        return buf; /* ptsname succeeded and the buffer was not truncated */
+
+      buf_len *= 2;
+      buf = xrealloc (buf, buf_len);
+    }
+}
+
+void
+support_openpty (int *a_outer, int *a_inner, char **a_name,
+                 const struct termios *termp,
+                 const struct winsize *winp)
+{
+  int outer = -1, inner = -1;
+  char *namebuf = 0;
+
+  outer = posix_openpt (O_RDWR | O_NOCTTY);
+  if (outer == -1)
+    FAIL_EXIT1 ("posix_openpt: %s", strerror (errno));
+
+  if (grantpt (outer))
+    FAIL_EXIT1 ("grantpt: %s", strerror (errno));
+
+  if (unlockpt (outer))
+    FAIL_EXIT1 ("unlockpt: %s", strerror (errno));
+
+
+#ifdef TIOCGPTPEER
+  inner = ioctl (outer, TIOCGPTPEER, O_RDWR | O_NOCTTY);
+#endif
+  if (inner == -1)
+    {
+      /* The kernel might not support TIOCGPTPEER, fall back to open
+         by name.  */
+      namebuf = xptsname (outer);
+      inner = open (namebuf, O_RDWR | O_NOCTTY);
+      if (inner == -1)
+        FAIL_EXIT1 ("%s: %s", namebuf, strerror (errno));
+    }
+
+  if (termp)
+    {
+      if (tcsetattr (inner, TCSAFLUSH, termp))
+        FAIL_EXIT1 ("tcsetattr: %s", strerror (errno));
+    }
+#ifdef TIOCSWINSZ
+  if (winp)
+    {
+      if (ioctl (inner, TIOCSWINSZ, winp))
+        FAIL_EXIT1 ("TIOCSWINSZ: %s", strerror (errno));
+    }
+#endif
+
+  if (a_name)
+    {
+      if (!namebuf)
+        namebuf = xptsname (outer);
+      *a_name = namebuf;
+    }
+  else
+    free (namebuf);
+  *a_outer = outer;
+  *a_inner = inner;
+}