Add freopen special-case tests: thread cancellation

Add tests of freopen adding or removing "c" (non-cancelling I/O) from
the mode string (so completing my planned tests of freopen with
different features used in the mode strings).  Note that it's in the
nature of the uncertain time at which cancellation might act (possibly
during freopen, possibly during subsequent reads) that these can leak
memory or file descriptors, so these do not include leak tests.

Tested for x86_64.

stdio-common/Makefile

@@ -224,10 +224,12 @@ tests := \
   tst-freopen4 \
   tst-freopen5 \
   tst-freopen6 \
+  tst-freopen7 \
   tst-freopen64-2 \
   tst-freopen64-3 \
   tst-freopen64-4 \
   tst-freopen64-6 \
+  tst-freopen64-7 \
   tst-fseek \
   tst-fwrite \
   tst-fwrite-memstrm \
@@ -623,3 +625,6 @@ $(objpfx)tst-setvbuf1-cmp.out: tst-setvbuf1.expect $(objpfx)tst-setvbuf1.out
 
 $(objpfx)tst-printf-round: $(libm)
 $(objpfx)tst-scanf-round: $(libm)
+
+$(objpfx)tst-freopen7: $(shared-thread-library)
+$(objpfx)tst-freopen64-7: $(shared-thread-library)

stdio-common/tst-freopen64-7.c

@@ -0,0 +1,2 @@
+#define FREOPEN freopen64
+#include <tst-freopen7-main.c>

stdio-common/tst-freopen7-main.c

@@ -0,0 +1,155 @@
+/* Test freopen cancellation handling.
+   Copyright (C) 2024 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
+   <https://www.gnu.org/licenses/>.  */
+
+#include <errno.h>
+#include <fcntl.h>
+#include <mcheck.h>
+#include <pthread.h>
+#include <semaphore.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <wchar.h>
+
+#include <support/check.h>
+#include <support/file_contents.h>
+#include <support/support.h>
+#include <support/temp_file.h>
+#include <support/test-driver.h>
+#include <support/xstdio.h>
+#include <support/xthread.h>
+#include <support/xunistd.h>
+
+char *file1, *file2, *file3, *fifo;
+
+sem_t sem;
+
+void *
+test_rc_to_r (void *p)
+{
+  int ret;
+  FILE *fp, *fp2;
+  ret = sem_post (&sem);
+  TEST_VERIFY_EXIT (ret == 0);
+  fp = xfopen (file1, "rc");
+  for (int i = 0; i < 1000000; i++)
+    {
+      fgetc (fp);
+      fseek (fp, 0, SEEK_SET);
+    }
+  fp2 = xfopen (file3, "wc");
+  fputs ("rc_to_r got to freopen", fp2);
+  xfclose (fp2);
+  /* Cancellation should occur at some point from here onwards
+     (possibly leaking memory and file descriptors associated with the
+     FILE).  */
+  fp = FREOPEN (file2, "r", fp);
+  TEST_VERIFY_EXIT (fp != NULL);
+  for (;;)
+    {
+      fgetc (fp);
+      fseek (fp, 0, SEEK_SET);
+    }
+}
+
+void *
+test_r_to_rc (void *p)
+{
+  int ret;
+  FILE *fp;
+  fp = xfopen (file1, "r");
+  fp = FREOPEN (fifo, "rc", fp);
+  TEST_VERIFY_EXIT (fp != NULL);
+  ret = sem_post (&sem);
+  TEST_VERIFY_EXIT (ret == 0);
+  /* No cancellation should occur for I/O on fifo.  */
+  ret = fgetc (fp);
+  /* At this point, the other thread has called pthread_cancel and
+     then written a byte to the fifo, so this thread is cancelled at
+     the next cancellation point.  */
+  TEST_VERIFY (ret == 'x');
+  xfclose (fp);
+  fp = xfopen (file3, "wc");
+  fputs ("r_to_rc got to fclose", fp);
+  xfclose (fp);
+  pthread_testcancel ();
+  FAIL_EXIT1 ("test_r_to_rc not cancelled\n");
+}
+
+int
+do_test (void)
+{
+  char *temp_dir = support_create_temp_directory ("tst-freopen-cancel");
+  file1 = xasprintf ("%s/file1", temp_dir);
+  support_write_file_string (file1, "file1");
+  add_temp_file (file1);
+  file2 = xasprintf ("%s/file2", temp_dir);
+  support_write_file_string (file2, "file2");
+  add_temp_file (file2);
+  file3 = xasprintf ("%s/file3", temp_dir);
+  support_write_file_string (file3, "file3");
+  add_temp_file (file3);
+  fifo = xasprintf ("%s/fifo", temp_dir);
+  xmkfifo (fifo, 0666);
+  add_temp_file (fifo);
+  int ret;
+  pthread_t thr;
+  void *retval;
+
+  /* Test changing to/from c (cancellation disabled).  */
+
+  verbose_printf ("Testing rc -> r\n");
+  ret = sem_init (&sem, 0, 0);
+  TEST_VERIFY_EXIT (ret == 0);
+  thr = xpthread_create (NULL, test_rc_to_r, NULL);
+  ret = sem_wait (&sem);
+  TEST_VERIFY_EXIT (ret == 0);
+  xpthread_cancel (thr);
+  ret = pthread_join (thr, &retval);
+  TEST_COMPARE (ret, 0);
+  TEST_VERIFY (retval == PTHREAD_CANCELED);
+  TEST_OPEN_AND_COMPARE_FILE_STRING (file3, "rc_to_r got to freopen");
+
+  verbose_printf ("Testing r -> rc\n");
+  ret = sem_init (&sem, 0, 0);
+  TEST_VERIFY_EXIT (ret == 0);
+  thr = xpthread_create (NULL, test_r_to_rc, NULL);
+  FILE *fp = xfopen (fifo, "w");
+  ret = sem_wait (&sem);
+  TEST_VERIFY_EXIT (ret == 0);
+  /* This call happens while, or before, the other thread is waiting
+     to read a character from the fifo.  It thus verifies that
+     cancellation does not occur from the fgetc call in that thread
+     (it should instead occur only in pthread_testcancel call),
+     because the expected string is only written to file3 after that
+     thread closes the fifo.  */
+  xpthread_cancel (thr);
+  fputc ('x', fp);
+  xfclose (fp);
+  ret = pthread_join (thr, &retval);
+  TEST_COMPARE (ret, 0);
+  TEST_VERIFY (retval == PTHREAD_CANCELED);
+  TEST_OPEN_AND_COMPARE_FILE_STRING (file3, "r_to_rc got to fclose");
+
+  free (temp_dir);
+  free (file1);
+  free (file2);
+  free (file3);
+  return 0;
+}
+
+#include <support/test-driver.c>

stdio-common/tst-freopen7.c

@@ -0,0 +1,2 @@
+#define FREOPEN freopen
+#include <tst-freopen7-main.c>