[PATCH] libio: Add test case for fflush

[Frédéric Bérat]

Hello,

This patch adds a test to verify that `fflush (FILE)` and `fflush (NULL)` are
semantically equivalent from the FILE perspective.

Fred.

--- 8< ---
Subject: [PATCH] libio: Add test case for fflush

Since one path uses _IO_SYNC and the other _IO_OVERFLOW, the newly added
test case verifies that `fflush (FILE)` and `fflush (NULL)` are
semantically equivalent from the FILE perspective.
---
 libio/Makefile     |   1 +
 libio/tst-fflush.c | 171 +++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 172 insertions(+)
 create mode 100644 libio/tst-fflush.c

diff --git a/libio/Makefile b/libio/Makefile
index ae704d8767..dff4b603e7 100644
--- a/libio/Makefile
+++ b/libio/Makefile
@@ -98,6 +98,7 @@ tests = \
   tst-fclose-unopened \
   tst-fclose-unopened2 \
   tst-fdopen-seek-failure \
+  tst-fflush \
   tst-fgetc-after-eof \
   tst-fgetwc \
   tst-fgetws \
diff --git a/libio/tst-fflush.c b/libio/tst-fflush.c
new file mode 100644
index 0000000000..498fa94884
--- /dev/null
+++ b/libio/tst-fflush.c
@@ -0,0 +1,171 @@
+/* Test that fflush (FILE) and fflush (NULL) are semantically equivalent.
+
+   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/>.  */
+
+/* A success on this test doesn't imply the effectiveness of fflush as
+   we can't ensure that the file wasn't already in the expected state
+   before the call of the function. It only ensures that, if the test
+   fails, fflush is broken.  */
+
+#include <fcntl.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <unistd.h>
+
+#include <sys/stat.h>
+#include <sys/mman.h>
+
+#include <support/check.h>
+#include <support/support.h>
+#include <support/temp_file.h>
+#include <support/test-driver.h>
+#include <support/xstdio.h>
+#include <support/xunistd.h>
+
+#define CONTENT_SZ_MAX 32
+#define TEST_FILE_COUNT 10
+
+#define FILE_FLUSH 0
+#define GLOBAL_FLUSH 1
+
+#define FILE_UNCHANGED 0
+#define FILE_CHANGED 1
+
+struct
+{
+  FILE *file;
+  char *name;
+  int fd;
+  char *mfile;
+} files[TEST_FILE_COUNT];
+
+static void
+base_init (int file)
+{
+  files[file].file = NULL;
+  files[file].fd = -1;
+  files[file].name = NULL;
+  files[file].mfile = NULL;
+}
+
+static void
+file_init (int file)
+{
+  int fd = -1;
+
+  base_init (file);
+
+  if (file >= TEST_FILE_COUNT)
+    return;
+
+  xclose (create_temp_file ("tst-fflush", &files[file].name));
+
+  fd = xopen (files[file].name, O_RDONLY, 0);
+  files[file].mfile = (char *) xmmap (NULL, CONTENT_SZ_MAX, PROT_READ,
+				      MAP_SHARED, fd);
+  xclose (fd);
+
+  files[file].file = xfopen (files[file].name, "w");
+  TEST_VERIFY_EXIT (files[file].file != NULL);
+  files[file].fd = fileno (files[file].file);
+}
+
+static void
+file_cleanup (int file)
+{
+  xfclose (files[file].file);
+  free (files[file].name);
+  xmunmap (files[file].mfile, CONTENT_SZ_MAX);
+
+  base_init (file);
+}
+
+static int
+file_changed (int to_check, int global_flush)
+{
+  struct stat stats = { };
+  bool content_matches = 0;
+  char expected[CONTENT_SZ_MAX] = { };
+
+  verbose_printf ("Check that %s (%d) exactly contains the data we put in\n",
+		  files[to_check].name, to_check);
+
+  /* File should contain "N:M" where both N and M are one digit exactly.  */
+  snprintf (expected, sizeof (expected), "%d:%d", global_flush, to_check);
+  content_matches
+    = (strncmp (files[to_check].mfile, expected, sizeof (expected)) == 0);
+
+  TEST_VERIFY_EXIT (content_matches != 0);
+
+  TEST_VERIFY_EXIT (fstat (files[to_check].fd, &stats) >= 0);
+  TEST_VERIFY_EXIT (stats.st_size == 3);
+
+  /* Not reached if the data doesn't match.  */
+  return FILE_CHANGED;
+}
+
+static void
+file_flush (int global_flush)
+{
+  for (int i = 0; i < TEST_FILE_COUNT; i++)
+    file_init (i);
+
+  /* Print a unique identifier in each file, that is not too long nor contain
+     new line to not trigger _IO_OVERFLOW/_IO_SYNC.  */
+  for (int i = 0; i < TEST_FILE_COUNT; i++)
+    fprintf (files[i].file, "%d:%d", global_flush, i);
+
+  if (global_flush)
+    {
+      fflush (NULL);
+    }
+  else
+    {
+      for (int i = 0; i < TEST_FILE_COUNT; i++)
+	fflush (files[i].file);
+    }
+
+  for (int i = 0; i < TEST_FILE_COUNT; i++)
+    {
+      int changed = file_changed (i, global_flush);
+
+      verbose_printf ("Check that file %s has been modified after fflush\n",
+		      files[i].name);
+      verbose_printf ("File %s; changed %d; global fflush %d\n",
+		      files[i].name, changed, !!global_flush);
+      TEST_VERIFY_EXIT (changed != FILE_UNCHANGED);
+    }
+
+  for (int i = 0; i < TEST_FILE_COUNT; i++)
+    file_cleanup (i);
+}
+
+static int
+do_test (void)
+{
+  verbose_printf ("Checking fflush(FILE)\n");
+  file_flush (FILE_FLUSH);
+
+  verbose_printf ("checking fflush(NULL)\n");
+  file_flush (GLOBAL_FLUSH);
+
+  return 0;
+}
+
+#include <support/test-driver.c>
-- 
2.46.0