misc: FUSE-based tests for mkstemp

The tests check that O_EXCL is used properly, that 0600 is used
as the mode, that the characters used are as expected, and that
the distribution of names generated is reasonably random.

The tests run very slowly on some kernel versions, so make them
xtests.

Reviewed-by: DJ Delorie <dj@redhat.com>

3 files changed, 422 insertions, 0 deletions

diff --git a/misc/Makefile b/misc/Makefile
index 7b7f8351bf..1422c95317 100644
--- a/misc/Makefile
+++ b/misc/Makefile
@@ -292,6 +292,12 @@ tests-static := tst-empty
 tests-internal += tst-fd_to_filename
 tests-static += tst-fd_to_filename
 
+# Tests with long run times.
+xtests += \
+  tst-mkstemp-fuse \
+  tst-mkstemp-fuse-parallel \
+  # xtests
+
 ifeq ($(run-built-tests),yes)
 ifeq (yes,$(build-shared))
 ifneq ($(PERL),no)
diff --git a/misc/tst-mkstemp-fuse-parallel.c b/misc/tst-mkstemp-fuse-parallel.c
new file mode 100644
index 0000000000..219f26cb3b
--- /dev/null
+++ b/misc/tst-mkstemp-fuse-parallel.c
@@ -0,0 +1,219 @@
+/* FUSE-based test for mkstemp.  Parallel collision statistics.
+   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 <stdlib.h>
+
+#include <array_length.h>
+#include <errno.h>
+#include <fcntl.h>
+#include <limits.h>
+#include <stdint.h>
+#include <stdio.h>
+#include <string.h>
+#include <support/check.h>
+#include <support/fuse.h>
+#include <support/support.h>
+#include <support/xthread.h>
+#include <support/xunistd.h>
+
+/* The number of subprocesses that call mkstemp.  */
+static pid_t processes[4];
+
+/* Enough space to record the expected number of replies (62**3) for
+   each process.  */
+enum { results_allocated = array_length (processes) * 62 * 62 * 62  };
+
+/* The thread will store the results there.  */
+static uint64_t *results;
+
+/* Currently used part of the results array.  */
+static size_t results_used;
+
+/* Fail with EEXIST (so that mkstemp tries again).  Record observed
+   names for later statistical analysis.  */
+static void
+fuse_thread (struct support_fuse *f, void *closure)
+{
+  struct fuse_in_header *inh;
+  while ((inh = support_fuse_next (f)) != NULL)
+    {
+      if (support_fuse_handle_mountpoint (f)
+          || (inh->nodeid == 1 && support_fuse_handle_directory (f)))
+        continue;
+      if (inh->opcode != FUSE_LOOKUP || results_used >= results_allocated)
+        {
+          support_fuse_reply_error (f, EIO);
+          continue;
+        }
+
+      char *name = support_fuse_cast (LOOKUP, inh);
+      TEST_COMPARE_BLOB (name, 3, "new", 3);
+      TEST_COMPARE (strlen (name), 9);
+      /* Extract 8 bytes of the name: 'w', the X replacements, and the
+         null terminator.  Treat it as an uint64_t for easy sorting
+         below.  Endianess does not matter because the relative order
+         of the entries is not important; sorting is only used to find
+         duplicates.  */
+      TEST_VERIFY_EXIT (results_used < results_allocated);
+      memcpy (&results[results_used], name + 2, 8);
+      ++results_used;
+      struct fuse_entry_out *out = support_fuse_prepare_entry (f, 2);
+      out->attr.mode = S_IFREG | 0600;
+      support_fuse_reply_prepared (f);
+    }
+}
+
+/* Used to sort the results array, to find duplicates.  */
+static int
+results_sort (const void *a1, const void *b1)
+{
+  const uint64_t *a = a1;
+  const uint64_t *b = b1;
+  if (*a < *b)
+    return -1;
+  if (*a == *b)
+    return 0;
+  return 1;
+}
+
+/* Number of occurrences of certain streak lengths.  */
+static size_t streak_lengths[6];
+
+/* Called for every encountered streak.  */
+static inline void
+report_streak (uint64_t current, size_t length)
+{
+  if (length > 1)
+    {
+      printf ("info: name \"ne%.8s\" repeats: %zu\n",
+              (char *) &current, length);
+      TEST_VERIFY_EXIT (length < array_length (streak_lengths));
+    }
+  TEST_VERIFY_EXIT (length < array_length (streak_lengths));
+  ++streak_lengths[length];
+}
+
+static int
+do_test (void)
+{
+  support_fuse_init ();
+
+  results = xmalloc (results_allocated * sizeof (*results));
+
+  struct shared
+  {
+    /* Used to synchronize the start of all subprocesses, to make it
+       more likely to expose concurrency-related bugs.  */
+    pthread_barrier_t barrier1;
+    pthread_barrier_t barrier2;
+
+    /* Filled in after fork.  */
+    char mountpoint[4096];
+  };
+
+  /* Used to synchronize the start of all subprocesses, to make it
+     more likely to expose concurrency-related bugs.  */
+  struct shared *pshared = support_shared_allocate (sizeof (*pshared));
+  {
+    pthread_barrierattr_t attr;
+    xpthread_barrierattr_init (&attr);
+    xpthread_barrierattr_setpshared (&attr, PTHREAD_PROCESS_SHARED);
+    xpthread_barrierattr_destroy (&attr);
+    xpthread_barrier_init (&pshared->barrier1, &attr,
+                           array_length (processes) + 1);
+    xpthread_barrier_init (&pshared->barrier2, &attr,
+                           array_length (processes) + 1);
+    xpthread_barrierattr_destroy (&attr);
+  }
+
+  for (int i = 0; i < array_length (processes); ++i)
+    {
+      processes[i] = xfork ();
+      if (processes[i] == 0)
+        {
+          /* Wait for mountpoint initialization.  */
+          xpthread_barrier_wait (&pshared->barrier1);
+          char *path = xasprintf ("%s/newXXXXXX", pshared->mountpoint);
+
+          /* Park this process until all processes have started.  */
+          xpthread_barrier_wait (&pshared->barrier2);
+          errno = 0;
+          TEST_COMPARE (mkstemp (path), -1);
+          TEST_COMPARE (errno, EEXIST);
+          free (path);
+          _exit (0);
+        }
+    }
+
+  /* Do this after the forking, to minimize initialization inteference.  */
+  struct support_fuse *f = support_fuse_mount (fuse_thread, NULL);
+  TEST_VERIFY (strlcpy (pshared->mountpoint, support_fuse_mountpoint (f),
+                        sizeof (pshared->mountpoint))
+               < sizeof (pshared->mountpoint));
+  xpthread_barrier_wait (&pshared->barrier1);
+
+  puts ("info: performing mkstemp calls");
+  xpthread_barrier_wait (&pshared->barrier2);
+
+  for (int i = 0; i < array_length (processes); ++i)
+    {
+      int status;
+      xwaitpid (processes[i], &status, 0);
+      TEST_COMPARE (status, 0);
+    }
+
+  support_fuse_unmount (f);
+  xpthread_barrier_destroy (&pshared->barrier2);
+  xpthread_barrier_destroy (&pshared->barrier1);
+
+  printf ("info: checking results (count %zu)\n", results_used);
+  qsort (results, results_used, sizeof (*results), results_sort);
+
+  uint64_t current = -1;
+  size_t streak = 0;
+  for (size_t i = 0; i < results_used; ++i)
+    if (results[i] == current)
+      ++streak;
+    else
+      {
+        report_streak (current, streak);
+        current = results[i];
+        streak = 1;
+      }
+  report_streak (current, streak);
+
+  puts ("info: repetition count distribution:");
+  for (int i = 1; i < array_length (streak_lengths); ++i)
+    printf ("  length %d: %zu\n", i, streak_lengths[i]);
+  /* Some arbitrary threshold, hopefully unlikely enough.  In over
+     260,000 runs of a simulation of this test, at most 26 pairs were
+     observed, and only one three-way collisions.  */
+  if (streak_lengths[2] > 30)
+    FAIL ("unexpected repetition count 2: %zu", streak_lengths[2]);
+  if (streak_lengths[3] > 2)
+    FAIL ("unexpected repetition count 3: %zu", streak_lengths[3]);
+  for (int i = 4; i < array_length (streak_lengths); ++i)
+    if (streak_lengths[i] > 0)
+      FAIL ("too many repeats of count %d: %zu", i, streak_lengths[i]);
+
+  free (results);
+
+  return 0;
+}
+
+#include <support/test-driver.c>
diff --git a/misc/tst-mkstemp-fuse.c b/misc/tst-mkstemp-fuse.c
new file mode 100644
index 0000000000..5ac6a6872a
--- /dev/null
+++ b/misc/tst-mkstemp-fuse.c
@@ -0,0 +1,197 @@
+/* FUSE-based test for mkstemp.
+   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 <stdlib.h>
+
+#include <errno.h>
+#include <fcntl.h>
+#include <stdint.h>
+#include <stdio.h>
+#include <string.h>
+#include <support/check.h>
+#include <support/fuse.h>
+#include <support/support.h>
+#include <support/xunistd.h>
+
+/* Set to true in do_test to cause the first FUSE_CREATE attempt to fail.  */
+static _Atomic bool simulate_creat_race;
+
+/* Basic tests with eventually successful creation.  */
+static void
+fuse_thread_basic (struct support_fuse *f, void *closure)
+{
+  char *previous_name = NULL;
+  int state = 0;
+  struct fuse_in_header *inh;
+  while ((inh = support_fuse_next (f)) != NULL)
+    {
+      if (support_fuse_handle_mountpoint (f)
+          || (inh->nodeid == 1 && support_fuse_handle_directory (f)))
+        continue;
+
+      switch (inh->opcode)
+        {
+        case FUSE_LOOKUP:
+          /* File does not exist initially.  */
+          TEST_COMPARE (inh->nodeid, 1);
+          if (simulate_creat_race)
+            {
+              if (state < 3)
+                ++state;
+              else
+                FAIL ("invalid state: %d", state);
+            }
+          else
+            {
+              TEST_COMPARE (state, 0);
+              state = 3;
+            }
+          support_fuse_reply_error (f, ENOENT);
+          break;
+        case FUSE_CREATE:
+          {
+            TEST_COMPARE (inh->nodeid, 1);
+            char *name;
+            struct fuse_create_in *p
+              = support_fuse_cast_name (CREATE, inh, &name);
+            /* Name follows after struct fuse_create_in.  */
+            TEST_COMPARE (p->flags & O_ACCMODE, O_RDWR);
+            TEST_VERIFY (p->flags & O_EXCL);
+            TEST_VERIFY (p->flags & O_CREAT);
+            TEST_COMPARE (p->mode & 07777, 0600);
+            TEST_VERIFY (S_ISREG (p->mode));
+            TEST_COMPARE_BLOB (name, 3, "new", 3);
+
+            if (state != 3 && simulate_creat_race)
+              {
+                ++state;
+                support_fuse_reply_error (f, EEXIST);
+              }
+            else
+              {
+                if (previous_name != NULL)
+                  /* This test has a very small probability of failure
+                     due to a harmless collision (one in 62**6 tests).  */
+                  TEST_VERIFY (strcmp (name, previous_name) != 0);
+                TEST_COMPARE (state, 3);
+                ++state;
+                struct fuse_entry_out *entry;
+                struct fuse_open_out *open;
+                support_fuse_prepare_create (f, 2, &entry, &open);
+                entry->attr.mode = S_IFREG | 0600;
+                support_fuse_reply_prepared (f);
+              }
+            free (previous_name);
+            previous_name = xstrdup (name);
+          }
+          break;
+        case FUSE_FLUSH:
+        case FUSE_RELEASE:
+          TEST_COMPARE (state, 4);
+          TEST_COMPARE (inh->nodeid, 2);
+          support_fuse_reply_empty (f);
+          break;
+        default:
+          support_fuse_reply_error (f, EIO);
+        }
+    }
+  free (previous_name);
+}
+
+/* Reply that all files exist.  */
+static void
+fuse_thread_eexist (struct support_fuse *f, void *closure)
+{
+  uint64_t counter = 0;
+  struct fuse_in_header *inh;
+  while ((inh = support_fuse_next (f)) != NULL)
+    {
+      if (support_fuse_handle_mountpoint (f)
+          || (inh->nodeid == 1 && support_fuse_handle_directory (f)))
+        continue;
+
+      switch (inh->opcode)
+        {
+        case FUSE_LOOKUP:
+          ++counter;
+          TEST_COMPARE (inh->nodeid, 1);
+          char *name = support_fuse_cast (LOOKUP, inh);
+          TEST_COMPARE_BLOB (name, 3, "new", 3);
+          TEST_COMPARE (strlen (name), 9);
+          for (int i = 3; i <= 8; ++i)
+            {
+              /* The glibc implementation uses letters and digits only.  */
+              char ch = name[i];
+              TEST_VERIFY (('0' <= ch && ch <= '9')
+                           || ('a' <= ch && ch <= 'z')
+                           || ('A' <= ch && ch <= 'Z'));
+            }
+          struct fuse_entry_out out =
+            {
+              .nodeid = 2,
+              .attr = {
+                .mode = S_IFREG | 0600,
+                .ino = 2,
+              },
+            };
+          support_fuse_reply (f, &out, sizeof (out));
+          break;
+        default:
+          support_fuse_reply_error (f, EIO);
+        }
+    }
+  /* Verify that mkstemp has retried a lot.  The current
+     implementation tries 62 * 62 * 62 times until it goves up.  */
+  TEST_VERIFY (counter >= 200000);
+}
+
+static int
+do_test (void)
+{
+  support_fuse_init ();
+
+  for (int do_simulate_creat_race = 0; do_simulate_creat_race < 2;
+       ++do_simulate_creat_race)
+    {
+      simulate_creat_race = do_simulate_creat_race;
+      printf ("info: testing with simulate_creat_race == %d\n",
+              (int) simulate_creat_race);
+      struct support_fuse *f = support_fuse_mount (fuse_thread_basic, NULL);
+      char *path = xasprintf ("%s/newXXXXXX", support_fuse_mountpoint (f));
+      int fd = mkstemp (path);
+      TEST_VERIFY (fd > 2);
+      xclose (fd);
+      free (path);
+      support_fuse_unmount (f);
+    }
+
+  puts ("info: testing EEXIST failure case for mkstemp");
+  {
+    struct support_fuse *f = support_fuse_mount (fuse_thread_eexist, NULL);
+    char *path = xasprintf ("%s/newXXXXXX", support_fuse_mountpoint (f));
+    errno = 0;
+    TEST_COMPARE (mkstemp (path), -1);
+    TEST_COMPARE (errno, EEXIST);
+    free (path);
+    support_fuse_unmount (f);
+  }
+
+  return 0;
+}
+
+#include <support/test-driver.c>