dirent: Add tst-rewinddir

It verifies that rewinddir allows restarting the directory
iteration.

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

dirent/Makefile

@@ -62,6 +62,7 @@ tests := \
   tst-fdopendir \
   tst-fdopendir2 \
   tst-readdir-long \
+  tst-rewinddir \
   tst-scandir \
   tst-scandir64 \
   tst-seekdir \

dirent/tst-rewinddir.c

@@ -0,0 +1,207 @@
+/* Test for rewinddir, using FUSE.
+   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 <dirent.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <support/check.h>
+#include <support/fuse.h>
+#include <support/readdir.h>
+#include <support/support.h>
+#include <support/xdirent.h>
+
+/* Return the file name at the indicated directory offset.  */
+static char *
+name_at_offset (unsigned int offset)
+{
+  if (offset <= 1)
+    return xstrdup (".." + !offset); /* "." or "..".  */
+  else
+    /* Pad the name with a lot of zeros, so that the dirent buffer gets
+       filled more quickly.  */
+    return xasprintf ("file%0240u", offset);
+}
+
+/* This many directory entries, including "." and "..".  */
+enum { directory_entries = 200 };
+
+/* Add the directory entry at OFFSET to the stream D.  */
+static uint64_t
+add_directory_entry (struct support_fuse_dirstream *d, uint64_t offset)
+{
+  if (offset >= directory_entries)
+    return 0;
+
+  char *name = name_at_offset (offset);
+  uint64_t ino = 1000 + offset; /* Arbitrary value, distinct from 1.  */
+  uint32_t type = DT_REG;
+  if (offset <= 1)
+    {
+      type = DT_DIR;
+      ino = 1;
+    }
+
+  ++offset;
+  bool added = support_fuse_dirstream_add (d, ino, offset, type, name);
+  free (name);
+  if (added)
+    return offset;
+  else
+    return 0;
+}
+
+/* Set to true if getdents64 should produce only one entry.  */
+static bool one_entry_per_getdents64;
+
+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;
+      switch (inh->opcode)
+        {
+        case FUSE_READDIR:
+          if (inh->nodeid == 1)
+            {
+              uint64_t offset = support_fuse_cast (READ, inh)->offset;
+              struct support_fuse_dirstream *d
+                = support_fuse_prepare_readdir (f);
+              while (true)
+                {
+                  offset = add_directory_entry (d, offset);
+                  if (offset == 0 || one_entry_per_getdents64)
+                    break;
+                }
+              support_fuse_reply_prepared (f);
+            }
+          else
+            support_fuse_reply_error (f, EIO);
+          break;
+        default:
+          FAIL ("unexpected event %s", support_fuse_opcode (inh->opcode));
+          support_fuse_reply_error (f, EIO);
+        }
+    }
+}
+
+/* Lists the entire directory from start to end.  */
+static void
+verify_directory (DIR *dir, enum support_readdir_op op)
+{
+  struct support_dirent e = { 0, };
+
+  TEST_VERIFY (support_readdir (dir, op, &e));
+  TEST_COMPARE_STRING (e.d_name, ".");
+  TEST_VERIFY (support_readdir (dir, op, &e));
+  TEST_COMPARE_STRING (e.d_name, "..");
+  for (int i = 2; i < directory_entries; ++i)
+    {
+      char *expected = name_at_offset (i);
+      TEST_VERIFY (support_readdir (dir, op, &e));
+      TEST_COMPARE_STRING (e.d_name, expected);
+      free (expected);
+    }
+  TEST_VERIFY (!support_readdir (dir, op, &e));
+  free (e.d_name);
+}
+
+/* Run tests with rewinding after ENTRIES readdir calls.  */
+static void
+rewind_after (unsigned int rewind_at)
+{
+  for (enum support_readdir_op op = 0; op <= support_readdir_op_last (); ++op)
+    {
+      printf ("info: testing %s (rewind_at=%u)\n",
+              support_readdir_function (op), rewind_at);
+
+      struct support_fuse *f = support_fuse_mount (fuse_thread, NULL);
+      DIR *dir = xopendir (support_fuse_mountpoint (f));
+      struct support_dirent e = { 0, };
+
+      switch (rewind_at)
+        {
+        case 0:
+          break;
+        case 1:
+          TEST_VERIFY (support_readdir (dir, op, &e));
+          TEST_COMPARE_STRING (e.d_name, ".");
+          break;
+        default:
+          TEST_VERIFY (support_readdir (dir, op, &e));
+          TEST_COMPARE_STRING (e.d_name, ".");
+          TEST_VERIFY (support_readdir (dir, op, &e));
+          TEST_COMPARE_STRING (e.d_name, "..");
+          for (int i = 2; i < directory_entries; ++i)
+            {
+              if (i == rewind_at)
+                break;
+              char *expected = name_at_offset (i);
+              TEST_VERIFY (support_readdir (dir, op, &e));
+              TEST_COMPARE_STRING (e.d_name, expected);
+              free (expected);
+            }
+          break;
+        }
+
+      errno = 0;
+      rewinddir (dir);
+      TEST_COMPARE (errno, 0);
+      verify_directory (dir, op);
+
+      free (e.d_name);
+      xclosedir (dir);
+      support_fuse_unmount (f);
+    }
+}
+
+static int
+do_test (void)
+{
+  support_fuse_init ();
+
+  /* One pass without rewinding to verify that the generated directory
+     content matches expectations.  */
+  {
+    struct support_fuse *f = support_fuse_mount (fuse_thread, NULL);
+    DIR *dir = xopendir (support_fuse_mountpoint (f));
+    verify_directory (dir, SUPPORT_READDIR64);
+    xclosedir (dir);
+    support_fuse_unmount (f);
+  }
+
+  for (int do_unbuffered = 0; do_unbuffered < 2; ++do_unbuffered)
+    {
+      one_entry_per_getdents64 = do_unbuffered;
+
+      for (int i = 0; i < 20; ++i)
+        rewind_after (i);
+      rewind_after (50);
+      rewind_after (100);
+      rewind_after (150);
+      rewind_after (180);
+      rewind_after (199);
+    }
+
+  return 0;
+}
+
+#include <support/test-driver.c>