dirent: Add tst-readdir-long

It tests long names and ENAMETOOLONG handling, specifically
for readdir_r.  This is a regression test for bug 14699,
bug 32124, and bug 32128.

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

dirent/Makefile

@@ -61,6 +61,7 @@ tests := \
   tst-closedir-leaks \
   tst-fdopendir \
   tst-fdopendir2 \
+  tst-readdir-long \
   tst-scandir \
   tst-scandir64 \
   tst-seekdir \

dirent/tst-readdir-long.c

@@ -0,0 +1,231 @@
+/* Test readdir (+variants) behavior with file names of varying length.
+   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 <errno.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <support/check.h>
+#include <support/fuse.h>
+#include <support/support.h>
+#include <support/xdirent.h>
+#include <support/readdir.h>
+
+/* If positive, at this length an EMSGSIZE error is injected.  */
+static _Atomic int inject_error_at_length;
+
+/* Return a file name, LENGTH bytes long.  */
+static char *
+name_of_length (size_t length)
+{
+  char *result = xmalloc (length + 1);
+  unsigned int prefix = snprintf (result, length + 1, "%zu-", length);
+  for (size_t i = prefix; i < length; ++i)
+    result[i] = 'A' + ((length + i) % 26);
+  result[length] = '\0';
+  return result;
+}
+
+/* Add the directory entry at OFFSET to the stream D.  */
+static uint64_t
+add_directory_entry (struct support_fuse_dirstream *d, uint64_t offset)
+{
+  unsigned int length = offset + 1;
+  if (length > 1000)
+    /* Longer than what is possible to produce with 256
+       UTF-8-encoded Unicode code points.  */
+    return 0;
+
+  char *to_free = NULL;
+  const char *name;
+  uint64_t ino = 1000 + length; /* Arbitrary value, distinct from 1.  */
+  uint32_t type = DT_REG;
+  if (offset <= 1)
+    {
+      type = DT_DIR;
+      name = ".." + !offset;    /* "." or "..".  */
+      ino = 1;
+    }
+  else if (length == 1000)
+    name = "short";
+  else
+    {
+      to_free = name_of_length (length);
+      name = to_free;
+    }
+
+  ++offset;
+  bool added = support_fuse_dirstream_add (d, ino, offset, type, name);
+  free (to_free);
+  if (added)
+    return offset;
+  else
+    return 0;
+}
+
+/* Set to true if getdents64 should produce only one entry.  */
+static _Atomic 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;
+              if (inject_error_at_length == offset + 1)
+                support_fuse_reply_error (f, EMSGSIZE);
+              else
+                {
+                  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
+                          /* Error will be reported at next READDIR.  */
+                          || offset + 1 == inject_error_at_length)
+                        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);
+        }
+    }
+}
+
+/* Run the tests for the specified readdir variant OP.  */
+static void
+run_readdir_tests (struct support_fuse *f, enum support_readdir_op op)
+{
+  printf ("info: testing %s (inject_error=%d unbuffered=%d)\n",
+          support_readdir_function (op), inject_error_at_length,
+          (int) one_entry_per_getdents64);
+
+  bool testing_r = support_readdir_r_variant (op);
+
+  DIR *dir = xopendir (support_fuse_mountpoint (f));
+  struct support_dirent e = { 0, };
+  TEST_VERIFY (support_readdir (dir, op, &e));
+  TEST_COMPARE (e.d_ino, 1);
+  TEST_COMPARE_STRING (e.d_name, ".");
+
+  TEST_VERIFY (support_readdir (dir, op, &e));
+  TEST_COMPARE (e.d_ino, 1);
+  TEST_COMPARE_STRING (e.d_name, "..");
+
+  for (unsigned int i = 3; i < 1000; ++i)
+    {
+      if (i == inject_error_at_length)
+        /* Error expected below.  */
+        break;
+
+      if (i >= sizeof ((struct dirent) { 0, }.d_name) && testing_r)
+        /* This is a readir_r test.  The longer names are not
+           available because they do not fit into struct dirent.  */
+        break;
+
+      char *expected_name = name_of_length (i);
+      TEST_COMPARE (strlen (expected_name), i);
+      TEST_VERIFY (support_readdir (dir, op, &e));
+      TEST_COMPARE (e.d_ino, 1000 + i);
+      TEST_COMPARE_STRING (e.d_name, expected_name);
+      free (expected_name);
+    }
+
+  if (inject_error_at_length == 0)
+    {
+      /* Check that the ENAMETOOLONG error does not prevent reading a
+         later short name.  */
+      TEST_VERIFY (support_readdir (dir, op, &e));
+      TEST_COMPARE (e.d_ino, 2000);
+      TEST_COMPARE_STRING (e.d_name, "short");
+
+      if (testing_r)
+        /* An earlier name was too long.  */
+        support_readdir_expect_error (dir, op, ENAMETOOLONG);
+      else
+        /* Entire directory read without error.  */
+        TEST_VERIFY (!support_readdir (dir, op, &e));
+    }
+  else
+    support_readdir_expect_error (dir, op, EMSGSIZE);
+
+  free (e.d_name);
+  xclosedir (dir);
+}
+
+/* Run all readdir variants for both fully-buffered an unbuffered
+   (one-at-a-time) directory streams.  */
+static void
+run_fully_buffered_and_singleton_buffers (struct support_fuse *f)
+{
+  for (int do_one_entry = 0; do_one_entry < 2; ++do_one_entry)
+    {
+      one_entry_per_getdents64 = do_one_entry;
+      for (enum support_readdir_op op = 0; op <= support_readdir_op_last();
+           ++op)
+        run_readdir_tests (f, op);
+    }
+}
+
+static int
+do_test (void)
+{
+  /* Smoke test for name_of_length.  */
+  {
+    char *name = name_of_length (5);
+    TEST_COMPARE_STRING (name, "5-HIJ");
+    free (name);
+
+    name = name_of_length (6);
+    TEST_COMPARE_STRING (name, "6-IJKL");
+    free (name);
+  }
+
+  support_fuse_init ();
+  struct support_fuse *f = support_fuse_mount (fuse_thread, NULL);
+
+  run_fully_buffered_and_singleton_buffers (f);
+
+  inject_error_at_length = 100;
+  run_fully_buffered_and_singleton_buffers (f);
+
+  inject_error_at_length = 300;
+  run_fully_buffered_and_singleton_buffers (f);
+
+  support_fuse_unmount (f);
+  return 0;
+}
+
+#include <support/test-driver.c>