[PATCH v2 1/3] support: Add helpers to create paths longer than PATH_MAX

[Siddhesh Poyarekar <siddhesh@sourceware.org>]

Add new helpers support_create_and_chdir_toolong_temp_directory and
support_chdir_toolong_temp_directory to create and descend into
directory trees longer than PATH_MAX.

Signed-off-by: Siddhesh Poyarekar <siddhesh@sourceware.org>
---
 support/temp_file.c | 173 +++++++++++++++++++++++++++++++++++++++++---
 support/temp_file.h |   9 +++
 2 files changed, 173 insertions(+), 9 deletions(-)

diff --git a/support/temp_file.c b/support/temp_file.c
index e7bb8aadb9..59060e573f 100644
--- a/support/temp_file.c
+++ b/support/temp_file.c
@@ -1,5 +1,6 @@
 /* Temporary file handling for tests.
    Copyright (C) 1998-2022 Free Software Foundation, Inc.
+   Copyright The GNU Tools Authors.
    This file is part of the GNU C Library.
 
    The GNU C Library is free software; you can redistribute it and/or
@@ -20,15 +21,17 @@
    some 32-bit platforms. */
 #define _FILE_OFFSET_BITS 64
 
+#include <support/check.h>
 #include <support/temp_file.h>
 #include <support/temp_file-internal.h>
 #include <support/support.h>
 
+#include <errno.h>
 #include <paths.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
-#include <unistd.h>
+#include <xunistd.h>
 
 /* List of temporary files.  */
 static struct temp_name_list
@@ -36,14 +39,32 @@ static struct temp_name_list
   struct temp_name_list *next;
   char *name;
   pid_t owner;
+  bool toolong;
 } *temp_name_list;
 
 /* Location of the temporary files.  Set by the test skeleton via
    support_set_test_dir.  The string is not be freed.  */
 static const char *test_dir = _PATH_TMP;
 
-void
-add_temp_file (const char *name)
+/* Name of subdirectories in a too long temporary directory tree.  */
+static char *toolong_subdir;
+static bool toolong_subdir_initialized;
+
+/* Return the maximum size of path on the target.  */
+static inline size_t
+get_path_max (void)
+{
+#ifdef PATH_MAX
+  return PATH_MAX;
+#else
+  size_t path_max = pathconf ("/", _PC_PATH_MAX);
+  return (path_max < 0 ? 1024
+	  : path_max <= PTRDIFF_MAX ? path_max : PTRDIFF_MAX);
+#endif
+}
+
+static void
+add_temp_file_internal (const char *name, bool toolong)
 {
   struct temp_name_list *newp
     = (struct temp_name_list *) xcalloc (sizeof (*newp), 1);
@@ -53,12 +74,19 @@ add_temp_file (const char *name)
       newp->name = newname;
       newp->next = temp_name_list;
       newp->owner = getpid ();
+      newp->toolong = toolong;
       temp_name_list = newp;
     }
   else
     free (newp);
 }
 
+void
+add_temp_file (const char *name)
+{
+  add_temp_file_internal (name, false);
+}
+
 int
 create_temp_file_in_dir (const char *base, const char *dir, char **filename)
 {
@@ -90,8 +118,8 @@ create_temp_file (const char *base, char **filename)
   return create_temp_file_in_dir (base, test_dir, filename);
 }
 
-char *
-support_create_temp_directory (const char *base)
+static char *
+create_temp_directory_internal (const char *base, bool toolong)
 {
   char *path = xasprintf ("%s/%sXXXXXX", test_dir, base);
   if (mkdtemp (path) == NULL)
@@ -99,16 +127,132 @@ support_create_temp_directory (const char *base)
       printf ("error: mkdtemp (\"%s\"): %m", path);
       exit (1);
     }
-  add_temp_file (path);
+  add_temp_file_internal (path, toolong);
   return path;
 }
 
-/* Helper functions called by the test skeleton follow.  */
+char *
+support_create_temp_directory (const char *base)
+{
+  return create_temp_directory_internal (base, false);
+}
+
+static void
+ensure_toolong_subdir_initialized (void)
+{
+  if (!toolong_subdir_initialized)
+    FAIL_EXIT1 ("uninitialized toolong directory tree\n");
+}
+
+static void
+initialize_toolong_subdir (void)
+{
+  size_t sz = NAME_MAX;
+  char testname[NAME_MAX];
+  int ret;
+
+  if (toolong_subdir_initialized)
+    return;
+
+  memset (testname, 'X', sz - 1);
+
+  /* Explore the name limit on the file system.  This should typically be
+     NAME_MAX, but it could be less on some fuse filesystems.  */
+  do
+    {
+      struct stat statbuf;
+
+      testname[sz - 1] = '\0';
+      ret = stat (testname, &statbuf);
+    }
+  while (ret != 0 && errno == ENAMETOOLONG && (sz = sz / 2) > 0);
+
+  if (ret != 0 && errno == ENAMETOOLONG)
+    FAIL_EXIT1 ("stat (%s) failed with ENAMETOOLONG\n", testname);
+
+  toolong_subdir = xmalloc (sz);
+  strcpy (toolong_subdir, testname);
+  toolong_subdir_initialized = true;
+}
+
+char *
+support_create_and_chdir_toolong_temp_directory (const char *basename)
+{
+  size_t path_max = get_path_max ();
+
+  char *base = create_temp_directory_internal (basename, true);
+
+  xchdir (base);
+
+  initialize_toolong_subdir ();
+
+  size_t sz = strlen (toolong_subdir);
+
+  /* Create directories and descend into them so that the final path is larger
+     than PATH_MAX.  */
+  for (size_t i = 0; i <= path_max / sz; i++)
+    {
+      xmkdir (toolong_subdir, S_IRWXU);
+      xchdir (toolong_subdir);
+    }
+  return base;
+}
 
 void
-support_set_test_dir (const char *path)
+support_chdir_toolong_temp_directory (const char *base)
 {
-  test_dir = path;
+  size_t path_max = get_path_max ();
+  ensure_toolong_subdir_initialized ();
+
+  xchdir (base);
+
+  size_t sz = strlen (toolong_subdir);
+  for (size_t i = 0; i <= path_max / sz; i++)
+    xchdir (toolong_subdir);
+}
+
+/* Helper functions called by the test skeleton follow.  */
+
+static void
+remove_toolong_subdirs (const char *base)
+{
+  size_t path_max = get_path_max ();
+
+  ensure_toolong_subdir_initialized ();
+
+  if (chdir (base) != 0)
+    {
+      printf ("warning: toolong cleanup base failed: chdir (\"%s\"): %m\n",
+	      base);
+      return;
+    }
+
+  /* Descend.  */
+  int levels = 0;
+  size_t sz = strlen (toolong_subdir);
+  for (levels = 0; levels <= path_max / sz; levels++)
+    if (chdir (toolong_subdir) != 0)
+      {
+	printf ("warning: toolong cleanup failed: chdir (\"%s\"): %m\n",
+		toolong_subdir);
+	return;
+      }
+
+  /* Ascend and remove.  */
+  while (--levels >= 0)
+    {
+      if (chdir ("..") != 0)
+	{
+	  printf ("warning: toolong cleanup failed: chdir (\"..\"): %m\n");
+	  return;
+	}
+      if (remove (toolong_subdir) != 0)
+	{
+	  printf ("warning: could not remove subdirectory: %s: %m\n",
+		  toolong_subdir);
+	  return;
+	}
+    }
 }
 
 void
@@ -123,6 +267,9 @@ support_delete_temp_files (void)
 	 around, to prevent PID reuse.)  */
       if (temp_name_list->owner == pid)
 	{
+	  if (temp_name_list->toolong)
+	    remove_toolong_subdirs (temp_name_list->name);
+
 	  if (remove (temp_name_list->name) != 0)
 	    printf ("warning: could not remove temporary file: %s: %m\n",
 		    temp_name_list->name);
@@ -133,6 +280,8 @@ support_delete_temp_files (void)
       free (temp_name_list);
       temp_name_list = next;
     }
+
+  free (toolong_subdir);
 }
 
 void
@@ -147,3 +296,9 @@ support_print_temp_files (FILE *f)
       fprintf (f, ")\n");
     }
 }
+
+void
+support_set_test_dir (const char *path)
+{
+  test_dir = path;
+}
diff --git a/support/temp_file.h b/support/temp_file.h
index 50a443abe4..8459ddda72 100644
--- a/support/temp_file.h
+++ b/support/temp_file.h
@@ -44,6 +44,15 @@ int create_temp_file_in_dir (const char *base, const char *dir,
    returns.  The caller should free this string.  */
 char *support_create_temp_directory (const char *base);
 
+/* Create a temporary directory tree that is longer than PATH_MAX and schedule
+   it for deletion.  BASENAME is used as a prefix for the unique directory
+   name, which the function returns.  The caller should free this string.  */
+char *support_create_and_chdir_toolong_temp_directory (const char *basename);
+
+/* Change into the innermost directory of the directory tree BASE, which was
+   created using support_create_and_chdir_toolong_temp_directory.  */
+void support_chdir_toolong_temp_directory (const char *base);
+
 __END_DECLS
 
 #endif /* SUPPORT_TEMP_FILE_H */
-- 
2.34.1