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/* fchdir replacement.
   Copyright (C) 2006-2017 Free Software Foundation, Inc.

   This program is free software: you can redistribute it and/or modify
   it under the terms of the GNU General Public License as published by
   the Free Software Foundation; either version 3 of the License, or
   (at your option) any later version.

   This program is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   GNU General Public License for more details.

   You should have received a copy of the GNU General Public License
   along with this program.  If not, see <>.  */

#include <config.h>

/* Specification.  */
#include <unistd.h>

#include <dirent.h>
#include <errno.h>
#include <fcntl.h>
#include <stdbool.h>
#include <stdlib.h>
#include <string.h>
#include <sys/types.h>
#include <sys/stat.h>

#include "assure.h"
#include "dosname.h"
#include "filenamecat.h"


/* This replacement assumes that a directory is not renamed while opened
   through a file descriptor.

   FIXME: On mingw, this would be possible to enforce if we were to
   also open a HANDLE to each directory currently visited by a file
   descriptor, since mingw refuses to rename any in-use file system
   object.  */

/* Array of file descriptors opened.  If REPLACE_OPEN_DIRECTORY or if it points
   to a directory, it stores info about this directory.  */
typedef struct
  char *name;       /* Absolute name of the directory, or NULL.  */
  /* FIXME - add a DIR* member to make dirfd possible on mingw?  */
} dir_info_t;
static dir_info_t *dirs;
static size_t dirs_allocated;

/* Try to ensure dirs has enough room for a slot at index fd; free any
   contents already in that slot.  Return false and set errno to
   ENOMEM on allocation failure.  */
static bool
ensure_dirs_slot (size_t fd)
  if (fd < dirs_allocated)
    free (dirs[fd].name);
      size_t new_allocated;
      dir_info_t *new_dirs;

      new_allocated = 2 * dirs_allocated + 1;
      if (new_allocated <= fd)
        new_allocated = fd + 1;
      new_dirs =
        (dirs != NULL
         ? (dir_info_t *) realloc (dirs, new_allocated * sizeof *dirs)
         : (dir_info_t *) malloc (new_allocated * sizeof *dirs));
      if (new_dirs == NULL)
        return false;
      memset (new_dirs + dirs_allocated, 0,
              (new_allocated - dirs_allocated) * sizeof *dirs);
      dirs = new_dirs;
      dirs_allocated = new_allocated;
  return true;

/* Return an absolute name of DIR in malloc'd storage.  */
static char *
get_name (char const *dir)
  char *cwd;
  char *result;
  int saved_errno;

    return strdup (dir);

  /* We often encounter "."; treat it as a special case.  */
  cwd = getcwd (NULL, 0);
  if (!cwd || (dir[0] == '.' && dir[1] == '\0'))
    return cwd;

  result = mfile_name_concat (cwd, dir, NULL);
  saved_errno = errno;
  free (cwd);
  errno = saved_errno;
  return result;

/* Hook into the gnulib replacements for open() and close() to keep track
   of the open file descriptors.  */

/* Close FD, cleaning up any fd to name mapping if fd was visiting a
   directory.  */
_gl_unregister_fd (int fd)
  if (fd >= 0 && fd < dirs_allocated)
      free (dirs[fd].name);
      dirs[fd].name = NULL;

/* Mark FD as visiting FILENAME.  FD must be non-negative, and refer
   to an open file descriptor.  If REPLACE_OPEN_DIRECTORY is non-zero,
   this should only be called if FD is visiting a directory.  Close FD
   and return -1 if there is insufficient memory to track the
   directory name; otherwise return FD.  */
_gl_register_fd (int fd, const char *filename)
  struct stat statbuf;

  assure (0 <= fd);
      || (fstat (fd, &statbuf) == 0 && S_ISDIR (statbuf.st_mode)))
      if (!ensure_dirs_slot (fd)
          || (dirs[fd].name = get_name (filename)) == NULL)
          int saved_errno = errno;
          close (fd);
          errno = saved_errno;
          return -1;
  return fd;

/* Mark NEWFD as a duplicate of OLDFD; useful from dup, dup2, dup3,
   and fcntl.  Both arguments must be valid and distinct file
   descriptors.  Close NEWFD and return -1 if OLDFD is tracking a
   directory, but there is insufficient memory to track the same
   directory in NEWFD; otherwise return NEWFD.  */
_gl_register_dup (int oldfd, int newfd)
  assure (0 <= oldfd && 0 <= newfd && oldfd != newfd);
  if (oldfd < dirs_allocated && dirs[oldfd].name)
      /* Duplicated a directory; must ensure newfd is allocated.  */
      if (!ensure_dirs_slot (newfd)
          || (dirs[newfd].name = strdup (dirs[oldfd].name)) == NULL)
          int saved_errno = errno;
          close (newfd);
          errno = saved_errno;
          newfd = -1;
  else if (newfd < dirs_allocated)
      /* Duplicated a non-directory; ensure newfd is cleared.  */
      free (dirs[newfd].name);
      dirs[newfd].name = NULL;
  return newfd;

/* If FD is currently visiting a directory, then return the name of
   that directory.  Otherwise, return NULL and set errno.  */
const char *
_gl_directory_name (int fd)
  if (0 <= fd && fd < dirs_allocated && dirs[fd].name != NULL)
    return dirs[fd].name;
  /* At this point, fd is either invalid, or open but not a directory.
     If dup2 fails, errno is correctly EBADF.  */
  if (0 <= fd)
      if (dup2 (fd, fd) == fd)
        errno = ENOTDIR;
    errno = EBADF;
  return NULL;

/* Implement fchdir() in terms of chdir().  */

fchdir (int fd)
  const char *name = _gl_directory_name (fd);
  return name ? chdir (name) : -1;