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/* fchdir replacement.
Copyright (C) 2006-2021 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 "filename.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.
Upon failure, return NULL with errno set. */
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 with errno set 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;