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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
- MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
- 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 <https://www.gnu.org/licenses/>. */
- #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"
- #ifndef REPLACE_OPEN_DIRECTORY
- # define REPLACE_OPEN_DIRECTORY 0
- #endif
- /* 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);
- else
- {
- 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;
- if (IS_ABSOLUTE_FILE_NAME (dir))
- 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. */
- void
- _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. */
- int
- _gl_register_fd (int fd, const char *filename)
- {
- struct stat statbuf;
- assure (0 <= fd);
- if (REPLACE_OPEN_DIRECTORY
- || (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. */
- int
- _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;
- }
- else
- errno = EBADF;
- return NULL;
- }
- /* Implement fchdir() in terms of chdir(). */
- int
- fchdir (int fd)
- {
- const char *name = _gl_directory_name (fd);
- return name ? chdir (name) : -1;
- }
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