| 1 | /* fchdir replacement. |
| 2 | Copyright (C) 2006-2016 Free Software Foundation, Inc. |
| 3 | |
| 4 | This program is free software: you can redistribute it and/or modify |
| 5 | it under the terms of the GNU General Public License as published by |
| 6 | the Free Software Foundation; either version 3 of the License, or |
| 7 | (at your option) any later version. |
| 8 | |
| 9 | This program is distributed in the hope that it will be useful, |
| 10 | but WITHOUT ANY WARRANTY; without even the implied warranty of |
| 11 | MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the |
| 12 | GNU General Public License for more details. |
| 13 | |
| 14 | You should have received a copy of the GNU General Public License |
| 15 | along with this program. If not, see <http://www.gnu.org/licenses/>. */ |
| 16 | |
| 17 | #include <config.h> |
| 18 | |
| 19 | /* Specification. */ |
| 20 | #include <unistd.h> |
| 21 | |
| 22 | #include <dirent.h> |
| 23 | #include <errno.h> |
| 24 | #include <fcntl.h> |
| 25 | #include <stdbool.h> |
| 26 | #include <stdlib.h> |
| 27 | #include <string.h> |
| 28 | #include <sys/types.h> |
| 29 | #include <sys/stat.h> |
| 30 | |
| 31 | #include "assure.h" |
| 32 | #include "dosname.h" |
| 33 | #include "filenamecat.h" |
| 34 | |
| 35 | #ifndef REPLACE_OPEN_DIRECTORY |
| 36 | # define REPLACE_OPEN_DIRECTORY 0 |
| 37 | #endif |
| 38 | |
| 39 | /* This replacement assumes that a directory is not renamed while opened |
| 40 | through a file descriptor. |
| 41 | |
| 42 | FIXME: On mingw, this would be possible to enforce if we were to |
| 43 | also open a HANDLE to each directory currently visited by a file |
| 44 | descriptor, since mingw refuses to rename any in-use file system |
| 45 | object. */ |
| 46 | |
| 47 | /* Array of file descriptors opened. If REPLACE_OPEN_DIRECTORY or if it points |
| 48 | to a directory, it stores info about this directory. */ |
| 49 | typedef struct |
| 50 | { |
| 51 | char *name; /* Absolute name of the directory, or NULL. */ |
| 52 | /* FIXME - add a DIR* member to make dirfd possible on mingw? */ |
| 53 | } dir_info_t; |
| 54 | static dir_info_t *dirs; |
| 55 | static size_t dirs_allocated; |
| 56 | |
| 57 | /* Try to ensure dirs has enough room for a slot at index fd; free any |
| 58 | contents already in that slot. Return false and set errno to |
| 59 | ENOMEM on allocation failure. */ |
| 60 | static bool |
| 61 | ensure_dirs_slot (size_t fd) |
| 62 | { |
| 63 | if (fd < dirs_allocated) |
| 64 | free (dirs[fd].name); |
| 65 | else |
| 66 | { |
| 67 | size_t new_allocated; |
| 68 | dir_info_t *new_dirs; |
| 69 | |
| 70 | new_allocated = 2 * dirs_allocated + 1; |
| 71 | if (new_allocated <= fd) |
| 72 | new_allocated = fd + 1; |
| 73 | new_dirs = |
| 74 | (dirs != NULL |
| 75 | ? (dir_info_t *) realloc (dirs, new_allocated * sizeof *dirs) |
| 76 | : (dir_info_t *) malloc (new_allocated * sizeof *dirs)); |
| 77 | if (new_dirs == NULL) |
| 78 | return false; |
| 79 | memset (new_dirs + dirs_allocated, 0, |
| 80 | (new_allocated - dirs_allocated) * sizeof *dirs); |
| 81 | dirs = new_dirs; |
| 82 | dirs_allocated = new_allocated; |
| 83 | } |
| 84 | return true; |
| 85 | } |
| 86 | |
| 87 | /* Return an absolute name of DIR in malloc'd storage. */ |
| 88 | static char * |
| 89 | get_name (char const *dir) |
| 90 | { |
| 91 | char *cwd; |
| 92 | char *result; |
| 93 | int saved_errno; |
| 94 | |
| 95 | if (IS_ABSOLUTE_FILE_NAME (dir)) |
| 96 | return strdup (dir); |
| 97 | |
| 98 | /* We often encounter "."; treat it as a special case. */ |
| 99 | cwd = getcwd (NULL, 0); |
| 100 | if (!cwd || (dir[0] == '.' && dir[1] == '\0')) |
| 101 | return cwd; |
| 102 | |
| 103 | result = mfile_name_concat (cwd, dir, NULL); |
| 104 | saved_errno = errno; |
| 105 | free (cwd); |
| 106 | errno = saved_errno; |
| 107 | return result; |
| 108 | } |
| 109 | |
| 110 | /* Hook into the gnulib replacements for open() and close() to keep track |
| 111 | of the open file descriptors. */ |
| 112 | |
| 113 | /* Close FD, cleaning up any fd to name mapping if fd was visiting a |
| 114 | directory. */ |
| 115 | void |
| 116 | _gl_unregister_fd (int fd) |
| 117 | { |
| 118 | if (fd >= 0 && fd < dirs_allocated) |
| 119 | { |
| 120 | free (dirs[fd].name); |
| 121 | dirs[fd].name = NULL; |
| 122 | } |
| 123 | } |
| 124 | |
| 125 | /* Mark FD as visiting FILENAME. FD must be non-negative, and refer |
| 126 | to an open file descriptor. If REPLACE_OPEN_DIRECTORY is non-zero, |
| 127 | this should only be called if FD is visiting a directory. Close FD |
| 128 | and return -1 if there is insufficient memory to track the |
| 129 | directory name; otherwise return FD. */ |
| 130 | int |
| 131 | _gl_register_fd (int fd, const char *filename) |
| 132 | { |
| 133 | struct stat statbuf; |
| 134 | |
| 135 | assure (0 <= fd); |
| 136 | if (REPLACE_OPEN_DIRECTORY |
| 137 | || (fstat (fd, &statbuf) == 0 && S_ISDIR (statbuf.st_mode))) |
| 138 | { |
| 139 | if (!ensure_dirs_slot (fd) |
| 140 | || (dirs[fd].name = get_name (filename)) == NULL) |
| 141 | { |
| 142 | int saved_errno = errno; |
| 143 | close (fd); |
| 144 | errno = saved_errno; |
| 145 | return -1; |
| 146 | } |
| 147 | } |
| 148 | return fd; |
| 149 | } |
| 150 | |
| 151 | /* Mark NEWFD as a duplicate of OLDFD; useful from dup, dup2, dup3, |
| 152 | and fcntl. Both arguments must be valid and distinct file |
| 153 | descriptors. Close NEWFD and return -1 if OLDFD is tracking a |
| 154 | directory, but there is insufficient memory to track the same |
| 155 | directory in NEWFD; otherwise return NEWFD. */ |
| 156 | int |
| 157 | _gl_register_dup (int oldfd, int newfd) |
| 158 | { |
| 159 | assure (0 <= oldfd && 0 <= newfd && oldfd != newfd); |
| 160 | if (oldfd < dirs_allocated && dirs[oldfd].name) |
| 161 | { |
| 162 | /* Duplicated a directory; must ensure newfd is allocated. */ |
| 163 | if (!ensure_dirs_slot (newfd) |
| 164 | || (dirs[newfd].name = strdup (dirs[oldfd].name)) == NULL) |
| 165 | { |
| 166 | int saved_errno = errno; |
| 167 | close (newfd); |
| 168 | errno = saved_errno; |
| 169 | newfd = -1; |
| 170 | } |
| 171 | } |
| 172 | else if (newfd < dirs_allocated) |
| 173 | { |
| 174 | /* Duplicated a non-directory; ensure newfd is cleared. */ |
| 175 | free (dirs[newfd].name); |
| 176 | dirs[newfd].name = NULL; |
| 177 | } |
| 178 | return newfd; |
| 179 | } |
| 180 | |
| 181 | /* If FD is currently visiting a directory, then return the name of |
| 182 | that directory. Otherwise, return NULL and set errno. */ |
| 183 | const char * |
| 184 | _gl_directory_name (int fd) |
| 185 | { |
| 186 | if (0 <= fd && fd < dirs_allocated && dirs[fd].name != NULL) |
| 187 | return dirs[fd].name; |
| 188 | /* At this point, fd is either invalid, or open but not a directory. |
| 189 | If dup2 fails, errno is correctly EBADF. */ |
| 190 | if (0 <= fd) |
| 191 | { |
| 192 | if (dup2 (fd, fd) == fd) |
| 193 | errno = ENOTDIR; |
| 194 | } |
| 195 | else |
| 196 | errno = EBADF; |
| 197 | return NULL; |
| 198 | } |
| 199 | |
| 200 | |
| 201 | /* Implement fchdir() in terms of chdir(). */ |
| 202 | |
| 203 | int |
| 204 | fchdir (int fd) |
| 205 | { |
| 206 | const char *name = _gl_directory_name (fd); |
| 207 | return name ? chdir (name) : -1; |
| 208 | } |