src/basic/fs-util.c

   1 /***
   2   This file is part of systemd.
   3
   4   Copyright 2010 Lennart Poettering
   5
   6   systemd is free software; you can redistribute it and/or modify it
   7   under the terms of the GNU Lesser General Public License as published by
   8   the Free Software Foundation; either version 2.1 of the License, or
   9   (at your option) any later version.
  10
  11   systemd is distributed in the hope that it will be useful, but
  12   WITHOUT ANY WARRANTY; without even the implied warranty of
  13   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
  14   Lesser General Public License for more details.
  15
  16   You should have received a copy of the GNU Lesser General Public License
  17   along with systemd; If not, see <http://www.gnu.org/licenses/>.
  18 ***/
  19
  20 #include <errno.h>
  21 #include <stddef.h>
  22 #include <stdio.h>
  23 #include <stdlib.h>
  24 #include <string.h>
  25 #include <sys/stat.h>
  26 #include <time.h>
  27 #include <unistd.h>
  28
  29 #include "alloc-util.h"
  30 #include "dirent-util.h"
  31 #include "fd-util.h"
  32 #include "fileio.h"
  33 #include "fs-util.h"
  34 #include "log.h"
  35 #include "macro.h"
  36 #include "missing.h"
  37 #include "mkdir.h"
  38 #include "parse-util.h"
  39 #include "path-util.h"
  40 #include "stat-util.h"
  41 #include "stdio-util.h"
  42 #include "string-util.h"
  43 #include "strv.h"
  44 #include "time-util.h"
  45 #include "user-util.h"
  46 #include "util.h"
  47
  48 int unlink_noerrno(const char *path) {
  49         PROTECT_ERRNO;
  50         int r;
  51
  52         r = unlink(path);
  53         if (r < 0)
  54                 return -errno;
  55
  56         return 0;
  57 }
  58
  59 int rmdir_parents(const char *path, const char *stop) {
  60         size_t l;
  61         int r = 0;
  62
  63         assert(path);
  64         assert(stop);
  65
  66         l = strlen(path);
  67
  68         /* Skip trailing slashes */
  69         while (l > 0 && path[l-1] == '/')
  70                 l--;
  71
  72         while (l > 0) {
  73                 char *t;
  74
  75                 /* Skip last component */
  76                 while (l > 0 && path[l-1] != '/')
  77                         l--;
  78
  79                 /* Skip trailing slashes */
  80                 while (l > 0 && path[l-1] == '/')
  81                         l--;
  82
  83                 if (l <= 0)
  84                         break;
  85
  86                 t = strndup(path, l);
  87                 if (!t)
  88                         return -ENOMEM;
  89
  90                 if (path_startswith(stop, t)) {
  91                         free(t);
  92                         return 0;
  93                 }
  94
  95                 r = rmdir(t);
  96                 free(t);
  97
  98                 if (r < 0)
  99                         if (errno != ENOENT)
 100                                 return -errno;
 101         }
 102
 103         return 0;
 104 }
 105
 106
 107 int rename_noreplace(int olddirfd, const char *oldpath, int newdirfd, const char *newpath) {
 108         struct stat buf;
 109         int ret;
 110
 111         ret = renameat2(olddirfd, oldpath, newdirfd, newpath, RENAME_NOREPLACE);
 112         if (ret >= 0)
 113                 return 0;
 114
 115         /* renameat2() exists since Linux 3.15, btrfs added support for it later.
 116          * If it is not implemented, fallback to another method. */
 117         if (!IN_SET(errno, EINVAL, ENOSYS))
 118                 return -errno;
 119
 120         /* The link()/unlink() fallback does not work on directories. But
 121          * renameat() without RENAME_NOREPLACE gives the same semantics on
 122          * directories, except when newpath is an *empty* directory. This is
 123          * good enough. */
 124         ret = fstatat(olddirfd, oldpath, &buf, AT_SYMLINK_NOFOLLOW);
 125         if (ret >= 0 && S_ISDIR(buf.st_mode)) {
 126                 ret = renameat(olddirfd, oldpath, newdirfd, newpath);
 127                 return ret >= 0 ? 0 : -errno;
 128         }
 129
 130         /* If it is not a directory, use the link()/unlink() fallback. */
 131         ret = linkat(olddirfd, oldpath, newdirfd, newpath, 0);
 132         if (ret < 0)
 133                 return -errno;
 134
 135         ret = unlinkat(olddirfd, oldpath, 0);
 136         if (ret < 0) {
 137                 /* backup errno before the following unlinkat() alters it */
 138                 ret = errno;
 139                 (void) unlinkat(newdirfd, newpath, 0);
 140                 errno = ret;
 141                 return -errno;
 142         }
 143
 144         return 0;
 145 }
 146
 147 int readlinkat_malloc(int fd, const char *p, char **ret) {
 148         size_t l = 100;
 149         int r;
 150
 151         assert(p);
 152         assert(ret);
 153
 154         for (;;) {
 155                 char *c;
 156                 ssize_t n;
 157
 158                 c = new(char, l);
 159                 if (!c)
 160                         return -ENOMEM;
 161
 162                 n = readlinkat(fd, p, c, l-1);
 163                 if (n < 0) {
 164                         r = -errno;
 165                         free(c);
 166                         return r;
 167                 }
 168
 169                 if ((size_t) n < l-1) {
 170                         c[n] = 0;
 171                         *ret = c;
 172                         return 0;
 173                 }
 174
 175                 free(c);
 176                 l *= 2;
 177         }
 178 }
 179
 180 int readlink_malloc(const char *p, char **ret) {
 181         return readlinkat_malloc(AT_FDCWD, p, ret);
 182 }
 183
 184 int readlink_value(const char *p, char **ret) {
 185         _cleanup_free_ char *link = NULL;
 186         char *value;
 187         int r;
 188
 189         r = readlink_malloc(p, &link);
 190         if (r < 0)
 191                 return r;
 192
 193         value = basename(link);
 194         if (!value)
 195                 return -ENOENT;
 196
 197         value = strdup(value);
 198         if (!value)
 199                 return -ENOMEM;
 200
 201         *ret = value;
 202
 203         return 0;
 204 }
 205
 206 int readlink_and_make_absolute(const char *p, char **r) {
 207         _cleanup_free_ char *target = NULL;
 208         char *k;
 209         int j;
 210
 211         assert(p);
 212         assert(r);
 213
 214         j = readlink_malloc(p, &target);
 215         if (j < 0)
 216                 return j;
 217
 218         k = file_in_same_dir(p, target);
 219         if (!k)
 220                 return -ENOMEM;
 221
 222         *r = k;
 223         return 0;
 224 }
 225
 226 int readlink_and_canonicalize(const char *p, const char *root, char **ret) {
 227         char *t, *s;
 228         int r;
 229
 230         assert(p);
 231         assert(ret);
 232
 233         r = readlink_and_make_absolute(p, &t);
 234         if (r < 0)
 235                 return r;
 236
 237         r = chase_symlinks(t, root, 0, &s);
 238         if (r < 0)
 239                 /* If we can't follow up, then let's return the original string, slightly cleaned up. */
 240                 *ret = path_kill_slashes(t);
 241         else {
 242                 *ret = s;
 243                 free(t);
 244         }
 245
 246         return 0;
 247 }
 248
 249 int readlink_and_make_absolute_root(const char *root, const char *path, char **ret) {
 250         _cleanup_free_ char *target = NULL, *t = NULL;
 251         const char *full;
 252         int r;
 253
 254         full = prefix_roota(root, path);
 255         r = readlink_malloc(full, &target);
 256         if (r < 0)
 257                 return r;
 258
 259         t = file_in_same_dir(path, target);
 260         if (!t)
 261                 return -ENOMEM;
 262
 263         *ret = t;
 264         t = NULL;
 265
 266         return 0;
 267 }
 268
 269 int chmod_and_chown(const char *path, mode_t mode, uid_t uid, gid_t gid) {
 270         assert(path);
 271
 272         /* Under the assumption that we are running privileged we
 273          * first change the access mode and only then hand out
 274          * ownership to avoid a window where access is too open. */
 275
 276         if (mode != MODE_INVALID)
 277                 if (chmod(path, mode) < 0)
 278                         return -errno;
 279
 280         if (uid != UID_INVALID || gid != GID_INVALID)
 281                 if (chown(path, uid, gid) < 0)
 282                         return -errno;
 283
 284         return 0;
 285 }
 286
 287 int fchmod_umask(int fd, mode_t m) {
 288         mode_t u;
 289         int r;
 290
 291         u = umask(0777);
 292         r = fchmod(fd, m & (~u)) < 0 ? -errno : 0;
 293         umask(u);
 294
 295         return r;
 296 }
 297
 298 int fd_warn_permissions(const char *path, int fd) {
 299         struct stat st;
 300
 301         if (fstat(fd, &st) < 0)
 302                 return -errno;
 303
 304         if (st.st_mode & 0111)
 305                 log_warning("Configuration file %s is marked executable. Please remove executable permission bits. Proceeding anyway.", path);
 306
 307         if (st.st_mode & 0002)
 308                 log_warning("Configuration file %s is marked world-writable. Please remove world writability permission bits. Proceeding anyway.", path);
 309
 310         if (getpid() == 1 && (st.st_mode & 0044) != 0044)
 311                 log_warning("Configuration file %s is marked world-inaccessible. This has no effect as configuration data is accessible via APIs without restrictions. Proceeding anyway.", path);
 312
 313         return 0;
 314 }
 315
 316 int touch_file(const char *path, bool parents, usec_t stamp, uid_t uid, gid_t gid, mode_t mode) {
 317         _cleanup_close_ int fd;
 318         int r;
 319
 320         assert(path);
 321
 322         if (parents)
 323                 mkdir_parents(path, 0755);
 324
 325         fd = open(path, O_WRONLY|O_CREAT|O_CLOEXEC|O_NOCTTY,
 326                         (mode == 0 || mode == MODE_INVALID) ? 0644 : mode);
 327         if (fd < 0)
 328                 return -errno;
 329
 330         if (mode != MODE_INVALID) {
 331                 r = fchmod(fd, mode);
 332                 if (r < 0)
 333                         return -errno;
 334         }
 335
 336         if (uid != UID_INVALID || gid != GID_INVALID) {
 337                 r = fchown(fd, uid, gid);
 338                 if (r < 0)
 339                         return -errno;
 340         }
 341
 342         if (stamp != USEC_INFINITY) {
 343                 struct timespec ts[2];
 344
 345                 timespec_store(&ts[0], stamp);
 346                 ts[1] = ts[0];
 347                 r = futimens(fd, ts);
 348         } else
 349                 r = futimens(fd, NULL);
 350         if (r < 0)
 351                 return -errno;
 352
 353         return 0;
 354 }
 355
 356 int touch(const char *path) {
 357         return touch_file(path, false, USEC_INFINITY, UID_INVALID, GID_INVALID, MODE_INVALID);
 358 }
 359
 360 int symlink_idempotent(const char *from, const char *to) {
 361         _cleanup_free_ char *p = NULL;
 362         int r;
 363
 364         assert(from);
 365         assert(to);
 366
 367         if (symlink(from, to) < 0) {
 368                 if (errno != EEXIST)
 369                         return -errno;
 370
 371                 r = readlink_malloc(to, &p);
 372                 if (r < 0)
 373                         return r;
 374
 375                 if (!streq(p, from))
 376                         return -EINVAL;
 377         }
 378
 379         return 0;
 380 }
 381
 382 int symlink_atomic(const char *from, const char *to) {
 383         _cleanup_free_ char *t = NULL;
 384         int r;
 385
 386         assert(from);
 387         assert(to);
 388
 389         r = tempfn_random(to, NULL, &t);
 390         if (r < 0)
 391                 return r;
 392
 393         if (symlink(from, t) < 0)
 394                 return -errno;
 395
 396         if (rename(t, to) < 0) {
 397                 unlink_noerrno(t);
 398                 return -errno;
 399         }
 400
 401         return 0;
 402 }
 403
 404 int mknod_atomic(const char *path, mode_t mode, dev_t dev) {
 405         _cleanup_free_ char *t = NULL;
 406         int r;
 407
 408         assert(path);
 409
 410         r = tempfn_random(path, NULL, &t);
 411         if (r < 0)
 412                 return r;
 413
 414         if (mknod(t, mode, dev) < 0)
 415                 return -errno;
 416
 417         if (rename(t, path) < 0) {
 418                 unlink_noerrno(t);
 419                 return -errno;
 420         }
 421
 422         return 0;
 423 }
 424
 425 int mkfifo_atomic(const char *path, mode_t mode) {
 426         _cleanup_free_ char *t = NULL;
 427         int r;
 428
 429         assert(path);
 430
 431         r = tempfn_random(path, NULL, &t);
 432         if (r < 0)
 433                 return r;
 434
 435         if (mkfifo(t, mode) < 0)
 436                 return -errno;
 437
 438         if (rename(t, path) < 0) {
 439                 unlink_noerrno(t);
 440                 return -errno;
 441         }
 442
 443         return 0;
 444 }
 445
 446 int get_files_in_directory(const char *path, char ***list) {
 447         _cleanup_closedir_ DIR *d = NULL;
 448         struct dirent *de;
 449         size_t bufsize = 0, n = 0;
 450         _cleanup_strv_free_ char **l = NULL;
 451
 452         assert(path);
 453
 454         /* Returns all files in a directory in *list, and the number
 455          * of files as return value. If list is NULL returns only the
 456          * number. */
 457
 458         d = opendir(path);
 459         if (!d)
 460                 return -errno;
 461
 462         FOREACH_DIRENT_ALL(de, d, return -errno) {
 463                 dirent_ensure_type(d, de);
 464
 465                 if (!dirent_is_file(de))
 466                         continue;
 467
 468                 if (list) {
 469                         /* one extra slot is needed for the terminating NULL */
 470                         if (!GREEDY_REALLOC(l, bufsize, n + 2))
 471                                 return -ENOMEM;
 472
 473                         l[n] = strdup(de->d_name);
 474                         if (!l[n])
 475                                 return -ENOMEM;
 476
 477                         l[++n] = NULL;
 478                 } else
 479                         n++;
 480         }
 481
 482         if (list) {
 483                 *list = l;
 484                 l = NULL; /* avoid freeing */
 485         }
 486
 487         return n;
 488 }
 489
 490 static int getenv_tmp_dir(const char **ret_path) {
 491         const char *n;
 492         int r, ret = 0;
 493
 494         assert(ret_path);
 495
 496         /* We use the same order of environment variables python uses in tempfile.gettempdir():
 497          * https://docs.python.org/3/library/tempfile.html#tempfile.gettempdir */
 498         FOREACH_STRING(n, "TMPDIR", "TEMP", "TMP") {
 499                 const char *e;
 500
 501                 e = secure_getenv(n);
 502                 if (!e)
 503                         continue;
 504                 if (!path_is_absolute(e)) {
 505                         r = -ENOTDIR;
 506                         goto next;
 507                 }
 508                 if (!path_is_safe(e)) {
 509                         r = -EPERM;
 510                         goto next;
 511                 }
 512
 513                 r = is_dir(e, true);
 514                 if (r < 0)
 515                         goto next;
 516                 if (r == 0) {
 517                         r = -ENOTDIR;
 518                         goto next;
 519                 }
 520
 521                 *ret_path = e;
 522                 return 1;
 523
 524         next:
 525                 /* Remember first error, to make this more debuggable */
 526                 if (ret >= 0)
 527                         ret = r;
 528         }
 529
 530         if (ret < 0)
 531                 return ret;
 532
 533         *ret_path = NULL;
 534         return ret;
 535 }
 536
 537 static int tmp_dir_internal(const char *def, const char **ret) {
 538         const char *e;
 539         int r, k;
 540
 541         assert(def);
 542         assert(ret);
 543
 544         r = getenv_tmp_dir(&e);
 545         if (r > 0) {
 546                 *ret = e;
 547                 return 0;
 548         }
 549
 550         k = is_dir(def, true);
 551         if (k == 0)
 552                 k = -ENOTDIR;
 553         if (k < 0)
 554                 return r < 0 ? r : k;
 555
 556         *ret = def;
 557         return 0;
 558 }
 559
 560 int var_tmp_dir(const char **ret) {
 561
 562         /* Returns the location for "larger" temporary files, that is backed by physical storage if available, and thus
 563          * even might survive a boot: /var/tmp. If $TMPDIR (or related environment variables) are set, its value is
 564          * returned preferably however. Note that both this function and tmp_dir() below are affected by $TMPDIR,
 565          * making it a variable that overrides all temporary file storage locations. */
 566
 567         return tmp_dir_internal("/var/tmp", ret);
 568 }
 569
 570 int tmp_dir(const char **ret) {
 571
 572         /* Similar to var_tmp_dir() above, but returns the location for "smaller" temporary files, which is usually
 573          * backed by an in-memory file system: /tmp. */
 574
 575         return tmp_dir_internal("/tmp", ret);
 576 }
 577
 578 int inotify_add_watch_fd(int fd, int what, uint32_t mask) {
 579         char path[strlen("/proc/self/fd/") + DECIMAL_STR_MAX(int) + 1];
 580         int r;
 581
 582         /* This is like inotify_add_watch(), except that the file to watch is not referenced by a path, but by an fd */
 583         xsprintf(path, "/proc/self/fd/%i", what);
 584
 585         r = inotify_add_watch(fd, path, mask);
 586         if (r < 0)
 587                 return -errno;
 588
 589         return r;
 590 }
 591
 592 int chase_symlinks(const char *path, const char *original_root, unsigned flags, char **ret) {
 593         _cleanup_free_ char *buffer = NULL, *done = NULL, *root = NULL;
 594         _cleanup_close_ int fd = -1;
 595         unsigned max_follow = 32; /* how many symlinks to follow before giving up and returning ELOOP */
 596         bool exists = true;
 597         char *todo;
 598         int r;
 599
 600         assert(path);
 601
 602         /* This is a lot like canonicalize_file_name(), but takes an additional "root" parameter, that allows following
 603          * symlinks relative to a root directory, instead of the root of the host.
 604          *
 605          * Note that "root" primarily matters if we encounter an absolute symlink. It is also used when following
 606          * relative symlinks to ensure they cannot be used to "escape" the root directory. The path parameter passed is
 607          * assumed to be already prefixed by it, except if the CHASE_PREFIX_ROOT flag is set, in which case it is first
 608          * prefixed accordingly.
 609          *
 610          * Algorithmically this operates on two path buffers: "done" are the components of the path we already
 611          * processed and resolved symlinks, "." and ".." of. "todo" are the components of the path we still need to
 612          * process. On each iteration, we move one component from "todo" to "done", processing it's special meaning
 613          * each time. The "todo" path always starts with at least one slash, the "done" path always ends in no
 614          * slash. We always keep an O_PATH fd to the component we are currently processing, thus keeping lookup races
 615          * at a minimum.
 616          *
 617          * Suggested usage: whenever you want to canonicalize a path, use this function. Pass the absolute path you got
 618          * as-is: fully qualified and relative to your host's root. Optionally, specify the root parameter to tell this
 619          * function what to do when encountering a symlink with an absolute path as directory: prefix it by the
 620          * specified path.
 621          *
 622          * Note: there's also chase_symlinks_prefix() (see below), which as first step prefixes the passed path by the
 623          * passed root. */
 624
 625         if (original_root) {
 626                 r = path_make_absolute_cwd(original_root, &root);
 627                 if (r < 0)
 628                         return r;
 629
 630                 if (flags & CHASE_PREFIX_ROOT)
 631                         path = prefix_roota(root, path);
 632         }
 633
 634         r = path_make_absolute_cwd(path, &buffer);
 635         if (r < 0)
 636                 return r;
 637
 638         fd = open("/", O_CLOEXEC|O_NOFOLLOW|O_PATH);
 639         if (fd < 0)
 640                 return -errno;
 641
 642         todo = buffer;
 643         for (;;) {
 644                 _cleanup_free_ char *first = NULL;
 645                 _cleanup_close_ int child = -1;
 646                 struct stat st;
 647                 size_t n, m;
 648
 649                 /* Determine length of first component in the path */
 650                 n = strspn(todo, "/");                  /* The slashes */
 651                 m = n + strcspn(todo + n, "/");         /* The entire length of the component */
 652
 653                 /* Extract the first component. */
 654                 first = strndup(todo, m);
 655                 if (!first)
 656                         return -ENOMEM;
 657
 658                 todo += m;
 659
 660                 /* Just a single slash? Then we reached the end. */
 661                 if (isempty(first) || path_equal(first, "/"))
 662                         break;
 663
 664                 /* Just a dot? Then let's eat this up. */
 665                 if (path_equal(first, "/."))
 666                         continue;
 667
 668                 /* Two dots? Then chop off the last bit of what we already found out. */
 669                 if (path_equal(first, "/..")) {
 670                         _cleanup_free_ char *parent = NULL;
 671                         int fd_parent = -1;
 672
 673                         /* If we already are at the top, then going up will not change anything. This is in-line with
 674                          * how the kernel handles this. */
 675                         if (isempty(done) || path_equal(done, "/"))
 676                                 continue;
 677
 678                         parent = dirname_malloc(done);
 679                         if (!parent)
 680                                 return -ENOMEM;
 681
 682                         /* Don't allow this to leave the root dir.  */
 683                         if (root &&
 684                             path_startswith(done, root) &&
 685                             !path_startswith(parent, root))
 686                                 continue;
 687
 688                         free_and_replace(done, parent);
 689
 690                         fd_parent = openat(fd, "..", O_CLOEXEC|O_NOFOLLOW|O_PATH);
 691                         if (fd_parent < 0)
 692                                 return -errno;
 693
 694                         safe_close(fd);
 695                         fd = fd_parent;
 696
 697                         continue;
 698                 }
 699
 700                 /* Otherwise let's see what this is. */
 701                 child = openat(fd, first + n, O_CLOEXEC|O_NOFOLLOW|O_PATH);
 702                 if (child < 0) {
 703
 704                         if (errno == ENOENT &&
 705                             (flags & CHASE_NONEXISTENT) &&
 706                             (isempty(todo) || path_is_safe(todo))) {
 707
 708                                 /* If CHASE_NONEXISTENT is set, and the path does not exist, then that's OK, return
 709                                  * what we got so far. But don't allow this if the remaining path contains "../ or "./"
 710                                  * or something else weird. */
 711
 712                                 if (!strextend(&done, first, todo, NULL))
 713                                         return -ENOMEM;
 714
 715                                 exists = false;
 716                                 break;
 717                         }
 718
 719                         return -errno;
 720                 }
 721
 722                 if (fstat(child, &st) < 0)
 723                         return -errno;
 724
 725                 if (S_ISLNK(st.st_mode)) {
 726                         _cleanup_free_ char *destination = NULL;
 727
 728                         /* This is a symlink, in this case read the destination. But let's make sure we don't follow
 729                          * symlinks without bounds. */
 730                         if (--max_follow <= 0)
 731                                 return -ELOOP;
 732
 733                         r = readlinkat_malloc(fd, first + n, &destination);
 734                         if (r < 0)
 735                                 return r;
 736                         if (isempty(destination))
 737                                 return -EINVAL;
 738
 739                         if (path_is_absolute(destination)) {
 740
 741                                 /* An absolute destination. Start the loop from the beginning, but use the root
 742                                  * directory as base. */
 743
 744                                 safe_close(fd);
 745                                 fd = open(root ?: "/", O_CLOEXEC|O_NOFOLLOW|O_PATH);
 746                                 if (fd < 0)
 747                                         return -errno;
 748
 749                                 free_and_replace(buffer, destination);
 750
 751                                 todo = buffer;
 752                                 free(done);
 753
 754                                 /* Note that we do not revalidate the root, we take it as is. */
 755                                 if (isempty(root))
 756                                         done = NULL;
 757                                 else {
 758                                         done = strdup(root);
 759                                         if (!done)
 760                                                 return -ENOMEM;
 761                                 }
 762
 763                         } else {
 764                                 char *joined;
 765
 766                                 /* A relative destination. If so, this is what we'll prefix what's left to do with what
 767                                  * we just read, and start the loop again, but remain in the current directory. */
 768
 769                                 joined = strjoin("/", destination, todo);
 770                                 if (!joined)
 771                                         return -ENOMEM;
 772
 773                                 free(buffer);
 774                                 todo = buffer = joined;
 775                         }
 776
 777                         continue;
 778                 }
 779
 780                 /* If this is not a symlink, then let's just add the name we read to what we already verified. */
 781                 if (!done) {
 782                         done = first;
 783                         first = NULL;
 784                 } else {
 785                         if (!strextend(&done, first, NULL))
 786                                 return -ENOMEM;
 787                 }
 788
 789                 /* And iterate again, but go one directory further down. */
 790                 safe_close(fd);
 791                 fd = child;
 792                 child = -1;
 793         }
 794
 795         if (!done) {
 796                 /* Special case, turn the empty string into "/", to indicate the root directory. */
 797                 done = strdup("/");
 798                 if (!done)
 799                         return -ENOMEM;
 800         }
 801
 802         *ret = done;
 803         done = NULL;
 804
 805         return exists;
 806 }