path.c

   1 /*
   2  * I'm tired of doing "vsnprintf()" etc just to open a
   3  * file, so here's a "return static buffer with printf"
   4  * interface for paths.
   5  *
   6  * It's obviously not thread-safe. Sue me. But it's quite
   7  * useful for doing things like
   8  *
   9  *   f = open(mkpath("%s/%s.git", base, name), O_RDONLY);
  10  *
  11  * which is what it's designed for.
  12  */
  13 #include "cache.h"
  14 #include "strbuf.h"
  15
  16 static char bad_path[] = "/bad-path/";
  17
  18 static char *get_pathname(void)
  19 {
  20         static char pathname_array[4][PATH_MAX];
  21         static int index;
  22         return pathname_array[3 & ++index];
  23 }
  24
  25 static char *cleanup_path(char *path)
  26 {
  27         /* Clean it up */
  28         if (!memcmp(path, "./", 2)) {
  29                 path += 2;
  30                 while (*path == '/')
  31                         path++;
  32         }
  33         return path;
  34 }
  35
  36 char *mksnpath(char *buf, size_t n, const char *fmt, ...)
  37 {
  38         va_list args;
  39         unsigned len;
  40
  41         va_start(args, fmt);
  42         len = vsnprintf(buf, n, fmt, args);
  43         va_end(args);
  44         if (len >= n) {
  45                 strlcpy(buf, bad_path, n);
  46                 return buf;
  47         }
  48         return cleanup_path(buf);
  49 }
  50
  51 static char *git_vsnpath(char *buf, size_t n, const char *fmt, va_list args)
  52 {
  53         const char *git_dir = get_git_dir();
  54         size_t len;
  55
  56         len = strlen(git_dir);
  57         if (n < len + 1)
  58                 goto bad;
  59         memcpy(buf, git_dir, len);
  60         if (len && !is_dir_sep(git_dir[len-1]))
  61                 buf[len++] = '/';
  62         len += vsnprintf(buf + len, n - len, fmt, args);
  63         if (len >= n)
  64                 goto bad;
  65         return cleanup_path(buf);
  66 bad:
  67         strlcpy(buf, bad_path, n);
  68         return buf;
  69 }
  70
  71 char *git_snpath(char *buf, size_t n, const char *fmt, ...)
  72 {
  73         va_list args;
  74         va_start(args, fmt);
  75         (void)git_vsnpath(buf, n, fmt, args);
  76         va_end(args);
  77         return buf;
  78 }
  79
  80 char *git_pathdup(const char *fmt, ...)
  81 {
  82         char path[PATH_MAX];
  83         va_list args;
  84         va_start(args, fmt);
  85         (void)git_vsnpath(path, sizeof(path), fmt, args);
  86         va_end(args);
  87         return xstrdup(path);
  88 }
  89
  90 char *mkpath(const char *fmt, ...)
  91 {
  92         va_list args;
  93         unsigned len;
  94         char *pathname = get_pathname();
  95
  96         va_start(args, fmt);
  97         len = vsnprintf(pathname, PATH_MAX, fmt, args);
  98         va_end(args);
  99         if (len >= PATH_MAX)
 100                 return bad_path;
 101         return cleanup_path(pathname);
 102 }
 103
 104 char *git_path(const char *fmt, ...)
 105 {
 106         const char *git_dir = get_git_dir();
 107         char *pathname = get_pathname();
 108         va_list args;
 109         unsigned len;
 110
 111         len = strlen(git_dir);
 112         if (len > PATH_MAX-100)
 113                 return bad_path;
 114         memcpy(pathname, git_dir, len);
 115         if (len && git_dir[len-1] != '/')
 116                 pathname[len++] = '/';
 117         va_start(args, fmt);
 118         len += vsnprintf(pathname + len, PATH_MAX - len, fmt, args);
 119         va_end(args);
 120         if (len >= PATH_MAX)
 121                 return bad_path;
 122         return cleanup_path(pathname);
 123 }
 124
 125 char *git_path_submodule(const char *path, const char *fmt, ...)
 126 {
 127         char *pathname = get_pathname();
 128         struct strbuf buf = STRBUF_INIT;
 129         const char *git_dir;
 130         va_list args;
 131         unsigned len;
 132
 133         len = strlen(path);
 134         if (len > PATH_MAX-100)
 135                 return bad_path;
 136
 137         strbuf_addstr(&buf, path);
 138         if (len && path[len-1] != '/')
 139                 strbuf_addch(&buf, '/');
 140         strbuf_addstr(&buf, ".git");
 141
 142         git_dir = read_gitfile_gently(buf.buf);
 143         if (git_dir) {
 144                 strbuf_reset(&buf);
 145                 strbuf_addstr(&buf, git_dir);
 146         }
 147         strbuf_addch(&buf, '/');
 148
 149         if (buf.len >= PATH_MAX)
 150                 return bad_path;
 151         memcpy(pathname, buf.buf, buf.len + 1);
 152
 153         strbuf_release(&buf);
 154         len = strlen(pathname);
 155
 156         va_start(args, fmt);
 157         len += vsnprintf(pathname + len, PATH_MAX - len, fmt, args);
 158         va_end(args);
 159         if (len >= PATH_MAX)
 160                 return bad_path;
 161         return cleanup_path(pathname);
 162 }
 163
 164 /* git_mkstemp() - create tmp file honoring TMPDIR variable */
 165 int git_mkstemp(char *path, size_t len, const char *template)
 166 {
 167         const char *tmp;
 168         size_t n;
 169
 170         tmp = getenv("TMPDIR");
 171         if (!tmp)
 172                 tmp = "/tmp";
 173         n = snprintf(path, len, "%s/%s", tmp, template);
 174         if (len <= n) {
 175                 errno = ENAMETOOLONG;
 176                 return -1;
 177         }
 178         return mkstemp(path);
 179 }
 180
 181 /* git_mkstemps() - create tmp file with suffix honoring TMPDIR variable. */
 182 int git_mkstemps(char *path, size_t len, const char *template, int suffix_len)
 183 {
 184         const char *tmp;
 185         size_t n;
 186
 187         tmp = getenv("TMPDIR");
 188         if (!tmp)
 189                 tmp = "/tmp";
 190         n = snprintf(path, len, "%s/%s", tmp, template);
 191         if (len <= n) {
 192                 errno = ENAMETOOLONG;
 193                 return -1;
 194         }
 195         return mkstemps(path, suffix_len);
 196 }
 197
 198 /* Adapted from libiberty's mkstemp.c. */
 199
 200 #undef TMP_MAX
 201 #define TMP_MAX 16384
 202
 203 int git_mkstemps_mode(char *pattern, int suffix_len, int mode)
 204 {
 205         static const char letters[] =
 206                 "abcdefghijklmnopqrstuvwxyz"
 207                 "ABCDEFGHIJKLMNOPQRSTUVWXYZ"
 208                 "0123456789";
 209         static const int num_letters = 62;
 210         uint64_t value;
 211         struct timeval tv;
 212         char *template;
 213         size_t len;
 214         int fd, count;
 215
 216         len = strlen(pattern);
 217
 218         if (len < 6 + suffix_len) {
 219                 errno = EINVAL;
 220                 return -1;
 221         }
 222
 223         if (strncmp(&pattern[len - 6 - suffix_len], "XXXXXX", 6)) {
 224                 errno = EINVAL;
 225                 return -1;
 226         }
 227
 228         /*
 229          * Replace pattern's XXXXXX characters with randomness.
 230          * Try TMP_MAX different filenames.
 231          */
 232         gettimeofday(&tv, NULL);
 233         value = ((size_t)(tv.tv_usec << 16)) ^ tv.tv_sec ^ getpid();
 234         template = &pattern[len - 6 - suffix_len];
 235         for (count = 0; count < TMP_MAX; ++count) {
 236                 uint64_t v = value;
 237                 /* Fill in the random bits. */
 238                 template[0] = letters[v % num_letters]; v /= num_letters;
 239                 template[1] = letters[v % num_letters]; v /= num_letters;
 240                 template[2] = letters[v % num_letters]; v /= num_letters;
 241                 template[3] = letters[v % num_letters]; v /= num_letters;
 242                 template[4] = letters[v % num_letters]; v /= num_letters;
 243                 template[5] = letters[v % num_letters]; v /= num_letters;
 244
 245                 fd = open(pattern, O_CREAT | O_EXCL | O_RDWR, mode);
 246                 if (fd > 0)
 247                         return fd;
 248                 /*
 249                  * Fatal error (EPERM, ENOSPC etc).
 250                  * It doesn't make sense to loop.
 251                  */
 252                 if (errno != EEXIST)
 253                         break;
 254                 /*
 255                  * This is a random value.  It is only necessary that
 256                  * the next TMP_MAX values generated by adding 7777 to
 257                  * VALUE are different with (module 2^32).
 258                  */
 259                 value += 7777;
 260         }
 261         /* We return the null string if we can't find a unique file name.  */
 262         pattern[0] = '\0';
 263         return -1;
 264 }
 265
 266 int git_mkstemp_mode(char *pattern, int mode)
 267 {
 268         /* mkstemp is just mkstemps with no suffix */
 269         return git_mkstemps_mode(pattern, 0, mode);
 270 }
 271
 272 int gitmkstemps(char *pattern, int suffix_len)
 273 {
 274         return git_mkstemps_mode(pattern, suffix_len, 0600);
 275 }
 276
 277 int validate_headref(const char *path)
 278 {
 279         struct stat st;
 280         char *buf, buffer[256];
 281         unsigned char sha1[20];
 282         int fd;
 283         ssize_t len;
 284
 285         if (lstat(path, &st) < 0)
 286                 return -1;
 287
 288         /* Make sure it is a "refs/.." symlink */
 289         if (S_ISLNK(st.st_mode)) {
 290                 len = readlink(path, buffer, sizeof(buffer)-1);
 291                 if (len >= 5 && !memcmp("refs/", buffer, 5))
 292                         return 0;
 293                 return -1;
 294         }
 295
 296         /*
 297          * Anything else, just open it and try to see if it is a symbolic ref.
 298          */
 299         fd = open(path, O_RDONLY);
 300         if (fd < 0)
 301                 return -1;
 302         len = read_in_full(fd, buffer, sizeof(buffer)-1);
 303         close(fd);
 304
 305         /*
 306          * Is it a symbolic ref?
 307          */
 308         if (len < 4)
 309                 return -1;
 310         if (!memcmp("ref:", buffer, 4)) {
 311                 buf = buffer + 4;
 312                 len -= 4;
 313                 while (len && isspace(*buf))
 314                         buf++, len--;
 315                 if (len >= 5 && !memcmp("refs/", buf, 5))
 316                         return 0;
 317         }
 318
 319         /*
 320          * Is this a detached HEAD?
 321          */
 322         if (!get_sha1_hex(buffer, sha1))
 323                 return 0;
 324
 325         return -1;
 326 }
 327
 328 static struct passwd *getpw_str(const char *username, size_t len)
 329 {
 330         struct passwd *pw;
 331         char *username_z = xmalloc(len + 1);
 332         memcpy(username_z, username, len);
 333         username_z[len] = '\0';
 334         pw = getpwnam(username_z);
 335         free(username_z);
 336         return pw;
 337 }
 338
 339 /*
 340  * Return a string with ~ and ~user expanded via getpw*.  If buf != NULL,
 341  * then it is a newly allocated string. Returns NULL on getpw failure or
 342  * if path is NULL.
 343  */
 344 char *expand_user_path(const char *path)
 345 {
 346         struct strbuf user_path = STRBUF_INIT;
 347         const char *first_slash = strchrnul(path, '/');
 348         const char *to_copy = path;
 349
 350         if (path == NULL)
 351                 goto return_null;
 352         if (path[0] == '~') {
 353                 const char *username = path + 1;
 354                 size_t username_len = first_slash - username;
 355                 if (username_len == 0) {
 356                         const char *home = getenv("HOME");
 357                         if (!home)
 358                                 goto return_null;
 359                         strbuf_add(&user_path, home, strlen(home));
 360                 } else {
 361                         struct passwd *pw = getpw_str(username, username_len);
 362                         if (!pw)
 363                                 goto return_null;
 364                         strbuf_add(&user_path, pw->pw_dir, strlen(pw->pw_dir));
 365                 }
 366                 to_copy = first_slash;
 367         }
 368         strbuf_add(&user_path, to_copy, strlen(to_copy));
 369         return strbuf_detach(&user_path, NULL);
 370 return_null:
 371         strbuf_release(&user_path);
 372         return NULL;
 373 }
 374
 375 /*
 376  * First, one directory to try is determined by the following algorithm.
 377  *
 378  * (0) If "strict" is given, the path is used as given and no DWIM is
 379  *     done. Otherwise:
 380  * (1) "~/path" to mean path under the running user's home directory;
 381  * (2) "~user/path" to mean path under named user's home directory;
 382  * (3) "relative/path" to mean cwd relative directory; or
 383  * (4) "/absolute/path" to mean absolute directory.
 384  *
 385  * Unless "strict" is given, we try access() for existence of "%s.git/.git",
 386  * "%s/.git", "%s.git", "%s" in this order.  The first one that exists is
 387  * what we try.
 388  *
 389  * Second, we try chdir() to that.  Upon failure, we return NULL.
 390  *
 391  * Then, we try if the current directory is a valid git repository.
 392  * Upon failure, we return NULL.
 393  *
 394  * If all goes well, we return the directory we used to chdir() (but
 395  * before ~user is expanded), avoiding getcwd() resolving symbolic
 396  * links.  User relative paths are also returned as they are given,
 397  * except DWIM suffixing.
 398  */
 399 char *enter_repo(char *path, int strict)
 400 {
 401         static char used_path[PATH_MAX];
 402         static char validated_path[PATH_MAX];
 403
 404         if (!path)
 405                 return NULL;
 406
 407         if (!strict) {
 408                 static const char *suffix[] = {
 409                         ".git/.git", "/.git", ".git", "", NULL,
 410                 };
 411                 int len = strlen(path);
 412                 int i;
 413                 while ((1 < len) && (path[len-1] == '/')) {
 414                         path[len-1] = 0;
 415                         len--;
 416                 }
 417                 if (PATH_MAX <= len)
 418                         return NULL;
 419                 if (path[0] == '~') {
 420                         char *newpath = expand_user_path(path);
 421                         if (!newpath || (PATH_MAX - 10 < strlen(newpath))) {
 422                                 free(newpath);
 423                                 return NULL;
 424                         }
 425                         /*
 426                          * Copy back into the static buffer. A pity
 427                          * since newpath was not bounded, but other
 428                          * branches of the if are limited by PATH_MAX
 429                          * anyway.
 430                          */
 431                         strcpy(used_path, newpath); free(newpath);
 432                         strcpy(validated_path, path);
 433                         path = used_path;
 434                 }
 435                 else if (PATH_MAX - 10 < len)
 436                         return NULL;
 437                 else {
 438                         path = strcpy(used_path, path);
 439                         strcpy(validated_path, path);
 440                 }
 441                 len = strlen(path);
 442                 for (i = 0; suffix[i]; i++) {
 443                         strcpy(path + len, suffix[i]);
 444                         if (!access(path, F_OK)) {
 445                                 strcat(validated_path, suffix[i]);
 446                                 break;
 447                         }
 448                 }
 449                 if (!suffix[i] || chdir(path))
 450                         return NULL;
 451                 path = validated_path;
 452         }
 453         else if (chdir(path))
 454                 return NULL;
 455
 456         if (access("objects", X_OK) == 0 && access("refs", X_OK) == 0 &&
 457             validate_headref("HEAD") == 0) {
 458                 set_git_dir(".");
 459                 check_repository_format();
 460                 return path;
 461         }
 462
 463         return NULL;
 464 }
 465
 466 int set_shared_perm(const char *path, int mode)
 467 {
 468         struct stat st;
 469         int tweak, shared, orig_mode;
 470
 471         if (!shared_repository) {
 472                 if (mode)
 473                         return chmod(path, mode & ~S_IFMT);
 474                 return 0;
 475         }
 476         if (!mode) {
 477                 if (lstat(path, &st) < 0)
 478                         return -1;
 479                 mode = st.st_mode;
 480                 orig_mode = mode;
 481         } else
 482                 orig_mode = 0;
 483         if (shared_repository < 0)
 484                 shared = -shared_repository;
 485         else
 486                 shared = shared_repository;
 487         tweak = shared;
 488
 489         if (!(mode & S_IWUSR))
 490                 tweak &= ~0222;
 491         if (mode & S_IXUSR)
 492                 /* Copy read bits to execute bits */
 493                 tweak |= (tweak & 0444) >> 2;
 494         if (shared_repository < 0)
 495                 mode = (mode & ~0777) | tweak;
 496         else
 497                 mode |= tweak;
 498
 499         if (S_ISDIR(mode)) {
 500                 /* Copy read bits to execute bits */
 501                 mode |= (shared & 0444) >> 2;
 502                 mode |= FORCE_DIR_SET_GID;
 503         }
 504
 505         if (((shared_repository < 0
 506               ? (orig_mode & (FORCE_DIR_SET_GID | 0777))
 507               : (orig_mode & mode)) != mode) &&
 508             chmod(path, (mode & ~S_IFMT)) < 0)
 509                 return -2;
 510         return 0;
 511 }
 512
 513 const char *make_relative_path(const char *abs, const char *base)
 514 {
 515         static char buf[PATH_MAX + 1];
 516         int i = 0, j = 0;
 517
 518         if (!base || !base[0])
 519                 return abs;
 520         while (base[i]) {
 521                 if (is_dir_sep(base[i])) {
 522                         if (!is_dir_sep(abs[j]))
 523                                 return abs;
 524                         while (is_dir_sep(base[i]))
 525                                 i++;
 526                         while (is_dir_sep(abs[j]))
 527                                 j++;
 528                         continue;
 529                 } else if (abs[j] != base[i]) {
 530                         return abs;
 531                 }
 532                 i++;
 533                 j++;
 534         }
 535         if (
 536             /* "/foo" is a prefix of "/foo" */
 537             abs[j] &&
 538             /* "/foo" is not a prefix of "/foobar" */
 539             !is_dir_sep(base[i-1]) && !is_dir_sep(abs[j])
 540            )
 541                 return abs;
 542         while (is_dir_sep(abs[j]))
 543                 j++;
 544         if (!abs[j])
 545                 strcpy(buf, ".");
 546         else
 547                 strcpy(buf, abs + j);
 548         return buf;
 549 }
 550
 551 /*
 552  * It is okay if dst == src, but they should not overlap otherwise.
 553  *
 554  * Performs the following normalizations on src, storing the result in dst:
 555  * - Ensures that components are separated by '/' (Windows only)
 556  * - Squashes sequences of '/'.
 557  * - Removes "." components.
 558  * - Removes ".." components, and the components the precede them.
 559  * Returns failure (non-zero) if a ".." component appears as first path
 560  * component anytime during the normalization. Otherwise, returns success (0).
 561  *
 562  * Note that this function is purely textual.  It does not follow symlinks,
 563  * verify the existence of the path, or make any system calls.
 564  */
 565 int normalize_path_copy(char *dst, const char *src)
 566 {
 567         char *dst0;
 568
 569         if (has_dos_drive_prefix(src)) {
 570                 *dst++ = *src++;
 571                 *dst++ = *src++;
 572         }
 573         dst0 = dst;
 574
 575         if (is_dir_sep(*src)) {
 576                 *dst++ = '/';
 577                 while (is_dir_sep(*src))
 578                         src++;
 579         }
 580
 581         for (;;) {
 582                 char c = *src;
 583
 584                 /*
 585                  * A path component that begins with . could be
 586                  * special:
 587                  * (1) "." and ends   -- ignore and terminate.
 588                  * (2) "./"           -- ignore them, eat slash and continue.
 589                  * (3) ".." and ends  -- strip one and terminate.
 590                  * (4) "../"          -- strip one, eat slash and continue.
 591                  */
 592                 if (c == '.') {
 593                         if (!src[1]) {
 594                                 /* (1) */
 595                                 src++;
 596                         } else if (is_dir_sep(src[1])) {
 597                                 /* (2) */
 598                                 src += 2;
 599                                 while (is_dir_sep(*src))
 600                                         src++;
 601                                 continue;
 602                         } else if (src[1] == '.') {
 603                                 if (!src[2]) {
 604                                         /* (3) */
 605                                         src += 2;
 606                                         goto up_one;
 607                                 } else if (is_dir_sep(src[2])) {
 608                                         /* (4) */
 609                                         src += 3;
 610                                         while (is_dir_sep(*src))
 611                                                 src++;
 612                                         goto up_one;
 613                                 }
 614                         }
 615                 }
 616
 617                 /* copy up to the next '/', and eat all '/' */
 618                 while ((c = *src++) != '\0' && !is_dir_sep(c))
 619                         *dst++ = c;
 620                 if (is_dir_sep(c)) {
 621                         *dst++ = '/';
 622                         while (is_dir_sep(c))
 623                                 c = *src++;
 624                         src--;
 625                 } else if (!c)
 626                         break;
 627                 continue;
 628
 629         up_one:
 630                 /*
 631                  * dst0..dst is prefix portion, and dst[-1] is '/';
 632                  * go up one level.
 633                  */
 634                 dst--;  /* go to trailing '/' */
 635                 if (dst <= dst0)
 636                         return -1;
 637                 /* Windows: dst[-1] cannot be backslash anymore */
 638                 while (dst0 < dst && dst[-1] != '/')
 639                         dst--;
 640         }
 641         *dst = '\0';
 642         return 0;
 643 }
 644
 645 /*
 646  * path = Canonical absolute path
 647  * prefix_list = Colon-separated list of absolute paths
 648  *
 649  * Determines, for each path in prefix_list, whether the "prefix" really
 650  * is an ancestor directory of path.  Returns the length of the longest
 651  * ancestor directory, excluding any trailing slashes, or -1 if no prefix
 652  * is an ancestor.  (Note that this means 0 is returned if prefix_list is
 653  * "/".) "/foo" is not considered an ancestor of "/foobar".  Directories
 654  * are not considered to be their own ancestors.  path must be in a
 655  * canonical form: empty components, or "." or ".." components are not
 656  * allowed.  prefix_list may be null, which is like "".
 657  */
 658 int longest_ancestor_length(const char *path, const char *prefix_list)
 659 {
 660         char buf[PATH_MAX+1];
 661         const char *ceil, *colon;
 662         int len, max_len = -1;
 663
 664         if (prefix_list == NULL || !strcmp(path, "/"))
 665                 return -1;
 666
 667         for (colon = ceil = prefix_list; *colon; ceil = colon+1) {
 668                 for (colon = ceil; *colon && *colon != PATH_SEP; colon++);
 669                 len = colon - ceil;
 670                 if (len == 0 || len > PATH_MAX || !is_absolute_path(ceil))
 671                         continue;
 672                 strlcpy(buf, ceil, len+1);
 673                 if (normalize_path_copy(buf, buf) < 0)
 674                         continue;
 675                 len = strlen(buf);
 676                 if (len > 0 && buf[len-1] == '/')
 677                         buf[--len] = '\0';
 678
 679                 if (!strncmp(path, buf, len) &&
 680                     path[len] == '/' &&
 681                     len > max_len) {
 682                         max_len = len;
 683                 }
 684         }
 685
 686         return max_len;
 687 }
 688
 689 /* strip arbitrary amount of directory separators at end of path */
 690 static inline int chomp_trailing_dir_sep(const char *path, int len)
 691 {
 692         while (len && is_dir_sep(path[len - 1]))
 693                 len--;
 694         return len;
 695 }
 696
 697 /*
 698  * If path ends with suffix (complete path components), returns the
 699  * part before suffix (sans trailing directory separators).
 700  * Otherwise returns NULL.
 701  */
 702 char *strip_path_suffix(const char *path, const char *suffix)
 703 {
 704         int path_len = strlen(path), suffix_len = strlen(suffix);
 705
 706         while (suffix_len) {
 707                 if (!path_len)
 708                         return NULL;
 709
 710                 if (is_dir_sep(path[path_len - 1])) {
 711                         if (!is_dir_sep(suffix[suffix_len - 1]))
 712                                 return NULL;
 713                         path_len = chomp_trailing_dir_sep(path, path_len);
 714                         suffix_len = chomp_trailing_dir_sep(suffix, suffix_len);
 715                 }
 716                 else if (path[--path_len] != suffix[--suffix_len])
 717                         return NULL;
 718         }
 719
 720         if (path_len && !is_dir_sep(path[path_len - 1]))
 721                 return NULL;
 722         return xstrndup(path, chomp_trailing_dir_sep(path, path_len));
 723 }
 724
 725 int daemon_avoid_alias(const char *p)
 726 {
 727         int sl, ndot;
 728
 729         /*
 730          * This resurrects the belts and suspenders paranoia check by HPA
 731          * done in <435560F7.4080006@zytor.com> thread, now enter_repo()
 732          * does not do getcwd() based path canonicalization.
 733          *
 734          * sl becomes true immediately after seeing '/' and continues to
 735          * be true as long as dots continue after that without intervening
 736          * non-dot character.
 737          */
 738         if (!p || (*p != '/' && *p != '~'))
 739                 return -1;
 740         sl = 1; ndot = 0;
 741         p++;
 742
 743         while (1) {
 744                 char ch = *p++;
 745                 if (sl) {
 746                         if (ch == '.')
 747                                 ndot++;
 748                         else if (ch == '/') {
 749                                 if (ndot < 3)
 750                                         /* reject //, /./ and /../ */
 751                                         return -1;
 752                                 ndot = 0;
 753                         }
 754                         else if (ch == 0) {
 755                                 if (0 < ndot && ndot < 3)
 756                                         /* reject /.$ and /..$ */
 757                                         return -1;
 758                                 return 0;
 759                         }
 760                         else
 761                                 sl = ndot = 0;
 762                 }
 763                 else if (ch == 0)
 764                         return 0;
 765                 else if (ch == '/') {
 766                         sl = 1;
 767                         ndot = 0;
 768                 }
 769         }
 770 }
 771
 772 int offset_1st_component(const char *path)
 773 {
 774         if (has_dos_drive_prefix(path))
 775                 return 2 + is_dir_sep(path[2]);
 776         return is_dir_sep(path[0]);
 777 }