src/pwd.c

   1 /* pwd - print current directory
   2    Copyright (C) 1994-2012 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 #include <getopt.h>
  19 #include <stdio.h>
  20 #include <sys/types.h>
  21
  22 #include "system.h"
  23 #include "error.h"
  24 #include "quote.h"
  25 #include "root-dev-ino.h"
  26 #include "xgetcwd.h"
  27
  28 /* The official name of this program (e.g., no 'g' prefix).  */
  29 #define PROGRAM_NAME "pwd"
  30
  31 #define AUTHORS proper_name ("Jim Meyering")
  32
  33 struct file_name
  34 {
  35   char *buf;
  36   size_t n_alloc;
  37   char *start;
  38 };
  39
  40 static struct option const longopts[] =
  41 {
  42   {"logical", no_argument, NULL, 'L'},
  43   {"physical", no_argument, NULL, 'P'},
  44   {GETOPT_HELP_OPTION_DECL},
  45   {GETOPT_VERSION_OPTION_DECL},
  46   {NULL, 0, NULL, 0}
  47 };
  48
  49 void
  50 usage (int status)
  51 {
  52   if (status != EXIT_SUCCESS)
  53     emit_try_help ();
  54   else
  55     {
  56       printf (_("Usage: %s [OPTION]...\n"), program_name);
  57       fputs (_("\
  58 Print the full filename of the current working directory.\n\
  59 \n\
  60 "), stdout);
  61       fputs (_("\
  62   -L, --logical   use PWD from environment, even if it contains symlinks\n\
  63   -P, --physical  avoid all symlinks\n\
  64 "), stdout);
  65       fputs (HELP_OPTION_DESCRIPTION, stdout);
  66       fputs (VERSION_OPTION_DESCRIPTION, stdout);
  67       printf (USAGE_BUILTIN_WARNING, PROGRAM_NAME);
  68       emit_ancillary_info ();
  69     }
  70   exit (status);
  71 }
  72
  73 static void
  74 file_name_free (struct file_name *p)
  75 {
  76   free (p->buf);
  77   free (p);
  78 }
  79
  80 static struct file_name *
  81 file_name_init (void)
  82 {
  83   struct file_name *p = xmalloc (sizeof *p);
  84
  85   /* Start with a buffer larger than PATH_MAX, but beware of systems
  86      on which PATH_MAX is very large -- e.g., INT_MAX.  */
  87   p->n_alloc = MIN (2 * PATH_MAX, 32 * 1024);
  88
  89   p->buf = xmalloc (p->n_alloc);
  90   p->start = p->buf + (p->n_alloc - 1);
  91   p->start[0] = '\0';
  92   return p;
  93 }
  94
  95 /* Prepend the name S of length S_LEN, to the growing file_name, P.  */
  96 static void
  97 file_name_prepend (struct file_name *p, char const *s, size_t s_len)
  98 {
  99   size_t n_free = p->start - p->buf;
 100   if (n_free < 1 + s_len)
 101     {
 102       size_t half = p->n_alloc + 1 + s_len;
 103       /* Use xnmalloc+free rather than xnrealloc, since with the latter
 104          we'd end up copying the data twice: once via realloc, then again
 105          to align it with the end of the new buffer.  With xnmalloc, we
 106          copy it only once.  */
 107       char *q = xnmalloc (2, half);
 108       size_t n_used = p->n_alloc - n_free;
 109       p->start = q + 2 * half - n_used;
 110       memcpy (p->start, p->buf + n_free, n_used);
 111       free (p->buf);
 112       p->buf = q;
 113       p->n_alloc = 2 * half;
 114     }
 115
 116   p->start -= 1 + s_len;
 117   p->start[0] = '/';
 118   memcpy (p->start + 1, s, s_len);
 119 }
 120
 121 /* Return a string (malloc'd) consisting of N '/'-separated ".." components.  */
 122 static char *
 123 nth_parent (size_t n)
 124 {
 125   char *buf = xnmalloc (3, n);
 126   char *p = buf;
 127   size_t i;
 128
 129   for (i = 0; i < n; i++)
 130     {
 131       memcpy (p, "../", 3);
 132       p += 3;
 133     }
 134   p[-1] = '\0';
 135   return buf;
 136 }
 137
 138 /* Determine the basename of the current directory, where DOT_SB is the
 139    result of lstat'ing "." and prepend that to the file name in *FILE_NAME.
 140    Find the directory entry in '..' that matches the dev/i-node of DOT_SB.
 141    Upon success, update *DOT_SB with stat information of '..', chdir to '..',
 142    and prepend "/basename" to FILE_NAME.
 143    Otherwise, exit with a diagnostic.
 144    PARENT_HEIGHT is the number of levels '..' is above the starting directory.
 145    The first time this function is called (from the initial directory),
 146    PARENT_HEIGHT is 1.  This is solely for diagnostics.
 147    Exit nonzero upon error.  */
 148
 149 static void
 150 find_dir_entry (struct stat *dot_sb, struct file_name *file_name,
 151                 size_t parent_height)
 152 {
 153   DIR *dirp;
 154   int fd;
 155   struct stat parent_sb;
 156   bool use_lstat;
 157   bool found;
 158
 159   dirp = opendir ("..");
 160   if (dirp == NULL)
 161     error (EXIT_FAILURE, errno, _("cannot open directory %s"),
 162            quote (nth_parent (parent_height)));
 163
 164   fd = dirfd (dirp);
 165   if ((0 <= fd ? fchdir (fd) : chdir ("..")) < 0)
 166     error (EXIT_FAILURE, errno, _("failed to chdir to %s"),
 167            quote (nth_parent (parent_height)));
 168
 169   if ((0 <= fd ? fstat (fd, &parent_sb) : stat (".", &parent_sb)) < 0)
 170     error (EXIT_FAILURE, errno, _("failed to stat %s"),
 171            quote (nth_parent (parent_height)));
 172
 173   /* If parent and child directory are on different devices, then we
 174      can't rely on d_ino for useful i-node numbers; use lstat instead.  */
 175   use_lstat = (parent_sb.st_dev != dot_sb->st_dev);
 176
 177   found = false;
 178   while (1)
 179     {
 180       struct dirent const *dp;
 181       struct stat ent_sb;
 182       ino_t ino;
 183
 184       errno = 0;
 185       if ((dp = readdir_ignoring_dot_and_dotdot (dirp)) == NULL)
 186         {
 187           if (errno)
 188             {
 189               /* Save/restore errno across closedir call.  */
 190               int e = errno;
 191               closedir (dirp);
 192               errno = e;
 193
 194               /* Arrange to give a diagnostic after exiting this loop.  */
 195               dirp = NULL;
 196             }
 197           break;
 198         }
 199
 200       ino = D_INO (dp);
 201
 202       if (ino == NOT_AN_INODE_NUMBER || use_lstat)
 203         {
 204           if (lstat (dp->d_name, &ent_sb) < 0)
 205             {
 206               /* Skip any entry we can't stat.  */
 207               continue;
 208             }
 209           ino = ent_sb.st_ino;
 210         }
 211
 212       if (ino != dot_sb->st_ino)
 213         continue;
 214
 215       /* If we're not crossing a device boundary, then a simple i-node
 216          match is enough.  */
 217       if ( ! use_lstat || ent_sb.st_dev == dot_sb->st_dev)
 218         {
 219           file_name_prepend (file_name, dp->d_name, _D_EXACT_NAMLEN (dp));
 220           found = true;
 221           break;
 222         }
 223     }
 224
 225   if (dirp == NULL || closedir (dirp) != 0)
 226     {
 227       /* Note that this diagnostic serves for both readdir
 228          and closedir failures.  */
 229       error (EXIT_FAILURE, errno, _("reading directory %s"),
 230              quote (nth_parent (parent_height)));
 231     }
 232
 233   if ( ! found)
 234     error (EXIT_FAILURE, 0,
 235            _("couldn't find directory entry in %s with matching i-node"),
 236              quote (nth_parent (parent_height)));
 237
 238   *dot_sb = parent_sb;
 239 }
 240
 241 /* Construct the full, absolute name of the current working
 242    directory and store it in *FILE_NAME.
 243    The getcwd function performs nearly the same task, but is typically
 244    unable to handle names longer than PATH_MAX.  This function has
 245    no such limitation.  However, this function *can* fail due to
 246    permission problems or a lack of memory, while GNU/Linux's getcwd
 247    function works regardless of restricted permissions on parent
 248    directories.  Upon failure, give a diagnostic and exit nonzero.
 249
 250    Note: although this function is similar to getcwd, it has a fundamental
 251    difference in that it gives a diagnostic and exits upon failure.
 252    I would have liked a function that did not exit, and that could be
 253    used as a getcwd replacement.  Unfortunately, considering all of
 254    the information the caller would require in order to produce good
 255    diagnostics, it doesn't seem worth the added complexity.
 256    In any case, any getcwd replacement must *not* exceed the PATH_MAX
 257    limitation.  Otherwise, functions like 'chdir' would fail with
 258    ENAMETOOLONG.
 259
 260    FIXME-maybe: if find_dir_entry fails due to permissions, try getcwd,
 261    in case the unreadable directory is close enough to the root that
 262    getcwd works from there.  */
 263
 264 static void
 265 robust_getcwd (struct file_name *file_name)
 266 {
 267   size_t height = 1;
 268   struct dev_ino dev_ino_buf;
 269   struct dev_ino *root_dev_ino = get_root_dev_ino (&dev_ino_buf);
 270   struct stat dot_sb;
 271
 272   if (root_dev_ino == NULL)
 273     error (EXIT_FAILURE, errno, _("failed to get attributes of %s"),
 274            quote ("/"));
 275
 276   if (stat (".", &dot_sb) < 0)
 277     error (EXIT_FAILURE, errno, _("failed to stat %s"), quote ("."));
 278
 279   while (1)
 280     {
 281       /* If we've reached the root, we're done.  */
 282       if (SAME_INODE (dot_sb, *root_dev_ino))
 283         break;
 284
 285       find_dir_entry (&dot_sb, file_name, height++);
 286     }
 287
 288   /* See if a leading slash is needed; file_name_prepend adds one.  */
 289   if (file_name->start[0] == '\0')
 290     file_name_prepend (file_name, "", 0);
 291 }
 292
 293
 294 /* Return PWD from the environment if it is acceptable for 'pwd -L'
 295    output, otherwise NULL.  */
 296 static char *
 297 logical_getcwd (void)
 298 {
 299   struct stat st1;
 300   struct stat st2;
 301   char *wd = getenv ("PWD");
 302   char *p;
 303
 304   /* Textual validation first.  */
 305   if (!wd || wd[0] != '/')
 306     return NULL;
 307   p = wd;
 308   while ((p = strstr (p, "/.")))
 309     {
 310       if (!p[2] || p[2] == '/'
 311           || (p[2] == '.' && (!p[3] || p[3] == '/')))
 312         return NULL;
 313       p++;
 314     }
 315
 316   /* System call validation.  */
 317   if (stat (wd, &st1) == 0 && stat (".", &st2) == 0 && SAME_INODE (st1, st2))
 318     return wd;
 319   return NULL;
 320 }
 321
 322
 323 int
 324 main (int argc, char **argv)
 325 {
 326   char *wd;
 327   /* POSIX requires a default of -L, but most scripts expect -P.  */
 328   bool logical = (getenv ("POSIXLY_CORRECT") != NULL);
 329
 330   initialize_main (&argc, &argv);
 331   set_program_name (argv[0]);
 332   setlocale (LC_ALL, "");
 333   bindtextdomain (PACKAGE, LOCALEDIR);
 334   textdomain (PACKAGE);
 335
 336   atexit (close_stdout);
 337
 338   while (1)
 339     {
 340       int c = getopt_long (argc, argv, "LP", longopts, NULL);
 341       if (c == -1)
 342         break;
 343       switch (c)
 344         {
 345         case 'L':
 346           logical = true;
 347           break;
 348         case 'P':
 349           logical = false;
 350           break;
 351
 352         case_GETOPT_HELP_CHAR;
 353
 354         case_GETOPT_VERSION_CHAR (PROGRAM_NAME, AUTHORS);
 355
 356         default:
 357           usage (EXIT_FAILURE);
 358         }
 359     }
 360
 361   if (optind < argc)
 362     error (0, 0, _("ignoring non-option arguments"));
 363
 364   if (logical)
 365     {
 366       wd = logical_getcwd ();
 367       if (wd)
 368         {
 369           puts (wd);
 370           exit (EXIT_SUCCESS);
 371         }
 372     }
 373
 374   wd = xgetcwd ();
 375   if (wd != NULL)
 376     {
 377       puts (wd);
 378       free (wd);
 379     }
 380   else
 381     {
 382       struct file_name *file_name = file_name_init ();
 383       robust_getcwd (file_name);
 384       puts (file_name->start);
 385       file_name_free (file_name);
 386     }
 387
 388   exit (EXIT_SUCCESS);
 389 }