getcwd.c   [plain text]

/* Copyright (C) 1991,92,93,94,95,96,97,98,99,2004,2005,2006,2007 Free Software
   Foundation, Inc.
   This file is part of the GNU C Library.

   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 2, 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, write to the Free Software Foundation,
   Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.  */

#if !_LIBC
# include <config.h>
# include <unistd.h>
# include "dirfd.h"
#endif

#include <errno.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <stdbool.h>
#include <stddef.h>

#include <fcntl.h> /* For AT_FDCWD on Solaris 9.  */

#ifndef __set_errno
# define __set_errno(val) (errno = (val))
#endif

#include <dirent.h>
#ifndef _D_EXACT_NAMLEN
# define _D_EXACT_NAMLEN(d) strlen ((d)->d_name)
#endif
#ifndef _D_ALLOC_NAMLEN
# define _D_ALLOC_NAMLEN(d) (_D_EXACT_NAMLEN (d) + 1)
#endif

#include <unistd.h>
#include <stdlib.h>
#include <string.h>

#if _LIBC
# ifndef mempcpy
#  define mempcpy __mempcpy
# endif
#endif

#include <limits.h>

/* Work around a bug in Solaris 9 and 10: AT_FDCWD is positive.  Its
   value exceeds INT_MAX, so its use as an int doesn't conform to the
   C standard, and GCC and Sun C complain in some cases.  */
#if 0 < AT_FDCWD && AT_FDCWD == 0xffd19553
# undef AT_FDCWD
# define AT_FDCWD (-3041965)
#endif

#ifdef ENAMETOOLONG
# define is_ENAMETOOLONG(x) ((x) == ENAMETOOLONG)
#else
# define is_ENAMETOOLONG(x) 0
#endif

#ifndef MAX
# define MAX(a, b) ((a) < (b) ? (b) : (a))
#endif
#ifndef MIN
# define MIN(a, b) ((a) < (b) ? (a) : (b))
#endif

#ifndef PATH_MAX
# ifdef	MAXPATHLEN
#  define PATH_MAX MAXPATHLEN
# else
#  define PATH_MAX 1024
# endif
#endif

#if D_INO_IN_DIRENT
# define MATCHING_INO(dp, ino) ((dp)->d_ino == (ino))
#else
# define MATCHING_INO(dp, ino) true
#endif

#if !_LIBC
# define __getcwd getcwd
# define __lstat lstat
# define __closedir closedir
# define __opendir opendir
# define __readdir readdir
#endif

/* The results of opendir() in this file are not used with dirfd and fchdir,
   therefore save some unnecessary recursion in fchdir.c.  */
#undef opendir
#undef closedir

/* Get the name of the current working directory, and put it in SIZE
   bytes of BUF.  Returns NULL if the directory couldn't be determined or
   SIZE was too small.  If successful, returns BUF.  In GNU, if BUF is
   NULL, an array is allocated with `malloc'; the array is SIZE bytes long,
   unless SIZE == 0, in which case it is as big as necessary.  */

char *
__getcwd (char *buf, size_t size)
{
  /* Lengths of big file name components and entire file names, and a
     deep level of file name nesting.  These numbers are not upper
     bounds; they are merely large values suitable for initial
     allocations, designed to be large enough for most real-world
     uses.  */
  enum
    {
      BIG_FILE_NAME_COMPONENT_LENGTH = 255,
      BIG_FILE_NAME_LENGTH = MIN (4095, PATH_MAX - 1),
      DEEP_NESTING = 100
    };

#ifdef AT_FDCWD
  int fd = AT_FDCWD;
  bool fd_needs_closing = false;
#else
  char dots[DEEP_NESTING * sizeof ".." + BIG_FILE_NAME_COMPONENT_LENGTH + 1];
  char *dotlist = dots;
  size_t dotsize = sizeof dots;
  size_t dotlen = 0;
#endif
  DIR *dirstream = NULL;
  dev_t rootdev, thisdev;
  ino_t rootino, thisino;
  char *dir;
  register char *dirp;
  struct stat st;
  size_t allocated = size;
  size_t used;

#if HAVE_PARTLY_WORKING_GETCWD
  /* The system getcwd works, except it sometimes fails when it
     shouldn't, setting errno to ERANGE, ENAMETOOLONG, or ENOENT.  If
     AT_FDCWD is not defined, the algorithm below is O(N**2) and this
     is much slower than the system getcwd (at least on GNU/Linux).
     So trust the system getcwd's results unless they look
     suspicious.

     Use the system getcwd even if we have openat support, since the
     system getcwd works even when a parent is unreadable, while the
     openat-based approach does not.  */

# undef getcwd
  dir = getcwd (buf, size);
  if (dir || (errno != ERANGE && !is_ENAMETOOLONG (errno) && errno != ENOENT))
    return dir;
#endif

  if (size == 0)
    {
      if (buf != NULL)
	{
	  __set_errno (EINVAL);
	  return NULL;
	}

      allocated = BIG_FILE_NAME_LENGTH + 1;
    }

  if (buf == NULL)
    {
      dir = malloc (allocated);
      if (dir == NULL)
	return NULL;
    }
  else
    dir = buf;

  dirp = dir + allocated;
  *--dirp = '\0';

  if (__lstat (".", &st) < 0)
    goto lose;
  thisdev = st.st_dev;
  thisino = st.st_ino;

  if (__lstat ("/", &st) < 0)
    goto lose;
  rootdev = st.st_dev;
  rootino = st.st_ino;

  while (!(thisdev == rootdev && thisino == rootino))
    {
      struct dirent *d;
      dev_t dotdev;
      ino_t dotino;
      bool mount_point;
      int parent_status;
      size_t dirroom;
      size_t namlen;
      bool use_d_ino = true;

      /* Look at the parent directory.  */
#ifdef AT_FDCWD
      fd = openat (fd, "..", O_RDONLY);
      if (fd < 0)
	goto lose;
      fd_needs_closing = true;
      parent_status = fstat (fd, &st);
#else
      dotlist[dotlen++] = '.';
      dotlist[dotlen++] = '.';
      dotlist[dotlen] = '\0';
      parent_status = __lstat (dotlist, &st);
#endif
      if (parent_status != 0)
	goto lose;

      if (dirstream && __closedir (dirstream) != 0)
	{
	  dirstream = NULL;
	  goto lose;
	}

      /* Figure out if this directory is a mount point.  */
      dotdev = st.st_dev;
      dotino = st.st_ino;
      mount_point = dotdev != thisdev;

      /* Search for the last directory.  */
#ifdef AT_FDCWD
      dirstream = fdopendir (fd);
      if (dirstream == NULL)
	goto lose;
      /* Reset fd.  It may have been closed by fdopendir.  */
      fd = dirfd (dirstream);
      fd_needs_closing = false;
#else
      dirstream = __opendir (dotlist);
      if (dirstream == NULL)
	goto lose;
      dotlist[dotlen++] = '/';
#endif
      for (;;)
	{
	  /* Clear errno to distinguish EOF from error if readdir returns
	     NULL.  */
	  __set_errno (0);
	  d = __readdir (dirstream);

	  /* When we've iterated through all directory entries without finding
	     one with a matching d_ino, rewind the stream and consider each
	     name again, but this time, using lstat.  This is necessary in a
	     chroot on at least one system (glibc-2.3.6 + linux 2.6.12), where
	     .., ../.., ../../.., etc. all had the same device number, yet the
	     d_ino values for entries in / did not match those obtained
	     via lstat.  */
	  if (d == NULL && errno == 0 && use_d_ino)
	    {
	      use_d_ino = false;
	      rewinddir (dirstream);
	      d = __readdir (dirstream);
	    }

	  if (d == NULL)
	    {
	      if (errno == 0)
		/* EOF on dirstream, which can mean e.g., that the current
		   directory has been removed.  */
		__set_errno (ENOENT);
	      goto lose;
	    }
	  if (d->d_name[0] == '.' &&
	      (d->d_name[1] == '\0' ||
	       (d->d_name[1] == '.' && d->d_name[2] == '\0')))
	    continue;

	  if (use_d_ino)
	    {
	      bool match = (MATCHING_INO (d, thisino) || mount_point);
	      if (! match)
		continue;
	    }

	  {
	    int entry_status;
#ifdef AT_FDCWD
	    entry_status = fstatat (fd, d->d_name, &st, AT_SYMLINK_NOFOLLOW);
#else
	    /* Compute size needed for this file name, or for the file
	       name ".." in the same directory, whichever is larger.
	       Room for ".." might be needed the next time through
	       the outer loop.  */
	    size_t name_alloc = _D_ALLOC_NAMLEN (d);
	    size_t filesize = dotlen + MAX (sizeof "..", name_alloc);

	    if (filesize < dotlen)
	      goto memory_exhausted;

	    if (dotsize < filesize)
	      {
		/* My, what a deep directory tree you have, Grandma.  */
		size_t newsize = MAX (filesize, dotsize * 2);
		size_t i;
		if (newsize < dotsize)
		  goto memory_exhausted;
		if (dotlist != dots)
		  free (dotlist);
		dotlist = malloc (newsize);
		if (dotlist == NULL)
		  goto lose;
		dotsize = newsize;

		i = 0;
		do
		  {
		    dotlist[i++] = '.';
		    dotlist[i++] = '.';
		    dotlist[i++] = '/';
		  }
		while (i < dotlen);
	      }

	    memcpy (dotlist + dotlen, d->d_name, _D_ALLOC_NAMLEN (d));
	    entry_status = __lstat (dotlist, &st);
#endif
	    /* We don't fail here if we cannot stat() a directory entry.
	       This can happen when (network) file systems fail.  If this
	       entry is in fact the one we are looking for we will find
	       out soon as we reach the end of the directory without
	       having found anything.  */
	    if (entry_status == 0 && S_ISDIR (st.st_mode)
		&& st.st_dev == thisdev && st.st_ino == thisino)
	      break;
	  }
	}

      dirroom = dirp - dir;
      namlen = _D_EXACT_NAMLEN (d);

      if (dirroom <= namlen)
	{
	  if (size != 0)
	    {
	      __set_errno (ERANGE);
	      goto lose;
	    }
	  else
	    {
	      char *tmp;
	      size_t oldsize = allocated;

	      allocated += MAX (allocated, namlen);
	      if (allocated < oldsize
		  || ! (tmp = realloc (dir, allocated)))
		goto memory_exhausted;

	      /* Move current contents up to the end of the buffer.
		 This is guaranteed to be non-overlapping.  */
	      dirp = memcpy (tmp + allocated - (oldsize - dirroom),
			     tmp + dirroom,
			     oldsize - dirroom);
	      dir = tmp;
	    }
	}
      dirp -= namlen;
      memcpy (dirp, d->d_name, namlen);
      *--dirp = '/';

      thisdev = dotdev;
      thisino = dotino;
    }

  if (dirstream && __closedir (dirstream) != 0)
    {
      dirstream = NULL;
      goto lose;
    }

  if (dirp == &dir[allocated - 1])
    *--dirp = '/';

#ifndef AT_FDCWD
  if (dotlist != dots)
    free (dotlist);
#endif

  used = dir + allocated - dirp;
  memmove (dir, dirp, used);

  if (size == 0)
    /* Ensure that the buffer is only as large as necessary.  */
    buf = realloc (dir, used);

  if (buf == NULL)
    /* Either buf was NULL all along, or `realloc' failed but
       we still have the original string.  */
    buf = dir;

  return buf;

 memory_exhausted:
  __set_errno (ENOMEM);
 lose:
  {
    int save = errno;
    if (dirstream)
      __closedir (dirstream);
#ifdef AT_FDCWD
    if (fd_needs_closing)
      close (fd);
#else
    if (dotlist != dots)
      free (dotlist);
#endif
    if (buf == NULL)
      free (dir);
    __set_errno (save);
  }
  return NULL;
}

#ifdef weak_alias
weak_alias (__getcwd, getcwd)
#endif