getcwd.c

标准c库代码,可以应用于各个系统提供了大量的基本函数

/*
 * Copyright (c) 1989, 1991 The Regents of the University of California.
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. All advertising materials mentioning features or use of this software
 *    must display the following acknowledgement:
 *	This product includes software developed by the University of
 *	California, Berkeley and its contributors.
 * 4. Neither the name of the University nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 */

#if defined(LIBC_SCCS) && !defined(lint)
static char sccsid[] = "@(#)getcwd.c	5.11 (Berkeley) 2/24/91";
#endif /* LIBC_SCCS and not lint */

#include <sys/stat.h>
#include <errno.h>
#include <dirent.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <reent.h>
#include <_syslist.h>

#define bcopy(a,b,c)	memmove (b,a,c)

#define	ISDOT(dp) \
	(dp->d_name[0] == '.' && (dp->d_name[1] == '\0' || \
	    dp->d_name[1] == '.' && dp->d_name[2] == '\0'))

#ifndef _REENT_ONLY

char *
getcwd (pt, size)
     char *pt;
     size_t size;
{
  register struct dirent *dp;
  register DIR *dir;
  register dev_t dev;
  register ino_t ino;
  register int first;
  register char *bpt, *bup;
  struct stat s;
  dev_t root_dev;
  ino_t root_ino;
  size_t ptsize, upsize;
  int save_errno;
  char *ept, *eup, *up;

  /*
   * If no buffer specified by the user, allocate one as necessary.
   * If a buffer is specified, the size has to be non-zero.  The path
   * is built from the end of the buffer backwards.
   */

  if (pt)
    {
      ptsize = 0;
      if (!size)
	{
	  errno = EINVAL;
	  return (char *) NULL;
	}
      ept = pt + size;
    }
  else
    {
      if (!(pt = (char *) malloc (ptsize = 1024 - 4)))
	{
	  return (char *) NULL;
	}
      ept = pt + ptsize;
    }
  bpt = ept - 1;
  *bpt = '\0';

  /*
   * Allocate bytes (1024 - malloc space) for the string of "../"'s.
   * Should always be enough (it's 340 levels).  If it's not, allocate
   * as necessary.  Special * case the first stat, it's ".", not "..".
   */

  if (!(up = (char *) malloc (upsize = 1024 - 4)))
    {
      goto err;
    }
  eup = up + MAXPATHLEN;
  bup = up;
  up[0] = '.';
  up[1] = '\0';

  /* Save root values, so know when to stop. */
  if (stat ("/", &s))
    goto err;
  root_dev = s.st_dev;
  root_ino = s.st_ino;

  errno = 0;			/* XXX readdir has no error return. */

  for (first = 1;; first = 0)
    {
      /* Stat the current level. */
      if (_stat (up, &s))
	goto err;

      /* Save current node values. */
      ino = s.st_ino;
      dev = s.st_dev;

      /* Check for reaching root. */
      if (root_dev == dev && root_ino == ino)
	{
	  *--bpt = '/';
	  /*
	   * It's unclear that it's a requirement to copy the
	   * path to the beginning of the buffer, but it's always
	   * been that way and stuff would probably break.
	   */
	  (void) bcopy (bpt, pt, ept - bpt);
	  free (up);
	  return pt;
	}

      /*
       * Build pointer to the parent directory, allocating memory
       * as necessary.  Max length is 3 for "../", the largest
       * possible component name, plus a trailing NULL.
       */

      if (bup + 3 + MAXNAMLEN + 1 >= eup)
	{
	  if (!(up = (char *) realloc (up, upsize *= 2)))
	    {
	      goto err;
	    }
	  bup = up;
	  eup = up + upsize;
	}
      *bup++ = '.';
      *bup++ = '.';
      *bup = '\0';

      /* Open and stat parent directory. */
      if (!(dir = _opendir (up)) || _fstat (__dirfd (dir), &s))
	goto err;

      /* Add trailing slash for next directory. */
      *bup++ = '/';

      /*
       * If it's a mount point, have to stat each element because
       * the inode number in the directory is for the entry in the
       * parent directory, not the inode number of the mounted file.
       */

      save_errno = 0;
      if (s.st_dev == dev)
	{
	  for (;;)
	    {
	      if (!(dp = _readdir (dir)))
		goto notfound;
	      if (dp->d_ino == ino)
		break;
	    }
	}
      else
	for (;;)
	  {
	    if (!(dp = _readdir (dir)))
	      goto notfound;
	    if (ISDOT (dp))
	      continue;
	    bcopy (dp->d_name, bup, strlen (dp->d_name) + 1);

	    /* Save the first error for later. */
	    if (stat (up, &s))
	      {
		if (!save_errno)
		  save_errno = errno;
		errno = 0;
		continue;
	      }
	    if (s.st_dev == dev && s.st_ino == ino)
	      break;
	  }

      /*
       * Check for length of the current name, preceding slash,
       * leading slash.
       */

      if (bpt - pt <= strlen (dp->d_name) + (first ? 1 : 2))
	{
	  size_t len, off;

	  if (!ptsize)
	    {
	      errno = ERANGE;
	      goto err;
	    }
	  off = bpt - pt;
	  len = ept - bpt;
	  if (!(pt = (char *) realloc (pt, ptsize *= 2)))
	    {
	      goto err;
	    }
	  bpt = pt + off;
	  ept = pt + ptsize;
	  (void) bcopy (bpt, ept - len, len);
	  bpt = ept - len;
	}
      if (!first)
	*--bpt = '/';
      bpt -= strlen (dp->d_name);
      bcopy (dp->d_name, bpt, strlen (dp->d_name));
      (void) _closedir (dir);

      /* Truncate any file name. */
      *bup = '\0';
    }

notfound:
  /*
   * If readdir set errno, use it, not any saved error; otherwise,
   * didn't find the current directory in its parent directory, set
   * errno to ENOENT.
   */

  if (!errno)
    errno = save_errno ? save_errno : ENOENT;
  /* FALLTHROUGH */

err:
  if (ptsize)
    free (pt);
  free (up);
  return (char *) NULL;
}

#endif /* _REENT_ONLY */