getcwd.c revision 28235 
1/*
2 * Copyright (c) 1989, 1991, 1993, 1995
3 *	The Regents of the University of California.  All rights reserved.
4 *
5 * Redistribution and use in source and binary forms, with or without
6 * modification, are permitted provided that the following conditions
7 * are met:
8 * 1. Redistributions of source code must retain the above copyright
9 *    notice, this list of conditions and the following disclaimer.
10 * 2. Redistributions in binary form must reproduce the above copyright
11 *    notice, this list of conditions and the following disclaimer in the
12 *    documentation and/or other materials provided with the distribution.
13 * 3. All advertising materials mentioning features or use of this software
14 *    must display the following acknowledgement:
15 *	This product includes software developed by the University of
16 *	California, Berkeley and its contributors.
17 * 4. Neither the name of the University nor the names of its contributors
18 *    may be used to endorse or promote products derived from this software
19 *    without specific prior written permission.
20 *
21 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
22 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
23 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
24 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
25 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
26 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
27 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
28 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
29 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
30 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
31 * SUCH DAMAGE.
32 */
33
34#if defined(LIBC_SCCS) && !defined(lint)
35static char sccsid[] = "@(#)getcwd.c	8.5 (Berkeley) 2/7/95";
36#endif /* LIBC_SCCS and not lint */
37
38#include <sys/param.h>
39#include <sys/stat.h>
40
41#include <dirent.h>
42#include <errno.h>
43#include <fcntl.h>
44#include <stdio.h>
45#include <stdlib.h>
46#include <string.h>
47#include <unistd.h>
48
49#define	ISDOT(dp) \
50	(dp->d_name[0] == '.' && (dp->d_name[1] == '\0' || \
51	    (dp->d_name[1] == '.' && dp->d_name[2] == '\0')))
52
53char *
54getcwd(pt, size)
55	char *pt;
56	size_t size;
57{
58	register struct dirent *dp;
59	register DIR *dir = NULL;
60	register dev_t dev;
61	register ino_t ino;
62	register int first;
63	register char *bpt, *bup;
64	struct stat s;
65	dev_t root_dev;
66	ino_t root_ino;
67	size_t ptsize, upsize;
68	int save_errno;
69	char *ept, *eup, *up;
70
71	/*
72	 * If no buffer specified by the user, allocate one as necessary.
73	 * If a buffer is specified, the size has to be non-zero.  The path
74	 * is built from the end of the buffer backwards.
75	 */
76	if (pt) {
77		ptsize = 0;
78		if (!size) {
79			errno = EINVAL;
80			return (NULL);
81		}
82		if (size == 1) {
83			errno = ERANGE;
84			return (NULL);
85		}
86		ept = pt + size;
87	} else {
88		if ((pt = malloc(ptsize = 1024 - 4)) == NULL)
89			return (NULL);
90		ept = pt + ptsize;
91	}
92	bpt = ept - 1;
93	*bpt = '\0';
94
95	/*
96	 * Allocate bytes (1024 - malloc space) for the string of "../"'s.
97	 * Should always be enough (it's 340 levels).  If it's not, allocate
98	 * as necessary.  Special case the first stat, it's ".", not "..".
99	 */
100	if ((up = malloc(upsize = 1024 - 4)) == NULL)
101		goto err;
102	eup = up + MAXPATHLEN;
103	bup = up;
104	up[0] = '.';
105	up[1] = '\0';
106
107	/* Save root values, so know when to stop. */
108	if (stat("/", &s))
109		goto err;
110	root_dev = s.st_dev;
111	root_ino = s.st_ino;
112
113	errno = 0;			/* XXX readdir has no error return. */
114
115	for (first = 1;; first = 0) {
116		/* Stat the current level. */
117		if (lstat(up, &s))
118			goto err;
119
120		/* Save current node values. */
121		ino = s.st_ino;
122		dev = s.st_dev;
123
124		/* Check for reaching root. */
125		if (root_dev == dev && root_ino == ino) {
126			*--bpt = '/';
127			/*
128			 * It's unclear that it's a requirement to copy the
129			 * path to the beginning of the buffer, but it's always
130			 * been that way and stuff would probably break.
131			 */
132			bcopy(bpt, pt, ept - bpt);
133			free(up);
134			return (pt);
135		}
136
137		/*
138		 * Build pointer to the parent directory, allocating memory
139		 * as necessary.  Max length is 3 for "../", the largest
140		 * possible component name, plus a trailing NULL.
141		 */
142		if (bup + 3  + MAXNAMLEN + 1 >= eup) {
143			if ((up = realloc(up, upsize *= 2)) == NULL)
144				goto err;
145			bup = up;
146			eup = up + upsize;
147		}
148		*bup++ = '.';
149		*bup++ = '.';
150		*bup = '\0';
151
152		/* Open and stat parent directory. */
153		if (!(dir = opendir(up)) || fstat(dirfd(dir), &s))
154			goto err;
155
156		/* Add trailing slash for next directory. */
157		*bup++ = '/';
158		*bup = '\0';
159
160		/*
161		 * If it's a mount point, have to stat each element because
162		 * the inode number in the directory is for the entry in the
163		 * parent directory, not the inode number of the mounted file.
164		 */
165		save_errno = 0;
166		if (s.st_dev == dev) {
167			for (;;) {
168				if (!(dp = readdir(dir)))
169					goto notfound;
170				if (dp->d_fileno == ino)
171					break;
172			}
173		} else
174			for (;;) {
175				if (!(dp = readdir(dir)))
176					goto notfound;
177				if (ISDOT(dp))
178					continue;
179				bcopy(dp->d_name, bup, dp->d_namlen + 1);
180
181				/* Save the first error for later. */
182				if (lstat(up, &s)) {
183					if (!save_errno)
184						save_errno = errno;
185					errno = 0;
186					continue;
187				}
188				if (s.st_dev == dev && s.st_ino == ino)
189					break;
190			}
191
192		/*
193		 * Check for length of the current name, preceding slash,
194		 * leading slash.
195		 */
196		if (bpt - pt < dp->d_namlen + (first ? 1 : 2)) {
197			size_t len, off;
198
199			if (!ptsize) {
200				errno = ERANGE;
201				goto err;
202			}
203			off = bpt - pt;
204			len = ept - bpt;
205			if ((pt = realloc(pt, ptsize *= 2)) == NULL)
206				goto err;
207			bpt = pt + off;
208			ept = pt + ptsize;
209			bcopy(bpt, ept - len, len);
210			bpt = ept - len;
211		}
212		if (!first)
213			*--bpt = '/';
214		bpt -= dp->d_namlen;
215		bcopy(dp->d_name, bpt, dp->d_namlen);
216		(void) closedir(dir);
217		dir = NULL;
218
219		/* Truncate any file name. */
220		*bup = '\0';
221	}
222
223notfound:
224	/*
225	 * If readdir set errno, use it, not any saved error; otherwise,
226	 * didn't find the current directory in its parent directory, set
227	 * errno to ENOENT.
228	 */
229	if (!errno)
230		errno = save_errno ? save_errno : ENOENT;
231	/* FALLTHROUGH */
232err:
233	if (ptsize)
234		free(pt);
235	if (dir)
236		(void) closedir(dir);
237	free(up);
238	return (NULL);
239}
240