/*-
 * SPDX-License-Identifier: BSD-3-Clause
 *
 * Copyright (c) 1989, 1991, 1993, 1995
 *	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. 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.
 */

#include <sys/cdefs.h>
__SCCSID("@(#)getcwd.c	8.5 (Berkeley) 2/7/95");
__FBSDID("$FreeBSD: releng/12.0/lib/libc/gen/getcwd.c 335898 2018-07-03 17:31:45Z jhb $");

#include "namespace.h"
#include <sys/param.h>
#include <sys/stat.h>

#include <dirent.h>
#include <errno.h>
#include <fcntl.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include "un-namespace.h"

#include "gen-private.h"

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

extern int __getcwd(char *, size_t);

char *
getcwd(char *pt, size_t size)
{
	struct dirent *dp;
	DIR *dir = NULL;
	dev_t dev;
	ino_t ino;
	int first;
	char *bpt;
	struct stat s;
	dev_t root_dev;
	ino_t root_ino;
	size_t ptsize;
	int save_errno;
	char *ept, c;
	int fd;

	/*
	 * 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 (NULL);
		}
		if (size == 1) {
			errno = ERANGE;
			return (NULL);
		}
		ept = pt + size;
	} else {
		if ((pt = malloc(ptsize = PATH_MAX)) == NULL)
			return (NULL);
		ept = pt + ptsize;
	}
	if (__getcwd(pt, ept - pt) == 0) {
		if (*pt != '/') {
			bpt = pt;
			ept = pt + strlen(pt) - 1;
			while (bpt < ept) {
				c = *bpt;
				*bpt++ = *ept;
				*ept-- = c;
			}
		}
		return (pt);
	}
	bpt = ept - 1;
	*bpt = '\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 (dir != NULL ? _fstat(_dirfd(dir), &s) : lstat(".", &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.
			 */
			bcopy(bpt, pt, ept - bpt);
			if (dir)
				(void) closedir(dir);
			return (pt);
		}

		/* Open and stat parent directory. */
		fd = _openat(dir != NULL ? _dirfd(dir) : AT_FDCWD,
				"..", O_RDONLY | O_CLOEXEC);
		if (fd == -1)
			goto err;
		if (dir)
			(void) closedir(dir);
		if (!(dir = fdopendir(fd)) || _fstat(_dirfd(dir), &s)) {
			_close(fd);
			goto err;
		}

		/*
		 * 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_fileno == ino)
					break;
			}
		} else
			for (;;) {
				if (!(dp = readdir(dir)))
					goto notfound;
				if (ISDOT(dp))
					continue;

				/* Save the first error for later. */
				if (fstatat(_dirfd(dir), dp->d_name, &s,
				    AT_SYMLINK_NOFOLLOW)) {
					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.
		 */
		while (bpt - pt < dp->d_namlen + (first ? 1 : 2)) {
			size_t len, off;

			if (!ptsize) {
				errno = ERANGE;
				goto err;
			}
			off = bpt - pt;
			len = ept - bpt;
			if ((pt = reallocf(pt, ptsize *= 2)) == NULL)
				goto err;
			bpt = pt + off;
			ept = pt + ptsize;
			bcopy(bpt, ept - len, len);
			bpt = ept - len;
		}
		if (!first)
			*--bpt = '/';
		bpt -= dp->d_namlen;
		bcopy(dp->d_name, bpt, dp->d_namlen);
	}

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:
	save_errno = errno;

	if (ptsize)
		free(pt);
	if (dir)
		(void) closedir(dir);

	errno = save_errno;
	return (NULL);
}
