path: root/lib/fts.c

/* Traverse a file hierarchy.

   Copyright (C) 2004, 2005, 2006 Free Software Foundation, Inc.

   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.  */

/*-
 * Copyright (c) 1990, 1993, 1994
 *	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.
 * 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.
 */

#ifdef HAVE_CONFIG_H
# include <config.h>
#endif

#if defined(LIBC_SCCS) && !defined(lint)
static char sccsid[] = "@(#)fts.c	8.6 (Berkeley) 8/14/94";
#endif /* LIBC_SCCS and not lint */

#include "fts_.h"

#if HAVE_SYS_PARAM_H || defined _LIBC
# include <sys/param.h>
#endif
#ifdef _LIBC
# include <include/sys/stat.h>
#else
# include <sys/stat.h>
#endif
#include <fcntl.h>
#include <errno.h>
#include "dirfd.h"
#include <stdbool.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>

#if ! _LIBC
# include "fcntl--.h"
# include "lstat.h"
# include "openat.h"
# include "unistd--.h"
#endif

#if defined _LIBC
# include <dirent.h>
# define NAMLEN(dirent) _D_EXACT_NAMLEN (dirent)
#else
# if HAVE_DIRENT_H
#  include <dirent.h>
#  define NAMLEN(dirent) strlen ((dirent)->d_name)
# else
#  define dirent direct
#  define NAMLEN(dirent) (dirent)->d_namlen
#  if HAVE_SYS_NDIR_H
#   include <sys/ndir.h>
#  endif
#  if HAVE_SYS_DIR_H
#   include <sys/dir.h>
#  endif
#  if HAVE_NDIR_H
#   include <ndir.h>
#  endif
# endif
#endif

#ifdef _LIBC
# undef close
# define close __close
# undef closedir
# define closedir __closedir
# undef open
# define open __open
# undef opendir
# define opendir __opendir
# undef readdir
# define readdir __readdir
#else
# undef internal_function
# define internal_function /* empty */
#endif

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

#ifndef __attribute__
# if __GNUC__ < 2 || (__GNUC__ == 2 && __GNUC_MINOR__ < 8) || __STRICT_ANSI__
#  define __attribute__(x) /* empty */
# endif
#endif

#ifndef ATTRIBUTE_UNUSED
# define ATTRIBUTE_UNUSED __attribute__ ((__unused__))
#endif

/* If this host provides the openat function, then we can avoid
   attempting to open "." in some initialization code below.  */
#ifdef HAVE_OPENAT
# define HAVE_OPENAT_SUPPORT 1
#else
# define HAVE_OPENAT_SUPPORT 0
#endif

static FTSENT	*fts_alloc (FTS *, const char *, size_t) internal_function;
static FTSENT	*fts_build (FTS *, int) internal_function;
static void	 fts_lfree (FTSENT *) internal_function;
static void	 fts_load (FTS *, FTSENT *) internal_function;
static size_t	 fts_maxarglen (char * const *) internal_function;
static void	 fts_padjust (FTS *, FTSENT *) internal_function;
static bool	 fts_palloc (FTS *, size_t) internal_function;
static FTSENT	*fts_sort (FTS *, FTSENT *, size_t) internal_function;
static unsigned short int fts_stat (FTS *, FTSENT *, bool) internal_function;
static int      fts_safe_changedir (FTS *, FTSENT *, int, const char *)
     internal_function;

#if _LGPL_PACKAGE
static bool enter_dir (FTS *fts, FTSENT *ent) { return true; }
static void leave_dir (FTS *fts, FTSENT *ent) {}
static bool setup_dir (FTS *fts) { return true; }
static void free_dir (FTS *fts) {}
#else
# include "fcntl--.h"
# include "fts-cycle.c"
#endif

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

#ifndef SIZE_MAX
# define SIZE_MAX ((size_t) -1)
#endif

#ifndef O_DIRECTORY
# define O_DIRECTORY 0
#endif

#define ISDOT(a)	(a[0] == '.' && (!a[1] || (a[1] == '.' && !a[2])))

#define CLR(opt)	(sp->fts_options &= ~(opt))
#define ISSET(opt)	(sp->fts_options & (opt))
#define SET(opt)	(sp->fts_options |= (opt))

#define FCHDIR(sp, fd)	(!ISSET(FTS_NOCHDIR) \
			 && (cwd_advance_fd (sp, fd), 0))


/* fts_build flags */
#define BCHILD		1		/* fts_children */
#define BNAMES		2		/* fts_children, names only */
#define BREAD		3		/* fts_read */

#if FTS_DEBUG
# include <inttypes.h>
# include <stdint.h>
# include <stdio.h>
bool fts_debug = false;
# define Dprintf(x) do { if (fts_debug) printf x; } while (0)
#else
# define Dprintf(x)
#endif

#define LEAVE_DIR(Fts, Ent, Tag)				\
  do								\
    {								\
      Dprintf (("  %s-leaving: %s\n", Tag, (Ent)->fts_path));	\
      leave_dir (Fts, Ent);					\
    }								\
  while (false)

/* Open the directory DIR if possible, and return a file descriptor.
   As with openat-like functions, if DIR is a relative name,
   interpret it relative to the directory open on file descriptor FD.
   Return -1 and set errno on failure.  */
static int
internal_function
diropen_fd (int cwd_fd, char const *dir)
{
  int fd = openat (cwd_fd, dir,
		   O_RDONLY | O_DIRECTORY | O_NOCTTY | O_NONBLOCK);
  return fd;
}

/* file-descriptor-relative opendir.  */
/* FIXME: if others need this function, move it into lib/openat.c */
static inline DIR *
internal_function
opendirat (int fd, char const *dir)
{
  int new_fd = openat (fd, dir, O_RDONLY);
  DIR *dirp;

  if (new_fd < 0)
    return NULL;
  dirp = fdopendir (new_fd);
  if (dirp == NULL)
    {
      int saved_errno = errno;
      close (new_fd);
      errno = saved_errno;
    }
  return dirp;
}

/* Virtual fchdir.  Advance SP's working directory
   file descriptor, SP->fts_cwd_fd, to FD, and close
   the previous one, ignoring any error.  */
static void
internal_function
cwd_advance_fd (FTS *sp, int fd)
{
  int old = sp->fts_cwd_fd;
  if (old == fd && old != AT_FDCWD)
    abort ();
  sp->fts_cwd_fd = fd;
  if (0 <= old)
    close (old); /* ignore any close failure */
}

/* Open the directory DIR if possible, and return a file
   descriptor.  Return -1 and set errno on failure.  It doesn't matter
   whether the file descriptor has read or write access.  */

static inline int
internal_function
diropen (FTS const *sp, char const *dir)
{
  return diropen_fd (sp->fts_cwd_fd, dir);
}

FTS *
fts_open (char * const *argv,
	  register int options,
	  int (*compar) (FTSENT const **, FTSENT const **))
{
	register FTS *sp;
	register FTSENT *p, *root;
	register size_t nitems;
	FTSENT *parent, *tmp = NULL;	/* pacify gcc */
	size_t len;

	/* Options check. */
	if (options & ~FTS_OPTIONMASK) {
		__set_errno (EINVAL);
		return (NULL);
	}

	/* Allocate/initialize the stream */
	if ((sp = malloc(sizeof(FTS))) == NULL)
		return (NULL);
	memset(sp, 0, sizeof(FTS));
	sp->fts_compar = compar;
	sp->fts_options = options;

	/* Logical walks turn on NOCHDIR; symbolic links are too hard. */
	if (ISSET(FTS_LOGICAL))
		SET(FTS_NOCHDIR);

	/* Initialize fts_cwd_fd.  */
	sp->fts_cwd_fd = AT_FDCWD;
	if ( ! ISSET(FTS_NOCHDIR) && ! HAVE_OPENAT_SUPPORT)
	  {
	    /* While it isn't technically necessary to open "." this
	       early, doing it here saves us the trouble of ensuring
	       later (where it'd be messier) that "." can in fact
	       be opened.  If not, revert to FTS_NOCHDIR mode.  */
	    int fd = open (".", O_RDONLY);
	    if (fd < 0)
	      {
		/* Even if `.' is unreadable, don't revert to FTS_NOCHDIR mode
		   on systems like Linux+PROC_FS, where our openat emulation
		   is good enough.  Note: on a system that emulates
		   openat via /proc, this technique can still fail, but
		   only in extreme conditions, e.g., when the working
		   directory cannot be saved (i.e. save_cwd fails) --
		   and that happens only on Linux only when "." is unreadable
		   and the CWD would be longer than PATH_MAX.
		   FIXME: once Linux kernel openat support is well established,
		   replace the above open call and this entire if/else block
		   with the body of the if-block below.  */
		if ( openat_needs_fchdir ())
		  {
		    SET(FTS_NOCHDIR);
		    sp->fts_cwd_fd = -1;
		  }
	      }
	    else
	      {
		close (fd);
	      }
	  }

	/*
	 * Start out with 1K of file name space, and enough, in any case,
	 * to hold the user's file names.
	 */
#ifndef MAXPATHLEN
# define MAXPATHLEN 1024
#endif
	{
	  size_t maxarglen = fts_maxarglen(argv);
	  if (! fts_palloc(sp, MAX(maxarglen, MAXPATHLEN)))
		  goto mem1;
	}

	/* Allocate/initialize root's parent. */
	if ((parent = fts_alloc(sp, "", 0)) == NULL)
		goto mem2;
	parent->fts_level = FTS_ROOTPARENTLEVEL;

	/* Allocate/initialize root(s). */
	for (root = NULL, nitems = 0; *argv != NULL; ++argv, ++nitems) {
		/* Don't allow zero-length file names. */
		if ((len = strlen(*argv)) == 0) {
			__set_errno (ENOENT);
			goto mem3;
		}

		if ((p = fts_alloc(sp, *argv, len)) == NULL)
			goto mem3;
		p->fts_level = FTS_ROOTLEVEL;
		p->fts_parent = parent;
		p->fts_accpath = p->fts_name;
		p->fts_info = fts_stat(sp, p, ISSET(FTS_COMFOLLOW) != 0);

		/* Command-line "." and ".." are real directories. */
		if (p->fts_info == FTS_DOT)
			p->fts_info = FTS_D;

		/*
		 * If comparison routine supplied, traverse in sorted
		 * order; otherwise traverse in the order specified.
		 */
		if (compar) {
			p->fts_link = root;
			root = p;
		} else {
			p->fts_link = NULL;
			if (root == NULL)
				tmp = root = p;
			else {
				tmp->fts_link = p;
				tmp = p;
			}
		}
	}
	if (compar && nitems > 1)
		root = fts_sort(sp, root, nitems);

	/*
	 * Allocate a dummy pointer and make fts_read think that we've just
	 * finished the node before the root(s); set p->fts_info to FTS_INIT
	 * so that everything about the "current" node is ignored.
	 */
	if ((sp->fts_cur = fts_alloc(sp, "", 0)) == NULL)
		goto mem3;
	sp->fts_cur->fts_link = root;
	sp->fts_cur->fts_info = FTS_INIT;
	if (! setup_dir (sp))
	  goto mem3;

	return (sp);

mem3:	fts_lfree(root);
	free(parent);
mem2:	free(sp->fts_path);
mem1:	free(sp);
	return (NULL);
}

static void
internal_function
fts_load (FTS *sp, register FTSENT *p)
{
	register size_t len;
	register char *cp;

	/*
	 * Load the stream structure for the next traversal.  Since we don't
	 * actually enter the directory until after the preorder visit, set
	 * the fts_accpath field specially so the chdir gets done to the right
	 * place and the user can access the first node.  From fts_open it's
	 * known that the file name will fit.
	 */
	len = p->fts_pathlen = p->fts_namelen;
	memmove(sp->fts_path, p->fts_name, len + 1);
	if ((cp = strrchr(p->fts_name, '/')) && (cp != p->fts_name || cp[1])) {
		len = strlen(++cp);
		memmove(p->fts_name, cp, len + 1);
		p->fts_namelen = len;
	}
	p->fts_accpath = p->fts_path = sp->fts_path;
	sp->fts_dev = p->fts_statp->st_dev;
}

int
fts_close (FTS *sp)
{
	register FTSENT *freep, *p;
	int saved_errno = 0;

	/*
	 * This still works if we haven't read anything -- the dummy structure
	 * points to the root list, so we step through to the end of the root
	 * list which has a valid parent pointer.
	 */
	if (sp->fts_cur) {
		for (p = sp->fts_cur; p->fts_level >= FTS_ROOTLEVEL;) {
			freep = p;
			p = p->fts_link != NULL ? p->fts_link : p->fts_parent;
			free(freep);
		}
		free(p);
	}

	/* Free up child linked list, sort array, file name buffer. */
	if (sp->fts_child)
		fts_lfree(sp->fts_child);
	if (sp->fts_array)
		free(sp->fts_array);
	free(sp->fts_path);

	if (0 <= sp->fts_cwd_fd)
	  close (sp->fts_cwd_fd);

	free_dir (sp);

	/* Free up the stream pointer. */
	free(sp);

	/* Set errno and return. */
	if (saved_errno) {
		__set_errno (saved_errno);
		return (-1);
	}

	return (0);
}

/*
 * Special case of "/" at the end of the file name so that slashes aren't
 * appended which would cause file names to be written as "....//foo".
 */
#define NAPPEND(p)							\
	(p->fts_path[p->fts_pathlen - 1] == '/'				\
	    ? p->fts_pathlen - 1 : p->fts_pathlen)

FTSENT *
fts_read (register FTS *sp)
{
	register FTSENT *p, *tmp;
	register unsigned short int instr;
	register char *t;

	/* If finished or unrecoverable error, return NULL. */
	if (sp->fts_cur == NULL || ISSET(FTS_STOP))
		return (NULL);

	/* Set current node pointer. */
	p = sp->fts_cur;

	/* Save and zero out user instructions. */
	instr = p->fts_instr;
	p->fts_instr = FTS_NOINSTR;

	/* Any type of file may be re-visited; re-stat and re-turn. */
	if (instr == FTS_AGAIN) {
		p->fts_info = fts_stat(sp, p, false);
		return (p);
	}
	Dprintf (("fts_read: p=%s\n",
		  p->fts_info == FTS_INIT ? "" : p->fts_path));

	/*
	 * Following a symlink -- SLNONE test allows application to see
	 * SLNONE and recover.  If indirecting through a symlink, have
	 * keep a pointer to current location.  If unable to get that
	 * pointer, follow fails.
	 */
	if (instr == FTS_FOLLOW &&
	    (p->fts_info == FTS_SL || p->fts_info == FTS_SLNONE)) {
		p->fts_info = fts_stat(sp, p, true);
		if (p->fts_info == FTS_D && !ISSET(FTS_NOCHDIR)) {
			if ((p->fts_symfd = diropen (sp, ".")) < 0) {
				p->fts_errno = errno;
				p->fts_info = FTS_ERR;
			} else
				p->fts_flags |= FTS_SYMFOLLOW;
		}
		goto check_for_dir;
	}

	/* Directory in pre-order. */
	if (p->fts_info == FTS_D) {
		/* If skipped or crossed mount point, do post-order visit. */
		if (instr == FTS_SKIP ||
		    (ISSET(FTS_XDEV) && p->fts_statp->st_dev != sp->fts_dev)) {
			if (p->fts_flags & FTS_SYMFOLLOW)
				(void)close(p->fts_symfd);
			if (sp->fts_child) {
				fts_lfree(sp->fts_child);
				sp->fts_child = NULL;
			}
			p->fts_info = FTS_DP;
			LEAVE_DIR (sp, p, "1");
			return (p);
		}

		/* Rebuild if only read the names and now traversing. */
		if (sp->fts_child != NULL && ISSET(FTS_NAMEONLY)) {
			CLR(FTS_NAMEONLY);
			fts_lfree(sp->fts_child);
			sp->fts_child = NULL;
		}

		/*
		 * Cd to the subdirectory.
		 *
		 * If have already read and now fail to chdir, whack the list
		 * to make the names come out right, and set the parent errno
		 * so the application will eventually get an error condition.
		 * Set the FTS_DONTCHDIR flag so that when we logically change
		 * directories back to the parent we don't do a chdir.
		 *
		 * If haven't read do so.  If the read fails, fts_build sets
		 * FTS_STOP or the fts_info field of the node.
		 */
		if (sp->fts_child != NULL) {
			if (fts_safe_changedir(sp, p, -1, p->fts_accpath)) {
				p->fts_errno = errno;
				p->fts_flags |= FTS_DONTCHDIR;
				for (p = sp->fts_child; p != NULL;
				     p = p->fts_link)
					p->fts_accpath =
					    p->fts_parent->fts_accpath;
			}
		} else if ((sp->fts_child = fts_build(sp, BREAD)) == NULL) {
			if (ISSET(FTS_STOP))
				return (NULL);
			/* If fts_build's call to fts_safe_changedir failed
			   because it was not able to fchdir into a
			   subdirectory, tell the caller.  */
			if (p->fts_errno)
				p->fts_info = FTS_ERR;
			LEAVE_DIR (sp, p, "2");
			return (p);
		}
		p = sp->fts_child;
		sp->fts_child = NULL;
		goto name;
	}

	/* Move to the next node on this level. */
next:	tmp = p;
	if ((p = p->fts_link) != NULL) {
		free(tmp);

		/*
		 * If reached the top, return to the original directory (or
		 * the root of the tree), and load the file names for the next
		 * root.
		 */
		if (p->fts_level == FTS_ROOTLEVEL) {
			FCHDIR(sp, AT_FDCWD);
			fts_load(sp, p);
			goto check_for_dir;
		}

		/*
		 * User may have called fts_set on the node.  If skipped,
		 * ignore.  If followed, get a file descriptor so we can
		 * get back if necessary.
		 */
		if (p->fts_instr == FTS_SKIP)
			goto next;
		if (p->fts_instr == FTS_FOLLOW) {
			p->fts_info = fts_stat(sp, p, true);
			if (p->fts_info == FTS_D && !ISSET(FTS_NOCHDIR)) {
				if ((p->fts_symfd = diropen (sp, ".")) < 0) {
					p->fts_errno = errno;
					p->fts_info = FTS_ERR;
				} else
					p->fts_flags |= FTS_SYMFOLLOW;
			}
			p->fts_instr = FTS_NOINSTR;
		}

name:		t = sp->fts_path + NAPPEND(p->fts_parent);
		*t++ = '/';
		memmove(t, p->fts_name, p->fts_namelen + 1);
check_for_dir:
		sp->fts_cur = p;
		if (p->fts_info == FTS_D)
		  {
		    Dprintf (("  %s-entering: %s\n", sp, p->fts_path));
		    if (! enter_dir (sp, p))
		      {
			__set_errno (ENOMEM);
			return NULL;
		      }
		  }
		return p;
	}

	/* Move up to the parent node. */
	p = tmp->fts_parent;
	free(tmp);

	if (p->fts_level == FTS_ROOTPARENTLEVEL) {
		/*
		 * Done; free everything up and set errno to 0 so the user
		 * can distinguish between error and EOF.
		 */
		free(p);
		__set_errno (0);
		return (sp->fts_cur = NULL);
	}

	/* NUL terminate the file name.  */
	sp->fts_path[p->fts_pathlen] = '\0';

	/*
	 * Return to the parent directory.  If at a root node, just set
	 * sp->fts_cwd_fd to AT_FDCWD.  If we came through a symlink,
	 * go back through the file descriptor.  Otherwise, move up
	 * one level, via "..".
	 */
	if (p->fts_level == FTS_ROOTLEVEL) {
		FCHDIR(sp, AT_FDCWD);
	} else if (p->fts_flags & FTS_SYMFOLLOW) {
		FCHDIR(sp, p->fts_symfd);
		(void)close(p->fts_symfd);
	} else if (!(p->fts_flags & FTS_DONTCHDIR) &&
		   fts_safe_changedir(sp, p->fts_parent, -1, "..")) {
		p->fts_errno = errno;
		SET(FTS_STOP);
	}
	p->fts_info = p->fts_errno ? FTS_ERR : FTS_DP;
	if (p->fts_errno == 0)
		LEAVE_DIR (sp, p, "3");
	sp->fts_cur = p;
	return ISSET(FTS_STOP) ? NULL : p;
}

/*
 * Fts_set takes the stream as an argument although it's not used in this
 * implementation; it would be necessary if anyone wanted to add global
 * semantics to fts using fts_set.  An error return is allowed for similar
 * reasons.
 */
/* ARGSUSED */
int
fts_set(FTS *sp ATTRIBUTE_UNUSED, FTSENT *p, int instr)
{
	if (instr != 0 && instr != FTS_AGAIN && instr != FTS_FOLLOW &&
	    instr != FTS_NOINSTR && instr != FTS_SKIP) {
		__set_errno (EINVAL);
		return (1);
	}
	p->fts_instr = instr;
	return (0);
}

FTSENT *
fts_children (register FTS *sp, int instr)
{
	register FTSENT *p;
	int fd;

	if (instr != 0 && instr != FTS_NAMEONLY) {
		__set_errno (EINVAL);
		return (NULL);
	}

	/* Set current node pointer. */
	p = sp->fts_cur;

	/*
	 * Errno set to 0 so user can distinguish empty directory from
	 * an error.
	 */
	__set_errno (0);

	/* Fatal errors stop here. */
	if (ISSET(FTS_STOP))
		return (NULL);

	/* Return logical hierarchy of user's arguments. */
	if (p->fts_info == FTS_INIT)
		return (p->fts_link);

	/*
	 * If not a directory being visited in pre-order, stop here.  Could
	 * allow FTS_DNR, assuming the user has fixed the problem, but the
	 * same effect is available with FTS_AGAIN.
	 */
	if (p->fts_info != FTS_D /* && p->fts_info != FTS_DNR */)
		return (NULL);

	/* Free up any previous child list. */
	if (sp->fts_child != NULL)
		fts_lfree(sp->fts_child);

	if (instr == FTS_NAMEONLY) {
		SET(FTS_NAMEONLY);
		instr = BNAMES;
	} else
		instr = BCHILD;

	/*
	 * If using chdir on a relative file name and called BEFORE fts_read
	 * does its chdir to the root of a traversal, we can lose -- we need to
	 * chdir into the subdirectory, and we don't know where the current
	 * directory is, so we can't get back so that the upcoming chdir by
	 * fts_read will work.
	 */
	if (p->fts_level != FTS_ROOTLEVEL || p->fts_accpath[0] == '/' ||
	    ISSET(FTS_NOCHDIR))
		return (sp->fts_child = fts_build(sp, instr));

	if ((fd = diropen (sp, ".")) < 0)
		return (sp->fts_child = NULL);
	sp->fts_child = fts_build(sp, instr);
	cwd_advance_fd (sp, fd);
	return (sp->fts_child);
}

/*
 * This is the tricky part -- do not casually change *anything* in here.  The
 * idea is to build the linked list of entries that are used by fts_children
 * and fts_read.  There are lots of special cases.
 *
 * The real slowdown in walking the tree is the stat calls.  If FTS_NOSTAT is
 * set and it's a physical walk (so that symbolic links can't be directories),
 * we can do things quickly.  First, if it's a 4.4BSD file system, the type
 * of the file is in the directory entry.  Otherwise, we assume that the number
 * of subdirectories in a node is equal to the number of links to the parent.
 * The former skips all stat calls.  The latter skips stat calls in any leaf
 * directories and for any files after the subdirectories in the directory have
 * been found, cutting the stat calls by about 2/3.
 */
static FTSENT *
internal_function
fts_build (register FTS *sp, int type)
{
	register struct dirent *dp;
	register FTSENT *p, *head;
	register size_t nitems;
	FTSENT *cur, *tail;
	DIR *dirp;
	void *oldaddr;
	int cderrno;
	int saved_errno;
	bool descend;
	bool doadjust;
	ptrdiff_t level;
	nlink_t nlinks;
	bool nostat;
	size_t len, maxlen, new_len;
	char *cp;

	/* Set current node pointer. */
	cur = sp->fts_cur;

	/*
	 * Open the directory for reading.  If this fails, we're done.
	 * If being called from fts_read, set the fts_info field.
	 */
#if defined FTS_WHITEOUT && 0
	if (ISSET(FTS_WHITEOUT))
		oflag = DTF_NODUP|DTF_REWIND;
	else
		oflag = DTF_HIDEW|DTF_NODUP|DTF_REWIND;
#else
# define __opendir2(file, flag) \
	(ISSET(FTS_NOCHDIR) \
	 ? opendir(file) \
	 : opendirat(sp->fts_cwd_fd, file))
#endif
       if ((dirp = __opendir2(cur->fts_accpath, oflag)) == NULL) {
		if (type == BREAD) {
			cur->fts_info = FTS_DNR;
			cur->fts_errno = errno;
		}
		return (NULL);
	}

	/*
	 * Nlinks is the number of possible entries of type directory in the
	 * directory if we're cheating on stat calls, 0 if we're not doing
	 * any stat calls at all, (nlink_t) -1 if we're statting everything.
	 */
	if (type == BNAMES) {
		nlinks = 0;
		/* Be quiet about nostat, GCC. */
		nostat = false;
	} else if (ISSET(FTS_NOSTAT) && ISSET(FTS_PHYSICAL)) {
		nlinks = (cur->fts_statp->st_nlink
			  - (ISSET(FTS_SEEDOT) ? 0 : 2));
		nostat = true;
	} else {
		nlinks = -1;
		nostat = false;
	}

	/*
	 * If we're going to need to stat anything or we want to descend
	 * and stay in the directory, chdir.  If this fails we keep going,
	 * but set a flag so we don't chdir after the post-order visit.
	 * We won't be able to stat anything, but we can still return the
	 * names themselves.  Note, that since fts_read won't be able to
	 * chdir into the directory, it will have to return different file
	 * names than before, i.e. "a/b" instead of "b".  Since the node
	 * has already been visited in pre-order, have to wait until the
	 * post-order visit to return the error.  There is a special case
	 * here, if there was nothing to stat then it's not an error to
	 * not be able to stat.  This is all fairly nasty.  If a program
	 * needed sorted entries or stat information, they had better be
	 * checking FTS_NS on the returned nodes.
	 */
	cderrno = 0;
	if (nlinks || type == BREAD) {
		int dir_fd = dup (dirfd(dirp));
		if (dir_fd < 0 || fts_safe_changedir(sp, cur, dir_fd, NULL)) {
			if (nlinks && type == BREAD)
				cur->fts_errno = errno;
			cur->fts_flags |= FTS_DONTCHDIR;
			descend = false;
			cderrno = errno;
			closedir(dirp);
			if (0 <= dir_fd)
				close (dir_fd);
			dirp = NULL;
		} else
			descend = true;
	} else
		descend = false;

	/*
	 * Figure out the max file name length that can be stored in the
	 * current buffer -- the inner loop allocates more space as necessary.
	 * We really wouldn't have to do the maxlen calculations here, we
	 * could do them in fts_read before returning the name, but it's a
	 * lot easier here since the length is part of the dirent structure.
	 *
	 * If not changing directories set a pointer so that can just append
	 * each new component into the file name.
	 */
	len = NAPPEND(cur);
	if (ISSET(FTS_NOCHDIR)) {
		cp = sp->fts_path + len;
		*cp++ = '/';
	} else {
		/* GCC, you're too verbose. */
		cp = NULL;
	}
	len++;
	maxlen = sp->fts_pathlen - len;

	level = cur->fts_level + 1;

	/* Read the directory, attaching each entry to the `link' pointer. */
	doadjust = false;
	for (head = tail = NULL, nitems = 0; dirp && (dp = readdir(dirp));) {
		if (!ISSET(FTS_SEEDOT) && ISDOT(dp->d_name))
			continue;

		if ((p = fts_alloc(sp, dp->d_name, NAMLEN (dp))) == NULL)
			goto mem1;
		if (NAMLEN (dp) >= maxlen) {/* include space for NUL */
			oldaddr = sp->fts_path;
			if (! fts_palloc(sp, NAMLEN (dp) + len + 1)) {
				/*
				 * No more memory.  Save
				 * errno, free up the current structure and the
				 * structures already allocated.
				 */
mem1:				saved_errno = errno;
				if (p)
					free(p);
				fts_lfree(head);
				closedir(dirp);
				cur->fts_info = FTS_ERR;
				SET(FTS_STOP);
				__set_errno (saved_errno);
				return (NULL);
			}
			/* Did realloc() change the pointer? */
			if (oldaddr != sp->fts_path) {
				doadjust = true;
				if (ISSET(FTS_NOCHDIR))
					cp = sp->fts_path + len;
			}
			maxlen = sp->fts_pathlen - len;
		}

		new_len = len + NAMLEN (dp);
		if (new_len < len) {
			/*
			 * In the unlikely even that we would end up
			 * with a file name longer than SIZE_MAX, free up
			 * the current structure and the structures already
			 * allocated, then error out with ENAMETOOLONG.
			 */
			free(p);
			fts_lfree(head);
			closedir(dirp);
			cur->fts_info = FTS_ERR;
			SET(FTS_STOP);
			__set_errno (ENAMETOOLONG);
			return (NULL);
		}
		p->fts_level = level;
		p->fts_parent = sp->fts_cur;
		p->fts_pathlen = new_len;

#if defined FTS_WHITEOUT && 0
		if (dp->d_type == DT_WHT)
			p->fts_flags |= FTS_ISW;
#endif

		if (cderrno) {
			if (nlinks) {
				p->fts_info = FTS_NS;
				p->fts_errno = cderrno;
			} else
				p->fts_info = FTS_NSOK;
			p->fts_accpath = cur->fts_accpath;
		} else if (nlinks == 0
#if HAVE_STRUCT_DIRENT_D_TYPE
			   || (nostat &&
			       dp->d_type != DT_DIR && dp->d_type != DT_UNKNOWN)
#endif
		    ) {
			p->fts_accpath =
			    ISSET(FTS_NOCHDIR) ? p->fts_path : p->fts_name;
			p->fts_info = FTS_NSOK;
		} else {
			/* Build a file name for fts_stat to stat. */
			if (ISSET(FTS_NOCHDIR)) {
				p->fts_accpath = p->fts_path;
				memmove(cp, p->fts_name, p->fts_namelen + 1);
			} else
				p->fts_accpath = p->fts_name;
			/* Stat it. */
			p->fts_info = fts_stat(sp, p, false);

			/* Decrement link count if applicable. */
			if (nlinks > 0 && (p->fts_info == FTS_D ||
			    p->fts_info == FTS_DC || p->fts_info == FTS_DOT))
				nlinks -= nostat;
		}

		/* We walk in directory order so "ls -f" doesn't get upset. */
		p->fts_link = NULL;
		if (head == NULL)
			head = tail = p;
		else {
			tail->fts_link = p;
			tail = p;
		}
		++nitems;
	}
	if (dirp)
		closedir(dirp);

	/*
	 * If realloc() changed the address of the file name, adjust the
	 * addresses for the rest of the tree and the dir list.
	 */
	if (doadjust)
		fts_padjust(sp, head);

	/*
	 * If not changing directories, reset the file name back to original
	 * state.
	 */
	if (ISSET(FTS_NOCHDIR)) {
		if (len == sp->fts_pathlen || nitems == 0)
			--cp;
		*cp = '\0';
	}

	/*
	 * If descended after called from fts_children or after called from
	 * fts_read and nothing found, get back.  At the root level we use
	 * the saved fd; if one of fts_open()'s arguments is a relative name
	 * to an empty directory, we wind up here with no other way back.  If
	 * can't get back, we're done.
	 */
	if (descend && (type == BCHILD || !nitems) &&
	    (cur->fts_level == FTS_ROOTLEVEL ?
	     FCHDIR(sp, AT_FDCWD) :
	     fts_safe_changedir(sp, cur->fts_parent, -1, ".."))) {
		cur->fts_info = FTS_ERR;
		SET(FTS_STOP);
		return (NULL);
	}

	/* If didn't find anything, return NULL. */
	if (!nitems) {
		if (type == BREAD)
			cur->fts_info = FTS_DP;
		return (NULL);
	}

	/* Sort the entries. */
	if (sp->fts_compar && nitems > 1)
		head = fts_sort(sp, head, nitems);
	return (head);
}

#if FTS_DEBUG

/* Walk ->fts_parent links starting at E_CURR, until the root of the
   current hierarchy.  There should be a directory with dev/inode
   matching those of AD.  If not, print a lot of diagnostics.  */
static void
find_matching_ancestor (FTSENT const *e_curr, struct Active_dir const *ad)
{
  FTSENT const *ent;
  for (ent = e_curr; ent->fts_level >= FTS_ROOTLEVEL; ent = ent->fts_parent)
    {
      if (ad->ino == ent->fts_statp->st_ino
	  && ad->dev == ent->fts_statp->st_dev)
	return;
    }
  printf ("ERROR: tree dir, %s, not active\n", ad->fts_ent->fts_accpath);
  printf ("active dirs:\n");
  for (ent = e_curr;
       ent->fts_level >= FTS_ROOTLEVEL; ent = ent->fts_parent)
    printf ("  %s(%"PRIuMAX"/%"PRIuMAX") to %s(%"PRIuMAX"/%"PRIuMAX")...\n",
	    ad->fts_ent->fts_accpath,
	    (uintmax_t) ad->dev,
	    (uintmax_t) ad->ino,
	    ent->fts_accpath,
	    (uintmax_t) ent->fts_statp->st_dev,
	    (uintmax_t) ent->fts_statp->st_ino);
}

void
fts_cross_check (FTS const *sp)
{
  FTSENT const *ent = sp->fts_cur;
  FTSENT const *t;
  if ( ! ISSET (FTS_TIGHT_CYCLE_CHECK))
    return;

  Dprintf (("fts-cross-check cur=%s\n", ent->fts_path));
  /* Make sure every parent dir is in the tree.  */
  for (t = ent->fts_parent; t->fts_level >= FTS_ROOTLEVEL; t = t->fts_parent)
    {
      struct Active_dir ad;
      ad.ino = t->fts_statp->st_ino;
      ad.dev = t->fts_statp->st_dev;
      if ( ! hash_lookup (sp->fts_cycle.ht, &ad))
	printf ("ERROR: active dir, %s, not in tree\n", t->fts_path);
    }

  /* Make sure every dir in the tree is an active dir.
     But ENT is not necessarily a directory.  If so, just skip this part. */
  if (ent->fts_parent->fts_level >= FTS_ROOTLEVEL
      && (ent->fts_info == FTS_DP
	  || ent->fts_info == FTS_D))
    {
      struct Active_dir *ad;
      for (ad = hash_get_first (sp->fts_cycle.ht); ad != NULL;
	   ad = hash_get_next (sp->fts_cycle.ht, ad))
	{
	  find_matching_ancestor (ent, ad);
	}
    }
}
#endif

static unsigned short int
internal_function
fts_stat(FTS *sp, register FTSENT *p, bool follow)
{
	struct stat *sbp = p->fts_statp;
	int saved_errno;

#if defined FTS_WHITEOUT && 0
	/* check for whiteout */
	if (p->fts_flags & FTS_ISW) {
		memset(sbp, '\0', sizeof (*sbp));
		sbp->st_mode = S_IFWHT;
		return (FTS_W);
       }
#endif

	/*
	 * If doing a logical walk, or application requested FTS_FOLLOW, do
	 * a stat(2).  If that fails, check for a non-existent symlink.  If
	 * fail, set the errno from the stat call.
	 */
	if (ISSET(FTS_LOGICAL) || follow) {
		if (stat(p->fts_accpath, sbp)) {
			saved_errno = errno;
			if (errno == ENOENT
			    && lstat(p->fts_accpath, sbp) == 0) {
				__set_errno (0);
				return (FTS_SLNONE);
			}
			p->fts_errno = saved_errno;
			goto err;
		}
	} else if (fstatat(sp->fts_cwd_fd, p->fts_accpath, sbp,
			   AT_SYMLINK_NOFOLLOW)) {
		p->fts_errno = errno;
err:		memset(sbp, 0, sizeof(struct stat));
		return (FTS_NS);
	}

	if (S_ISDIR(sbp->st_mode)) {
		if (ISDOT(p->fts_name))
			return (FTS_DOT);

#if _LGPL_PACKAGE
		{
		  /*
		   * Cycle detection is done by brute force when the directory
		   * is first encountered.  If the tree gets deep enough or the
		   * number of symbolic links to directories is high enough,
		   * something faster might be worthwhile.
		   */
		  FTSENT *t;

		  for (t = p->fts_parent;
		       t->fts_level >= FTS_ROOTLEVEL; t = t->fts_parent)
		    if (sbp->st_ino == t->fts_statp->st_ino
			&& sbp->st_dev == t->fts_statp->st_dev)
		      {
			p->fts_cycle = t;
			return (FTS_DC);
		      }
		}
#endif

		return (FTS_D);
	}
	if (S_ISLNK(sbp->st_mode))
		return (FTS_SL);
	if (S_ISREG(sbp->st_mode))
		return (FTS_F);
	return (FTS_DEFAULT);
}

static int
fts_compar (void const *a, void const *b)
{
  /* Convert A and B to the correct types, to pacify the compiler, and
     for portability to bizarre hosts where "void const *" and "FTSENT
     const **" differ in runtime representation.  The comparison
     function cannot modify *a and *b, but there is no compile-time
     check for this.  */
  FTSENT const **pa = (FTSENT const **) a;
  FTSENT const **pb = (FTSENT const **) b;
  return pa[0]->fts_fts->fts_compar (pa, pb);
}

static FTSENT *
internal_function
fts_sort (FTS *sp, FTSENT *head, register size_t nitems)
{
	register FTSENT **ap, *p;

	/* On most modern hosts, void * and FTSENT ** have the same
	   run-time representation, and one can convert sp->fts_compar to
	   the type qsort expects without problem.  Use the heuristic that
	   this is OK if the two pointer types are the same size, and if
	   converting FTSENT ** to long int is the same as converting
	   FTSENT ** to void * and then to long int.  This heuristic isn't
	   valid in general but we don't know of any counterexamples.  */
	FTSENT *dummy;
	int (*compare) (void const *, void const *) =
	  ((sizeof &dummy == sizeof (void *)
	    && (long int) &dummy == (long int) (void *) &dummy)
	   ? (int (*) (void const *, void const *)) sp->fts_compar
	   : fts_compar);

	/*
	 * Construct an array of pointers to the structures and call qsort(3).
	 * Reassemble the array in the order returned by qsort.  If unable to
	 * sort for memory reasons, return the directory entries in their
	 * current order.  Allocate enough space for the current needs plus
	 * 40 so don't realloc one entry at a time.
	 */
	if (nitems > sp->fts_nitems) {
		struct _ftsent **a;

		sp->fts_nitems = nitems + 40;
		if (SIZE_MAX / sizeof *a < sp->fts_nitems
		    || ! (a = realloc (sp->fts_array,
				       sp->fts_nitems * sizeof *a))) {
			free(sp->fts_array);
			sp->fts_array = NULL;
			sp->fts_nitems = 0;
			return (head);
		}
		sp->fts_array = a;
	}
	for (ap = sp->fts_array, p = head; p; p = p->fts_link)
		*ap++ = p;
	qsort((void *)sp->fts_array, nitems, sizeof(FTSENT *), compare);
	for (head = *(ap = sp->fts_array); --nitems; ++ap)
		ap[0]->fts_link = ap[1];
	ap[0]->fts_link = NULL;
	return (head);
}

static FTSENT *
internal_function
fts_alloc (FTS *sp, const char *name, register size_t namelen)
{
	register FTSENT *p;
	size_t len;

	/*
	 * The file name is a variable length array.  Allocate the FTSENT
	 * structure and the file name in one chunk.
	 */
	len = sizeof(FTSENT) + namelen;
	if ((p = malloc(len)) == NULL)
		return (NULL);

	/* Copy the name and guarantee NUL termination. */
	memmove(p->fts_name, name, namelen);
	p->fts_name[namelen] = '\0';

	p->fts_namelen = namelen;
	p->fts_fts = sp;
	p->fts_path = sp->fts_path;
	p->fts_errno = 0;
	p->fts_flags = 0;
	p->fts_instr = FTS_NOINSTR;
	p->fts_number = 0;
	p->fts_pointer = NULL;
	return (p);
}

static void
internal_function
fts_lfree (register FTSENT *head)
{
	register FTSENT *p;

	/* Free a linked list of structures. */
	while ((p = head)) {
		head = head->fts_link;
		free(p);
	}
}

/*
 * Allow essentially unlimited file name lengths; find, rm, ls should
 * all work on any tree.  Most systems will allow creation of file
 * names much longer than MAXPATHLEN, even though the kernel won't
 * resolve them.  Add the size (not just what's needed) plus 256 bytes
 * so don't realloc the file name 2 bytes at a time.
 */
static bool
internal_function
fts_palloc (FTS *sp, size_t more)
{
	char *p;
	size_t new_len = sp->fts_pathlen + more + 256;

	/*
	 * See if fts_pathlen would overflow.
	 */
	if (new_len < sp->fts_pathlen) {
		if (sp->fts_path) {
			free(sp->fts_path);
			sp->fts_path = NULL;
		}
		sp->fts_path = NULL;
		__set_errno (ENAMETOOLONG);
		return false;
	}
	sp->fts_pathlen = new_len;
	p = realloc(sp->fts_path, sp->fts_pathlen);
	if (p == NULL) {
		free(sp->fts_path);
		sp->fts_path = NULL;
		return false;
	}
	sp->fts_path = p;
	return true;
}

/*
 * When the file name is realloc'd, have to fix all of the pointers in
 *  structures already returned.
 */
static void
internal_function
fts_padjust (FTS *sp, FTSENT *head)
{
	FTSENT *p;
	char *addr = sp->fts_path;

#define ADJUST(p) do {							\
	if ((p)->fts_accpath != (p)->fts_name) {			\
		(p)->fts_accpath =					\
		    (char *)addr + ((p)->fts_accpath - (p)->fts_path);	\
	}								\
	(p)->fts_path = addr;						\
} while (0)
	/* Adjust the current set of children. */
	for (p = sp->fts_child; p; p = p->fts_link)
		ADJUST(p);

	/* Adjust the rest of the tree, including the current level. */
	for (p = head; p->fts_level >= FTS_ROOTLEVEL;) {
		ADJUST(p);
		p = p->fts_link ? p->fts_link : p->fts_parent;
	}
}

static size_t
internal_function
fts_maxarglen (char * const *argv)
{
	size_t len, max;

	for (max = 0; *argv; ++argv)
		if ((len = strlen(*argv)) > max)
			max = len;
	return (max + 1);
}

/*
 * Change to dir specified by fd or file name without getting
 * tricked by someone changing the world out from underneath us.
 * Assumes p->fts_statp->st_dev and p->fts_statp->st_ino are filled in.
 * If FD is non-negative, expect it to be used after this function returns,
 * and to be closed eventually.  So don't pass e.g., `dirfd(dirp)' and then
 * do closedir(dirp), because that would invalidate the saved FD.
 * Upon failure, close FD immediately and return nonzero.
 */
static int
internal_function
fts_safe_changedir (FTS *sp, FTSENT *p, int fd, char const *dir)
{
	struct stat sb;
	int newfd = fd;
	if (ISSET(FTS_NOCHDIR)) {
		if (0 <= fd)
			close (fd);
		return (0);
	}
	if (fd < 0 && (newfd = diropen (sp, dir)) < 0)
		return (-1);
	if (fstat(newfd, &sb)) {
		if (0 <= fd) {
			int saved_errno = errno;
			close (fd);
			errno = saved_errno;
		}
		return -1;
	}
	if (p->fts_statp->st_dev != sb.st_dev
	    || p->fts_statp->st_ino != sb.st_ino) {
		if (0 <= fd)
			close (fd);
		__set_errno (ENOENT);		/* disinformation */
		return -1;
	}
	cwd_advance_fd (sp, newfd);
	return 0;
}