support: Also return fd when it is 0

[glibc.git] / io / fts.c

/* File tree traversal functions.
   Copyright (C) 1994-2021 Free Software Foundation, Inc.
   This file is part of the GNU C Library.

   The GNU C Library is free software; you can redistribute it and/or
   modify it under the terms of the GNU Lesser General Public
   License as published by the Free Software Foundation; either
   version 2.1 of the License, or (at your option) any later version.

   The GNU C Library 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
   Lesser General Public License for more details.

   You should have received a copy of the GNU Lesser General Public
   License along with the GNU C Library; if not, see
   <https://www.gnu.org/licenses/>.  */

/*-
 * 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.
 */

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

#include <sys/param.h>
#include <include/sys/stat.h>
#include <fcntl.h>
#include <dirent.h>
#include <errno.h>
#include <fts.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>


/* Largest alignment size needed, minus one.
   Usually long double is the worst case.  */
#ifndef ALIGNBYTES
#define ALIGNBYTES      (__alignof__ (long double) - 1)
#endif
/* Align P to that size.  */
#ifndef ALIGN
#define ALIGN(p)        (((unsigned long int) (p) + ALIGNBYTES) & ~ALIGNBYTES)
#endif


/* Support for the LFS API version.  */
#ifndef FTS_OPEN
#define FTS_OPEN fts_open
#define FTS_CLOSE fts_close
#define FTS_READ fts_read
#define FTS_SET fts_set
#define FTS_CHILDREN fts_children
# define FTSOBJ FTS
# define FTSENTRY FTSENT
# define INO_T ino_t
# define STRUCT_STAT stat
# define STAT __stat
# define LSTAT __lstat
#endif

static FTSENTRY *fts_alloc (FTSOBJ *, const char *, size_t);
static FTSENTRY *fts_build (FTSOBJ *, int);
static void      fts_lfree (FTSENTRY *);
static void      fts_load (FTSOBJ *, FTSENTRY *);
static size_t    fts_maxarglen (char * const *);
static void      fts_padjust (FTSOBJ *, FTSENTRY *);
static int       fts_palloc (FTSOBJ *, size_t);
static FTSENTRY *fts_sort (FTSOBJ *, FTSENTRY *, int);
static u_short   fts_stat (FTSOBJ *, FTSENTRY *, int);
static int      fts_safe_changedir (FTSOBJ *, FTSENTRY *, int, const char *);

#ifndef MAX
#define MAX(a, b)       ({ __typeof__ (a) _a = (a); \
                           __typeof__ (b) _b = (b); \
                           _a > _b ? _a : _b; })
#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) && __fchdir(fd))

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

FTSOBJ *
FTS_OPEN (char * const *argv, int options,
          int (*compar) (const FTSENTRY **, const FTSENTRY **))
{
        FTSOBJ *sp;
        FTSENTRY *p, *root;
        int nitems;
        FTSENTRY *parent = NULL;
        FTSENTRY *tmp;

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

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

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

        /*
         * Start out with 1K of path space, and enough, in any case,
         * to hold the user's paths.
         */
#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 (*argv != NULL) {
                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 paths. */
                size_t len = strlen(*argv);
                if (len == 0) {
                        __set_errno (ENOENT);
                        goto mem3;
                }

                p = fts_alloc(sp, *argv, len);
                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));

                /* 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 using chdir(2), grab a file descriptor pointing to dot to ensure
         * that we can get back here; this could be avoided for some paths,
         * but almost certainly not worth the effort.  Slashes, symbolic links,
         * and ".." are all fairly nasty problems.  Note, if we can't get the
         * descriptor we run anyway, just more slowly.
         */
        if (!ISSET(FTS_NOCHDIR)
            && (sp->fts_rfd = __open(".", O_RDONLY, 0)) < 0)
                SET(FTS_NOCHDIR);

        return (sp);

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

static void
fts_load (FTSOBJ *sp, FTSENTRY *p)
{
        int len;
        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 path 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_dev;
}

int
FTS_CLOSE (FTSOBJ *sp)
{
        FTSENTRY *freep, *p;
        int saved_errno;

        /*
         * 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, path buffer. */
        if (sp->fts_child)
                fts_lfree(sp->fts_child);
        free(sp->fts_array);
        free(sp->fts_path);

        /* Return to original directory, save errno if necessary. */
        if (!ISSET(FTS_NOCHDIR)) {
                saved_errno = __fchdir(sp->fts_rfd) ? errno : 0;
                (void)__close(sp->fts_rfd);

                /* Set errno and return. */
                if (saved_errno != 0) {
                        /* Free up the stream pointer. */
                        free(sp);
                        __set_errno (saved_errno);
                        return (-1);
                }
        }

        /* Free up the stream pointer. */
        free(sp);
        return (0);
}

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

FTSENTRY *
FTS_READ (FTSOBJ *sp)
{
        FTSENTRY *p, *tmp;
        int instr;
        char *t;
        int saved_errno;

        /* 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, 0);
                return (p);
        }

        /*
         * 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, 1);
                if (p->fts_info == FTS_D && !ISSET(FTS_NOCHDIR)) {
                        if ((p->fts_symfd = __open(".", O_RDONLY, 0)) < 0) {
                                p->fts_errno = errno;
                                p->fts_info = FTS_ERR;
                        } else
                                p->fts_flags |= FTS_SYMFOLLOW;
                }
                return (p);
        }

        /* 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_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;
                        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);
                        return (p);
                }
                p = sp->fts_child;
                sp->fts_child = NULL;
                sp->fts_cur = p;
                goto name;
        }

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

                /*
                 * If reached the top, return to the original directory (or
                 * the root of the tree), and load the paths for the next root.
                 */
                if (p->fts_level == FTS_ROOTLEVEL) {
                        if (FCHDIR(sp, sp->fts_rfd)) {
                                SET(FTS_STOP);
                                return (NULL);
                        }
                        fts_load(sp, p);
                        return p;
                }

                /*
                 * 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, 1);
                        if (p->fts_info == FTS_D && !ISSET(FTS_NOCHDIR)) {
                                if ((p->fts_symfd =
                                    __open(".", O_RDONLY, 0)) < 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);
                return p;
        }

        /* Move up to the parent node. */
        p = tmp->fts_parent;
        sp->fts_cur = p;
        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 pathname. */
        sp->fts_path[p->fts_pathlen] = '\0';

        /*
         * Return to the parent directory.  If at a root node or came through
         * a symlink, go back through the file descriptor.  Otherwise, cd up
         * one directory.
         */
        if (p->fts_level == FTS_ROOTLEVEL) {
                if (FCHDIR(sp, sp->fts_rfd)) {
                        SET(FTS_STOP);
                        return (NULL);
                }
        } else if (p->fts_flags & FTS_SYMFOLLOW) {
                if (FCHDIR(sp, p->fts_symfd)) {
                        saved_errno = errno;
                        (void)__close(p->fts_symfd);
                        __set_errno (saved_errno);
                        SET(FTS_STOP);
                        return (NULL);
                }
                (void)__close(p->fts_symfd);
        } else if (!(p->fts_flags & FTS_DONTCHDIR) &&
                   fts_safe_changedir(sp, p->fts_parent, -1, "..")) {
                SET(FTS_STOP);
                return (NULL);
        }
        p->fts_info = p->fts_errno ? FTS_ERR : FTS_DP;
        return 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 (FTSOBJ *sp, FTSENTRY *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);
}

FTSENTRY *
FTS_CHILDREN(FTSOBJ *sp, int instr)
{
        FTSENTRY *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 path 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 = __open(".", O_RDONLY, 0)) < 0)
                return (NULL);
        sp->fts_child = fts_build(sp, instr);
        if (__fchdir(fd))
                return (NULL);
        (void)__close(fd);
        return (sp->fts_child);
}

static inline int
dirent_not_directory(const struct dirent *dp)
{
#if defined DT_DIR && defined _DIRENT_HAVE_D_TYPE
        return dp->d_type != DT_DIR && dp->d_type != DT_UNKNOWN;
#else
        return 0;
#endif
}

/*
 * 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 FTSENTRY *
fts_build (FTSOBJ *sp, int type)
{
        struct dirent *dp;
        FTSENTRY *p, *head;
        int nitems;
        FTSENTRY *cur, *tail;
        DIR *dirp;
        void *oldaddr;
        int cderrno, descend, len, level, nlinks, saved_errno,
            nostat, doadjust;
        size_t maxlen;
        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(path, flag) __opendir(path)
#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, -1 if we're doing stats on everything.
         */
        if (type == BNAMES) {
                nlinks = 0;
                /* Be quiet about nostat, GCC. */
                nostat = 0;
        } else if (ISSET(FTS_NOSTAT) && ISSET(FTS_PHYSICAL)) {
                nlinks = cur->fts_nlink - (ISSET(FTS_SEEDOT) ? 0 : 2);
                nostat = 1;
        } else {
                nlinks = -1;
                nostat = 0;
        }

#ifdef notdef
        (void)printf("nlinks == %d (cur: %d)\n", nlinks, cur->fts_nlink);
        (void)printf("NOSTAT %d PHYSICAL %d SEEDOT %d\n",
            ISSET(FTS_NOSTAT), ISSET(FTS_PHYSICAL), ISSET(FTS_SEEDOT));
#endif
        /*
         * 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 path
         * 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) {
                if (fts_safe_changedir(sp, cur, dirfd(dirp), NULL)) {
                        if (nlinks && type == BREAD)
                                cur->fts_errno = errno;
                        cur->fts_flags |= FTS_DONTCHDIR;
                        descend = 0;
                        cderrno = errno;
                        (void)__closedir(dirp);
                        dirp = NULL;
                } else
                        descend = 1;
        } else
                descend = 0;

        /*
         * Figure out the max file name length that can be stored in the
         * current path -- the inner loop allocates more path as necessary.
         * We really wouldn't have to do the maxlen calculations here, we
         * could do them in fts_read before returning the path, 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 name into the path.
         */
        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 = 0;
        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, _D_EXACT_NAMLEN (dp))) == NULL)
                        goto mem1;
                if (_D_EXACT_NAMLEN (dp) >= maxlen) {/* include space for NUL */
                        oldaddr = sp->fts_path;
                        if (fts_palloc(sp, _D_EXACT_NAMLEN (dp) + len + 1)) {
                                /*
                                 * No more memory for path or structures.  Save
                                 * errno, free up the current structure and the
                                 * structures already allocated.
                                 */
mem1:                           saved_errno = errno;
                                free(p);
                                fts_lfree(head);
                                (void)__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 = 1;
                                if (ISSET(FTS_NOCHDIR))
                                        cp = sp->fts_path + len;
                        }
                        maxlen = sp->fts_pathlen - len;
                }

                if (len + _D_EXACT_NAMLEN (dp) >= USHRT_MAX) {
                        /*
                         * In an FTSENT, fts_pathlen is a u_short so it is
                         * possible to wraparound here.  If we do, free up
                         * the current structure and the structures already
                         * allocated, then error out with ENAMETOOLONG.
                         */
                        free(p);
                        fts_lfree(head);
                        (void)__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 = len + _D_EXACT_NAMLEN (dp);

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

                /* Unreachable code.  cderrno is only ever set to a nonnull
                   value if dirp is closed at the same time.  But then we
                   cannot enter this loop.  */
                if (0 && 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
                           || (nostat && dirent_not_directory(dp))) {
                        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, 0);

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

                /* 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)
                (void)__closedir(dirp);

        /*
         * If realloc() changed the address of the path, 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 path 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 path
         * 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, sp->fts_rfd) :
             fts_safe_changedir(sp, cur->fts_parent, -1, ".."))) {
                cur->fts_info = FTS_ERR;
                SET(FTS_STOP);
                fts_lfree(head);
                return (NULL);
        }

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

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

static u_short
fts_stat (FTSOBJ *sp, FTSENTRY *p, int follow)
{
        FTSENTRY *t;
        dev_t dev;
        INO_T ino;
        struct STRUCT_STAT *sbp, sb;
        int saved_errno;

        /* If user needs stat info, stat buffer already allocated. */
        sbp = ISSET(FTS_NOSTAT) ? &sb : p->fts_statp;

#if defined FTS_WHITEOUT && 0
        /* check for whiteout */
        if (p->fts_flags & FTS_ISW) {
                if (sbp != &sb) {
                        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 (!LSTAT(p->fts_accpath, sbp)) {
                                __set_errno (0);
                                return (FTS_SLNONE);
                        }
                        p->fts_errno = saved_errno;
                        goto err;
                }
        } else if (LSTAT(p->fts_accpath, sbp)) {
                p->fts_errno = errno;
err:            memset(sbp, 0, sizeof(struct STRUCT_STAT));
                return (FTS_NS);
        }

        if (S_ISDIR(sbp->st_mode)) {
                /*
                 * Set the device/inode.  Used to find cycles and check for
                 * crossing mount points.  Also remember the link count, used
                 * in fts_build to limit the number of stat calls.  It is
                 * understood that these fields are only referenced if fts_info
                 * is set to FTS_D.
                 */
                dev = p->fts_dev = sbp->st_dev;
                ino = p->fts_ino = sbp->st_ino;
                p->fts_nlink = sbp->st_nlink;

                if (ISDOT(p->fts_name))
                        return (FTS_DOT);

                /*
                 * 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.
                 */
                for (t = p->fts_parent;
                    t->fts_level >= FTS_ROOTLEVEL; t = t->fts_parent)
                        if (ino == t->fts_ino && dev == t->fts_dev) {
                                p->fts_cycle = t;
                                return (FTS_DC);
                        }
                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 FTSENTRY *
fts_sort (FTSOBJ *sp, FTSENTRY *head, int nitems)
{
        FTSENTRY **ap, *p;

        /*
         * 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) {
                FTSENTRY **a;

                sp->fts_nitems = nitems + 40;
                if ((a = realloc(sp->fts_array,
                    (size_t)(sp->fts_nitems * sizeof(FTSENTRY *)))) == NULL) {
                        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(FTSENTRY *), sp->fts_compar);
        for (head = *(ap = sp->fts_array); --nitems; ++ap)
                ap[0]->fts_link = ap[1];
        ap[0]->fts_link = NULL;
        return (head);
}

static FTSENTRY *
fts_alloc (FTSOBJ *sp, const char *name, size_t namelen)
{
        FTSENTRY *p;
        size_t len;

        /*
         * The file name is a variable length array and no stat structure is
         * necessary if the user has set the nostat bit.  Allocate the FTSENT
         * structure, the file name and the stat structure in one chunk, but
         * be careful that the stat structure is reasonably aligned.  Since the
         * fts_name field is declared to be of size 1, the fts_name pointer is
         * namelen + 2 before the first possible address of the stat structure.
         */
        len = sizeof(FTSENTRY) + namelen;
        if (!ISSET(FTS_NOSTAT))
                len += sizeof(struct STRUCT_STAT) + ALIGNBYTES;
        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';

        if (!ISSET(FTS_NOSTAT))
                p->fts_statp = (struct STRUCT_STAT *)ALIGN(p->fts_name + namelen + 2);
        p->fts_namelen = namelen;
        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
fts_lfree (FTSENTRY *head)
{
        FTSENTRY *p;

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

/*
 * Allow essentially unlimited paths; find, rm, ls should all work on any tree.
 * Most systems will allow creation of paths 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 path 2 bytes at a time.
 */
static int
fts_palloc (FTSOBJ *sp, size_t more)
{
        char *p;

        sp->fts_pathlen += more + 256;
        /*
         * Check for possible wraparound.  In an FTS, fts_pathlen is
         * a signed int but in an FTSENT it is an unsigned short.
         * We limit fts_pathlen to USHRT_MAX to be safe in both cases.
         */
        if (sp->fts_pathlen < 0 || sp->fts_pathlen >= USHRT_MAX) {
                free(sp->fts_path);
                sp->fts_path = NULL;
                __set_errno (ENAMETOOLONG);
                return (1);
        }
        p = realloc(sp->fts_path, sp->fts_pathlen);
        if (p == NULL) {
                free(sp->fts_path);
                sp->fts_path = NULL;
                return 1;
        }
        sp->fts_path = p;
        return 0;
}

/*
 * When the path is realloc'd, have to fix all of the pointers in structures
 * already returned.
 */
static void
fts_padjust (FTSOBJ *sp, FTSENTRY *head)
{
        FTSENTRY *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
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 p->fts_accpath without getting
 * tricked by someone changing the world out from underneath us.
 * Assumes p->fts_dev and p->fts_ino are filled in.
 */
static int
fts_safe_changedir (FTSOBJ *sp, FTSENTRY *p, int fd, const char *path)
{
        int ret, oerrno, newfd;
        struct stat64 sb;

        newfd = fd;
        if (ISSET(FTS_NOCHDIR))
                return (0);
        if (fd < 0 && (newfd = __open(path, O_RDONLY, 0)) < 0)
                return (-1);
        if (__fstat64(newfd, &sb)) {
                ret = -1;
                goto bail;
        }
        if (p->fts_dev != sb.st_dev || p->fts_ino != sb.st_ino) {
                __set_errno (ENOENT);           /* disinformation */
                ret = -1;
                goto bail;
        }
        ret = __fchdir(newfd);
bail:
        oerrno = errno;
        if (fd < 0)
                (void)__close(newfd);
        __set_errno (oerrno);
        return (ret);
}