Libc-1244.30.3.tar.gz

[apple/libc.git] / gen / fts.c

/*
 * Copyright (c) 1999, 2000, 2003, 2005, 2008, 2012, 2016 Apple Inc. All rights reserved.
 *
 * @APPLE_LICENSE_HEADER_START@
 * 
 * This file contains Original Code and/or Modifications of Original Code
 * as defined in and that are subject to the Apple Public Source License
 * Version 2.0 (the 'License'). You may not use this file except in
 * compliance with the License. Please obtain a copy of the License at
 * http://www.opensource.apple.com/apsl/ and read it before using this
 * file.
 * 
 * The Original Code and all software distributed under the License are
 * distributed on an 'AS IS' basis, WITHOUT WARRANTY OF ANY KIND, EITHER
 * EXPRESS OR IMPLIED, AND APPLE HEREBY DISCLAIMS ALL SUCH WARRANTIES,
 * INCLUDING WITHOUT LIMITATION, ANY WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE, QUIET ENJOYMENT OR NON-INFRINGEMENT.
 * Please see the License for the specific language governing rights and
 * limitations under the License.
 * 
 * @APPLE_LICENSE_HEADER_END@
 */
/*
 * 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.
 * 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.
 */

/*      $OpenBSD: fts.c,v 1.51 2015/09/12 13:32:24 guenther Exp $       */

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

#include <dirent.h>
#include <errno.h>
#include <fcntl.h>
#include <fts.h>
#include <limits.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <stdbool.h>
#include <sys/vnode.h>
#include <sys/attr.h>
#include <os/assumes.h>

#ifdef __BLOCKS__
#include <Block.h>
#endif /* __BLOCKS__ */
#include <malloc_private.h>

static FTSENT   *fts_alloc(FTS *, char *, ssize_t);
static FTSENT   *fts_build(FTS *, int);
static void      fts_lfree(FTSENT *);
static void      fts_load(FTS *, FTSENT *);
static size_t    fts_maxarglen(char * const *);
static void      fts_padjust(FTS *, FTSENT *);
static int       fts_palloc(FTS *, size_t);
static FTSENT   *fts_sort(FTS *, FTSENT *, int);
static u_short   fts_stat(FTS *, FTSENT *, int, int);
static u_short   fts_stat2(FTS *, FTSENT *, int, int, struct stat *);
static int       fts_safe_changedir(FTS *, FTSENT *, int, char *);

#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 */

/* 5653270
 * For directories containing > 64k subdirectories (or HFS+ with > 64k files
 * and subdirectories), struct stat's st_nlink (16 bits) will overflow.  This
 * causes the case with FTS_NOSTAT and FTS_PHYSICAL set to prematurely stop
 * recursing into subdirectories, because of an optimization that expects
 * st_nlink to be the number of subdirectories (once that number has been
 * encountered, no further calls to stat should be needed).
 *
 * However, on Mac OS X, another optimization largely nullifies the st_nlink
 * optimization.  struct dirent contains d_type, which can distinguish
 * directories from files without initially calling stat. So stat is only
 * called on known directories, rather than on other files.  With this
 * optimization, the difference in also using the st_nlink optimization is
 * pretty minimal (tests show an improvement of a percent or two, probably
 * due to additional if statement clauses that need to be evaluated). 
 *
 * So removing the st_nlink optimization code will fix the > 64k subdirectories
 * problem.  And if we replace the multiple if clause logic with a single
 * switch statement, we can recover the minimal performance lose.  We can
 * go even further and for the case of FTS_NOSTAT and FTS_LOGICAL set, we
 * can use d_type to also distinguish symbolic links, and so we only need to
 * call stat on directories and symlinks, not on all files.  This provides
 * a significant performance boost in that special case.
 */
/*
 * The following macros defines values of the dostat variable, which is or-ed
 * with the value of d_type, and the result used in a switch statement to
 * determine whether to call stat or not.  (We order the macros to minimize
 * the size of any jump table that the compiler may generate.)
 */
#define F_SHIFT         4               /* shift to leave space for d_type */
#define F_NOSTAT        (0 << F_SHIFT)  /* don't do any stat's */
#define F_STATDIRSYM    (1 << F_SHIFT)  /* only stat directories and symlinks (and unknowns) */
#define F_ALWAYSSTAT    (2 << F_SHIFT)  /* always stat */
#define F_STATDIR       (3 << F_SHIFT)  /* only stat directories (and unknowns) */
#define F_D_TYPE        (4 << F_SHIFT)  /* only stat directories but use d_type */
#define F_D_TYPESYM     (5 << F_SHIFT)  /* only stat directories and symlinks but use d_type */

static FTS *
__fts_open(char * const *argv, FTS *sp)
{
        FTSENT *p, *root;
        int nitems;
        FTSENT *parent, *tmp;
        ssize_t len;

        /* 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.
         */
        if (fts_palloc(sp, MAX(fts_maxarglen(argv), PATH_MAX)))
                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; ++argv, ++nitems) {
                len = strlen(*argv);
                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_COMFOLLOWDIR) ? -1 : ISSET(FTS_COMFOLLOW), -1);

                /* 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 (sp->fts_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 (sp->fts_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 | O_CLOEXEC)) < 0)
                SET(FTS_NOCHDIR);

        if (nitems == 0)
                free(parent);

        return (sp);

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

FTS *
fts_open(char * const *argv, int options, int (*compar)())
{
        FTS *sp;

        /* Options check. */
        if (options & ~FTS_OPTIONMASK) {
                errno = EINVAL;
                return (NULL);
        }
        if (options & FTS_NOSTAT_TYPE) options |= FTS_NOSTAT;

        /* Allocate/initialize the stream */
        if ((sp = calloc(1, sizeof(FTS))) == NULL)
                return (NULL);
        sp->fts_compar = compar;
        sp->fts_options = options;

        return __fts_open(argv, sp);
}

#ifdef __BLOCKS__
FTS *
fts_open_b(char * const *argv, int options, int (^compar)(const FTSENT **, const FTSENT **))
{
        FTS *sp;

        /* Options check. */
        if (options & ~FTS_OPTIONMASK) {
                errno = EINVAL;
                return (NULL);
        }
        if (options & FTS_NOSTAT_TYPE) options |= FTS_NOSTAT;

        /* Allocate/initialize the stream */
        if ((sp = calloc(1, sizeof(FTS))) == NULL)
                return (NULL);
        sp->fts_compar_b = (int (^)())Block_copy(compar);
        sp->fts_options = options | FTS_BLOCK_COMPAR;

        return __fts_open(argv, sp);
}
#endif /* __BLOCKS__ */

static void
fts_load(FTS *sp, FTSENT *p)
{
        ssize_t 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(FTS *sp)
{
        FTSENT *freep, *p;
        int rfd, error = 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 ? p->fts_link : p->fts_parent;
                        free(freep);
                }
                free(p);
        }

        /* Stash the original directory fd if needed. */
        rfd = ISSET(FTS_NOCHDIR) ? -1 : sp->fts_rfd;

        /* Free up child linked list, sort array, path buffer, stream ptr.*/
        if (sp->fts_child){
                fts_lfree(sp->fts_child);
        }
        free(sp->fts_array); sp->fts_array = NULL;
        free(sp->fts_path); sp->fts_path = NULL;

#ifdef __BLOCKS__
        /* Free up any block pointer. */
        if (ISSET(FTS_BLOCK_COMPAR) && sp->fts_compar_b != NULL)
                Block_release(sp->fts_compar_b);
#endif /* __BLOCKS__ */

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

        /* Return to original directory, checking for error. */
        if (rfd != -1) {
                int saved_errno = errno;
                if (fchdir(rfd) != 0){
                        error = -1;
                        saved_errno = errno;
                }
                if (close(rfd) != 0){
                        error = -1;
                        saved_errno = errno;
                }
                errno = saved_errno;
        }

        return (error);
}

/*
 * Special case a root of "/" so that slashes aren't appended which would
 * cause paths to be written as "//foo".
 */
#define NAPPEND(p)                                                      \
        (p->fts_level == FTS_ROOTLEVEL && p->fts_pathlen == 1 &&        \
            p->fts_path[0] == '/' ? 0 : p->fts_pathlen)

FTSENT *
fts_read(FTS *sp)
{
        FTSENT *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, -1);
                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, -1);
                if (p->fts_info == FTS_D && !ISSET(FTS_NOCHDIR)) {
                        if ((p->fts_symfd =
                            open(".", O_RDONLY | O_CLOEXEC)) < 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 && 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) {
                        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; 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;
                goto name;
        }

        /* Move to the next node on this level. */
next:   tmp = p;
        if ((p = p->fts_link)) {
                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 (sp->fts_cur = 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, -1);
                        if (p->fts_info == FTS_D && !ISSET(FTS_NOCHDIR)) {
                                if ((p->fts_symfd =
                                    open(".", O_RDONLY | O_CLOEXEC, 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 (sp->fts_cur = 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);
                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);
                        sp->fts_cur = p;
                        return (NULL);
                }
        } else if (p->fts_flags & FTS_SYMFOLLOW) {
                if (FCHDIR(sp, p->fts_symfd)) {
                        saved_errno = errno;
                        (void)close(p->fts_symfd);
                        errno = saved_errno;
                        SET(FTS_STOP);
                        sp->fts_cur = p;
                        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);
                sp->fts_cur = p;
                return (NULL);
        }
        p->fts_info = p->fts_errno ? FTS_ERR : FTS_DP;
        return (sp->fts_cur = 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 __unused *sp, FTSENT *p, int instr)
{
        if (instr && instr != FTS_AGAIN && instr != FTS_FOLLOW &&
            instr != FTS_NOINSTR && instr != FTS_SKIP) {
                errno = EINVAL;
                return (1);
        }
        p->fts_instr = instr;
        return (0);
}

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

        if (instr && instr != FTS_NAMEONLY) {
                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.
         */
        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)
                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 | O_CLOEXEC, 0)) < 0)
                return (NULL);
        sp->fts_child = fts_build(sp, instr);
        if (fchdir(fd)) {
                (void)close(fd);
                return (NULL);
        }
        (void)close(fd);
        return (sp->fts_child);
}

typedef struct __attribute__((packed)) __attribute__((__aligned__(4))) {
        uint32_t length;

        /* common attributes */
        attribute_set_t attrset;
        attrreference_t name;
        dev_t st_dev;
        fsobj_type_t objtype;
        struct timespec st_birthtimespec;
        struct timespec st_mtimespec;
        struct timespec st_ctimespec;
        struct timespec st_atimespec;
        uid_t st_uid;
        gid_t st_gid;
        uint32_t accessmask;
        uint32_t st_flags;
        uint64_t st_ino;

        /* non-directory attributes */
        uint32_t st_nlink;
        off_t allocsize;
        uint32_t st_blksize;
        uint32_t st_rdev;
        off_t st_size;
} attrListAttributes;

typedef struct __attribute__((packed)) {
        uint32_t length;

        /* common attributes */
        attribute_set_t attrset;
        attrreference_t name;
        dev_t st_dev;
        fsobj_type_t objtype;
        uint64_t st_ino;

        /* non-directory attributes */
        uint32_t st_nlink;
        uint32_t st_rdev;
} attrListAttributes_nostat;

#define ATTR_BUF_SIZE (32*1024)

typedef struct {
        DIR *dirp;

        struct attrlist requested_attrs;
        void *attrbuf;
        union {
                attrListAttributes *curattr;
                attrListAttributes_nostat *curattr_nostat;
        };
        int dirfd;
        bool done;
        bool nostat;
        bool needs_dot;
        bool needs_dotdot;

        int entry_count;
        int cur_entry;
} dir_handle;

typedef struct {
        char *d_name;
        size_t d_namlen;
        struct stat sb;
        int d_type;
        bool stat_valid;
} dir_entry;

static bool
advance_directory(dir_handle *handle)
{
        if (handle->done) return true;

        os_assert(handle->dirfd != -1);
        handle->entry_count = getattrlistbulk(handle->dirfd, &handle->requested_attrs,
                        handle->attrbuf, ATTR_BUF_SIZE, FSOPT_PACK_INVAL_ATTRS);
        if (handle->entry_count == -1) {
                goto error;
        } else if (handle->entry_count == 0) {
                /* No more entries. */
                handle->done = true;
        }
        handle->cur_entry = 0;
        handle->curattr = handle->attrbuf;
        return true;

error: {
                int saved_errno = errno;
                close(handle->dirfd);
                handle->dirfd = -1;
                errno = saved_errno;
                return false;
        }
}

static bool
open_directory(FTS *sp, dir_handle *handle, const char *path)
{
        memset(handle, 0, sizeof(*handle));

        handle->nostat = ISSET(FTS_NOSTAT);
        handle->needs_dot = handle->needs_dotdot = ISSET(FTS_SEEDOT);

        handle->dirfd = open(path, O_RDONLY | O_NONBLOCK | O_DIRECTORY | O_CLOEXEC);
        if (handle->dirfd == -1) goto fallback;

        handle->attrbuf = malloc(ATTR_BUF_SIZE);
        if (!handle->attrbuf) goto fallback;

        handle->requested_attrs.bitmapcount = ATTR_BIT_MAP_COUNT;
        if (!handle->nostat) {
                handle->requested_attrs.commonattr =
                                ATTR_CMN_RETURNED_ATTRS|
                                ATTR_CMN_NAME|ATTR_CMN_DEVID|ATTR_CMN_OBJTYPE|
                                ATTR_CMN_CRTIME|ATTR_CMN_MODTIME|ATTR_CMN_CHGTIME|ATTR_CMN_ACCTIME|
                                ATTR_CMN_OWNERID|ATTR_CMN_GRPID|ATTR_CMN_ACCESSMASK|ATTR_CMN_FLAGS|
                                ATTR_CMN_FILEID;
                handle->requested_attrs.fileattr = ATTR_FILE_LINKCOUNT|ATTR_FILE_ALLOCSIZE|
                                ATTR_FILE_IOBLOCKSIZE|ATTR_FILE_DEVTYPE|ATTR_FILE_DATALENGTH;
        } else {
                handle->requested_attrs.commonattr = ATTR_CMN_RETURNED_ATTRS|
                                ATTR_CMN_NAME|ATTR_CMN_DEVID|ATTR_CMN_OBJTYPE|
                                ATTR_CMN_FILEID;
                handle->requested_attrs.fileattr = ATTR_FILE_LINKCOUNT;
        }

        if (advance_directory(handle)) {
                /*
                 * We successfully read the first attribute buffer,
                 * so we'll use getdirentriesattr/getattrlistbulk.
                 */
                return true;
        }

fallback:
        if (handle->dirfd != -1) close(handle->dirfd);
        handle->dirfd = -1;
        free(handle->attrbuf);
        handle->attrbuf = NULL;
        handle->dirp = opendir(path);
        return (handle->dirp != NULL);
}

static bool
read_dirent(dir_handle *handle, dir_entry *entry)
{
        if (handle->dirp) {
                struct dirent *de = readdir(handle->dirp);
                if (de == NULL) return false;
                entry->d_name = de->d_name;
                entry->d_namlen = de->d_namlen;
                entry->d_type = de->d_type;
                entry->stat_valid = false;
                return true;
        }

        /*
         * There are three states that our dir_handle can be in:
         *   - real getattrlistbulk use (entry_count >= 0) - the rest of this function
         *   - fallback - handled above with dirp
         *   - closed fallback (dirp == NULL) - handled with this check
         */
        if (handle->dirfd == -1) {
                return false;
        }

        if (handle->needs_dot) {
                handle->needs_dot = false;
                entry->d_name = ".";
                entry->d_namlen = strlen(".");
                entry->d_type = DT_DIR;
                entry->stat_valid = false;
                return true;
        } else if (handle->needs_dotdot) {
                handle->needs_dotdot = false;
                entry->d_name = "..";
                entry->d_namlen = strlen("..");
                entry->d_type = DT_DIR;
                entry->stat_valid = false;
                return true;
        }

        if (handle->cur_entry == handle->entry_count) {
                if (handle->done) return false;                /* Already done with the directory. */
                if (!advance_directory(handle)) return false;  /* Reading the next buffer failed. */
                if (handle->done) return false;                /* We're now done with the directory. */
        }

        bzero(entry, sizeof(*entry));

        attrListAttributes *curattr_stat = NULL;
        attrListAttributes_nostat *curattr_nostat = NULL;
        if (!handle->nostat) {
                curattr_stat = handle->curattr;
                handle->cur_entry++;
                handle->curattr = (attrListAttributes*)(((char*)curattr_stat) + curattr_stat->length);
                os_assert((handle->cur_entry == handle->entry_count) ||
                                (void*)handle->curattr + handle->curattr->length <= (void*)handle->attrbuf + ATTR_BUF_SIZE);

                os_assert(curattr_stat->name.attr_length > 0);
                entry->d_name = ((char*)&curattr_stat->name) + curattr_stat->name.attr_dataoffset;
                /* attr_length includes the null terminator, but readdir's d_namlen doesn't. */
                entry->d_namlen = curattr_stat->name.attr_length - 1;
                os_assert((void*)entry->d_name + curattr_stat->name.attr_length <= (void*)handle->attrbuf + ATTR_BUF_SIZE);
        } else {
                curattr_nostat = handle->curattr_nostat;
                handle->cur_entry++;
                handle->curattr_nostat = (attrListAttributes_nostat*)(((char*)curattr_nostat) + curattr_nostat->length);
                os_assert((handle->cur_entry == handle->entry_count) ||
                                (void*)handle->curattr + handle->curattr->length <= (void*)handle->attrbuf + ATTR_BUF_SIZE);

                os_assert(curattr_nostat->name.attr_length > 0);
                entry->d_name = ((char*)&curattr_nostat->name) + curattr_nostat->name.attr_dataoffset;
                /* attr_length includes the null terminator, but readdir's d_namlen doesn't. */
                entry->d_namlen = curattr_nostat->name.attr_length - 1;
                os_assert((void*)entry->d_name + curattr_nostat->name.attr_length <= (void*)handle->attrbuf + ATTR_BUF_SIZE);
        }

        int stat_type = 0;

        switch (handle->nostat ? curattr_nostat->objtype : curattr_stat->objtype) {
        case VREG:
                entry->d_type = DT_REG;
                stat_type = S_IFREG;
                break;
        case VDIR:
                entry->d_type = DT_DIR;
                /* Force a stat call so we don't have to guess on st_size, st_blocks, etc. */
                // stat_type = S_IFDIR;
                break;
        case VBLK:
                entry->d_type = DT_BLK;
                stat_type = S_IFBLK;
                break;
        case VCHR:
                entry->d_type = DT_CHR;
                stat_type = S_IFCHR;
                break;
        case VLNK:
                entry->d_type = DT_LNK;
                stat_type = S_IFLNK;
                break;
        case VSOCK:
                entry->d_type = DT_SOCK;
                stat_type = S_IFSOCK;
                break;
        case VFIFO:
                entry->d_type = DT_FIFO;
                stat_type = S_IFIFO;
                break;
        default:
                entry->d_type = DT_UNKNOWN;
                break;
        }

        if (!handle->nostat && stat_type) {
                entry->stat_valid = true;

                /*
                 * Make sure we got all the attributes we need to fill out a stat structure.
                 */

                attrgroup_t requiredCommon = handle->requested_attrs.commonattr;
                attrgroup_t requiredFile = handle->requested_attrs.fileattr;

                if ((entry->d_type != DT_BLK) && (entry->d_type != DT_CHR)) {
                        /* It's okay for ATTR_FILE_DEVTYPE to be missing if the entry isn't a block or character device. */
                        curattr_stat->st_rdev = 0;
                        requiredFile &= ~ATTR_FILE_DEVTYPE;
                }

                if ((curattr_stat->attrset.commonattr & ATTR_CMN_CRTIME) == 0) {
                        /* Many (most?) file systems don't support create time (see vn_stat_noauth in xnu) */
                        curattr_stat->st_birthtimespec.tv_sec = curattr_stat->st_birthtimespec.tv_nsec = 0;
                        requiredCommon &= ~ ATTR_CMN_CRTIME;
                }

                if ((curattr_stat->attrset.commonattr & requiredCommon) != requiredCommon ||
                                (curattr_stat->attrset.fileattr & requiredFile) != requiredFile) {
                        /* Some of our required attributes are missing. */
                        entry->stat_valid = false;
                }
        } else {
                entry->stat_valid = false;
        }

        if (entry->stat_valid) {

#define COPY_FIELD(fld) entry->sb.fld = curattr_stat->fld
                COPY_FIELD(st_dev);
                /* COPY_FIELD(st_mode);      Handled below. */
                COPY_FIELD(st_nlink);
                COPY_FIELD(st_ino);
                COPY_FIELD(st_uid);
                COPY_FIELD(st_gid);
                COPY_FIELD(st_rdev);
                COPY_FIELD(st_atimespec);
                COPY_FIELD(st_mtimespec);
                COPY_FIELD(st_ctimespec);
#if __DARWIN_64_BIT_INO_T
                COPY_FIELD(st_birthtimespec);
#endif /* __DARWIN_64_BIT_INO_T */
                COPY_FIELD(st_size);
                /* COPY_FIELD(st_blocks);    Handled below. */
                COPY_FIELD(st_blksize);
                COPY_FIELD(st_flags);
#undef COPY_FIELD

                /* We have to handle some fields specially. */
                entry->sb.st_mode = (curattr_stat->accessmask & ~S_IFMT) | stat_type;
                entry->sb.st_blocks = howmany(curattr_stat->allocsize, 512); /* Matches vn_stat implementation in xnu. */
        }
        return true;
}

static int
dir_fd(dir_handle *handle)
{
        return handle->dirp ? dirfd(handle->dirp) : handle->dirfd;
}

static void
close_directory(dir_handle *handle)
{
        if (handle->dirp) {
                closedir(handle->dirp);
                handle->dirp = NULL;
        }
        if (handle->dirfd != -1) {
                close(handle->dirfd);
                handle->dirfd = -1;
        }
        free(handle->attrbuf);
        handle->attrbuf = NULL;
}

/*
 * 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, we can use d_type to determine if the entry is a directory (or for
 * logical walks, a directory or symlink) and not call stat for other file
 * types.  This cuts the number of stat calls significantly.
 */
static FTSENT *
fts_build(FTS *sp, int type)
{
        dir_entry de = { 0 };
        dir_entry *dp = &de;
        FTSENT *p, *head;
        int nitems;
        FTSENT *cur, *tail;
        dir_handle dirp;
        void *oldaddr;
        int len, maxlen;
        int cderrno, descend, level, dostat, doadjust;
        int saved_errno;
        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 (!open_directory(sp, &dirp, cur->fts_accpath)) {
                if (type == BREAD) {
                        cur->fts_info = FTS_DNR;
                        cur->fts_errno = errno;
                }
                return (NULL);
        }

        if (type == BNAMES)
                dostat = F_NOSTAT;
        else if (ISSET(FTS_NOSTAT_TYPE))
                dostat = ISSET(FTS_PHYSICAL) ? F_D_TYPE : F_D_TYPESYM;
        else if (ISSET(FTS_NOSTAT))
                dostat = ISSET(FTS_PHYSICAL) ? F_STATDIR : F_STATDIRSYM;
        else
                dostat = F_ALWAYSSTAT;

#ifdef notdef
        (void)printf("dostat == %d\n", dostat);
        (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 (dostat || type == BREAD) {
                if (fts_safe_changedir(sp, cur, dir_fd(&dirp), NULL)) {
                        if (dostat && type == BREAD) {
                                cur->fts_errno = errno;
                        }
                        cur->fts_flags |= FTS_DONTCHDIR;
                        descend = 0;
                        cderrno = errno;
                        close_directory(&dirp);
                } 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++ = '/';
        }
        len++;
        maxlen = sp->fts_pathlen - len;

        /*
         * fts_level is signed so we must prevent it from wrapping
         * around to FTS_ROOTLEVEL and FTS_ROOTPARENTLEVEL.
         */
        level = cur->fts_level;
        if (level < FTS_MAXLEVEL)
            level++;

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

                if ((p = fts_alloc(sp, dp->d_name, (int)dp->d_namlen)) == NULL)
                        goto mem1;
                if (dp->d_namlen >= (size_t)maxlen) {   /* include space for NUL */
                        oldaddr = sp->fts_path;
                        if (fts_palloc(sp, dp->d_namlen +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);
                                close_directory(&dirp);
                                cur->fts_info = FTS_ERR;
                                SET(FTS_STOP);
                                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 + dp->d_namlen >= 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);
                        close_directory(&dirp);
                        cur->fts_info = FTS_ERR;
                        SET(FTS_STOP);
                        errno = ENAMETOOLONG;
                        return (NULL);
                }
                p->fts_level = level;
                p->fts_parent = sp->fts_cur;
                p->fts_pathlen = len + dp->d_namlen;

                if (cderrno) {
                        if (dostat) {
                                p->fts_info = FTS_NS;
                                p->fts_errno = cderrno;
                        } else
                                p->fts_info = FTS_NSOK;
                        p->fts_accpath = cur->fts_accpath;
                } else {
                        /*
                         * We need to know all file types values that d_type may
                         * be set to.  So if that changes, the following needs
                         * to be modified appropriately.
                         */
                        switch(dostat | dp->d_type) {
                        case (F_STATDIR | DT_UNKNOWN):
                        case (F_STATDIR | DT_DIR):
                        case (F_STATDIRSYM | DT_UNKNOWN):
                        case (F_STATDIRSYM | DT_DIR):
                        case (F_STATDIRSYM | DT_LNK):
                        case (F_ALWAYSSTAT | DT_UNKNOWN):
                        case (F_ALWAYSSTAT | DT_FIFO):
                        case (F_ALWAYSSTAT | DT_CHR):
                        case (F_ALWAYSSTAT | DT_DIR):
                        case (F_ALWAYSSTAT | DT_BLK):
                        case (F_ALWAYSSTAT | DT_REG):
                        case (F_ALWAYSSTAT | DT_LNK):
                        case (F_ALWAYSSTAT | DT_SOCK):
                        case (F_ALWAYSSTAT | DT_WHT):
                        case (F_D_TYPE | DT_UNKNOWN):
                        case (F_D_TYPE | DT_DIR):
                        case (F_D_TYPESYM | DT_UNKNOWN):
                        case (F_D_TYPESYM | DT_DIR):
                        case (F_D_TYPESYM | DT_LNK):
                                /* 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);
                                        p->fts_info = fts_stat2(sp, p, 0, dir_fd(&dirp), dp->stat_valid ? &dp->sb : NULL);
                                } else {
                                        p->fts_accpath = p->fts_name;
                                        p->fts_info = fts_stat2(sp, p, 0, -1, dp->stat_valid ? &dp->sb : NULL);
                                }
                                break;
                        case (F_D_TYPE | DT_FIFO):
                        case (F_D_TYPE | DT_CHR):
                        case (F_D_TYPE | DT_BLK):
                        case (F_D_TYPE | DT_SOCK):
                        case (F_D_TYPESYM | DT_FIFO):
                        case (F_D_TYPESYM | DT_CHR):
                        case (F_D_TYPESYM | DT_BLK):
                        case (F_D_TYPESYM | DT_SOCK):
                                p->fts_info = FTS_DEFAULT;
                                goto common_no_stat;
                        case (F_D_TYPE | DT_REG):
                        case (F_D_TYPESYM | DT_REG):
                                p->fts_info = FTS_F;
                                goto common_no_stat;
                        case (F_D_TYPE | DT_LNK):
                                p->fts_info = FTS_SL;
                                goto common_no_stat;
                        case (F_D_TYPE | DT_WHT):
                        case (F_D_TYPESYM | DT_WHT):
                                p->fts_info = FTS_W;
                                goto common_no_stat;
                        default:
                                /* No stat necessary */
                                p->fts_info = FTS_NSOK;
common_no_stat:
                                p->fts_accpath =
                                    ISSET(FTS_NOCHDIR) ? p->fts_path : p->fts_name;
                                break;
                        }
                }

                /* 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;
        }
        close_directory(&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);
                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);
}

static u_short
fts_stat(FTS *sp, FTSENT *p, int follow, int dfd)
{
        return fts_stat2(sp, p, follow, dfd, NULL);
}

static u_short
fts_stat2(FTS *sp, FTSENT *p, int follow, int dfd, struct stat *insb)
{
        FTSENT *t;
        dev_t dev;
        ino_t ino;
        struct stat *sbp, sb;
        int saved_errno;
        const char *path;

        if (dfd == -1) {
                path = p->fts_accpath;
                dfd = AT_FDCWD;
        } else {
                path = p->fts_name;
        }

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

        /*
         * getattrlistbulk always returns information about the link, not its
         * destination, so if we are doing a logical walk we need to detect links
         * and do a stat anyway.
         */
        if (follow) {
                insb = NULL;
        } else if (insb && ISSET(FTS_LOGICAL) && ((insb->st_mode & S_IFLNK) == S_IFLNK)) {
                insb = NULL;
        }

        if (insb) {
                memcpy(sbp, insb, sizeof(*insb));
        } else if (ISSET(FTS_LOGICAL) || follow) {
                /*
                 * 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 (fstatat(dfd, path, sbp, 0)) {
                        saved_errno = errno;
                        if (!fstatat(dfd, path, sbp, AT_SYMLINK_NOFOLLOW)) {
                                if (saved_errno == ELOOP)
                                        p->fts_errno = ELOOP;
                                errno = 0;
                                return (FTS_SLNONE);
                        }
                        p->fts_errno = saved_errno;
                        goto err;
                }
                /*
                 * For FTS_COMFOLLOWDIR, drop back to lstat unless we have
                 * a directory
                 */
                if (follow == -1 && !S_ISDIR(sbp->st_mode)) {
                        if (fstatat(dfd, path, sbp, AT_SYMLINK_NOFOLLOW)) {
                                p->fts_errno = errno;
                                goto err;
                        }
                }
        } else if (fstatat(dfd, path, sbp, AT_SYMLINK_NOFOLLOW)) {
                p->fts_errno = errno;
err:            memset(sbp, 0, sizeof(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 FTSENT *
fts_sort(FTS *sp, FTSENT *head, int nitems)
{
        FTSENT **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) {
                struct _ftsent **a;

                sp->fts_nitems = nitems + 40;
                if ((a = reallocarray(sp->fts_array,
                    sp->fts_nitems, sizeof(FTSENT *))) == 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;
#ifdef __BLOCKS__
        if (ISSET(FTS_BLOCK_COMPAR))
                qsort_b((void *)sp->fts_array, nitems, sizeof(FTSENT *), (int (^)(const void *, const void *))sp->fts_compar_b);
        else
#endif /* __BLOCKS__ */
                qsort((void *)sp->fts_array, nitems, sizeof(FTSENT *), 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 FTSENT *
fts_alloc(FTS *sp, char *name, ssize_t namelen)
{
        FTSENT *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(FTSENT) + namelen;
        if (!ISSET(FTS_NOSTAT))
                len += sizeof(struct stat) + ALIGNBYTES;
        if ((p = calloc(1, len)) == NULL)
                return (NULL);

        p->fts_path = sp->fts_path;
        p->fts_namelen = namelen;
        p->fts_instr = FTS_NOINSTR;
        if (!ISSET(FTS_NOSTAT))
                p->fts_statp = (struct stat *)ALIGN(p->fts_name + namelen + 2);
        memcpy(p->fts_name, name, namelen);

        return (p);
}

static void
fts_lfree(FTSENT *head)
{
        FTSENT *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 PATH_MAX, 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(FTS *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;
                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(FTS *sp, FTSENT *head)
{
        FTSENT *p;
        char *addr = sp->fts_path;

#define ADJUST(p) {                                                     \
        if ((p)->fts_accpath != (p)->fts_name) {                        \
                (p)->fts_accpath =                                      \
                    (char *)addr + ((p)->fts_accpath - (p)->fts_path);  \
        }                                                               \
        (p)->fts_path = addr;                                           \
}
        /* 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(FTS *sp, FTSENT *p, int fd, char *path)
{
        int ret, oerrno, newfd;
        struct stat sb;

        newfd = fd;
        if (ISSET(FTS_NOCHDIR))
                return (0);
        if (fd < 0 && (newfd = open(path, O_RDONLY|O_DIRECTORY|O_CLOEXEC)) < 0)
                return (-1);
        if (fstat(newfd, &sb)) {
                ret = -1;
                goto bail;
        }
        /*
         * On Darwin this check causes us to not correctly descend into automounts,
         * since the mount point and trigger will have a different devices and
         * inodes.  It would be preferable to find a way to use
         * ATTR_DIR_MOUNTSTATUS and DIR_MNTSTATUS_TRIGGER to detect these cases,
         * but plumbing that through will be challenging.  Instead, will just
         * disable it for now.
         */
#if 0
        if (p->fts_dev != sb.st_dev || p->fts_ino != sb.st_ino) {
                errno = ENOENT;         /* disinformation */
                ret = -1;
                goto bail;
        }
#endif

        ret = fchdir(newfd);
bail:
        oerrno = errno;
        if (fd < 0)
                (void)close(newfd);
        errno = oerrno;
        return (ret);
}