[wimlib] / src / dentry.c

/*
 * dentry.c
 *
 * A dentry (directory entry) contains the metadata for a file.  In the WIM file
 * format, the dentries are stored in the "metadata resource" section right
 * after the security data.  Each image in the WIM file has its own metadata
 * resource with its own security data and dentry tree.  Dentries in different
 * images may share file resources by referring to the same lookup table
 * entries.
 */

/*
 *
 * Copyright (C) 2010 Carl Thijssen
 * Copyright (C) 2012 Eric Biggers
 *
 * This file is part of wimlib, a library for working with WIM files.
 *
 * wimlib 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.
 *
 * wimlib 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 wimlib; if not, see http://www.gnu.org/licenses/.
 */

#include <errno.h>
#include <sys/stat.h>
#include <time.h>
#include <unistd.h>

#include "dentry.h"
#include "io.h"
#include "lookup_table.h"
#include "sha1.h"
#include "timestamp.h"
#include "wimlib_internal.h"

/*
 * Returns true if @dentry has the UTF-8 file name @name that has length
 * @name_len.
 */
static bool dentry_has_name(const struct dentry *dentry, const char *name, 
                            size_t name_len)
{
        if (dentry->file_name_utf8_len != name_len)
                return false;
        return memcmp(dentry->file_name_utf8, name, name_len) == 0;
}

static u64 __dentry_correct_length_unaligned(u16 file_name_len,
                                             u16 short_name_len)
{
        u64 length = WIM_DENTRY_DISK_SIZE;
        if (file_name_len)
                length += file_name_len + 2;
        if (short_name_len)
                length += short_name_len + 2;
        return length;
}

static u64 dentry_correct_length_unaligned(const struct dentry *dentry)
{
        return __dentry_correct_length_unaligned(dentry->file_name_len,
                                                 dentry->short_name_len);
}

/* Return the "correct" value to write in the length field of the dentry, based
 * on the file name length and short name length */
static u64 dentry_correct_length(const struct dentry *dentry)
{
        return (dentry_correct_length_unaligned(dentry) + 7) & ~7;
}

static u64 __dentry_total_length(const struct dentry *dentry, u64 length)
{
        for (u16 i = 0; i < dentry->num_ads; i++)
                length += ads_entry_total_length(&dentry->ads_entries[i]);
        return (length + 7) & ~7;
}

u64 dentry_correct_total_length(const struct dentry *dentry)
{
        return __dentry_total_length(dentry,
                                     dentry_correct_length_unaligned(dentry));
}

/* Real length of a dentry, including the alternate data stream entries, which
 * are not included in the dentry->length field... */
u64 dentry_total_length(const struct dentry *dentry)
{
        return __dentry_total_length(dentry, dentry->length);
}

/* Transfers file attributes from a `stat' buffer to a struct dentry. */
void stbuf_to_dentry(const struct stat *stbuf, struct dentry *dentry)
{
        if (S_ISLNK(stbuf->st_mode)) {
                dentry->attributes = FILE_ATTRIBUTE_REPARSE_POINT;
                dentry->reparse_tag = WIM_IO_REPARSE_TAG_SYMLINK;
        } else if (S_ISDIR(stbuf->st_mode)) {
                dentry->attributes = FILE_ATTRIBUTE_DIRECTORY;
        } else {
                dentry->attributes = FILE_ATTRIBUTE_NORMAL;
        }
        if (sizeof(ino_t) >= 8)
                dentry->hard_link = (u64)stbuf->st_ino;
        else
                dentry->hard_link = (u64)stbuf->st_ino |
                                   ((u64)stbuf->st_dev << (sizeof(ino_t) * 8));
        /* Set timestamps */
        dentry->creation_time = timespec_to_wim_timestamp(&stbuf->st_mtim);
        dentry->last_write_time = timespec_to_wim_timestamp(&stbuf->st_mtim);
        dentry->last_access_time = timespec_to_wim_timestamp(&stbuf->st_atim);
}


/* Sets all the timestamp fields of the dentry to the current time. */
void dentry_update_all_timestamps(struct dentry *dentry)
{
        u64 now = get_wim_timestamp();
        dentry->creation_time    = now;
        dentry->last_access_time = now;
        dentry->last_write_time  = now;
}

/* Returns the alternate data stream entry belonging to @dentry that has the
 * stream name @stream_name. */
struct ads_entry *dentry_get_ads_entry(struct dentry *dentry,
                                       const char *stream_name)
{
        size_t stream_name_len;
        if (!stream_name)
                return NULL;
        if (dentry->num_ads) {
                u16 i = 0;
                stream_name_len = strlen(stream_name);
                do {
                        if (ads_entry_has_name(&dentry->ads_entries[i],
                                               stream_name, stream_name_len))
                                return &dentry->ads_entries[i];
                } while (++i != dentry->num_ads);
        }
        return NULL;
}

static void ads_entry_init(struct ads_entry *ads_entry)
{
        memset(ads_entry, 0, sizeof(struct ads_entry));
        INIT_LIST_HEAD(&ads_entry->lte_group_list.list);
        ads_entry->lte_group_list.type = STREAM_TYPE_ADS;
}

/* 
 * Add an alternate stream entry to a dentry and return a pointer to it, or NULL
 * if memory could not be allocated.
 */
struct ads_entry *dentry_add_ads(struct dentry *dentry, const char *stream_name)
{
        u16 num_ads;
        struct ads_entry *ads_entries;
        struct ads_entry *new_entry;

        DEBUG("Add alternate data stream %s:%s",
               dentry->file_name_utf8, stream_name);

        if (dentry->num_ads == 0xffff)
                return NULL;
        num_ads = dentry->num_ads + 1;
        ads_entries = REALLOC(dentry->ads_entries,
                              num_ads * sizeof(struct ads_entry));
        if (!ads_entries)
                return NULL;
        if (ads_entries != dentry->ads_entries) {
                /* We moved the ADS entries.  Adjust the stream lists. */
                for (u16 i = 0; i < dentry->num_ads; i++) {
                        struct list_head *cur = &ads_entries[i].lte_group_list.list;
                        cur->prev->next = cur;
                        cur->next->prev = cur;
                }
        }

        new_entry = &ads_entries[num_ads - 1];
        ads_entry_init(new_entry);
        if (change_ads_name(new_entry, stream_name) != 0)
                return NULL;
        dentry->ads_entries = ads_entries;
        dentry->num_ads = num_ads;
        return new_entry;
}

/* Remove an alternate data stream from a dentry.
 *
 * The corresponding lookup table entry for the stream is NOT changed.
 *
 * @dentry:     The dentry
 * @ads_entry:  The alternate data stream entry (it MUST be one of the
 *                 ads_entry's in the array dentry->ads_entries).
 */
void dentry_remove_ads(struct dentry *dentry, struct ads_entry *ads_entry)
{
        u16 idx;
        u16 following;

        wimlib_assert(dentry->num_ads);
        idx = ads_entry - dentry->ads_entries;
        wimlib_assert(idx < dentry->num_ads);
        following = dentry->num_ads - idx - 1;

        destroy_ads_entry(ads_entry);
        memcpy(ads_entry, ads_entry + 1, following * sizeof(struct ads_entry));

        /* We moved the ADS entries.  Adjust the stream lists. */
        for (u16 i = 0; i < following; i++) {
                struct list_head *cur = &ads_entry[i].lte_group_list.list;
                cur->prev->next = cur;
                cur->next->prev = cur;
        }

        dentry->num_ads--;
}

/* 
 * Calls a function on all directory entries in a directory tree.  It is called
 * on a parent before its children.
 */
int for_dentry_in_tree(struct dentry *root, 
                       int (*visitor)(struct dentry*, void*), void *arg)
{
        int ret;
        struct dentry *child;

        ret = visitor(root, arg);

        if (ret != 0)
                return ret;

        child = root->children;

        if (!child)
                return 0;

        do {
                ret = for_dentry_in_tree(child, visitor, arg);
                if (ret != 0)
                        return ret;
                child = child->next;
        } while (child != root->children);
        return 0;
}

/* 
 * Like for_dentry_in_tree(), but the visitor function is always called on a
 * dentry's children before on itself.
 */
int for_dentry_in_tree_depth(struct dentry *root, 
                             int (*visitor)(struct dentry*, void*), void *arg)
{
        int ret;
        struct dentry *child;
        struct dentry *next;

        child = root->children;
        if (child) {
                do {
                        next = child->next;
                        ret = for_dentry_in_tree_depth(child, visitor, arg);
                        if (ret != 0)
                                return ret;
                        child = next;
                } while (child != root->children);
        }
        return visitor(root, arg);
}

/* 
 * Calculate the full path of @dentry, based on its parent's full path and on
 * its UTF-8 file name. 
 */
int calculate_dentry_full_path(struct dentry *dentry, void *ignore)
{
        char *full_path;
        u32 full_path_len;
        if (dentry_is_root(dentry)) {
                full_path = MALLOC(2);
                if (!full_path)
                        goto oom;
                full_path[0] = '/';
                full_path[1] = '\0';
                full_path_len = 1;
        } else {
                char *parent_full_path;
                u32 parent_full_path_len;
                const struct dentry *parent = dentry->parent;

                if (dentry_is_root(parent)) {
                        parent_full_path = "";
                        parent_full_path_len = 0;
                } else {
                        parent_full_path = parent->full_path_utf8;
                        parent_full_path_len = parent->full_path_utf8_len;
                }

                full_path_len = parent_full_path_len + 1 +
                                dentry->file_name_utf8_len;
                full_path = MALLOC(full_path_len + 1);
                if (!full_path)
                        goto oom;

                memcpy(full_path, parent_full_path, parent_full_path_len);
                full_path[parent_full_path_len] = '/';
                memcpy(full_path + parent_full_path_len + 1,
                       dentry->file_name_utf8,
                       dentry->file_name_utf8_len);
                full_path[full_path_len] = '\0';
        }
        FREE(dentry->full_path_utf8);
        dentry->full_path_utf8 = full_path;
        dentry->full_path_utf8_len = full_path_len;
        return 0;
oom:
        ERROR("Out of memory while calculating dentry full path");
        return WIMLIB_ERR_NOMEM;
}

/* 
 * Recursively calculates the subdir offsets for a directory tree. 
 *
 * @dentry:  The root of the directory tree.
 * @subdir_offset_p:  The current subdirectory offset; i.e., the subdirectory
 *      offset for @dentry. 
 */
void calculate_subdir_offsets(struct dentry *dentry, u64 *subdir_offset_p)
{
        struct dentry *child;

        child = dentry->children;
        dentry->subdir_offset = *subdir_offset_p;

        if (child) {
                /* Advance the subdir offset by the amount of space the children
                 * of this dentry take up. */
                do {
                        *subdir_offset_p += dentry_correct_total_length(child);
                        child = child->next;
                } while (child != dentry->children);

                /* End-of-directory dentry on disk. */
                *subdir_offset_p += 8;

                /* Recursively call calculate_subdir_offsets() on all the
                 * children. */
                do {
                        calculate_subdir_offsets(child, subdir_offset_p);
                        child = child->next;
                } while (child != dentry->children);
        } else {
                /* On disk, childless directories have a valid subdir_offset
                 * that points to an 8-byte end-of-directory dentry.  Regular
                 * files or reparse points have a subdir_offset of 0. */
                if (dentry_is_directory(dentry))
                        *subdir_offset_p += 8;
                else
                        dentry->subdir_offset = 0;
        }
}


/* Returns the child of @dentry that has the file name @name.  
 * Returns NULL if no child has the name. */
struct dentry *get_dentry_child_with_name(const struct dentry *dentry, 
                                          const char *name)
{
        struct dentry *child;
        size_t name_len;
        
        child = dentry->children;
        if (child) {
                name_len = strlen(name);
                do {
                        if (dentry_has_name(child, name, name_len))
                                return child;
                        child = child->next;
                } while (child != dentry->children);
        }
        return NULL;
}

/* Retrieves the dentry that has the UTF-8 @path relative to the dentry
 * @cur_dir.  Returns NULL if no dentry having the path is found. */
static struct dentry *get_dentry_relative_path(struct dentry *cur_dir,
                                               const char *path)
{
        struct dentry *child;
        size_t base_len;
        const char *new_path;

        if (*path == '\0')
                return cur_dir;

        child = cur_dir->children;
        if (child) {
                new_path = path_next_part(path, &base_len);
                do {
                        if (dentry_has_name(child, path, base_len))
                                return get_dentry_relative_path(child, new_path);
                        child = child->next;
                } while (child != cur_dir->children);
        }
        return NULL;
}

/* Returns the dentry corresponding to the UTF-8 @path, or NULL if there is no
 * such dentry. */
struct dentry *get_dentry(WIMStruct *w, const char *path)
{
        struct dentry *root = wim_root_dentry(w);
        while (*path == '/')
                path++;
        return get_dentry_relative_path(root, path);
}

/* Returns the dentry that corresponds to the parent directory of @path, or NULL
 * if the dentry is not found. */
struct dentry *get_parent_dentry(WIMStruct *w, const char *path)
{
        size_t path_len = strlen(path);
        char buf[path_len + 1];

        memcpy(buf, path, path_len + 1);

        to_parent_name(buf, path_len);

        return get_dentry(w, buf);
}

/* Prints the full path of a dentry. */
int print_dentry_full_path(struct dentry *dentry, void *ignore)
{
        if (dentry->full_path_utf8)
                puts(dentry->full_path_utf8);
        return 0;
}

/* We want to be able to show the names of the file attribute flags that are
 * set. */
struct file_attr_flag {
        u32 flag;
        const char *name;
};
struct file_attr_flag file_attr_flags[] = {
        {FILE_ATTRIBUTE_READONLY,           "READONLY"},
        {FILE_ATTRIBUTE_HIDDEN,             "HIDDEN"},
        {FILE_ATTRIBUTE_SYSTEM,             "SYSTEM"},
        {FILE_ATTRIBUTE_DIRECTORY,          "DIRECTORY"},
        {FILE_ATTRIBUTE_ARCHIVE,            "ARCHIVE"},
        {FILE_ATTRIBUTE_DEVICE,             "DEVICE"},
        {FILE_ATTRIBUTE_NORMAL,             "NORMAL"},
        {FILE_ATTRIBUTE_TEMPORARY,          "TEMPORARY"},
        {FILE_ATTRIBUTE_SPARSE_FILE,        "SPARSE_FILE"},
        {FILE_ATTRIBUTE_REPARSE_POINT,      "REPARSE_POINT"},
        {FILE_ATTRIBUTE_COMPRESSED,         "COMPRESSED"},
        {FILE_ATTRIBUTE_OFFLINE,            "OFFLINE"},
        {FILE_ATTRIBUTE_NOT_CONTENT_INDEXED,"NOT_CONTENT_INDEXED"},
        {FILE_ATTRIBUTE_ENCRYPTED,          "ENCRYPTED"},
        {FILE_ATTRIBUTE_VIRTUAL,            "VIRTUAL"},
};

/* Prints a directory entry.  @lookup_table is a pointer to the lookup table, if
 * available.  If the dentry is unresolved and the lookup table is NULL, the
 * lookup table entries will not be printed.  Otherwise, they will be. */
int print_dentry(struct dentry *dentry, void *lookup_table)
{
        const u8 *hash;
        struct lookup_table_entry *lte;
        time_t time;
        char *p;

        printf("[DENTRY]\n");
        printf("Length            = %"PRIu64"\n", dentry->length);
        printf("Attributes        = 0x%x\n", dentry->attributes);
        for (unsigned i = 0; i < ARRAY_LEN(file_attr_flags); i++)
                if (file_attr_flags[i].flag & dentry->attributes)
                        printf("    FILE_ATTRIBUTE_%s is set\n",
                                file_attr_flags[i].name);
        printf("Security ID       = %d\n", dentry->security_id);
        printf("Subdir offset     = %"PRIu64"\n", dentry->subdir_offset);
#if 0
        printf("Unused1           = 0x%"PRIu64"\n", dentry->unused1);
        printf("Unused2           = %"PRIu64"\n", dentry->unused2);
#endif
#if 0
        printf("Creation Time     = 0x%"PRIx64"\n");
        printf("Last Access Time  = 0x%"PRIx64"\n");
        printf("Last Write Time   = 0x%"PRIx64"\n");
#endif

        /* Translate the timestamps into something readable */
        time_t creat_time = wim_timestamp_to_unix(dentry->creation_time);
        time_t access_time = wim_timestamp_to_unix(dentry->last_access_time);
        time_t mod_time = wim_timestamp_to_unix(dentry->last_write_time);

        time = wim_timestamp_to_unix(dentry->creation_time);
        p = asctime(gmtime(&time));
        *(strrchr(p, '\n')) = '\0';
        printf("Creation Time     = %s UTC\n", p);

        time = wim_timestamp_to_unix(dentry->last_access_time);
        p = asctime(gmtime(&time));
        *(strrchr(p, '\n')) = '\0';
        printf("Last Access Time  = %s UTC\n", p);

        time = wim_timestamp_to_unix(dentry->last_write_time);
        p = asctime(gmtime(&time));
        *(strrchr(p, '\n')) = '\0';
        printf("Last Write Time   = %s UTC\n", p);

        printf("Reparse Tag       = 0x%"PRIx32"\n", dentry->reparse_tag);
        printf("Hard Link Group   = 0x%"PRIx64"\n", dentry->hard_link);
        printf("Number of Alternate Data Streams = %hu\n", dentry->num_ads);
        printf("Filename          = \"");
        print_string(dentry->file_name, dentry->file_name_len);
        puts("\"");
        printf("Filename Length   = %hu\n", dentry->file_name_len);
        printf("Filename (UTF-8)  = \"%s\"\n", dentry->file_name_utf8);
        printf("Filename (UTF-8) Length = %hu\n", dentry->file_name_utf8_len);
        printf("Short Name        = \"");
        print_string(dentry->short_name, dentry->short_name_len);
        puts("\"");
        printf("Short Name Length = %hu\n", dentry->short_name_len);
        printf("Full Path (UTF-8) = \"%s\"\n", dentry->full_path_utf8);
        lte = dentry_stream_lte(dentry, 0, lookup_table);
        if (lte) {
                print_lookup_table_entry(lte);
        } else {
                hash = dentry_stream_hash(dentry, 0);
                if (hash) {
                        printf("Hash              = 0x"); 
                        print_hash(hash);
                        putchar('\n');
                        putchar('\n');
                }
        }
        for (u16 i = 0; i < dentry->num_ads; i++) {
                printf("[Alternate Stream Entry %u]\n", i);
                printf("Name = \"%s\"\n", dentry->ads_entries[i].stream_name_utf8);
                printf("Name Length (UTF-16) = %u\n",
                                dentry->ads_entries[i].stream_name_len);
                hash = dentry_stream_hash(dentry, i + 1);
                if (hash) {
                        printf("Hash              = 0x"); 
                        print_hash(hash);
                        putchar('\n');
                }
                print_lookup_table_entry(dentry_stream_lte(dentry, i + 1,
                                                           lookup_table));
        }
        return 0;
}

/* Initializations done on every `struct dentry'. */
static void dentry_common_init(struct dentry *dentry)
{
        memset(dentry, 0, sizeof(struct dentry));
        dentry->refcnt = 1;
        dentry->security_id = -1;
        dentry->ads_entries_status = ADS_ENTRIES_DEFAULT;
        dentry->lte_group_list.type = STREAM_TYPE_NORMAL;
}

/* 
 * Creates an unlinked directory entry.
 *
 * @name:  The UTF-8 filename of the new dentry.
 *
 * Returns a pointer to the new dentry, or NULL if out of memory.
 */
struct dentry *new_dentry(const char *name)
{
        struct dentry *dentry;
        
        dentry = MALLOC(sizeof(struct dentry));
        if (!dentry)
                goto err;

        dentry_common_init(dentry);
        if (change_dentry_name(dentry, name) != 0)
                goto err;

        dentry_update_all_timestamps(dentry);
        dentry->next   = dentry;
        dentry->prev   = dentry;
        dentry->parent = dentry;
        INIT_LIST_HEAD(&dentry->link_group_list);
        return dentry;
err:
        FREE(dentry);
        ERROR("Failed to allocate new dentry");
        return NULL;
}

void dentry_free_ads_entries(struct dentry *dentry)
{
        for (u16 i = 0; i < dentry->num_ads; i++)
                destroy_ads_entry(&dentry->ads_entries[i]);
        FREE(dentry->ads_entries);
        dentry->ads_entries = NULL;
        dentry->num_ads = 0;
}

static void __destroy_dentry(struct dentry *dentry)
{
        FREE(dentry->file_name);
        FREE(dentry->file_name_utf8);
        FREE(dentry->short_name);
        FREE(dentry->full_path_utf8);
        FREE(dentry->extracted_file);
}

/* Frees a WIM dentry. */
void free_dentry(struct dentry *dentry)
{
        wimlib_assert(dentry);
        __destroy_dentry(dentry);
        /* Don't destroy the ADS entries if they "belong" to a different dentry
         * */
        if (dentry->ads_entries_status != ADS_ENTRIES_USER)
                dentry_free_ads_entries(dentry);
        FREE(dentry);
}

/* Like free_dentry(), but assigns a new ADS entries owner if this dentry was
 * the previous owner, and also deletes the dentry from its link_group_list */
void put_dentry(struct dentry *dentry)
{
        if (dentry->ads_entries_status == ADS_ENTRIES_OWNER) {
                struct dentry *new_owner;
                list_for_each_entry(new_owner, &dentry->link_group_list,
                                    link_group_list)
                {
                        if (new_owner->ads_entries_status == ADS_ENTRIES_USER) {
                                new_owner->ads_entries_status = ADS_ENTRIES_OWNER;
                                break;
                        }
                }
                dentry->ads_entries_status = ADS_ENTRIES_USER;
        }
        struct list_head *next;
        list_del(&dentry->link_group_list);
        free_dentry(dentry);
}


/* Partically clones a dentry.
 *
 * Beware:
 *      - memory for file names is not cloned (the pointers are all set to NULL
 *        and the lengths are set to zero)
 *      - next, prev, and children pointers and not touched
 *      - stream entries are not cloned (pointer left untouched).
 */
struct dentry *clone_dentry(struct dentry *old)
{
        struct dentry *new = MALLOC(sizeof(struct dentry));
        if (!new)
                return NULL;
        memcpy(new, old, sizeof(struct dentry));
        new->file_name          = NULL;
        new->file_name_len      = 0;
        new->file_name_utf8     = NULL;
        new->file_name_utf8_len = 0;
        new->short_name         = NULL;
        new->short_name_len     = 0;
        return new;
}

/* 
 * This function is passed as an argument to for_dentry_in_tree_depth() in order
 * to free a directory tree.  __args is a pointer to a `struct free_dentry_args'.
 */
static int do_free_dentry(struct dentry *dentry, void *__lookup_table)
{
        struct lookup_table *lookup_table = __lookup_table;
        struct lookup_table_entry *lte;
        unsigned i;

        if (lookup_table) {
                for (i = 0; i <= dentry->num_ads; i++) {
                        lte = dentry_stream_lte(dentry, i, lookup_table);
                        lte_decrement_refcnt(lte, lookup_table);
                }
        }

        wimlib_assert(dentry->refcnt != 0);
        if (--dentry->refcnt == 0)
                free_dentry(dentry);
        return 0;
}

/* 
 * Unlinks and frees a dentry tree.
 *
 * @root:               The root of the tree.
 * @lookup_table:       The lookup table for dentries.  If non-NULL, the
 *                      reference counts in the lookup table for the lookup
 *                      table entries corresponding to the dentries will be
 *                      decremented.
 */
void free_dentry_tree(struct dentry *root, struct lookup_table *lookup_table)
{
        if (!root || !root->parent)
                return;
        for_dentry_in_tree_depth(root, do_free_dentry, lookup_table);
}

int increment_dentry_refcnt(struct dentry *dentry, void *ignore)
{
        dentry->refcnt++;
        return 0;
}

/* 
 * Links a dentry into the directory tree.
 *
 * @dentry: The dentry to link.
 * @parent: The dentry that will be the parent of @dentry.
 */
void link_dentry(struct dentry *dentry, struct dentry *parent)
{
        wimlib_assert(dentry_is_directory(parent));
        dentry->parent = parent;
        if (parent->children) {
                /* Not an only child; link to siblings. */
                dentry->next = parent->children;
                dentry->prev = parent->children->prev;
                dentry->next->prev = dentry;
                dentry->prev->next = dentry;
        } else {
                /* Only child; link to parent. */
                parent->children = dentry;
                dentry->next = dentry;
                dentry->prev = dentry;
        }
}


/* Unlink a dentry from the directory tree. 
 *
 * Note: This merely removes it from the in-memory tree structure.  See
 * remove_dentry() in mount.c for a function implemented on top of this one that
 * frees the dentry and implements reference counting for the lookup table
 * entries. */
void unlink_dentry(struct dentry *dentry)
{
        if (dentry_is_root(dentry))
                return;
        if (dentry_is_only_child(dentry)) {
                dentry->parent->children = NULL;
        } else {
                if (dentry_is_first_sibling(dentry))
                        dentry->parent->children = dentry->next;
                dentry->next->prev = dentry->prev;
                dentry->prev->next = dentry->next;
        }
}

/* Duplicates a UTF-8 name into UTF-8 and UTF-16 strings and returns the strings
 * and their lengths in the pointer arguments */
int get_names(char **name_utf16_ret, char **name_utf8_ret,
              u16 *name_utf16_len_ret, u16 *name_utf8_len_ret,
              const char *name)
{
        size_t utf8_len;
        size_t utf16_len;
        char *name_utf16, *name_utf8;

        utf8_len = strlen(name);

        name_utf16 = utf8_to_utf16(name, utf8_len, &utf16_len);

        if (!name_utf16)
                return WIMLIB_ERR_NOMEM;

        name_utf8 = MALLOC(utf8_len + 1);
        if (!name_utf8) {
                FREE(name_utf8);
                return WIMLIB_ERR_NOMEM;
        }
        memcpy(name_utf8, name, utf8_len + 1);
        FREE(*name_utf8_ret);
        FREE(*name_utf16_ret);
        *name_utf8_ret      = name_utf8;
        *name_utf16_ret     = name_utf16;
        *name_utf8_len_ret  = utf8_len;
        *name_utf16_len_ret = utf16_len;
        return 0;
}

/* Changes the name of a dentry to @new_name.  Only changes the file_name and
 * file_name_utf8 fields; does not change the short_name, short_name_utf8, or
 * full_path_utf8 fields.  Also recalculates its length. */
int change_dentry_name(struct dentry *dentry, const char *new_name)
{
        int ret;

        ret = get_names(&dentry->file_name, &dentry->file_name_utf8,
                        &dentry->file_name_len, &dentry->file_name_utf8_len,
                         new_name);
        if (ret == 0)
                dentry->length = dentry_correct_length(dentry);
        return ret;
}

/*
 * Changes the name of an alternate data stream */
int change_ads_name(struct ads_entry *entry, const char *new_name)
{
        return get_names(&entry->stream_name, &entry->stream_name_utf8,
                         &entry->stream_name_len,
                         &entry->stream_name_utf8_len,
                         new_name);
}

/* Parameters for calculate_dentry_statistics(). */
struct image_statistics {
        struct lookup_table *lookup_table;
        u64 *dir_count;
        u64 *file_count;
        u64 *total_bytes;
        u64 *hard_link_bytes;
};

static int calculate_dentry_statistics(struct dentry *dentry, void *arg)
{
        struct image_statistics *stats;
        struct lookup_table_entry *lte; 
        
        stats = arg;

        if (dentry_is_directory(dentry) && !dentry_is_root(dentry))
                ++*stats->dir_count;
        else
                ++*stats->file_count;

        for (unsigned i = 0; i <= dentry->num_ads; i++) {
                lte = dentry_stream_lte(dentry, i, stats->lookup_table);
                if (lte) {
                        *stats->total_bytes += wim_resource_size(lte);
                        if (++lte->out_refcnt == 1)
                                *stats->hard_link_bytes += wim_resource_size(lte);
                }
        }
        return 0;
}

/* Calculates some statistics about a dentry tree. */
void calculate_dir_tree_statistics(struct dentry *root, struct lookup_table *table, 
                                   u64 *dir_count_ret, u64 *file_count_ret, 
                                   u64 *total_bytes_ret, 
                                   u64 *hard_link_bytes_ret)
{
        struct image_statistics stats;
        *dir_count_ret         = 0;
        *file_count_ret        = 0;
        *total_bytes_ret       = 0;
        *hard_link_bytes_ret   = 0;
        stats.lookup_table     = table;
        stats.dir_count       = dir_count_ret;
        stats.file_count      = file_count_ret;
        stats.total_bytes     = total_bytes_ret;
        stats.hard_link_bytes = hard_link_bytes_ret;
        for_lookup_table_entry(table, zero_out_refcnts, NULL);
        for_dentry_in_tree(root, calculate_dentry_statistics, &stats);
}


/* 
 * Reads the alternate data stream entries for a dentry.
 *
 * @p:  Pointer to buffer that starts with the first alternate stream entry.
 *
 * @dentry:     Dentry to load the alternate data streams into.
 *                      @dentry->num_ads must have been set to the number of
 *                      alternate data streams that are expected.
 *
 * @remaining_size:     Number of bytes of data remaining in the buffer pointed
 *                              to by @p.
 *
 * The format of the on-disk alternate stream entries is as follows:
 *
 * struct ads_entry_on_disk {
 *      u64  length;          // Length of the entry, in bytes.  This includes
 *                                  all fields (including the stream name and 
 *                                  null terminator if present, AND the padding!).
 *      u64  reserved;        // Seems to be unused
 *      u8   hash[20];        // SHA1 message digest of the uncompressed stream
 *      u16  stream_name_len; // Length of the stream name, in bytes
 *      char stream_name[];   // Stream name in UTF-16LE, @stream_name_len bytes long,
 *                                  not including null terminator
 *      u16  zero;            // UTF-16 null terminator for the stream name, NOT
 *                                  included in @stream_name_len.  Based on what
 *                                  I've observed from filenames in dentries,
 *                                  this field should not exist when
 *                                  (@stream_name_len == 0), but you can't
 *                                  actually tell because of the padding anyway
 *                                  (provided that the padding is zeroed, which
 *                                  it always seems to be).
 *      char padding[];       // Padding to make the size a multiple of 8 bytes.
 * };
 *
 * In addition, the entries are 8-byte aligned.
 *
 * Return 0 on success or nonzero on failure.  On success, dentry->ads_entries
 * is set to an array of `struct ads_entry's of length dentry->num_ads.  On
 * failure, @dentry is not modified.
 */
static int read_ads_entries(const u8 *p, struct dentry *dentry,
                            u64 remaining_size)
{
        u16 num_ads;
        struct ads_entry *ads_entries;
        int ret;

        num_ads = dentry->num_ads;
        ads_entries = CALLOC(num_ads, sizeof(struct ads_entry));
        if (!ads_entries) {
                ERROR("Could not allocate memory for %"PRIu16" "
                      "alternate data stream entries", num_ads);
                return WIMLIB_ERR_NOMEM;
        }

        for (u16 i = 0; i < num_ads; i++) {
                struct ads_entry *cur_entry = &ads_entries[i];
                u64 length;
                u64 length_no_padding;
                u64 total_length;
                size_t utf8_len;
                const char *p_save = p;

                /* Read the base stream entry, excluding the stream name. */
                if (remaining_size < WIM_ADS_ENTRY_DISK_SIZE) {
                        ERROR("Stream entries go past end of metadata resource");
                        ERROR("(remaining_size = %"PRIu64")", remaining_size);
                        ret = WIMLIB_ERR_INVALID_DENTRY;
                        goto out_free_ads_entries;
                }

                p = get_u64(p, &length);
                p += 8; /* Skip the reserved field */
                p = get_bytes(p, SHA1_HASH_SIZE, (u8*)cur_entry->hash);
                p = get_u16(p, &cur_entry->stream_name_len);

                cur_entry->stream_name = NULL;
                cur_entry->stream_name_utf8 = NULL;

                /* Length including neither the null terminator nor the padding
                 * */
                length_no_padding = WIM_ADS_ENTRY_DISK_SIZE +
                                    cur_entry->stream_name_len;

                /* Length including the null terminator and the padding */
                total_length = ((length_no_padding + 2) + 7) & ~7;

                wimlib_assert(total_length == ads_entry_total_length(cur_entry));

                if (remaining_size < length_no_padding) {
                        ERROR("Stream entries go past end of metadata resource");
                        ERROR("(remaining_size = %"PRIu64" bytes, "
                              "length_no_padding = %"PRIu16" bytes)",
                              remaining_size, length_no_padding);
                        ret = WIMLIB_ERR_INVALID_DENTRY;
                        goto out_free_ads_entries;
                }

                /* The @length field in the on-disk ADS entry is expected to be
                 * equal to @total_length, which includes all of the entry and
                 * the padding that follows it to align the next ADS entry to an
                 * 8-byte boundary.  However, to be safe, we'll accept the
                 * length field as long as it's not less than the un-padded
                 * total length and not more than the padded total length. */
                if (length < length_no_padding || length > total_length) {
                        ERROR("Stream entry has unexpected length "
                              "field (length field = %"PRIu64", "
                              "unpadded total length = %"PRIu64", "
                              "padded total length = %"PRIu64")",
                              length, length_no_padding, total_length);
                        ret = WIMLIB_ERR_INVALID_DENTRY;
                        goto out_free_ads_entries;
                }

                if (cur_entry->stream_name_len) {
                        cur_entry->stream_name = MALLOC(cur_entry->stream_name_len);
                        if (!cur_entry->stream_name) {
                                ret = WIMLIB_ERR_NOMEM;
                                goto out_free_ads_entries;
                        }
                        get_bytes(p, cur_entry->stream_name_len,
                                  (u8*)cur_entry->stream_name);
                        cur_entry->stream_name_utf8 = utf16_to_utf8(cur_entry->stream_name,
                                                                    cur_entry->stream_name_len,
                                                                    &utf8_len);
                        cur_entry->stream_name_utf8_len = utf8_len;

                        if (!cur_entry->stream_name_utf8) {
                                ret = WIMLIB_ERR_NOMEM;
                                goto out_free_ads_entries;
                        }
                }
                /* It's expected that the size of every ADS entry is a multiple
                 * of 8.  However, to be safe, I'm allowing the possibility of
                 * an ADS entry at the very end of the metadata resource ending
                 * un-aligned.  So although we still need to increment the input
                 * pointer by @total_length to reach the next ADS entry, it's
                 * possible that less than @total_length is actually remaining
                 * in the metadata resource. We should set the remaining size to
                 * 0 bytes if this happens. */
                p = p_save + total_length;
                if (remaining_size < total_length)
                        remaining_size = 0;
                else
                        remaining_size -= total_length;
        }
        dentry->ads_entries = ads_entries;
        return 0;
out_free_ads_entries:
        for (u16 i = 0; i < num_ads; i++) {
                FREE(ads_entries[i].stream_name);
                FREE(ads_entries[i].stream_name_utf8);
        }
        FREE(ads_entries);
        return ret;
}

/* 
 * Reads a directory entry, including all alternate data stream entries that
 * follow it, from the WIM image's metadata resource.
 *
 * @metadata_resource:  Buffer containing the uncompressed metadata resource.
 * @metadata_resource_len:   Length of the metadata resource.
 * @offset:     Offset of this directory entry in the metadata resource.
 * @dentry:     A `struct dentry' that will be filled in by this function.
 *
 * Return 0 on success or nonzero on failure.  On failure, @dentry have been
 * modified, bu it will be left with no pointers to any allocated buffers.
 * On success, the dentry->length field must be examined.  If zero, this was a
 * special "end of directory" dentry and not a real dentry.  If nonzero, this
 * was a real dentry.
 */
int read_dentry(const u8 metadata_resource[], u64 metadata_resource_len, 
                u64 offset, struct dentry *dentry)
{
        const u8 *p;
        u64 calculated_size;
        char *file_name = NULL;
        char *file_name_utf8 = NULL;
        char *short_name = NULL;
        u16 short_name_len;
        u16 file_name_len;
        size_t file_name_utf8_len;
        int ret;

        dentry_common_init(dentry);

        /*Make sure the dentry really fits into the metadata resource.*/
        if (offset + 8 > metadata_resource_len || offset + 8 < offset) {
                ERROR("Directory entry starting at %"PRIu64" ends past the "
                      "end of the metadata resource (size %"PRIu64")",
                      offset, metadata_resource_len);
                return WIMLIB_ERR_INVALID_DENTRY;
        }

        /* Before reading the whole dentry, we need to read just the length.
         * This is because a dentry of length 8 (that is, just the length field)
         * terminates the list of sibling directory entries. */

        p = get_u64(&metadata_resource[offset], &dentry->length);

        /* A zero length field (really a length of 8, since that's how big the
         * directory entry is...) indicates that this is the end of directory
         * dentry.  We do not read it into memory as an actual dentry, so just
         * return successfully in that case. */
        if (dentry->length == 0)
                return 0;

        /* If the dentry does not overflow the metadata resource buffer and is
         * not too short, read the rest of it (excluding the alternate data
         * streams, but including the file name and short name variable-length
         * fields) into memory. */
        if (offset + dentry->length >= metadata_resource_len
            || offset + dentry->length < offset)
        {
                ERROR("Directory entry at offset %"PRIu64" and with size "
                      "%"PRIu64" ends past the end of the metadata resource "
                      "(size %"PRIu64")",
                      offset, dentry->length, metadata_resource_len);
                return WIMLIB_ERR_INVALID_DENTRY;
        }

        if (dentry->length < WIM_DENTRY_DISK_SIZE) {
                ERROR("Directory entry has invalid length of %"PRIu64" bytes",
                      dentry->length);
                return WIMLIB_ERR_INVALID_DENTRY;
        }

        p = get_u32(p, &dentry->attributes);
        p = get_u32(p, (u32*)&dentry->security_id);
        p = get_u64(p, &dentry->subdir_offset);

        /* 2 unused fields */
        p += 2 * sizeof(u64);
        /*p = get_u64(p, &dentry->unused1);*/
        /*p = get_u64(p, &dentry->unused2);*/

        p = get_u64(p, &dentry->creation_time);
        p = get_u64(p, &dentry->last_access_time);
        p = get_u64(p, &dentry->last_write_time);

        p = get_bytes(p, SHA1_HASH_SIZE, dentry->hash);
        
        /*
         * I don't know what's going on here.  It seems like M$ screwed up the
         * reparse points, then put the fields in the same place and didn't
         * document it.  The WIM_HDR_FLAG_RP_FIX flag in the WIM header might
         * have something to do with this, but it's not documented.
         */
        if (dentry->attributes & FILE_ATTRIBUTE_REPARSE_POINT) {
                /* ??? */
                p += 4;
                p = get_u32(p, &dentry->reparse_tag);
                p += 4;
        } else {
                p = get_u32(p, &dentry->reparse_tag);
                p = get_u64(p, &dentry->hard_link);
        }

        /* By the way, the reparse_reserved field does not actually exist (at
         * least when the file is not a reparse point) */
        
        p = get_u16(p, &dentry->num_ads);

        p = get_u16(p, &short_name_len);
        p = get_u16(p, &file_name_len);

        /* We now know the length of the file name and short name.  Make sure
         * the length of the dentry is large enough to actually hold them. 
         *
         * The calculated length here is unaligned to allow for the possibility
         * that the dentry->length names an unaligned length, although this
         * would be unexpected. */
        calculated_size = __dentry_correct_length_unaligned(file_name_len,
                                                            short_name_len);

        if (dentry->length < calculated_size) {
                ERROR("Unexpected end of directory entry! (Expected "
                      "at least %"PRIu64" bytes, got %"PRIu64" bytes. "
                      "short_name_len = %hu, file_name_len = %hu)", 
                      calculated_size, dentry->length,
                      short_name_len, file_name_len);
                return WIMLIB_ERR_INVALID_DENTRY;
        }

        /* Read the filename if present.  Note: if the filename is empty, there
         * is no null terminator following it. */
        if (file_name_len) {
                file_name = MALLOC(file_name_len);
                if (!file_name) {
                        ERROR("Failed to allocate %hu bytes for dentry file name",
                              file_name_len);
                        return WIMLIB_ERR_NOMEM;
                }
                p = get_bytes(p, file_name_len, file_name);

                /* Convert filename to UTF-8. */
                file_name_utf8 = utf16_to_utf8(file_name, file_name_len, 
                                               &file_name_utf8_len);

                if (!file_name_utf8) {
                        ERROR("Failed to allocate memory to convert UTF-16 "
                              "filename (%hu bytes) to UTF-8", file_name_len);
                        ret = WIMLIB_ERR_NOMEM;
                        goto out_free_file_name;
                }
                if (*(u16*)p)
                        WARNING("Expected two zero bytes following the file name "
                                "`%s', but found non-zero bytes", file_name_utf8);
                p += 2;
        }

        /* Align the calculated size */
        calculated_size = (calculated_size + 7) & ~7;

        if (dentry->length > calculated_size) {
                /* Weird; the dentry says it's longer than it should be.  Note
                 * that the length field does NOT include the size of the
                 * alternate stream entries. */

                /* Strangely, some directory entries inexplicably have a little
                 * over 70 bytes of extra data.  The exact amount of data seems
                 * to be 72 bytes, but it is aligned on the next 8-byte
                 * boundary.  It does NOT seem to be alternate data stream
                 * entries.  Here's an example of the aligned data:
                 *
                 * 01000000 40000000 6c786bba c58ede11 b0bb0026 1870892a b6adb76f
                 * e63a3e46 8fca8653 0d2effa1 6c786bba c58ede11 b0bb0026 1870892a
                 * 00000000 00000000 00000000 00000000
                 *
                 * Here's one interpretation of how the data is laid out.
                 *
                 * struct unknown {
                 *      u32 field1; (always 0x00000001)
                 *      u32 field2; (always 0x40000000)
                 *      u8  data[48]; (???)
                 *      u64 reserved1; (always 0)
                 *      u64 reserved2; (always 0)
                 * };*/
                WARNING("Dentry for file or directory `%s' has %zu extra "
                        "bytes of data",
                        file_name_utf8, dentry->length - calculated_size);
        }

        /* Read the short filename if present.  Note: if there is no short
         * filename, there is no null terminator following it. */
        if (short_name_len) {
                short_name = MALLOC(short_name_len);
                if (!short_name) {
                        ERROR("Failed to allocate %hu bytes for short filename",
                              short_name_len);
                        ret = WIMLIB_ERR_NOMEM;
                        goto out_free_file_name_utf8;
                }

                p = get_bytes(p, short_name_len, short_name);
                if (*(u16*)p)
                        WARNING("Expected two zero bytes following the file name "
                                "`%s', but found non-zero bytes", file_name_utf8);
                p += 2;
        }

        /* 
         * Read the alternate data streams, if present.  dentry->num_ads tells
         * us how many they are, and they will directly follow the dentry
         * on-disk.
         *
         * Note that each alternate data stream entry begins on an 8-byte
         * aligned boundary, and the alternate data stream entries are NOT
         * included in the dentry->length field for some reason.
         */
        if (dentry->num_ads != 0) {
                if (calculated_size > metadata_resource_len - offset) {
                        ERROR("Not enough space in metadata resource for "
                              "alternate stream entries");
                        ret = WIMLIB_ERR_INVALID_DENTRY;
                        goto out_free_short_name;
                }
                ret = read_ads_entries(&metadata_resource[offset + calculated_size],
                                       dentry,
                                       metadata_resource_len - offset - calculated_size);
                if (ret != 0)
                        goto out_free_short_name;
        }

        /* We've read all the data for this dentry.  Set the names and their
         * lengths, and we've done. */
        dentry->file_name          = file_name;
        dentry->file_name_utf8     = file_name_utf8;
        dentry->short_name         = short_name;
        dentry->file_name_len      = file_name_len;
        dentry->file_name_utf8_len = file_name_utf8_len;
        dentry->short_name_len     = short_name_len;
        return 0;
out_free_short_name:
        FREE(short_name);
out_free_file_name_utf8:
        FREE(file_name_utf8);
out_free_file_name:
        FREE(file_name);
        return ret;
}

/* Run some miscellaneous verifications on a WIM dentry */
int verify_dentry(struct dentry *dentry, void *wim)
{
        const WIMStruct *w = wim;
        const struct lookup_table *table = w->lookup_table;
        const struct wim_security_data *sd = wim_const_security_data(w);
        int ret = WIMLIB_ERR_INVALID_DENTRY;

        /* Check the security ID */
        if (dentry->security_id < -1) {
                ERROR("Dentry `%s' has an invalid security ID (%d)",
                        dentry->full_path_utf8, dentry->security_id);
                goto out;
        }
        if (dentry->security_id >= sd->num_entries) {
                ERROR("Dentry `%s' has an invalid security ID (%d) "
                      "(there are only %u entries in the security table)",
                        dentry->full_path_utf8, dentry->security_id,
                        sd->num_entries);
                goto out;
        }

        /* Check that lookup table entries for all the resources exist, except
         * if the SHA1 message digest is all 0's, which indicates there is
         * intentionally no resource there.  */
        if (w->hdr.total_parts == 1) {
                for (unsigned i = 0; i <= dentry->num_ads; i++) {
                        struct lookup_table_entry *lte;
                        const u8 *hash;
                        hash = dentry_stream_hash_unresolved(dentry, i);
                        lte = __lookup_resource(table, hash);
                        if (!lte && !is_zero_hash(hash)) {
                                ERROR("Could not find lookup table entry for stream "
                                      "%u of dentry `%s'", i, dentry->full_path_utf8);
                                goto out;
                        }
                }
        }

        /* Make sure there is only one un-named stream. */
        unsigned num_unnamed_streams = 0;
        unsigned unnamed_stream_idx;
        for (unsigned i = 0; i <= dentry->num_ads; i++) {
                const u8 *hash;
                hash = dentry_stream_hash_unresolved(dentry, i);
                if (!dentry_stream_name_len(dentry, i) && !is_zero_hash(hash)) {
                        num_unnamed_streams++;
                        unnamed_stream_idx = i;
                }
        }
        if (num_unnamed_streams > 1) {
                ERROR("Dentry `%s' has multiple (%u) un-named streams", 
                      dentry->full_path_utf8, num_unnamed_streams);
                goto out;
        }

#if 0
        /* Check timestamps */
        if (dentry->last_access_time < dentry->creation_time ||
            dentry->last_write_time < dentry->creation_time) {
                WARNING("Dentry `%s' was created after it was last accessed or "
                      "written to", dentry->full_path_utf8);
        }
#endif

        ret = 0;
out:
        return ret;
}

/* 
 * Writes a WIM dentry to an output buffer.
 *
 * @dentry:  The dentry structure.
 * @p:       The memory location to write the data to.
 * @return:  Pointer to the byte after the last byte we wrote as part of the
 *              dentry.
 */
static u8 *write_dentry(const struct dentry *dentry, u8 *p)
{
        u8 *orig_p = p;
        unsigned padding;
        const u8 *hash;

        /* We calculate the correct length of the dentry ourselves because the
         * dentry->length field may been set to an unexpected value from when we
         * read the dentry in (for example, there may have been unknown data
         * appended to the end of the dentry...) */
        u64 length = dentry_correct_length(dentry);

        p = put_u64(p, length);
        p = put_u32(p, dentry->attributes);
        p = put_u32(p, dentry->security_id);
        p = put_u64(p, dentry->subdir_offset);
        p = put_u64(p, 0); /* unused1 */
        p = put_u64(p, 0); /* unused2 */
        p = put_u64(p, dentry->creation_time);
        p = put_u64(p, dentry->last_access_time);
        p = put_u64(p, dentry->last_write_time);
        if (dentry->resolved && dentry->lte)
                hash = dentry->lte->hash;
        else
                hash = dentry->hash;
        p = put_bytes(p, SHA1_HASH_SIZE, hash);
        if (dentry->attributes & FILE_ATTRIBUTE_REPARSE_POINT) {
                p = put_zeroes(p, 4);
                p = put_u32(p, dentry->reparse_tag);
                p = put_zeroes(p, 4);
        } else {
                u64 hard_link;
                p = put_u32(p, 0);
                if (dentry->link_group_list.next == &dentry->link_group_list)
                        hard_link = 0;
                else
                        hard_link = dentry->hard_link;
                p = put_u64(p, hard_link);
        }
        p = put_u16(p, dentry->num_ads);
        p = put_u16(p, dentry->short_name_len);
        p = put_u16(p, dentry->file_name_len);
        if (dentry->file_name_len) {
                p = put_bytes(p, dentry->file_name_len, (u8*)dentry->file_name);
                p = put_u16(p, 0); /* filename padding, 2 bytes. */
        }
        if (dentry->short_name) {
                p = put_bytes(p, dentry->short_name_len, (u8*)dentry->short_name);
                p = put_u16(p, 0); /* short name padding, 2 bytes */
        }

        /* Align to 8-byte boundary */
        wimlib_assert(length >= (p - orig_p)
                        && length - (p - orig_p) <= 7);
        p = put_zeroes(p, length - (p - orig_p));

        /* Write the alternate data streams, if there are any.  Please see
         * read_ads_entries() for comments about the format of the on-disk
         * alternate data stream entries. */
        for (u16 i = 0; i < dentry->num_ads; i++) {
                p = put_u64(p, ads_entry_total_length(&dentry->ads_entries[i]));
                p = put_u64(p, 0); /* Unused */
                if (dentry->resolved && dentry->ads_entries[i].lte)
                        hash = dentry->ads_entries[i].lte->hash;
                else
                        hash = dentry->ads_entries[i].hash;
                p = put_bytes(p, SHA1_HASH_SIZE, hash);
                p = put_u16(p, dentry->ads_entries[i].stream_name_len);
                if (dentry->ads_entries[i].stream_name_len) {
                        p = put_bytes(p, dentry->ads_entries[i].stream_name_len,
                                         (u8*)dentry->ads_entries[i].stream_name);
                        p = put_u16(p, 0);
                }
                p = put_zeroes(p, (8 - (p - orig_p) % 8) % 8);
        }
#ifdef ENABLE_ASSERTIONS
        wimlib_assert(p - orig_p == __dentry_total_length(dentry, length));
#endif
        return p;
}

/* Recursive function that writes a dentry tree rooted at @parent, not including
 * @parent itself, which has already been written. */
static u8 *write_dentry_tree_recursive(const struct dentry *parent, u8 *p)
{
        const struct dentry *child;

        /* Nothing to do if this dentry has no children. */
        if (parent->subdir_offset == 0)
                return p;

        /* Write child dentries and end-of-directory entry. 
         *
         * Note: we need to write all of this dentry's children before
         * recursively writing the directory trees rooted at each of the child
         * dentries, since the on-disk dentries for a dentry's children are
         * always located at consecutive positions in the metadata resource! */
        child = parent->children;
        if (child) {
                do {
                        p = write_dentry(child, p);
                        child = child->next;
                } while (child != parent->children);
        }

        /* write end of directory entry */
        p = put_u64(p, 0);

        /* Recurse on children. */
        if (child) {
                do {
                        p = write_dentry_tree_recursive(child, p);
                        child = child->next;
                } while (child != parent->children);
        }
        return p;
}

/* Writes a directory tree to the metadata resource.
 *
 * @root:       Root of the dentry tree.
 * @p:          Pointer to a buffer with enough space for the dentry tree.
 *
 * Returns pointer to the byte after the last byte we wrote.
 */
u8 *write_dentry_tree(const struct dentry *root, u8 *p)
{
        wimlib_assert(dentry_is_root(root));

        /* If we're the root dentry, we have no parent that already
         * wrote us, so we need to write ourselves. */
        p = write_dentry(root, p);

        /* Write end of directory entry after the root dentry just to be safe;
         * however the root dentry obviously cannot have any siblings. */
        p = put_u64(p, 0);

        /* Recursively write the rest of the dentry tree. */
        return write_dentry_tree_recursive(root, p);
}

/* Reads the children of a dentry, and all their children, ..., etc. from the
 * metadata resource and into the dentry tree.
 *
 * @metadata_resource:  An array that contains the uncompressed metadata
 *                      resource for the WIM file.
 *
 * @metadata_resource_len:  The length of the uncompressed metadata resource, in
 *                          bytes.
 *
 * @dentry:     A pointer to a `struct dentry' that is the root of the directory
 *              tree and has already been read from the metadata resource.  It
 *              does not need to be the real root because this procedure is
 *              called recursively.
 *
 * @return:     Zero on success, nonzero on failure.
 */
int read_dentry_tree(const u8 metadata_resource[], u64 metadata_resource_len,
                     struct dentry *dentry)
{
        u64 cur_offset = dentry->subdir_offset;
        struct dentry *prev_child = NULL;
        struct dentry *first_child = NULL;
        struct dentry *child;
        struct dentry cur_child;
        int ret;

        /* 
         * If @dentry has no child dentries, nothing more needs to be done for
         * this branch.  This is the case for regular files, symbolic links, and
         * *possibly* empty directories (although an empty directory may also
         * have one child dentry that is the special end-of-directory dentry)
         */
        if (cur_offset == 0)
                return 0;

        /* Find and read all the children of @dentry. */
        while (1) {

                /* Read next child of @dentry into @cur_child. */
                ret = read_dentry(metadata_resource, metadata_resource_len, 
                                  cur_offset, &cur_child);
                if (ret != 0)
                        break;

                /* Check for end of directory. */
                if (cur_child.length == 0)
                        break;

                /* Not end of directory.  Allocate this child permanently and
                 * link it to the parent and previous child. */
                child = MALLOC(sizeof(struct dentry));
                if (!child) {
                        ERROR("Failed to allocate %zu bytes for new dentry",
                              sizeof(struct dentry));
                        ret = WIMLIB_ERR_NOMEM;
                        break;
                }
                memcpy(child, &cur_child, sizeof(struct dentry));

                if (prev_child) {
                        prev_child->next = child;
                        child->prev = prev_child;
                } else {
                        first_child = child;
                }

                child->parent = dentry;
                prev_child = child;

                /* If there are children of this child, call this procedure
                 * recursively. */
                if (child->subdir_offset != 0) {
                        ret = read_dentry_tree(metadata_resource, 
                                               metadata_resource_len, child);
                        if (ret != 0)
                                break;
                }

                /* Advance to the offset of the next child.  Note: We need to
                 * advance by the TOTAL length of the dentry, not by the length
                 * child->length, which although it does take into account the
                 * padding, it DOES NOT take into account alternate stream
                 * entries. */
                cur_offset += dentry_total_length(child);
        }

        /* Link last child to first one, and set parent's children pointer to
         * the first child.  */
        if (prev_child) {
                prev_child->next = first_child;
                first_child->prev = prev_child;
        }
        dentry->children = first_child;
        return ret;
}