]> wimlib.net Git - wimlib/blobdiff - src/dentry.c
Add kind-of-working LZMS decompression using cabinet.dll API
[wimlib] / src / dentry.c
index d8c2fd0a2fc87cd98b9521658b8002a8660eadc1..cc3304ef1e0d4b14f044081655726ae58b5a875b 100644 (file)
@@ -217,7 +217,7 @@ struct wim_dentry_on_disk {
  * a file name and short name that take the specified numbers of bytes.  This
  * excludes any alternate data stream entries that may follow the dentry. */
 static u64
-_dentry_correct_length_unaligned(u16 file_name_nbytes, u16 short_name_nbytes)
+dentry_correct_length_unaligned(u16 file_name_nbytes, u16 short_name_nbytes)
 {
        u64 length = sizeof(struct wim_dentry_on_disk);
        if (file_name_nbytes)
@@ -232,10 +232,13 @@ _dentry_correct_length_unaligned(u16 file_name_nbytes, u16 short_name_nbytes)
  * ignored; also, this excludes any alternate data stream entries that may
  * follow the dentry. */
 static u64
-dentry_correct_length_unaligned(const struct wim_dentry *dentry)
+dentry_correct_length_aligned(const struct wim_dentry *dentry)
 {
-       return _dentry_correct_length_unaligned(dentry->file_name_nbytes,
-                                               dentry->short_name_nbytes);
+       u64 len;
+
+       len = dentry_correct_length_unaligned(dentry->file_name_nbytes,
+                                             dentry->short_name_nbytes);
+       return (len + 7) & ~7;
 }
 
 /* Duplicates a string of system-dependent encoding into a UTF-16LE string and
@@ -251,7 +254,7 @@ get_utf16le_name(const tchar *name, utf16lechar **name_utf16le_ret,
 #if TCHAR_IS_UTF16LE
        name_utf16le_nbytes = tstrlen(name) * sizeof(utf16lechar);
        name_utf16le = MALLOC(name_utf16le_nbytes + sizeof(utf16lechar));
-       if (!name_utf16le)
+       if (name_utf16le == NULL)
                return WIMLIB_ERR_NOMEM;
        memcpy(name_utf16le, name, name_utf16le_nbytes + sizeof(utf16lechar));
        ret = 0;
@@ -305,31 +308,58 @@ ads_entry_total_length(const struct wim_ads_entry *entry)
        return (len + 7) & ~7;
 }
 
+/*
+ * Determine whether to include a "dummy" stream when writing a WIM dentry:
+ *
+ * Some versions of Microsoft's WIM software (the boot driver(s) in WinPE 3.0,
+ * for example) contain a bug where they assume the first alternate data stream
+ * (ADS) entry of a dentry with a nonzero ADS count specifies the unnamed
+ * stream, even if it has a name and the unnamed stream is already specified in
+ * the hash field of the dentry itself.
+ *
+ * wimlib has to work around this behavior by carefully emulating the behavior
+ * of (most versions of) ImageX/WIMGAPI, which move the unnamed stream reference
+ * into the alternate stream entries whenever there are named data streams, even
+ * though there is already a field in the dentry itself for the unnamed stream
+ * reference, which then goes to waste.
+ */
+static inline bool inode_needs_dummy_stream(const struct wim_inode *inode)
+{
+       return (inode->i_num_ads > 0 &&
+               inode->i_num_ads < 0xffff && /* overflow check */
+               inode->i_canonical_streams); /* assume the dentry is okay if it
+                                               already had an unnamed ADS entry
+                                               when it was read in  */
+}
 
-static u64
-_dentry_total_length(const struct wim_dentry *dentry, u64 length)
+/* Calculate the total number of bytes that will be consumed when a WIM dentry
+ * is written.  This includes base dentry and name fields as well as all
+ * alternate data stream entries and alignment bytes.  */
+u64
+dentry_out_total_length(const struct wim_dentry *dentry)
 {
+       u64 length = dentry_correct_length_aligned(dentry);
        const struct wim_inode *inode = dentry->d_inode;
+
+       if (inode_needs_dummy_stream(inode))
+               length += ads_entry_total_length(&(struct wim_ads_entry){});
+
        for (u16 i = 0; i < inode->i_num_ads; i++)
                length += ads_entry_total_length(&inode->i_ads_entries[i]);
-       return (length + 7) & ~7;
-}
 
-/* Calculate the aligned *total* length of an on-disk WIM dentry.  This includes
- * all alternate data streams. */
-u64
-dentry_correct_total_length(const struct wim_dentry *dentry)
-{
-       return _dentry_total_length(dentry,
-                                   dentry_correct_length_unaligned(dentry));
+       return length;
 }
 
-/* Like dentry_correct_total_length(), but use the existing dentry->length field
- * instead of calculating its "correct" value. */
+/* Calculate the aligned, total length of a dentry, including all alternate data
+ * stream entries.  Uses dentry->length.  */
 static u64
-dentry_total_length(const struct wim_dentry *dentry)
+dentry_in_total_length(const struct wim_dentry *dentry)
 {
-       return _dentry_total_length(dentry, dentry->length);
+       u64 length = dentry->length;
+       const struct wim_inode *inode = dentry->d_inode;
+       for (u16 i = 0; i < inode->i_num_ads; i++)
+               length += ads_entry_total_length(&inode->i_ads_entries[i]);
+       return (length + 7) & ~7;
 }
 
 int
@@ -413,7 +443,7 @@ for_dentry_in_tree(struct wim_dentry *root,
 {
        int ret;
 
-       if (!root)
+       if (root == NULL)
                return 0;
        ret = (*visitor)(root, arg);
        if (ret)
@@ -431,7 +461,7 @@ for_dentry_in_tree_depth(struct wim_dentry *root,
 {
        int ret;
 
-       if (!root)
+       if (root == NULL)
                return 0;
        ret = for_dentry_tree_in_rbtree_depth(root->d_inode->i_children.rb_node,
                                              visitor, arg);
@@ -455,7 +485,7 @@ calculate_dentry_full_path(struct wim_dentry *dentry)
        if (dentry_is_root(dentry)) {
                static const tchar _root_path[] = {WIM_PATH_SEPARATOR, T('\0')};
                full_path = TSTRDUP(_root_path);
-               if (!full_path)
+               if (full_path == NULL)
                        return WIMLIB_ERR_NOMEM;
                full_path_nbytes = 1 * sizeof(tchar);
        } else {
@@ -469,7 +499,7 @@ calculate_dentry_full_path(struct wim_dentry *dentry)
                        parent_full_path = T("");
                        parent_full_path_nbytes = 0;
                } else {
-                       if (!parent->_full_path) {
+                       if (parent->_full_path == NULL) {
                                ret = calculate_dentry_full_path(parent);
                                if (ret)
                                        return ret;
@@ -495,7 +525,7 @@ calculate_dentry_full_path(struct wim_dentry *dentry)
                full_path_nbytes = parent_full_path_nbytes + sizeof(tchar) +
                                   filename_nbytes;
                full_path = MALLOC(full_path_nbytes + sizeof(tchar));
-               if (!full_path)
+               if (full_path == NULL)
                        return WIMLIB_ERR_NOMEM;
                memcpy(full_path, parent_full_path, parent_full_path_nbytes);
                full_path[parent_full_path_nbytes / sizeof(tchar)] = WIM_PATH_SEPARATOR;
@@ -537,7 +567,7 @@ dentry_full_path(struct wim_dentry *dentry)
 static int
 increment_subdir_offset(struct wim_dentry *dentry, void *subdir_offset_p)
 {
-       *(u64*)subdir_offset_p += dentry_correct_total_length(dentry);
+       *(u64*)subdir_offset_p += dentry_out_total_length(dentry);
        return 0;
 }
 
@@ -760,7 +790,7 @@ get_dentry_utf16le(WIMStruct *wim, const utf16lechar *path)
        const utf16lechar *p, *pp;
 
        cur_dentry = parent_dentry = wim_root_dentry(wim);
-       if (!cur_dentry) {
+       if (cur_dentry == NULL) {
                errno = ENOENT;
                return NULL;
        }
@@ -791,8 +821,12 @@ get_dentry_utf16le(WIMStruct *wim, const utf16lechar *path)
        return cur_dentry;
 }
 
-/* Returns the dentry corresponding to the @path, or NULL if there is no such
- * dentry. */
+/*
+ * Returns the dentry in the currently selected WIM image named by @path
+ * starting from the root of the WIM image, or NULL if there is no such dentry.
+ *
+ * On Windows, the search is done case-insensitively.
+ */
 struct wim_dentry *
 get_dentry(WIMStruct *wim, const tchar *path)
 {
@@ -983,6 +1017,7 @@ new_timeless_inode(void)
                inode->i_nlink = 1;
                inode->i_next_stream_id = 1;
                inode->i_not_rpfixed = 1;
+               inode->i_canonical_streams = 1;
                INIT_LIST_HEAD(&inode->i_list);
                INIT_LIST_HEAD(&inode->i_dentry);
        }
@@ -1010,7 +1045,7 @@ new_dentry(const tchar *name, struct wim_dentry **dentry_ret)
        int ret;
 
        dentry = MALLOC(sizeof(struct wim_dentry));
-       if (!dentry)
+       if (dentry == NULL)
                return WIMLIB_ERR_NOMEM;
 
        dentry_common_init(dentry);
@@ -1042,7 +1077,7 @@ _new_dentry_with_inode(const tchar *name, struct wim_dentry **dentry_ret,
                dentry->d_inode = new_timeless_inode();
        else
                dentry->d_inode = new_inode();
-       if (!dentry->d_inode) {
+       if (dentry->d_inode == NULL) {
                free_dentry(dentry);
                return WIMLIB_ERR_NOMEM;
        }
@@ -1082,6 +1117,19 @@ new_filler_directory(const tchar *name, struct wim_dentry **dentry_ret)
        return 0;
 }
 
+static int
+dentry_clear_inode_visited(struct wim_dentry *dentry, void *_ignore)
+{
+       dentry->d_inode->i_visited = 0;
+       return 0;
+}
+
+void
+dentry_tree_clear_inode_visited(struct wim_dentry *root)
+{
+       for_dentry_in_tree(root, dentry_clear_inode_visited, NULL);
+}
+
 static int
 init_ads_entry(struct wim_ads_entry *ads_entry, const void *name,
               size_t name_nbytes, bool is_utf16le)
@@ -1091,7 +1139,7 @@ init_ads_entry(struct wim_ads_entry *ads_entry, const void *name,
 
        if (is_utf16le) {
                utf16lechar *p = MALLOC(name_nbytes + sizeof(utf16lechar));
-               if (!p)
+               if (p == NULL)
                        return WIMLIB_ERR_NOMEM;
                memcpy(p, name, name_nbytes);
                p[name_nbytes / 2] = cpu_to_le16(0);
@@ -1188,11 +1236,13 @@ do_free_dentry(struct wim_dentry *dentry, void *_lookup_table)
 /*
  * 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.
+ * @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 wim_dentry *root, struct wim_lookup_table *lookup_table)
@@ -1330,7 +1380,11 @@ unlink_dentry(struct wim_dentry *dentry)
 
 /*
  * Returns the alternate data stream entry belonging to @inode that has the
- * stream name @stream_name.
+ * stream name @stream_name, or NULL if the inode has no alternate data stream
+ * with that name.
+ *
+ * If @p stream_name is the empty string, NULL is returned --- that is, this
+ * function will not return "unnamed" alternate data stream entries.
  */
 struct wim_ads_entry *
 inode_get_ads_entry(struct wim_inode *inode, const tchar *stream_name,
@@ -1343,6 +1397,9 @@ inode_get_ads_entry(struct wim_inode *inode, const tchar *stream_name,
                u16 i;
                struct wim_ads_entry *result;
 
+               if (stream_name[0] == T('\0'))
+                       return NULL;
+
        #if TCHAR_IS_UTF16LE
                const utf16lechar *stream_name_utf16le;
 
@@ -1389,6 +1446,8 @@ do_inode_add_ads(struct wim_inode *inode, const void *stream_name,
        struct wim_ads_entry *ads_entries;
        struct wim_ads_entry *new_entry;
 
+       wimlib_assert(stream_name_nbytes != 0);
+
        if (inode->i_num_ads >= 0xfffe) {
                ERROR("Too many alternate data streams in one inode!");
                return NULL;
@@ -1396,7 +1455,7 @@ do_inode_add_ads(struct wim_inode *inode, const void *stream_name,
        num_ads = inode->i_num_ads + 1;
        ads_entries = REALLOC(inode->i_ads_entries,
                              num_ads * sizeof(inode->i_ads_entries[0]));
-       if (!ads_entries) {
+       if (ads_entries == NULL) {
                ERROR("Failed to allocate memory for new alternate data stream");
                return NULL;
        }
@@ -1420,8 +1479,10 @@ inode_add_ads_utf16le(struct wim_inode *inode,
 }
 
 /*
- * Add an alternate stream entry to a WIM inode and return a pointer to it, or
- * NULL if memory could not be allocated.
+ * Add an alternate stream entry to a WIM inode.  On success, returns a pointer
+ * to the new entry; on failure, returns NULL.
+ *
+ * @stream_name must be a nonempty string.
  */
 struct wim_ads_entry *
 inode_add_ads(struct wim_inode *inode, const tchar *stream_name)
@@ -1440,24 +1501,24 @@ add_stream_from_data_buffer(const void *buffer, size_t size,
        struct wim_lookup_table_entry *lte, *existing_lte;
 
        sha1_buffer(buffer, size, hash);
-       existing_lte = __lookup_resource(lookup_table, hash);
+       existing_lte = lookup_resource(lookup_table, hash);
        if (existing_lte) {
-               wimlib_assert(wim_resource_size(existing_lte) == size);
+               wimlib_assert(existing_lte->size == size);
                lte = existing_lte;
                lte->refcnt++;
        } else {
                void *buffer_copy;
                lte = new_lookup_table_entry();
-               if (!lte)
+               if (lte == NULL)
                        return NULL;
                buffer_copy = memdup(buffer, size);
-               if (!buffer_copy) {
+               if (buffer_copy == NULL) {
                        free_lookup_table_entry(lte);
                        return NULL;
                }
-               lte->resource_location            = RESOURCE_IN_ATTACHED_BUFFER;
-               lte->attached_buffer              = buffer_copy;
-               lte->resource_entry.original_size = size;
+               lte->resource_location  = RESOURCE_IN_ATTACHED_BUFFER;
+               lte->attached_buffer    = buffer_copy;
+               lte->size               = size;
                copy_hash(lte->hash, hash);
                lookup_table_insert(lookup_table, lte);
        }
@@ -1474,12 +1535,12 @@ inode_add_ads_with_data(struct wim_inode *inode, const tchar *name,
        wimlib_assert(inode->i_resolved);
 
        new_ads_entry = inode_add_ads(inode, name);
-       if (!new_ads_entry)
+       if (new_ads_entry == NULL)
                return WIMLIB_ERR_NOMEM;
 
        new_ads_entry->lte = add_stream_from_data_buffer(value, size,
                                                         lookup_table);
-       if (!new_ads_entry->lte) {
+       if (new_ads_entry->lte == NULL) {
                inode_remove_ads(inode, new_ads_entry - inode->i_ads_entries,
                                 lookup_table);
                return WIMLIB_ERR_NOMEM;
@@ -1487,6 +1548,15 @@ inode_add_ads_with_data(struct wim_inode *inode, const tchar *name,
        return 0;
 }
 
+bool
+inode_has_named_stream(const struct wim_inode *inode)
+{
+       for (u16 i = 0; i < inode->i_num_ads; i++)
+               if (ads_entry_is_named_stream(&inode->i_ads_entries[i]))
+                       return true;
+       return false;
+}
+
 /* Set the unnamed stream of a WIM inode, given a data buffer containing the
  * stream contents. */
 int
@@ -1494,7 +1564,7 @@ inode_set_unnamed_stream(struct wim_inode *inode, const void *data, size_t len,
                         struct wim_lookup_table *lookup_table)
 {
        inode->i_lte = add_stream_from_data_buffer(data, len, lookup_table);
-       if (!inode->i_lte)
+       if (inode->i_lte == NULL)
                return WIMLIB_ERR_NOMEM;
        inode->i_resolved = 1;
        return 0;
@@ -1527,6 +1597,15 @@ inode_remove_ads(struct wim_inode *inode, u16 idx,
        inode->i_num_ads--;
 }
 
+bool
+inode_has_unix_data(const struct wim_inode *inode)
+{
+       for (u16 i = 0; i < inode->i_num_ads; i++)
+               if (ads_entry_is_unix_data(&inode->i_ads_entries[i]))
+                       return true;
+       return false;
+}
+
 #ifndef __WIN32__
 int
 inode_get_unix_data(const struct wim_inode *inode,
@@ -1542,21 +1621,21 @@ inode_get_unix_data(const struct wim_inode *inode,
 
        ads_entry = inode_get_ads_entry((struct wim_inode*)inode,
                                        WIMLIB_UNIX_DATA_TAG, NULL);
-       if (!ads_entry)
+       if (ads_entry == NULL)
                return NO_UNIX_DATA;
 
        if (stream_idx_ret)
                *stream_idx_ret = ads_entry - inode->i_ads_entries;
 
        lte = ads_entry->lte;
-       if (!lte)
+       if (lte == NULL)
                return NO_UNIX_DATA;
 
-       size = wim_resource_size(lte);
+       size = lte->size;
        if (size != sizeof(struct wimlib_unix_data))
                return BAD_UNIX_DATA;
 
-       ret = read_full_resource_into_buf(lte, unix_data);
+       ret = read_full_stream_into_buf(lte, unix_data);
        if (ret)
                return ret;
 
@@ -1602,19 +1681,24 @@ inode_set_unix_data(struct wim_inode *inode, uid_t uid, gid_t gid, mode_t mode,
 /*
  * Reads the alternate data stream entries of a WIM dentry.
  *
- * @p: Pointer to buffer that starts with the first alternate stream entry.
+ * @p:
+ *     Pointer to buffer that starts with the first alternate stream entry.
  *
- * @inode:     Inode to load the alternate data streams into.
- *             @inode->i_num_ads must have been set to the number of
- *             alternate data streams that are expected.
+ * @inode:
+ *     Inode to load the alternate data streams into.  @inode->i_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.
+ * @remaining_size:
+ *     Number of bytes of data remaining in the buffer pointed to by @p.
  *
+ * On success, inode->i_ads_entries is set to an array of `struct
+ * wim_ads_entry's of length inode->i_num_ads.  On failure, @inode is not
+ * modified.
  *
- * Return 0 on success or nonzero on failure.  On success, inode->i_ads_entries
- * is set to an array of `struct wim_ads_entry's of length inode->i_num_ads.  On
- * failure, @inode is not modified.
+ * Return values:
+ *     WIMLIB_ERR_SUCCESS (0)
+ *     WIMLIB_ERR_INVALID_METADATA_RESOURCE
+ *     WIMLIB_ERR_NOMEM
  */
 static int
 read_ads_entries(const u8 * restrict p, struct wim_inode * restrict inode,
@@ -1630,7 +1714,7 @@ read_ads_entries(const u8 * restrict p, struct wim_inode * restrict inode,
         * data stream entries. */
        num_ads = inode->i_num_ads;
        ads_entries = CALLOC(num_ads, sizeof(inode->i_ads_entries[0]));
-       if (!ads_entries)
+       if (ads_entries == NULL)
                goto out_of_memory;
 
        /* Read the entries into our newly allocated buffer. */
@@ -1685,13 +1769,16 @@ read_ads_entries(const u8 * restrict p, struct wim_inode * restrict inode,
                                goto out_invalid;
 
                        cur_entry->stream_name = MALLOC(cur_entry->stream_name_nbytes + 2);
-                       if (!cur_entry->stream_name)
+                       if (cur_entry->stream_name == NULL)
                                goto out_of_memory;
 
                        memcpy(cur_entry->stream_name,
                               disk_entry->stream_name,
                               cur_entry->stream_name_nbytes);
                        cur_entry->stream_name[cur_entry->stream_name_nbytes / 2] = cpu_to_le16(0);
+               } else {
+                       /* Mark inode as having weird stream entries.  */
+                       inode->i_canonical_streams = 0;
                }
 
                /* It's expected that the size of every ADS entry is a multiple
@@ -1718,7 +1805,7 @@ out_of_memory:
        goto out_free_ads_entries;
 out_invalid:
        ERROR("An alternate data stream entry is invalid");
-       ret = WIMLIB_ERR_INVALID_DENTRY;
+       ret = WIMLIB_ERR_INVALID_METADATA_RESOURCE;
 out_free_ads_entries:
        if (ads_entries) {
                for (u16 i = 0; i < num_ads; i++)
@@ -1739,7 +1826,7 @@ out:
  * @metadata_resource_len:
  *             Length of the metadata resource buffer, in bytes.
  *
- * @offset:    Offset of the dentry within the metadata resource.
+ * @offset:    Offset of the dentry within the metadata resource.
  *
  * @dentry:    A `struct wim_dentry' that will be filled in by this function.
  *
@@ -1749,9 +1836,10 @@ out:
  * this was a special "end of directory" dentry and not a real dentry.  If
  * nonzero, this was a real dentry.
  *
- * Possible errors include:
- *     WIMLIB_ERR_NOMEM
- *     WIMLIB_ERR_INVALID_DENTRY
+ * Return values:
+ *     WIMLIB_ERR_SUCCESS (0)
+ *     WIMLIB_ERR_INVALID_METADATA_RESOURCE
+ *     WIMLIB_ERR_NOMEM
  */
 int
 read_dentry(const u8 * restrict metadata_resource, u64 metadata_resource_len,
@@ -1785,7 +1873,7 @@ read_dentry(const u8 * restrict metadata_resource, u64 metadata_resource_len,
                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;
+               return WIMLIB_ERR_INVALID_METADATA_RESOURCE;
        }
        dentry->length = le64_to_cpu(disk_dentry->length);
 
@@ -1807,7 +1895,7 @@ read_dentry(const u8 * restrict metadata_resource, u64 metadata_resource_len,
                      "%"PRIu64" ends past the end of the metadata resource "
                      "(size %"PRIu64")",
                      offset, dentry->length, metadata_resource_len);
-               return WIMLIB_ERR_INVALID_DENTRY;
+               return WIMLIB_ERR_INVALID_METADATA_RESOURCE;
        }
 
        /* Make sure the dentry length is at least as large as the number of
@@ -1815,12 +1903,12 @@ read_dentry(const u8 * restrict metadata_resource, u64 metadata_resource_len,
        if (dentry->length < sizeof(struct wim_dentry_on_disk)) {
                ERROR("Directory entry has invalid length of %"PRIu64" bytes",
                      dentry->length);
-               return WIMLIB_ERR_INVALID_DENTRY;
+               return WIMLIB_ERR_INVALID_METADATA_RESOURCE;
        }
 
        /* Allocate a `struct wim_inode' for this `struct wim_dentry'. */
        inode = new_timeless_inode();
-       if (!inode)
+       if (inode == NULL)
                return WIMLIB_ERR_NOMEM;
 
        /* Read more fields; some into the dentry, and some into the inode. */
@@ -1861,7 +1949,7 @@ read_dentry(const u8 * restrict metadata_resource, u64 metadata_resource_len,
        if ((short_name_nbytes & 1) | (file_name_nbytes & 1))
        {
                ERROR("Dentry name is not valid UTF-16LE (odd number of bytes)!");
-               ret = WIMLIB_ERR_INVALID_DENTRY;
+               ret = WIMLIB_ERR_INVALID_METADATA_RESOURCE;
                goto out_free_inode;
        }
 
@@ -1871,14 +1959,14 @@ read_dentry(const u8 * restrict metadata_resource, u64 metadata_resource_len,
         * 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_nbytes,
-                                                          short_name_nbytes);
+       calculated_size = dentry_correct_length_unaligned(file_name_nbytes,
+                                                         short_name_nbytes);
 
        if (dentry->length < calculated_size) {
                ERROR("Unexpected end of directory entry! (Expected "
                      "at least %"PRIu64" bytes, got %"PRIu64" bytes.)",
                      calculated_size, dentry->length);
-               ret = WIMLIB_ERR_INVALID_DENTRY;
+               ret = WIMLIB_ERR_INVALID_METADATA_RESOURCE;
                goto out_free_inode;
        }
 
@@ -1888,7 +1976,7 @@ read_dentry(const u8 * restrict metadata_resource, u64 metadata_resource_len,
         * is no null terminator following it. */
        if (file_name_nbytes) {
                file_name = MALLOC(file_name_nbytes + 2);
-               if (!file_name) {
+               if (file_name == NULL) {
                        ERROR("Failed to allocate %d bytes for dentry file name",
                              file_name_nbytes + 2);
                        ret = WIMLIB_ERR_NOMEM;
@@ -1906,7 +1994,7 @@ read_dentry(const u8 * restrict metadata_resource, u64 metadata_resource_len,
         * filename, there is no null terminator following it. */
        if (short_name_nbytes) {
                short_name = MALLOC(short_name_nbytes + 2);
-               if (!short_name) {
+               if (short_name == NULL) {
                        ERROR("Failed to allocate %d bytes for dentry short name",
                              short_name_nbytes + 2);
                        ret = WIMLIB_ERR_NOMEM;
@@ -1932,7 +2020,7 @@ read_dentry(const u8 * restrict metadata_resource, u64 metadata_resource_len,
         * be included in the dentry->length field for some reason.
         */
        if (inode->i_num_ads != 0) {
-               ret = WIMLIB_ERR_INVALID_DENTRY;
+               ret = WIMLIB_ERR_INVALID_METADATA_RESOURCE;
                if (offset + dentry->length > metadata_resource_len ||
                    (ret = read_ads_entries(&metadata_resource[offset + dentry->length],
                                            inode,
@@ -1977,18 +2065,22 @@ dentry_get_file_type_string(const struct wim_dentry *dentry)
 /* 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:
+ *     An array that contains the uncompressed metadata resource for the WIM
+ *     file.
  *
- * @metadata_resource_len:  The length of the uncompressed metadata resource, in
- *                         bytes.
+ * @metadata_resource_len:
+ *     The length of the uncompressed metadata resource, in bytes.
  *
- * @dentry:    A pointer to a `struct wim_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.
+ * @dentry:
+ *     A pointer to a `struct wim_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.
  *
- * Returns zero on success; nonzero on failure.
+ * Return values:
+ *     WIMLIB_ERR_SUCCESS (0)
+ *     WIMLIB_ERR_INVALID_METADATA_RESOURCE
+ *     WIMLIB_ERR_NOMEM
  */
 int
 read_dentry_tree(const u8 * restrict metadata_resource,
@@ -2019,7 +2111,7 @@ read_dentry_tree(const u8 * restrict metadata_resource,
                              "of \"%"TS"\" coincide with children of \"%"TS"\"",
                              dentry_full_path(dentry),
                              dentry_full_path(parent));
-                       return WIMLIB_ERR_INVALID_DENTRY;
+                       return WIMLIB_ERR_INVALID_METADATA_RESOURCE;
                }
        }
 
@@ -2039,7 +2131,7 @@ read_dentry_tree(const u8 * restrict metadata_resource,
                /* Not end of directory.  Allocate this child permanently and
                 * link it to the parent and previous child. */
                child = memdup(&cur_child, sizeof(struct wim_dentry));
-               if (!child) {
+               if (child == NULL) {
                        ERROR("Failed to allocate new dentry!");
                        ret = WIMLIB_ERR_NOMEM;
                        break;
@@ -2050,7 +2142,7 @@ read_dentry_tree(const u8 * restrict metadata_resource,
                 * cur_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);
+               cur_offset += dentry_in_total_length(child);
 
                if (unlikely(!dentry_has_long_name(child))) {
                        WARNING("Ignoring unnamed dentry in "
@@ -2093,6 +2185,38 @@ read_dentry_tree(const u8 * restrict metadata_resource,
        return ret;
 }
 
+/*
+ * Writes a WIM alternate data stream (ADS) entry to an output buffer.
+ *
+ * @ads_entry:  The ADS entry structure.
+ * @hash:       The hash field to use (instead of the one in the ADS entry).
+ * @p:          The memory location to write the data to.
+ *
+ * Returns a pointer to the byte after the last byte written.
+ */
+static u8 *
+write_ads_entry(const struct wim_ads_entry *ads_entry,
+               const u8 *hash, u8 * restrict p)
+{
+       struct wim_ads_entry_on_disk *disk_ads_entry =
+                       (struct wim_ads_entry_on_disk*)p;
+       u8 *orig_p = p;
+
+       disk_ads_entry->reserved = cpu_to_le64(ads_entry->reserved);
+       copy_hash(disk_ads_entry->hash, hash);
+       disk_ads_entry->stream_name_nbytes = cpu_to_le16(ads_entry->stream_name_nbytes);
+       p += sizeof(struct wim_ads_entry_on_disk);
+       if (ads_entry->stream_name_nbytes) {
+               p = mempcpy(p, ads_entry->stream_name,
+                           ads_entry->stream_name_nbytes + 2);
+       }
+       /* Align to 8-byte boundary */
+       while ((uintptr_t)p & 7)
+               *p++ = 0;
+       disk_ads_entry->length = cpu_to_le64(p - orig_p);
+       return p;
+}
+
 /*
  * Writes a WIM dentry to an output buffer.
  *
@@ -2109,11 +2233,14 @@ write_dentry(const struct wim_dentry * restrict dentry, u8 * restrict p)
        struct wim_dentry_on_disk *disk_dentry;
        const u8 *orig_p;
        const u8 *hash;
+       bool use_dummy_stream;
+       u16 num_ads;
 
        wimlib_assert(((uintptr_t)p & 7) == 0); /* 8 byte aligned */
        orig_p = p;
 
-       inode = dentry->d_inode;
+       inode = dentry->d_inode;
+       use_dummy_stream = inode_needs_dummy_stream(inode);
        disk_dentry = (struct wim_dentry_on_disk*)p;
 
        disk_dentry->attributes = cpu_to_le32(inode->i_attributes);
@@ -2124,7 +2251,10 @@ write_dentry(const struct wim_dentry * restrict dentry, u8 * restrict p)
        disk_dentry->creation_time = cpu_to_le64(inode->i_creation_time);
        disk_dentry->last_access_time = cpu_to_le64(inode->i_last_access_time);
        disk_dentry->last_write_time = cpu_to_le64(inode->i_last_write_time);
-       hash = inode_stream_hash(inode, 0);
+       if (use_dummy_stream)
+               hash = zero_hash;
+       else
+               hash = inode_stream_hash(inode, 0);
        copy_hash(disk_dentry->unnamed_stream_hash, hash);
        if (inode->i_attributes & FILE_ATTRIBUTE_REPARSE_POINT) {
                disk_dentry->reparse.rp_unknown_1 = cpu_to_le32(inode->i_rp_unknown_1);
@@ -2136,7 +2266,10 @@ write_dentry(const struct wim_dentry * restrict dentry, u8 * restrict p)
                disk_dentry->nonreparse.hard_link_group_id =
                        cpu_to_le64((inode->i_nlink == 1) ? 0 : inode->i_ino);
        }
-       disk_dentry->num_alternate_data_streams = cpu_to_le16(inode->i_num_ads);
+       num_ads = inode->i_num_ads;
+       if (use_dummy_stream)
+               num_ads++;
+       disk_dentry->num_alternate_data_streams = cpu_to_le16(num_ads);
        disk_dentry->short_name_nbytes = cpu_to_le16(dentry->short_name_nbytes);
        disk_dentry->file_name_nbytes = cpu_to_le16(dentry->file_name_nbytes);
        p += sizeof(struct wim_dentry_on_disk);
@@ -2160,29 +2293,17 @@ write_dentry(const struct wim_dentry * restrict dentry, u8 * restrict p)
         * have been renamed, thus changing its needed length. */
        disk_dentry->length = cpu_to_le64(p - orig_p);
 
+       if (use_dummy_stream) {
+               hash = inode_unnamed_stream_hash(inode);
+               p = write_ads_entry(&(struct wim_ads_entry){}, hash, p);
+       }
+
        /* Write the alternate data streams entries, if any. */
        for (u16 i = 0; i < inode->i_num_ads; i++) {
-               const struct wim_ads_entry *ads_entry =
-                               &inode->i_ads_entries[i];
-               struct wim_ads_entry_on_disk *disk_ads_entry =
-                               (struct wim_ads_entry_on_disk*)p;
-               orig_p = p;
-
-               disk_ads_entry->reserved = cpu_to_le64(ads_entry->reserved);
-
                hash = inode_stream_hash(inode, i + 1);
-               copy_hash(disk_ads_entry->hash, hash);
-               disk_ads_entry->stream_name_nbytes = cpu_to_le16(ads_entry->stream_name_nbytes);
-               p += sizeof(struct wim_ads_entry_on_disk);
-               if (ads_entry->stream_name_nbytes) {
-                       p = mempcpy(p, ads_entry->stream_name,
-                                   ads_entry->stream_name_nbytes + 2);
-               }
-               /* Align to 8-byte boundary */
-               while ((uintptr_t)p & 7)
-                       *p++ = 0;
-               disk_ads_entry->length = cpu_to_le64(p - orig_p);
+               p = write_ads_entry(&inode->i_ads_entries[i], hash, p);
        }
+
        return p;
 }
 
@@ -2261,12 +2382,14 @@ write_dentry_tree(const struct wim_dentry * restrict root, u8 * restrict p)
 static int
 init_wimlib_dentry(struct wimlib_dir_entry *wdentry,
                   struct wim_dentry *dentry,
-                  const WIMStruct *wim)
+                  const WIMStruct *wim,
+                  int flags)
 {
        int ret;
        size_t dummy;
        const struct wim_inode *inode = dentry->d_inode;
        struct wim_lookup_table_entry *lte;
+       const u8 *hash;
 
 #if TCHAR_IS_UTF16LE
        wdentry->filename = dentry->file_name;
@@ -2311,17 +2434,30 @@ init_wimlib_dentry(struct wimlib_dir_entry *wdentry,
        wdentry->last_access_time = wim_timestamp_to_timespec(inode->i_last_access_time);
 
        lte = inode_unnamed_lte(inode, wim->lookup_table);
-       if (lte)
+       if (lte) {
                lte_to_wimlib_resource_entry(lte, &wdentry->streams[0].resource);
+       } else if (!is_zero_hash(hash = inode_unnamed_stream_hash(inode))) {
+               if (flags & WIMLIB_ITERATE_DIR_TREE_FLAG_RESOURCES_NEEDED)
+                       return resource_not_found_error(inode, hash);
+               copy_hash(wdentry->streams[0].resource.sha1_hash, hash);
+               wdentry->streams[0].resource.is_missing = 1;
+       }
 
        for (unsigned i = 0; i < inode->i_num_ads; i++) {
-               if (inode->i_ads_entries[i].stream_name == NULL)
+               if (!ads_entry_is_named_stream(&inode->i_ads_entries[i]))
                        continue;
                lte = inode_stream_lte(inode, i + 1, wim->lookup_table);
                wdentry->num_named_streams++;
                if (lte) {
                        lte_to_wimlib_resource_entry(lte, &wdentry->streams[
-                                                               wdentry->num_named_streams].resource);
+                                                               wdentry->num_named_streams].resource);
+               } else if (!is_zero_hash(hash = inode_stream_hash(inode, i + 1))) {
+                       if (flags & WIMLIB_ITERATE_DIR_TREE_FLAG_RESOURCES_NEEDED)
+                               return resource_not_found_error(inode, hash);
+                       copy_hash(wdentry->streams[
+                                 wdentry->num_named_streams].resource.sha1_hash, hash);
+                       wdentry->streams[
+                               wdentry->num_named_streams].resource.is_missing = 1;
                }
        #if TCHAR_IS_UTF16LE
                wdentry->streams[wdentry->num_named_streams].stream_name =
@@ -2332,7 +2468,7 @@ init_wimlib_dentry(struct wimlib_dir_entry *wdentry,
                ret = utf16le_to_tstr(inode->i_ads_entries[i].stream_name,
                                      inode->i_ads_entries[i].stream_name_nbytes,
                                      (tchar**)&wdentry->streams[
-                                               wdentry->num_named_streams].stream_name,
+                                               wdentry->num_named_streams].stream_name,
                                      &dummy);
                if (ret)
                        return ret;
@@ -2380,18 +2516,17 @@ do_iterate_dir_tree(WIMStruct *wim,
                    wimlib_iterate_dir_tree_callback_t cb,
                    void *user_ctx)
 {
-       u32 level;
        struct wimlib_dir_entry *wdentry;
        int ret = WIMLIB_ERR_NOMEM;
 
 
        wdentry = CALLOC(1, sizeof(struct wimlib_dir_entry) +
-                                 (1 + dentry->d_inode->i_num_ads) *
-                                       sizeof(struct wimlib_stream_entry));
-       if (!wdentry)
+                                 (1 + dentry->d_inode->i_num_ads) *
+                                       sizeof(struct wimlib_stream_entry));
+       if (wdentry == NULL)
                goto out;
 
-       ret = init_wimlib_dentry(wdentry, dentry, wim);
+       ret = init_wimlib_dentry(wdentry, dentry, wim, flags);
        if (ret)
                goto out_free_wimlib_dentry;
 
@@ -2433,18 +2568,17 @@ image_do_iterate_dir_tree(WIMStruct *wim)
        struct wim_dentry *dentry;
 
        dentry = get_dentry(wim, ctx->path);
-       if (!dentry)
+       if (dentry == NULL)
                return WIMLIB_ERR_PATH_DOES_NOT_EXIST;
        return do_iterate_dir_tree(wim, dentry, ctx->flags, ctx->cb, ctx->user_ctx);
 }
 
+/* API function documented in wimlib.h  */
 WIMLIBAPI int
 wimlib_iterate_dir_tree(WIMStruct *wim, int image, const tchar *path,
                        int flags,
                        wimlib_iterate_dir_tree_callback_t cb, void *user_ctx)
 {
-       int ret;
-       struct wim_dentry *dentry;
        struct image_iterate_dir_tree_ctx ctx = {
                .path = path,
                .flags = flags,
@@ -2454,3 +2588,211 @@ wimlib_iterate_dir_tree(WIMStruct *wim, int image, const tchar *path,
        wim->private = &ctx;
        return for_image(wim, image, image_do_iterate_dir_tree);
 }
+
+/* Returns %true iff the metadata of @inode and @template_inode are reasonably
+ * consistent with them being the same, unmodified file.  */
+static bool
+inode_metadata_consistent(const struct wim_inode *inode,
+                         const struct wim_inode *template_inode,
+                         const struct wim_lookup_table *template_lookup_table)
+{
+       /* Must have exact same creation time and last write time.  */
+       if (inode->i_creation_time != template_inode->i_creation_time ||
+           inode->i_last_write_time != template_inode->i_last_write_time)
+               return false;
+
+       /* Last access time may have stayed the same or increased, but certainly
+        * shouldn't have decreased.  */
+       if (inode->i_last_access_time < template_inode->i_last_access_time)
+               return false;
+
+       /* Must have same number of alternate data stream entries.  */
+       if (inode->i_num_ads != template_inode->i_num_ads)
+               return false;
+
+       /* If the stream entries for the inode are for some reason not resolved,
+        * then the hashes are already available and the point of this function
+        * is defeated.  */
+       if (!inode->i_resolved)
+               return false;
+
+       /* Iterate through each stream and do some more checks.  */
+       for (unsigned i = 0; i <= inode->i_num_ads; i++) {
+               const struct wim_lookup_table_entry *lte, *template_lte;
+
+               lte = inode_stream_lte_resolved(inode, i);
+               template_lte = inode_stream_lte(template_inode, i,
+                                               template_lookup_table);
+
+               /* Compare stream sizes.  */
+               if (lte && template_lte) {
+                       if (lte->size != template_lte->size)
+                               return false;
+
+                       /* If hash happens to be available, compare with template.  */
+                       if (!lte->unhashed && !template_lte->unhashed &&
+                           !hashes_equal(lte->hash, template_lte->hash))
+                               return false;
+
+               } else if (lte && lte->size) {
+                       return false;
+               } else if (template_lte && template_lte->size) {
+                       return false;
+               }
+       }
+
+       /* All right, barring a full checksum and given that the inodes share a
+        * path and the user isn't trying to trick us, these inodes most likely
+        * refer to the same file.  */
+       return true;
+}
+
+/**
+ * Given an inode @inode that has been determined to be "the same" as another
+ * inode @template_inode in either the same WIM or another WIM, retrieve some
+ * useful stream information (e.g. checksums) from @template_inode.
+ *
+ * This assumes that the streams for @inode have been resolved (to point
+ * directly to the appropriate `struct wim_lookup_table_entry's)  but do not
+ * necessarily have checksum information filled in.
+ */
+static int
+inode_copy_checksums(struct wim_inode *inode,
+                    struct wim_inode *template_inode,
+                    WIMStruct *wim,
+                    WIMStruct *template_wim)
+{
+       for (unsigned i = 0; i <= inode->i_num_ads; i++) {
+               struct wim_lookup_table_entry *lte, *template_lte;
+               struct wim_lookup_table_entry *replace_lte;
+
+               lte = inode_stream_lte_resolved(inode, i);
+               template_lte = inode_stream_lte(template_inode, i,
+                                               template_wim->lookup_table);
+
+               /* Only take action if both entries exist, the entry for @inode
+                * has no checksum calculated, but the entry for @template_inode
+                * does.  */
+               if (lte == NULL || template_lte == NULL ||
+                   !lte->unhashed || template_lte->unhashed)
+                       continue;
+
+               wimlib_assert(lte->refcnt == inode->i_nlink);
+
+               /* If the WIM of the template image is the same as the WIM of
+                * the new image, then @template_lte can be used directly.
+                *
+                * Otherwise, look for a stream with the same hash in the WIM of
+                * the new image.  If found, use it; otherwise re-use the entry
+                * being discarded, filling in the hash.  */
+
+               if (wim == template_wim)
+                       replace_lte = template_lte;
+               else
+                       replace_lte = lookup_resource(wim->lookup_table,
+                                                     template_lte->hash);
+
+               list_del(&lte->unhashed_list);
+               if (replace_lte) {
+                       free_lookup_table_entry(lte);
+               } else {
+                       copy_hash(lte->hash, template_lte->hash);
+                       lte->unhashed = 0;
+                       lookup_table_insert(wim->lookup_table, lte);
+                       lte->refcnt = 0;
+                       replace_lte = lte;
+               }
+
+               if (i == 0)
+                       inode->i_lte = replace_lte;
+               else
+                       inode->i_ads_entries[i - 1].lte = replace_lte;
+
+               replace_lte->refcnt += inode->i_nlink;
+       }
+       return 0;
+}
+
+struct reference_template_args {
+       WIMStruct *wim;
+       WIMStruct *template_wim;
+};
+
+static int
+dentry_reference_template(struct wim_dentry *dentry, void *_args)
+{
+       int ret;
+       struct wim_dentry *template_dentry;
+       struct wim_inode *inode, *template_inode;
+       struct reference_template_args *args = _args;
+       WIMStruct *wim = args->wim;
+       WIMStruct *template_wim = args->template_wim;
+
+       if (dentry->d_inode->i_visited)
+               return 0;
+
+       ret = calculate_dentry_full_path(dentry);
+       if (ret)
+               return ret;
+
+       template_dentry = get_dentry(template_wim, dentry->_full_path);
+       if (template_dentry == NULL) {
+               DEBUG("\"%"TS"\": newly added file", dentry->_full_path);
+               return 0;
+       }
+
+       inode = dentry->d_inode;
+       template_inode = template_dentry->d_inode;
+
+       if (inode_metadata_consistent(inode, template_inode,
+                                     template_wim->lookup_table)) {
+               /*DEBUG("\"%"TS"\": No change detected", dentry->_full_path);*/
+               ret = inode_copy_checksums(inode, template_inode,
+                                          wim, template_wim);
+               inode->i_visited = 1;
+       } else {
+               DEBUG("\"%"TS"\": change detected!", dentry->_full_path);
+               ret = 0;
+       }
+       return ret;
+}
+
+/* API function documented in wimlib.h  */
+WIMLIBAPI int
+wimlib_reference_template_image(WIMStruct *wim, int new_image,
+                               WIMStruct *template_wim, int template_image,
+                               int flags, wimlib_progress_func_t progress_func)
+{
+       int ret;
+       struct wim_image_metadata *new_imd;
+
+       if (wim == NULL || template_wim == NULL)
+               return WIMLIB_ERR_INVALID_PARAM;
+
+       if (wim == template_wim && new_image == template_image)
+               return WIMLIB_ERR_INVALID_PARAM;
+
+       if (new_image < 1 || new_image > wim->hdr.image_count)
+               return WIMLIB_ERR_INVALID_IMAGE;
+
+       if (!wim_has_metadata(wim))
+               return WIMLIB_ERR_METADATA_NOT_FOUND;
+
+       new_imd = wim->image_metadata[new_image - 1];
+       if (!new_imd->modified)
+               return WIMLIB_ERR_INVALID_PARAM;
+
+       ret = select_wim_image(template_wim, template_image);
+       if (ret)
+               return ret;
+
+       struct reference_template_args args = {
+               .wim = wim,
+               .template_wim = template_wim,
+       };
+
+       ret = for_dentry_in_tree(new_imd->root_dentry,
+                                dentry_reference_template, &args);
+       dentry_tree_clear_inode_visited(new_imd->root_dentry);
+       return ret;
+}