]> wimlib.net Git - wimlib/blobdiff - src/write.c
Fixes, comments
[wimlib] / src / write.c
index 56fbab0ea1c08e5b33c7671e01f768c257821962..ccad7f07caa5c3f4b7af309995ab5974d2742aa0 100644 (file)
@@ -6,8 +6,7 @@
  */
 
 /*
- * Copyright (C) 2010 Carl Thijssen
- * Copyright (C) 2012 Eric Biggers
+ * Copyright (C) 2012, 2013 Eric Biggers
  *
  * This file is part of wimlib, a library for working with WIM files.
  *
  * along with wimlib; if not, see http://www.gnu.org/licenses/.
  */
 
+#include "config.h"
+
+#if defined(HAVE_SYS_FILE_H) && defined(HAVE_FLOCK)
+/* On BSD, this should be included before "list.h" so that "list.h" can
+ * overwrite the LIST_HEAD macro. */
+#  include <sys/file.h>
+#endif
+
+#ifdef __WIN32__
+#  include "win32.h"
+#endif
+
+#include "list.h"
 #include "wimlib_internal.h"
-#include "io.h"
+#include "buffer_io.h"
 #include "dentry.h"
 #include "lookup_table.h"
 #include "xml.h"
-#include "lzx.h"
-#include "xpress.h"
+
+#ifdef ENABLE_MULTITHREADED_COMPRESSION
+#  include <pthread.h>
+#endif
+
 #include <unistd.h>
-#include <semaphore.h>
-#include <pthread.h>
 #include <errno.h>
 
 #ifdef WITH_NTFS_3G
-#include <time.h>
-#include <ntfs-3g/attrib.h>
-#include <ntfs-3g/inode.h>
-#include <ntfs-3g/dir.h>
+#  include <time.h>
+#  include <ntfs-3g/attrib.h>
+#  include <ntfs-3g/inode.h>
+#  include <ntfs-3g/dir.h>
 #endif
 
-
 #ifdef HAVE_ALLOCA_H
-#include <alloca.h>
+#  include <alloca.h>
+#else
+#  include <stdlib.h>
 #endif
 
+#include <limits.h>
 
-/* Reopens the FILE* for a WIM read-write. */
-static int reopen_rw(WIMStruct *w)
-{
-       FILE *fp;
-
-       if (fclose(w->fp) != 0)
-               ERROR_WITH_ERRNO("Failed to close the file `%s'", w->filename);
-       w->fp = NULL;
-       fp = fopen(w->filename, "r+b");
-       if (!fp) {
-               ERROR_WITH_ERRNO("Failed to open `%s' for reading and writing",
-                                w->filename);
-               return WIMLIB_ERR_OPEN;
-       }
-       w->fp = fp;
-       return 0;
-}
-
-
+#if defined(__WIN32__) && !defined(INVALID_HANDLE_VALUE)
+#  define INVALID_HANDLE_VALUE ((HANDLE)(-1))
+#endif
 
-/*
- * Writes a WIM file to the original file that it was read from, overwriting it.
- */
-WIMLIBAPI int wimlib_overwrite(WIMStruct *w, int write_flags)
+static int
+fflush_and_ftruncate(FILE *fp, off_t size)
 {
-       const char *wimfile_name;
-       size_t wim_name_len;
        int ret;
 
-       if (!w)
-               return WIMLIB_ERR_INVALID_PARAM;
-
-       write_flags &= ~WIMLIB_WRITE_FLAG_NO_LOOKUP_TABLE;
-
-       wimfile_name = w->filename;
-
-       DEBUG("Replacing WIM file `%s'.", wimfile_name);
-
-       if (!wimfile_name)
-               return WIMLIB_ERR_NO_FILENAME;
-
-       /* Write the WIM to a temporary file. */
-       /* XXX should the temporary file be somewhere else? */
-       wim_name_len = strlen(wimfile_name);
-       char tmpfile[wim_name_len + 10];
-       memcpy(tmpfile, wimfile_name, wim_name_len);
-       randomize_char_array_with_alnum(tmpfile + wim_name_len, 9);
-       tmpfile[wim_name_len + 9] = '\0';
-
-       ret = wimlib_write(w, tmpfile, WIM_ALL_IMAGES, write_flags);
+       ret = fflush(fp);
        if (ret != 0) {
-               ERROR("Failed to write the WIM file `%s'", tmpfile);
-               if (unlink(tmpfile) != 0)
-                       WARNING("Failed to remove `%s'", tmpfile);
-               return ret;
-       }
-
-       DEBUG("Closing original WIM file.");
-       /* Close the original WIM file that was opened for reading. */
-       if (w->fp) {
-               if (fclose(w->fp) != 0) {
-                       WARNING("Failed to close the file `%s'", wimfile_name);
-               }
-               w->fp = NULL;
-       }
-
-       DEBUG("Renaming `%s' to `%s'", tmpfile, wimfile_name);
-
-       /* Rename the new file to the old file .*/
-       if (rename(tmpfile, wimfile_name) != 0) {
-               ERROR_WITH_ERRNO("Failed to rename `%s' to `%s'",
-                                tmpfile, wimfile_name);
-               /* Remove temporary file. */
-               if (unlink(tmpfile) != 0)
-                       ERROR_WITH_ERRNO("Failed to remove `%s'", tmpfile);
-               return WIMLIB_ERR_RENAME;
-       }
-
-       if (write_flags & WIMLIB_WRITE_FLAG_VERBOSE)
-               printf("Successfully renamed `%s' to `%s'\n", tmpfile, wimfile_name);
-
-       return 0;
-}
-
-static int check_resource_offset(struct lookup_table_entry *lte, void *arg)
-{
-       u64 xml_data_offset = *(u64*)arg;
-       if (lte->resource_entry.offset > xml_data_offset) {
-               ERROR("The following resource is *after* the XML data:");
-               print_lookup_table_entry(lte);
-               return WIMLIB_ERR_RESOURCE_ORDER;
-       }
-       return 0;
-}
-
-WIMLIBAPI int wimlib_overwrite_xml_and_header(WIMStruct *w, int write_flags)
-{
-       int ret;
-       FILE *fp;
-       u8 *integrity_table = NULL;
-       off_t xml_end;
-       off_t xml_size;
-       size_t bytes_written;
-
-       DEBUG("Overwriting XML and header of `%s', write_flags = %#x",
-             w->filename, write_flags);
-
-       if (!w->filename)
-               return WIMLIB_ERR_NO_FILENAME;
-
-       write_flags &= ~WIMLIB_WRITE_FLAG_NO_LOOKUP_TABLE;
-
-       /* Make sure that the integrity table (if present) is after the XML
-        * data, and that there are no stream resources, metadata resources, or
-        * lookup tables after the XML data.  Otherwise, these data would be
-        * destroyed by this function. */
-       if (w->hdr.integrity.offset != 0 &&
-           w->hdr.integrity.offset < w->hdr.xml_res_entry.offset) {
-               ERROR("Didn't expect the integrity table to be before the XML data");
-               return WIMLIB_ERR_RESOURCE_ORDER;
-       }
-
-       if (w->hdr.lookup_table_res_entry.offset >
-           w->hdr.xml_res_entry.offset) {
-               ERROR("Didn't expect the lookup table to be after the XML data");
-               return WIMLIB_ERR_RESOURCE_ORDER;
-       }
-
-       ret = for_lookup_table_entry(w->lookup_table, check_resource_offset,
-                                    &w->hdr.xml_res_entry.offset);
-       if (ret != 0)
-               return ret;
-
-       ret = reopen_rw(w);
-       if (ret != 0)
-               return ret;
-
-       fp = w->fp;
-
-       /* The old integrity table is still OK, as the SHA1 message digests in
-        * the integrity table include neither the header nor the XML data.
-        * Save it for later if it exists and an integrity table was required.
-        * */
-       if ((write_flags & WIMLIB_WRITE_FLAG_CHECK_INTEGRITY)
-            && w->hdr.integrity.offset != 0)
-       {
-               DEBUG("Reading existing integrity table.");
-               integrity_table = MALLOC(w->hdr.integrity.size);
-               if (!integrity_table)
-                       return WIMLIB_ERR_NOMEM;
-
-               ret = read_uncompressed_resource(fp, w->hdr.integrity.offset,
-                                                w->hdr.integrity.original_size,
-                                                integrity_table);
-               if (ret != 0)
-                       goto err;
-               DEBUG("Done reading existing integrity table.");
-       }
-
-       DEBUG("Overwriting XML data.");
-       /* Overwrite the XML data. */
-       if (fseeko(fp, w->hdr.xml_res_entry.offset, SEEK_SET) != 0) {
-               ERROR_WITH_ERRNO("Failed to seek to byte %"PRIu64" "
-                                "for XML data", w->hdr.xml_res_entry.offset);
-               ret = WIMLIB_ERR_WRITE;
-               goto err;
-       }
-       ret = write_xml_data(w->wim_info, WIM_ALL_IMAGES, fp, 0);
-       if (ret != 0)
-               goto err;
-
-       DEBUG("Updating XML resource entry.");
-       /* Update the XML resource entry in the WIM header. */
-       xml_end = ftello(fp);
-       if (xml_end == -1) {
-               ret = WIMLIB_ERR_WRITE;
-               goto err;
-       }
-       xml_size = xml_end - w->hdr.xml_res_entry.offset;
-       w->hdr.xml_res_entry.size = xml_size;
-       w->hdr.xml_res_entry.original_size = xml_size;
-       /* XML data offset is unchanged. */
-
-       if (write_flags & WIMLIB_WRITE_FLAG_CHECK_INTEGRITY) {
-               DEBUG("Writing integrity table.");
-               w->hdr.integrity.offset = xml_end;
-               if (integrity_table) {
-                       /* The existing integrity table was saved. */
-                       bytes_written = fwrite(integrity_table, 1,
-                                              w->hdr.integrity.size, fp);
-                       if (bytes_written != w->hdr.integrity.size) {
-                               ERROR_WITH_ERRNO("Failed to write integrity "
-                                                "table");
-                               ret = WIMLIB_ERR_WRITE;
-                               goto err;
-                       }
-                       FREE(integrity_table);
-               } else {
-                       /* There was no existing integrity table, so a new one
-                        * must be calculated. */
-                       ret = write_integrity_table(fp, WIM_HEADER_DISK_SIZE,
-                                       w->hdr.lookup_table_res_entry.offset +
-                                       w->hdr.lookup_table_res_entry.size,
-                                       write_flags & WIMLIB_WRITE_FLAG_SHOW_PROGRESS);
-                       if (ret != 0)
-                               return ret;
-
-                       off_t end_integrity = ftello(fp);
-                       if (end_integrity == -1)
-                               return WIMLIB_ERR_WRITE;
-
-                       off_t integrity_size           = end_integrity - xml_end;
-                       w->hdr.integrity.size          = integrity_size;
-                       w->hdr.integrity.original_size = integrity_size;
-                       w->hdr.integrity.flags         = 0;
-               }
-       } else {
-               DEBUG("Truncating file to end of XML data.");
-               /* No integrity table to write.  The file should be truncated
-                * because it's possible that the old file was longer (due to it
-                * including an integrity table, or due to its XML data being
-                * longer) */
-               if (fflush(fp) != 0) {
-                       ERROR_WITH_ERRNO("Failed to flush stream for file `%s'",
-                                        w->filename);
-                       return WIMLIB_ERR_WRITE;
-               }
-               if (ftruncate(fileno(fp), xml_end) != 0) {
-                       ERROR_WITH_ERRNO("Failed to truncate `%s' to %"PRIu64" "
-                                        "bytes", w->filename, xml_end);
-                       return WIMLIB_ERR_WRITE;
-               }
-               memset(&w->hdr.integrity, 0, sizeof(struct resource_entry));
-       }
-
-       DEBUG("Overwriting header.");
-       /* Overwrite the header. */
-       if (fseeko(fp, 0, SEEK_SET) != 0) {
-               ERROR_WITH_ERRNO("Failed to seek to beginning of `%s'",
-                                w->filename);
+               ERROR_WITH_ERRNO("Failed to flush data to output WIM file");
                return WIMLIB_ERR_WRITE;
        }
-
-       ret = write_header(&w->hdr, fp);
-       if (ret != 0)
-               return ret;
-
-       DEBUG("Closing `%s'.", w->filename);
-       if (fclose(fp) != 0) {
-               ERROR_WITH_ERRNO("Failed to close `%s'", w->filename);
+       ret = ftruncate(fileno(fp), size);
+       if (ret != 0) {
+               ERROR_WITH_ERRNO("Failed to truncate output WIM file to "
+                                "%"PRIu64" bytes", size);
                return WIMLIB_ERR_WRITE;
        }
-       w->fp = NULL;
-       DEBUG("Done.");
        return 0;
-err:
-       FREE(integrity_table);
-       return ret;
 }
 
-
 /* Chunk table that's located at the beginning of each compressed resource in
  * the WIM.  (This is not the on-disk format; the on-disk format just has an
  * array of offsets.) */
@@ -330,7 +107,7 @@ struct chunk_table {
  * output file.
  */
 static int
-begin_wim_resource_chunk_tab(const struct lookup_table_entry *lte,
+begin_wim_resource_chunk_tab(const struct wim_lookup_table_entry *lte,
                             FILE *out_fp,
                             off_t file_offset,
                             struct chunk_table **chunk_tab_ret)
@@ -370,42 +147,39 @@ out:
        return ret;
 }
 
-typedef int (*compress_func_t)(const void *, unsigned, void *, unsigned *);
-
-compress_func_t get_compress_func(int out_ctype)
-{
-       if (out_ctype == WIM_COMPRESSION_TYPE_LZX)
-               return lzx_compress;
-       else
-               return xpress_compress;
-}
-
-
 /*
- * Compresses a chunk of a WIM resource.
+ * compress_func_t- Pointer to a function to compresses a chunk
+ *                  of a WIM resource.  This may be either
+ *                  wimlib_xpress_compress() (xpress-compress.c) or
+ *                  wimlib_lzx_compress() (lzx-compress.c).
+ *
+ * @chunk:       Uncompressed data of the chunk.
+ * @chunk_size:          Size of the uncompressed chunk, in bytes.
+ * @out:         Pointer to output buffer of size at least (@chunk_size - 1) bytes.
+ *
+ * Returns the size of the compressed data written to @out in bytes, or 0 if the
+ * data could not be compressed to (@chunk_size - 1) bytes or fewer.
  *
- * @chunk:             Uncompressed data of the chunk.
- * @chunk_size:                Size of the uncompressed chunk in bytes.
- * @compressed_chunk:  Pointer to output buffer of size at least
- *                             (@chunk_size - 1) bytes.
- * @compressed_chunk_len_ret:  Pointer to an unsigned int into which the size
- *                                     of the compressed chunk will be
- *                                     returned.
- * @ctype:     Type of compression to use.  Must be WIM_COMPRESSION_TYPE_LZX
- *             or WIM_COMPRESSION_TYPE_XPRESS.
+ * As a special requirement, the compression code is optimized for the WIM
+ * format and therefore requires (@chunk_size <= 32768).
  *
- * Returns zero if compressed succeeded, and nonzero if the chunk could not be
- * compressed to any smaller than @chunk_size.  This function cannot fail for
- * any other reasons.
+ * As another special requirement, the compression code will read up to 8 bytes
+ * off the end of the @chunk array for performance reasons.  The values of these
+ * bytes will not affect the output of the compression, but the calling code
+ * must make sure that the buffer holding the uncompressed chunk is actually at
+ * least (@chunk_size + 8) bytes, or at least that these extra bytes are in
+ * mapped memory that will not cause a memory access violation if accessed.
  */
-static int compress_chunk(const u8 chunk[], unsigned chunk_size,
-                         u8 compressed_chunk[],
-                         unsigned *compressed_chunk_len_ret,
-                         int ctype)
+typedef unsigned (*compress_func_t)(const void *chunk, unsigned chunk_size,
+                                   void *out);
+
+compress_func_t
+get_compress_func(int out_ctype)
 {
-       compress_func_t compress = get_compress_func(ctype);
-       return (*compress)(chunk, chunk_size, compressed_chunk,
-                          compressed_chunk_len_ret);
+       if (out_ctype == WIMLIB_COMPRESSION_TYPE_LZX)
+               return wimlib_lzx_compress;
+       else
+               return wimlib_xpress_compress;
 }
 
 /*
@@ -413,42 +187,40 @@ static int compress_chunk(const u8 chunk[], unsigned chunk_size,
  *
  * @chunk:       Uncompressed data of the chunk.
  * @chunk_size:          Size of the chunk (<= WIM_CHUNK_SIZE)
- * @out_fp:      FILE * to write tho chunk to.
- * @out_ctype:   Compression type to use when writing the chunk (ignored if no
- *                     chunk table provided)
+ * @out_fp:      FILE * to write the chunk to.
+ * @compress:     Compression function to use (NULL if writing uncompressed
+ *                     data).
  * @chunk_tab:   Pointer to chunk table being created.  It is updated with the
  *                     offset of the chunk we write.
  *
  * Returns 0 on success; nonzero on failure.
  */
-static int write_wim_resource_chunk(const u8 chunk[], unsigned chunk_size,
-                                   FILE *out_fp, int out_ctype,
-                                   struct chunk_table *chunk_tab)
+static int
+write_wim_resource_chunk(const void *chunk, unsigned chunk_size,
+                        FILE *out_fp, compress_func_t compress,
+                        struct chunk_table *chunk_tab)
 {
        const u8 *out_chunk;
        unsigned out_chunk_size;
-
-       wimlib_assert(chunk_size <= WIM_CHUNK_SIZE);
-
-       if (!chunk_tab) {
-               out_chunk = chunk;
-               out_chunk_size = chunk_size;
-       } else {
+       if (compress) {
                u8 *compressed_chunk = alloca(chunk_size);
-               int ret;
 
-               ret = compress_chunk(chunk, chunk_size, compressed_chunk,
-                                    &out_chunk_size, out_ctype);
-               if (ret == 0) {
+               out_chunk_size = compress(chunk, chunk_size, compressed_chunk);
+               if (out_chunk_size) {
+                       /* Write compressed */
                        out_chunk = compressed_chunk;
                } else {
+                       /* Write uncompressed */
                        out_chunk = chunk;
                        out_chunk_size = chunk_size;
                }
                *chunk_tab->cur_offset_p++ = chunk_tab->cur_offset;
                chunk_tab->cur_offset += out_chunk_size;
+       } else {
+               /* Write uncompressed */
+               out_chunk = chunk;
+               out_chunk_size = chunk_size;
        }
-
        if (fwrite(out_chunk, 1, out_chunk_size, out_fp) != out_chunk_size) {
                ERROR_WITH_ERRNO("Failed to write WIM resource chunk");
                return WIMLIB_ERR_WRITE;
@@ -457,7 +229,7 @@ static int write_wim_resource_chunk(const u8 chunk[], unsigned chunk_size,
 }
 
 /*
- * Finishes a WIM chunk tale and writes it to the output file at the correct
+ * Finishes a WIM chunk table and writes it to the output file at the correct
  * offset.
  *
  * The final size of the full compressed resource is returned in the
@@ -497,357 +269,246 @@ finish_wim_resource_chunk_tab(struct chunk_table *chunk_tab,
        return 0;
 }
 
-static int prepare_resource_for_read(struct lookup_table_entry *lte
-
-                                       #ifdef WITH_NTFS_3G
-                                       , ntfs_inode **ni_ret
-                                       #endif
-               )
+static int
+write_uncompressed_resource_and_truncate(struct wim_lookup_table_entry *lte,
+                                        FILE *out_fp,
+                                        off_t file_offset,
+                                        struct resource_entry *out_res_entry)
 {
-       if (lte->resource_location == RESOURCE_IN_FILE_ON_DISK
-            && !lte->file_on_disk_fp)
-       {
-               wimlib_assert(lte->file_on_disk);
-               lte->file_on_disk_fp = fopen(lte->file_on_disk, "rb");
-               if (!lte->file_on_disk_fp) {
-                       ERROR_WITH_ERRNO("Failed to open the file `%s' for "
-                                        "reading", lte->file_on_disk);
-                       return WIMLIB_ERR_OPEN;
-               }
-       }
-#ifdef WITH_NTFS_3G
-       else if (lte->resource_location == RESOURCE_IN_NTFS_VOLUME
-                 && !lte->attr)
-       {
-               struct ntfs_location *loc = lte->ntfs_loc;
-               ntfs_inode *ni;
-               wimlib_assert(loc);
-               ni = ntfs_pathname_to_inode(*loc->ntfs_vol_p, NULL, loc->path_utf8);
-               if (!ni) {
-                       ERROR_WITH_ERRNO("Failed to open inode `%s' in NTFS "
-                                        "volume", loc->path_utf8);
-                       return WIMLIB_ERR_NTFS_3G;
-               }
-               lte->attr = ntfs_attr_open(ni,
-                                          loc->is_reparse_point ? AT_REPARSE_POINT : AT_DATA,
-                                          (ntfschar*)loc->stream_name_utf16,
-                                          loc->stream_name_utf16_num_chars);
-               if (!lte->attr) {
-                       ERROR_WITH_ERRNO("Failed to open attribute of `%s' in "
-                                        "NTFS volume", loc->path_utf8);
-                       ntfs_inode_close(ni);
-                       return WIMLIB_ERR_NTFS_3G;
-               }
-               *ni_ret = ni;
+       int ret;
+       if (fseeko(out_fp, file_offset, SEEK_SET) != 0) {
+               ERROR_WITH_ERRNO("Failed to seek to byte %"PRIu64" of "
+                                "output WIM file", file_offset);
+               return WIMLIB_ERR_WRITE;
        }
-#endif
-       return 0;
+       ret = write_wim_resource(lte, out_fp,
+                                WIMLIB_COMPRESSION_TYPE_NONE,
+                                out_res_entry,
+                                0);
+       if (ret)
+               return ret;
+
+       return fflush_and_ftruncate(out_fp,
+                                   file_offset + wim_resource_size(lte));
 }
 
-static void end_wim_resource_read(struct lookup_table_entry *lte
-                               #ifdef WITH_NTFS_3G
-                                       , ntfs_inode *ni
-                               #endif
-                                       )
+struct write_resource_ctx {
+       compress_func_t compress;
+       struct chunk_table *chunk_tab;
+       FILE *out_fp;
+       SHA_CTX sha_ctx;
+       bool doing_sha;
+};
+
+static int
+write_resource_cb(const void *chunk, size_t chunk_size, void *_ctx)
 {
-       if (lte->resource_location == RESOURCE_IN_FILE_ON_DISK
-           && lte->file_on_disk_fp) {
-               fclose(lte->file_on_disk_fp);
-               lte->file_on_disk_fp = NULL;
-       }
-#ifdef WITH_NTFS_3G
-       else if (lte->resource_location == RESOURCE_IN_NTFS_VOLUME) {
-               if (lte->attr) {
-                       ntfs_attr_close(lte->attr);
-                       lte->attr = NULL;
+       struct write_resource_ctx *ctx = _ctx;
+
+       if (ctx->doing_sha)
+               sha1_update(&ctx->sha_ctx, chunk, chunk_size);
+
+       if (ctx->compress) {
+               return write_wim_resource_chunk(chunk, chunk_size,
+                                               ctx->out_fp, ctx->compress,
+                                               ctx->chunk_tab);
+       } else {
+               if (fwrite(chunk, 1, chunk_size, ctx->out_fp) != chunk_size) {
+                       ERROR_WITH_ERRNO("Error writing to output WIM");
+                       return WIMLIB_ERR_WRITE;
+               } else {
+                       return 0;
                }
-               if (ni)
-                       ntfs_inode_close(ni);
        }
-#endif
 }
 
-/*
- * Writes a WIM resource to a FILE * opened for writing.  The resource may be
- * written uncompressed or compressed depending on the @out_ctype parameter.
- *
- * If by chance the resource compresses to more than the original size (this may
- * happen with random data or files than are pre-compressed), the resource is
- * instead written uncompressed (and this is reflected in the @out_res_entry by
- * removing the WIM_RESHDR_FLAG_COMPRESSED flag).
- *
- * @lte:       The lookup table entry for the WIM resource.
- * @out_fp:    The FILE * to write the resource to.
- * @out_ctype:  The compression type of the resource to write.  Note: if this is
- *                     the same as the compression type of the WIM resource we
- *                     need to read, we simply copy the data (i.e. we do not
- *                     uncompress it, then compress it again).
- * @out_res_entry:  If non-NULL, a resource entry that is filled in with the
- *                 offset, original size, compressed size, and compression flag
- *                 of the output resource.
- *
- * Returns 0 on success; nonzero on failure.
- */
-int write_wim_resource(struct lookup_table_entry *lte,
-                      FILE *out_fp, int out_ctype,
-                      struct resource_entry *out_res_entry,
-                      int flags)
+int
+write_wim_resource(struct wim_lookup_table_entry *lte,
+                  FILE *out_fp, int out_ctype,
+                  struct resource_entry *out_res_entry,
+                  int flags)
 {
-       u64 bytes_remaining;
-       u64 original_size;
-       u64 old_compressed_size;
-       u64 new_compressed_size;
-       u64 offset;
+       struct write_resource_ctx write_ctx;
+       u64 new_size;
+       off_t offset;
        int ret;
-       struct chunk_table *chunk_tab = NULL;
-       bool raw;
-       off_t file_offset;
-#ifdef WITH_NTFS_3G
-       ntfs_inode *ni = NULL;
-#endif
-
-       wimlib_assert(lte);
 
-       /* Original size of the resource */
-       original_size = wim_resource_size(lte);
-
-       /* Compressed size of the resource (as it exists now) */
-       old_compressed_size = wim_resource_compressed_size(lte);
+       if (wim_resource_size(lte) == 0) {
+               /* Empty resource; nothing needs to be done, so just return
+                * success. */
+               return 0;
+       }
 
-       /* Current offset in output file */
-       file_offset = ftello(out_fp);
-       if (file_offset == -1) {
-               ERROR_WITH_ERRNO("Failed to get offset in output "
-                                "stream");
+       offset = ftello(out_fp);
+       if (offset == -1) {
+               ERROR_WITH_ERRNO("Can't get position in output WIM");
                return WIMLIB_ERR_WRITE;
        }
 
-       /* Are the compression types the same?  If so, do a raw copy (copy
-        * without decompressing and recompressing the data). */
-       raw = (wim_resource_compression_type(lte) == out_ctype
-              && out_ctype != WIM_COMPRESSION_TYPE_NONE);
+       /* Can we simply copy the compressed data without recompressing it? */
 
-       if (raw) {
+       if (!(flags & WIMLIB_RESOURCE_FLAG_RECOMPRESS) &&
+           lte->resource_location == RESOURCE_IN_WIM &&
+           wimlib_get_compression_type(lte->wim) == out_ctype)
+       {
                flags |= WIMLIB_RESOURCE_FLAG_RAW;
-               bytes_remaining = old_compressed_size;
+               write_ctx.doing_sha = false;
        } else {
-               flags &= ~WIMLIB_RESOURCE_FLAG_RAW;
-               bytes_remaining = original_size;
-       }
-
-       /* Empty resource; nothing needs to be done, so just return success. */
-       if (bytes_remaining == 0)
-               return 0;
-
-       /* Buffer for reading chunks for the resource */
-       u8 buf[min(WIM_CHUNK_SIZE, bytes_remaining)];
-
-       /* If we are writing a compressed resource and not doing a raw copy, we
-        * need to initialize the chunk table */
-       if (out_ctype != WIM_COMPRESSION_TYPE_NONE && !raw) {
-               ret = begin_wim_resource_chunk_tab(lte, out_fp, file_offset,
-                                                  &chunk_tab);
-               if (ret != 0)
-                       goto out;
+               write_ctx.doing_sha = true;
+               sha1_init(&write_ctx.sha_ctx);
        }
 
-       /* If the WIM resource is in an external file, open a FILE * to it so we
-        * don't have to open a temporary one in read_wim_resource() for each
-        * chunk. */
-#ifdef WITH_NTFS_3G
-       ret = prepare_resource_for_read(lte, &ni);
-#else
-       ret = prepare_resource_for_read(lte);
-#endif
-       if (ret != 0)
-               goto out;
-
-       /* If we aren't doing a raw copy, we will compute the SHA1 message
-        * digest of the resource as we read it, and verify it's the same as the
-        * hash given in the lookup table entry once we've finished reading the
-        * resource. */
-       SHA_CTX ctx;
-       if (!raw)
-               sha1_init(&ctx);
-
-       /* While there are still bytes remaining in the WIM resource, read a
-        * chunk of the resource, update SHA1, then write that chunk using the
-        * desired compression type. */
-       offset = 0;
-       do {
-               u64 to_read = min(bytes_remaining, WIM_CHUNK_SIZE);
-               ret = read_wim_resource(lte, buf, to_read, offset, flags);
-               if (ret != 0)
-                       goto out_fclose;
-               if (!raw)
-                       sha1_update(&ctx, buf, to_read);
-               ret = write_wim_resource_chunk(buf, to_read, out_fp,
-                                              out_ctype, chunk_tab);
-               if (ret != 0)
-                       goto out_fclose;
-               bytes_remaining -= to_read;
-               offset += to_read;
-       } while (bytes_remaining);
-
-       /* Raw copy:  The new compressed size is the same as the old compressed
-        * size
-        *
-        * Using WIM_COMPRESSION_TYPE_NONE:  The new compressed size is the
-        * original size
-        *
-        * Using a different compression type:  Call
-        * finish_wim_resource_chunk_tab() and it will provide the new
-        * compressed size.
-        */
-       if (raw) {
-               new_compressed_size = old_compressed_size;
+       /* Initialize the chunk table and set the compression function if
+        * compressing the resource. */
+       if (out_ctype == WIMLIB_COMPRESSION_TYPE_NONE ||
+           (flags & WIMLIB_RESOURCE_FLAG_RAW)) {
+               write_ctx.compress = NULL;
+               write_ctx.chunk_tab = NULL;
        } else {
-               if (out_ctype == WIM_COMPRESSION_TYPE_NONE)
-                       new_compressed_size = original_size;
-               else {
-                       ret = finish_wim_resource_chunk_tab(chunk_tab, out_fp,
-                                                           &new_compressed_size);
-                       if (ret != 0)
-                               goto out_fclose;
-               }
+               write_ctx.compress = get_compress_func(out_ctype);
+               ret = begin_wim_resource_chunk_tab(lte, out_fp,
+                                                  offset,
+                                                  &write_ctx.chunk_tab);
+               if (ret)
+                       return ret;
        }
 
-       /* Verify SHA1 message digest of the resource, unless we are doing a raw
-        * write (in which case we never even saw the uncompressed data).  Or,
-        * if the hash we had before is all 0's, just re-set it to be the new
-        * hash. */
-       if (!raw) {
+       /* Write the data */
+       write_ctx.out_fp = out_fp;
+       ret = read_resource_prefix(lte, wim_resource_size(lte),
+                                  write_resource_cb, &write_ctx, 0);
+
+       /* Verify SHA1 message digest of the resource, or set the hash for the
+        * first time. */
+       if (write_ctx.doing_sha) {
                u8 md[SHA1_HASH_SIZE];
-               sha1_final(md, &ctx);
-               if (is_zero_hash(lte->hash)) {
+               sha1_final(md, &write_ctx.sha_ctx);
+               if (lte->unhashed) {
                        copy_hash(lte->hash, md);
                } else if (!hashes_equal(md, lte->hash)) {
                        ERROR("WIM resource has incorrect hash!");
-                       if (lte->resource_location == RESOURCE_IN_FILE_ON_DISK) {
-                               ERROR("We were reading it from `%s'; maybe it changed "
-                                     "while we were reading it.",
+                       if (lte_filename_valid(lte)) {
+                               ERROR("We were reading it from \"%"TS"\"; maybe "
+                                     "it changed while we were reading it.",
                                      lte->file_on_disk);
                        }
                        ret = WIMLIB_ERR_INVALID_RESOURCE_HASH;
-                       goto out_fclose;
+                       goto out_free_chunk_tab;
                }
        }
 
-       if (!raw && new_compressed_size >= original_size &&
-           out_ctype != WIM_COMPRESSION_TYPE_NONE)
-       {
-               /* Oops!  We compressed the resource to larger than the original
-                * size.  Write the resource uncompressed instead. */
-               if (fseeko(out_fp, file_offset, SEEK_SET) != 0) {
-                       ERROR_WITH_ERRNO("Failed to seek to byte %"PRIu64" "
-                                        "of output WIM file", file_offset);
-                       ret = WIMLIB_ERR_WRITE;
-                       goto out_fclose;
-               }
-               ret = write_wim_resource(lte, out_fp, WIM_COMPRESSION_TYPE_NONE,
-                                        out_res_entry, flags);
-               if (ret != 0)
-                       goto out_fclose;
-               if (fflush(out_fp) != 0) {
-                       ERROR_WITH_ERRNO("Failed to flush output WIM file");
-                       ret = WIMLIB_ERR_WRITE;
-                       goto out_fclose;
-               }
-               if (ftruncate(fileno(out_fp), file_offset + out_res_entry->size) != 0) {
-                       ERROR_WITH_ERRNO("Failed to truncate output WIM file");
-                       ret = WIMLIB_ERR_WRITE;
-                       goto out_fclose;
-               }
+       out_res_entry->flags = lte->resource_entry.flags;
+       out_res_entry->original_size = wim_resource_size(lte);
+       out_res_entry->offset = offset;
+       if (flags & WIMLIB_RESOURCE_FLAG_RAW) {
+               /* Doing a raw write:  The new compressed size is the same as
+                * the compressed size in the other WIM. */
+               new_size = lte->resource_entry.size;
+       } else if (out_ctype == WIMLIB_COMPRESSION_TYPE_NONE) {
+               /* Using WIMLIB_COMPRESSION_TYPE_NONE:  The new compressed size
+                * is the original size. */
+               new_size = lte->resource_entry.original_size;
+               out_res_entry->flags &= ~WIM_RESHDR_FLAG_COMPRESSED;
        } else {
-               if (out_res_entry) {
-                       out_res_entry->size          = new_compressed_size;
-                       out_res_entry->original_size = original_size;
-                       out_res_entry->offset        = file_offset;
-                       out_res_entry->flags         = lte->resource_entry.flags
-                                                       & ~WIM_RESHDR_FLAG_COMPRESSED;
-                       if (out_ctype != WIM_COMPRESSION_TYPE_NONE)
-                               out_res_entry->flags |= WIM_RESHDR_FLAG_COMPRESSED;
+               /* Using a different compression type:  Call
+                * finish_wim_resource_chunk_tab() and it will provide the new
+                * compressed size. */
+               ret = finish_wim_resource_chunk_tab(write_ctx.chunk_tab, out_fp,
+                                                   &new_size);
+               if (ret)
+                       goto out_free_chunk_tab;
+               if (new_size >= wim_resource_size(lte)) {
+                       /* Oops!  We compressed the resource to larger than the original
+                        * size.  Write the resource uncompressed instead. */
+                       ret = write_uncompressed_resource_and_truncate(lte,
+                                                                      out_fp,
+                                                                      offset,
+                                                                      out_res_entry);
+                       goto out_free_chunk_tab;
                }
+               out_res_entry->flags |= WIM_RESHDR_FLAG_COMPRESSED;
        }
+       out_res_entry->size = new_size;
        ret = 0;
-out_fclose:
-#ifdef WITH_NTFS_3G
-       end_wim_resource_read(lte, ni);
-#else
-       end_wim_resource_read(lte);
-#endif
-out:
-       FREE(chunk_tab);
+out_free_chunk_tab:
+       FREE(write_ctx.chunk_tab);
        return ret;
 }
 
+#ifdef ENABLE_MULTITHREADED_COMPRESSION
 
+/* Blocking shared queue (solves the producer-consumer problem) */
 struct shared_queue {
-       sem_t filled_slots;
-       sem_t empty_slots;
-       pthread_mutex_t lock;
+       unsigned size;
        unsigned front;
        unsigned back;
+       unsigned filled_slots;
        void **array;
-       unsigned size;
+       pthread_mutex_t lock;
+       pthread_cond_t msg_avail_cond;
+       pthread_cond_t space_avail_cond;
 };
 
-static int shared_queue_init(struct shared_queue *q, unsigned size)
+static int
+shared_queue_init(struct shared_queue *q, unsigned size)
 {
+       wimlib_assert(size != 0);
        q->array = CALLOC(sizeof(q->array[0]), size);
        if (!q->array)
                return WIMLIB_ERR_NOMEM;
-
-       sem_init(&q->filled_slots, 0, 0);
-       sem_init(&q->empty_slots, 0, size);
-       pthread_mutex_init(&q->lock, NULL);
+       q->filled_slots = 0;
        q->front = 0;
        q->back = size - 1;
        q->size = size;
+       pthread_mutex_init(&q->lock, NULL);
+       pthread_cond_init(&q->msg_avail_cond, NULL);
+       pthread_cond_init(&q->space_avail_cond, NULL);
        return 0;
 }
 
-static void shared_queue_destroy(struct shared_queue *q)
+static void
+shared_queue_destroy(struct shared_queue *q)
 {
-       sem_destroy(&q->filled_slots);
-       sem_destroy(&q->empty_slots);
-       pthread_mutex_destroy(&q->lock);
        FREE(q->array);
+       pthread_mutex_destroy(&q->lock);
+       pthread_cond_destroy(&q->msg_avail_cond);
+       pthread_cond_destroy(&q->space_avail_cond);
 }
 
-static void shared_queue_put(struct shared_queue *q, void *obj)
+static void
+shared_queue_put(struct shared_queue *q, void *obj)
 {
-       sem_wait(&q->empty_slots);
        pthread_mutex_lock(&q->lock);
+       while (q->filled_slots == q->size)
+               pthread_cond_wait(&q->space_avail_cond, &q->lock);
 
        q->back = (q->back + 1) % q->size;
        q->array[q->back] = obj;
+       q->filled_slots++;
 
-       sem_post(&q->filled_slots);
+       pthread_cond_broadcast(&q->msg_avail_cond);
        pthread_mutex_unlock(&q->lock);
 }
 
-static void *shared_queue_get(struct shared_queue *q)
+static void *
+shared_queue_get(struct shared_queue *q)
 {
-       sem_wait(&q->filled_slots);
+       void *obj;
+
        pthread_mutex_lock(&q->lock);
+       while (q->filled_slots == 0)
+               pthread_cond_wait(&q->msg_avail_cond, &q->lock);
 
-       void *obj = q->array[q->front];
+       obj = q->array[q->front];
        q->array[q->front] = NULL;
        q->front = (q->front + 1) % q->size;
+       q->filled_slots--;
 
-       sem_post(&q->empty_slots);
+       pthread_cond_broadcast(&q->space_avail_cond);
        pthread_mutex_unlock(&q->lock);
        return obj;
 }
 
-static inline int shared_queue_get_filled(struct shared_queue *q)
-{
-       int sval;
-       sem_getvalue(&q->filled_slots, &sval);
-       return sval;
-}
-
 struct compressor_thread_params {
        struct shared_queue *res_to_compress_queue;
        struct shared_queue *compressed_res_queue;
@@ -857,7 +518,7 @@ struct compressor_thread_params {
 #define MAX_CHUNKS_PER_MSG 2
 
 struct message {
-       struct lookup_table_entry *lte;
+       struct wim_lookup_table_entry *lte;
        u8 *uncompressed_chunks[MAX_CHUNKS_PER_MSG];
        u8 *out_compressed_chunks[MAX_CHUNKS_PER_MSG];
        u8 *compressed_chunks[MAX_CHUNKS_PER_MSG];
@@ -869,24 +530,34 @@ struct message {
        u64 begin_chunk;
 };
 
-static void compress_chunks(struct message *msg, compress_func_t compress)
+static void
+compress_chunks(struct message *msg, compress_func_t compress)
 {
        for (unsigned i = 0; i < msg->num_chunks; i++) {
                DEBUG2("compress chunk %u of %u", i, msg->num_chunks);
-               int ret = compress(msg->uncompressed_chunks[i],
-                                  msg->uncompressed_chunk_sizes[i],
-                                  msg->compressed_chunks[i],
-                                  &msg->compressed_chunk_sizes[i]);
-               if (ret == 0) {
+               unsigned len = compress(msg->uncompressed_chunks[i],
+                                       msg->uncompressed_chunk_sizes[i],
+                                       msg->compressed_chunks[i]);
+               if (len) {
+                       /* To be written compressed */
                        msg->out_compressed_chunks[i] = msg->compressed_chunks[i];
+                       msg->compressed_chunk_sizes[i] = len;
                } else {
+                       /* To be written uncompressed */
                        msg->out_compressed_chunks[i] = msg->uncompressed_chunks[i];
                        msg->compressed_chunk_sizes[i] = msg->uncompressed_chunk_sizes[i];
+
                }
        }
 }
 
-static void *compressor_thread_proc(void *arg)
+/* Compressor thread routine.  This is a lot simpler than the main thread
+ * routine: just repeatedly get a group of chunks from the
+ * res_to_compress_queue, compress them, and put them in the
+ * compressed_res_queue.  A NULL pointer indicates that the thread should stop.
+ * */
+static void *
+compressor_thread_proc(void *arg)
 {
        struct compressor_thread_params *params = arg;
        struct shared_queue *res_to_compress_queue = params->res_to_compress_queue;
@@ -900,37 +571,171 @@ static void *compressor_thread_proc(void *arg)
                shared_queue_put(compressed_res_queue, msg);
        }
        DEBUG("Compressor thread terminating");
+       return NULL;
 }
+#endif /* ENABLE_MULTITHREADED_COMPRESSION */
 
-static int write_stream_list_serial(struct list_head *stream_list,
-                                   FILE *out_fp, int out_ctype,
-                                   int write_flags)
+static void
+do_write_streams_progress(union wimlib_progress_info *progress,
+                         wimlib_progress_func_t progress_func,
+                         uint64_t size_added)
 {
-       struct lookup_table_entry *lte;
-       int ret;
-
-       list_for_each_entry(lte, stream_list, staging_list) {
-               ret = write_wim_resource(lte, out_fp, out_ctype,
-                                        &lte->output_resource_entry, 0);
-               if (ret != 0)
-                       return ret;
+       progress->write_streams.completed_bytes += size_added;
+       progress->write_streams.completed_streams++;
+       if (progress_func &&
+           progress->write_streams.completed_bytes >= progress->write_streams._private)
+       {
+               progress_func(WIMLIB_PROGRESS_MSG_WRITE_STREAMS,
+                             progress);
+               if (progress->write_streams._private == progress->write_streams.total_bytes) {
+                       progress->write_streams._private = ~0;
+               } else {
+                       progress->write_streams._private =
+                               min(progress->write_streams.total_bytes,
+                                   progress->write_streams.completed_bytes +
+                                       progress->write_streams.total_bytes / 100);
+               }
        }
+}
+
+static int
+sha1_chunk(const void *buf, size_t len, void *ctx)
+{
+       sha1_update(ctx, buf, len);
        return 0;
 }
 
-static int write_wim_chunks(struct message *msg, FILE *out_fp,
-                           struct chunk_table *chunk_tab)
+static int
+sha1_resource(struct wim_lookup_table_entry *lte)
 {
-       for (unsigned i = 0; i < msg->num_chunks; i++) {
-               unsigned chunk_csize = msg->compressed_chunk_sizes[i];
+       int ret;
+       SHA_CTX sha_ctx;
 
-               DEBUG2("Write wim chunk %u of %u (csize = %u)",
-                     i, msg->num_chunks, chunk_csize);
+       sha1_init(&sha_ctx);
+       ret = read_resource_prefix(lte, wim_resource_size(lte),
+                                  sha1_chunk, &sha_ctx, 0);
+       if (ret == 0)
+               sha1_final(lte->hash, &sha_ctx);
+       return ret;
+}
+
+enum {
+       STREAMS_MERGED = 0,
+       STREAMS_NOT_MERGED = 1,
+};
+
+static int
+do_write_stream_list(struct list_head *my_resources,
+                    struct wim_lookup_table *lookup_table,
+                    FILE *out_fp,
+                    int out_ctype,
+                    wimlib_progress_func_t progress_func,
+                    union wimlib_progress_info *progress,
+                    int write_resource_flags)
+{
+       int ret;
+       struct wim_lookup_table_entry *lte;
+
+       while (!list_empty(my_resources)) {
+               lte = container_of(my_resources->next,
+                                  struct wim_lookup_table_entry,
+                                  write_streams_list);
+               list_del(&lte->write_streams_list);
+               if (lte->unhashed && !lte->unique_size) {
+                       struct wim_lookup_table_entry *duplicate_lte;
+                       struct wim_lookup_table_entry **my_ptr;
+
+                       my_ptr = lte->my_ptr;
+                       ret = sha1_resource(lte);
+                       if (ret)
+                               return ret;
+                       duplicate_lte = __lookup_resource(lookup_table, lte->hash);
+                       if (duplicate_lte) {
+                               bool new_stream = (duplicate_lte->out_refcnt == 0);
+                               duplicate_lte->refcnt += lte->refcnt;
+                               duplicate_lte->out_refcnt += lte->refcnt;
+                               *my_ptr = duplicate_lte;
+                               free_lookup_table_entry(lte);
+
+                               if (new_stream) {
+                                       lte = duplicate_lte;
+                                       DEBUG("Stream of length %"PRIu64" is duplicate "
+                                             "with one already in WIM",
+                                             wim_resource_size(duplicate_lte));
+                               } else {
+                                       DEBUG("Discarding duplicate stream of length %"PRIu64,
+                                             wim_resource_size(duplicate_lte));
+                                       goto skip_to_progress;
+                               }
+
+                       } else {
+                               lookup_table_insert(lookup_table, lte);
+                               lte->out_refcnt = lte->refcnt;
+                               lte->unhashed = 0;
+                       }
+               }
+
+               wimlib_assert(lte->out_refcnt != 0);
+
+               ret = write_wim_resource(lte,
+                                        out_fp,
+                                        out_ctype,
+                                        &lte->output_resource_entry,
+                                        write_resource_flags);
+               if (ret)
+                       return ret;
+               if (lte->unhashed) {
+                       lookup_table_insert(lookup_table, lte);
+                       lte->unhashed = 0;
+               }
+       skip_to_progress:
+               do_write_streams_progress(progress,
+                                         progress_func,
+                                         wim_resource_size(lte));
+       }
+       return 0;
+}
+
+static int
+write_stream_list_serial(struct list_head *stream_list,
+                        struct wim_lookup_table *lookup_table,
+                        FILE *out_fp,
+                        int out_ctype,
+                        int write_flags,
+                        wimlib_progress_func_t progress_func,
+                        union wimlib_progress_info *progress)
+{
+       int write_resource_flags;
+
+       if (write_flags & WIMLIB_WRITE_FLAG_RECOMPRESS)
+               write_resource_flags = WIMLIB_RESOURCE_FLAG_RECOMPRESS;
+       else
+               write_resource_flags = 0;
+       progress->write_streams.num_threads = 1;
+       if (progress_func)
+               progress_func(WIMLIB_PROGRESS_MSG_WRITE_STREAMS, progress);
+       return do_write_stream_list(stream_list,
+                                   lookup_table,
+                                   out_fp,
+                                   out_ctype, progress_func,
+                                   progress, write_resource_flags);
+}
+
+#ifdef ENABLE_MULTITHREADED_COMPRESSION
+static int
+write_wim_chunks(struct message *msg, FILE *out_fp,
+                struct chunk_table *chunk_tab)
+{
+       for (unsigned i = 0; i < msg->num_chunks; i++) {
+               unsigned chunk_csize = msg->compressed_chunk_sizes[i];
+
+               DEBUG2("Write wim chunk %u of %u (csize = %u)",
+                     i, msg->num_chunks, chunk_csize);
 
                if (fwrite(msg->out_compressed_chunks[i], 1, chunk_csize, out_fp)
                    != chunk_csize)
                {
-                       ERROR_WITH_ERRNO("Failed to write WIM");
+                       ERROR_WITH_ERRNO("Failed to write WIM chunk");
                        return WIMLIB_ERR_WRITE;
                }
 
@@ -952,22 +757,31 @@ static int write_wim_chunks(struct message *msg, FILE *out_fp,
  * res_to_compress_queue, and it is passed back through the
  * compressed_res_queue.
  */
-static int main_writer_thread_proc(struct list_head *stream_list,
-                                  FILE *out_fp,
-                                  int out_ctype,
-                                  struct shared_queue *res_to_compress_queue,
-                                  struct shared_queue *compressed_res_queue,
-                                  size_t queue_size)
+static int
+main_writer_thread_proc(struct list_head *stream_list,
+                       FILE *out_fp,
+                       int out_ctype,
+                       struct shared_queue *res_to_compress_queue,
+                       struct shared_queue *compressed_res_queue,
+                       size_t num_messages,
+                       int write_flags,
+                       wimlib_progress_func_t progress_func,
+                       union wimlib_progress_info *progress)
 {
        int ret;
-
-
-       struct message msgs[queue_size];
-       ZERO_ARRAY(msgs);
+       struct chunk_table *cur_chunk_tab = NULL;
+       struct message *msgs = CALLOC(num_messages, sizeof(struct message));
+       struct wim_lookup_table_entry *next_lte = NULL;
 
        // Initially, all the messages are available to use.
        LIST_HEAD(available_msgs);
-       for (size_t i = 0; i < ARRAY_LEN(msgs); i++)
+
+       if (!msgs) {
+               ret = WIMLIB_ERR_NOMEM;
+               goto out;
+       }
+
+       for (size_t i = 0; i < num_messages; i++)
                list_add(&msgs[i].list, &available_msgs);
 
        // outstanding_resources is the list of resources that currently have
@@ -987,66 +801,146 @@ static int main_writer_thread_proc(struct list_head *stream_list,
        //
        LIST_HEAD(outstanding_resources);
        struct list_head *next_resource = stream_list->next;
-       struct lookup_table_entry *next_lte = container_of(next_resource,
-                                                          struct lookup_table_entry,
-                                                          staging_list);
-       next_resource = next_resource->next;
        u64 next_chunk = 0;
-       u64 next_num_chunks = wim_resource_chunks(next_lte);
-       INIT_LIST_HEAD(&next_lte->msg_list);
-       list_add_tail(&next_lte->staging_list, &outstanding_resources);
+       u64 next_num_chunks = 0;
 
        // As in write_wim_resource(), each resource we read is checksummed.
        SHA_CTX next_sha_ctx;
-       sha1_init(&next_sha_ctx);
        u8 next_hash[SHA1_HASH_SIZE];
 
        // Resources that don't need any chunks compressed are added to this
        // list and written directly by the main thread.
        LIST_HEAD(my_resources);
 
-       struct lookup_table_entry *cur_lte = next_lte;
-       struct chunk_table *cur_chunk_tab = NULL;
-       struct lookup_table_entry *lte;
+       struct wim_lookup_table_entry *cur_lte = NULL;
        struct message *msg;
 
 #ifdef WITH_NTFS_3G
        ntfs_inode *ni = NULL;
 #endif
 
-#ifdef WITH_NTFS_3G
-       ret = prepare_resource_for_read(next_lte, &ni);
-#else
-       ret = prepare_resource_for_read(next_lte);
-#endif
-
        DEBUG("Initializing buffers for uncompressed "
              "and compressed data (%zu bytes needed)",
-             queue_size * MAX_CHUNKS_PER_MSG * WIM_CHUNK_SIZE * 2);
+             num_messages * MAX_CHUNKS_PER_MSG * WIM_CHUNK_SIZE * 2);
 
        // Pre-allocate all the buffers that will be needed to do the chunk
        // compression.
-       for (size_t i = 0; i < ARRAY_LEN(msgs); i++) {
+       for (size_t i = 0; i < num_messages; i++) {
                for (size_t j = 0; j < MAX_CHUNKS_PER_MSG; j++) {
                        msgs[i].compressed_chunks[j] = MALLOC(WIM_CHUNK_SIZE);
-                       msgs[i].uncompressed_chunks[j] = MALLOC(WIM_CHUNK_SIZE);
+
+                       // The extra 8 bytes is because longest_match() in
+                       // lz77.c may read a little bit off the end of the
+                       // uncompressed data.  It doesn't need to be
+                       // initialized--- we really just need to avoid accessing
+                       // an unmapped page.
+                       msgs[i].uncompressed_chunks[j] = MALLOC(WIM_CHUNK_SIZE + 8);
                        if (msgs[i].compressed_chunks[j] == NULL ||
                            msgs[i].uncompressed_chunks[j] == NULL)
                        {
-                               ERROR("Could not allocate enough memory for "
-                                     "multi-threaded compression");
                                ret = WIMLIB_ERR_NOMEM;
                                goto out;
                        }
                }
        }
 
+       // This loop is executed until all resources have been written, except
+       // possibly a few that have been added to the @my_resources list for
+       // writing later.
        while (1) {
                // Send chunks to the compressor threads until either (a) there
                // are no more messages available since they were all sent off,
                // or (b) there are no more resources that need to be
                // compressed.
-               while (!list_empty(&available_msgs) && next_lte != NULL) {
+               while (!list_empty(&available_msgs)) {
+                       if (next_chunk == next_num_chunks) {
+                               // If next_chunk == next_num_chunks, there are
+                               // no more chunks to write in the current
+                               // stream.  So, check the SHA1 message digest of
+                               // the stream that was just finished (unless
+                               // next_lte == NULL, which is the case the very
+                               // first time this loop is entered, and also
+                               // near the very end of the compression when
+                               // there are no more streams.)  Then, advance to
+                               // the next stream (if there is one).
+                               if (next_lte != NULL) {
+                               #ifdef WITH_NTFS_3G
+                                       end_wim_resource_read(next_lte, ni);
+                                       ni = NULL;
+                               #else
+                                       end_wim_resource_read(next_lte);
+                               #endif
+                                       DEBUG2("Finalize SHA1 md (next_num_chunks=%zu)",
+                                              next_num_chunks);
+                                       sha1_final(next_hash, &next_sha_ctx);
+                                       if (!hashes_equal(next_lte->hash, next_hash)) {
+                                               ERROR("WIM resource has incorrect hash!");
+                                               if (next_lte->resource_location ==
+                                                   RESOURCE_IN_FILE_ON_DISK)
+                                               {
+                                                       ERROR("We were reading it from `%"TS"'; "
+                                                             "maybe it changed while we were "
+                                                             "reading it.",
+                                                             next_lte->file_on_disk);
+                                               }
+                                               ret = WIMLIB_ERR_INVALID_RESOURCE_HASH;
+                                               goto out;
+                                       }
+                               }
+
+                               // Advance to the next resource.
+                               //
+                               // If the next resource needs no compression, just write
+                               // it with this thread (not now though--- we could be in
+                               // the middle of writing another resource.)  Keep doing
+                               // this until we either get to the end of the resources
+                               // list, or we get to a resource that needs compression.
+                               while (1) {
+                                       if (next_resource == stream_list) {
+                                               // No more resources to send for
+                                               // compression
+                                               next_lte = NULL;
+                                               break;
+                                       }
+                                       next_lte = container_of(next_resource,
+                                                               struct wim_lookup_table_entry,
+                                                               staging_list);
+                                       next_resource = next_resource->next;
+                                       if ((!(write_flags & WIMLIB_WRITE_FLAG_RECOMPRESS)
+                                              && wim_resource_compression_type(next_lte) == out_ctype)
+                                           || wim_resource_size(next_lte) == 0)
+                                       {
+                                               list_add_tail(&next_lte->staging_list,
+                                                             &my_resources);
+                                       } else {
+                                               list_add_tail(&next_lte->staging_list,
+                                                             &outstanding_resources);
+                                               next_chunk = 0;
+                                               next_num_chunks = wim_resource_chunks(next_lte);
+                                               sha1_init(&next_sha_ctx);
+                                               INIT_LIST_HEAD(&next_lte->msg_list);
+                                       #ifdef WITH_NTFS_3G
+                                               ret = prepare_resource_for_read(next_lte, &ni);
+                                       #else
+                                               ret = prepare_resource_for_read(next_lte);
+                                       #endif
+
+                                               if (ret != 0)
+                                                       goto out;
+                                               if (cur_lte == NULL) {
+                                                       // Set cur_lte for the
+                                                       // first time
+                                                       cur_lte = next_lte;
+                                               }
+                                               break;
+                                       }
+                               }
+                       }
+
+                       if (next_lte == NULL) {
+                               // No more resources to send for compression
+                               break;
+                       }
 
                        // Get a message from the available messages
                        // list
@@ -1073,13 +967,11 @@ static int main_writer_thread_proc(struct list_head *stream_list,
                                // message so that a compressor thread can
                                // compress it.
 
-                               if (next_chunk == next_num_chunks - 1 &&
-                                    wim_resource_size(next_lte) % WIM_CHUNK_SIZE != 0)
-                               {
-                                       size = wim_resource_size(next_lte) % WIM_CHUNK_SIZE;
+                               if (next_chunk == next_num_chunks - 1) {
+                                       size = MODULO_NONZERO(wim_resource_size(next_lte),
+                                                             WIM_CHUNK_SIZE);
                                }
 
-
                                DEBUG2("Read resource (size=%u, offset=%zu)",
                                      size, next_chunk * WIM_CHUNK_SIZE);
 
@@ -1101,80 +993,11 @@ static int main_writer_thread_proc(struct list_head *stream_list,
                        list_add_tail(&msg->list, &next_lte->msg_list);
                        shared_queue_put(res_to_compress_queue, msg);
                        DEBUG2("Compression request sent");
-
-                       if (next_chunk != next_num_chunks)
-                               // More chunks to send for this resource
-                               continue;
-
-                       // Done sending compression requests for a resource!
-                       // Check the SHA1 message digest.
-                       DEBUG2("Finalize SHA1 md (next_num_chunks=%zu)", next_num_chunks);
-                       sha1_final(next_hash, &next_sha_ctx);
-                       if (!hashes_equal(next_lte->hash, next_hash)) {
-                               ERROR("WIM resource has incorrect hash!");
-                               if (next_lte->resource_location == RESOURCE_IN_FILE_ON_DISK) {
-                                       ERROR("We were reading it from `%s'; maybe it changed "
-                                             "while we were reading it.",
-                                             next_lte->file_on_disk);
-                               }
-                               ret = WIMLIB_ERR_INVALID_RESOURCE_HASH;
-                               goto out;
-                       }
-
-                       // Advance to the next resource.
-                       //
-                       // If the next resource needs no compression, just write
-                       // it with this thread (not now though--- we could be in
-                       // the middle of writing another resource.)  Keep doing
-                       // this until we either get to the end of the resources
-                       // list, or we get to a resource that needs compression.
-
-                       while (1) {
-                               if (next_resource == stream_list) {
-                                       next_lte = NULL;
-                                       break;
-                               }
-                       #ifdef WITH_NTFS_3G
-                               end_wim_resource_read(next_lte, ni);
-                               ni = NULL;
-                       #else
-                               end_wim_resource_read(next_lte);
-                       #endif
-
-                               next_lte = container_of(next_resource,
-                                                       struct lookup_table_entry,
-                                                       staging_list);
-                               next_resource = next_resource->next;
-                               if ((next_lte->resource_location == RESOURCE_IN_WIM
-                                   && wimlib_get_compression_type(next_lte->wim) == out_ctype)
-                                   || wim_resource_size(next_lte) == 0)
-                               {
-                                       list_add_tail(&next_lte->staging_list,
-                                                     &my_resources);
-                               } else {
-                                       list_add_tail(&next_lte->staging_list,
-                                                     &outstanding_resources);
-                                       next_chunk = 0;
-                                       next_num_chunks = wim_resource_chunks(next_lte);
-                                       sha1_init(&next_sha_ctx);
-                                       INIT_LIST_HEAD(&next_lte->msg_list);
-                               #ifdef WITH_NTFS_3G
-                                       ret = prepare_resource_for_read(next_lte, &ni);
-                               #else
-                                       ret = prepare_resource_for_read(next_lte);
-                               #endif
-                                       if (ret != 0)
-                                               goto out;
-                                       DEBUG2("Updated next_lte");
-                                       break;
-                               }
-                       }
                }
 
                // If there are no outstanding resources, there are no more
                // resources that need to be written.
                if (list_empty(&outstanding_resources)) {
-                       DEBUG("No outstanding resources! Done");
                        ret = 0;
                        goto out;
                }
@@ -1182,30 +1005,25 @@ static int main_writer_thread_proc(struct list_head *stream_list,
                // Get the next message from the queue and process it.
                // The message will contain 1 or more data chunks that have been
                // compressed.
-               DEBUG2("Waiting for message");
                msg = shared_queue_get(compressed_res_queue);
                msg->complete = true;
 
-               DEBUG2("Received msg (begin_chunk=%"PRIu64")", msg->begin_chunk);
-
-               list_for_each_entry(msg, &cur_lte->msg_list, list) {
-                       DEBUG2("complete=%d", msg->complete);
-               }
-
                // Is this the next chunk in the current resource?  If it's not
                // (i.e., an earlier chunk in a same or different resource
                // hasn't been compressed yet), do nothing, and keep this
                // message around until all earlier chunks are received.
                //
                // Otherwise, write all the chunks we can.
-               while (!list_empty(&cur_lte->msg_list)
-                       && (msg = container_of(cur_lte->msg_list.next,
-                                              struct message,
-                                              list))->complete)
+               while (cur_lte != NULL &&
+                      !list_empty(&cur_lte->msg_list) &&
+                      (msg = container_of(cur_lte->msg_list.next,
+                                          struct message,
+                                          list))->complete)
                {
                        DEBUG2("Complete msg (begin_chunk=%"PRIu64")", msg->begin_chunk);
                        if (msg->begin_chunk == 0) {
                                DEBUG2("Begin chunk tab");
+
                                // This is the first set of chunks.  Leave space
                                // for the chunk table in the output file.
                                off_t cur_offset = ftello(out_fp);
@@ -1232,8 +1050,8 @@ static int main_writer_thread_proc(struct list_head *stream_list,
                        // now.
                        list_add(&msg->list, &available_msgs);
 
-                       // Was this the last chunk of the stream?  If so,
-                       // finish it.
+                       // Was this the last chunk of the stream?  If so, finish
+                       // it.
                        if (list_empty(&cur_lte->msg_list) &&
                            msg->begin_chunk + msg->num_chunks == cur_chunk_tab->num_chunks)
                        {
@@ -1245,19 +1063,34 @@ static int main_writer_thread_proc(struct list_head *stream_list,
                                if (ret != 0)
                                        goto out;
 
+                               if (res_csize >= wim_resource_size(cur_lte)) {
+                                       /* Oops!  We compressed the resource to
+                                        * larger than the original size.  Write
+                                        * the resource uncompressed instead. */
+                                       ret = write_uncompressed_resource_and_truncate(
+                                                        cur_lte,
+                                                        out_fp,
+                                                        cur_chunk_tab->file_offset,
+                                                        &cur_lte->output_resource_entry);
+                                       if (ret != 0)
+                                               goto out;
+                               } else {
+                                       cur_lte->output_resource_entry.size =
+                                               res_csize;
 
-                               cur_lte->output_resource_entry.size =
-                                       res_csize;
+                                       cur_lte->output_resource_entry.original_size =
+                                               cur_lte->resource_entry.original_size;
 
-                               cur_lte->output_resource_entry.original_size =
-                                       cur_lte->resource_entry.original_size;
+                                       cur_lte->output_resource_entry.offset =
+                                               cur_chunk_tab->file_offset;
 
-                               cur_lte->output_resource_entry.offset =
-                                       cur_chunk_tab->file_offset;
+                                       cur_lte->output_resource_entry.flags =
+                                               cur_lte->resource_entry.flags |
+                                                       WIM_RESHDR_FLAG_COMPRESSED;
+                               }
 
-                               cur_lte->output_resource_entry.flags =
-                                       cur_lte->resource_entry.flags |
-                                               WIM_RESHDR_FLAG_COMPRESSED;
+                               do_write_streams_progress(progress, progress_func,
+                                                         wim_resource_size(cur_lte));
 
                                FREE(cur_chunk_tab);
                                cur_chunk_tab = NULL;
@@ -1265,15 +1098,12 @@ static int main_writer_thread_proc(struct list_head *stream_list,
                                struct list_head *next = cur_lte->staging_list.next;
                                list_del(&cur_lte->staging_list);
 
-                               if (next == &outstanding_resources) {
-                                       DEBUG("No more outstanding resources");
-                                       ret = 0;
-                                       goto out;
-                               } else {
+                               if (next == &outstanding_resources)
+                                       cur_lte = NULL;
+                               else
                                        cur_lte = container_of(cur_lte->staging_list.next,
-                                                              struct lookup_table_entry,
+                                                              struct wim_lookup_table_entry,
                                                               staging_list);
-                               }
 
                                // Since we just finished writing a stream,
                                // write any streams that have been added to the
@@ -1282,141 +1112,165 @@ static int main_writer_thread_proc(struct list_head *stream_list,
                                // to be compressed because the desired
                                // compression type is the same as the previous
                                // compression type).
-                               struct lookup_table_entry *tmp;
-                               list_for_each_entry_safe(lte,
-                                                        tmp,
-                                                        &my_resources,
-                                                        staging_list)
-                               {
-                                       ret = write_wim_resource(lte,
-                                                                out_fp,
-                                                                out_ctype,
-                                                                &lte->output_resource_entry,
-                                                                0);
-                                       list_del(&lte->staging_list);
-                                       if (ret != 0)
-                                               goto out;
-                               }
+                               ret = do_write_stream_list(&my_resources,
+                                                          out_fp,
+                                                          out_ctype,
+                                                          progress_func,
+                                                          progress,
+                                                          0);
+                               if (ret != 0)
+                                       goto out;
                        }
                }
        }
 
 out:
+       if (ret == WIMLIB_ERR_NOMEM) {
+               ERROR("Could not allocate enough memory for "
+                     "multi-threaded compression");
+       }
+
+       if (next_lte) {
 #ifdef WITH_NTFS_3G
-       end_wim_resource_read(cur_lte, ni);
+               end_wim_resource_read(next_lte, ni);
 #else
-       end_wim_resource_read(cur_lte);
+               end_wim_resource_read(next_lte);
 #endif
+       }
+
        if (ret == 0) {
-               list_for_each_entry(lte, &my_resources, staging_list) {
-                       ret = write_wim_resource(lte, out_fp,
-                                                out_ctype,
-                                                &lte->output_resource_entry,
-                                                0);
-                       if (ret != 0)
-                               break;
-               }
+               ret = do_write_stream_list(&my_resources, out_fp,
+                                          out_ctype, progress_func,
+                                          progress, 0);
        } else {
-               size_t num_available_msgs = 0;
-               struct list_head *cur;
+               if (msgs) {
+                       size_t num_available_msgs = 0;
+                       struct list_head *cur;
 
-               list_for_each(cur, &available_msgs) {
-                       num_available_msgs++;
-               }
+                       list_for_each(cur, &available_msgs) {
+                               num_available_msgs++;
+                       }
 
-               while (num_available_msgs < ARRAY_LEN(msgs)) {
-                       shared_queue_get(compressed_res_queue);
-                       num_available_msgs++;
+                       while (num_available_msgs < num_messages) {
+                               shared_queue_get(compressed_res_queue);
+                               num_available_msgs++;
+                       }
                }
        }
 
-       DEBUG("Freeing messages");
-
-       for (size_t i = 0; i < ARRAY_LEN(msgs); i++) {
-               for (size_t j = 0; j < MAX_CHUNKS_PER_MSG; j++) {
-                       FREE(msgs[i].compressed_chunks[j]);
-                       FREE(msgs[i].uncompressed_chunks[j]);
+       if (msgs) {
+               for (size_t i = 0; i < num_messages; i++) {
+                       for (size_t j = 0; j < MAX_CHUNKS_PER_MSG; j++) {
+                               FREE(msgs[i].compressed_chunks[j]);
+                               FREE(msgs[i].uncompressed_chunks[j]);
+                       }
                }
+               FREE(msgs);
        }
 
-       if (cur_chunk_tab != NULL)
-               FREE(cur_chunk_tab);
+       FREE(cur_chunk_tab);
        return ret;
 }
 
-static int write_stream_list_parallel(struct list_head *stream_list,
-                                     FILE *out_fp, int out_ctype,
-                                     int write_flags)
+static long
+get_default_num_threads()
+{
+#ifdef __WIN32__
+       return win32_get_number_of_processors();
+#else
+       return sysconf(_SC_NPROCESSORS_ONLN);
+#endif
+}
+
+static int
+write_stream_list_parallel(struct list_head *stream_list,
+                          struct wim_lookup_table *lookup_table,
+                          FILE *out_fp,
+                          int out_ctype,
+                          int write_flags,
+                          unsigned num_threads,
+                          wimlib_progress_func_t progress_func,
+                          union wimlib_progress_info *progress)
 {
        int ret;
-       long nthreads;
        struct shared_queue res_to_compress_queue;
        struct shared_queue compressed_res_queue;
+       pthread_t *compressor_threads = NULL;
 
-       nthreads = sysconf(_SC_NPROCESSORS_ONLN);
-       if (nthreads < 1) {
-               WARNING("Could not determine number of processors! Assuming 1");
-               goto out_serial;
+       if (num_threads == 0) {
+               long nthreads = get_default_num_threads();
+               if (nthreads < 1 || nthreads > UINT_MAX) {
+                       WARNING("Could not determine number of processors! Assuming 1");
+                       goto out_serial;
+               } else {
+                       num_threads = nthreads;
+               }
        }
 
+       progress->write_streams.num_threads = num_threads;
        wimlib_assert(stream_list->next != stream_list);
 
-       {
-               pthread_t compressor_threads[nthreads];
+       static const double MESSAGES_PER_THREAD = 2.0;
+       size_t queue_size = (size_t)(num_threads * MESSAGES_PER_THREAD);
 
-               static const double MESSAGES_PER_THREAD = 2.0;
-               size_t queue_size = (size_t)(nthreads * MESSAGES_PER_THREAD);
+       DEBUG("Initializing shared queues (queue_size=%zu)", queue_size);
 
-               DEBUG("Initializing shared queues (queue_size=%zu)", queue_size);
+       ret = shared_queue_init(&res_to_compress_queue, queue_size);
+       if (ret != 0)
+               goto out_serial;
 
-               ret = shared_queue_init(&res_to_compress_queue, queue_size);
-               if (ret != 0)
-                       goto out_serial;
+       ret = shared_queue_init(&compressed_res_queue, queue_size);
+       if (ret != 0)
+               goto out_destroy_res_to_compress_queue;
 
-               ret = shared_queue_init(&compressed_res_queue, queue_size);
-               if (ret != 0)
-                       goto out_destroy_res_to_compress_queue;
-
-               struct compressor_thread_params params;
-               params.res_to_compress_queue = &res_to_compress_queue;
-               params.compressed_res_queue = &compressed_res_queue;
-               params.compress = get_compress_func(out_ctype);
-
-               for (long i = 0; i < nthreads; i++) {
-                       DEBUG("pthread_create thread %ld", i);
-                       ret = pthread_create(&compressor_threads[i], NULL,
-                                            compressor_thread_proc, &params);
-                       if (ret != 0) {
-                               ERROR_WITH_ERRNO("Failed to create compressor "
-                                                "thread %ld", i);
-                               nthreads = i;
-                               goto out_join;
-                       }
-               }
+       struct compressor_thread_params params;
+       params.res_to_compress_queue = &res_to_compress_queue;
+       params.compressed_res_queue = &compressed_res_queue;
+       params.compress = get_compress_func(out_ctype);
 
-               if (write_flags & WIMLIB_WRITE_FLAG_VERBOSE) {
-                       printf("Writing compressed data using %ld threads...\n",
-                              nthreads);
+       compressor_threads = MALLOC(num_threads * sizeof(pthread_t));
+       if (!compressor_threads) {
+               ret = WIMLIB_ERR_NOMEM;
+               goto out_destroy_compressed_res_queue;
+       }
+
+       for (unsigned i = 0; i < num_threads; i++) {
+               DEBUG("pthread_create thread %u", i);
+               ret = pthread_create(&compressor_threads[i], NULL,
+                                    compressor_thread_proc, &params);
+               if (ret != 0) {
+                       ret = -1;
+                       ERROR_WITH_ERRNO("Failed to create compressor "
+                                        "thread %u", i);
+                       num_threads = i;
+                       goto out_join;
                }
+       }
 
-               ret = main_writer_thread_proc(stream_list,
-                                             out_fp,
-                                             out_ctype,
-                                             &res_to_compress_queue,
-                                             &compressed_res_queue,
-                                             queue_size);
-
-       out_join:
-               for (long i = 0; i < nthreads; i++)
-                       shared_queue_put(&res_to_compress_queue, NULL);
-
-               for (long i = 0; i < nthreads; i++) {
-                       if (pthread_join(compressor_threads[i], NULL)) {
-                               WARNING("Failed to join compressor thread %ld: %s",
-                                       i, strerror(errno));
-                       }
+       if (progress_func)
+               progress_func(WIMLIB_PROGRESS_MSG_WRITE_STREAMS, progress);
+
+       ret = main_writer_thread_proc(stream_list,
+                                     out_fp,
+                                     out_ctype,
+                                     &res_to_compress_queue,
+                                     &compressed_res_queue,
+                                     queue_size,
+                                     write_flags,
+                                     progress_func,
+                                     progress);
+out_join:
+       for (unsigned i = 0; i < num_threads; i++)
+               shared_queue_put(&res_to_compress_queue, NULL);
+
+       for (unsigned i = 0; i < num_threads; i++) {
+               if (pthread_join(compressor_threads[i], NULL)) {
+                       WARNING_WITH_ERRNO("Failed to join compressor "
+                                          "thread %u", i);
                }
        }
+       FREE(compressor_threads);
+out_destroy_compressed_res_queue:
        shared_queue_destroy(&compressed_res_queue);
 out_destroy_res_to_compress_queue:
        shared_queue_destroy(&res_to_compress_queue);
@@ -1424,167 +1278,389 @@ out_destroy_res_to_compress_queue:
                return ret;
 out_serial:
        WARNING("Falling back to single-threaded compression");
-       return write_stream_list_serial(stream_list, out_fp,
-                                       out_ctype, write_flags);
+       return write_stream_list_serial(stream_list,
+                                       lookup_table,
+                                       out_fp,
+                                       out_ctype,
+                                       write_flags,
+                                       progress_func,
+                                       progress);
+
 }
+#endif
 
-static int write_stream_list(struct list_head *stream_list, FILE *out_fp,
-                            int out_ctype, int write_flags)
+/*
+ * Write a list of streams to a WIM (@out_fp) using the compression type
+ * @out_ctype and up to @num_threads compressor threads.
+ */
+static int
+write_stream_list(struct list_head *stream_list,
+                 struct wim_lookup_table *lookup_table,
+                 FILE *out_fp, int out_ctype, int write_flags,
+                 unsigned num_threads, wimlib_progress_func_t progress_func)
 {
-       struct lookup_table_entry *lte;
+       struct wim_lookup_table_entry *lte;
        size_t num_streams = 0;
-       u64 total_size = 0;
-       bool compression_needed = false;
+       u64 total_bytes = 0;
+       u64 total_compression_bytes = 0;
+       union wimlib_progress_info progress;
+       int ret;
 
-       list_for_each_entry(lte, stream_list, staging_list) {
+       list_for_each_entry(lte, stream_list, write_streams_list) {
                num_streams++;
-               total_size += wim_resource_size(lte);
-               if (!compression_needed
-                   && out_ctype != WIM_COMPRESSION_TYPE_NONE
-                   && (lte->resource_location != RESOURCE_IN_WIM
-                       || wimlib_get_compression_type(lte->wim) != out_ctype)
-                   && wim_resource_size(lte) != 0)
-                       compression_needed = true;
-       }
-
-       if (write_flags & WIMLIB_WRITE_FLAG_VERBOSE) {
-               printf("Preparing to write %zu streams "
-                      "(%"PRIu64" total bytes uncompressed)\n",
-                      num_streams, total_size);
-               printf("Using compression type %s\n",
-                      wimlib_get_compression_type_string(out_ctype));
-       }
-
-       if (compression_needed && total_size >= 1000000) {
-               return write_stream_list_parallel(stream_list, out_fp,
-                                                 out_ctype, write_flags);
-       } else {
-               if (write_flags & WIMLIB_WRITE_FLAG_VERBOSE) {
-                       puts("Using 1 thread (no compression needed)");
+               total_bytes += wim_resource_size(lte);
+               if (out_ctype != WIMLIB_COMPRESSION_TYPE_NONE
+                      && (wim_resource_compression_type(lte) != out_ctype ||
+                          (write_flags & WIMLIB_WRITE_FLAG_RECOMPRESS)))
+               {
+                       total_compression_bytes += wim_resource_size(lte);
                }
+       }
+       progress.write_streams.total_bytes       = total_bytes;
+       progress.write_streams.total_streams     = num_streams;
+       progress.write_streams.completed_bytes   = 0;
+       progress.write_streams.completed_streams = 0;
+       progress.write_streams.num_threads       = num_threads;
+       progress.write_streams.compression_type  = out_ctype;
+       progress.write_streams._private          = 0;
+
+#ifdef ENABLE_MULTITHREADED_COMPRESSION
+       if (total_compression_bytes >= 1000000 && num_threads != 1)
+               ret = write_stream_list_parallel(stream_list,
+                                                lookup_table,
+                                                out_fp,
+                                                out_ctype,
+                                                write_flags,
+                                                num_threads,
+                                                progress_func,
+                                                &progress);
+       else
+#endif
+               ret = write_stream_list_serial(stream_list,
+                                              lookup_table,
+                                              out_fp,
+                                              out_ctype,
+                                              write_flags,
+                                              progress_func,
+                                              &progress);
+       return ret;
+}
+
+struct lte_overwrite_prepare_args {
+       WIMStruct *wim;
+       off_t end_offset;
+       struct list_head *stream_list;
+};
+
+static int
+lte_overwrite_prepare(struct wim_lookup_table_entry *lte, void *arg)
+{
+       struct lte_overwrite_prepare_args *args = arg;
+
+       if (lte->resource_location == RESOURCE_IN_WIM &&
+           lte->wim == args->wim &&
+           lte->resource_entry.offset + lte->resource_entry.size > args->end_offset)
+       {
+       #ifdef ENABLE_ERROR_MESSAGES
+               ERROR("The following resource is after the XML data:");
+               print_lookup_table_entry(lte, stderr);
+       #endif
+               return WIMLIB_ERR_RESOURCE_ORDER;
+       }
+
+       lte->out_refcnt = lte->refcnt;
+       memcpy(&lte->output_resource_entry, &lte->resource_entry,
+              sizeof(struct resource_entry));
+       if (!(lte->resource_entry.flags & WIM_RESHDR_FLAG_METADATA))
+               if (lte->resource_location != RESOURCE_IN_WIM || lte->wim != args->wim)
+                       list_add(&lte->staging_list, args->stream_list);
+       return 0;
+}
+
+static int
+wim_prepare_streams(WIMStruct *wim, off_t end_offset,
+                   struct list_head *stream_list)
+{
+       struct lte_overwrite_prepare_args args = {
+               .wim         = wim,
+               .end_offset  = end_offset,
+               .stream_list = stream_list,
+       };
+       int ret;
 
-               return write_stream_list_serial(stream_list, out_fp,
-                                               out_ctype, write_flags);
+       for (int i = 0; i < wim->hdr.image_count; i++) {
+               ret = lte_overwrite_prepare(wim->image_metadata[i]->metadata_lte,
+                                           &args);
+               if (ret)
+                       return ret;
        }
+       return for_lookup_table_entry(wim->lookup_table,
+                                     lte_overwrite_prepare, &args);
 }
 
+struct stream_size_table {
+       struct hlist_head *array;
+       size_t num_entries;
+       size_t capacity;
+};
+
+static int
+init_stream_size_table(struct stream_size_table *tab, size_t capacity)
+{
+       tab->array = CALLOC(capacity, sizeof(tab->array[0]));
+       if (!tab->array)
+               return WIMLIB_ERR_NOMEM;
+       tab->num_entries = 0;
+       tab->capacity = capacity;
+       return 0;
+}
 
-static int dentry_find_streams_to_write(struct dentry *dentry,
-                                       void *wim)
+static void
+destroy_stream_size_table(struct stream_size_table *tab)
 {
-       WIMStruct *w = wim;
-       struct list_head *stream_list = w->private;
-       struct lookup_table_entry *lte;
-       for (unsigned i = 0; i <= dentry->d_inode->num_ads; i++) {
-               lte = inode_stream_lte(dentry->d_inode, i, w->lookup_table);
-               if (lte && ++lte->out_refcnt == 1)
-                       list_add(&lte->staging_list, stream_list);
+       FREE(tab->array);
+}
+
+static int
+stream_size_table_insert(struct wim_lookup_table_entry *lte, void *_tab)
+{
+       struct stream_size_table *tab = _tab;
+       size_t pos;
+       struct wim_lookup_table_entry *hashed_lte;
+       struct hlist_node *tmp;
+
+       pos = hash_u64(wim_resource_size(lte)) % tab->capacity;
+       lte->unique_size = 1;
+       hlist_for_each_entry(hashed_lte, tmp, &tab->array[pos], hash_list_2) {
+               if (wim_resource_size(hashed_lte) == wim_resource_size(lte)) {
+                       lte->unique_size = 0;
+                       hashed_lte->unique_size = 0;
+                       break;
+               }
        }
+
+       hlist_add_head(&lte->hash_list_2, &tab->array[pos]);
+       tab->num_entries++;
        return 0;
 }
 
-static int find_streams_to_write(WIMStruct *w)
+
+struct find_streams_ctx {
+       struct list_head stream_list;
+       struct stream_size_table stream_size_tab;
+};
+
+static int
+inode_find_streams_to_write(struct wim_inode *inode,
+                           struct wim_lookup_table *table,
+                           struct list_head *stream_list,
+                           struct stream_size_table *tab)
 {
-       return for_dentry_in_tree(wim_root_dentry(w),
-                                 dentry_find_streams_to_write, w);
+       struct wim_lookup_table_entry *lte;
+       for (unsigned i = 0; i <= inode->i_num_ads; i++) {
+               lte = inode_stream_lte(inode, i, table);
+               if (lte) {
+                       if (lte->out_refcnt == 0) {
+                               if (lte->unhashed)
+                                       stream_size_table_insert(lte, tab);
+                               list_add_tail(&lte->write_streams_list, stream_list);
+                       }
+                       lte->out_refcnt += inode->i_nlink;
+               }
+       }
+       return 0;
 }
 
-static int write_wim_streams(WIMStruct *w, int image, int write_flags)
+static int
+image_find_streams_to_write(WIMStruct *w)
 {
+       struct wim_image_metadata *imd;
+       struct find_streams_ctx *ctx;
+       struct wim_inode *inode;
+       struct wim_lookup_table_entry *lte;
+
+       ctx = w->private;
+       imd = wim_get_current_image_metadata(w);
+
+       image_for_each_unhashed_stream(lte, imd) {
+               lte->out_refcnt = 0;
+               wimlib_assert(lte->unhashed);
+               wimlib_assert(lte->my_ptr != NULL);
+       }
 
-       LIST_HEAD(stream_list);
+       /* Go through this image's inodes to find any streams that have not been
+        * found yet. */
+       image_for_each_inode(inode, imd) {
+               inode_find_streams_to_write(inode, w->lookup_table,
+                                           &ctx->stream_list,
+                                           &ctx->stream_size_tab);
+       }
+       return 0;
+}
+
+/* Given a WIM that from which one or all of the images is being written, build
+ * the list of unique streams ('struct wim_lookup_table_entry's) that must be
+ * written, plus any unhashed streams that need to be written but may be
+ * identical to other hashed or unhashed streams being written.  These unhashed
+ * streams are checksummed while the streams are being written.  To aid this
+ * process, the member @unique_size is set to 1 on streams that have a unique
+ * size and therefore must be written.
+ *
+ * The out_refcnt member of each 'struct wim_lookup_table_entry' is set to
+ * indicate the number of times the stream is referenced in only the streams
+ * that are being written; this may still be adjusted later when unhashed
+ * streams are being resolved.
+ */
+static int
+prepare_stream_list(WIMStruct *wim, int image, struct list_head *stream_list)
+{
+       int ret;
+       struct find_streams_ctx ctx;
+
+       for_lookup_table_entry(wim->lookup_table, lte_zero_out_refcnt, NULL);
+       ret = init_stream_size_table(&ctx.stream_size_tab, 9001);
+       if (ret)
+               return ret;
+       for_lookup_table_entry(wim->lookup_table, stream_size_table_insert,
+                              &ctx.stream_size_tab);
+       INIT_LIST_HEAD(&ctx.stream_list);
+       wim->private = &ctx;
+       for_image(wim, image, image_find_streams_to_write);
+       destroy_stream_size_table(&ctx.stream_size_tab);
+
+       INIT_LIST_HEAD(stream_list);
+       list_splice(&ctx.stream_list, stream_list);
+       return 0;
+}
 
-       w->private = &stream_list;
-       for_image(w, image, find_streams_to_write);
-       return write_stream_list(&stream_list, w->out_fp,
-                                wimlib_get_compression_type(w), write_flags);
+/* Writes the streams for the specified @image in @wim to @wim->out_fp.
+ */
+static int
+write_wim_streams(WIMStruct *wim, int image, int write_flags,
+                 unsigned num_threads,
+                 wimlib_progress_func_t progress_func)
+{
+       int ret;
+       struct list_head stream_list;
+
+       ret = prepare_stream_list(wim, image, &stream_list);
+       if (ret)
+               return ret;
+       return write_stream_list(&stream_list,
+                                wim->lookup_table,
+                                wim->out_fp,
+                                wimlib_get_compression_type(wim),
+                                write_flags,
+                                num_threads,
+                                progress_func);
 }
 
 /*
- * Write the lookup table, xml data, and integrity table, then overwrite the WIM
- * header.
+ * Finish writing a WIM file: write the lookup table, xml data, and integrity
+ * table (optional), then overwrite the WIM header.
+ *
+ * write_flags is a bitwise OR of the following:
+ *
+ *     (public)  WIMLIB_WRITE_FLAG_CHECK_INTEGRITY:
+ *             Include an integrity table.
+ *
+ *     (public)  WIMLIB_WRITE_FLAG_SHOW_PROGRESS:
+ *             Show progress information when (if) writing the integrity table.
+ *
+ *     (private) WIMLIB_WRITE_FLAG_NO_LOOKUP_TABLE:
+ *             Don't write the lookup table.
+ *
+ *     (private) WIMLIB_WRITE_FLAG_REUSE_INTEGRITY_TABLE:
+ *             When (if) writing the integrity table, re-use entries from the
+ *             existing integrity table, if possible.
+ *
+ *     (private) WIMLIB_WRITE_FLAG_CHECKPOINT_AFTER_XML:
+ *             After writing the XML data but before writing the integrity
+ *             table, write a temporary WIM header and flush the stream so that
+ *             the WIM is less likely to become corrupted upon abrupt program
+ *             termination.
+ *
+ *     (private) WIMLIB_WRITE_FLAG_FSYNC:
+ *             fsync() the output file before closing it.
+ *
  */
-int finish_write(WIMStruct *w, int image, int write_flags)
+int
+finish_write(WIMStruct *w, int image, int write_flags,
+            wimlib_progress_func_t progress_func)
 {
-       off_t lookup_table_offset;
-       off_t xml_data_offset;
-       off_t lookup_table_size;
-       off_t integrity_offset;
-       off_t xml_data_size;
-       off_t end_offset;
-       off_t integrity_size;
        int ret;
        struct wim_header hdr;
        FILE *out = w->out_fp;
 
-       if (!(write_flags & WIMLIB_WRITE_FLAG_NO_LOOKUP_TABLE)) {
-               /* Write the lookup table. */
-               lookup_table_offset = ftello(out);
-               if (lookup_table_offset == -1)
-                       return WIMLIB_ERR_WRITE;
-
-               DEBUG("Writing lookup table (offset %"PRIu64")",
-                     lookup_table_offset);
-               ret = write_lookup_table(w->lookup_table, out);
-               if (ret != 0)
-                       return ret;
-       }
-
-       xml_data_offset = ftello(out);
-       if (xml_data_offset == -1)
-               return WIMLIB_ERR_WRITE;
-
        /* @hdr will be the header for the new WIM.  First copy all the data
         * from the header in the WIMStruct; then set all the fields that may
         * have changed, including the resource entries, boot index, and image
         * count.  */
        memcpy(&hdr, &w->hdr, sizeof(struct wim_header));
+
        if (!(write_flags & WIMLIB_WRITE_FLAG_NO_LOOKUP_TABLE)) {
-               lookup_table_size = xml_data_offset - lookup_table_offset;
-               hdr.lookup_table_res_entry.offset = lookup_table_offset;
-               hdr.lookup_table_res_entry.size = lookup_table_size;
+               ret = write_lookup_table(w, image, &hdr.lookup_table_res_entry);
+               if (ret != 0)
+                       goto out;
        }
-       hdr.lookup_table_res_entry.original_size = hdr.lookup_table_res_entry.size;
-       hdr.lookup_table_res_entry.flags = WIM_RESHDR_FLAG_METADATA;
 
-       DEBUG("Writing XML data (offset %"PRIu64")", xml_data_offset);
        ret = write_xml_data(w->wim_info, image, out,
                             (write_flags & WIMLIB_WRITE_FLAG_NO_LOOKUP_TABLE) ?
-                               wim_info_get_total_bytes(w->wim_info) : 0);
+                             wim_info_get_total_bytes(w->wim_info) : 0,
+                            &hdr.xml_res_entry);
        if (ret != 0)
-               return ret;
+               goto out;
 
-       integrity_offset = ftello(out);
-       if (integrity_offset == -1)
-               return WIMLIB_ERR_WRITE;
-       xml_data_size = integrity_offset - xml_data_offset;
+       if (write_flags & WIMLIB_WRITE_FLAG_CHECK_INTEGRITY) {
+               if (write_flags & WIMLIB_WRITE_FLAG_CHECKPOINT_AFTER_XML) {
+                       struct wim_header checkpoint_hdr;
+                       memcpy(&checkpoint_hdr, &hdr, sizeof(struct wim_header));
+                       memset(&checkpoint_hdr.integrity, 0, sizeof(struct resource_entry));
+                       if (fseeko(out, 0, SEEK_SET) != 0) {
+                               ERROR_WITH_ERRNO("Failed to seek to beginning "
+                                                "of WIM being written");
+                               ret = WIMLIB_ERR_WRITE;
+                               goto out;
+                       }
+                       ret = write_header(&checkpoint_hdr, out);
+                       if (ret != 0)
+                               goto out;
 
-       hdr.xml_res_entry.offset                 = xml_data_offset;
-       hdr.xml_res_entry.size                   = xml_data_size;
-       hdr.xml_res_entry.original_size          = xml_data_size;
-       hdr.xml_res_entry.flags                  = 0;
+                       if (fflush(out) != 0) {
+                               ERROR_WITH_ERRNO("Can't write data to WIM");
+                               ret = WIMLIB_ERR_WRITE;
+                               goto out;
+                       }
 
-       if (write_flags & WIMLIB_WRITE_FLAG_CHECK_INTEGRITY) {
-               ret = write_integrity_table(out, WIM_HEADER_DISK_SIZE,
-                                           xml_data_offset,
-                                           write_flags & WIMLIB_WRITE_FLAG_SHOW_PROGRESS);
+                       if (fseeko(out, 0, SEEK_END) != 0) {
+                               ERROR_WITH_ERRNO("Failed to seek to end "
+                                                "of WIM being written");
+                               ret = WIMLIB_ERR_WRITE;
+                               goto out;
+                       }
+               }
+
+               off_t old_lookup_table_end;
+               off_t new_lookup_table_end;
+               if (write_flags & WIMLIB_WRITE_FLAG_REUSE_INTEGRITY_TABLE) {
+                       old_lookup_table_end = w->hdr.lookup_table_res_entry.offset +
+                                              w->hdr.lookup_table_res_entry.size;
+               } else {
+                       old_lookup_table_end = 0;
+               }
+               new_lookup_table_end = hdr.lookup_table_res_entry.offset +
+                                      hdr.lookup_table_res_entry.size;
+
+               ret = write_integrity_table(out,
+                                           &hdr.integrity,
+                                           new_lookup_table_end,
+                                           old_lookup_table_end,
+                                           progress_func);
                if (ret != 0)
-                       return ret;
-               end_offset = ftello(out);
-               if (end_offset == -1)
-                       return WIMLIB_ERR_WRITE;
-               integrity_size              = end_offset - integrity_offset;
-               hdr.integrity.offset        = integrity_offset;
-               hdr.integrity.size          = integrity_size;
-               hdr.integrity.original_size = integrity_size;
+                       goto out;
        } else {
-               hdr.integrity.offset        = 0;
-               hdr.integrity.size          = 0;
-               hdr.integrity.original_size = 0;
+               memset(&hdr.integrity, 0, sizeof(struct resource_entry));
        }
-       hdr.integrity.flags = 0;
-
-       DEBUG("Updating WIM header.");
 
        /*
         * In the WIM header, there is room for the resource entry for a
@@ -1593,19 +1669,9 @@ int finish_write(WIMStruct *w, int image, int write_flags)
         * it should be a copy of the resource entry for the image that is
         * marked as bootable.  This is not well documented...
         */
-       if (hdr.boot_idx == 0 || !w->image_metadata
-                       || (image != WIM_ALL_IMAGES && image != hdr.boot_idx)) {
-               memset(&hdr.boot_metadata_res_entry, 0,
-                      sizeof(struct resource_entry));
-       } else {
-               memcpy(&hdr.boot_metadata_res_entry,
-                      &w->image_metadata[
-                         hdr.boot_idx - 1].metadata_lte->output_resource_entry,
-                      sizeof(struct resource_entry));
-       }
 
        /* Set image count and boot index correctly for single image writes */
-       if (image != WIM_ALL_IMAGES) {
+       if (image != WIMLIB_ALL_IMAGES) {
                hdr.image_count = 1;
                if (hdr.boot_idx == image)
                        hdr.boot_idx = 1;
@@ -1613,104 +1679,443 @@ int finish_write(WIMStruct *w, int image, int write_flags)
                        hdr.boot_idx = 0;
        }
 
+       if (hdr.boot_idx == 0) {
+               memset(&hdr.boot_metadata_res_entry, 0,
+                      sizeof(struct resource_entry));
+       } else {
+               memcpy(&hdr.boot_metadata_res_entry,
+                      &w->image_metadata[
+                         hdr.boot_idx - 1]->metadata_lte->output_resource_entry,
+                      sizeof(struct resource_entry));
+       }
 
-       if (fseeko(out, 0, SEEK_SET) != 0)
-               return WIMLIB_ERR_WRITE;
+       if (fseeko(out, 0, SEEK_SET) != 0) {
+               ERROR_WITH_ERRNO("Failed to seek to beginning of WIM "
+                                "being written");
+               ret = WIMLIB_ERR_WRITE;
+               goto out;
+       }
 
        ret = write_header(&hdr, out);
-       if (ret != 0)
-               return ret;
+       if (ret)
+               goto out;
 
-       DEBUG("Closing output file.");
-       wimlib_assert(w->out_fp != NULL);
-       if (fclose(w->out_fp) != 0) {
+       if (write_flags & WIMLIB_WRITE_FLAG_FSYNC) {
+               if (fflush(out) != 0
+                   || fsync(fileno(out)) != 0)
+               {
+                       ERROR_WITH_ERRNO("Error flushing data to WIM file");
+                       ret = WIMLIB_ERR_WRITE;
+               }
+       }
+out:
+       if (fclose(out) != 0) {
                ERROR_WITH_ERRNO("Failed to close the WIM file");
-               ret = WIMLIB_ERR_WRITE;
+               if (ret == 0)
+                       ret = WIMLIB_ERR_WRITE;
        }
        w->out_fp = NULL;
        return ret;
 }
 
-/* Open file stream and write dummy header for WIM. */
-int begin_write(WIMStruct *w, const char *path, int write_flags)
+#if defined(HAVE_SYS_FILE_H) && defined(HAVE_FLOCK)
+int
+lock_wim(WIMStruct *w, FILE *fp)
 {
-       const char *mode;
-       DEBUG("Opening `%s' for new WIM", path);
-
-       /* checking the integrity requires going back over the file to read it.
-        * XXX
-        * (It also would be possible to keep a running sha1sum as the file is
-        * written-- this would be faster, but a bit more complicated) */
-       if (write_flags & WIMLIB_WRITE_FLAG_CHECK_INTEGRITY)
-               mode = "w+b";
-       else
-               mode = "wb";
+       int ret = 0;
+       if (fp && !w->wim_locked) {
+               ret = flock(fileno(fp), LOCK_EX | LOCK_NB);
+               if (ret != 0) {
+                       if (errno == EWOULDBLOCK) {
+                               ERROR("`%"TS"' is already being modified or has been "
+                                     "mounted read-write\n"
+                                     "        by another process!", w->filename);
+                               ret = WIMLIB_ERR_ALREADY_LOCKED;
+                       } else {
+                               WARNING_WITH_ERRNO("Failed to lock `%"TS"'",
+                                                  w->filename);
+                               ret = 0;
+                       }
+               } else {
+                       w->wim_locked = 1;
+               }
+       }
+       return ret;
+}
+#endif
 
-       if (w->out_fp)
-               fclose(w->out_fp);
+static int
+open_wim_writable(WIMStruct *w, const tchar *path,
+                 bool trunc, bool also_readable)
+{
+       const tchar *mode;
+       if (trunc)
+               if (also_readable)
+                       mode = T("w+b");
+               else
+                       mode = T("wb");
+       else
+               mode = T("r+b");
 
-       w->out_fp = fopen(path, mode);
-       if (!w->out_fp) {
-               ERROR_WITH_ERRNO("Failed to open the file `%s' for writing",
-                                path);
+       wimlib_assert(w->out_fp == NULL);
+       w->out_fp = tfopen(path, mode);
+       if (w->out_fp) {
+               return 0;
+       } else {
+               ERROR_WITH_ERRNO("Failed to open `%"TS"' for writing", path);
                return WIMLIB_ERR_OPEN;
        }
+}
+
 
+void
+close_wim_writable(WIMStruct *w)
+{
+       if (w->out_fp) {
+               if (fclose(w->out_fp) != 0) {
+                       WARNING_WITH_ERRNO("Failed to close output WIM");
+               }
+               w->out_fp = NULL;
+       }
+}
+
+/* Open file stream and write dummy header for WIM. */
+int
+begin_write(WIMStruct *w, const tchar *path, int write_flags)
+{
+       int ret;
+       ret = open_wim_writable(w, path, true,
+                               (write_flags & WIMLIB_WRITE_FLAG_CHECK_INTEGRITY) != 0);
+       if (ret != 0)
+               return ret;
        /* Write dummy header. It will be overwritten later. */
        return write_header(&w->hdr, w->out_fp);
 }
 
 /* Writes a stand-alone WIM to a file.  */
-WIMLIBAPI int wimlib_write(WIMStruct *w, const char *path,
-                          int image, int write_flags)
+WIMLIBAPI int
+wimlib_write(WIMStruct *w, const tchar *path,
+            int image, int write_flags, unsigned num_threads,
+            wimlib_progress_func_t progress_func)
 {
        int ret;
 
-       if (!w || !path)
+       if (!path)
                return WIMLIB_ERR_INVALID_PARAM;
 
-       write_flags &= ~WIMLIB_WRITE_FLAG_NO_LOOKUP_TABLE;
+       write_flags &= WIMLIB_WRITE_MASK_PUBLIC;
 
-       if (image != WIM_ALL_IMAGES &&
+       if (image != WIMLIB_ALL_IMAGES &&
             (image < 1 || image > w->hdr.image_count))
                return WIMLIB_ERR_INVALID_IMAGE;
 
-
        if (w->hdr.total_parts != 1) {
                ERROR("Cannot call wimlib_write() on part of a split WIM");
                return WIMLIB_ERR_SPLIT_UNSUPPORTED;
        }
 
-       if (image == WIM_ALL_IMAGES)
-               DEBUG("Writing all images to `%s'.", path);
-       else
-               DEBUG("Writing image %d to `%s'.", image, path);
-
        ret = begin_write(w, path, write_flags);
+       if (ret)
+               goto out;
+
+       ret = write_wim_streams(w, image, write_flags, num_threads,
+                               progress_func);
+       if (ret)
+               goto out;
+
+       if (progress_func)
+               progress_func(WIMLIB_PROGRESS_MSG_WRITE_METADATA_BEGIN, NULL);
+
+       ret = for_image(w, image, write_metadata_resource);
+       if (ret)
+               goto out;
+
+       if (progress_func)
+               progress_func(WIMLIB_PROGRESS_MSG_WRITE_METADATA_END, NULL);
+
+       ret = finish_write(w, image, write_flags, progress_func);
+out:
+       close_wim_writable(w);
+       DEBUG("wimlib_write(path=%"TS") = %d", path, ret);
+       return ret;
+}
+
+static bool
+any_images_modified(WIMStruct *w)
+{
+       for (int i = 0; i < w->hdr.image_count; i++)
+               if (w->image_metadata[i]->modified)
+                       return true;
+       return false;
+}
+
+/*
+ * Overwrite a WIM, possibly appending streams to it.
+ *
+ * A WIM looks like (or is supposed to look like) the following:
+ *
+ *                   Header (212 bytes)
+ *                   Streams and metadata resources (variable size)
+ *                   Lookup table (variable size)
+ *                   XML data (variable size)
+ *                   Integrity table (optional) (variable size)
+ *
+ * If we are not adding any streams or metadata resources, the lookup table is
+ * unchanged--- so we only need to overwrite the XML data, integrity table, and
+ * header.  This operation is potentially unsafe if the program is abruptly
+ * terminated while the XML data or integrity table are being overwritten, but
+ * before the new header has been written.  To partially alleviate this problem,
+ * a special flag (WIMLIB_WRITE_FLAG_CHECKPOINT_AFTER_XML) is passed to
+ * finish_write() to cause a temporary WIM header to be written after the XML
+ * data has been written.  This may prevent the WIM from becoming corrupted if
+ * the program is terminated while the integrity table is being calculated (but
+ * no guarantees, due to write re-ordering...).
+ *
+ * If we are adding new streams or images (metadata resources), the lookup table
+ * needs to be changed, and those streams need to be written.  In this case, we
+ * try to perform a safe update of the WIM file by writing the streams *after*
+ * the end of the previous WIM, then writing the new lookup table, XML data, and
+ * (optionally) integrity table following the new streams.  This will produce a
+ * layout like the following:
+ *
+ *                   Header (212 bytes)
+ *                   (OLD) Streams and metadata resources (variable size)
+ *                   (OLD) Lookup table (variable size)
+ *                   (OLD) XML data (variable size)
+ *                   (OLD) Integrity table (optional) (variable size)
+ *                   (NEW) Streams and metadata resources (variable size)
+ *                   (NEW) Lookup table (variable size)
+ *                   (NEW) XML data (variable size)
+ *                   (NEW) Integrity table (optional) (variable size)
+ *
+ * At all points, the WIM is valid as nothing points to the new data yet.  Then,
+ * the header is overwritten to point to the new lookup table, XML data, and
+ * integrity table, to produce the following layout:
+ *
+ *                   Header (212 bytes)
+ *                   Streams and metadata resources (variable size)
+ *                   Nothing (variable size)
+ *                   More Streams and metadata resources (variable size)
+ *                   Lookup table (variable size)
+ *                   XML data (variable size)
+ *                   Integrity table (optional) (variable size)
+ *
+ * This method allows an image to be appended to a large WIM very quickly, and
+ * is is crash-safe except in the case of write re-ordering, but the
+ * disadvantage is that a small hole is left in the WIM where the old lookup
+ * table, xml data, and integrity table were.  (These usually only take up a
+ * small amount of space compared to the streams, however.)
+ */
+static int
+overwrite_wim_inplace(WIMStruct *w, int write_flags,
+                     unsigned num_threads,
+                     wimlib_progress_func_t progress_func)
+{
+       int ret;
+       struct list_head stream_list;
+       off_t old_wim_end;
+
+       DEBUG("Overwriting `%"TS"' in-place", w->filename);
+
+       /* Make sure that the integrity table (if present) is after the XML
+        * data, and that there are no stream resources, metadata resources, or
+        * lookup tables after the XML data.  Otherwise, these data would be
+        * overwritten. */
+       if (w->hdr.integrity.offset != 0 &&
+           w->hdr.integrity.offset < w->hdr.xml_res_entry.offset) {
+               ERROR("Didn't expect the integrity table to be before the XML data");
+               return WIMLIB_ERR_RESOURCE_ORDER;
+       }
+
+       if (w->hdr.lookup_table_res_entry.offset > w->hdr.xml_res_entry.offset) {
+               ERROR("Didn't expect the lookup table to be after the XML data");
+               return WIMLIB_ERR_RESOURCE_ORDER;
+       }
+
+
+       if (w->hdr.integrity.offset)
+               old_wim_end = w->hdr.integrity.offset + w->hdr.integrity.size;
+       else
+               old_wim_end = w->hdr.xml_res_entry.offset + w->hdr.xml_res_entry.size;
+
+       if (!w->deletion_occurred && !any_images_modified(w)) {
+               /* If no images have been modified and no images have been
+                * deleted, a new lookup table does not need to be written. */
+               old_wim_end = w->hdr.lookup_table_res_entry.offset +
+                             w->hdr.lookup_table_res_entry.size;
+               write_flags |= WIMLIB_WRITE_FLAG_NO_LOOKUP_TABLE |
+                              WIMLIB_WRITE_FLAG_CHECKPOINT_AFTER_XML;
+       }
+       INIT_LIST_HEAD(&stream_list);
+       ret = wim_prepare_streams(w, old_wim_end, &stream_list);
        if (ret != 0)
                return ret;
 
-       for_lookup_table_entry(w->lookup_table, lte_zero_out_refcnt, NULL);
-
-       ret = write_wim_streams(w, image, write_flags);
+       ret = open_wim_writable(w, w->filename, false,
+                               (write_flags & WIMLIB_WRITE_FLAG_CHECK_INTEGRITY) != 0);
+       if (ret != 0)
+               return ret;
 
+       ret = lock_wim(w, w->out_fp);
        if (ret != 0) {
-               /*ERROR("Failed to write WIM file resources to `%s'", path);*/
+               fclose(w->out_fp);
+               w->out_fp = NULL;
                return ret;
        }
 
-       ret = for_image(w, image, write_metadata_resource);
+       if (fseeko(w->out_fp, old_wim_end, SEEK_SET) != 0) {
+               ERROR_WITH_ERRNO("Can't seek to end of WIM");
+               fclose(w->out_fp);
+               w->out_fp = NULL;
+               w->wim_locked = 0;
+               return WIMLIB_ERR_WRITE;
+       }
+
+       if (!list_empty(&stream_list)) {
+               DEBUG("Writing newly added streams (offset = %"PRIu64")",
+                     old_wim_end);
+               ret = write_stream_list(&stream_list,
+                                       w->lookup_table,
+                                       w->out_fp,
+                                       wimlib_get_compression_type(w),
+                                       write_flags, num_threads,
+                                       progress_func);
+               if (ret != 0)
+                       goto out_ftruncate;
+       } else {
+               DEBUG("No new streams were added");
+       }
+
+       for (int i = 0; i < w->hdr.image_count; i++) {
+               if (w->image_metadata[i]->modified) {
+                       select_wim_image(w, i + 1);
+                       ret = write_metadata_resource(w);
+                       if (ret)
+                               goto out_ftruncate;
+               }
+       }
+       write_flags |= WIMLIB_WRITE_FLAG_REUSE_INTEGRITY_TABLE;
+       ret = finish_write(w, WIMLIB_ALL_IMAGES, write_flags,
+                          progress_func);
+out_ftruncate:
+       close_wim_writable(w);
+       if (ret != 0 && !(write_flags & WIMLIB_WRITE_FLAG_NO_LOOKUP_TABLE)) {
+               WARNING("Truncating `%"TS"' to its original size (%"PRIu64" bytes)",
+                       w->filename, old_wim_end);
+               /* Return value of truncate() is ignored because this is already
+                * an error path. */
+               (void)ttruncate(w->filename, old_wim_end);
+       }
+       w->wim_locked = 0;
+       return ret;
+}
+
+static int
+overwrite_wim_via_tmpfile(WIMStruct *w, int write_flags,
+                         unsigned num_threads,
+                         wimlib_progress_func_t progress_func)
+{
+       size_t wim_name_len;
+       int ret;
+
+       DEBUG("Overwriting `%"TS"' via a temporary file", w->filename);
+
+       /* Write the WIM to a temporary file in the same directory as the
+        * original WIM. */
+       wim_name_len = tstrlen(w->filename);
+       tchar tmpfile[wim_name_len + 10];
+       tmemcpy(tmpfile, w->filename, wim_name_len);
+       randomize_char_array_with_alnum(tmpfile + wim_name_len, 9);
+       tmpfile[wim_name_len + 9] = T('\0');
 
+       ret = wimlib_write(w, tmpfile, WIMLIB_ALL_IMAGES,
+                          write_flags | WIMLIB_WRITE_FLAG_FSYNC,
+                          num_threads, progress_func);
        if (ret != 0) {
-               /*ERROR("Failed to write WIM image metadata to `%s'", path);*/
-               return ret;
+               ERROR("Failed to write the WIM file `%"TS"'", tmpfile);
+               goto err;
        }
 
-       ret = finish_write(w, image, write_flags);
-       if (ret != 0)
-               return ret;
+       DEBUG("Renaming `%"TS"' to `%"TS"'", tmpfile, w->filename);
 
-       if (write_flags & WIMLIB_WRITE_FLAG_VERBOSE)
-               printf("Successfully wrote `%s'\n", path);
-       return 0;
+#ifdef __WIN32__
+       /* Windows won't let you delete open files unless FILE_SHARE_DELETE was
+        * specified to CreateFile().  The WIM was opened with fopen(), which
+        * didn't provided this flag to CreateFile, so the handle must be closed
+        * before executing the rename(). */
+       if (w->fp != NULL) {
+               fclose(w->fp);
+               w->fp = NULL;
+       }
+#endif
+
+       /* Rename the new file to the old file .*/
+       if (trename(tmpfile, w->filename) != 0) {
+               ERROR_WITH_ERRNO("Failed to rename `%"TS"' to `%"TS"'",
+                                tmpfile, w->filename);
+               ret = WIMLIB_ERR_RENAME;
+               goto err;
+       }
+
+       if (progress_func) {
+               union wimlib_progress_info progress;
+               progress.rename.from = tmpfile;
+               progress.rename.to = w->filename;
+               progress_func(WIMLIB_PROGRESS_MSG_RENAME, &progress);
+       }
+
+       /* Close the original WIM file that was opened for reading. */
+       if (w->fp != NULL) {
+               fclose(w->fp);
+               w->fp = NULL;
+       }
+
+       /* Re-open the WIM read-only. */
+       w->fp = tfopen(w->filename, T("rb"));
+       if (w->fp == NULL) {
+               ret = WIMLIB_ERR_REOPEN;
+               WARNING_WITH_ERRNO("Failed to re-open `%"TS"' read-only",
+                                  w->filename);
+               FREE(w->filename);
+               w->filename = NULL;
+       }
+       return ret;
+err:
+       /* Remove temporary file. */
+       if (tunlink(tmpfile) != 0)
+               WARNING_WITH_ERRNO("Failed to remove `%"TS"'", tmpfile);
+       return ret;
+}
+
+/*
+ * Writes a WIM file to the original file that it was read from, overwriting it.
+ */
+WIMLIBAPI int
+wimlib_overwrite(WIMStruct *w, int write_flags,
+                unsigned num_threads,
+                wimlib_progress_func_t progress_func)
+{
+       write_flags &= WIMLIB_WRITE_MASK_PUBLIC;
+
+       if (!w->filename)
+               return WIMLIB_ERR_NO_FILENAME;
+
+       if (w->hdr.total_parts != 1) {
+               ERROR("Cannot modify a split WIM");
+               return WIMLIB_ERR_SPLIT_UNSUPPORTED;
+       }
+
+       if ((!w->deletion_occurred || (write_flags & WIMLIB_WRITE_FLAG_SOFT_DELETE))
+           && !(write_flags & WIMLIB_WRITE_FLAG_REBUILD))
+       {
+               int ret;
+               ret = overwrite_wim_inplace(w, write_flags, num_threads,
+                                           progress_func);
+               if (ret == WIMLIB_ERR_RESOURCE_ORDER)
+                       WARNING("Falling back to re-building entire WIM");
+               else
+                       return ret;
+       }
+       return overwrite_wim_via_tmpfile(w, write_flags, num_threads,
+                                        progress_func);
 }