]> wimlib.net Git - wimlib/blobdiff - src/write.c
Use pthread condition variables instead of semaphores
[wimlib] / src / write.c
index 668c7abd03c0c21353aa2ec65cd4c6adb1a4e40d..5b586ceea23f8795cff7c28623ce2ff573df59a1 100644 (file)
  * 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
+
+#include "list.h"
 #include "wimlib_internal.h"
 #include "io.h"
 #include "dentry.h"
 #include "xml.h"
 #include "lzx.h"
 #include "xpress.h"
-#include <unistd.h>
 
 #ifdef ENABLE_MULTITHREADED_COMPRESSION
-#include <semaphore.h>
 #include <pthread.h>
-#include <errno.h>
 #endif
 
+#include <unistd.h>
+#include <errno.h>
+
 #ifdef WITH_NTFS_3G
 #include <time.h>
 #include <ntfs-3g/attrib.h>
 #include <ntfs-3g/dir.h>
 #endif
 
-
 #ifdef HAVE_ALLOCA_H
 #include <alloca.h>
 #else
 #include <stdlib.h>
 #endif
 
-/* 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;
-}
-
 
-
-/*
- * 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)
+static int do_fflush(FILE *fp)
 {
-       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,
-                          num_threads);
+       int 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_SHOW_PROGRESS)
-               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;
+               ERROR_WITH_ERRNO("Failed to flush data to output WIM file");
+               return WIMLIB_ERR_WRITE;
        }
        return 0;
 }
 
-WIMLIBAPI int wimlib_overwrite_xml_and_header(WIMStruct *w, int write_flags)
+static int fflush_and_ftruncate(FILE *fp, off_t size)
 {
        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);
-               return WIMLIB_ERR_WRITE;
-       }
-
-       ret = write_header(&w->hdr, fp);
+       ret = do_fflush(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.) */
@@ -376,19 +148,8 @@ 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.
+ * Pointer to function to compresses a chunk of a WIM resource.
  *
  * @chunk:             Uncompressed data of the chunk.
  * @chunk_size:                Size of the uncompressed chunk in bytes.
@@ -397,21 +158,19 @@ compress_func_t get_compress_func(int out_ctype)
  * @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.
  *
  * 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.
  */
-static int compress_chunk(const u8 chunk[], unsigned chunk_size,
-                         u8 compressed_chunk[],
-                         unsigned *compressed_chunk_len_ret,
-                         int ctype)
+typedef int (*compress_func_t)(const void *, unsigned, void *, unsigned *);
+
+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 lzx_compress;
+       else
+               return xpress_compress;
 }
 
 /*
@@ -428,23 +187,17 @@ static int compress_chunk(const u8 chunk[], unsigned chunk_size,
  * 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,
+                                   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 (chunk_tab) {
                u8 *compressed_chunk = alloca(chunk_size);
                int ret;
 
-               ret = compress_chunk(chunk, chunk_size, compressed_chunk,
-                                    &out_chunk_size, out_ctype);
+               ret = compress(chunk, chunk_size, compressed_chunk,
+                              &out_chunk_size);
                if (ret == 0) {
                        out_chunk = compressed_chunk;
                } else {
@@ -453,8 +206,10 @@ static int write_wim_resource_chunk(const u8 chunk[], unsigned chunk_size,
                }
                *chunk_tab->cur_offset_p++ = chunk_tab->cur_offset;
                chunk_tab->cur_offset += out_chunk_size;
+       } else {
+               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;
@@ -503,6 +258,8 @@ finish_wim_resource_chunk_tab(struct chunk_table *chunk_tab,
        return 0;
 }
 
+/* Prepare for multiple reads to a resource by caching a FILE * or NTFS
+ * attribute pointer in the lookup table entry. */
 static int prepare_resource_for_read(struct lookup_table_entry *lte
 
                                        #ifdef WITH_NTFS_3G
@@ -550,6 +307,8 @@ static int prepare_resource_for_read(struct lookup_table_entry *lte
        return 0;
 }
 
+/* Undo prepare_resource_for_read() by closing the cached FILE * or NTFS
+ * attribute. */
 static void end_wim_resource_read(struct lookup_table_entry *lte
                                #ifdef WITH_NTFS_3G
                                        , ntfs_inode *ni
@@ -608,6 +367,7 @@ int write_wim_resource(struct lookup_table_entry *lte,
        struct chunk_table *chunk_tab = NULL;
        bool raw;
        off_t file_offset;
+       compress_func_t compress = NULL;
 #ifdef WITH_NTFS_3G
        ntfs_inode *ni = NULL;
 #endif
@@ -631,7 +391,8 @@ int write_wim_resource(struct lookup_table_entry *lte,
        /* 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);
+              && out_ctype != WIMLIB_COMPRESSION_TYPE_NONE
+              && !(flags & WIMLIB_RESOURCE_FLAG_RECOMPRESS));
 
        if (raw) {
                flags |= WIMLIB_RESOURCE_FLAG_RAW;
@@ -650,7 +411,7 @@ int write_wim_resource(struct lookup_table_entry *lte,
 
        /* 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) {
+       if (out_ctype != WIMLIB_COMPRESSION_TYPE_NONE && !raw) {
                ret = begin_wim_resource_chunk_tab(lte, out_fp, file_offset,
                                                   &chunk_tab);
                if (ret != 0)
@@ -673,13 +434,15 @@ int write_wim_resource(struct lookup_table_entry *lte,
         * hash given in the lookup table entry once we've finished reading the
         * resource. */
        SHA_CTX ctx;
-       if (!raw)
+       if (!raw) {
                sha1_init(&ctx);
+               compress = get_compress_func(out_ctype);
+       }
+       offset = 0;
 
        /* 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);
@@ -688,7 +451,7 @@ int write_wim_resource(struct lookup_table_entry *lte,
                if (!raw)
                        sha1_update(&ctx, buf, to_read);
                ret = write_wim_resource_chunk(buf, to_read, out_fp,
-                                              out_ctype, chunk_tab);
+                                              compress, chunk_tab);
                if (ret != 0)
                        goto out_fclose;
                bytes_remaining -= to_read;
@@ -698,7 +461,7 @@ int write_wim_resource(struct lookup_table_entry *lte,
        /* 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
+        * Using WIMLIB_COMPRESSION_TYPE_NONE:  The new compressed size is the
         * original size
         *
         * Using a different compression type:  Call
@@ -708,7 +471,7 @@ int write_wim_resource(struct lookup_table_entry *lte,
        if (raw) {
                new_compressed_size = old_compressed_size;
        } else {
-               if (out_ctype == WIM_COMPRESSION_TYPE_NONE)
+               if (out_ctype == WIMLIB_COMPRESSION_TYPE_NONE)
                        new_compressed_size = original_size;
                else {
                        ret = finish_wim_resource_chunk_tab(chunk_tab, out_fp,
@@ -740,7 +503,7 @@ int write_wim_resource(struct lookup_table_entry *lte,
        }
 
        if (!raw && new_compressed_size >= original_size &&
-           out_ctype != WIM_COMPRESSION_TYPE_NONE)
+           out_ctype != WIMLIB_COMPRESSION_TYPE_NONE)
        {
                /* Oops!  We compressed the resource to larger than the original
                 * size.  Write the resource uncompressed instead. */
@@ -750,20 +513,14 @@ int write_wim_resource(struct lookup_table_entry *lte,
                        ret = WIMLIB_ERR_WRITE;
                        goto out_fclose;
                }
-               ret = write_wim_resource(lte, out_fp, WIM_COMPRESSION_TYPE_NONE,
+               ret = write_wim_resource(lte, out_fp, WIMLIB_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;
+
+               ret = fflush_and_ftruncate(out_fp, file_offset + out_res_entry->size);
+               if (ret != 0)
                        goto out_fclose;
-               }
        } else {
                if (out_res_entry) {
                        out_res_entry->size          = new_compressed_size;
@@ -771,7 +528,7 @@ int write_wim_resource(struct lookup_table_entry *lte,
                        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)
+                       if (out_ctype != WIMLIB_COMPRESSION_TYPE_NONE)
                                out_res_entry->flags |= WIM_RESHDR_FLAG_COMPRESSED;
                }
        }
@@ -787,16 +544,16 @@ out:
        return ret;
 }
 
-
 #ifdef ENABLE_MULTITHREADED_COMPRESSION
 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)
@@ -804,57 +561,56 @@ static int shared_queue_init(struct shared_queue *q, unsigned size)
        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)
 {
-       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)
 {
-       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)
 {
-       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;
@@ -907,62 +663,61 @@ static void *compressor_thread_proc(void *arg)
                shared_queue_put(compressed_res_queue, msg);
        }
        DEBUG("Compressor thread terminating");
+       return NULL;
 }
 #endif
 
-static void show_stream_write_progress(u64 *cur_size, u64 *next_size,
-                                      u64 total_size, u64 one_percent,
-                                      unsigned *cur_percent,
-                                      const struct lookup_table_entry *cur_lte)
-{
-       if (*cur_size >= *next_size) {
-               printf("\r%"PRIu64" MiB of %"PRIu64" MiB "
-                      "(uncompressed) written (%u%% done)",
-                      *cur_size >> 20,
-                      total_size >> 20, *cur_percent);
-               fflush(stdout);
-               *next_size += one_percent;
-               (*cur_percent)++;
-       }
-       *cur_size += wim_resource_size(cur_lte);
-}
-
-static void finish_stream_write_progress(u64 total_size)
-{
-       printf("\r%"PRIu64" MiB of %"PRIu64" MiB "
-              "(uncompressed) written (100%% done)\n",
-              total_size >> 20, total_size >> 20);
-       fflush(stdout);
-}
-
-static int write_stream_list_serial(struct list_head *stream_list,
-                                   FILE *out_fp, int out_ctype,
-                                   int write_flags, u64 total_size)
+static int do_write_stream_list(struct list_head *my_resources,
+                               FILE *out_fp,
+                               int out_ctype,
+                               wimlib_progress_func_t progress_func,
+                               union wimlib_progress_info *progress,
+                               int write_resource_flags)
 {
-       struct lookup_table_entry *lte;
        int ret;
-
-       u64 one_percent = total_size / 100;
-       u64 cur_size = 0;
-       u64 next_size = 0;
-       unsigned cur_percent = 0;
-
-       list_for_each_entry(lte, stream_list, staging_list) {
-               if (write_flags & WIMLIB_WRITE_FLAG_SHOW_PROGRESS) {
-                       show_stream_write_progress(&cur_size, &next_size,
-                                                  total_size, one_percent,
-                                                  &cur_percent, lte);
-               }
-               ret = write_wim_resource(lte, out_fp, out_ctype,
-                                        &lte->output_resource_entry, 0);
+       struct lookup_table_entry *lte, *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,
+                                        write_resource_flags);
                if (ret != 0)
                        return ret;
+               list_del(&lte->staging_list);
+               progress->write_streams.completed_bytes +=
+                       wim_resource_size(lte);
+               progress->write_streams.completed_streams++;
+               if (progress_func) {
+                       progress_func(WIMLIB_PROGRESS_MSG_WRITE_STREAMS,
+                                     progress);
+               }
        }
-       if (write_flags & WIMLIB_WRITE_FLAG_SHOW_PROGRESS)
-               finish_stream_write_progress(total_size);
        return 0;
 }
 
+static int write_stream_list_serial(struct list_head *stream_list,
+                                   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, 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)
@@ -976,7 +731,7 @@ static int write_wim_chunks(struct message *msg, FILE *out_fp,
                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;
                }
 
@@ -1005,11 +760,11 @@ static int main_writer_thread_proc(struct list_head *stream_list,
                                   struct shared_queue *compressed_res_queue,
                                   size_t queue_size,
                                   int write_flags,
-                                  u64 total_size)
+                                  wimlib_progress_func_t progress_func,
+                                  union wimlib_progress_info *progress)
 {
        int ret;
 
-
        struct message msgs[queue_size];
        ZERO_ARRAY(msgs);
 
@@ -1055,14 +810,8 @@ static int main_writer_thread_proc(struct list_head *stream_list,
 
        struct lookup_table_entry *cur_lte = next_lte;
        struct chunk_table *cur_chunk_tab = NULL;
-       struct lookup_table_entry *lte;
        struct message *msg;
 
-       u64 one_percent = total_size / 100;
-       u64 cur_size = 0;
-       u64 next_size = 0;
-       unsigned cur_percent = 0;
-
 #ifdef WITH_NTFS_3G
        ntfs_inode *ni = NULL;
 #endif
@@ -1203,8 +952,9 @@ static int main_writer_thread_proc(struct list_head *stream_list,
                                                        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)
+                               if ((!(write_flags & WIMLIB_WRITE_FLAG_RECOMPRESS)
+                                     && 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,
@@ -1264,14 +1014,6 @@ static int main_writer_thread_proc(struct list_head *stream_list,
                        DEBUG2("Complete msg (begin_chunk=%"PRIu64")", msg->begin_chunk);
                        if (msg->begin_chunk == 0) {
                                DEBUG2("Begin chunk tab");
-                               if (write_flags & WIMLIB_WRITE_FLAG_SHOW_PROGRESS) {
-                                       show_stream_write_progress(&cur_size,
-                                                                  &next_size,
-                                                                  total_size,
-                                                                  one_percent,
-                                                                  &cur_percent,
-                                                                  cur_lte);
-                               }
 
                                // This is the first set of chunks.  Leave space
                                // for the chunk table in the output file.
@@ -1312,6 +1054,14 @@ static int main_writer_thread_proc(struct list_head *stream_list,
                                if (ret != 0)
                                        goto out;
 
+                               progress->write_streams.completed_bytes +=
+                                               wim_resource_size(cur_lte);
+                               progress->write_streams.completed_streams++;
+
+                               if (progress_func) {
+                                       progress_func(WIMLIB_PROGRESS_MSG_WRITE_STREAMS,
+                                                     progress);
+                               }
 
                                cur_lte->output_resource_entry.size =
                                        res_csize;
@@ -1349,30 +1099,14 @@ 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)
-                               {
-                                       if (write_flags & WIMLIB_WRITE_FLAG_SHOW_PROGRESS) {
-                                               show_stream_write_progress(&cur_size,
-                                                                          &next_size,
-                                                                          total_size,
-                                                                          one_percent,
-                                                                          &cur_percent,
-                                                                          lte);
-                                       }
-
-                                       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;
                        }
                }
        }
@@ -1384,24 +1118,9 @@ out:
        end_wim_resource_read(cur_lte);
 #endif
        if (ret == 0) {
-               list_for_each_entry(lte, &my_resources, staging_list) {
-                       if (write_flags & WIMLIB_WRITE_FLAG_SHOW_PROGRESS) {
-                               show_stream_write_progress(&cur_size,
-                                                          &next_size,
-                                                          total_size,
-                                                          one_percent,
-                                                          &cur_percent,
-                                                          lte);
-                       }
-                       ret = write_wim_resource(lte, out_fp,
-                                                out_ctype,
-                                                &lte->output_resource_entry,
-                                                0);
-                       if (ret != 0)
-                               break;
-               }
-               if (write_flags & WIMLIB_WRITE_FLAG_SHOW_PROGRESS)
-                       finish_stream_write_progress(total_size);
+               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;
@@ -1416,8 +1135,6 @@ out:
                }
        }
 
-       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]);
@@ -1431,22 +1148,13 @@ out:
 }
 
 
-static const char *get_data_type(int ctype)
-{
-       switch (ctype) {
-       case WIM_COMPRESSION_TYPE_NONE:
-               return "uncompressed";
-       case WIM_COMPRESSION_TYPE_LZX:
-               return "LZX-compressed";
-       case WIM_COMPRESSION_TYPE_XPRESS:
-               return "XPRESS-compressed";
-       }
-}
-
 static int write_stream_list_parallel(struct list_head *stream_list,
-                                     FILE *out_fp, int out_ctype,
-                                     int write_flags, u64 total_size,
-                                     unsigned num_threads)
+                                     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;
        struct shared_queue res_to_compress_queue;
@@ -1463,9 +1171,9 @@ static int write_stream_list_parallel(struct list_head *stream_list,
                }
        }
 
+       progress->write_streams.num_threads = num_threads;
        wimlib_assert(stream_list->next != stream_list);
 
-
        static const double MESSAGES_PER_THREAD = 2.0;
        size_t queue_size = (size_t)(num_threads * MESSAGES_PER_THREAD);
 
@@ -1499,10 +1207,8 @@ static int write_stream_list_parallel(struct list_head *stream_list,
                }
        }
 
-       if (write_flags & WIMLIB_WRITE_FLAG_SHOW_PROGRESS) {
-               printf("Writing %s compressed data using %u threads...\n",
-                      get_data_type(out_ctype), num_threads);
-       }
+       if (progress_func)
+               progress_func(WIMLIB_PROGRESS_MSG_WRITE_STREAMS, progress);
 
        ret = main_writer_thread_proc(stream_list,
                                      out_fp,
@@ -1511,8 +1217,8 @@ static int write_stream_list_parallel(struct list_head *stream_list,
                                      &compressed_res_queue,
                                      queue_size,
                                      write_flags,
-                                     total_size);
-
+                                     progress_func,
+                                     progress);
 out_join:
        for (unsigned i = 0; i < num_threads; i++)
                shared_queue_put(&res_to_compress_queue, NULL);
@@ -1531,60 +1237,78 @@ 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, total_size);
+       return write_stream_list_serial(stream_list,
+                                       out_fp,
+                                       out_ctype,
+                                       write_flags,
+                                       progress_func,
+                                       progress);
+
 }
 #endif
 
+/*
+ * 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, FILE *out_fp,
                             int out_ctype, int write_flags,
-                            unsigned num_threads)
+                            unsigned num_threads,
+                            wimlib_progress_func_t progress_func)
 {
        struct lookup_table_entry *lte;
        size_t num_streams = 0;
-       u64 total_size = 0;
+       u64 total_bytes = 0;
        bool compression_needed = false;
+       union wimlib_progress_info progress;
+       int ret;
 
        list_for_each_entry(lte, stream_list, staging_list) {
                num_streams++;
-               total_size += wim_resource_size(lte);
+               total_bytes += 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)
+                   &&
+                   (out_ctype != WIMLIB_COMPRESSION_TYPE_NONE
+                      && (lte->resource_location != RESOURCE_IN_WIM
+                          || wimlib_get_compression_type(lte->wim) != out_ctype
+                          || (write_flags & WIMLIB_WRITE_FLAG_REBUILD)))
                    && 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));
+       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;
+
+       if (num_streams == 0) {
+               ret = 0;
+               goto out;
        }
 
 #ifdef ENABLE_MULTITHREADED_COMPRESSION
-       if (compression_needed && total_size >= 1000000 && num_threads != 1) {
-               return write_stream_list_parallel(stream_list, out_fp,
-                                                 out_ctype, write_flags,
-                                                 total_size, num_threads);
+       if (compression_needed && total_bytes >= 1000000 && num_threads != 1) {
+               ret = write_stream_list_parallel(stream_list,
+                                                out_fp,
+                                                out_ctype,
+                                                write_flags,
+                                                num_threads,
+                                                progress_func,
+                                                &progress);
        }
        else
 #endif
        {
-               if (write_flags & WIMLIB_WRITE_FLAG_SHOW_PROGRESS) {
-                       const char *reason = "";
-                       if (!compression_needed)
-                               reason = " (no compression needed)";
-                       printf("Writing %s data using 1 thread%s\n",
-                              get_data_type(out_ctype), reason);
-               }
-
-               return write_stream_list_serial(stream_list, out_fp,
-                                               out_ctype, write_flags,
-                                               total_size);
+               ret = write_stream_list_serial(stream_list,
+                                              out_fp,
+                                              out_ctype,
+                                              write_flags,
+                                              progress_func,
+                                              &progress);
        }
+out:
+       return ret;
 }
 
 
@@ -1597,7 +1321,7 @@ static int dentry_find_streams_to_write(struct dentry *dentry,
        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);
+                       list_add_tail(&lte->staging_list, stream_list);
        }
        return 0;
 }
@@ -1609,103 +1333,120 @@ static int find_streams_to_write(WIMStruct *w)
 }
 
 static int write_wim_streams(WIMStruct *w, int image, int write_flags,
-                            unsigned num_threads)
+                            unsigned num_threads,
+                            wimlib_progress_func_t progress_func)
 {
 
+       for_lookup_table_entry(w->lookup_table, lte_zero_out_refcnt, NULL);
        LIST_HEAD(stream_list);
-
        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,
-                                num_threads);
+                                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->lookup_table, out, &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) {
+                               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) {
+                               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
@@ -1715,7 +1456,7 @@ int finish_write(WIMStruct *w, int image, int write_flags)
         * marked as bootable.  This is not well documented...
         */
        if (hdr.boot_idx == 0 || !w->image_metadata
-                       || (image != WIM_ALL_IMAGES && image != hdr.boot_idx)) {
+                       || (image != WIMLIB_ALL_IMAGES && image != hdr.boot_idx)) {
                memset(&hdr.boot_metadata_res_entry, 0,
                       sizeof(struct resource_entry));
        } else {
@@ -1726,7 +1467,7 @@ int finish_write(WIMStruct *w, int image, int write_flags)
        }
 
        /* 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;
@@ -1734,107 +1475,456 @@ int finish_write(WIMStruct *w, int image, int write_flags)
                        hdr.boot_idx = 0;
        }
 
-
-       if (fseeko(out, 0, SEEK_SET) != 0)
-               return WIMLIB_ERR_WRITE;
+       if (fseeko(out, 0, SEEK_SET) != 0) {
+               ret = WIMLIB_ERR_WRITE;
+               goto out;
+       }
 
        ret = write_header(&hdr, out);
        if (ret != 0)
-               return 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(FILE *fp, const char *path)
 {
-       const char *mode;
-       DEBUG("Opening `%s' for new WIM", path);
+       int ret = 0;
+       if (fp) {
+               ret = flock(fileno(fp), LOCK_EX | LOCK_NB);
+               if (ret != 0) {
+                       if (errno == EWOULDBLOCK) {
+                               ERROR("`%s' is already being modified or has been "
+                                     "mounted read-write\n"
+                                     "        by another process!", path);
+                               ret = WIMLIB_ERR_ALREADY_LOCKED;
+                       } else {
+                               WARNING("Failed to lock `%s': %s",
+                                       path, strerror(errno));
+                               ret = 0;
+                       }
+               }
+       }
+       return ret;
+}
+#endif
 
-       /* 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";
+static int open_wim_writable(WIMStruct *w, const char *path,
+                            bool trunc, bool readable)
+{
+       const char *mode;
+       int ret = 0;
+       if (trunc)
+               if (readable)
+                       mode = "w+b";
+               else
+                       mode = "wb";
        else
-               mode = "wb";
-
-       if (w->out_fp)
-               fclose(w->out_fp);
+               mode = "r+b";
 
+       DEBUG("Opening `%s' read-write", path);
+       wimlib_assert(w->out_fp == NULL);
+       wimlib_assert(path != NULL);
        w->out_fp = fopen(path, mode);
        if (!w->out_fp) {
-               ERROR_WITH_ERRNO("Failed to open the file `%s' for writing",
-                                path);
+               ERROR_WITH_ERRNO("Failed to open `%s' for writing", path);
                return WIMLIB_ERR_OPEN;
        }
+       if (trunc) {
+               ret = lock_wim(w->out_fp, path);
+               if (ret != 0) {
+                       fclose(w->out_fp);
+                       w->out_fp = NULL;
+               }
+       }
+       return ret;
+}
+
+
+static void close_wim_writable(WIMStruct *w)
+{
+       if (w->out_fp) {
+               if (fclose(w->out_fp) != 0) {
+                       WARNING("Failed to close output WIM: %s",
+                               strerror(errno));
+               }
+               w->out_fp = NULL;
+       }
+}
+
+/* Open file stream and write dummy header for WIM. */
+int begin_write(WIMStruct *w, const char *path, int write_flags)
+{
+       int ret;
+       bool need_readable = false;
+       bool trunc = true;
+       if (write_flags & WIMLIB_WRITE_FLAG_CHECK_INTEGRITY)
+               need_readable = true;
 
+       ret = open_wim_writable(w, path, trunc, need_readable);
+       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, unsigned num_threads)
+                          int image, int write_flags, unsigned num_threads,
+                          wimlib_progress_func_t progress_func)
 {
        int ret;
 
        if (!w || !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);
+       ret = begin_write(w, path, write_flags);
+       if (ret != 0)
+               goto out;
+
+       ret = write_wim_streams(w, image, write_flags, num_threads,
+                               progress_func);
+       if (ret != 0)
+               goto out;
+
+       if (progress_func)
+               progress_func(WIMLIB_PROGRESS_MSG_WRITE_METADATA_BEGIN, NULL);
+
+       ret = for_image(w, image, write_metadata_resource);
+       if (ret != 0)
+               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);
+       return ret;
+}
+
+static int lte_overwrite_prepare(struct lookup_table_entry *lte,
+                                void *ignore)
+{
+       memcpy(&lte->output_resource_entry, &lte->resource_entry,
+              sizeof(struct resource_entry));
+       lte->out_refcnt = 0;
+       return 0;
+}
+
+static int check_resource_offset(struct lookup_table_entry *lte, void *arg)
+{
+       off_t end_offset = *(u64*)arg;
+
+       wimlib_assert(lte->out_refcnt <= lte->refcnt);
+       if (lte->out_refcnt < lte->refcnt) {
+               if (lte->resource_entry.offset + lte->resource_entry.size > end_offset) {
+                       ERROR("The following resource is after the XML data:");
+                       print_lookup_table_entry(lte);
+                       return WIMLIB_ERR_RESOURCE_ORDER;
+               }
+       }
+       return 0;
+}
+
+static int find_new_streams(struct lookup_table_entry *lte, void *arg)
+{
+       if (lte->out_refcnt == lte->refcnt)
+               list_add(&lte->staging_list, (struct list_head*)arg);
        else
-               DEBUG("Writing image %d to `%s'.", image, path);
+               lte->out_refcnt = lte->refcnt;
+       return 0;
+}
 
-       ret = begin_write(w, path, write_flags);
+/*
+ * 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 modified_image_idx)
+{
+       int ret;
+       struct list_head stream_list;
+       off_t old_wim_end;
+
+       DEBUG("Overwriting `%s' 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;
+       }
+
+       DEBUG("Identifying newly added streams");
+       for_lookup_table_entry(w->lookup_table, lte_overwrite_prepare, NULL);
+       INIT_LIST_HEAD(&stream_list);
+       for (int i = modified_image_idx; i < w->hdr.image_count; i++) {
+               DEBUG("Identifiying streams in image %d", i + 1);
+               wimlib_assert(w->image_metadata[i].modified);
+               wimlib_assert(!w->image_metadata[i].has_been_mounted_rw);
+               wimlib_assert(w->image_metadata[i].root_dentry != NULL);
+               wimlib_assert(w->image_metadata[i].metadata_lte != NULL);
+               w->private = &stream_list;
+               for_dentry_in_tree(w->image_metadata[i].root_dentry,
+                                  dentry_find_streams_to_write, w);
+       }
+
+       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;
+
+       ret = for_lookup_table_entry(w->lookup_table, check_resource_offset,
+                                    &old_wim_end);
        if (ret != 0)
                return ret;
 
-       for_lookup_table_entry(w->lookup_table, lte_zero_out_refcnt, NULL);
+       if (modified_image_idx == w->hdr.image_count && !w->deletion_occurred) {
+               /* If no images have been modified and no images have been
+                * deleted, a new lookup table does not need to be written. */
+               wimlib_assert(list_empty(&stream_list));
+               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;
+       }
 
-       ret = write_wim_streams(w, image, write_flags, num_threads);
+       INIT_LIST_HEAD(&stream_list);
+       for_lookup_table_entry(w->lookup_table, find_new_streams,
+                              &stream_list);
 
-       if (ret != 0) {
-               /*ERROR("Failed to write WIM file resources to `%s'", path);*/
+       ret = open_wim_writable(w, w->filename, false,
+                               (write_flags & WIMLIB_WRITE_FLAG_CHECK_INTEGRITY) != 0);
+       if (ret != 0)
                return ret;
+
+       if (fseeko(w->out_fp, old_wim_end, SEEK_SET) != 0) {
+               ERROR_WITH_ERRNO("Can't seek to end of WIM");
+               return WIMLIB_ERR_WRITE;
        }
 
-       if (write_flags & WIMLIB_WRITE_FLAG_SHOW_PROGRESS)
-               printf("Writing image metadata...\n");
+       if (!list_empty(&stream_list)) {
+               DEBUG("Writing newly added streams (offset = %"PRIu64")",
+                     old_wim_end);
+               ret = write_stream_list(&stream_list, 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");
+       }
 
-       ret = for_image(w, image, write_metadata_resource);
+       for (int i = modified_image_idx; i < w->hdr.image_count; i++) {
+               select_wim_image(w, i + 1);
+               ret = write_metadata_resource(w);
+               if (ret != 0)
+                       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) {
+               WARNING("Truncating `%s' to its original size (%"PRIu64" bytes)",
+                       w->filename, old_wim_end);
+               truncate(w->filename, old_wim_end);
+       }
+       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 `%s' via a temporary file", w->filename);
+
+       /* Write the WIM to a temporary file in the same directory as the
+        * original WIM. */
+       wim_name_len = strlen(w->filename);
+       char tmpfile[wim_name_len + 10];
+       memcpy(tmpfile, w->filename, wim_name_len);
+       randomize_char_array_with_alnum(tmpfile + wim_name_len, 9);
+       tmpfile[wim_name_len + 9] = '\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 `%s'", tmpfile);
+               goto err;
        }
 
-       ret = finish_write(w, image, write_flags);
-       if (ret != 0)
-               return ret;
+       /* Close the original WIM file that was opened for reading. */
+       if (w->fp != NULL) {
+               fclose(w->fp);
+               w->fp = NULL;
+       }
 
-       if (write_flags & WIMLIB_WRITE_FLAG_SHOW_PROGRESS)
-               printf("Successfully wrote `%s'\n", path);
-       return 0;
+       DEBUG("Renaming `%s' to `%s'", tmpfile, w->filename);
+
+       /* Rename the new file to the old file .*/
+       if (rename(tmpfile, w->filename) != 0) {
+               ERROR_WITH_ERRNO("Failed to rename `%s' to `%s'",
+                                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);
+       }
+
+       /* Re-open the WIM read-only. */
+       w->fp = fopen(w->filename, "rb");
+       if (w->fp == NULL) {
+               ret = WIMLIB_ERR_REOPEN;
+               WARNING("Failed to re-open `%s' read-only: %s",
+                       w->filename, strerror(errno));
+       }
+       return ret;
+err:
+       /* Remove temporary file. */
+       if (unlink(tmpfile) != 0)
+               WARNING("Failed to remove `%s': %s", tmpfile, strerror(errno));
+       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)
+{
+       if (!w)
+               return WIMLIB_ERR_INVALID_PARAM;
+
+       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 i, modified_image_idx;
+               for (i = 0; i < w->hdr.image_count && !w->image_metadata[i].modified; i++)
+                       ;
+               modified_image_idx = i;
+               for (; i < w->hdr.image_count && w->image_metadata[i].modified &&
+                       !w->image_metadata[i].has_been_mounted_rw; i++)
+                       ;
+               if (i == w->hdr.image_count) {
+                       return overwrite_wim_inplace(w, write_flags, num_threads,
+                                                    progress_func,
+                                                    modified_image_idx);
+               }
+       }
+       return overwrite_wim_via_tmpfile(w, write_flags, num_threads,
+                                        progress_func);
 }