]> wimlib.net Git - wimlib/blobdiff - src/write.c
Delay xml_update_image_info() until write
[wimlib] / src / write.c
index 879a3102ddce6e246e46716eea37c9af2f9d37a0..23dda573a3aff33e63836ae843ea2629eaf543c5 100644 (file)
@@ -28,7 +28,7 @@
 
 #if defined(HAVE_SYS_FILE_H) && defined(HAVE_FLOCK)
 /* On BSD, this should be included before "wimlib/list.h" so that "wimlib/list.h" can
- * overwrite the LIST_HEAD macro. */
+ * override the LIST_HEAD macro. */
 #  include <sys/file.h>
 #endif
 
@@ -118,7 +118,7 @@ blob_filtered(const struct blob_descriptor *blob,
        write_flags = ctx->write_flags;
        wim = ctx->wim;
 
-       if (write_flags & WIMLIB_WRITE_FLAG_OVERWRITE &&
+       if (write_flags & WIMLIB_WRITE_FLAG_APPEND &&
            blob->blob_location == BLOB_IN_WIM &&
            blob->rdesc->wim == wim)
                return 1;
@@ -138,60 +138,77 @@ blob_hard_filtered(const struct blob_descriptor *blob,
        return blob_filtered(blob, ctx) < 0;
 }
 
-static inline int
+static inline bool
 may_soft_filter_blobs(const struct filter_context *ctx)
 {
-       if (ctx == NULL)
-               return 0;
-       return ctx->write_flags & WIMLIB_WRITE_FLAG_OVERWRITE;
+       return ctx && (ctx->write_flags & WIMLIB_WRITE_FLAG_APPEND);
 }
 
-static inline int
+static inline bool
 may_hard_filter_blobs(const struct filter_context *ctx)
 {
-       if (ctx == NULL)
-               return 0;
-       return ctx->write_flags & WIMLIB_WRITE_FLAG_SKIP_EXTERNAL_WIMS;
+       return ctx && (ctx->write_flags & WIMLIB_WRITE_FLAG_SKIP_EXTERNAL_WIMS);
 }
 
-static inline int
+static inline bool
 may_filter_blobs(const struct filter_context *ctx)
 {
        return (may_soft_filter_blobs(ctx) || may_hard_filter_blobs(ctx));
 }
 
-/* Return true if the specified resource is compressed and the compressed data
- * can be reused with the specified output parameters.  */
+/* Return true if the specified blob is located in a WIM resource which can be
+ * reused in the output WIM file, without being recompressed.  */
 static bool
-can_raw_copy(const struct blob_descriptor *blob,
-            int write_resource_flags, int out_ctype, u32 out_chunk_size)
+can_raw_copy(const struct blob_descriptor *blob, int write_resource_flags,
+            int out_ctype, u32 out_chunk_size)
 {
        const struct wim_resource_descriptor *rdesc;
 
+       /* Recompress everything if requested.  */
        if (write_resource_flags & WRITE_RESOURCE_FLAG_RECOMPRESS)
                return false;
 
-       if (out_ctype == WIMLIB_COMPRESSION_TYPE_NONE)
-               return false;
-
+       /* A blob not located in a WIM resource cannot be reused.  */
        if (blob->blob_location != BLOB_IN_WIM)
                return false;
 
        rdesc = blob->rdesc;
 
-       if (rdesc->is_pipable != !!(write_resource_flags & WRITE_RESOURCE_FLAG_PIPABLE))
+       /* In the case of an in-place compaction, always reuse resources located
+        * in the WIM being compacted.  */
+       if (rdesc->wim->being_compacted)
+               return true;
+
+       /* Otherwise, only reuse compressed resources.  */
+       if (out_ctype == WIMLIB_COMPRESSION_TYPE_NONE ||
+           !(rdesc->flags & (WIM_RESHDR_FLAG_COMPRESSED |
+                             WIM_RESHDR_FLAG_SOLID)))
+               return false;
+
+       /* When writing a pipable WIM, we can only reuse pipable resources; and
+        * when writing a non-pipable WIM, we can only reuse non-pipable
+        * resources.  */
+       if (rdesc->is_pipable !=
+           !!(write_resource_flags & WRITE_RESOURCE_FLAG_PIPABLE))
                return false;
 
+       /* When writing a solid WIM, we can only reuse solid resources; and when
+        * writing a non-solid WIM, we can only reuse non-solid resources.  */
+       if (!!(rdesc->flags & WIM_RESHDR_FLAG_SOLID) !=
+           !!(write_resource_flags & WRITE_RESOURCE_FLAG_SOLID))
+               return false;
+
+       /* Note: it is theoretically possible to copy chunks of compressed data
+        * between non-solid, solid, and pipable resources.  However, we don't
+        * currently implement this optimization because it would be complex and
+        * would usually go unused.  */
+
        if (rdesc->flags & WIM_RESHDR_FLAG_COMPRESSED) {
-               /* Normal compressed resource: Must use same compression type
-                * and chunk size.  */
+               /* To re-use a non-solid resource, it must use the desired
+                * compression type and chunk size.  */
                return (rdesc->compression_type == out_ctype &&
                        rdesc->chunk_size == out_chunk_size);
-       }
-
-       if ((rdesc->flags & WIM_RESHDR_FLAG_SOLID) &&
-           (write_resource_flags & WRITE_RESOURCE_FLAG_SOLID))
-       {
+       } else {
                /* Solid resource: Such resources may contain multiple blobs,
                 * and in general only a subset of them need to be written.  As
                 * a heuristic, re-use the raw data if more than two-thirds the
@@ -202,6 +219,10 @@ can_raw_copy(const struct blob_descriptor *blob,
                 * check if they are compatible with @out_ctype and
                 * @out_chunk_size.  */
 
+               /* Did we already decide to reuse the resource?  */
+               if (rdesc->raw_copy_ok)
+                       return true;
+
                struct blob_descriptor *res_blob;
                u64 write_size = 0;
 
@@ -211,8 +232,6 @@ can_raw_copy(const struct blob_descriptor *blob,
 
                return (write_size > rdesc->uncompressed_size * 2 / 3);
        }
-
-       return false;
 }
 
 static u32
@@ -300,8 +319,8 @@ do_write_blobs_progress(struct write_blobs_progress_data *progress_data,
                progress->write_streams.completed_streams += complete_count;
        }
 
-       if (progress->write_streams.completed_bytes >= progress_data->next_progress)
-       {
+       if (progress->write_streams.completed_bytes >= progress_data->next_progress) {
+
                ret = call_progress(progress_data->progfunc,
                                    WIMLIB_PROGRESS_MSG_WRITE_STREAMS,
                                    progress,
@@ -309,32 +328,9 @@ do_write_blobs_progress(struct write_blobs_progress_data *progress_data,
                if (ret)
                        return ret;
 
-               if (progress_data->next_progress == progress->write_streams.total_bytes) {
-                       progress_data->next_progress = ~(u64)0;
-               } else {
-                       /* Handle rate-limiting of messages  */
-
-                       /* Send new message as soon as another 1/128 of the
-                        * total has been written.  (Arbitrary number.)  */
-                       progress_data->next_progress =
-                               progress->write_streams.completed_bytes +
-                                       progress->write_streams.total_bytes / 128;
-
-                       /* ... Unless that would be more than 5000000 bytes, in
-                        * which case send the next after the next 5000000
-                        * bytes.  (Another arbitrary number.)  */
-                       if (progress->write_streams.completed_bytes + 5000000 <
-                           progress_data->next_progress)
-                               progress_data->next_progress =
-                                       progress->write_streams.completed_bytes + 5000000;
-
-                       /* ... But always send a message as soon as we're
-                        * completely done.  */
-                       if (progress->write_streams.total_bytes <
-                           progress_data->next_progress)
-                               progress_data->next_progress =
-                                       progress->write_streams.total_bytes;
-               }
+               set_next_progress(progress->write_streams.completed_bytes,
+                                 progress->write_streams.total_bytes,
+                                 &progress_data->next_progress);
        }
        return 0;
 }
@@ -361,10 +357,6 @@ struct write_blobs_ctx {
 
        struct filter_context *filter_ctx;
 
-       /* Upper bound on the total number of bytes that need to be compressed.
-        * */
-       u64 num_bytes_to_compress;
-
        /* Pointer to the chunk_compressor implementation being used for
         * compressing chunks of data, or NULL if chunks are being written
         * uncompressed.  */
@@ -571,9 +563,9 @@ end_chunk_table(struct write_blobs_ctx *ctx, u64 res_actual_size,
                        hdr.chunk_size = cpu_to_le32(ctx->out_chunk_size);
                        hdr.compression_format = cpu_to_le32(ctx->out_ctype);
 
-                       BUILD_BUG_ON(WIMLIB_COMPRESSION_TYPE_XPRESS != 1);
-                       BUILD_BUG_ON(WIMLIB_COMPRESSION_TYPE_LZX != 2);
-                       BUILD_BUG_ON(WIMLIB_COMPRESSION_TYPE_LZMS != 3);
+                       STATIC_ASSERT(WIMLIB_COMPRESSION_TYPE_XPRESS == 1);
+                       STATIC_ASSERT(WIMLIB_COMPRESSION_TYPE_LZX == 2);
+                       STATIC_ASSERT(WIMLIB_COMPRESSION_TYPE_LZMS == 3);
 
                        ret = full_pwrite(ctx->out_fd, &hdr, sizeof(hdr),
                                          chunk_table_offset - sizeof(hdr));
@@ -647,6 +639,8 @@ do_done_with_blob(struct blob_descriptor *blob,
 {
        int ret;
        struct wim_inode *inode;
+       tchar *cookie1;
+       tchar *cookie2;
 
        if (!blob->may_send_done_with_file)
                return 0;
@@ -654,42 +648,18 @@ do_done_with_blob(struct blob_descriptor *blob,
        inode = blob->file_inode;
 
        wimlib_assert(inode != NULL);
-       wimlib_assert(inode->num_remaining_streams > 0);
-       if (--inode->num_remaining_streams > 0)
+       wimlib_assert(inode->i_num_remaining_streams > 0);
+       if (--inode->i_num_remaining_streams > 0)
                return 0;
 
-#ifdef __WIN32__
-       /* XXX: This logic really should be somewhere else.  */
-
-       /* We want the path to the file, but blob->file_on_disk might actually
-        * refer to a named data stream.  Temporarily strip the named data
-        * stream from the path.  */
-       wchar_t *p_colon = NULL;
-       wchar_t *p_question_mark = NULL;
-       const wchar_t *p_stream_name;
-
-       p_stream_name = path_stream_name(blob->file_on_disk);
-       if (unlikely(p_stream_name)) {
-               p_colon = (wchar_t *)(p_stream_name - 1);
-               wimlib_assert(*p_colon == L':');
-               *p_colon = L'\0';
-       }
-
-       /* We also should use a fake Win32 path instead of a NT path  */
-       if (!wcsncmp(blob->file_on_disk, L"\\??\\", 4)) {
-               p_question_mark = &blob->file_on_disk[1];
-               *p_question_mark = L'\\';
-       }
-#endif
+       cookie1 = progress_get_streamless_path(blob->file_on_disk);
+       cookie2 = progress_get_win32_path(blob->file_on_disk);
 
        ret = done_with_file(blob->file_on_disk, progfunc, progctx);
 
-#ifdef __WIN32__
-       if (p_colon)
-               *p_colon = L':';
-       if (p_question_mark)
-               *p_question_mark = L'?';
-#endif
+       progress_put_win32_path(cookie2);
+       progress_put_streamless_path(cookie1);
+
        return ret;
 }
 
@@ -795,7 +765,7 @@ write_blob_uncompressed(struct blob_descriptor *blob, struct filedes *out_fd)
        if (filedes_seek(out_fd, begin_offset) == -1)
                return 0;
 
-       ret = extract_full_blob_to_fd(blob, out_fd);
+       ret = extract_blob_to_fd(blob, out_fd);
        if (ret) {
                /* Error reading the uncompressed data.  */
                if (out_fd->offset == begin_offset &&
@@ -814,13 +784,9 @@ write_blob_uncompressed(struct blob_descriptor *blob, struct filedes *out_fd)
 
        wimlib_assert(out_fd->offset - begin_offset == blob->size);
 
-       if (out_fd->offset < end_offset &&
-           0 != ftruncate(out_fd->fd, out_fd->offset))
-       {
-               ERROR_WITH_ERRNO("Can't truncate output file to "
-                                "offset %"PRIu64, out_fd->offset);
-               return WIMLIB_ERR_WRITE;
-       }
+       /* We could ftruncate() the file to 'out_fd->offset' here, but there
+        * isn't much point.  Usually we will only be truncating by a few bytes
+        * and will just overwrite the data immediately.  */
 
        blob->out_reshdr.size_in_wim = blob->size;
        blob->out_reshdr.flags &= ~(WIM_RESHDR_FLAG_COMPRESSED |
@@ -1143,11 +1109,16 @@ write_blob_end_read(struct blob_descriptor *blob, int status, void *_ctx)
        return status;
 }
 
-/* Compute statistics about a list of blobs that will be written.
+/*
+ * Compute statistics about a list of blobs that will be written.
  *
  * Assumes the blobs are sorted such that all blobs located in each distinct WIM
- * (specified by WIMStruct) are together.  */
-static void
+ * (specified by WIMStruct) are together.
+ *
+ * For compactions, also verify that there are no overlapping resources.  This
+ * really should be checked earlier, but for now it's easiest to check here.
+ */
+static int
 compute_blob_list_stats(struct list_head *blob_list,
                        struct write_blobs_ctx *ctx)
 {
@@ -1156,15 +1127,32 @@ compute_blob_list_stats(struct list_head *blob_list,
        u64 num_blobs = 0;
        u64 total_parts = 0;
        WIMStruct *prev_wim_part = NULL;
+       const struct wim_resource_descriptor *prev_rdesc = NULL;
 
        list_for_each_entry(blob, blob_list, write_blobs_list) {
                num_blobs++;
                total_bytes += blob->size;
                if (blob->blob_location == BLOB_IN_WIM) {
-                       if (prev_wim_part != blob->rdesc->wim) {
-                               prev_wim_part = blob->rdesc->wim;
+                       const struct wim_resource_descriptor *rdesc = blob->rdesc;
+                       WIMStruct *wim = rdesc->wim;
+
+                       if (prev_wim_part != wim) {
+                               prev_wim_part = wim;
                                total_parts++;
                        }
+                       if (unlikely(wim->being_compacted) && rdesc != prev_rdesc) {
+                               if (prev_rdesc != NULL &&
+                                   rdesc->offset_in_wim <
+                                               prev_rdesc->offset_in_wim +
+                                               prev_rdesc->size_in_wim)
+                               {
+                                       WARNING("WIM file contains overlapping "
+                                               "resources!  Compaction is not "
+                                               "possible.");
+                                       return WIMLIB_ERR_RESOURCE_ORDER;
+                               }
+                               prev_rdesc = rdesc;
+                       }
                }
        }
        ctx->progress_data.progress.write_streams.total_bytes       = total_bytes;
@@ -1175,6 +1163,7 @@ compute_blob_list_stats(struct list_head *blob_list,
        ctx->progress_data.progress.write_streams.total_parts       = total_parts;
        ctx->progress_data.progress.write_streams.completed_parts   = 0;
        ctx->progress_data.next_progress = 0;
+       return 0;
 }
 
 /* Find blobs in @blob_list that can be copied to the output WIM in raw form
@@ -1182,14 +1171,12 @@ compute_blob_list_stats(struct list_head *blob_list,
  * @raw_copy_blobs.  Return the total uncompressed size of the blobs that need
  * to be compressed.  */
 static u64
-find_raw_copy_blobs(struct list_head *blob_list,
-                   int write_resource_flags,
-                   int out_ctype,
-                   u32 out_chunk_size,
+find_raw_copy_blobs(struct list_head *blob_list, int write_resource_flags,
+                   int out_ctype, u32 out_chunk_size,
                    struct list_head *raw_copy_blobs)
 {
        struct blob_descriptor *blob, *tmp;
-       u64 num_bytes_to_compress = 0;
+       u64 num_nonraw_bytes = 0;
 
        INIT_LIST_HEAD(raw_copy_blobs);
 
@@ -1199,23 +1186,17 @@ find_raw_copy_blobs(struct list_head *blob_list,
                        blob->rdesc->raw_copy_ok = 0;
 
        list_for_each_entry_safe(blob, tmp, blob_list, write_blobs_list) {
-               if (blob->blob_location == BLOB_IN_WIM &&
-                   blob->rdesc->raw_copy_ok)
-               {
-                       list_move_tail(&blob->write_blobs_list,
-                                      raw_copy_blobs);
-               } else if (can_raw_copy(blob, write_resource_flags,
-                                       out_ctype, out_chunk_size))
+               if (can_raw_copy(blob, write_resource_flags,
+                                out_ctype, out_chunk_size))
                {
                        blob->rdesc->raw_copy_ok = 1;
-                       list_move_tail(&blob->write_blobs_list,
-                                      raw_copy_blobs);
+                       list_move_tail(&blob->write_blobs_list, raw_copy_blobs);
                } else {
-                       num_bytes_to_compress += blob->size;
+                       num_nonraw_bytes += blob->size;
                }
        }
 
-       return num_bytes_to_compress;
+       return num_nonraw_bytes;
 }
 
 /* Copy a raw compressed resource located in another WIM file to the WIM file
@@ -1247,21 +1228,37 @@ write_raw_copy_resource(struct wim_resource_descriptor *in_rdesc,
        }
        in_fd = &in_rdesc->wim->in_fd;
        wimlib_assert(cur_read_offset != end_read_offset);
-       do {
 
-               bytes_to_read = min(sizeof(buf), end_read_offset - cur_read_offset);
+       if (likely(!in_rdesc->wim->being_compacted) ||
+           in_rdesc->offset_in_wim > out_fd->offset) {
+               do {
+                       bytes_to_read = min(sizeof(buf),
+                                           end_read_offset - cur_read_offset);
 
-               ret = full_pread(in_fd, buf, bytes_to_read, cur_read_offset);
-               if (ret)
-                       return ret;
+                       ret = full_pread(in_fd, buf, bytes_to_read,
+                                        cur_read_offset);
+                       if (ret)
+                               return ret;
 
-               ret = full_write(out_fd, buf, bytes_to_read);
-               if (ret)
-                       return ret;
+                       ret = full_write(out_fd, buf, bytes_to_read);
+                       if (ret)
+                               return ret;
 
-               cur_read_offset += bytes_to_read;
+                       cur_read_offset += bytes_to_read;
 
-       } while (cur_read_offset != end_read_offset);
+               } while (cur_read_offset != end_read_offset);
+       } else {
+               /* Optimization: the WIM file is being compacted and the
+                * resource being written is already in the desired location.
+                * Skip over the data instead of re-writing it.  */
+
+               /* Due the earlier check for overlapping resources, it should
+                * never be the case that we already overwrote the resource.  */
+               wimlib_assert(!(in_rdesc->offset_in_wim < out_fd->offset));
+
+               if (-1 == filedes_seek(out_fd, out_fd->offset + in_rdesc->size_in_wim))
+                       return WIMLIB_ERR_WRITE;
+       }
 
        list_for_each_entry(blob, &in_rdesc->blob_list, rdesc_node) {
                if (blob->will_be_in_output_wim) {
@@ -1333,19 +1330,13 @@ finish_remaining_chunks(struct write_blobs_ctx *ctx)
 }
 
 static void
-remove_empty_blobs(struct list_head *blob_list)
+validate_blob_list(struct list_head *blob_list)
 {
-       struct blob_descriptor *blob, *tmp;
+       struct blob_descriptor *blob;
 
-       list_for_each_entry_safe(blob, tmp, blob_list, write_blobs_list) {
+       list_for_each_entry(blob, blob_list, write_blobs_list) {
                wimlib_assert(blob->will_be_in_output_wim);
-               if (blob->size == 0) {
-                       list_del(&blob->write_blobs_list);
-                       blob->out_reshdr.offset_in_wim = 0;
-                       blob->out_reshdr.size_in_wim = 0;
-                       blob->out_reshdr.uncompressed_size = 0;
-                       blob->out_reshdr.flags = reshdr_flags_for_blob(blob);
-               }
+               wimlib_assert(blob->size != 0);
        }
 }
 
@@ -1367,7 +1358,7 @@ init_done_with_file_info(struct list_head *blob_list)
 
        list_for_each_entry(blob, blob_list, write_blobs_list) {
                if (blob_is_in_file(blob)) {
-                       blob->file_inode->num_remaining_streams = 0;
+                       blob->file_inode->i_num_remaining_streams = 0;
                        blob->may_send_done_with_file = 1;
                } else {
                        blob->may_send_done_with_file = 0;
@@ -1376,7 +1367,7 @@ init_done_with_file_info(struct list_head *blob_list)
 
        list_for_each_entry(blob, blob_list, write_blobs_list)
                if (blob->may_send_done_with_file)
-                       blob->file_inode->num_remaining_streams++;
+                       blob->file_inode->i_num_remaining_streams++;
 }
 
 /*
@@ -1473,9 +1464,9 @@ init_done_with_file_info(struct list_head *blob_list)
  * identical to another blob already being written or one that would be filtered
  * out of the output WIM using blob_filtered() with the context @filter_ctx.
  * Each such duplicate blob will be removed from @blob_list, its reference count
- * transfered to the pre-existing duplicate blob, its memory freed, and will not
- * be written.  Alternatively, if a blob in @blob_list is a duplicate with any
- * blob in @blob_table that has not been marked for writing or would not be
+ * transferred to the pre-existing duplicate blob, its memory freed, and will
+ * not be written.  Alternatively, if a blob in @blob_list is a duplicate with
+ * any blob in @blob_table that has not been marked for writing or would not be
  * hard-filtered, it is freed and the pre-existing duplicate is written instead,
  * taking ownership of the reference count and slot in the @blob_table_list.
  *
@@ -1497,6 +1488,7 @@ write_blob_list(struct list_head *blob_list,
        int ret;
        struct write_blobs_ctx ctx;
        struct list_head raw_copy_blobs;
+       u64 num_nonraw_bytes;
 
        wimlib_assert((write_resource_flags &
                       (WRITE_RESOURCE_FLAG_SOLID |
@@ -1504,7 +1496,7 @@ write_blob_list(struct list_head *blob_list,
                                (WRITE_RESOURCE_FLAG_SOLID |
                                 WRITE_RESOURCE_FLAG_PIPABLE));
 
-       remove_empty_blobs(blob_list);
+       validate_blob_list(blob_list);
 
        if (list_empty(blob_list))
                return 0;
@@ -1542,7 +1534,9 @@ write_blob_list(struct list_head *blob_list,
        if (ret)
                return ret;
 
-       compute_blob_list_stats(blob_list, &ctx);
+       ret = compute_blob_list_stats(blob_list, &ctx);
+       if (ret)
+               return ret;
 
        if (write_resource_flags & WRITE_RESOURCE_FLAG_SOLID_SORT) {
                ret = sort_blob_list_for_solid_compression(blob_list);
@@ -1553,14 +1547,17 @@ write_blob_list(struct list_head *blob_list,
        ctx.progress_data.progfunc = progfunc;
        ctx.progress_data.progctx = progctx;
 
-       ctx.num_bytes_to_compress = find_raw_copy_blobs(blob_list,
-                                                       write_resource_flags,
-                                                       out_ctype,
-                                                       out_chunk_size,
-                                                       &raw_copy_blobs);
+       num_nonraw_bytes = find_raw_copy_blobs(blob_list, write_resource_flags,
+                                              out_ctype, out_chunk_size,
+                                              &raw_copy_blobs);
+
+       /* Copy any compressed resources for which the raw data can be reused
+        * without decompression.  */
+       ret = write_raw_copy_resources(&raw_copy_blobs, ctx.out_fd,
+                                      &ctx.progress_data);
 
-       if (ctx.num_bytes_to_compress == 0)
-               goto out_write_raw_copy_resources;
+       if (ret || num_nonraw_bytes == 0)
+               goto out_destroy_context;
 
        /* Unless uncompressed output was required, allocate a chunk_compressor
         * to do compression.  There are serial and parallel implementations of
@@ -1570,7 +1567,7 @@ write_blob_list(struct list_head *blob_list,
        if (out_ctype != WIMLIB_COMPRESSION_TYPE_NONE) {
 
        #ifdef ENABLE_MULTITHREADED_COMPRESSION
-               if (ctx.num_bytes_to_compress > max(2000000, out_chunk_size)) {
+               if (num_nonraw_bytes > max(2000000, out_chunk_size)) {
                        ret = new_parallel_chunk_compressor(out_ctype,
                                                            out_chunk_size,
                                                            num_threads, 0,
@@ -1607,7 +1604,7 @@ write_blob_list(struct list_head *blob_list,
                goto out_destroy_context;
 
        if (write_resource_flags & WRITE_RESOURCE_FLAG_SOLID) {
-               ret = begin_write_resource(&ctx, ctx.num_bytes_to_compress);
+               ret = begin_write_resource(&ctx, num_nonraw_bytes);
                if (ret)
                        goto out_destroy_context;
        }
@@ -1615,13 +1612,11 @@ write_blob_list(struct list_head *blob_list,
        /* Read the list of blobs needing to be compressed, using the specified
         * callbacks to execute processing of the data.  */
 
-       struct read_blob_list_callbacks cbs = {
-               .begin_blob             = write_blob_begin_read,
-               .begin_blob_ctx         = &ctx,
-               .consume_chunk          = write_blob_process_chunk,
-               .consume_chunk_ctx      = &ctx,
-               .end_blob               = write_blob_end_read,
-               .end_blob_ctx           = &ctx,
+       struct read_blob_callbacks cbs = {
+               .begin_blob     = write_blob_begin_read,
+               .consume_chunk  = write_blob_process_chunk,
+               .end_blob       = write_blob_end_read,
+               .ctx            = &ctx,
        };
 
        ret = read_blob_list(blob_list,
@@ -1662,12 +1657,6 @@ write_blob_list(struct list_head *blob_list,
                wimlib_assert(offset_in_res == reshdr.uncompressed_size);
        }
 
-out_write_raw_copy_resources:
-       /* Copy any compressed resources for which the raw data can be reused
-        * without decompression.  */
-       ret = write_raw_copy_resources(&raw_copy_blobs, ctx.out_fd,
-                                      &ctx.progress_data);
-
 out_destroy_context:
        FREE(ctx.chunk_csizes);
        if (ctx.compressor)
@@ -1689,16 +1678,6 @@ write_file_data_blobs(WIMStruct *wim,
 
        write_resource_flags = write_flags_to_resource_flags(write_flags);
 
-       /* wimlib v1.7.0: create a solid WIM file by default if the WIM version
-        * has been set to WIM_VERSION_SOLID and at least one blob in the WIM's
-        * blob table is located in a solid resource (may be the same WIM, or a
-        * different one in the case of export).  */
-       if (wim->out_hdr.wim_version == WIM_VERSION_SOLID &&
-           wim_has_solid_resources(wim))
-       {
-               write_resource_flags |= WRITE_RESOURCE_FLAG_SOLID;
-       }
-
        if (write_resource_flags & WRITE_RESOURCE_FLAG_SOLID) {
                out_chunk_size = wim->out_solid_chunk_size;
                out_ctype = wim->out_solid_compression_type;
@@ -1757,6 +1736,13 @@ write_wim_resource_from_buffer(const void *buf,
        int ret;
        struct blob_descriptor blob;
 
+       if (unlikely(buf_size == 0)) {
+               zero_reshdr(out_reshdr);
+               if (hash_ret)
+                       copy_hash(hash_ret, zero_hash);
+               return 0;
+       }
+
        blob_set_is_located_in_attached_buffer(&blob, (void *)buf, buf_size);
        sha1_buffer(buf, buf_size, blob.hash);
        blob.unhashed = 0;
@@ -2031,9 +2017,9 @@ filter_blob_list_for_write(struct list_head *blob_list,
  *     STREAMS_OK:  For writes of all images, assume that all blobs in the blob
  *     table of @wim and the per-image lists of unhashed blobs should be taken
  *     as-is, and image metadata should not be searched for references.  This
- *     does not exclude filtering with OVERWRITE and SKIP_EXTERNAL_WIMS, below.
+ *     does not exclude filtering with APPEND and SKIP_EXTERNAL_WIMS, below.
  *
- *     OVERWRITE:  Blobs already present in @wim shall not be returned in
+ *     APPEND:  Blobs already present in @wim shall not be returned in
  *     @blob_list_ret.
  *
  *     SKIP_EXTERNAL_WIMS:  Blobs already present in a WIM file, but not @wim,
@@ -2053,9 +2039,9 @@ filter_blob_list_for_write(struct list_head *blob_list,
  *     the blobs in @blob_list_ret.
  *
  *     This list will be a proper superset of @blob_list_ret if and only if
- *     WIMLIB_WRITE_FLAG_OVERWRITE was specified in @write_flags and some of
- *     the blobs that would otherwise need to be written were already located
- *     in the WIM file.
+ *     WIMLIB_WRITE_FLAG_APPEND was specified in @write_flags and some of the
+ *     blobs that would otherwise need to be written were already located in
+ *     the WIM file.
  *
  *     All blobs in this list will have @out_refcnt set to the number of
  *     references to the blob in the output WIM.  If
@@ -2193,16 +2179,28 @@ write_metadata_resources(WIMStruct *wim, int image, int write_flags)
                struct wim_image_metadata *imd;
 
                imd = wim->image_metadata[i - 1];
-               /* Build a new metadata resource only if image was modified from
-                * the original (or was newly added).  Otherwise just copy the
-                * existing one.  */
-               if (imd->modified) {
+               if (is_image_dirty(imd)) {
+                       /* The image was modified from the original, or was
+                        * newly added, so we have to build and write a new
+                        * metadata resource.  */
                        ret = write_metadata_resource(wim, i,
                                                      write_resource_flags);
-               } else if (write_flags & WIMLIB_WRITE_FLAG_OVERWRITE) {
-                       blob_set_out_reshdr_for_reuse(imd->metadata_blob);
+               } else if (is_image_unchanged_from_wim(imd, wim) &&
+                          (write_flags & (WIMLIB_WRITE_FLAG_UNSAFE_COMPACT |
+                                          WIMLIB_WRITE_FLAG_APPEND)))
+               {
+                       /* The metadata resource is already in the WIM file.
+                        * For appends, we don't need to write it at all.  For
+                        * compactions, we re-write existing metadata resources
+                        * along with the existing file resources, not here.  */
+                       if (write_flags & WIMLIB_WRITE_FLAG_APPEND)
+                               blob_set_out_reshdr_for_reuse(imd->metadata_blob);
                        ret = 0;
                } else {
+                       /* The metadata resource is in a WIM file other than the
+                        * one being written to.  We need to rewrite it,
+                        * possibly compressed differently; but rebuilding the
+                        * metadata itself isn't necessary.  */
                        ret = write_wim_resource(imd->metadata_blob,
                                                 &wim->out_fd,
                                                 wim->out_compression_type,
@@ -2274,7 +2272,7 @@ write_blob_table(WIMStruct *wim, int image, int write_flags,
        int ret;
 
        /* Set output resource metadata for blobs already present in WIM.  */
-       if (write_flags & WIMLIB_WRITE_FLAG_OVERWRITE) {
+       if (write_flags & WIMLIB_WRITE_FLAG_APPEND) {
                struct blob_descriptor *blob;
                list_for_each_entry(blob, blob_table_list, blob_table_list) {
                        if (blob->blob_location == BLOB_IN_WIM &&
@@ -2357,14 +2355,13 @@ finish_write(WIMStruct *wim, int image, int write_flags,
                                wim->out_hdr.boot_idx - 1]->metadata_blob->out_reshdr);
        }
 
-       /* If overwriting the WIM file containing an integrity table in-place,
-        * we'd like to re-use the information in the old integrity table
-        * instead of recalculating it.  But we might overwrite the old
-        * integrity table when we expand the XML data.  Read it into memory
-        * just in case.  */
-       if ((write_flags & (WIMLIB_WRITE_FLAG_OVERWRITE |
+       /* If appending to a WIM file containing an integrity table, we'd like
+        * to re-use the information in the old integrity table instead of
+        * recalculating it.  But we might overwrite the old integrity table
+        * when we expand the XML data.  Read it into memory just in case.  */
+       if ((write_flags & (WIMLIB_WRITE_FLAG_APPEND |
                            WIMLIB_WRITE_FLAG_CHECK_INTEGRITY)) ==
-               (WIMLIB_WRITE_FLAG_OVERWRITE |
+               (WIMLIB_WRITE_FLAG_APPEND |
                 WIMLIB_WRITE_FLAG_CHECK_INTEGRITY)
            && wim_has_integrity_table(wim))
        {
@@ -2445,6 +2442,14 @@ finish_write(WIMStruct *wim, int image, int write_flags,
        if (ret)
                return ret;
 
+       if (unlikely(write_flags & WIMLIB_WRITE_FLAG_UNSAFE_COMPACT)) {
+               /* Truncate any data the compaction freed up.  */
+               if (ftruncate(wim->out_fd.fd, wim->out_fd.offset)) {
+                       ERROR_WITH_ERRNO("Failed to truncate the output WIM file");
+                       return WIMLIB_ERR_WRITE;
+               }
+       }
+
        /* Possibly sync file data to disk before closing.  On POSIX systems, it
         * is necessary to do this before using rename() to overwrite an
         * existing file with a new file.  Otherwise, data loss would occur if
@@ -2625,6 +2630,34 @@ write_pipable_wim(WIMStruct *wim, int image, int write_flags,
         * finish_write().  */
 }
 
+static bool
+should_default_to_solid_compression(WIMStruct *wim, int write_flags)
+{
+       return wim->out_hdr.wim_version == WIM_VERSION_SOLID &&
+               !(write_flags & (WIMLIB_WRITE_FLAG_SOLID |
+                                WIMLIB_WRITE_FLAG_PIPABLE)) &&
+               wim_has_solid_resources(wim);
+}
+
+/* Update the images' filecount/bytecount stats (in the XML info) to take into
+ * account any recent modifications.  */
+static int
+update_image_stats(WIMStruct *wim)
+{
+       if (!wim_has_metadata(wim))
+               return 0;
+       for (int i = 0; i < wim->hdr.image_count; i++) {
+               struct wim_image_metadata *imd = wim->image_metadata[i];
+               if (imd->stats_outdated) {
+                       int ret = xml_update_image_info(wim, i + 1);
+                       if (ret)
+                               return ret;
+                       imd->stats_outdated = false;
+               }
+       }
+       return 0;
+}
+
 /* Write a standalone WIM or split WIM (SWM) part to a new file or to a file
  * descriptor.  */
 int
@@ -2671,6 +2704,10 @@ write_wim_part(WIMStruct *wim,
                                    WIMLIB_WRITE_FLAG_NOT_PIPABLE))
                return WIMLIB_ERR_INVALID_PARAM;
 
+       /* Only wimlib_overwrite() accepts UNSAFE_COMPACT.  */
+       if (write_flags & WIMLIB_WRITE_FLAG_UNSAFE_COMPACT)
+               return WIMLIB_ERR_INVALID_PARAM;
+
        /* Include an integrity table by default if no preference was given and
         * the WIM already had an integrity table.  */
        if (!(write_flags & (WIMLIB_WRITE_FLAG_CHECK_INTEGRITY |
@@ -2712,6 +2749,12 @@ write_wim_part(WIMStruct *wim,
        else
                wim->out_hdr.wim_version = WIM_VERSION_DEFAULT;
 
+       /* Default to solid compression if it is valid in the chosen WIM file
+        * format and the WIMStruct references any solid resources.  This is
+        * useful when exporting an image from a solid WIM.  */
+       if (should_default_to_solid_compression(wim, write_flags))
+               write_flags |= WIMLIB_WRITE_FLAG_SOLID;
+
        /* Set the header flags.  */
        wim->out_hdr.flags = (wim->hdr.flags & (WIM_HDR_FLAG_RP_FIX |
                                                WIM_HDR_FLAG_READONLY));
@@ -2739,9 +2782,9 @@ write_wim_part(WIMStruct *wim,
        if (write_flags & WIMLIB_WRITE_FLAG_RETAIN_GUID)
                guid = wim->hdr.guid;
        if (guid)
-               memcpy(wim->out_hdr.guid, guid, WIMLIB_GUID_LEN);
+               copy_guid(wim->out_hdr.guid, guid);
        else
-               randomize_byte_array(wim->out_hdr.guid, WIMLIB_GUID_LEN);
+               generate_guid(wim->out_hdr.guid);
 
        /* Set the part number and total parts.  */
        wim->out_hdr.part_number = part_number;
@@ -2762,6 +2805,11 @@ write_wim_part(WIMStruct *wim,
                        wim->out_hdr.boot_idx = 1;
        }
 
+       /* Update image stats if needed.  */
+       ret = update_image_stats(wim);
+       if (ret)
+               return ret;
+
        /* Set up the output file descriptor.  */
        if (write_flags & WIMLIB_WRITE_FLAG_FILE_DESCRIPTOR) {
                /* File descriptor was explicitly provided.  */
@@ -2864,11 +2912,16 @@ wimlib_write_to_fd(WIMStruct *wim, int fd,
        return write_standalone_wim(wim, &fd, image, write_flags, num_threads);
 }
 
+/* Have there been any changes to images in the specified WIM, including updates
+ * as well as deletions and additions of entire images, but excluding changes to
+ * the XML document?  */
 static bool
-any_images_modified(WIMStruct *wim)
+any_images_changed(WIMStruct *wim)
 {
+       if (wim->image_deletion_occurred)
+               return true;
        for (int i = 0; i < wim->hdr.image_count; i++)
-               if (wim->image_metadata[i]->modified)
+               if (!is_image_unchanged_from_wim(wim->image_metadata[i], wim))
                        return true;
        return false;
 }
@@ -2887,8 +2940,8 @@ check_resource_offset(struct blob_descriptor *blob, void *_wim)
 }
 
 /* Make sure no file or metadata resources are located after the XML data (or
- * integrity table if present)--- otherwise we can't safely overwrite the WIM in
- * place and we return WIMLIB_ERR_RESOURCE_ORDER.  */
+ * integrity table if present)--- otherwise we can't safely append to the WIM
+ * file and we return WIMLIB_ERR_RESOURCE_ORDER.  */
 static int
 check_resource_offsets(WIMStruct *wim, off_t end_offset)
 {
@@ -2958,18 +3011,30 @@ check_resource_offsets(WIMStruct *wim, off_t end_offset)
  *                   XML data (variable size)
  *                   Integrity table (optional) (variable size)
  *
- * This method allows an image to be appended to a large WIM very quickly, and
+ * This function allows an image to be appended to a large WIM very quickly, and
  * 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 blob table, xml data,
  * and integrity table were.  (These usually only take up a small amount of
  * space compared to the blobs, however.)
+ *
+ * Finally, this function also supports "compaction" overwrites as an
+ * alternative to the normal "append" overwrites described above.  In a
+ * compaction, data is written starting immediately from the end of the header.
+ * All existing resources are written first, in order by file offset.  New
+ * resources are written afterwards, and at the end any extra data is truncated
+ * from the file.  The advantage of this approach is that is that the WIM file
+ * ends up fully optimized, without any holes remaining.  The main disadavantage
+ * is that this operation is fundamentally unsafe and cannot be interrupted
+ * without data corruption.  Consequently, compactions are only ever done when
+ * explicitly requested by the library user with the flag
+ * WIMLIB_WRITE_FLAG_UNSAFE_COMPACT.  (Another disadvantage is that a compaction
+ * can be much slower than an append.)
  */
 static int
 overwrite_wim_inplace(WIMStruct *wim, int write_flags, unsigned num_threads)
 {
        int ret;
        off_t old_wim_end;
-       u64 old_blob_table_end, old_xml_begin, old_xml_end;
        struct list_head blob_list;
        struct list_head blob_table_list;
        struct filter_context filter_ctx;
@@ -2989,66 +3054,111 @@ overwrite_wim_inplace(WIMStruct *wim, int write_flags, unsigned num_threads)
        if (write_flags & WIMLIB_WRITE_FLAG_SOLID)
                wim->out_hdr.wim_version = WIM_VERSION_SOLID;
 
-       /* Set additional flags for overwrite.  */
-       write_flags |= WIMLIB_WRITE_FLAG_OVERWRITE |
-                      WIMLIB_WRITE_FLAG_STREAMS_OK;
-
-       /* Make sure there is no data after the XML data, except possibily an
-        * integrity table.  If this were the case, then this data would be
-        * overwritten.  */
-       old_xml_begin = wim->hdr.xml_data_reshdr.offset_in_wim;
-       old_xml_end = old_xml_begin + wim->hdr.xml_data_reshdr.size_in_wim;
-       old_blob_table_end = wim->hdr.blob_table_reshdr.offset_in_wim +
-                            wim->hdr.blob_table_reshdr.size_in_wim;
-       if (wim_has_integrity_table(wim) &&
-           wim->hdr.integrity_table_reshdr.offset_in_wim < old_xml_end) {
-               WARNING("Didn't expect the integrity table to be before the XML data");
-               ret = WIMLIB_ERR_RESOURCE_ORDER;
-               goto out;
-       }
+       /* Default to solid compression if it is valid in the chosen WIM file
+        * format and the WIMStruct references any solid resources.  This is
+        * useful when updating a solid WIM.  */
+       if (should_default_to_solid_compression(wim, write_flags))
+               write_flags |= WIMLIB_WRITE_FLAG_SOLID;
 
-       if (old_blob_table_end > old_xml_begin) {
-               WARNING("Didn't expect the blob table to be after the XML data");
-               ret = WIMLIB_ERR_RESOURCE_ORDER;
-               goto out;
-       }
+       if (unlikely(write_flags & WIMLIB_WRITE_FLAG_UNSAFE_COMPACT)) {
+
+               /* In-place compaction  */
+
+               WARNING("The WIM file \"%"TS"\" is being compacted in place.\n"
+                       "          Do *not* interrupt the operation, or else "
+                       "the WIM file will be\n"
+                       "          corrupted!", wim->filename);
+               wim->being_compacted = 1;
+               old_wim_end = WIM_HEADER_DISK_SIZE;
 
-       /* Set @old_wim_end, which indicates the point beyond which we don't
-        * allow any file and metadata resources to appear without returning
-        * WIMLIB_ERR_RESOURCE_ORDER (due to the fact that we would otherwise
-        * overwrite these resources). */
-       if (!wim->image_deletion_occurred && !any_images_modified(wim)) {
-               /* If no images have been modified and no images have been
-                * deleted, a new blob table does not need to be written.  We
-                * shall write the new XML data and optional integrity table
-                * immediately after the blob table.  Note that this may
-                * overwrite an existing integrity table. */
-               old_wim_end = old_blob_table_end;
-               write_flags |= WIMLIB_WRITE_FLAG_NO_NEW_BLOBS;
-       } else if (wim_has_integrity_table(wim)) {
-               /* Old WIM has an integrity table; begin writing new blobs after
-                * it. */
-               old_wim_end = wim->hdr.integrity_table_reshdr.offset_in_wim +
-                             wim->hdr.integrity_table_reshdr.size_in_wim;
+               ret = prepare_blob_list_for_write(wim, WIMLIB_ALL_IMAGES,
+                                                 write_flags, &blob_list,
+                                                 &blob_table_list, &filter_ctx);
+               if (ret)
+                       goto out;
+
+               if (wim_has_metadata(wim)) {
+                       /* Add existing metadata resources to be compacted along
+                        * with the file resources.  */
+                       for (int i = 0; i < wim->hdr.image_count; i++) {
+                               struct wim_image_metadata *imd = wim->image_metadata[i];
+                               if (is_image_unchanged_from_wim(imd, wim)) {
+                                       fully_reference_blob_for_write(imd->metadata_blob,
+                                                                      &blob_list);
+                               }
+                       }
+               }
        } else {
-               /* No existing integrity table; begin writing new blobs after
-                * the old XML data. */
-               old_wim_end = old_xml_end;
-       }
+               u64 old_blob_table_end, old_xml_begin, old_xml_end;
 
-       ret = check_resource_offsets(wim, old_wim_end);
-       if (ret)
-               goto out;
+               /* Set additional flags for append.  */
+               write_flags |= WIMLIB_WRITE_FLAG_APPEND |
+                              WIMLIB_WRITE_FLAG_STREAMS_OK;
 
-       ret = prepare_blob_list_for_write(wim, WIMLIB_ALL_IMAGES, write_flags,
-                                         &blob_list, &blob_table_list,
-                                         &filter_ctx);
+               /* Make sure there is no data after the XML data, except
+                * possibily an integrity table.  If this were the case, then
+                * this data would be overwritten.  */
+               old_xml_begin = wim->hdr.xml_data_reshdr.offset_in_wim;
+               old_xml_end = old_xml_begin + wim->hdr.xml_data_reshdr.size_in_wim;
+               old_blob_table_end = wim->hdr.blob_table_reshdr.offset_in_wim +
+                                    wim->hdr.blob_table_reshdr.size_in_wim;
+               if (wim_has_integrity_table(wim) &&
+                   wim->hdr.integrity_table_reshdr.offset_in_wim < old_xml_end) {
+                       WARNING("Didn't expect the integrity table to be "
+                               "before the XML data");
+                       ret = WIMLIB_ERR_RESOURCE_ORDER;
+                       goto out;
+               }
+
+               if (old_blob_table_end > old_xml_begin) {
+                       WARNING("Didn't expect the blob table to be after "
+                               "the XML data");
+                       ret = WIMLIB_ERR_RESOURCE_ORDER;
+                       goto out;
+               }
+               /* Set @old_wim_end, which indicates the point beyond which we
+                * don't allow any file and metadata resources to appear without
+                * returning WIMLIB_ERR_RESOURCE_ORDER (due to the fact that we
+                * would otherwise overwrite these resources). */
+               if (!any_images_changed(wim)) {
+                       /* If no images have been modified, added, or deleted,
+                        * then a new blob table does not need to be written.
+                        * We shall write the new XML data and optional
+                        * integrity table immediately after the blob table.
+                        * Note that this may overwrite an existing integrity
+                        * table.  */
+                       old_wim_end = old_blob_table_end;
+                       write_flags |= WIMLIB_WRITE_FLAG_NO_NEW_BLOBS;
+               } else if (wim_has_integrity_table(wim)) {
+                       /* Old WIM has an integrity table; begin writing new
+                        * blobs after it. */
+                       old_wim_end = wim->hdr.integrity_table_reshdr.offset_in_wim +
+                                     wim->hdr.integrity_table_reshdr.size_in_wim;
+               } else {
+                       /* No existing integrity table; begin writing new blobs
+                        * after the old XML data. */
+                       old_wim_end = old_xml_end;
+               }
+
+               ret = check_resource_offsets(wim, old_wim_end);
+               if (ret)
+                       goto out;
+
+               ret = prepare_blob_list_for_write(wim, WIMLIB_ALL_IMAGES,
+                                                 write_flags, &blob_list,
+                                                 &blob_table_list, &filter_ctx);
+               if (ret)
+                       goto out;
+
+               if (write_flags & WIMLIB_WRITE_FLAG_NO_NEW_BLOBS)
+                       wimlib_assert(list_empty(&blob_list));
+       }
+
+       /* Update image stats if needed.  */
+       ret = update_image_stats(wim);
        if (ret)
                goto out;
 
-       if (write_flags & WIMLIB_WRITE_FLAG_NO_NEW_BLOBS)
-               wimlib_assert(list_empty(&blob_list));
-
        ret = open_wim_writable(wim, wim->filename, O_RDWR);
        if (ret)
                goto out;
@@ -3090,7 +3200,8 @@ overwrite_wim_inplace(WIMStruct *wim, int write_flags, unsigned num_threads)
        return 0;
 
 out_truncate:
-       if (!(write_flags & WIMLIB_WRITE_FLAG_NO_NEW_BLOBS)) {
+       if (!(write_flags & (WIMLIB_WRITE_FLAG_NO_NEW_BLOBS |
+                            WIMLIB_WRITE_FLAG_UNSAFE_COMPACT))) {
                WARNING("Truncating \"%"TS"\" to its original size "
                        "(%"PRIu64" bytes)", wim->filename, old_wim_end);
                /* Return value of ftruncate() is ignored because this is
@@ -3104,6 +3215,7 @@ out_unlock_wim:
 out_close_wim:
        (void)close_wim_writable(wim, write_flags);
 out:
+       wim->being_compacted = 0;
        return ret;
 }
 
@@ -3159,8 +3271,8 @@ overwrite_wim_via_tmpfile(WIMStruct *wim, int write_flags, unsigned num_threads)
                             &progress, wim->progctx);
 }
 
-/* Determine if the specified WIM file may be updated by appending in-place
- * rather than writing and replacing it with an entirely new file.  */
+/* Determine if the specified WIM file may be updated in-place rather than by
+ * writing and replacing it with an entirely new file.  */
 static bool
 can_overwrite_wim_inplace(const WIMStruct *wim, int write_flags)
 {
@@ -3202,6 +3314,20 @@ wimlib_overwrite(WIMStruct *wim, int write_flags, unsigned num_threads)
        if (!wim->filename)
                return WIMLIB_ERR_NO_FILENAME;
 
+       if (unlikely(write_flags & WIMLIB_WRITE_FLAG_UNSAFE_COMPACT)) {
+               /*
+                * In UNSAFE_COMPACT mode:
+                *      - RECOMPRESS is forbidden
+                *      - REBUILD is ignored
+                *      - SOFT_DELETE and NO_SOLID_SORT are implied
+                */
+               if (write_flags & WIMLIB_WRITE_FLAG_RECOMPRESS)
+                       return WIMLIB_ERR_COMPACTION_NOT_POSSIBLE;
+               write_flags &= ~WIMLIB_WRITE_FLAG_REBUILD;
+               write_flags |= WIMLIB_WRITE_FLAG_SOFT_DELETE;
+               write_flags |= WIMLIB_WRITE_FLAG_NO_SOLID_SORT;
+       }
+
        orig_hdr_flags = wim->hdr.flags;
        if (write_flags & WIMLIB_WRITE_FLAG_IGNORE_READONLY_FLAG)
                wim->hdr.flags &= ~WIM_HDR_FLAG_READONLY;
@@ -3216,5 +3342,7 @@ wimlib_overwrite(WIMStruct *wim, int write_flags, unsigned num_threads)
                        return ret;
                WARNING("Falling back to re-building entire WIM");
        }
+       if (write_flags & WIMLIB_WRITE_FLAG_UNSAFE_COMPACT)
+               return WIMLIB_ERR_COMPACTION_NOT_POSSIBLE;
        return overwrite_wim_via_tmpfile(wim, write_flags, num_threads);
 }