write_stream_list(): Do not allocate chunk buffer if NONE compression

[wimlib] / src / write.c

/*
 * write.c
 *
 * Support for writing WIM files; write a WIM file, overwrite a WIM file, write
 * compressed file resources, etc.
 */

/*
 * Copyright (C) 2012, 2013 Eric Biggers
 *
 * This file is part of wimlib, a library for working with WIM files.
 *
 * wimlib is free software; you can redistribute it and/or modify it under the
 * terms of the GNU General Public License as published by the Free
 * Software Foundation; either version 3 of the License, or (at your option)
 * any later version.
 *
 * wimlib is distributed in the hope that it will be useful, but WITHOUT ANY
 * WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR
 * A PARTICULAR PURPOSE. See the GNU General Public License for more
 * details.
 *
 * You should have received a copy of the GNU General Public License
 * along with wimlib; if not, see http://www.gnu.org/licenses/.
 */

#ifdef HAVE_CONFIG_H
#  include "config.h"
#endif

#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. */
#  include <sys/file.h>
#endif

#include "wimlib/chunk_compressor.h"
#include "wimlib/endianness.h"
#include "wimlib/error.h"
#include "wimlib/file_io.h"
#include "wimlib/header.h"
#include "wimlib/integrity.h"
#include "wimlib/lookup_table.h"
#include "wimlib/metadata.h"
#include "wimlib/resource.h"
#ifdef __WIN32__
#  include "wimlib/win32.h" /* win32_rename_replacement() */
#endif
#include "wimlib/write.h"
#include "wimlib/xml.h"

#include <errno.h>
#include <fcntl.h>
#include <stdlib.h>
#include <unistd.h>

#ifdef HAVE_ALLOCA_H
#  include <alloca.h>
#endif

/* wimlib internal flags used when writing resources.  */
#define WRITE_RESOURCE_FLAG_RECOMPRESS          0x00000001
#define WRITE_RESOURCE_FLAG_PIPABLE             0x00000002
#define WRITE_RESOURCE_FLAG_PACK_STREAMS        0x00000004

static inline int
write_flags_to_resource_flags(int write_flags)
{
        int write_resource_flags = 0;

        if (write_flags & WIMLIB_WRITE_FLAG_RECOMPRESS)
                write_resource_flags |= WRITE_RESOURCE_FLAG_RECOMPRESS;
        if (write_flags & WIMLIB_WRITE_FLAG_PIPABLE)
                write_resource_flags |= WRITE_RESOURCE_FLAG_PIPABLE;
        if (write_flags & WIMLIB_WRITE_FLAG_PACK_STREAMS)
                write_resource_flags |= WRITE_RESOURCE_FLAG_PACK_STREAMS;
        return write_resource_flags;
}

struct filter_context {
        int write_flags;
        WIMStruct *wim;
};

/* Determine specified stream should be filtered out from the write.
 *
 * Return values:
 *
 *  < 0 : The stream should be hard-filtered; that is, not included in the
 *        output WIM at all.
 *    0 : The stream should not be filtered out.
 *  > 0 : The stream should be soft-filtered; that is, it already exists in the
 *        WIM file and may not need to be written again.
 */
static int
stream_filtered(const struct wim_lookup_table_entry *lte,
                const struct filter_context *ctx)
{
        int write_flags = ctx->write_flags;
        WIMStruct *wim = ctx->wim;

        if (ctx == NULL)
                return 0;

        if (write_flags & WIMLIB_WRITE_FLAG_OVERWRITE &&
            lte->resource_location == RESOURCE_IN_WIM &&
            lte->rspec->wim == wim)
                return 1;

        if (write_flags & WIMLIB_WRITE_FLAG_SKIP_EXTERNAL_WIMS &&
            lte->resource_location == RESOURCE_IN_WIM &&
            lte->rspec->wim != wim)
                return -1;

        return 0;
}

static bool
stream_hard_filtered(const struct wim_lookup_table_entry *lte,
                     struct filter_context *ctx)
{
        return stream_filtered(lte, ctx) < 0;
}

static inline int
may_soft_filter_streams(const struct filter_context *ctx)
{
        if (ctx == NULL)
                return 0;
        return ctx->write_flags & WIMLIB_WRITE_FLAG_OVERWRITE;
}

static inline int
may_hard_filter_streams(const struct filter_context *ctx)
{
        if (ctx == NULL)
                return 0;
        return ctx->write_flags & WIMLIB_WRITE_FLAG_SKIP_EXTERNAL_WIMS;
}

static inline int
may_filter_streams(const struct filter_context *ctx)
{
        return (may_soft_filter_streams(ctx) ||
                may_hard_filter_streams(ctx));
}


/* Return true if the specified resource is compressed and the compressed data
 * can be reused with the specified output parameters.  */
static bool
can_raw_copy(const struct wim_lookup_table_entry *lte,
             int write_resource_flags, int out_ctype, u32 out_chunk_size)
{
        const struct wim_resource_spec *rspec;

        if (write_resource_flags & WRITE_RESOURCE_FLAG_RECOMPRESS)
                return false;

        if (out_ctype == WIMLIB_COMPRESSION_TYPE_NONE)
                return false;

        if (lte->resource_location != RESOURCE_IN_WIM)
                return false;

        rspec = lte->rspec;

        if (rspec->is_pipable != !!(write_resource_flags & WRITE_RESOURCE_FLAG_PIPABLE))
                return false;


        if (rspec->flags & WIM_RESHDR_FLAG_COMPRESSED) {
                /* Normal compressed resource: Must use same compression type
                 * and chunk size.  */
                return (rspec->wim->compression_type == out_ctype &&
                        rspec->wim->chunk_size == out_chunk_size);
        }

        /* XXX: For compatibility, we can't allow multiple packed resources per
         * WIM.  */
#if 0
        if ((rspec->flags & WIM_RESHDR_FLAG_PACKED_STREAMS) &&
            (write_resource_flags & WRITE_RESOURCE_FLAG_PACK_STREAMS))
        {
                /* Packed resource: Such resources may contain multiple streams,
                 * and in general only a subset of them need to be written.  As
                 * a heuristic, re-use the raw data if at least half the
                 * uncompressed size is being written.  */

                /* Note: packed resources contain a header that specifies the
                 * compression type and chunk size; therefore we don't need to
                 * check if they are compatible with @out_ctype and
                 * @out_chunk_size.  */

                struct wim_lookup_table_entry *res_stream;
                u64 write_size = 0;

                list_for_each_entry(res_stream, &rspec->stream_list, rspec_node)
                        if (res_stream->will_be_in_output_wim)
                                write_size += res_stream->size;

                return (write_size > rspec->uncompressed_size / 2);
        }
#endif

        return false;
}

static u8
filter_resource_flags(u8 flags)
{
        return (flags & ~(WIM_RESHDR_FLAG_PACKED_STREAMS |
                          WIM_RESHDR_FLAG_COMPRESSED |
                          WIM_RESHDR_FLAG_SPANNED |
                          WIM_RESHDR_FLAG_FREE));
}

static void
stream_set_out_reshdr_for_reuse(struct wim_lookup_table_entry *lte)
{
        const struct wim_resource_spec *rspec;

        wimlib_assert(lte->resource_location == RESOURCE_IN_WIM);
        rspec = lte->rspec;

        if (rspec->flags & WIM_RESHDR_FLAG_PACKED_STREAMS) {

                wimlib_assert(lte->flags & WIM_RESHDR_FLAG_PACKED_STREAMS);

                lte->out_reshdr.offset_in_wim = lte->offset_in_res;
                lte->out_reshdr.uncompressed_size = 0;
                lte->out_reshdr.size_in_wim = lte->size;

                lte->out_res_offset_in_wim = rspec->offset_in_wim;
                lte->out_res_size_in_wim = rspec->size_in_wim;
                /*lte->out_res_uncompressed_size = rspec->uncompressed_size;*/
        } else {
                wimlib_assert(!(lte->flags & WIM_RESHDR_FLAG_PACKED_STREAMS));

                lte->out_reshdr.offset_in_wim = rspec->offset_in_wim;
                lte->out_reshdr.uncompressed_size = rspec->uncompressed_size;
                lte->out_reshdr.size_in_wim = rspec->size_in_wim;
        }
        lte->out_reshdr.flags = lte->flags;
}


/* Write the header for a stream in a pipable WIM.  */
static int
write_pwm_stream_header(const struct wim_lookup_table_entry *lte,
                        struct filedes *out_fd,
                        int additional_reshdr_flags)
{
        struct pwm_stream_hdr stream_hdr;
        u32 reshdr_flags;
        int ret;

        stream_hdr.magic = cpu_to_le64(PWM_STREAM_MAGIC);
        stream_hdr.uncompressed_size = cpu_to_le64(lte->size);
        if (additional_reshdr_flags & PWM_RESHDR_FLAG_UNHASHED) {
                zero_out_hash(stream_hdr.hash);
        } else {
                wimlib_assert(!lte->unhashed);
                copy_hash(stream_hdr.hash, lte->hash);
        }

        reshdr_flags = filter_resource_flags(lte->flags);
        reshdr_flags |= additional_reshdr_flags;
        stream_hdr.flags = cpu_to_le32(reshdr_flags);
        ret = full_write(out_fd, &stream_hdr, sizeof(stream_hdr));
        if (ret)
                ERROR_WITH_ERRNO("Write error");
        return ret;
}

struct write_streams_progress_data {
        wimlib_progress_func_t progress_func;
        union wimlib_progress_info progress;
        uint64_t next_progress;
        WIMStruct *prev_wim_part;
};

static void
do_write_streams_progress(struct write_streams_progress_data *progress_data,
                          u64 size,
                          bool discarded,
                          struct wim_lookup_table_entry *cur_stream)
{
        union wimlib_progress_info *progress = &progress_data->progress;
        bool new_wim_part;

        if (discarded) {
                progress->write_streams.total_bytes -= size;
                if (progress_data->next_progress != ~(uint64_t)0 &&
                    progress_data->next_progress > progress->write_streams.total_bytes)
                {
                        progress_data->next_progress = progress->write_streams.total_bytes;
                }
        } else {
                progress->write_streams.completed_bytes += size;
        }
        new_wim_part = false;
        if (cur_stream->resource_location == RESOURCE_IN_WIM &&
            cur_stream->rspec->wim != progress_data->prev_wim_part)
        {
                if (progress_data->prev_wim_part) {
                        new_wim_part = true;
                        progress->write_streams.completed_parts++;
                }
                progress_data->prev_wim_part = cur_stream->rspec->wim;
        }
        progress->write_streams.completed_streams++;
        if (progress_data->progress_func
            && (progress->write_streams.completed_bytes >= progress_data->next_progress
                || new_wim_part))
        {
                progress_data->progress_func(WIMLIB_PROGRESS_MSG_WRITE_STREAMS,
                                             progress);
                if (progress_data->next_progress == progress->write_streams.total_bytes) {
                        progress_data->next_progress = ~(uint64_t)0;
                } else {
                        progress_data->next_progress =
                                min(progress->write_streams.total_bytes,
                                    progress->write_streams.completed_bytes +
                                        progress->write_streams.total_bytes / 100);
                }
        }
}

struct write_streams_ctx {
        /* File descriptor the streams are being written to.  */
        struct filedes *out_fd;

        /* Lookup table for the WIMStruct on whose behalf the streams are being
         * written.  */
        struct wim_lookup_table *lookup_table;

        /* Compression format to use.  */
        int out_ctype;

        /* Maximum uncompressed chunk size in compressed resources to use.  */
        u32 out_chunk_size;

        /* Flags that affect how the streams will be written.  */
        int write_resource_flags;

        /* Data used for issuing WRITE_STREAMS progress.  */
        struct write_streams_progress_data progress_data;

        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.  */
        struct chunk_compressor *compressor;

        /* Buffer for dividing the read data into chunks of size
         * @out_chunk_size.  */
        u8 *chunk_buf;

        /* Number of bytes in @chunk_buf that are currently filled.  */
        size_t chunk_buf_filled;

        /* List of streams that currently have chunks being compressed.  */
        struct list_head pending_streams;

        /* Set to true if the stream currently being read was a duplicate, and
         * therefore the corresponding stream entry needs to be freed once the
         * read finishes.  (In this case we add the duplicate entry to
         * pending_streams rather than the entry being read.)  */
        bool stream_was_duplicate;

        /* Current uncompressed offset in the resource being read.  */
        u64 cur_read_res_offset;

        /* Uncompressed size of the resource currently being read.  */
        u64 cur_read_res_size;

        /* Current uncompressed offset in the resource being written.  */
        u64 cur_write_res_offset;

        /* Uncompressed size of resource currently being written.  */
        u64 cur_write_res_size;

        /* Array that is filled in with compressed chunk sizes as a resource is
         * being written.  */
        u64 *chunk_csizes;

        /* Index of next entry in @chunk_csizes to fill in.  */
        size_t chunk_index;

        /* Number of entries in @chunk_csizes currently allocated.  */
        size_t num_alloc_chunks;

        /* Offset in the output file of the start of the chunks of the resource
         * currently being written.  */
        u64 chunks_start_offset;
};

static u64
get_chunk_entry_size(u64 res_size, int write_resource_flags)
{
        if (res_size <= UINT32_MAX ||
            (write_resource_flags & WIM_RESHDR_FLAG_PACKED_STREAMS))
                return 4;
        else
                return 8;
}

/* Reserve space for the chunk table and prepare to accumulate the chunk table
 * in memory.  */
static int
begin_chunk_table(struct write_streams_ctx *ctx, u64 res_expected_size)
{
        u64 expected_num_chunks;
        u64 expected_num_chunk_entries;
        size_t reserve_size;
        int ret;

        /* Calculate the number of chunks and chunk entries that should be
         * needed for the resource.  These normally will be the final values,
         * but in PACKED_STREAMS mode some of the streams we're planning to
         * write into the resource may be duplicates, and therefore discarded,
         * potentially decreasing the number of chunk entries needed.  */
        expected_num_chunks = DIV_ROUND_UP(res_expected_size, ctx->out_chunk_size);
        expected_num_chunk_entries = expected_num_chunks;
        if (!(ctx->write_resource_flags & WRITE_RESOURCE_FLAG_PACK_STREAMS))
                expected_num_chunk_entries--;

        /* Make sure the chunk_csizes array is long enough to store the
         * compressed size of each chunk.  */
        if (expected_num_chunks > ctx->num_alloc_chunks) {
                u64 new_length = expected_num_chunks + 50;

                if ((size_t)new_length != new_length) {
                        ERROR("Resource size too large (%"PRIu64" bytes!",
                              res_expected_size);
                        return WIMLIB_ERR_NOMEM;
                }

                FREE(ctx->chunk_csizes);
                ctx->chunk_csizes = MALLOC(new_length * sizeof(ctx->chunk_csizes[0]));
                if (ctx->chunk_csizes == NULL) {
                        ctx->num_alloc_chunks = 0;
                        return WIMLIB_ERR_NOMEM;
                }
                ctx->num_alloc_chunks = new_length;
        }

        ctx->chunk_index = 0;

        if (!(ctx->write_resource_flags & WRITE_RESOURCE_FLAG_PIPABLE)) {
                /* Reserve space for the chunk table in the output file.  In the
                 * case of packed resources this reserves the upper bound for
                 * the needed space, not necessarily the exact space which will
                 * prove to be needed.  At this point, we just use @chunk_csizes
                 * for a buffer of 0's because the actual compressed chunk sizes
                 * are unknown.  */
                reserve_size = expected_num_chunk_entries *
                               get_chunk_entry_size(res_expected_size,
                                                    ctx->write_resource_flags);
                if (ctx->write_resource_flags & WRITE_RESOURCE_FLAG_PACK_STREAMS)
                        reserve_size += sizeof(struct alt_chunk_table_header_disk);
                memset(ctx->chunk_csizes, 0, reserve_size);
                ret = full_write(ctx->out_fd, ctx->chunk_csizes, reserve_size);
                if (ret)
                        return ret;
        }
        return 0;
}

static int
begin_write_resource(struct write_streams_ctx *ctx, u64 res_expected_size)
{
        int ret;

        wimlib_assert(res_expected_size != 0);

        if (ctx->compressor != NULL) {
                ret = begin_chunk_table(ctx, res_expected_size);
                if (ret)
                        return ret;
        }

        /* Output file descriptor is now positioned at the offset at which to
         * write the first chunk of the resource.  */
        ctx->chunks_start_offset = ctx->out_fd->offset;
        ctx->cur_write_res_offset = 0;
        ctx->cur_write_res_size = res_expected_size;
        return 0;
}

static int
end_chunk_table(struct write_streams_ctx *ctx, u64 res_actual_size,
                u64 *res_start_offset_ret, u64 *res_store_size_ret)
{
        size_t actual_num_chunks;
        size_t actual_num_chunk_entries;
        size_t chunk_entry_size;
        int ret;

        actual_num_chunks = ctx->chunk_index;
        actual_num_chunk_entries = actual_num_chunks;
        if (!(ctx->write_resource_flags & WRITE_RESOURCE_FLAG_PACK_STREAMS))
                actual_num_chunk_entries--;

        chunk_entry_size = get_chunk_entry_size(res_actual_size,
                                                ctx->write_resource_flags);

        typedef le64 __attribute__((may_alias)) aliased_le64_t;
        typedef le32 __attribute__((may_alias)) aliased_le32_t;

        if (chunk_entry_size == 4) {
                aliased_le32_t *entries = (aliased_le32_t*)ctx->chunk_csizes;

                if (ctx->write_resource_flags & WRITE_RESOURCE_FLAG_PACK_STREAMS) {
                        for (size_t i = 0; i < actual_num_chunk_entries; i++)
                                entries[i] = cpu_to_le32(ctx->chunk_csizes[i]);
                } else {
                        u32 offset = ctx->chunk_csizes[0];
                        for (size_t i = 0; i < actual_num_chunk_entries; i++) {
                                u32 next_size = ctx->chunk_csizes[i + 1];
                                entries[i] = cpu_to_le32(offset);
                                offset += next_size;
                        }
                }
        } else {
                aliased_le64_t *entries = (aliased_le64_t*)ctx->chunk_csizes;

                if (ctx->write_resource_flags & WRITE_RESOURCE_FLAG_PACK_STREAMS) {
                        for (size_t i = 0; i < actual_num_chunk_entries; i++)
                                entries[i] = cpu_to_le64(ctx->chunk_csizes[i]);
                } else {
                        u64 offset = ctx->chunk_csizes[0];
                        for (size_t i = 0; i < actual_num_chunk_entries; i++) {
                                u64 next_size = ctx->chunk_csizes[i + 1];
                                entries[i] = cpu_to_le64(offset);
                                offset += next_size;
                        }
                }
        }

        size_t chunk_table_size = actual_num_chunk_entries * chunk_entry_size;
        u64 res_start_offset;
        u64 res_end_offset;

        if (ctx->write_resource_flags & WRITE_RESOURCE_FLAG_PIPABLE) {
                ret = full_write(ctx->out_fd, ctx->chunk_csizes, chunk_table_size);
                if (ret)
                        goto error;
                res_end_offset = ctx->out_fd->offset;
                res_start_offset = ctx->chunks_start_offset;
        } else {
                res_end_offset = ctx->out_fd->offset;

                u64 chunk_table_offset;

                chunk_table_offset = ctx->chunks_start_offset - chunk_table_size;

                if (ctx->write_resource_flags & WRITE_RESOURCE_FLAG_PACK_STREAMS) {
                        struct alt_chunk_table_header_disk hdr;

                        hdr.res_usize = cpu_to_le64(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_LZX != 1);
                        BUILD_BUG_ON(WIMLIB_COMPRESSION_TYPE_XPRESS != 2);
                        BUILD_BUG_ON(WIMLIB_COMPRESSION_TYPE_LZMS != 3);

                        ret = full_pwrite(ctx->out_fd, &hdr, sizeof(hdr),
                                          chunk_table_offset - sizeof(hdr));
                        if (ret)
                                goto error;
                        res_start_offset = chunk_table_offset - sizeof(hdr);
                } else {
                        res_start_offset = chunk_table_offset;
                }

                ret = full_pwrite(ctx->out_fd, ctx->chunk_csizes,
                                  chunk_table_size, chunk_table_offset);
                if (ret)
                        goto error;
        }

        *res_start_offset_ret = res_start_offset;
        *res_store_size_ret = res_end_offset - res_start_offset;

        return 0;

error:
        ERROR_WITH_ERRNO("Write error");
        return ret;
}

/* Finish writing a WIM resource by writing or updating the chunk table (if not
 * writing the data uncompressed) and loading its metadata into @out_reshdr.  */
static int
end_write_resource(struct write_streams_ctx *ctx, struct wim_reshdr *out_reshdr)
{
        int ret;
        u64 res_size_in_wim;
        u64 res_uncompressed_size;
        u64 res_offset_in_wim;

        wimlib_assert(ctx->cur_write_res_size == ctx->cur_write_res_offset);
        res_uncompressed_size = ctx->cur_write_res_size;

        if (ctx->compressor) {
                ret = end_chunk_table(ctx, res_uncompressed_size,
                                      &res_offset_in_wim, &res_size_in_wim);
                if (ret)
                        return ret;
        } else {
                res_offset_in_wim = ctx->chunks_start_offset;
                res_size_in_wim = ctx->out_fd->offset - res_offset_in_wim;
        }
        out_reshdr->uncompressed_size = res_uncompressed_size;
        out_reshdr->size_in_wim = res_size_in_wim;
        out_reshdr->offset_in_wim = res_offset_in_wim;
        DEBUG("Finished writing resource: %"PRIu64" => %"PRIu64" @ %"PRIu64"",
              res_uncompressed_size, res_size_in_wim, res_offset_in_wim);
        return 0;
}

/* Begin processing a stream for writing.  */
static int
write_stream_begin_read(struct wim_lookup_table_entry *lte,
                        bool is_partial_res, void *_ctx)
{
        struct write_streams_ctx *ctx = _ctx;
        int ret;

        wimlib_assert(lte->size > 0);

        ctx->cur_read_res_offset = 0;
        ctx->cur_read_res_size = lte->size;

        /* As an optimization, we allow some streams to be "unhashed", meaning
         * their SHA1 message digests are unknown.  This is the case with
         * streams that are added by scanning a directry tree with
         * wimlib_add_image(), for example.  Since WIM uses single-instance
         * streams, we don't know whether such each such stream really need to
         * written until it is actually checksummed, unless it has a unique
         * size.  In such cases we read and checksum the stream in this
         * function, thereby advancing ahead of read_stream_list(), which will
         * still provide the data again to write_stream_process_chunk().  This
         * is okay because an unhashed stream cannot be in a WIM resource, which
         * might be costly to decompress.  */
        ctx->stream_was_duplicate = false;
        if (ctx->lookup_table != NULL && lte->unhashed && !lte->unique_size) {

                wimlib_assert(!is_partial_res);

                struct wim_lookup_table_entry *lte_new;

                ret = hash_unhashed_stream(lte, ctx->lookup_table, &lte_new);
                if (ret)
                        return ret;
                if (lte_new != lte) {
                        /* Duplicate stream detected.  */

                        if (lte_new->will_be_in_output_wim ||
                            stream_filtered(lte_new, ctx->filter_ctx))
                        {
                                /* The duplicate stream is already being
                                 * included in the output WIM, or it would be
                                 * filtered out if it had been.  Skip writing
                                 * this stream (and reading it again) entirely,
                                 * passing its output reference count to the
                                 * duplicate stream in the former case.  */
                                DEBUG("Discarding duplicate stream of "
                                      "length %"PRIu64, lte->size);
                                do_write_streams_progress(&ctx->progress_data,
                                                          lte->size, true, lte);
                                list_del(&lte->write_streams_list);
                                list_del(&lte->lookup_table_list);
                                if (lte_new->will_be_in_output_wim)
                                        lte_new->out_refcnt += lte->out_refcnt;
                                if (ctx->write_resource_flags & WRITE_RESOURCE_FLAG_PACK_STREAMS)
                                        ctx->cur_write_res_size -= lte->size;
                                free_lookup_table_entry(lte);
                                return BEGIN_STREAM_STATUS_SKIP_STREAM;
                        } else {
                                /* The duplicate stream can validly be written,
                                 * but was not marked as such.  Discard the
                                 * current stream entry and use the duplicate,
                                 * but actually freeing the current entry must
                                 * wait until read_stream_list() has finished
                                 * reading its data.  */
                                DEBUG("Stream duplicate, but not already "
                                      "selected for writing.");
                                list_replace(&lte->write_streams_list,
                                             &lte_new->write_streams_list);
                                list_replace(&lte->lookup_table_list,
                                             &lte_new->lookup_table_list);
                                lte_new->out_refcnt = lte->out_refcnt;
                                lte_new->will_be_in_output_wim = 1;
                                ctx->stream_was_duplicate = true;
                                lte = lte_new;
                        }
                }
        }
        list_move_tail(&lte->write_streams_list, &ctx->pending_streams);
        return 0;
}

/* Rewrite a stream that was just written compressed as uncompressed instead.
 * This function is optional, but if a stream did not compress to less than its
 * original size, it might as well be written uncompressed.  */
static int
write_stream_uncompressed(struct wim_lookup_table_entry *lte,
                          struct filedes *out_fd)
{
        int ret;
        u64 begin_offset = lte->out_reshdr.offset_in_wim;
        u64 end_offset = out_fd->offset;

        if (filedes_seek(out_fd, begin_offset) == -1)
                return 0;

        ret = extract_stream_to_fd(lte, out_fd, lte->size);
        if (ret) {
                /* Error reading the uncompressed data.  */
                if (out_fd->offset == begin_offset &&
                    filedes_seek(out_fd, end_offset) != -1)
                {
                        /* Nothing was actually written yet, and we successfully
                         * seeked to the end of the compressed resource, so
                         * don't issue a hard error; just keep the compressed
                         * resource instead.  */
                        WARNING("Recovered compressed stream of "
                                "size %"PRIu64", continuing on.",
                                lte->size);
                        return 0;
                }
                return ret;
        }

        wimlib_assert(out_fd->offset - begin_offset == lte->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;
        }

        lte->out_reshdr.size_in_wim = lte->size;
        lte->out_reshdr.flags &= ~(WIM_RESHDR_FLAG_COMPRESSED |
                                   WIM_RESHDR_FLAG_PACKED_STREAMS);
        return 0;
}

/* Write the next chunk of (typically compressed) data to the output WIM,
 * handling the writing of the chunk table.  */
static int
write_chunk(struct write_streams_ctx *ctx, const void *cchunk,
            size_t csize, size_t usize)
{
        int ret;

        struct wim_lookup_table_entry *lte;

        lte = list_entry(ctx->pending_streams.next,
                         struct wim_lookup_table_entry, write_streams_list);

        if (ctx->cur_write_res_offset == 0 &&
            !(ctx->write_resource_flags & WRITE_RESOURCE_FLAG_PACK_STREAMS))
        {
                /* Starting to write a new stream in non-packed mode.  */

                if (ctx->write_resource_flags & WRITE_RESOURCE_FLAG_PIPABLE) {
                        int additional_reshdr_flags = 0;
                        if (ctx->compressor != NULL)
                                additional_reshdr_flags |= WIM_RESHDR_FLAG_COMPRESSED;

                        DEBUG("Writing pipable WIM stream header "
                              "(offset=%"PRIu64")", ctx->out_fd->offset);

                        ret = write_pwm_stream_header(lte, ctx->out_fd,
                                                      additional_reshdr_flags);
                        if (ret)
                                return ret;
                }

                ret = begin_write_resource(ctx, lte->size);
                if (ret)
                        return ret;
        }

        if (ctx->compressor != NULL) {
                /* Record the compresed chunk size.  */
                wimlib_assert(ctx->chunk_index < ctx->num_alloc_chunks);
                ctx->chunk_csizes[ctx->chunk_index++] = csize;

               /* If writing a pipable WIM, before the chunk data write a chunk
                * header that provides the compressed chunk size.  */
                if (ctx->write_resource_flags & WRITE_RESOURCE_FLAG_PIPABLE) {
                        struct pwm_chunk_hdr chunk_hdr = {
                                .compressed_size = cpu_to_le32(csize),
                        };
                        ret = full_write(ctx->out_fd, &chunk_hdr,
                                         sizeof(chunk_hdr));
                        if (ret)
                                goto error;
                }
        }

        /* Write the chunk data.  */
        ret = full_write(ctx->out_fd, cchunk, csize);
        if (ret)
                goto error;

        ctx->cur_write_res_offset += usize;

        do_write_streams_progress(&ctx->progress_data,
                                  usize, false, lte);

        if (ctx->cur_write_res_offset == ctx->cur_write_res_size &&
            !(ctx->write_resource_flags & WRITE_RESOURCE_FLAG_PACK_STREAMS))
        {
                wimlib_assert(ctx->cur_write_res_offset == lte->size);

                /* Finished writing a stream in non-packed mode.  */

                ret = end_write_resource(ctx, &lte->out_reshdr);
                if (ret)
                        return ret;

                lte->out_reshdr.flags = filter_resource_flags(lte->flags);
                if (ctx->compressor != NULL)
                        lte->out_reshdr.flags |= WIM_RESHDR_FLAG_COMPRESSED;

                if (ctx->compressor != NULL &&
                    lte->out_reshdr.size_in_wim >= lte->out_reshdr.uncompressed_size &&
                    !(ctx->write_resource_flags & WRITE_RESOURCE_FLAG_PIPABLE) &&
                    !(lte->flags & WIM_RESHDR_FLAG_PACKED_STREAMS))
                {
                        /* Stream did not compress to less than its original
                         * size.  If we're not writing a pipable WIM (which
                         * could mean the output file descriptor is
                         * non-seekable), and the stream isn't located in a
                         * resource pack (which would make reading it again
                         * costly), truncate the file to the start of the stream
                         * and write it uncompressed instead.  */
                        DEBUG("Stream of size %"PRIu64" did not compress to "
                              "less than original size; writing uncompressed.",
                              lte->size);
                        ret = write_stream_uncompressed(lte, ctx->out_fd);
                        if (ret)
                                return ret;
                }

                wimlib_assert(lte->out_reshdr.uncompressed_size == lte->size);

                list_del(&lte->write_streams_list);
                ctx->cur_write_res_offset = 0;
        }

        return 0;

error:
        ERROR_WITH_ERRNO("Write error");
        return ret;
}

static int
submit_chunk_for_compression(struct write_streams_ctx *ctx,
                             const void *chunk, size_t size)
{
        /* While we are unable to submit the chunk for compression (due to too
         * many chunks already outstanding), retrieve and write the next
         * compressed chunk.  */
        while (!ctx->compressor->submit_chunk(ctx->compressor, chunk, size)) {
                const void *cchunk;
                unsigned csize;
                unsigned usize;
                bool bret;
                int ret;

                bret = ctx->compressor->get_chunk(ctx->compressor,
                                                  &cchunk, &csize, &usize);

                wimlib_assert(bret);

                ret = write_chunk(ctx, cchunk, csize, usize);
                if (ret)
                        return ret;
        }
        return 0;
}

/* Process the next chunk of data to be written to a WIM resource.  */
static int
write_stream_process_chunk(const void *chunk, size_t size, void *_ctx)
{
        struct write_streams_ctx *ctx = _ctx;
        int ret;
        const u8 *chunkptr, *chunkend;

        wimlib_assert(size != 0);

        if (ctx->compressor == NULL) {
                /* Write chunk uncompressed.  */
                 ret = write_chunk(ctx, chunk, size, size);
                 if (ret)
                         return ret;
                 ctx->cur_read_res_offset += size;
                 return 0;
        }

        /* Submit the chunk for compression, but take into account that the
         * @size the chunk was provided in may not correspond to the
         * @out_chunk_size being used for compression.  */
        chunkptr = chunk;
        chunkend = chunkptr + size;
        do {
                const u8 *resized_chunk;
                size_t needed_chunk_size;

                if (ctx->write_resource_flags & WRITE_RESOURCE_FLAG_PACK_STREAMS) {
                        needed_chunk_size = ctx->out_chunk_size;
                } else {
                        u64 res_bytes_remaining;

                        res_bytes_remaining = ctx->cur_read_res_size -
                                              ctx->cur_read_res_offset;
                        needed_chunk_size = min(ctx->out_chunk_size,
                                                ctx->chunk_buf_filled +
                                                        res_bytes_remaining);
                }

                if (ctx->chunk_buf_filled == 0 &&
                    chunkend - chunkptr >= needed_chunk_size)
                {
                        /* No intermediate buffering needed.  */
                        resized_chunk = chunkptr;
                        chunkptr += needed_chunk_size;
                        ctx->cur_read_res_offset += needed_chunk_size;
                } else {
                        /* Intermediate buffering needed.  */
                        size_t bytes_consumed;

                        bytes_consumed = min(chunkend - chunkptr,
                                             needed_chunk_size - ctx->chunk_buf_filled);

                        memcpy(&ctx->chunk_buf[ctx->chunk_buf_filled],
                               chunkptr, bytes_consumed);

                        resized_chunk = ctx->chunk_buf;

                        chunkptr += bytes_consumed;
                        ctx->cur_read_res_offset += bytes_consumed;
                        ctx->chunk_buf_filled += bytes_consumed;
                        if (ctx->chunk_buf_filled == needed_chunk_size) {
                                resized_chunk = ctx->chunk_buf;
                                ctx->chunk_buf_filled = 0;
                        } else {
                                break;
                        }

                }

                ret = submit_chunk_for_compression(ctx, resized_chunk,
                                                   needed_chunk_size);
                if (ret)
                        return ret;

        } while (chunkptr != chunkend);
        return 0;
}

/* Finish processing a stream for writing.  It may not have been completely
 * written yet, as the chunk_compressor implementation may still have chunks
 * buffered or being compressed.  */
static int
write_stream_end_read(struct wim_lookup_table_entry *lte, int status, void *_ctx)
{
        struct write_streams_ctx *ctx = _ctx;
        if (status == 0)
                wimlib_assert(ctx->cur_read_res_offset == ctx->cur_read_res_size);
        if (ctx->stream_was_duplicate) {
                free_lookup_table_entry(lte);
        } else if (lte->unhashed && ctx->lookup_table != NULL) {
                list_del(&lte->unhashed_list);
                lookup_table_insert(ctx->lookup_table, lte);
                lte->unhashed = 0;
        }
        return status;
}

/* Compute statistics about a list of streams that will be written.
 *
 * Assumes the streams are sorted such that all streams located in each distinct
 * WIM (specified by WIMStruct) are together.  */
static void
compute_stream_list_stats(struct list_head *stream_list,
                          struct write_streams_ctx *ctx)
{
        struct wim_lookup_table_entry *lte;
        u64 total_bytes = 0;
        u64 num_streams = 0;
        u64 total_parts = 0;
        WIMStruct *prev_wim_part = NULL;

        list_for_each_entry(lte, stream_list, write_streams_list) {
                num_streams++;
                total_bytes += lte->size;
                if (lte->resource_location == RESOURCE_IN_WIM) {
                        if (prev_wim_part != lte->rspec->wim) {
                                prev_wim_part = lte->rspec->wim;
                                total_parts++;
                        }
                }
        }
        ctx->progress_data.progress.write_streams.total_bytes       = total_bytes;
        ctx->progress_data.progress.write_streams.total_streams     = num_streams;
        ctx->progress_data.progress.write_streams.completed_bytes   = 0;
        ctx->progress_data.progress.write_streams.completed_streams = 0;
        ctx->progress_data.progress.write_streams.compression_type  = ctx->out_ctype;
        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;
        ctx->progress_data.prev_wim_part = NULL;
}

/* Find streams in @stream_list that can be copied to the output WIM in raw form
 * rather than compressed.  Delete these streams from @stream_list, and move one
 * per resource to @raw_copy_resources.  Return the total uncompressed size of
 * the streams that need to be compressed.  */
static u64
find_raw_copy_resources(struct list_head *stream_list,
                        int write_resource_flags,
                        int out_ctype,
                        u32 out_chunk_size,
                        struct list_head *raw_copy_resources)
{
        struct wim_lookup_table_entry *lte, *tmp;
        u64 num_bytes_to_compress = 0;

        INIT_LIST_HEAD(raw_copy_resources);

        /* Initialize temporary raw_copy_ok flag.  */
        list_for_each_entry(lte, stream_list, write_streams_list)
                if (lte->resource_location == RESOURCE_IN_WIM)
                        lte->rspec->raw_copy_ok = 0;

        list_for_each_entry_safe(lte, tmp, stream_list, write_streams_list) {
                if (lte->resource_location == RESOURCE_IN_WIM &&
                    lte->rspec->raw_copy_ok)
                {
                        list_del(&lte->write_streams_list);
                } else if (can_raw_copy(lte, write_resource_flags,
                                 out_ctype, out_chunk_size))
                {
                        lte->rspec->raw_copy_ok = 1;
                        list_move_tail(&lte->write_streams_list,
                                       raw_copy_resources);
                } else {
                        num_bytes_to_compress += lte->size;
                }
        }

        return num_bytes_to_compress;
}

/* Copy a raw compressed resource located in another WIM file to the WIM file
 * being written.  */
static int
write_raw_copy_resource(struct wim_resource_spec *in_rspec,
                        struct filedes *out_fd)
{
        u64 cur_read_offset;
        u64 end_read_offset;
        u8 buf[BUFFER_SIZE];
        size_t bytes_to_read;
        int ret;
        struct filedes *in_fd;
        struct wim_lookup_table_entry *lte;
        u64 out_offset_in_wim;

        DEBUG("Copying raw compressed data (size_in_wim=%"PRIu64", "
              "uncompressed_size=%"PRIu64")",
              in_rspec->size_in_wim, in_rspec->uncompressed_size);

        /* Copy the raw data.  */
        cur_read_offset = in_rspec->offset_in_wim;
        end_read_offset = cur_read_offset + in_rspec->size_in_wim;

        out_offset_in_wim = out_fd->offset;

        if (in_rspec->is_pipable) {
                if (cur_read_offset < sizeof(struct pwm_stream_hdr))
                        return WIMLIB_ERR_INVALID_PIPABLE_WIM;
                cur_read_offset -= sizeof(struct pwm_stream_hdr);
                out_offset_in_wim += sizeof(struct pwm_stream_hdr);
        }
        in_fd = &in_rspec->wim->in_fd;
        wimlib_assert(cur_read_offset != end_read_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_write(out_fd, buf, bytes_to_read);
                if (ret)
                        return ret;

                cur_read_offset += bytes_to_read;

        } while (cur_read_offset != end_read_offset);

        list_for_each_entry(lte, &in_rspec->stream_list, rspec_node) {
                if (lte->will_be_in_output_wim) {
                        stream_set_out_reshdr_for_reuse(lte);
                        if (in_rspec->flags & WIM_RESHDR_FLAG_PACKED_STREAMS)
                                lte->out_res_offset_in_wim = out_offset_in_wim;
                        else
                                lte->out_reshdr.offset_in_wim = out_offset_in_wim;

                }
        }
        return 0;
}

/* Copy a list of raw compressed resources located other WIM file(s) to the WIM
 * file being written.  */
static int
write_raw_copy_resources(struct list_head *raw_copy_resources,
                         struct filedes *out_fd,
                         struct write_streams_progress_data *progress_data)
{
        struct wim_lookup_table_entry *lte;
        int ret;

        list_for_each_entry(lte, raw_copy_resources, write_streams_list) {
                ret = write_raw_copy_resource(lte->rspec, out_fd);
                if (ret)
                        return ret;
                do_write_streams_progress(progress_data, lte->size, false, lte);
        }
        return 0;
}

/* Wait for and write all chunks pending in the compressor.  */
static int
finish_remaining_chunks(struct write_streams_ctx *ctx)
{
        const void *cdata;
        unsigned csize;
        unsigned usize;
        int ret;

        if (ctx->compressor == NULL)
                return 0;

        if (ctx->chunk_buf_filled != 0) {
                ret = submit_chunk_for_compression(ctx, ctx->chunk_buf,
                                                   ctx->chunk_buf_filled);
                if (ret)
                        return ret;
        }

        while (ctx->compressor->get_chunk(ctx->compressor, &cdata, &csize, &usize)) {
                ret = write_chunk(ctx, cdata, csize, usize);
                if (ret)
                        return ret;
        }
        return 0;
}

static void
remove_zero_length_streams(struct list_head *stream_list)
{
        struct wim_lookup_table_entry *lte, *tmp;

        list_for_each_entry_safe(lte, tmp, stream_list, write_streams_list) {
                wimlib_assert(lte->will_be_in_output_wim);
                if (lte->size == 0) {
                        list_del(&lte->write_streams_list);
                        lte->out_reshdr.offset_in_wim = 0;
                        lte->out_reshdr.size_in_wim = 0;
                        lte->out_reshdr.uncompressed_size = 0;
                        lte->out_reshdr.flags = filter_resource_flags(lte->flags);
                }
        }
}

/*
 * Write a list of streams to the output WIM file.
 *
 * @stream_list
 *      The list of streams to write, specifies a list of `struct
 *      wim_lookup_table_entry's linked by the 'write_streams_list' member.
 *
 * @out_fd
 *      The file descriptor, opened for writing, to which to write the streams.
 *
 * @write_resource_flags
 *      Flags to modify how the streams are written:
 *
 *      WRITE_RESOURCE_FLAG_RECOMPRESS:
 *              Force compression of all resources, even if they could otherwise
 *              be re-used by caping the raw data, due to being located in a WIM
 *              file with compatible compression parameters.
 *
 *      WRITE_RESOURCE_FLAG_PIPABLE:
 *              Write the resources in the wimlib-specific pipable format, and
 *              furthermore do so in such a way that no seeking backwards in
 *              @out_fd will be performed (so it may be a pipe, contrary to the
 *              default behavior).
 *
 *      WRITE_RESOURCE_FLAG_PACK_STREAMS:
 *              Pack all the streams into a single resource rather than writing
 *              them in separate resources.  This format is only valid if the
 *              WIM version number is WIM_VERSION_PACKED_STREAMS.  This flag
 *              currently may not be combined with WRITE_RESOURCE_FLAG_PIPABLE.
 *
 * @out_ctype
 *      Compression format to use to write the output streams, specified as one
 *      of the WIMLIB_COMPRESSION_TYPE_* constants, excepting
 *      WIMLIB_COMPRESSION_TYPE_INVALID but including
 *      WIMLIB_COMPRESSION_TYPE_NONE.
 *
 * @out_chunk_size
 *      Chunk size to use to write the streams.  It must be a valid chunk size
 *      for the specified compression format @out_ctype, unless @out_ctype is
 *      WIMLIB_COMPRESSION_TYPE_NONE, in which case this parameter is ignored.
 *
 * @num_threads
 *      Number of threads to use to compress data.  If 0, a default number of
 *      threads will be chosen.  The number of threads still may be decreased
 *      from the specified value if insufficient memory is detected.
 *
 * @lookup_table
 *      If on-the-fly deduplication of unhashed streams is desired, this
 *      parameter must be pointer to the lookup table for the WIMStruct on whose
 *      behalf the streams are being written.  Otherwise, this parameter can be
 *      NULL.
 *
 * @filter_ctx
 *      If on-the-fly deduplication of unhashed streams is desired, this
 *      parameter can be a pointer to a context for stream filtering used to
 *      detect whether the duplicate stream has been hard-filtered or not.  If
 *      no streams are hard-filtered or no streams are unhashed, this parameter
 *      can be NULL.
 *
 * @progress_func
 *      If non-NULL, a progress function that will be called periodically with
 *      WIMLIB_PROGRESS_MSG_WRITE_STREAMS messages.  Note that on-the-fly
 *      deduplication of unhashed streams may result in the total bytes provided
 *      in the progress data to decrease from one message to the next.
 *
 * This function will write the streams in @stream_list to resources in
 * consecutive positions in the output WIM file, or to a single packed resource
 * if WRITE_RESOURCE_FLAG_PACK_STREAMS was specified in @write_resource_flags.
 * In both cases, the @out_reshdr of the `struct wim_lookup_table_entry' for
 * each stream written will be updated to specify its location, size, and flags
 * in the output WIM.  In the packed resource case,
 * WIM_RESHDR_FLAG_PACKED_STREAMS shall be set in the @flags field of the
 * @out_reshdr, and @out_res_offset_in_wim and @out_res_size_in_wim will also
 * be set to the offset and size, respectively, in the output WIM of the full
 * packed resource containing the corresponding stream.
 *
 * Each of the streams to write may be in any location supported by the
 * resource-handling code (specifically, read_stream_list()), such as the
 * contents of external file that has been logically added to the output WIM, or
 * a stream in another WIM file that has been imported, or even stream in the
 * "same" WIM file of which a modified copy is being written.  In the case that
 * a stream is already in a WIM file and uses compatible compression parameters,
 * by default this function will re-use the raw data instead of decompressing
 * it, then recompressing it; however, with WRITE_RESOURCE_FLAG_RECOMPRESS
 * specified in @write_resource_flags, this is not done.
 *
 * As a further requirement, this function requires that the
 * @will_be_in_output_wim member be set on all streams in @stream_list as well
 * as any other streams not in @stream_list that will be in the output WIM file,
 * but not on any other streams in the output WIM's lookup table or sharing a
 * packed resource with a stream in @stream_list.  Still furthermore, if
 * on-the-fly deduplication of streams is possible, then all streams in
 * @stream_list must also be linked by @lookup_table_list along with any other
 * streams that have @will_be_in_output_wim set.
 *
 * This function handles on-the-fly deduplication of streams for which SHA1
 * message digests have not yet been calculated and it is therefore known
 * whether such streams are already in @stream_list or in the WIM's lookup table
 * at all.  If @lookup_table is non-NULL, then each stream in @stream_list that
 * has @unhashed set but not @unique_size set is checksummed immediately before
 * it would otherwise be read for writing in order to determine if it is
 * identical to another stream already being written or one that would be
 * filtered out of the output WIM using stream_filtered() with the context
 * @filter_ctx.  Each such duplicate stream will be removed from @stream_list, its
 * reference count transfered to the pre-existing duplicate stream, its memory
 * freed, and will not be written.  Alternatively, if a stream in @stream_list
 * is a duplicate with any stream in @lookup_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 @lookup_table_list.
 *
 * Returns 0 if all streams were written successfully (or did not need to be
 * written); otherwise a non-zero error code.
 */
static int
write_stream_list(struct list_head *stream_list,
                  struct filedes *out_fd,
                  int write_resource_flags,
                  int out_ctype,
                  u32 out_chunk_size,
                  unsigned num_threads,
                  struct wim_lookup_table *lookup_table,
                  struct filter_context *filter_ctx,
                  wimlib_progress_func_t progress_func)
{
        int ret;
        struct write_streams_ctx ctx;
        struct list_head raw_copy_resources;

        wimlib_assert((write_resource_flags &
                       (WRITE_RESOURCE_FLAG_PACK_STREAMS |
                        WRITE_RESOURCE_FLAG_PIPABLE)) !=
                                (WRITE_RESOURCE_FLAG_PACK_STREAMS |
                                 WRITE_RESOURCE_FLAG_PIPABLE));

        remove_zero_length_streams(stream_list);

        if (list_empty(stream_list)) {
                DEBUG("No streams to write.");
                return 0;
        }

        memset(&ctx, 0, sizeof(ctx));

        /* Pre-sorting the streams is required for compute_stream_list_stats().
         * Afterwards, read_stream_list() need not sort them again.  */
        ret = sort_stream_list_by_sequential_order(stream_list,
                                                   offsetof(struct wim_lookup_table_entry,
                                                            write_streams_list));
        if (ret)
                return ret;

        ctx.out_fd = out_fd;
        ctx.lookup_table = lookup_table;
        ctx.out_ctype = out_ctype;
        ctx.out_chunk_size = out_chunk_size;
        ctx.write_resource_flags = write_resource_flags;
        ctx.filter_ctx = filter_ctx;

        if (out_ctype != WIMLIB_COMPRESSION_TYPE_NONE) {
                wimlib_assert(out_chunk_size != 0);
                if (out_chunk_size <= STACK_MAX) {
                        ctx.chunk_buf = alloca(out_chunk_size);
                } else {
                        ctx.chunk_buf = MALLOC(out_chunk_size);
                        if (ctx.chunk_buf == NULL) {
                                ret = WIMLIB_ERR_NOMEM;
                                goto out_destroy_context;
                        }
                }
        }
        ctx.chunk_buf_filled = 0;

        compute_stream_list_stats(stream_list, &ctx);

        ctx.progress_data.progress_func = progress_func;

        ctx.num_bytes_to_compress = find_raw_copy_resources(stream_list,
                                                            write_resource_flags,
                                                            out_ctype,
                                                            out_chunk_size,
                                                            &raw_copy_resources);

        DEBUG("Writing stream list "
              "(offset = %"PRIu64", write_resource_flags=0x%08x, "
              "out_ctype=%d, out_chunk_size=%u, num_threads=%u, "
              "total_bytes=%"PRIu64", num_bytes_to_compress=%"PRIu64")",
              out_fd->offset, write_resource_flags,
              out_ctype, out_chunk_size, num_threads,
              ctx.progress_data.progress.write_streams.total_bytes,
              ctx.num_bytes_to_compress);

        if (ctx.num_bytes_to_compress == 0) {
                DEBUG("No compression needed; skipping to raw copy!");
                goto out_write_raw_copy_resources;
        }

        /* Unless uncompressed output was required, allocate a chunk_compressor
         * to do compression.  There are serial and parallel implementations of
         * the chunk_compressor interface.  We default to parallel using the
         * specified number of threads, unless the upper bound on the number
         * bytes needing to be compressed is less 2000000 (heuristic value).  */
        if (out_ctype != WIMLIB_COMPRESSION_TYPE_NONE) {

        #ifdef ENABLE_MULTITHREADED_COMPRESSION
                if (ctx.num_bytes_to_compress >= 2000000) {
                        ret = new_parallel_chunk_compressor(out_ctype,
                                                            out_chunk_size,
                                                            num_threads, 0,
                                                            &ctx.compressor);
                        if (ret) {
                                DEBUG("Couldn't create parallel chunk compressor "
                                      "(status %d)", ret);
                        }
                }
        #endif

                if (ctx.compressor == NULL) {
                        ret = new_serial_chunk_compressor(out_ctype, out_chunk_size,
                                                          &ctx.compressor);
                        if (ret)
                                goto out_destroy_context;
                }
        }

        if (ctx.compressor)
                ctx.progress_data.progress.write_streams.num_threads = ctx.compressor->num_threads;
        else
                ctx.progress_data.progress.write_streams.num_threads = 1;

        DEBUG("Actually using %u threads",
              ctx.progress_data.progress.write_streams.num_threads);

        INIT_LIST_HEAD(&ctx.pending_streams);

        if (ctx.progress_data.progress_func) {
                (*ctx.progress_data.progress_func)(WIMLIB_PROGRESS_MSG_WRITE_STREAMS,
                                                   &ctx.progress_data.progress);
        }

        if (write_resource_flags & WRITE_RESOURCE_FLAG_PACK_STREAMS) {
                ret = begin_write_resource(&ctx, ctx.num_bytes_to_compress);
                if (ret)
                        goto out_destroy_context;
        }

        /* Read the list of streams needing to be compressed, using the
         * specified callbacks to execute processing of the data.  */

        struct read_stream_list_callbacks cbs = {
                .begin_stream           = write_stream_begin_read,
                .begin_stream_ctx       = &ctx,
                .consume_chunk          = write_stream_process_chunk,
                .consume_chunk_ctx      = &ctx,
                .end_stream             = write_stream_end_read,
                .end_stream_ctx         = &ctx,
        };

        ret = read_stream_list(stream_list,
                               offsetof(struct wim_lookup_table_entry, write_streams_list),
                               &cbs,
                               STREAM_LIST_ALREADY_SORTED |
                                        VERIFY_STREAM_HASHES |
                                        COMPUTE_MISSING_STREAM_HASHES);

        if (ret)
                goto out_destroy_context;

        ret = finish_remaining_chunks(&ctx);
        if (ret)
                goto out_destroy_context;

        if (write_resource_flags & WRITE_RESOURCE_FLAG_PACK_STREAMS) {
                struct wim_reshdr reshdr;
                struct wim_lookup_table_entry *lte;
                u64 offset_in_res;

                ret = end_write_resource(&ctx, &reshdr);
                if (ret)
                        goto out_destroy_context;

                DEBUG("Ending packed resource: %lu %lu %lu.",
                      reshdr.offset_in_wim,
                      reshdr.size_in_wim,
                      reshdr.uncompressed_size);

                offset_in_res = 0;
                list_for_each_entry(lte, &ctx.pending_streams, write_streams_list) {
                        lte->out_reshdr.size_in_wim = lte->size;
                        lte->out_reshdr.flags = filter_resource_flags(lte->flags);
                        lte->out_reshdr.flags |= WIM_RESHDR_FLAG_PACKED_STREAMS;
                        lte->out_reshdr.uncompressed_size = 0;
                        lte->out_reshdr.offset_in_wim = offset_in_res;
                        lte->out_res_offset_in_wim = reshdr.offset_in_wim;
                        lte->out_res_size_in_wim = reshdr.size_in_wim;
                        /*lte->out_res_uncompressed_size = reshdr.uncompressed_size;*/
                        offset_in_res += lte->size;
                }
                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_resources, ctx.out_fd,
                                       &ctx.progress_data);

out_destroy_context:
        if (out_ctype != WIMLIB_COMPRESSION_TYPE_NONE && out_chunk_size > STACK_MAX)
                FREE(ctx.chunk_buf);
        FREE(ctx.chunk_csizes);
        if (ctx.compressor)
                ctx.compressor->destroy(ctx.compressor);
        DEBUG("Done (ret=%d)", ret);
        return ret;
}

static int
wim_write_stream_list(WIMStruct *wim,
                      struct list_head *stream_list,
                      int write_flags,
                      unsigned num_threads,
                      struct filter_context *filter_ctx,
                      wimlib_progress_func_t progress_func)
{
        int out_ctype;
        u32 out_chunk_size;
        int write_resource_flags;

        write_resource_flags = write_flags_to_resource_flags(write_flags);

        if (write_resource_flags & WRITE_RESOURCE_FLAG_PACK_STREAMS) {
                out_chunk_size = wim->out_pack_chunk_size;
                out_ctype = wim->out_pack_compression_type;
        } else {
                out_chunk_size = wim->out_chunk_size;
                out_ctype = wim->out_compression_type;
        }

        return write_stream_list(stream_list,
                                 &wim->out_fd,
                                 write_resource_flags,
                                 out_ctype,
                                 out_chunk_size,
                                 num_threads,
                                 wim->lookup_table,
                                 filter_ctx,
                                 progress_func);
}

static int
write_wim_resource(struct wim_lookup_table_entry *lte,
                   struct filedes *out_fd,
                   int out_ctype,
                   u32 out_chunk_size,
                   int write_resource_flags)
{
        LIST_HEAD(stream_list);
        list_add(&lte->write_streams_list, &stream_list);
        lte->will_be_in_output_wim = 1;
        return write_stream_list(&stream_list,
                                 out_fd,
                                 write_resource_flags & ~WRITE_RESOURCE_FLAG_PACK_STREAMS,
                                 out_ctype,
                                 out_chunk_size,
                                 1,
                                 NULL,
                                 NULL,
                                 NULL);
}

int
write_wim_resource_from_buffer(const void *buf, size_t buf_size,
                               int reshdr_flags, struct filedes *out_fd,
                               int out_ctype,
                               u32 out_chunk_size,
                               struct wim_reshdr *out_reshdr,
                               u8 *hash,
                               int write_resource_flags)
{
        int ret;
        struct wim_lookup_table_entry *lte;

        /* Set up a temporary lookup table entry to provide to
         * write_wim_resource().  */

        lte = new_lookup_table_entry();
        if (lte == NULL)
                return WIMLIB_ERR_NOMEM;

        lte->resource_location  = RESOURCE_IN_ATTACHED_BUFFER;
        lte->attached_buffer    = (void*)buf;
        lte->size               = buf_size;
        lte->flags              = reshdr_flags;

        if (write_resource_flags & WRITE_RESOURCE_FLAG_PIPABLE) {
                sha1_buffer(buf, buf_size, lte->hash);
                lte->unhashed = 0;
        } else {
                lte->unhashed = 1;
        }

        ret = write_wim_resource(lte, out_fd, out_ctype, out_chunk_size,
                                 write_resource_flags);
        if (ret)
                goto out_free_lte;

        copy_reshdr(out_reshdr, &lte->out_reshdr);

        if (hash)
                copy_hash(hash, lte->hash);
        ret = 0;
out_free_lte:
        lte->resource_location = RESOURCE_NONEXISTENT;
        free_lookup_table_entry(lte);
        return ret;
}

struct stream_size_table {
        struct hlist_head *array;
        size_t num_entries;
        size_t capacity;
};

static int
init_stream_size_table(struct stream_size_table *tab, size_t capacity)
{
        tab->array = CALLOC(capacity, sizeof(tab->array[0]));
        if (tab->array == NULL)
                return WIMLIB_ERR_NOMEM;
        tab->num_entries = 0;
        tab->capacity = capacity;
        return 0;
}

static void
destroy_stream_size_table(struct stream_size_table *tab)
{
        FREE(tab->array);
}

static int
stream_size_table_insert(struct wim_lookup_table_entry *lte, void *_tab)
{
        struct stream_size_table *tab = _tab;
        size_t pos;
        struct wim_lookup_table_entry *same_size_lte;
        struct hlist_node *tmp;

        pos = hash_u64(lte->size) % tab->capacity;
        lte->unique_size = 1;
        hlist_for_each_entry(same_size_lte, tmp, &tab->array[pos], hash_list_2) {
                if (same_size_lte->size == lte->size) {
                        lte->unique_size = 0;
                        same_size_lte->unique_size = 0;
                        break;
                }
        }

        hlist_add_head(&lte->hash_list_2, &tab->array[pos]);
        tab->num_entries++;
        return 0;
}

struct find_streams_ctx {
        WIMStruct *wim;
        int write_flags;
        struct list_head stream_list;
        struct stream_size_table stream_size_tab;
};

static void
reference_stream_for_write(struct wim_lookup_table_entry *lte,
                           struct list_head *stream_list, u32 nref)
{
        if (!lte->will_be_in_output_wim) {
                lte->out_refcnt = 0;
                list_add_tail(&lte->write_streams_list, stream_list);
                lte->will_be_in_output_wim = 1;
        }
        lte->out_refcnt += nref;
}

static int
fully_reference_stream_for_write(struct wim_lookup_table_entry *lte,
                                 void *_stream_list)
{
        struct list_head *stream_list = _stream_list;
        lte->will_be_in_output_wim = 0;
        reference_stream_for_write(lte, stream_list, lte->refcnt);
        return 0;
}

static int
inode_find_streams_to_reference(const struct wim_inode *inode,
                                const struct wim_lookup_table *table,
                                struct list_head *stream_list)
{
        struct wim_lookup_table_entry *lte;
        unsigned i;

        wimlib_assert(inode->i_nlink > 0);

        for (i = 0; i <= inode->i_num_ads; i++) {
                lte = inode_stream_lte(inode, i, table);
                if (lte)
                        reference_stream_for_write(lte, stream_list,
                                                   inode->i_nlink);
                else if (!is_zero_hash(inode_stream_hash(inode, i)))
                        return WIMLIB_ERR_RESOURCE_NOT_FOUND;
        }
        return 0;
}

static int
do_stream_set_not_in_output_wim(struct wim_lookup_table_entry *lte, void *_ignore)
{
        lte->will_be_in_output_wim = 0;
        return 0;
}

static int
image_find_streams_to_reference(WIMStruct *wim)
{
        struct wim_image_metadata *imd;
        struct wim_inode *inode;
        struct wim_lookup_table_entry *lte;
        struct list_head *stream_list;
        int ret;

        imd = wim_get_current_image_metadata(wim);

        image_for_each_unhashed_stream(lte, imd)
                lte->will_be_in_output_wim = 0;

        stream_list = wim->private;
        image_for_each_inode(inode, imd) {
                ret = inode_find_streams_to_reference(inode,
                                                      wim->lookup_table,
                                                      stream_list);
                if (ret)
                        return ret;
        }
        return 0;
}

static int
prepare_unfiltered_list_of_streams_in_output_wim(WIMStruct *wim,
                                                 int image,
                                                 int streams_ok,
                                                 struct list_head *stream_list_ret)
{
        int ret;

        INIT_LIST_HEAD(stream_list_ret);

        if (streams_ok && (image == WIMLIB_ALL_IMAGES ||
                           (image == 1 && wim->hdr.image_count == 1)))
        {
                /* Fast case:  Assume that all streams are being written and
                 * that the reference counts are correct.  */
                struct wim_lookup_table_entry *lte;
                struct wim_image_metadata *imd;
                unsigned i;

                for_lookup_table_entry(wim->lookup_table,
                                       fully_reference_stream_for_write,
                                       stream_list_ret);

                for (i = 0; i < wim->hdr.image_count; i++) {
                        imd = wim->image_metadata[i];
                        image_for_each_unhashed_stream(lte, imd)
                                fully_reference_stream_for_write(lte, stream_list_ret);
                }
        } else {
                /* Slow case:  Walk through the images being written and
                 * determine the streams referenced.  */
                for_lookup_table_entry(wim->lookup_table,
                                       do_stream_set_not_in_output_wim, NULL);
                wim->private = stream_list_ret;
                ret = for_image(wim, image, image_find_streams_to_reference);
                if (ret)
                        return ret;
        }

        return 0;
}

struct insert_other_if_hard_filtered_ctx {
        struct stream_size_table *tab;
        struct filter_context *filter_ctx;
};

static int
insert_other_if_hard_filtered(struct wim_lookup_table_entry *lte, void *_ctx)
{
        struct insert_other_if_hard_filtered_ctx *ctx = _ctx;

        if (!lte->will_be_in_output_wim &&
            stream_hard_filtered(lte, ctx->filter_ctx))
                stream_size_table_insert(lte, ctx->tab);
        return 0;
}

static int
determine_stream_size_uniquity(struct list_head *stream_list,
                               struct wim_lookup_table *lt,
                               struct filter_context *filter_ctx)
{
        int ret;
        struct stream_size_table tab;
        struct wim_lookup_table_entry *lte;

        ret = init_stream_size_table(&tab, lt->capacity);
        if (ret)
                return ret;

        if (may_hard_filter_streams(filter_ctx)) {
                struct insert_other_if_hard_filtered_ctx ctx = {
                        .tab = &tab,
                        .filter_ctx = filter_ctx,
                };
                for_lookup_table_entry(lt, insert_other_if_hard_filtered, &ctx);
        }

        list_for_each_entry(lte, stream_list, write_streams_list)
                stream_size_table_insert(lte, &tab);

        destroy_stream_size_table(&tab);
        return 0;
}

static void
filter_stream_list_for_write(struct list_head *stream_list,
                             struct filter_context *filter_ctx)
{
        struct wim_lookup_table_entry *lte, *tmp;

        list_for_each_entry_safe(lte, tmp,
                                 stream_list, write_streams_list)
        {
                int status = stream_filtered(lte, filter_ctx);

                if (status == 0) {
                        /* Not filtered.  */
                        continue;
                } else {
                        if (status > 0) {
                                /* Soft filtered.  */
                        } else {
                                /* Hard filtered.  */
                                lte->will_be_in_output_wim = 0;
                                list_del(&lte->lookup_table_list);
                        }
                        list_del(&lte->write_streams_list);
                }
        }
}

/*
 * prepare_stream_list_for_write() -
 *
 * Prepare the list of streams to write for writing a WIM containing the
 * specified image(s) with the specified write flags.
 *
 * @wim
 *      The WIMStruct on whose behalf the write is occurring.
 *
 * @image
 *      Image(s) from the WIM to write; may be WIMLIB_ALL_IMAGES.
 *
 * @write_flags
 *      WIMLIB_WRITE_FLAG_* flags for the write operation:
 *
 *      STREAMS_OK:  For writes of all images, assume that all streams in the
 *      lookup table of @wim and the per-image lists of unhashed streams 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.
 *
 *      OVERWRITE:  Streams already present in @wim shall not be returned in
 *      @stream_list_ret.
 *
 *      SKIP_EXTERNAL_WIMS:  Streams already present in a WIM file, but not
 *      @wim, shall be be returned in neither @stream_list_ret nor
 *      @lookup_table_list_ret.
 *
 * @stream_list_ret
 *      List of streams, linked by write_streams_list, that need to be written
 *      will be returned here.
 *
 *      Note that this function assumes that unhashed streams will be written;
 *      it does not take into account that they may become duplicates when
 *      actually hashed.
 *
 * @lookup_table_list_ret
 *      List of streams, linked by lookup_table_list, that need to be included
 *      in the WIM's lookup table will be returned here.  This will be a
 *      superset of the streams in @stream_list_ret.
 *
 *      This list will be a proper superset of @stream_list_ret if and only if
 *      WIMLIB_WRITE_FLAG_OVERWRITE was specified in @write_flags and some of
 *      the streams that would otherwise need to be written were already located
 *      in the WIM file.
 *
 *      All streams in this list will have @out_refcnt set to the number of
 *      references to the stream in the output WIM.  If
 *      WIMLIB_WRITE_FLAG_STREAMS_OK was specified in @write_flags, @out_refcnt
 *      may be as low as 0.
 *
 * @filter_ctx_ret
 *      A context for queries of stream filter status with stream_filtered() is
 *      returned in this location.
 *
 * In addition, @will_be_in_output_wim will be set to 1 in all stream entries
 * inserted into @lookup_table_list_ret and to 0 in all stream entries in the
 * lookup table of @wim not inserted into @lookup_table_list_ret.
 *
 * Still furthermore, @unique_size will be set to 1 on all stream entries in
 * @stream_list_ret that have unique size among all stream entries in
 * @stream_list_ret and among all stream entries in the lookup table of @wim
 * that are ineligible for being written due to filtering.
 *
 * Returns 0 on success; nonzero on read error, memory allocation error, or
 * otherwise.
 */
static int
prepare_stream_list_for_write(WIMStruct *wim, int image,
                              int write_flags,
                              struct list_head *stream_list_ret,
                              struct list_head *lookup_table_list_ret,
                              struct filter_context *filter_ctx_ret)
{
        int ret;
        struct wim_lookup_table_entry *lte;

        filter_ctx_ret->write_flags = write_flags;
        filter_ctx_ret->wim = wim;

        ret = prepare_unfiltered_list_of_streams_in_output_wim(
                                wim,
                                image,
                                write_flags & WIMLIB_WRITE_FLAG_STREAMS_OK,
                                stream_list_ret);
        if (ret)
                return ret;

        INIT_LIST_HEAD(lookup_table_list_ret);
        list_for_each_entry(lte, stream_list_ret, write_streams_list)
                list_add_tail(&lte->lookup_table_list, lookup_table_list_ret);

        ret = determine_stream_size_uniquity(stream_list_ret, wim->lookup_table,
                                             filter_ctx_ret);
        if (ret)
                return ret;

        if (may_filter_streams(filter_ctx_ret))
                filter_stream_list_for_write(stream_list_ret, filter_ctx_ret);

        return 0;
}

static int
write_wim_streams(WIMStruct *wim, int image, int write_flags,
                  unsigned num_threads,
                  wimlib_progress_func_t progress_func,
                  struct list_head *stream_list_override,
                  struct list_head *lookup_table_list_ret)
{
        int ret;
        struct list_head _stream_list;
        struct list_head *stream_list;
        struct wim_lookup_table_entry *lte;
        struct filter_context _filter_ctx;
        struct filter_context *filter_ctx;

        if (stream_list_override == NULL) {
                /* Normal case: prepare stream list from image(s) being written.
                 */
                stream_list = &_stream_list;
                filter_ctx = &_filter_ctx;
                ret = prepare_stream_list_for_write(wim, image, write_flags,
                                                    stream_list,
                                                    lookup_table_list_ret,
                                                    filter_ctx);
                if (ret)
                        return ret;
        } else {
                /* Currently only as a result of wimlib_split() being called:
                 * use stream list already explicitly provided.  Use existing
                 * reference counts.  */
                stream_list = stream_list_override;
                filter_ctx = NULL;
                INIT_LIST_HEAD(lookup_table_list_ret);
                list_for_each_entry(lte, stream_list, write_streams_list) {
                        lte->out_refcnt = lte->refcnt;
                        lte->will_be_in_output_wim = 1;
                        lte->unique_size = 0;
                        list_add_tail(&lte->lookup_table_list, lookup_table_list_ret);
                }
        }

        return wim_write_stream_list(wim,
                                     stream_list,
                                     write_flags,
                                     num_threads,
                                     filter_ctx,
                                     progress_func);
}

static int
write_wim_metadata_resources(WIMStruct *wim, int image, int write_flags,
                             wimlib_progress_func_t progress_func)
{
        int ret;
        int start_image;
        int end_image;
        int write_resource_flags;

        if (write_flags & WIMLIB_WRITE_FLAG_NO_METADATA) {
                DEBUG("Not writing any metadata resources.");
                return 0;
        }

        write_resource_flags = write_flags_to_resource_flags(write_flags);

        write_resource_flags &= ~WRITE_RESOURCE_FLAG_PACK_STREAMS;

        DEBUG("Writing metadata resources (offset=%"PRIu64")",
              wim->out_fd.offset);

        if (progress_func)
                progress_func(WIMLIB_PROGRESS_MSG_WRITE_METADATA_BEGIN, NULL);

        if (image == WIMLIB_ALL_IMAGES) {
                start_image = 1;
                end_image = wim->hdr.image_count;
        } else {
                start_image = image;
                end_image = image;
        }

        for (int i = start_image; i <= end_image; i++) {
                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) {
                        DEBUG("Image %u was modified; building and writing new "
                              "metadata resource", i);
                        ret = write_metadata_resource(wim, i,
                                                      write_resource_flags);
                } else if (write_flags & WIMLIB_WRITE_FLAG_OVERWRITE) {
                        DEBUG("Image %u was not modified; re-using existing "
                              "metadata resource.", i);
                        stream_set_out_reshdr_for_reuse(imd->metadata_lte);
                        ret = 0;
                } else {
                        DEBUG("Image %u was not modified; copying existing "
                              "metadata resource.", i);
                        ret = write_wim_resource(imd->metadata_lte,
                                                 &wim->out_fd,
                                                 wim->out_compression_type,
                                                 wim->out_chunk_size,
                                                 write_resource_flags);
                }
                if (ret)
                        return ret;
        }
        if (progress_func)
                progress_func(WIMLIB_PROGRESS_MSG_WRITE_METADATA_END, NULL);
        return 0;
}

static int
open_wim_writable(WIMStruct *wim, const tchar *path, int open_flags)
{
        int raw_fd;
        DEBUG("Opening \"%"TS"\" for writing.", path);

        raw_fd = topen(path, open_flags | O_BINARY, 0644);
        if (raw_fd < 0) {
                ERROR_WITH_ERRNO("Failed to open \"%"TS"\" for writing", path);
                return WIMLIB_ERR_OPEN;
        }
        filedes_init(&wim->out_fd, raw_fd);
        return 0;
}

static int
close_wim_writable(WIMStruct *wim, int write_flags)
{
        int ret = 0;

        if (!(write_flags & WIMLIB_WRITE_FLAG_FILE_DESCRIPTOR)) {
                DEBUG("Closing WIM file.");
                if (filedes_valid(&wim->out_fd))
                        if (filedes_close(&wim->out_fd))
                                ret = WIMLIB_ERR_WRITE;
        }
        filedes_invalidate(&wim->out_fd);
        return ret;
}

static int
cmp_streams_by_out_rspec(const void *p1, const void *p2)
{
        const struct wim_lookup_table_entry *lte1, *lte2;

        lte1 = *(const struct wim_lookup_table_entry**)p1;
        lte2 = *(const struct wim_lookup_table_entry**)p2;

        if (lte1->out_reshdr.flags & WIM_RESHDR_FLAG_PACKED_STREAMS) {
                if (lte2->out_reshdr.flags & WIM_RESHDR_FLAG_PACKED_STREAMS) {
                        if (lte1->out_res_offset_in_wim != lte2->out_res_offset_in_wim)
                                return cmp_u64(lte1->out_res_offset_in_wim,
                                               lte2->out_res_offset_in_wim);
                } else {
                        return 1;
                }
        } else {
                if (lte2->out_reshdr.flags & WIM_RESHDR_FLAG_PACKED_STREAMS)
                        return -1;
        }
        return cmp_u64(lte1->out_reshdr.offset_in_wim,
                       lte2->out_reshdr.offset_in_wim);
}

static int
write_wim_lookup_table(WIMStruct *wim, int image, int write_flags,
                       struct wim_reshdr *out_reshdr,
                       struct list_head *lookup_table_list)
{
        int ret;

        /* Set output resource metadata for streams already present in WIM.  */
        if (write_flags & WIMLIB_WRITE_FLAG_OVERWRITE) {
                struct wim_lookup_table_entry *lte;
                list_for_each_entry(lte, lookup_table_list, lookup_table_list)
                {
                        if (lte->resource_location == RESOURCE_IN_WIM &&
                            lte->rspec->wim == wim)
                        {
                                stream_set_out_reshdr_for_reuse(lte);
                        }
                }
        }

        ret = sort_stream_list(lookup_table_list,
                               offsetof(struct wim_lookup_table_entry, lookup_table_list),
                               cmp_streams_by_out_rspec);
        if (ret)
                return ret;

        /* Add entries for metadata resources.  */
        if (!(write_flags & WIMLIB_WRITE_FLAG_NO_METADATA)) {
                int start_image;
                int end_image;

                if (image == WIMLIB_ALL_IMAGES) {
                        start_image = 1;
                        end_image = wim->hdr.image_count;
                } else {
                        start_image = image;
                        end_image = image;
                }

                /* Push metadata resource lookup table entries onto the front of
                 * the list in reverse order, so that they're written in order.
                 */
                for (int i = end_image; i >= start_image; i--) {
                        struct wim_lookup_table_entry *metadata_lte;

                        metadata_lte = wim->image_metadata[i - 1]->metadata_lte;
                        wimlib_assert(metadata_lte->out_reshdr.flags & WIM_RESHDR_FLAG_METADATA);
                        metadata_lte->out_refcnt = 1;
                        list_add(&metadata_lte->lookup_table_list, lookup_table_list);
                }
        }

        return write_wim_lookup_table_from_stream_list(lookup_table_list,
                                                       &wim->out_fd,
                                                       wim->hdr.part_number,
                                                       out_reshdr,
                                                       write_flags_to_resource_flags(write_flags));
}

/*
 * finish_write():
 *
 * Finish writing a WIM file: write the lookup table, xml data, and integrity
 * table, then overwrite the WIM header.  By default, closes the WIM file
 * descriptor (@wim->out_fd) if successful.
 *
 * write_flags is a bitwise OR of the following:
 *
 *      (public) WIMLIB_WRITE_FLAG_CHECK_INTEGRITY:
 *              Include an integrity table.
 *
 *      (public) WIMLIB_WRITE_FLAG_FSYNC:
 *              fsync() the output file before closing it.
 *
 *      (public) WIMLIB_WRITE_FLAG_PIPABLE:
 *              Writing a pipable WIM, possibly to a pipe; include pipable WIM
 *              stream headers before the lookup table and XML data, and also
 *              write the WIM header at the end instead of seeking to the
 *              beginning.  Can't be combined with
 *              WIMLIB_WRITE_FLAG_CHECK_INTEGRITY.
 *
 *      (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_HEADER_AT_END:
 *              Instead of overwriting the WIM header at the beginning of the
 *              file, simply append it to the end of the file.  (Used when
 *              writing to pipe.)
 *      (private) WIMLIB_WRITE_FLAG_FILE_DESCRIPTOR:
 *              Do not close the file descriptor @wim->out_fd on either success
 *              on failure.
 *      (private) WIMLIB_WRITE_FLAG_USE_EXISTING_TOTALBYTES:
 *              Use the existing <TOTALBYTES> stored in the in-memory XML
 *              information, rather than setting it to the offset of the XML
 *              data being written.
 */
static int
finish_write(WIMStruct *wim, int image, int write_flags,
             wimlib_progress_func_t progress_func,
             struct list_head *lookup_table_list)
{
        int ret;
        off_t hdr_offset;
        int write_resource_flags;
        off_t old_lookup_table_end;
        off_t new_lookup_table_end;
        u64 xml_totalbytes;

        DEBUG("image=%d, write_flags=%08x", image, write_flags);

        write_resource_flags = write_flags_to_resource_flags(write_flags);

        /* In the WIM header, there is room for the resource entry for a
         * metadata resource labeled as the "boot metadata".  This entry should
         * be zeroed out if there is no bootable image (boot_idx 0).  Otherwise,
         * it should be a copy of the resource entry for the image that is
         * marked as bootable.  This is not well documented...  */
        if (wim->hdr.boot_idx == 0) {
                zero_reshdr(&wim->hdr.boot_metadata_reshdr);
        } else {
                copy_reshdr(&wim->hdr.boot_metadata_reshdr,
                            &wim->image_metadata[
                                wim->hdr.boot_idx - 1]->metadata_lte->out_reshdr);
        }

        /* Write lookup table.  (Save old position first.)  */
        old_lookup_table_end = wim->hdr.lookup_table_reshdr.offset_in_wim +
                               wim->hdr.lookup_table_reshdr.size_in_wim;
        if (!(write_flags & WIMLIB_WRITE_FLAG_NO_LOOKUP_TABLE)) {
                ret = write_wim_lookup_table(wim, image, write_flags,
                                             &wim->hdr.lookup_table_reshdr,
                                             lookup_table_list);
                if (ret)
                        return ret;
        }

        /* Write XML data.  */
        xml_totalbytes = wim->out_fd.offset;
        if (write_flags & WIMLIB_WRITE_FLAG_USE_EXISTING_TOTALBYTES)
                xml_totalbytes = WIM_TOTALBYTES_USE_EXISTING;
        ret = write_wim_xml_data(wim, image, xml_totalbytes,
                                 &wim->hdr.xml_data_reshdr,
                                 write_resource_flags);
        if (ret)
                return ret;

        /* Write integrity table (optional).  */
        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, &wim->hdr, sizeof(struct wim_header));
                        zero_reshdr(&checkpoint_hdr.integrity_table_reshdr);
                        checkpoint_hdr.flags |= WIM_HDR_FLAG_WRITE_IN_PROGRESS;
                        ret = write_wim_header_at_offset(&checkpoint_hdr,
                                                         &wim->out_fd, 0);
                        if (ret)
                                return ret;
                }

                if (!(write_flags & WIMLIB_WRITE_FLAG_REUSE_INTEGRITY_TABLE))
                        old_lookup_table_end = 0;

                new_lookup_table_end = wim->hdr.lookup_table_reshdr.offset_in_wim +
                                       wim->hdr.lookup_table_reshdr.size_in_wim;

                ret = write_integrity_table(wim,
                                            new_lookup_table_end,
                                            old_lookup_table_end,
                                            progress_func);
                if (ret)
                        return ret;
        } else {
                /* No integrity table.  */
                zero_reshdr(&wim->hdr.integrity_table_reshdr);
        }

        /* Now that all information in the WIM header has been determined, the
         * preliminary header written earlier can be overwritten, the header of
         * the existing WIM file can be overwritten, or the final header can be
         * written to the end of the pipable WIM.  */
        wim->hdr.flags &= ~WIM_HDR_FLAG_WRITE_IN_PROGRESS;
        hdr_offset = 0;
        if (write_flags & WIMLIB_WRITE_FLAG_HEADER_AT_END)
                hdr_offset = wim->out_fd.offset;
        DEBUG("Writing new header @ %"PRIu64".", hdr_offset);
        ret = write_wim_header_at_offset(&wim->hdr, &wim->out_fd, hdr_offset);
        if (ret)
                return ret;

        /* 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
         * the system is abruptly terminated when the metadata for the rename
         * operation has been written to disk, but the new file data has not.
         */
        if (write_flags & WIMLIB_WRITE_FLAG_FSYNC) {
                DEBUG("Syncing WIM file.");
                if (fsync(wim->out_fd.fd)) {
                        ERROR_WITH_ERRNO("Error syncing data to WIM file");
                        return WIMLIB_ERR_WRITE;
                }
        }

        if (close_wim_writable(wim, write_flags)) {
                ERROR_WITH_ERRNO("Failed to close the output WIM file");
                return WIMLIB_ERR_WRITE;
        }

        return 0;
}

#if defined(HAVE_SYS_FILE_H) && defined(HAVE_FLOCK)
int
lock_wim(WIMStruct *wim, int fd)
{
        int ret = 0;
        if (fd != -1 && !wim->wim_locked) {
                ret = flock(fd, LOCK_EX | LOCK_NB);
                if (ret != 0) {
                        if (errno == EWOULDBLOCK) {
                                ERROR("`%"TS"' is already being modified or has been "
                                      "mounted read-write\n"
                                      "        by another process!", wim->filename);
                                ret = WIMLIB_ERR_ALREADY_LOCKED;
                        } else {
                                WARNING_WITH_ERRNO("Failed to lock `%"TS"'",
                                                   wim->filename);
                                ret = 0;
                        }
                } else {
                        wim->wim_locked = 1;
                }
        }
        return ret;
}
#endif

/*
 * write_pipable_wim():
 *
 * Perform the intermediate stages of creating a "pipable" WIM (i.e. a WIM
 * capable of being applied from a pipe).
 *
 * Pipable WIMs are a wimlib-specific modification of the WIM format such that
 * images can be applied from them sequentially when the file data is sent over
 * a pipe.  In addition, a pipable WIM can be written sequentially to a pipe.
 * The modifications made to the WIM format for pipable WIMs are:
 *
 * - Magic characters in header are "WLPWM\0\0\0" (wimlib pipable WIM) instead
 *   of "MSWIM\0\0\0".  This lets wimlib know that the WIM is pipable and also
 *   stops other software from trying to read the file as a normal WIM.
 *
 * - The header at the beginning of the file does not contain all the normal
 *   information; in particular it will have all 0's for the lookup table and
 *   XML data resource entries.  This is because this information cannot be
 *   determined until the lookup table and XML data have been written.
 *   Consequently, wimlib will write the full header at the very end of the
 *   file.  The header at the end, however, is only used when reading the WIM
 *   from a seekable file (not a pipe).
 *
 * - An extra copy of the XML data is placed directly after the header.  This
 *   allows image names and sizes to be determined at an appropriate time when
 *   reading the WIM from a pipe.  This copy of the XML data is ignored if the
 *   WIM is read from a seekable file (not a pipe).
 *
 * - The format of resources, or streams, has been modified to allow them to be
 *   used before the "lookup table" has been read.  Each stream is prefixed with
 *   a `struct pwm_stream_hdr' that is basically an abbreviated form of `struct
 *   wim_lookup_table_entry_disk' that only contains the SHA1 message digest,
 *   uncompressed stream size, and flags that indicate whether the stream is
 *   compressed.  The data of uncompressed streams then follows literally, while
 *   the data of compressed streams follows in a modified format.  Compressed
 *   streams do not begin with a chunk table, since the chunk table cannot be
 *   written until all chunks have been compressed.  Instead, each compressed
 *   chunk is prefixed by a `struct pwm_chunk_hdr' that gives its size.
 *   Furthermore, the chunk table is written at the end of the resource instead
 *   of the start.  Note: chunk offsets are given in the chunk table as if the
 *   `struct pwm_chunk_hdr's were not present; also, the chunk table is only
 *   used if the WIM is being read from a seekable file (not a pipe).
 *
 * - Metadata resources always come before other file resources (streams).
 *   (This does not by itself constitute an incompatibility with normal WIMs,
 *   since this is valid in normal WIMs.)
 *
 * - At least up to the end of the file resources, all components must be packed
 *   as tightly as possible; there cannot be any "holes" in the WIM.  (This does
 *   not by itself consititute an incompatibility with normal WIMs, since this
 *   is valid in normal WIMs.)
 *
 * Note: the lookup table, XML data, and header at the end are not used when
 * applying from a pipe.  They exist to support functionality such as image
 * application and export when the WIM is *not* read from a pipe.
 *
 *   Layout of pipable WIM:
 *
 * ---------+----------+--------------------+----------------+--------------+-----------+--------+
 * | Header | XML data | Metadata resources | File resources | Lookup table | XML data  | Header |
 * ---------+----------+--------------------+----------------+--------------+-----------+--------+
 *
 *   Layout of normal WIM:
 *
 * +--------+-----------------------------+-------------------------+
 * | Header | File and metadata resources | Lookup table | XML data |
 * +--------+-----------------------------+-------------------------+
 *
 * An optional integrity table can follow the final XML data in both normal and
 * pipable WIMs.  However, due to implementation details, wimlib currently can
 * only include an integrity table in a pipable WIM when writing it to a
 * seekable file (not a pipe).
 *
 * Do note that since pipable WIMs are not supported by Microsoft's software,
 * wimlib does not create them unless explicitly requested (with
 * WIMLIB_WRITE_FLAG_PIPABLE) and as stated above they use different magic
 * characters to identify the file.
 */
static int
write_pipable_wim(WIMStruct *wim, int image, int write_flags,
                  unsigned num_threads, wimlib_progress_func_t progress_func,
                  struct list_head *stream_list_override,
                  struct list_head *lookup_table_list_ret)
{
        int ret;
        struct wim_reshdr xml_reshdr;

        WARNING("Creating a pipable WIM, which will "
                "be incompatible\n"
                "          with Microsoft's software (wimgapi/imagex/Dism).");

        /* At this point, the header at the beginning of the file has already
         * been written.  */

        /* For efficiency, when wimlib adds an image to the WIM with
         * wimlib_add_image(), the SHA1 message digests of files is not
         * calculated; instead, they are calculated while the files are being
         * written.  However, this does not work when writing a pipable WIM,
         * since when writing a stream to a pipable WIM, its SHA1 message digest
         * needs to be known before the stream data is written.  Therefore,
         * before getting much farther, we need to pre-calculate the SHA1
         * message digests of all streams that will be written.  */
        ret = wim_checksum_unhashed_streams(wim);
        if (ret)
                return ret;

        /* Write extra copy of the XML data.  */
        ret = write_wim_xml_data(wim, image, WIM_TOTALBYTES_OMIT,
                                 &xml_reshdr,
                                 WRITE_RESOURCE_FLAG_PIPABLE);
        if (ret)
                return ret;

        /* Write metadata resources for the image(s) being included in the
         * output WIM.  */
        ret = write_wim_metadata_resources(wim, image, write_flags,
                                           progress_func);
        if (ret)
                return ret;

        /* Write streams needed for the image(s) being included in the output
         * WIM, or streams needed for the split WIM part.  */
        return write_wim_streams(wim, image, write_flags, num_threads,
                                 progress_func, stream_list_override,
                                 lookup_table_list_ret);

        /* The lookup table, XML data, and header at end are handled by
         * finish_write().  */
}

/* Write a standalone WIM or split WIM (SWM) part to a new file or to a file
 * descriptor.  */
int
write_wim_part(WIMStruct *wim,
               const void *path_or_fd,
               int image,
               int write_flags,
               unsigned num_threads,
               wimlib_progress_func_t progress_func,
               unsigned part_number,
               unsigned total_parts,
               struct list_head *stream_list_override,
               const u8 *guid)
{
        int ret;
        struct wim_header hdr_save;
        struct list_head lookup_table_list;

        if (total_parts == 1)
                DEBUG("Writing standalone WIM.");
        else
                DEBUG("Writing split WIM part %u/%u", part_number, total_parts);
        if (image == WIMLIB_ALL_IMAGES)
                DEBUG("Including all images.");
        else
                DEBUG("Including image %d only.", image);
        if (write_flags & WIMLIB_WRITE_FLAG_FILE_DESCRIPTOR)
                DEBUG("File descriptor: %d", *(const int*)path_or_fd);
        else
                DEBUG("Path: \"%"TS"\"", (const tchar*)path_or_fd);
        DEBUG("Write flags: 0x%08x", write_flags);

        if (write_flags & WIMLIB_WRITE_FLAG_CHECK_INTEGRITY)
                DEBUG("\tCHECK_INTEGRITY");

        if (write_flags & WIMLIB_WRITE_FLAG_REBUILD)
                DEBUG("\tREBUILD");

        if (write_flags & WIMLIB_WRITE_FLAG_RECOMPRESS)
                DEBUG("\tRECOMPRESS");

        if (write_flags & WIMLIB_WRITE_FLAG_FSYNC)
                DEBUG("\tFSYNC");

        if (write_flags & WIMLIB_WRITE_FLAG_SOFT_DELETE)
                DEBUG("\tFSYNC");

        if (write_flags & WIMLIB_WRITE_FLAG_IGNORE_READONLY_FLAG)
                DEBUG("\tIGNORE_READONLY_FLAG");

        if (write_flags & WIMLIB_WRITE_FLAG_PIPABLE)
                DEBUG("\tPIPABLE");

        if (write_flags & WIMLIB_WRITE_FLAG_NOT_PIPABLE)
                DEBUG("\tNOT_PIPABLE");

        if (write_flags & WIMLIB_WRITE_FLAG_PACK_STREAMS)
                DEBUG("\tPACK_STREAMS");

        if (write_flags & WIMLIB_WRITE_FLAG_FILE_DESCRIPTOR)
                DEBUG("\tFILE_DESCRIPTOR");

        if (write_flags & WIMLIB_WRITE_FLAG_NO_METADATA)
                DEBUG("\tNO_METADATA");

        if (write_flags & WIMLIB_WRITE_FLAG_USE_EXISTING_TOTALBYTES)
                DEBUG("\tUSE_EXISTING_TOTALBYTES");

        if (num_threads == 0)
                DEBUG("Number of threads: autodetect");
        else
                DEBUG("Number of threads: %u", num_threads);
        DEBUG("Progress function: %s", (progress_func ? "yes" : "no"));
        DEBUG("Stream list:       %s", (stream_list_override ? "specified" : "autodetect"));
        DEBUG("GUID:              %s", ((guid || wim->guid_set_explicitly) ?
                                        "specified" : "generate new"));

        /* Internally, this is always called with a valid part number and total
         * parts.  */
        wimlib_assert(total_parts >= 1);
        wimlib_assert(part_number >= 1 && part_number <= total_parts);

        /* A valid image (or all images) must be specified.  */
        if (image != WIMLIB_ALL_IMAGES &&
             (image < 1 || image > wim->hdr.image_count))
                return WIMLIB_ERR_INVALID_IMAGE;

        /* If we need to write metadata resources, make sure the ::WIMStruct has
         * the needed information attached (e.g. is not a resource-only WIM,
         * such as a non-first part of a split WIM).  */
        if (!wim_has_metadata(wim) &&
            !(write_flags & WIMLIB_WRITE_FLAG_NO_METADATA))
                return WIMLIB_ERR_METADATA_NOT_FOUND;

        /* Check for contradictory flags.  */
        if ((write_flags & (WIMLIB_WRITE_FLAG_CHECK_INTEGRITY |
                            WIMLIB_WRITE_FLAG_NO_CHECK_INTEGRITY))
                                == (WIMLIB_WRITE_FLAG_CHECK_INTEGRITY |
                                    WIMLIB_WRITE_FLAG_NO_CHECK_INTEGRITY))
                return WIMLIB_ERR_INVALID_PARAM;

        if ((write_flags & (WIMLIB_WRITE_FLAG_PIPABLE |
                            WIMLIB_WRITE_FLAG_NOT_PIPABLE))
                                == (WIMLIB_WRITE_FLAG_PIPABLE |
                                    WIMLIB_WRITE_FLAG_NOT_PIPABLE))
                return WIMLIB_ERR_INVALID_PARAM;

        /* Save previous header, then start initializing the new one.  */
        memcpy(&hdr_save, &wim->hdr, sizeof(struct wim_header));

        /* Set default integrity, pipable, and packed stream flags.  */
        if (!(write_flags & (WIMLIB_WRITE_FLAG_PIPABLE |
                             WIMLIB_WRITE_FLAG_NOT_PIPABLE)))
                if (wim_is_pipable(wim)) {
                        DEBUG("WIM is pipable; default to PIPABLE.");
                        write_flags |= WIMLIB_WRITE_FLAG_PIPABLE;
                }

        if (!(write_flags & (WIMLIB_WRITE_FLAG_CHECK_INTEGRITY |
                             WIMLIB_WRITE_FLAG_NO_CHECK_INTEGRITY)))
                if (wim_has_integrity_table(wim)) {
                        DEBUG("Integrity table present; default to CHECK_INTEGRITY.");
                        write_flags |= WIMLIB_WRITE_FLAG_CHECK_INTEGRITY;
                }

        if ((write_flags & (WIMLIB_WRITE_FLAG_PIPABLE |
                            WIMLIB_WRITE_FLAG_PACK_STREAMS))
                                    == (WIMLIB_WRITE_FLAG_PIPABLE |
                                        WIMLIB_WRITE_FLAG_PACK_STREAMS))
        {
                ERROR("Cannot specify both PIPABLE and PACK_STREAMS!");
                return WIMLIB_ERR_INVALID_PARAM;
        }

        /* Set appropriate magic number.  */
        if (write_flags & WIMLIB_WRITE_FLAG_PIPABLE)
                wim->hdr.magic = PWM_MAGIC;
        else
                wim->hdr.magic = WIM_MAGIC;

        /* Set appropriate version number.  */
        if ((write_flags & WIMLIB_WRITE_FLAG_PACK_STREAMS) ||
            wim->out_compression_type == WIMLIB_COMPRESSION_TYPE_LZMS)
                wim->hdr.wim_version = WIM_VERSION_PACKED_STREAMS;
        else
                wim->hdr.wim_version = WIM_VERSION_DEFAULT;

        /* Clear header flags that will be set automatically.  */
        wim->hdr.flags &= ~(WIM_HDR_FLAG_METADATA_ONLY          |
                            WIM_HDR_FLAG_RESOURCE_ONLY          |
                            WIM_HDR_FLAG_SPANNED                |
                            WIM_HDR_FLAG_WRITE_IN_PROGRESS);

        /* Set SPANNED header flag if writing part of a split WIM.  */
        if (total_parts != 1)
                wim->hdr.flags |= WIM_HDR_FLAG_SPANNED;

        /* Set part number and total parts of split WIM.  This will be 1 and 1
         * if the WIM is standalone.  */
        wim->hdr.part_number = part_number;
        wim->hdr.total_parts = total_parts;

        /* Set compression type if different.  */
        if (wim->compression_type != wim->out_compression_type) {
                ret = set_wim_hdr_cflags(wim->out_compression_type, &wim->hdr);
                wimlib_assert(ret == 0);
        }

        /* Set chunk size if different.  */
        wim->hdr.chunk_size = wim->out_chunk_size;

        /* Use GUID if specified; otherwise generate a new one.  */
        if (guid)
                memcpy(wim->hdr.guid, guid, WIMLIB_GUID_LEN);
        else if (!wim->guid_set_explicitly)
                randomize_byte_array(wim->hdr.guid, WIMLIB_GUID_LEN);

        /* Clear references to resources that have not been written yet.  */
        zero_reshdr(&wim->hdr.lookup_table_reshdr);
        zero_reshdr(&wim->hdr.xml_data_reshdr);
        zero_reshdr(&wim->hdr.boot_metadata_reshdr);
        zero_reshdr(&wim->hdr.integrity_table_reshdr);

        /* Set image count and boot index correctly for single image writes.  */
        if (image != WIMLIB_ALL_IMAGES) {
                wim->hdr.image_count = 1;
                if (wim->hdr.boot_idx == image)
                        wim->hdr.boot_idx = 1;
                else
                        wim->hdr.boot_idx = 0;
        }

        /* Split WIMs can't be bootable.  */
        if (total_parts != 1)
                wim->hdr.boot_idx = 0;

        /* Initialize output file descriptor.  */
        if (write_flags & WIMLIB_WRITE_FLAG_FILE_DESCRIPTOR) {
                /* File descriptor was explicitly provided.  Return error if
                 * file descriptor is not seekable, unless writing a pipable WIM
                 * was requested.  */
                wim->out_fd.fd = *(const int*)path_or_fd;
                wim->out_fd.offset = 0;
                if (!filedes_is_seekable(&wim->out_fd)) {
                        ret = WIMLIB_ERR_INVALID_PARAM;
                        if (!(write_flags & WIMLIB_WRITE_FLAG_PIPABLE))
                                goto out_restore_hdr;
                        if (write_flags & WIMLIB_WRITE_FLAG_CHECK_INTEGRITY) {
                                ERROR("Can't include integrity check when "
                                      "writing pipable WIM to pipe!");
                                goto out_restore_hdr;
                        }
                }

        } else {
                /* Filename of WIM to write was provided; open file descriptor
                 * to it.  */
                ret = open_wim_writable(wim, (const tchar*)path_or_fd,
                                        O_TRUNC | O_CREAT | O_RDWR);
                if (ret)
                        goto out_restore_hdr;
        }

        /* Write initial header.  This is merely a "dummy" header since it
         * doesn't have all the information yet, so it will be overwritten later
         * (unless writing a pipable WIM).  */
        if (!(write_flags & WIMLIB_WRITE_FLAG_PIPABLE))
                wim->hdr.flags |= WIM_HDR_FLAG_WRITE_IN_PROGRESS;
        ret = write_wim_header(&wim->hdr, &wim->out_fd);
        wim->hdr.flags &= ~WIM_HDR_FLAG_WRITE_IN_PROGRESS;
        if (ret)
                goto out_restore_hdr;

        /* Write metadata resources and streams.  */
        if (!(write_flags & WIMLIB_WRITE_FLAG_PIPABLE)) {
                /* Default case: create a normal (non-pipable) WIM.  */
                ret = write_wim_streams(wim, image, write_flags, num_threads,
                                        progress_func, stream_list_override,
                                        &lookup_table_list);
                if (ret)
                        goto out_restore_hdr;

                ret = write_wim_metadata_resources(wim, image, write_flags,
                                                   progress_func);
                if (ret)
                        goto out_restore_hdr;
        } else {
                /* Non-default case: create pipable WIM.  */
                ret = write_pipable_wim(wim, image, write_flags, num_threads,
                                        progress_func, stream_list_override,
                                        &lookup_table_list);
                if (ret)
                        goto out_restore_hdr;
                write_flags |= WIMLIB_WRITE_FLAG_HEADER_AT_END;
        }


        /* Write lookup table, XML data, and (optional) integrity table.  */
        ret = finish_write(wim, image, write_flags, progress_func,
                           &lookup_table_list);
out_restore_hdr:
        memcpy(&wim->hdr, &hdr_save, sizeof(struct wim_header));
        (void)close_wim_writable(wim, write_flags);
        DEBUG("ret=%d", ret);
        return ret;
}

/* Write a standalone WIM to a file or file descriptor.  */
static int
write_standalone_wim(WIMStruct *wim, const void *path_or_fd,
                     int image, int write_flags, unsigned num_threads,
                     wimlib_progress_func_t progress_func)
{
        return write_wim_part(wim, path_or_fd, image, write_flags,
                              num_threads, progress_func, 1, 1, NULL, NULL);
}

/* API function documented in wimlib.h  */
WIMLIBAPI int
wimlib_write(WIMStruct *wim, const tchar *path,
             int image, int write_flags, unsigned num_threads,
             wimlib_progress_func_t progress_func)
{
        if (!path)
                return WIMLIB_ERR_INVALID_PARAM;

        write_flags &= WIMLIB_WRITE_MASK_PUBLIC;

        return write_standalone_wim(wim, path, image, write_flags,
                                    num_threads, progress_func);
}

/* API function documented in wimlib.h  */
WIMLIBAPI int
wimlib_write_to_fd(WIMStruct *wim, int fd,
                   int image, int write_flags, unsigned num_threads,
                   wimlib_progress_func_t progress_func)
{
        if (fd < 0)
                return WIMLIB_ERR_INVALID_PARAM;

        write_flags &= WIMLIB_WRITE_MASK_PUBLIC;
        write_flags |= WIMLIB_WRITE_FLAG_FILE_DESCRIPTOR;

        return write_standalone_wim(wim, &fd, image, write_flags,
                                    num_threads, progress_func);
}

static bool
any_images_modified(WIMStruct *wim)
{
        for (int i = 0; i < wim->hdr.image_count; i++)
                if (wim->image_metadata[i]->modified)
                        return true;
        return false;
}

static int
check_resource_offset(struct wim_lookup_table_entry *lte, void *_wim)
{
        const WIMStruct *wim = _wim;
        off_t end_offset = *(const off_t*)wim->private;

        if (lte->resource_location == RESOURCE_IN_WIM && lte->rspec->wim == wim &&
            lte->rspec->offset_in_wim + lte->rspec->size_in_wim > end_offset)
                return WIMLIB_ERR_RESOURCE_ORDER;
        return 0;
}

/* 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.  */
static int
check_resource_offsets(WIMStruct *wim, off_t end_offset)
{
        int ret;
        unsigned i;

        wim->private = &end_offset;
        ret = for_lookup_table_entry(wim->lookup_table, check_resource_offset, wim);
        if (ret)
                return ret;

        for (i = 0; i < wim->hdr.image_count; i++) {
                ret = check_resource_offset(wim->image_metadata[i]->metadata_lte, wim);
                if (ret)
                        return ret;
        }
        return 0;
}

/*
 * 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 *wim, int write_flags,
                      unsigned num_threads,
                      wimlib_progress_func_t progress_func)
{
        int ret;
        off_t old_wim_end;
        u64 old_lookup_table_end, old_xml_begin, old_xml_end;
        struct wim_header hdr_save;
        struct list_head stream_list;
        struct list_head lookup_table_list;
        struct filter_context filter_ctx;

        DEBUG("Overwriting `%"TS"' in-place", wim->filename);

        /* Save original header so it can be restored in case of error  */
        memcpy(&hdr_save, &wim->hdr, sizeof(struct wim_header));

        /* Set default integrity flag.  */
        if (!(write_flags & (WIMLIB_WRITE_FLAG_CHECK_INTEGRITY |
                             WIMLIB_WRITE_FLAG_NO_CHECK_INTEGRITY)))
                if (wim_has_integrity_table(wim))
                        write_flags |= WIMLIB_WRITE_FLAG_CHECK_INTEGRITY;

        /* Set WIM version if adding packed streams.  */
        if (write_flags & WIMLIB_WRITE_FLAG_PACK_STREAMS)
                wim->hdr.wim_version = WIM_VERSION_PACKED_STREAMS;

        /* Set additional flags for overwrite.  */
        write_flags |= WIMLIB_WRITE_FLAG_OVERWRITE |
                       WIMLIB_WRITE_FLAG_STREAMS_OK;

        /* 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. */
        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_lookup_table_end = wim->hdr.lookup_table_reshdr.offset_in_wim +
                               wim->hdr.lookup_table_reshdr.size_in_wim;
        if (wim->hdr.integrity_table_reshdr.offset_in_wim != 0 &&
            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_restore_memory_hdr;
        }

        if (old_lookup_table_end > old_xml_begin) {
                WARNING("Didn't expect the lookup table to be after the XML data");
                ret = WIMLIB_ERR_RESOURCE_ORDER;
                goto out_restore_memory_hdr;
        }

        /* 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->deletion_occurred && !any_images_modified(wim)) {
                /* If no images have been modified and no images have been
                 * deleted, a new lookup table does not need to be written.  We
                 * shall write the new XML data and optional integrity table
                 * immediately after the lookup table.  Note that this may
                 * overwrite an existing integrity table. */
                DEBUG("Skipping writing lookup table "
                      "(no images modified or deleted)");
                old_wim_end = old_lookup_table_end;
                write_flags |= WIMLIB_WRITE_FLAG_NO_LOOKUP_TABLE |
                               WIMLIB_WRITE_FLAG_CHECKPOINT_AFTER_XML;
        } else if (wim->hdr.integrity_table_reshdr.offset_in_wim != 0) {
                /* Old WIM has an integrity table; begin writing new streams
                 * 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 streams after
                 * the old XML data. */
                old_wim_end = old_xml_end;
        }

        ret = check_resource_offsets(wim, old_wim_end);
        if (ret)
                goto out_restore_memory_hdr;

        ret = prepare_stream_list_for_write(wim, WIMLIB_ALL_IMAGES, write_flags,
                                            &stream_list, &lookup_table_list,
                                            &filter_ctx);
        if (ret)
                goto out_restore_memory_hdr;

        ret = open_wim_writable(wim, wim->filename, O_RDWR);
        if (ret)
                goto out_restore_memory_hdr;

        ret = lock_wim(wim, wim->out_fd.fd);
        if (ret)
                goto out_close_wim;

        /* Set WIM_HDR_FLAG_WRITE_IN_PROGRESS flag in header. */
        wim->hdr.flags |= WIM_HDR_FLAG_WRITE_IN_PROGRESS;
        ret = write_wim_header_flags(wim->hdr.flags, &wim->out_fd);
        if (ret) {
                ERROR_WITH_ERRNO("Error updating WIM header flags");
                goto out_unlock_wim;
        }

        if (filedes_seek(&wim->out_fd, old_wim_end) == -1) {
                ERROR_WITH_ERRNO("Can't seek to end of WIM");
                ret = WIMLIB_ERR_WRITE;
                goto out_restore_physical_hdr;
        }

        ret = wim_write_stream_list(wim,
                                    &stream_list,
                                    write_flags,
                                    num_threads,
                                    &filter_ctx,
                                    progress_func);
        if (ret)
                goto out_truncate;

        ret = write_wim_metadata_resources(wim, WIMLIB_ALL_IMAGES,
                                           write_flags, progress_func);
        if (ret)
                goto out_truncate;

        write_flags |= WIMLIB_WRITE_FLAG_REUSE_INTEGRITY_TABLE;
        ret = finish_write(wim, WIMLIB_ALL_IMAGES, write_flags,
                           progress_func, &lookup_table_list);
        if (ret)
                goto out_truncate;

        wim->wim_locked = 0;
        return 0;

out_truncate:
        if (!(write_flags & WIMLIB_WRITE_FLAG_NO_LOOKUP_TABLE)) {
                WARNING("Truncating `%"TS"' to its original size (%"PRIu64" bytes)",
                        wim->filename, old_wim_end);
                /* Return value of ftruncate() is ignored because this is
                 * already an error path.  */
                (void)ftruncate(wim->out_fd.fd, old_wim_end);
        }
out_restore_physical_hdr:
        (void)write_wim_header_flags(hdr_save.flags, &wim->out_fd);
out_unlock_wim:
        wim->wim_locked = 0;
out_close_wim:
        (void)close_wim_writable(wim, write_flags);
out_restore_memory_hdr:
        memcpy(&wim->hdr, &hdr_save, sizeof(struct wim_header));
        return ret;
}

static int
overwrite_wim_via_tmpfile(WIMStruct *wim, int write_flags,
                          unsigned num_threads,
                          wimlib_progress_func_t progress_func)
{
        size_t wim_name_len;
        int ret;

        DEBUG("Overwriting `%"TS"' via a temporary file", wim->filename);

        /* Write the WIM to a temporary file in the same directory as the
         * original WIM. */
        wim_name_len = tstrlen(wim->filename);
        tchar tmpfile[wim_name_len + 10];
        tmemcpy(tmpfile, wim->filename, wim_name_len);
        randomize_char_array_with_alnum(tmpfile + wim_name_len, 9);
        tmpfile[wim_name_len + 9] = T('\0');

        ret = wimlib_write(wim, tmpfile, WIMLIB_ALL_IMAGES,
                           write_flags | WIMLIB_WRITE_FLAG_FSYNC,
                           num_threads, progress_func);
        if (ret) {
                tunlink(tmpfile);
                return ret;
        }

        close_wim(wim);

        /* Rename the new WIM file to the original WIM file.  Note: on Windows
         * this actually calls win32_rename_replacement(), not _wrename(), so
         * that removing the existing destination file can be handled.  */
        DEBUG("Renaming `%"TS"' to `%"TS"'", tmpfile, wim->filename);
        ret = trename(tmpfile, wim->filename);
        if (ret) {
                ERROR_WITH_ERRNO("Failed to rename `%"TS"' to `%"TS"'",
                                 tmpfile, wim->filename);
        #ifdef __WIN32__
                if (ret < 0)
        #endif
                {
                        tunlink(tmpfile);
                }
                return WIMLIB_ERR_RENAME;
        }

        if (progress_func) {
                union wimlib_progress_info progress;
                progress.rename.from = tmpfile;
                progress.rename.to = wim->filename;
                progress_func(WIMLIB_PROGRESS_MSG_RENAME, &progress);
        }
        return 0;
}

/* Determine if the specified WIM file may be updated by appending in-place
 * rather than writing and replacing it with an entirely new file.  */
static bool
can_overwrite_wim_inplace(const WIMStruct *wim, int write_flags)
{
        /* REBUILD flag forces full rebuild.  */
        if (write_flags & WIMLIB_WRITE_FLAG_REBUILD)
                return false;

        /* Deletions cause full rebuild by default.  */
        if (wim->deletion_occurred && !(write_flags & WIMLIB_WRITE_FLAG_SOFT_DELETE))
                return false;

        /* Pipable WIMs cannot be updated in place, nor can a non-pipable WIM be
         * turned into a pipable WIM in-place.  */
        if (wim_is_pipable(wim) || (write_flags & WIMLIB_WRITE_FLAG_PIPABLE))
                return false;

        /* wimlib allows multiple packs in a single WIM, but they don't seem to
         * be compatible with WIMGAPI, so force all streams to be repacked if
         * the WIM already may have contained a pack and PACK_STREAMS was
         * requested.  */
        if (write_flags & WIMLIB_WRITE_FLAG_PACK_STREAMS &&
            wim->hdr.wim_version == WIM_VERSION_PACKED_STREAMS)
                return false;

        /* The default compression type and compression chunk size selected for
         * the output WIM must be the same as those currently used for the WIM.
         */
        if (wim->compression_type != wim->out_compression_type)
                return false;
        if (wim->chunk_size != wim->out_chunk_size)
                return false;

        return true;
}

/* API function documented in wimlib.h  */
WIMLIBAPI int
wimlib_overwrite(WIMStruct *wim, int write_flags,
                 unsigned num_threads,
                 wimlib_progress_func_t progress_func)
{
        int ret;
        u32 orig_hdr_flags;

        write_flags &= WIMLIB_WRITE_MASK_PUBLIC;

        if (write_flags & WIMLIB_WRITE_FLAG_FILE_DESCRIPTOR)
                return WIMLIB_ERR_INVALID_PARAM;

        if (!wim->filename)
                return WIMLIB_ERR_NO_FILENAME;

        orig_hdr_flags = wim->hdr.flags;
        if (write_flags & WIMLIB_WRITE_FLAG_IGNORE_READONLY_FLAG)
                wim->hdr.flags &= ~WIM_HDR_FLAG_READONLY;
        ret = can_modify_wim(wim);
        wim->hdr.flags = orig_hdr_flags;
        if (ret)
                return ret;

        if (can_overwrite_wim_inplace(wim, write_flags)) {
                ret = overwrite_wim_inplace(wim, write_flags, num_threads,
                                            progress_func);
                if (ret != WIMLIB_ERR_RESOURCE_ORDER)
                        return ret;
                WARNING("Falling back to re-building entire WIM");
        }
        return overwrite_wim_via_tmpfile(wim, write_flags, num_threads,
                                         progress_func);
}