Forbid modifying multi-referenced images

[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, 2014, 2015 Eric Biggers
 *
 * This file is free software; you can redistribute it and/or modify it under
 * the terms of the GNU Lesser General Public License as published by the Free
 * Software Foundation; either version 3 of the License, or (at your option) any
 * later version.
 *
 * This file 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 Lesser General Public License for more
 * details.
 *
 * You should have received a copy of the GNU Lesser General Public License
 * along with this file; 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
 * override the LIST_HEAD macro. */
#  include <sys/file.h>
#endif

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

#include "wimlib/alloca.h"
#include "wimlib/assert.h"
#include "wimlib/blob_table.h"
#include "wimlib/chunk_compressor.h"
#include "wimlib/endianness.h"
#include "wimlib/error.h"
#include "wimlib/file_io.h"
#include "wimlib/header.h"
#include "wimlib/inode.h"
#include "wimlib/integrity.h"
#include "wimlib/metadata.h"
#include "wimlib/paths.h"
#include "wimlib/progress.h"
#include "wimlib/resource.h"
#include "wimlib/solid.h"
#include "wimlib/win32.h" /* win32_rename_replacement() */
#include "wimlib/write.h"
#include "wimlib/xml.h"


/* wimlib internal flags used when writing resources.  */
#define WRITE_RESOURCE_FLAG_RECOMPRESS          0x00000001
#define WRITE_RESOURCE_FLAG_PIPABLE             0x00000002
#define WRITE_RESOURCE_FLAG_SOLID               0x00000004
#define WRITE_RESOURCE_FLAG_SEND_DONE_WITH_FILE 0x00000008
#define WRITE_RESOURCE_FLAG_SOLID_SORT          0x00000010

static 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_SOLID)
                write_resource_flags |= WRITE_RESOURCE_FLAG_SOLID;

        if (write_flags & WIMLIB_WRITE_FLAG_SEND_DONE_WITH_FILE_MESSAGES)
                write_resource_flags |= WRITE_RESOURCE_FLAG_SEND_DONE_WITH_FILE;

        if ((write_flags & (WIMLIB_WRITE_FLAG_SOLID |
                            WIMLIB_WRITE_FLAG_NO_SOLID_SORT)) ==
            WIMLIB_WRITE_FLAG_SOLID)
                write_resource_flags |= WRITE_RESOURCE_FLAG_SOLID_SORT;

        return write_resource_flags;
}

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

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

        if (ctx == NULL)
                return 0;

        write_flags = ctx->write_flags;
        wim = ctx->wim;

        if (write_flags & WIMLIB_WRITE_FLAG_APPEND &&
            blob->blob_location == BLOB_IN_WIM &&
            blob->rdesc->wim == wim)
                return 1;

        if (write_flags & WIMLIB_WRITE_FLAG_SKIP_EXTERNAL_WIMS &&
            blob->blob_location == BLOB_IN_WIM &&
            blob->rdesc->wim != wim)
                return -1;

        return 0;
}

static bool
blob_hard_filtered(const struct blob_descriptor *blob,
                   struct filter_context *ctx)
{
        return blob_filtered(blob, ctx) < 0;
}

static inline bool
may_soft_filter_blobs(const struct filter_context *ctx)
{
        return ctx && (ctx->write_flags & WIMLIB_WRITE_FLAG_APPEND);
}

static inline bool
may_hard_filter_blobs(const struct filter_context *ctx)
{
        return ctx && (ctx->write_flags & WIMLIB_WRITE_FLAG_SKIP_EXTERNAL_WIMS);
}

static inline bool
may_filter_blobs(const struct filter_context *ctx)
{
        return (may_soft_filter_blobs(ctx) || may_hard_filter_blobs(ctx));
}

/* Return true if the specified blob is located in a WIM resource which can be
 * reused in the output WIM file, without being recompressed.  */
static bool
can_raw_copy(const struct blob_descriptor *blob, int write_resource_flags,
             int out_ctype, u32 out_chunk_size)
{
        const struct wim_resource_descriptor *rdesc;

        /* Recompress everything if requested.  */
        if (write_resource_flags & WRITE_RESOURCE_FLAG_RECOMPRESS)
                return false;

        /* A blob not located in a WIM resource cannot be reused.  */
        if (blob->blob_location != BLOB_IN_WIM)
                return false;

        rdesc = blob->rdesc;

        /* In the case of an in-place compaction, always reuse resources located
         * in the WIM being compacted.  */
        if (rdesc->wim->being_compacted)
                return true;

        /* Otherwise, only reuse compressed resources.  */
        if (out_ctype == WIMLIB_COMPRESSION_TYPE_NONE ||
            !(rdesc->flags & (WIM_RESHDR_FLAG_COMPRESSED |
                              WIM_RESHDR_FLAG_SOLID)))
                return false;

        /* When writing a pipable WIM, we can only reuse pipable resources; and
         * when writing a non-pipable WIM, we can only reuse non-pipable
         * resources.  */
        if (rdesc->is_pipable !=
            !!(write_resource_flags & WRITE_RESOURCE_FLAG_PIPABLE))
                return false;

        /* When writing a solid WIM, we can only reuse solid resources; and when
         * writing a non-solid WIM, we can only reuse non-solid resources.  */
        if (!!(rdesc->flags & WIM_RESHDR_FLAG_SOLID) !=
            !!(write_resource_flags & WRITE_RESOURCE_FLAG_SOLID))
                return false;

        /* Note: it is theoretically possible to copy chunks of compressed data
         * between non-solid, solid, and pipable resources.  However, we don't
         * currently implement this optimization because it would be complex and
         * would usually go unused.  */

        if (rdesc->flags & WIM_RESHDR_FLAG_COMPRESSED) {
                /* To re-use a non-solid resource, it must use the desired
                 * compression type and chunk size.  */
                return (rdesc->compression_type == out_ctype &&
                        rdesc->chunk_size == out_chunk_size);
        } else {
                /* Solid resource: Such resources may contain multiple blobs,
                 * and in general only a subset of them need to be written.  As
                 * a heuristic, re-use the raw data if more than two-thirds the
                 * uncompressed size is being written.  */

                /* Note: solid 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.  */

                /* Did we already decide to reuse the resource?  */
                if (rdesc->raw_copy_ok)
                        return true;

                struct blob_descriptor *res_blob;
                u64 write_size = 0;

                list_for_each_entry(res_blob, &rdesc->blob_list, rdesc_node)
                        if (res_blob->will_be_in_output_wim)
                                write_size += res_blob->size;

                return (write_size > rdesc->uncompressed_size * 2 / 3);
        }
}

static u32
reshdr_flags_for_blob(const struct blob_descriptor *blob)
{
        u32 reshdr_flags = 0;
        if (blob->is_metadata)
                reshdr_flags |= WIM_RESHDR_FLAG_METADATA;
        return reshdr_flags;
}

static void
blob_set_out_reshdr_for_reuse(struct blob_descriptor *blob)
{
        const struct wim_resource_descriptor *rdesc;

        wimlib_assert(blob->blob_location == BLOB_IN_WIM);
        rdesc = blob->rdesc;

        if (rdesc->flags & WIM_RESHDR_FLAG_SOLID) {
                blob->out_reshdr.offset_in_wim = blob->offset_in_res;
                blob->out_reshdr.uncompressed_size = 0;
                blob->out_reshdr.size_in_wim = blob->size;

                blob->out_res_offset_in_wim = rdesc->offset_in_wim;
                blob->out_res_size_in_wim = rdesc->size_in_wim;
                blob->out_res_uncompressed_size = rdesc->uncompressed_size;
        } else {
                blob->out_reshdr.offset_in_wim = rdesc->offset_in_wim;
                blob->out_reshdr.uncompressed_size = rdesc->uncompressed_size;
                blob->out_reshdr.size_in_wim = rdesc->size_in_wim;
        }
        blob->out_reshdr.flags = rdesc->flags;
}


/* Write the header for a blob in a pipable WIM.  */
static int
write_pwm_blob_header(const struct blob_descriptor *blob,
                      struct filedes *out_fd, bool compressed)
{
        struct pwm_blob_hdr blob_hdr;
        u32 reshdr_flags;
        int ret;

        wimlib_assert(!blob->unhashed);

        blob_hdr.magic = cpu_to_le64(PWM_BLOB_MAGIC);
        blob_hdr.uncompressed_size = cpu_to_le64(blob->size);
        copy_hash(blob_hdr.hash, blob->hash);
        reshdr_flags = reshdr_flags_for_blob(blob);
        if (compressed)
                reshdr_flags |= WIM_RESHDR_FLAG_COMPRESSED;
        blob_hdr.flags = cpu_to_le32(reshdr_flags);
        ret = full_write(out_fd, &blob_hdr, sizeof(blob_hdr));
        if (ret)
                ERROR_WITH_ERRNO("Write error");
        return ret;
}

struct write_blobs_progress_data {
        wimlib_progress_func_t progfunc;
        void *progctx;
        union wimlib_progress_info progress;
        u64 next_progress;
};

static int
do_write_blobs_progress(struct write_blobs_progress_data *progress_data,
                        u64 complete_size, u32 complete_count, bool discarded)
{
        union wimlib_progress_info *progress = &progress_data->progress;
        int ret;

        if (discarded) {
                progress->write_streams.total_bytes -= complete_size;
                progress->write_streams.total_streams -= complete_count;
                if (progress_data->next_progress != ~(u64)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 += complete_size;
                progress->write_streams.completed_streams += complete_count;
        }

        if (progress->write_streams.completed_bytes >= progress_data->next_progress) {

                ret = call_progress(progress_data->progfunc,
                                    WIMLIB_PROGRESS_MSG_WRITE_STREAMS,
                                    progress,
                                    progress_data->progctx);
                if (ret)
                        return ret;

                set_next_progress(progress->write_streams.completed_bytes,
                                  progress->write_streams.total_bytes,
                                  &progress_data->next_progress);
        }
        return 0;
}

struct write_blobs_ctx {
        /* File descriptor to which the blobs are being written.  */
        struct filedes *out_fd;

        /* Blob table for the WIMStruct on whose behalf the blobs are being
         * written.  */
        struct blob_table *blob_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 blobs will be written.  */
        int write_resource_flags;

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

        struct filter_context *filter_ctx;

        /* 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;

        /* A buffer of size @out_chunk_size that has been loaned out from the
         * chunk compressor and is currently being filled with the uncompressed
         * data of the next chunk.  */
        u8 *cur_chunk_buf;

        /* Number of bytes in @cur_chunk_buf that are currently filled.  */
        size_t cur_chunk_buf_filled;

        /* List of blobs that currently have chunks being compressed.  */
        struct list_head blobs_being_compressed;

        /* List of blobs in the solid resource.  Blobs are moved here after
         * @blobs_being_compressed only when writing a solid resource.  */
        struct list_head blobs_in_solid_resource;

        /* Current uncompressed offset in the blob being read.  */
        u64 cur_read_blob_offset;

        /* Uncompressed size of the blob currently being read.  */
        u64 cur_read_blob_size;

        /* Current uncompressed offset in the blob being written.  */
        u64 cur_write_blob_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;
};

/* Reserve space for the chunk table and prepare to accumulate the chunk table
 * in memory.  */
static int
begin_chunk_table(struct write_blobs_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 SOLID mode some of the blobs 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_SOLID))
                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 solid 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,
                                                    0 != (ctx->write_resource_flags &
                                                          WRITE_RESOURCE_FLAG_SOLID));
                if (ctx->write_resource_flags & WRITE_RESOURCE_FLAG_SOLID)
                        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_blobs_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_blob_offset = 0;
        ctx->cur_write_res_size = res_expected_size;
        return 0;
}

static int
end_chunk_table(struct write_blobs_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_SOLID))
                actual_num_chunk_entries--;

        chunk_entry_size = get_chunk_entry_size(res_actual_size,
                                                0 != (ctx->write_resource_flags &
                                                      WRITE_RESOURCE_FLAG_SOLID));

        typedef le64 _may_alias_attribute aliased_le64_t;
        typedef le32 _may_alias_attribute 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_SOLID) {
                        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_SOLID) {
                        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 write_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_SOLID) {
                        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);

                        STATIC_ASSERT(WIMLIB_COMPRESSION_TYPE_XPRESS == 1);
                        STATIC_ASSERT(WIMLIB_COMPRESSION_TYPE_LZX == 2);
                        STATIC_ASSERT(WIMLIB_COMPRESSION_TYPE_LZMS == 3);

                        ret = full_pwrite(ctx->out_fd, &hdr, sizeof(hdr),
                                          chunk_table_offset - sizeof(hdr));
                        if (ret)
                                goto write_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 write_error;
        }

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

        return 0;

write_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_blobs_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_blob_offset == ctx->cur_write_res_size ||
                      (ctx->write_resource_flags & WRITE_RESOURCE_FLAG_SOLID));
        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;
        return 0;
}

/* Call when no more data from the file at @path is needed.  */
static int
done_with_file(const tchar *path, wimlib_progress_func_t progfunc, void *progctx)
{
        union wimlib_progress_info info;

        info.done_with_file.path_to_file = path;

        return call_progress(progfunc, WIMLIB_PROGRESS_MSG_DONE_WITH_FILE,
                             &info, progctx);
}

static int
do_done_with_blob(struct blob_descriptor *blob,
                  wimlib_progress_func_t progfunc, void *progctx)
{
        int ret;
        struct wim_inode *inode;
        tchar *cookie1;
        tchar *cookie2;

        if (!blob->may_send_done_with_file)
                return 0;

        inode = blob->file_inode;

        wimlib_assert(inode != NULL);
        wimlib_assert(inode->i_num_remaining_streams > 0);
        if (--inode->i_num_remaining_streams > 0)
                return 0;

        cookie1 = progress_get_streamless_path(blob->file_on_disk);
        cookie2 = progress_get_win32_path(blob->file_on_disk);

        ret = done_with_file(blob->file_on_disk, progfunc, progctx);

        progress_put_win32_path(cookie2);
        progress_put_streamless_path(cookie1);

        return ret;
}

/* Handle WIMLIB_WRITE_FLAG_SEND_DONE_WITH_FILE_MESSAGES mode.  */
static inline int
done_with_blob(struct blob_descriptor *blob, struct write_blobs_ctx *ctx)
{
        if (likely(!(ctx->write_resource_flags &
                     WRITE_RESOURCE_FLAG_SEND_DONE_WITH_FILE)))
                return 0;
        return do_done_with_blob(blob, ctx->progress_data.progfunc,
                                 ctx->progress_data.progctx);
}

/* Begin processing a blob for writing.  */
static int
write_blob_begin_read(struct blob_descriptor *blob, void *_ctx)
{
        struct write_blobs_ctx *ctx = _ctx;
        int ret;

        wimlib_assert(blob->size > 0);

        ctx->cur_read_blob_offset = 0;
        ctx->cur_read_blob_size = blob->size;

        /* As an optimization, we allow some blobs to be "unhashed", meaning
         * their SHA-1 message digests are unknown.  This is the case with blobs
         * that are added by scanning a directory tree with wimlib_add_image(),
         * for example.  Since WIM uses single-instance blobs, we don't know
         * whether such each such blob really need to written until it is
         * actually checksummed, unless it has a unique size.  In such cases we
         * read and checksum the blob in this function, thereby advancing ahead
         * of read_blob_list(), which will still provide the data again to
         * write_blob_process_chunk().  This is okay because an unhashed blob
         * cannot be in a WIM resource, which might be costly to decompress.  */
        if (ctx->blob_table != NULL && blob->unhashed && !blob->unique_size) {

                struct blob_descriptor *new_blob;

                ret = hash_unhashed_blob(blob, ctx->blob_table, &new_blob);
                if (ret)
                        return ret;
                if (new_blob != blob) {
                        /* Duplicate blob detected.  */

                        if (new_blob->will_be_in_output_wim ||
                            blob_filtered(new_blob, ctx->filter_ctx))
                        {
                                /* The duplicate blob is already being included
                                 * in the output WIM, or it would be filtered
                                 * out if it had been.  Skip writing this blob
                                 * (and reading it again) entirely, passing its
                                 * output reference count to the duplicate blob
                                 * in the former case.  */
                                ret = do_write_blobs_progress(&ctx->progress_data,
                                                              blob->size, 1, true);
                                list_del(&blob->write_blobs_list);
                                list_del(&blob->blob_table_list);
                                if (new_blob->will_be_in_output_wim)
                                        new_blob->out_refcnt += blob->out_refcnt;
                                if (ctx->write_resource_flags & WRITE_RESOURCE_FLAG_SOLID)
                                        ctx->cur_write_res_size -= blob->size;
                                if (!ret)
                                        ret = done_with_blob(blob, ctx);
                                free_blob_descriptor(blob);
                                if (ret)
                                        return ret;
                                return BEGIN_BLOB_STATUS_SKIP_BLOB;
                        } else {
                                /* The duplicate blob can validly be written,
                                 * but was not marked as such.  Discard the
                                 * current blob descriptor and use the
                                 * duplicate, but actually freeing the current
                                 * blob descriptor must wait until
                                 * read_blob_list() has finished reading its
                                 * data.  */
                                list_replace(&blob->write_blobs_list,
                                             &new_blob->write_blobs_list);
                                list_replace(&blob->blob_table_list,
                                             &new_blob->blob_table_list);
                                blob->will_be_in_output_wim = 0;
                                new_blob->out_refcnt = blob->out_refcnt;
                                new_blob->will_be_in_output_wim = 1;
                                new_blob->may_send_done_with_file = 0;
                                blob = new_blob;
                        }
                }
        }
        list_move_tail(&blob->write_blobs_list, &ctx->blobs_being_compressed);
        return 0;
}

/* Rewrite a blob that was just written compressed (as a non-solid WIM resource)
 * as uncompressed instead.  */
static int
write_blob_uncompressed(struct blob_descriptor *blob, struct filedes *out_fd)
{
        int ret;
        u64 begin_offset = blob->out_reshdr.offset_in_wim;
        u64 end_offset = out_fd->offset;

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

        ret = extract_blob_to_fd(blob, out_fd);
        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 resource of "
                                "size %"PRIu64", continuing on.", blob->size);
                        return 0;
                }
                return ret;
        }

        wimlib_assert(out_fd->offset - begin_offset == blob->size);

        /* We could ftruncate() the file to 'out_fd->offset' here, but there
         * isn't much point.  Usually we will only be truncating by a few bytes
         * and will just overwrite the data immediately.  */

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

/* Returns true if the specified blob, which was written as a non-solid
 * resource, should be truncated from the WIM file and re-written uncompressed.
 * blob->out_reshdr must be filled in from the initial write of the blob.  */
static bool
should_rewrite_blob_uncompressed(const struct write_blobs_ctx *ctx,
                                 const struct blob_descriptor *blob)
{
        /* If the compressed data is smaller than the uncompressed data, prefer
         * the compressed data.  */
        if (blob->out_reshdr.size_in_wim < blob->out_reshdr.uncompressed_size)
                return false;

        /* If we're not actually writing compressed data, then there's no need
         * for re-writing.  */
        if (!ctx->compressor)
                return false;

        /* If writing a pipable WIM, everything we write to the output is final
         * (it might actually be a pipe!).  */
        if (ctx->write_resource_flags & WRITE_RESOURCE_FLAG_PIPABLE)
                return false;

        /* If the blob that would need to be re-read is located in a solid
         * resource in another WIM file, then re-reading it would be costly.  So
         * don't do it.
         *
         * Exception: if the compressed size happens to be *exactly* the same as
         * the uncompressed size, then the blob *must* be written uncompressed
         * in order to remain compatible with the Windows Overlay Filesystem
         * Filter Driver (WOF).
         *
         * TODO: we are currently assuming that the optimization for
         * single-chunk resources in maybe_rewrite_blob_uncompressed() prevents
         * this case from being triggered too often.  To fully prevent excessive
         * decompressions in degenerate cases, we really should obtain the
         * uncompressed data by decompressing the compressed data we wrote to
         * the output file.
         */
        if (blob->blob_location == BLOB_IN_WIM &&
            blob->size != blob->rdesc->uncompressed_size &&
            blob->size != blob->out_reshdr.size_in_wim)
                return false;

        return true;
}

static int
maybe_rewrite_blob_uncompressed(struct write_blobs_ctx *ctx,
                                struct blob_descriptor *blob)
{
        if (!should_rewrite_blob_uncompressed(ctx, blob))
                return 0;

        /* Regular (non-solid) WIM resources with exactly one chunk and
         * compressed size equal to uncompressed size are exactly the same as
         * the corresponding compressed data --- since there must be 0 entries
         * in the chunk table and the only chunk must be stored uncompressed.
         * In this case, there's no need to rewrite anything.  */
        if (ctx->chunk_index == 1 &&
            blob->out_reshdr.size_in_wim == blob->out_reshdr.uncompressed_size)
        {
                blob->out_reshdr.flags &= ~WIM_RESHDR_FLAG_COMPRESSED;
                return 0;
        }

        return write_blob_uncompressed(blob, ctx->out_fd);
}

/* 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_blobs_ctx *ctx, const void *cchunk,
            size_t csize, size_t usize)
{
        int ret;
        struct blob_descriptor *blob;
        u32 completed_blob_count;
        u32 completed_size;

        blob = list_entry(ctx->blobs_being_compressed.next,
                          struct blob_descriptor, write_blobs_list);

        if (ctx->cur_write_blob_offset == 0 &&
            !(ctx->write_resource_flags & WRITE_RESOURCE_FLAG_SOLID))
        {
                /* Starting to write a new blob in non-solid mode.  */

                if (ctx->write_resource_flags & WRITE_RESOURCE_FLAG_PIPABLE) {
                        ret = write_pwm_blob_header(blob, ctx->out_fd,
                                                    ctx->compressor != NULL);
                        if (ret)
                                return ret;
                }

                ret = begin_write_resource(ctx, blob->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 write_error;
                }
        }

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

        ctx->cur_write_blob_offset += usize;

        completed_size = usize;
        completed_blob_count = 0;
        if (ctx->write_resource_flags & WRITE_RESOURCE_FLAG_SOLID) {
                /* Wrote chunk in solid mode.  It may have finished multiple
                 * blobs.  */
                struct blob_descriptor *next_blob;

                while (blob && ctx->cur_write_blob_offset >= blob->size) {

                        ctx->cur_write_blob_offset -= blob->size;

                        if (ctx->cur_write_blob_offset)
                                next_blob = list_entry(blob->write_blobs_list.next,
                                                      struct blob_descriptor,
                                                      write_blobs_list);
                        else
                                next_blob = NULL;

                        ret = done_with_blob(blob, ctx);
                        if (ret)
                                return ret;
                        list_move_tail(&blob->write_blobs_list, &ctx->blobs_in_solid_resource);
                        completed_blob_count++;

                        blob = next_blob;
                }
        } else {
                /* Wrote chunk in non-solid mode.  It may have finished a
                 * blob.  */
                if (ctx->cur_write_blob_offset == blob->size) {

                        wimlib_assert(ctx->cur_write_blob_offset ==
                                      ctx->cur_write_res_size);

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

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

                        ret = maybe_rewrite_blob_uncompressed(ctx, blob);
                        if (ret)
                                return ret;

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

                        ctx->cur_write_blob_offset = 0;

                        ret = done_with_blob(blob, ctx);
                        if (ret)
                                return ret;
                        list_del(&blob->write_blobs_list);
                        completed_blob_count++;
                }
        }

        return do_write_blobs_progress(&ctx->progress_data, completed_size,
                                       completed_blob_count, false);

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

static int
prepare_chunk_buffer(struct write_blobs_ctx *ctx)
{
        /* While we are unable to get a new chunk buffer due to too many chunks
         * already outstanding, retrieve and write the next compressed chunk. */
        while (!(ctx->cur_chunk_buf =
                 ctx->compressor->get_chunk_buffer(ctx->compressor)))
        {
                const void *cchunk;
                u32 csize;
                u32 usize;
                bool bret;
                int ret;

                bret = ctx->compressor->get_compression_result(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_blob_process_chunk(const void *chunk, size_t size, void *_ctx)
{
        struct write_blobs_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_blob_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 {
                size_t needed_chunk_size;
                size_t bytes_consumed;

                if (!ctx->cur_chunk_buf) {
                        ret = prepare_chunk_buffer(ctx);
                        if (ret)
                                return ret;
                }

                if (ctx->write_resource_flags & WRITE_RESOURCE_FLAG_SOLID) {
                        needed_chunk_size = ctx->out_chunk_size;
                } else {
                        needed_chunk_size = min(ctx->out_chunk_size,
                                                ctx->cur_chunk_buf_filled +
                                                        (ctx->cur_read_blob_size -
                                                         ctx->cur_read_blob_offset));
                }

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

                memcpy(&ctx->cur_chunk_buf[ctx->cur_chunk_buf_filled],
                       chunkptr, bytes_consumed);

                chunkptr += bytes_consumed;
                ctx->cur_read_blob_offset += bytes_consumed;
                ctx->cur_chunk_buf_filled += bytes_consumed;

                if (ctx->cur_chunk_buf_filled == needed_chunk_size) {
                        ctx->compressor->signal_chunk_filled(ctx->compressor,
                                                             ctx->cur_chunk_buf_filled);
                        ctx->cur_chunk_buf = NULL;
                        ctx->cur_chunk_buf_filled = 0;
                }
        } while (chunkptr != chunkend);
        return 0;
}

/* Finish processing a blob 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_blob_end_read(struct blob_descriptor *blob, int status, void *_ctx)
{
        struct write_blobs_ctx *ctx = _ctx;

        wimlib_assert(ctx->cur_read_blob_offset == ctx->cur_read_blob_size || status);

        if (!blob->will_be_in_output_wim) {
                /* The blob was a duplicate.  Now that its data has finished
                 * being read, it is being discarded in favor of the duplicate
                 * entry.  It therefore is no longer needed, and we can fire the
                 * DONE_WITH_FILE callback because the file will not be read
                 * again.
                 *
                 * Note: we can't yet fire DONE_WITH_FILE for non-duplicate
                 * blobs, since it needs to be possible to re-read the file if
                 * it does not compress to less than its original size.  */
                if (!status)
                        status = done_with_blob(blob, ctx);
                free_blob_descriptor(blob);
        } else if (!status && blob->unhashed && ctx->blob_table != NULL) {
                /* The blob was not a duplicate and was previously unhashed.
                 * Since we passed COMPUTE_MISSING_BLOB_HASHES to
                 * read_blob_list(), blob->hash is now computed and valid.  So
                 * turn this blob into a "hashed" blob.  */
                list_del(&blob->unhashed_list);
                blob_table_insert(ctx->blob_table, blob);
                blob->unhashed = 0;
        }
        return status;
}

/*
 * Compute statistics about a list of blobs that will be written.
 *
 * Assumes the blobs are sorted such that all blobs located in each distinct WIM
 * (specified by WIMStruct) are together.
 *
 * For compactions, also verify that there are no overlapping resources.  This
 * really should be checked earlier, but for now it's easiest to check here.
 */
static int
compute_blob_list_stats(struct list_head *blob_list,
                        struct write_blobs_ctx *ctx)
{
        struct blob_descriptor *blob;
        u64 total_bytes = 0;
        u64 num_blobs = 0;
        u64 total_parts = 0;
        WIMStruct *prev_wim_part = NULL;
        const struct wim_resource_descriptor *prev_rdesc = NULL;

        list_for_each_entry(blob, blob_list, write_blobs_list) {
                num_blobs++;
                total_bytes += blob->size;
                if (blob->blob_location == BLOB_IN_WIM) {
                        const struct wim_resource_descriptor *rdesc = blob->rdesc;
                        WIMStruct *wim = rdesc->wim;

                        if (prev_wim_part != wim) {
                                prev_wim_part = wim;
                                total_parts++;
                        }
                        if (unlikely(wim->being_compacted) && rdesc != prev_rdesc) {
                                if (prev_rdesc != NULL &&
                                    rdesc->offset_in_wim <
                                                prev_rdesc->offset_in_wim +
                                                prev_rdesc->size_in_wim)
                                {
                                        WARNING("WIM file contains overlapping "
                                                "resources!  Compaction is not "
                                                "possible.");
                                        return WIMLIB_ERR_RESOURCE_ORDER;
                                }
                                prev_rdesc = rdesc;
                        }
                }
        }
        ctx->progress_data.progress.write_streams.total_bytes       = total_bytes;
        ctx->progress_data.progress.write_streams.total_streams     = num_blobs;
        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;
        return 0;
}

/* Find blobs in @blob_list that can be copied to the output WIM in raw form
 * rather than compressed.  Delete these blobs from @blob_list and move them to
 * @raw_copy_blobs.  Return the total uncompressed size of the blobs that need
 * to be compressed.  */
static u64
find_raw_copy_blobs(struct list_head *blob_list, int write_resource_flags,
                    int out_ctype, u32 out_chunk_size,
                    struct list_head *raw_copy_blobs)
{
        struct blob_descriptor *blob, *tmp;
        u64 num_nonraw_bytes = 0;

        INIT_LIST_HEAD(raw_copy_blobs);

        /* Initialize temporary raw_copy_ok flag.  */
        list_for_each_entry(blob, blob_list, write_blobs_list)
                if (blob->blob_location == BLOB_IN_WIM)
                        blob->rdesc->raw_copy_ok = 0;

        list_for_each_entry_safe(blob, tmp, blob_list, write_blobs_list) {
                if (can_raw_copy(blob, write_resource_flags,
                                 out_ctype, out_chunk_size))
                {
                        blob->rdesc->raw_copy_ok = 1;
                        list_move_tail(&blob->write_blobs_list, raw_copy_blobs);
                } else {
                        num_nonraw_bytes += blob->size;
                }
        }

        return num_nonraw_bytes;
}

/* 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_descriptor *in_rdesc,
                        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 blob_descriptor *blob;
        u64 out_offset_in_wim;

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

        out_offset_in_wim = out_fd->offset;

        if (in_rdesc->is_pipable) {
                if (cur_read_offset < sizeof(struct pwm_blob_hdr))
                        return WIMLIB_ERR_INVALID_PIPABLE_WIM;
                cur_read_offset -= sizeof(struct pwm_blob_hdr);
                out_offset_in_wim += sizeof(struct pwm_blob_hdr);
        }
        in_fd = &in_rdesc->wim->in_fd;
        wimlib_assert(cur_read_offset != end_read_offset);

        if (likely(!in_rdesc->wim->being_compacted) ||
            in_rdesc->offset_in_wim > out_fd->offset) {
                do {
                        bytes_to_read = min(sizeof(buf),
                                            end_read_offset - cur_read_offset);

                        ret = full_pread(in_fd, buf, bytes_to_read,
                                         cur_read_offset);
                        if (ret)
                                return ret;

                        ret = full_write(out_fd, buf, bytes_to_read);
                        if (ret)
                                return ret;

                        cur_read_offset += bytes_to_read;

                } while (cur_read_offset != end_read_offset);
        } else {
                /* Optimization: the WIM file is being compacted and the
                 * resource being written is already in the desired location.
                 * Skip over the data instead of re-writing it.  */

                /* Due the earlier check for overlapping resources, it should
                 * never be the case that we already overwrote the resource.  */
                wimlib_assert(!(in_rdesc->offset_in_wim < out_fd->offset));

                if (-1 == filedes_seek(out_fd, out_fd->offset + in_rdesc->size_in_wim))
                        return WIMLIB_ERR_WRITE;
        }

        list_for_each_entry(blob, &in_rdesc->blob_list, rdesc_node) {
                if (blob->will_be_in_output_wim) {
                        blob_set_out_reshdr_for_reuse(blob);
                        if (in_rdesc->flags & WIM_RESHDR_FLAG_SOLID)
                                blob->out_res_offset_in_wim = out_offset_in_wim;
                        else
                                blob->out_reshdr.offset_in_wim = out_offset_in_wim;

                }
        }
        return 0;
}

/* Copy a list of raw compressed resources located in other WIM file(s) to the
 * WIM file being written.  */
static int
write_raw_copy_resources(struct list_head *raw_copy_blobs,
                         struct filedes *out_fd,
                         struct write_blobs_progress_data *progress_data)
{
        struct blob_descriptor *blob;
        int ret;

        list_for_each_entry(blob, raw_copy_blobs, write_blobs_list)
                blob->rdesc->raw_copy_ok = 1;

        list_for_each_entry(blob, raw_copy_blobs, write_blobs_list) {
                if (blob->rdesc->raw_copy_ok) {
                        /* Write each solid resource only one time.  */
                        ret = write_raw_copy_resource(blob->rdesc, out_fd);
                        if (ret)
                                return ret;
                        blob->rdesc->raw_copy_ok = 0;
                }
                ret = do_write_blobs_progress(progress_data, blob->size,
                                              1, false);
                if (ret)
                        return ret;
        }
        return 0;
}

/* Wait for and write all chunks pending in the compressor.  */
static int
finish_remaining_chunks(struct write_blobs_ctx *ctx)
{
        const void *cdata;
        u32 csize;
        u32 usize;
        int ret;

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

        if (ctx->cur_chunk_buf_filled != 0) {
                ctx->compressor->signal_chunk_filled(ctx->compressor,
                                                     ctx->cur_chunk_buf_filled);
        }

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

static void
validate_blob_list(struct list_head *blob_list)
{
        struct blob_descriptor *blob;

        list_for_each_entry(blob, blob_list, write_blobs_list) {
                wimlib_assert(blob->will_be_in_output_wim);
                wimlib_assert(blob->size != 0);
        }
}

static inline bool
blob_is_in_file(const struct blob_descriptor *blob)
{
        return blob->blob_location == BLOB_IN_FILE_ON_DISK
#ifdef __WIN32__
            || blob->blob_location == BLOB_IN_WINNT_FILE_ON_DISK
            || blob->blob_location == BLOB_WIN32_ENCRYPTED
#endif
           ;
}

static void
init_done_with_file_info(struct list_head *blob_list)
{
        struct blob_descriptor *blob;

        list_for_each_entry(blob, blob_list, write_blobs_list) {
                if (blob_is_in_file(blob)) {
                        blob->file_inode->i_num_remaining_streams = 0;
                        blob->may_send_done_with_file = 1;
                } else {
                        blob->may_send_done_with_file = 0;
                }
        }

        list_for_each_entry(blob, blob_list, write_blobs_list)
                if (blob->may_send_done_with_file)
                        blob->file_inode->i_num_remaining_streams++;
}

/*
 * Write a list of blobs to the output WIM file.
 *
 * @blob_list
 *      The list of blobs to write, specified by a list of 'struct blob_descriptor' linked
 *      by the 'write_blobs_list' member.
 *
 * @out_fd
 *      The file descriptor, opened for writing, to which to write the blobs.
 *
 * @write_resource_flags
 *      Flags to modify how the blobs are written:
 *
 *      WRITE_RESOURCE_FLAG_RECOMPRESS:
 *              Force compression of all resources, even if they could otherwise
 *              be re-used by copying 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).
 *
 *      WRITE_RESOURCE_FLAG_SOLID:
 *              Combine all the blobs into a single resource rather than writing
 *              them in separate resources.  This flag is only valid if the WIM
 *              version number has been, or will be, set to WIM_VERSION_SOLID.
 *              This flag may not be combined with WRITE_RESOURCE_FLAG_PIPABLE.
 *
 * @out_ctype
 *      Compression format to use in the output resources, specified as one of
 *      the WIMLIB_COMPRESSION_TYPE_* constants.  WIMLIB_COMPRESSION_TYPE_NONE
 *      is allowed.
 *
 * @out_chunk_size
 *      Compression chunk size to use in the output resources.  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.
 *
 * @blob_table
 *      If on-the-fly deduplication of unhashed blobs is desired, this parameter
 *      must be pointer to the blob table for the WIMStruct on whose behalf the
 *      blobs are being written.  Otherwise, this parameter can be NULL.
 *
 * @filter_ctx
 *      If on-the-fly deduplication of unhashed blobs is desired, this parameter
 *      can be a pointer to a context for blob filtering used to detect whether
 *      the duplicate blob has been hard-filtered or not.  If no blobs are
 *      hard-filtered or no blobs are unhashed, this parameter can be NULL.
 *
 * This function will write the blobs in @blob_list to resources in
 * consecutive positions in the output WIM file, or to a single solid resource
 * if WRITE_RESOURCE_FLAG_SOLID was specified in @write_resource_flags.  In both
 * cases, the @out_reshdr of the `struct blob_descriptor' for each blob written will be
 * updated to specify its location, size, and flags in the output WIM.  In the
 * solid resource case, WIM_RESHDR_FLAG_SOLID will be set in the @flags field of
 * each @out_reshdr, and furthermore @out_res_offset_in_wim and
 * @out_res_size_in_wim of each @out_reshdr will be set to the offset and size,
 * respectively, in the output WIM of the solid resource containing the
 * corresponding blob.
 *
 * Each of the blobs to write may be in any location supported by the
 * resource-handling code (specifically, read_blob_list()), such as the contents
 * of external file that has been logically added to the output WIM, or a blob
 * in another WIM file that has been imported, or even a blob in the "same" WIM
 * file of which a modified copy is being written.  In the case that a blob 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 to 1 on all blobs in @blob_list as well
 * as any other blobs not in @blob_list that will be in the output WIM file, but
 * set to 0 on any other blobs in the output WIM's blob table or sharing a solid
 * resource with a blob in @blob_list.  Still furthermore, if on-the-fly
 * deduplication of blobs is possible, then all blobs in @blob_list must also be
 * linked by @blob_table_list along with any other blobs that have
 * @will_be_in_output_wim set.
 *
 * This function handles on-the-fly deduplication of blobs for which SHA-1
 * message digests have not yet been calculated.  Such blobs may or may not need
 * to be written.  If @blob_table is non-NULL, then each blob in @blob_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 blob already being written or one that would be filtered
 * out of the output WIM using blob_filtered() with the context @filter_ctx.
 * Each such duplicate blob will be removed from @blob_list, its reference count
 * transferred to the pre-existing duplicate blob, its memory freed, and will
 * not be written.  Alternatively, if a blob in @blob_list is a duplicate with
 * any blob in @blob_table that has not been marked for writing or would not be
 * hard-filtered, it is freed and the pre-existing duplicate is written instead,
 * taking ownership of the reference count and slot in the @blob_table_list.
 *
 * Returns 0 if every blob was either written successfully or did not need to be
 * written; otherwise returns a non-zero error code.
 */
static int
write_blob_list(struct list_head *blob_list,
                struct filedes *out_fd,
                int write_resource_flags,
                int out_ctype,
                u32 out_chunk_size,
                unsigned num_threads,
                struct blob_table *blob_table,
                struct filter_context *filter_ctx,
                wimlib_progress_func_t progfunc,
                void *progctx)
{
        int ret;
        struct write_blobs_ctx ctx;
        struct list_head raw_copy_blobs;
        u64 num_nonraw_bytes;

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

        validate_blob_list(blob_list);

        if (list_empty(blob_list))
                return 0;

        /* If needed, set auxiliary information so that we can detect when the
         * library has finished using each external file.  */
        if (unlikely(write_resource_flags & WRITE_RESOURCE_FLAG_SEND_DONE_WITH_FILE))
                init_done_with_file_info(blob_list);

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

        ctx.out_fd = out_fd;
        ctx.blob_table = blob_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;

        /*
         * We normally sort the blobs to write by a "sequential" order that is
         * optimized for reading.  But when using solid compression, we instead
         * sort the blobs by file extension and file name (when applicable; and
         * we don't do this for blobs from solid resources) so that similar
         * files are grouped together, which improves the compression ratio.
         * This is somewhat of a hack since a blob does not necessarily
         * correspond one-to-one with a filename, nor is there any guarantee
         * that two files with similar names or extensions are actually similar
         * in content.  A potential TODO is to sort the blobs based on some
         * measure of similarity of their actual contents.
         */

        ret = sort_blob_list_by_sequential_order(blob_list,
                                                 offsetof(struct blob_descriptor,
                                                          write_blobs_list));
        if (ret)
                return ret;

        ret = compute_blob_list_stats(blob_list, &ctx);
        if (ret)
                return ret;

        if (write_resource_flags & WRITE_RESOURCE_FLAG_SOLID_SORT) {
                ret = sort_blob_list_for_solid_compression(blob_list);
                if (unlikely(ret))
                        WARNING("Failed to sort blobs for solid compression. Continuing anyways.");
        }

        ctx.progress_data.progfunc = progfunc;
        ctx.progress_data.progctx = progctx;

        num_nonraw_bytes = find_raw_copy_blobs(blob_list, write_resource_flags,
                                               out_ctype, out_chunk_size,
                                               &raw_copy_blobs);

        /* Copy any compressed resources for which the raw data can be reused
         * without decompression.  */
        ret = write_raw_copy_resources(&raw_copy_blobs, ctx.out_fd,
                                       &ctx.progress_data);

        if (ret || num_nonraw_bytes == 0)
                goto out_destroy_context;

        /* Unless uncompressed output was required, allocate a chunk_compressor
         * to do compression.  There are serial and parallel implementations of
         * 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 than a heuristic value.  */
        if (out_ctype != WIMLIB_COMPRESSION_TYPE_NONE) {

        #ifdef ENABLE_MULTITHREADED_COMPRESSION
                if (num_nonraw_bytes > max(2000000, out_chunk_size)) {
                        ret = new_parallel_chunk_compressor(out_ctype,
                                                            out_chunk_size,
                                                            num_threads, 0,
                                                            &ctx.compressor);
                        if (ret > 0) {
                                WARNING("Couldn't create parallel chunk compressor: %"TS".\n"
                                        "          Falling back to single-threaded compression.",
                                        wimlib_get_error_string(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;

        INIT_LIST_HEAD(&ctx.blobs_being_compressed);
        INIT_LIST_HEAD(&ctx.blobs_in_solid_resource);

        ret = call_progress(ctx.progress_data.progfunc,
                            WIMLIB_PROGRESS_MSG_WRITE_STREAMS,
                            &ctx.progress_data.progress,
                            ctx.progress_data.progctx);
        if (ret)
                goto out_destroy_context;

        if (write_resource_flags & WRITE_RESOURCE_FLAG_SOLID) {
                ret = begin_write_resource(&ctx, num_nonraw_bytes);
                if (ret)
                        goto out_destroy_context;
        }

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

        struct read_blob_callbacks cbs = {
                .begin_blob     = write_blob_begin_read,
                .consume_chunk  = write_blob_process_chunk,
                .end_blob       = write_blob_end_read,
                .ctx            = &ctx,
        };

        ret = read_blob_list(blob_list,
                             offsetof(struct blob_descriptor, write_blobs_list),
                             &cbs,
                             BLOB_LIST_ALREADY_SORTED |
                                VERIFY_BLOB_HASHES |
                                COMPUTE_MISSING_BLOB_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_SOLID) {
                struct wim_reshdr reshdr;
                struct blob_descriptor *blob;
                u64 offset_in_res;

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

                offset_in_res = 0;
                list_for_each_entry(blob, &ctx.blobs_in_solid_resource, write_blobs_list) {
                        blob->out_reshdr.size_in_wim = blob->size;
                        blob->out_reshdr.flags = reshdr_flags_for_blob(blob) |
                                                 WIM_RESHDR_FLAG_SOLID;
                        blob->out_reshdr.uncompressed_size = 0;
                        blob->out_reshdr.offset_in_wim = offset_in_res;
                        blob->out_res_offset_in_wim = reshdr.offset_in_wim;
                        blob->out_res_size_in_wim = reshdr.size_in_wim;
                        blob->out_res_uncompressed_size = reshdr.uncompressed_size;
                        offset_in_res += blob->size;
                }
                wimlib_assert(offset_in_res == reshdr.uncompressed_size);
        }

out_destroy_context:
        FREE(ctx.chunk_csizes);
        if (ctx.compressor)
                ctx.compressor->destroy(ctx.compressor);
        return ret;
}


static int
write_file_data_blobs(WIMStruct *wim,
                      struct list_head *blob_list,
                      int write_flags,
                      unsigned num_threads,
                      struct filter_context *filter_ctx)
{
        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_SOLID) {
                out_chunk_size = wim->out_solid_chunk_size;
                out_ctype = wim->out_solid_compression_type;
        } else {
                out_chunk_size = wim->out_chunk_size;
                out_ctype = wim->out_compression_type;
        }

        return write_blob_list(blob_list,
                               &wim->out_fd,
                               write_resource_flags,
                               out_ctype,
                               out_chunk_size,
                               num_threads,
                               wim->blob_table,
                               filter_ctx,
                               wim->progfunc,
                               wim->progctx);
}

/* Write the contents of the specified blob as a WIM resource.  */
static int
write_wim_resource(struct blob_descriptor *blob,
                   struct filedes *out_fd,
                   int out_ctype,
                   u32 out_chunk_size,
                   int write_resource_flags)
{
        LIST_HEAD(blob_list);
        list_add(&blob->write_blobs_list, &blob_list);
        blob->will_be_in_output_wim = 1;
        return write_blob_list(&blob_list,
                               out_fd,
                               write_resource_flags & ~WRITE_RESOURCE_FLAG_SOLID,
                               out_ctype,
                               out_chunk_size,
                               1,
                               NULL,
                               NULL,
                               NULL,
                               NULL);
}

/* Write the contents of the specified buffer as a WIM resource.  */
int
write_wim_resource_from_buffer(const void *buf,
                               size_t buf_size,
                               bool is_metadata,
                               struct filedes *out_fd,
                               int out_ctype,
                               u32 out_chunk_size,
                               struct wim_reshdr *out_reshdr,
                               u8 *hash_ret,
                               int write_resource_flags)
{
        int ret;
        struct blob_descriptor blob;

        if (unlikely(buf_size == 0)) {
                zero_reshdr(out_reshdr);
                if (hash_ret)
                        copy_hash(hash_ret, zero_hash);
                return 0;
        }

        blob_set_is_located_in_attached_buffer(&blob, (void *)buf, buf_size);
        sha1_buffer(buf, buf_size, blob.hash);
        blob.unhashed = 0;
        blob.is_metadata = is_metadata;

        ret = write_wim_resource(&blob, out_fd, out_ctype, out_chunk_size,
                                 write_resource_flags);
        if (ret)
                return ret;

        copy_reshdr(out_reshdr, &blob.out_reshdr);

        if (hash_ret)
                copy_hash(hash_ret, blob.hash);
        return 0;
}

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

static int
init_blob_size_table(struct blob_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_blob_size_table(struct blob_size_table *tab)
{
        FREE(tab->array);
}

static int
blob_size_table_insert(struct blob_descriptor *blob, void *_tab)
{
        struct blob_size_table *tab = _tab;
        size_t pos;
        struct blob_descriptor *same_size_blob;

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

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

struct find_blobs_ctx {
        WIMStruct *wim;
        int write_flags;
        struct list_head blob_list;
        struct blob_size_table blob_size_tab;
};

static void
reference_blob_for_write(struct blob_descriptor *blob,
                         struct list_head *blob_list, u32 nref)
{
        if (!blob->will_be_in_output_wim) {
                blob->out_refcnt = 0;
                list_add_tail(&blob->write_blobs_list, blob_list);
                blob->will_be_in_output_wim = 1;
        }
        blob->out_refcnt += nref;
}

static int
fully_reference_blob_for_write(struct blob_descriptor *blob, void *_blob_list)
{
        struct list_head *blob_list = _blob_list;
        blob->will_be_in_output_wim = 0;
        reference_blob_for_write(blob, blob_list, blob->refcnt);
        return 0;
}

static int
inode_find_blobs_to_reference(const struct wim_inode *inode,
                              const struct blob_table *table,
                              struct list_head *blob_list)
{
        wimlib_assert(inode->i_nlink > 0);

        for (unsigned i = 0; i < inode->i_num_streams; i++) {
                struct blob_descriptor *blob;
                const u8 *hash;

                blob = stream_blob(&inode->i_streams[i], table);
                if (blob) {
                        reference_blob_for_write(blob, blob_list, inode->i_nlink);
                } else {
                        hash = stream_hash(&inode->i_streams[i]);
                        if (!is_zero_hash(hash))
                                return blob_not_found_error(inode, hash);
                }
        }
        return 0;
}

static int
do_blob_set_not_in_output_wim(struct blob_descriptor *blob, void *_ignore)
{
        blob->will_be_in_output_wim = 0;
        return 0;
}

static int
image_find_blobs_to_reference(WIMStruct *wim)
{
        struct wim_image_metadata *imd;
        struct wim_inode *inode;
        struct blob_descriptor *blob;
        struct list_head *blob_list;
        int ret;

        imd = wim_get_current_image_metadata(wim);

        image_for_each_unhashed_blob(blob, imd)
                blob->will_be_in_output_wim = 0;

        blob_list = wim->private;
        image_for_each_inode(inode, imd) {
                ret = inode_find_blobs_to_reference(inode,
                                                    wim->blob_table,
                                                    blob_list);
                if (ret)
                        return ret;
        }
        return 0;
}

static int
prepare_unfiltered_list_of_blobs_in_output_wim(WIMStruct *wim,
                                               int image,
                                               int blobs_ok,
                                               struct list_head *blob_list_ret)
{
        int ret;

        INIT_LIST_HEAD(blob_list_ret);

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

                for_blob_in_table(wim->blob_table,
                                  fully_reference_blob_for_write,
                                  blob_list_ret);

                for (i = 0; i < wim->hdr.image_count; i++) {
                        imd = wim->image_metadata[i];
                        image_for_each_unhashed_blob(blob, imd)
                                fully_reference_blob_for_write(blob, blob_list_ret);
                }
        } else {
                /* Slow case:  Walk through the images being written and
                 * determine the blobs referenced.  */
                for_blob_in_table(wim->blob_table,
                                  do_blob_set_not_in_output_wim, NULL);
                wim->private = blob_list_ret;
                ret = for_image(wim, image, image_find_blobs_to_reference);
                if (ret)
                        return ret;
        }

        return 0;
}

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

static int
insert_other_if_hard_filtered(struct blob_descriptor *blob, void *_ctx)
{
        struct insert_other_if_hard_filtered_ctx *ctx = _ctx;

        if (!blob->will_be_in_output_wim &&
            blob_hard_filtered(blob, ctx->filter_ctx))
                blob_size_table_insert(blob, ctx->tab);
        return 0;
}

static int
determine_blob_size_uniquity(struct list_head *blob_list,
                             struct blob_table *lt,
                             struct filter_context *filter_ctx)
{
        int ret;
        struct blob_size_table tab;
        struct blob_descriptor *blob;

        ret = init_blob_size_table(&tab, 9001);
        if (ret)
                return ret;

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

        list_for_each_entry(blob, blob_list, write_blobs_list)
                blob_size_table_insert(blob, &tab);

        destroy_blob_size_table(&tab);
        return 0;
}

static void
filter_blob_list_for_write(struct list_head *blob_list,
                           struct filter_context *filter_ctx)
{
        struct blob_descriptor *blob, *tmp;

        list_for_each_entry_safe(blob, tmp, blob_list, write_blobs_list) {
                int status = blob_filtered(blob, filter_ctx);

                if (status == 0) {
                        /* Not filtered.  */
                        continue;
                } else {
                        if (status > 0) {
                                /* Soft filtered.  */
                        } else {
                                /* Hard filtered.  */
                                blob->will_be_in_output_wim = 0;
                                list_del(&blob->blob_table_list);
                        }
                        list_del(&blob->write_blobs_list);
                }
        }
}

/*
 * prepare_blob_list_for_write() -
 *
 * Prepare the list of blobs 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 blobs in the blob
 *      table of @wim and the per-image lists of unhashed blobs should be taken
 *      as-is, and image metadata should not be searched for references.  This
 *      does not exclude filtering with APPEND and SKIP_EXTERNAL_WIMS, below.
 *
 *      APPEND:  Blobs already present in @wim shall not be returned in
 *      @blob_list_ret.
 *
 *      SKIP_EXTERNAL_WIMS:  Blobs already present in a WIM file, but not @wim,
 *      shall be returned in neither @blob_list_ret nor @blob_table_list_ret.
 *
 * @blob_list_ret
 *      List of blobs, linked by write_blobs_list, that need to be written will
 *      be returned here.
 *
 *      Note that this function assumes that unhashed blobs will be written; it
 *      does not take into account that they may become duplicates when actually
 *      hashed.
 *
 * @blob_table_list_ret
 *      List of blobs, linked by blob_table_list, that need to be included in
 *      the WIM's blob table will be returned here.  This will be a superset of
 *      the blobs in @blob_list_ret.
 *
 *      This list will be a proper superset of @blob_list_ret if and only if
 *      WIMLIB_WRITE_FLAG_APPEND was specified in @write_flags and some of the
 *      blobs that would otherwise need to be written were already located in
 *      the WIM file.
 *
 *      All blobs in this list will have @out_refcnt set to the number of
 *      references to the blob in the output WIM.  If
 *      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 blob filter status with blob_filtered() is
 *      returned in this location.
 *
 * In addition, @will_be_in_output_wim will be set to 1 in all blobs inserted
 * into @blob_table_list_ret and to 0 in all blobs in the blob table of @wim not
 * inserted into @blob_table_list_ret.
 *
 * Still furthermore, @unique_size will be set to 1 on all blobs in
 * @blob_list_ret that have unique size among all blobs in @blob_list_ret and
 * among all blobs in the blob 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_blob_list_for_write(WIMStruct *wim, int image,
                            int write_flags,
                            struct list_head *blob_list_ret,
                            struct list_head *blob_table_list_ret,
                            struct filter_context *filter_ctx_ret)
{
        int ret;
        struct blob_descriptor *blob;

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

        ret = prepare_unfiltered_list_of_blobs_in_output_wim(
                                wim,
                                image,
                                write_flags & WIMLIB_WRITE_FLAG_STREAMS_OK,
                                blob_list_ret);
        if (ret)
                return ret;

        INIT_LIST_HEAD(blob_table_list_ret);
        list_for_each_entry(blob, blob_list_ret, write_blobs_list)
                list_add_tail(&blob->blob_table_list, blob_table_list_ret);

        ret = determine_blob_size_uniquity(blob_list_ret, wim->blob_table,
                                           filter_ctx_ret);
        if (ret)
                return ret;

        if (may_filter_blobs(filter_ctx_ret))
                filter_blob_list_for_write(blob_list_ret, filter_ctx_ret);

        return 0;
}

static int
write_file_data(WIMStruct *wim, int image, int write_flags,
                unsigned num_threads,
                struct list_head *blob_list_override,
                struct list_head *blob_table_list_ret)
{
        int ret;
        struct list_head _blob_list;
        struct list_head *blob_list;
        struct blob_descriptor *blob;
        struct filter_context _filter_ctx;
        struct filter_context *filter_ctx;

        if (blob_list_override == NULL) {
                /* Normal case: prepare blob list from image(s) being written.
                 */
                blob_list = &_blob_list;
                filter_ctx = &_filter_ctx;
                ret = prepare_blob_list_for_write(wim, image, write_flags,
                                                  blob_list,
                                                  blob_table_list_ret,
                                                  filter_ctx);
                if (ret)
                        return ret;
        } else {
                /* Currently only as a result of wimlib_split() being called:
                 * use blob list already explicitly provided.  Use existing
                 * reference counts.  */
                blob_list = blob_list_override;
                filter_ctx = NULL;
                INIT_LIST_HEAD(blob_table_list_ret);
                list_for_each_entry(blob, blob_list, write_blobs_list) {
                        blob->out_refcnt = blob->refcnt;
                        blob->will_be_in_output_wim = 1;
                        blob->unique_size = 0;
                        list_add_tail(&blob->blob_table_list, blob_table_list_ret);
                }
        }

        return write_file_data_blobs(wim,
                                     blob_list,
                                     write_flags,
                                     num_threads,
                                     filter_ctx);
}

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

        if (write_flags & WIMLIB_WRITE_FLAG_NO_METADATA)
                return 0;

        write_resource_flags = write_flags_to_resource_flags(write_flags);

        write_resource_flags &= ~WRITE_RESOURCE_FLAG_SOLID;

        ret = call_progress(wim->progfunc,
                            WIMLIB_PROGRESS_MSG_WRITE_METADATA_BEGIN,
                            NULL, wim->progctx);
        if (ret)
                return ret;

        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];
                if (is_image_dirty(imd)) {
                        /* The image was modified from the original, or was
                         * newly added, so we have to build and write a new
                         * metadata resource.  */
                        ret = write_metadata_resource(wim, i,
                                                      write_resource_flags);
                } else if (is_image_unchanged_from_wim(imd, wim) &&
                           (write_flags & (WIMLIB_WRITE_FLAG_UNSAFE_COMPACT |
                                           WIMLIB_WRITE_FLAG_APPEND)))
                {
                        /* The metadata resource is already in the WIM file.
                         * For appends, we don't need to write it at all.  For
                         * compactions, we re-write existing metadata resources
                         * along with the existing file resources, not here.  */
                        if (write_flags & WIMLIB_WRITE_FLAG_APPEND)
                                blob_set_out_reshdr_for_reuse(imd->metadata_blob);
                        ret = 0;
                } else {
                        /* The metadata resource is in a WIM file other than the
                         * one being written to.  We need to rewrite it,
                         * possibly compressed differently; but rebuilding the
                         * metadata itself isn't necessary.  */
                        ret = write_wim_resource(imd->metadata_blob,
                                                 &wim->out_fd,
                                                 wim->out_compression_type,
                                                 wim->out_chunk_size,
                                                 write_resource_flags);
                }
                if (ret)
                        return ret;
        }

        return call_progress(wim->progfunc,
                             WIMLIB_PROGRESS_MSG_WRITE_METADATA_END,
                             NULL, wim->progctx);
}

static int
open_wim_writable(WIMStruct *wim, const tchar *path, int open_flags)
{
        int 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))
                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_blobs_by_out_rdesc(const void *p1, const void *p2)
{
        const struct blob_descriptor *blob1, *blob2;

        blob1 = *(const struct blob_descriptor**)p1;
        blob2 = *(const struct blob_descriptor**)p2;

        if (blob1->out_reshdr.flags & WIM_RESHDR_FLAG_SOLID) {
                if (blob2->out_reshdr.flags & WIM_RESHDR_FLAG_SOLID) {
                        if (blob1->out_res_offset_in_wim != blob2->out_res_offset_in_wim)
                                return cmp_u64(blob1->out_res_offset_in_wim,
                                               blob2->out_res_offset_in_wim);
                } else {
                        return 1;
                }
        } else {
                if (blob2->out_reshdr.flags & WIM_RESHDR_FLAG_SOLID)
                        return -1;
        }
        return cmp_u64(blob1->out_reshdr.offset_in_wim,
                       blob2->out_reshdr.offset_in_wim);
}

static int
write_blob_table(WIMStruct *wim, int image, int write_flags,
                 struct list_head *blob_table_list)
{
        int ret;

        /* Set output resource metadata for blobs already present in WIM.  */
        if (write_flags & WIMLIB_WRITE_FLAG_APPEND) {
                struct blob_descriptor *blob;
                list_for_each_entry(blob, blob_table_list, blob_table_list) {
                        if (blob->blob_location == BLOB_IN_WIM &&
                            blob->rdesc->wim == wim)
                        {
                                blob_set_out_reshdr_for_reuse(blob);
                        }
                }
        }

        ret = sort_blob_list(blob_table_list,
                             offsetof(struct blob_descriptor, blob_table_list),
                             cmp_blobs_by_out_rdesc);
        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 blob 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 blob_descriptor *metadata_blob;

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

        return write_blob_table_from_blob_list(blob_table_list,
                                               &wim->out_fd,
                                               wim->out_hdr.part_number,
                                               &wim->out_hdr.blob_table_reshdr,
                                               write_flags_to_resource_flags(write_flags));
}

/*
 * Finish writing a WIM file: write the blob table, xml data, and integrity
 * table, then overwrite the WIM header.
 *
 * The output file descriptor is closed on success, except when writing to a
 * user-specified file descriptor (WIMLIB_WRITE_FLAG_FILE_DESCRIPTOR set).
 */
static int
finish_write(WIMStruct *wim, int image, int write_flags,
             struct list_head *blob_table_list)
{
        int write_resource_flags;
        off_t old_blob_table_end = 0;
        struct integrity_table *old_integrity_table = NULL;
        off_t new_blob_table_end;
        u64 xml_totalbytes;
        int ret;

        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.  */
        if (wim->out_hdr.boot_idx == 0) {
                zero_reshdr(&wim->out_hdr.boot_metadata_reshdr);
        } else {
                copy_reshdr(&wim->out_hdr.boot_metadata_reshdr,
                            &wim->image_metadata[
                                wim->out_hdr.boot_idx - 1]->metadata_blob->out_reshdr);
        }

        /* If appending to a WIM file containing an integrity table, we'd like
         * to re-use the information in the old integrity table instead of
         * recalculating it.  But we might overwrite the old integrity table
         * when we expand the XML data.  Read it into memory just in case.  */
        if ((write_flags & (WIMLIB_WRITE_FLAG_APPEND |
                            WIMLIB_WRITE_FLAG_CHECK_INTEGRITY)) ==
                (WIMLIB_WRITE_FLAG_APPEND |
                 WIMLIB_WRITE_FLAG_CHECK_INTEGRITY)
            && wim_has_integrity_table(wim))
        {
                old_blob_table_end = wim->hdr.blob_table_reshdr.offset_in_wim +
                                     wim->hdr.blob_table_reshdr.size_in_wim;
                (void)read_integrity_table(wim,
                                           old_blob_table_end - WIM_HEADER_DISK_SIZE,
                                           &old_integrity_table);
                /* If we couldn't read the old integrity table, we can still
                 * re-calculate the full integrity table ourselves.  Hence the
                 * ignoring of the return value.  */
        }

        /* Write blob table if needed.  */
        if (!(write_flags & WIMLIB_WRITE_FLAG_NO_NEW_BLOBS)) {
                ret = write_blob_table(wim, image, write_flags,
                                       blob_table_list);
                if (ret) {
                        free_integrity_table(old_integrity_table);
                        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->out_hdr.xml_data_reshdr,
                                 write_resource_flags);
        if (ret) {
                free_integrity_table(old_integrity_table);
                return ret;
        }

        /* Write integrity table if needed.  */
        if (write_flags & WIMLIB_WRITE_FLAG_CHECK_INTEGRITY) {
                if (write_flags & WIMLIB_WRITE_FLAG_NO_NEW_BLOBS) {
                        /* The XML data we wrote may have overwritten part of
                         * the old integrity table, so while calculating the new
                         * integrity table we should temporarily update the WIM
                         * header to remove the integrity table reference.   */
                        struct wim_header checkpoint_hdr;
                        memcpy(&checkpoint_hdr, &wim->out_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(&checkpoint_hdr, &wim->out_fd, 0);
                        if (ret) {
                                free_integrity_table(old_integrity_table);
                                return ret;
                        }
                }

                new_blob_table_end = wim->out_hdr.blob_table_reshdr.offset_in_wim +
                                     wim->out_hdr.blob_table_reshdr.size_in_wim;

                ret = write_integrity_table(wim,
                                            new_blob_table_end,
                                            old_blob_table_end,
                                            old_integrity_table);
                free_integrity_table(old_integrity_table);
                if (ret)
                        return ret;
        } else {
                /* No integrity table.  */
                zero_reshdr(&wim->out_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->out_hdr.flags &= ~WIM_HDR_FLAG_WRITE_IN_PROGRESS;
        if (write_flags & WIMLIB_WRITE_FLAG_PIPABLE)
                ret = write_wim_header(&wim->out_hdr, &wim->out_fd, wim->out_fd.offset);
        else
                ret = write_wim_header(&wim->out_hdr, &wim->out_fd, 0);
        if (ret)
                return ret;

        if (unlikely(write_flags & WIMLIB_WRITE_FLAG_UNSAFE_COMPACT)) {
                /* Truncate any data the compaction freed up.  */
                if (ftruncate(wim->out_fd.fd, wim->out_fd.offset)) {
                        ERROR_WITH_ERRNO("Failed to truncate the output WIM file");
                        return WIMLIB_ERR_WRITE;
                }
        }

        /* Possibly sync file data to disk before closing.  On POSIX systems, it
         * is necessary to do this before using rename() to overwrite an
         * existing file with a new file.  Otherwise, data loss would occur if
         * 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) {
                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)

/* Set advisory lock on WIM file (if not already done so)  */
int
lock_wim_for_append(WIMStruct *wim)
{
        if (wim->locked_for_append)
                return 0;
        if (!flock(wim->in_fd.fd, LOCK_EX | LOCK_NB)) {
                wim->locked_for_append = 1;
                return 0;
        }
        if (errno != EWOULDBLOCK)
                return 0;
        return WIMLIB_ERR_ALREADY_LOCKED;
}

/* Remove advisory lock on WIM file (if present)  */
void
unlock_wim_for_append(WIMStruct *wim)
{
        if (wim->locked_for_append) {
                flock(wim->in_fd.fd, LOCK_UN);
                wim->locked_for_append = 0;
        }
}
#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 blob table and XML
 *   data resource entries.  This is because this information cannot be
 *   determined until the blob 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).
 *
 * - Solid resources are not allowed.  Each blob is always stored in its own
 *   resource.
 *
 * - The format of resources, or blobs, has been modified to allow them to be
 *   used before the "blob table" has been read.  Each blob is prefixed with a
 *   `struct pwm_blob_hdr' that is basically an abbreviated form of `struct
 *   blob_descriptor_disk' that only contains the SHA-1 message digest,
 *   uncompressed blob size, and flags that indicate whether the blob is
 *   compressed.  The data of uncompressed blobs then follows literally, while
 *   the data of compressed blobs follows in a modified format.  Compressed
 *   blobs 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 blobs always come before non-metadata blobs.  (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 blobs, 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 blob 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 |  Blob table  | XML data  | Header |
 * ---------+----------+--------------------+----------------+--------------+-----------+--------+
 *
 *   Layout of normal WIM:
 *
 * +--------+-----------------------------+-------------------------+
 * | Header | File and metadata resources |  Blob 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,
                  struct list_head *blob_list_override,
                  struct list_head *blob_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 SHA-1 message digests of files are 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 blob to a pipable WIM, its SHA-1 message digest
         * needs to be known before the blob data is written.  Therefore, before
         * getting much farther, we need to pre-calculate the SHA-1 message
         * digests of all blobs that will be written.  */
        ret = wim_checksum_unhashed_blobs(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_metadata_resources(wim, image, write_flags);
        if (ret)
                return ret;

        /* Write file data needed for the image(s) being included in the output
         * WIM, or file data needed for the split WIM part.  */
        return write_file_data(wim, image, write_flags,
                               num_threads, blob_list_override,
                               blob_table_list_ret);

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

static bool
should_default_to_solid_compression(WIMStruct *wim, int write_flags)
{
        return wim->out_hdr.wim_version == WIM_VERSION_SOLID &&
                !(write_flags & (WIMLIB_WRITE_FLAG_SOLID |
                                 WIMLIB_WRITE_FLAG_PIPABLE)) &&
                wim_has_solid_resources(wim);
}

/* 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,
               unsigned part_number,
               unsigned total_parts,
               struct list_head *blob_list_override,
               const u8 *guid)
{
        int ret;
        struct list_head blob_table_list;

        /* 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;

        /* Only wimlib_overwrite() accepts UNSAFE_COMPACT.  */
        if (write_flags & WIMLIB_WRITE_FLAG_UNSAFE_COMPACT)
                return WIMLIB_ERR_INVALID_PARAM;

        /* Include an integrity table by default if no preference was given and
         * the WIM already had an integrity table.  */
        if (!(write_flags & (WIMLIB_WRITE_FLAG_CHECK_INTEGRITY |
                             WIMLIB_WRITE_FLAG_NO_CHECK_INTEGRITY))) {
                if (wim_has_integrity_table(wim))
                        write_flags |= WIMLIB_WRITE_FLAG_CHECK_INTEGRITY;
        }

        /* Write a pipable WIM by default if no preference was given and the WIM
         * was already pipable.  */
        if (!(write_flags & (WIMLIB_WRITE_FLAG_PIPABLE |
                             WIMLIB_WRITE_FLAG_NOT_PIPABLE))) {
                if (wim_is_pipable(wim))
                        write_flags |= WIMLIB_WRITE_FLAG_PIPABLE;
        }

        if ((write_flags & (WIMLIB_WRITE_FLAG_PIPABLE |
                            WIMLIB_WRITE_FLAG_SOLID))
                                    == (WIMLIB_WRITE_FLAG_PIPABLE |
                                        WIMLIB_WRITE_FLAG_SOLID))
        {
                ERROR("Solid compression is unsupported in pipable WIMs");
                return WIMLIB_ERR_INVALID_PARAM;
        }

        /* Start initializing the new file header.  */
        memset(&wim->out_hdr, 0, sizeof(wim->out_hdr));

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

        /* Set the version number.  */
        if ((write_flags & WIMLIB_WRITE_FLAG_SOLID) ||
            wim->out_compression_type == WIMLIB_COMPRESSION_TYPE_LZMS)
                wim->out_hdr.wim_version = WIM_VERSION_SOLID;
        else
                wim->out_hdr.wim_version = WIM_VERSION_DEFAULT;

        /* Default to solid compression if it is valid in the chosen WIM file
         * format and the WIMStruct references any solid resources.  This is
         * useful when exporting an image from a solid WIM.  */
        if (should_default_to_solid_compression(wim, write_flags))
                write_flags |= WIMLIB_WRITE_FLAG_SOLID;

        /* Set the header flags.  */
        wim->out_hdr.flags = (wim->hdr.flags & (WIM_HDR_FLAG_RP_FIX |
                                                WIM_HDR_FLAG_READONLY));
        if (total_parts != 1)
                wim->out_hdr.flags |= WIM_HDR_FLAG_SPANNED;
        if (wim->out_compression_type != WIMLIB_COMPRESSION_TYPE_NONE) {
                wim->out_hdr.flags |= WIM_HDR_FLAG_COMPRESSION;
                switch (wim->out_compression_type) {
                case WIMLIB_COMPRESSION_TYPE_XPRESS:
                        wim->out_hdr.flags |= WIM_HDR_FLAG_COMPRESS_XPRESS;
                        break;
                case WIMLIB_COMPRESSION_TYPE_LZX:
                        wim->out_hdr.flags |= WIM_HDR_FLAG_COMPRESS_LZX;
                        break;
                case WIMLIB_COMPRESSION_TYPE_LZMS:
                        wim->out_hdr.flags |= WIM_HDR_FLAG_COMPRESS_LZMS;
                        break;
                }
        }

        /* Set the chunk size.  */
        wim->out_hdr.chunk_size = wim->out_chunk_size;

        /* Set the GUID.  */
        if (write_flags & WIMLIB_WRITE_FLAG_RETAIN_GUID)
                guid = wim->hdr.guid;
        if (guid)
                copy_guid(wim->out_hdr.guid, guid);
        else
                generate_guid(wim->out_hdr.guid);

        /* Set the part number and total parts.  */
        wim->out_hdr.part_number = part_number;
        wim->out_hdr.total_parts = total_parts;

        /* Set the image count.  */
        if (image == WIMLIB_ALL_IMAGES)
                wim->out_hdr.image_count = wim->hdr.image_count;
        else
                wim->out_hdr.image_count = 1;

        /* Set the boot index.  */
        wim->out_hdr.boot_idx = 0;
        if (total_parts == 1) {
                if (image == WIMLIB_ALL_IMAGES)
                        wim->out_hdr.boot_idx = wim->hdr.boot_idx;
                else if (image == wim->hdr.boot_idx)
                        wim->out_hdr.boot_idx = 1;
        }

        /* Set up the output file descriptor.  */
        if (write_flags & WIMLIB_WRITE_FLAG_FILE_DESCRIPTOR) {
                /* File descriptor was explicitly provided.  */
                filedes_init(&wim->out_fd, *(const int *)path_or_fd);
                if (!filedes_is_seekable(&wim->out_fd)) {
                        /* The file descriptor is a pipe.  */
                        ret = WIMLIB_ERR_INVALID_PARAM;
                        if (!(write_flags & WIMLIB_WRITE_FLAG_PIPABLE))
                                goto out_cleanup;
                        if (write_flags & WIMLIB_WRITE_FLAG_CHECK_INTEGRITY) {
                                ERROR("Can't include integrity check when "
                                      "writing pipable WIM to pipe!");
                                goto out_cleanup;
                        }
                }
        } 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_cleanup;
        }

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

        /* Write file data and metadata resources.  */
        if (!(write_flags & WIMLIB_WRITE_FLAG_PIPABLE)) {
                /* Default case: create a normal (non-pipable) WIM.  */
                ret = write_file_data(wim, image, write_flags,
                                      num_threads,
                                      blob_list_override,
                                      &blob_table_list);
                if (ret)
                        goto out_cleanup;

                ret = write_metadata_resources(wim, image, write_flags);
                if (ret)
                        goto out_cleanup;
        } else {
                /* Non-default case: create pipable WIM.  */
                ret = write_pipable_wim(wim, image, write_flags, num_threads,
                                        blob_list_override,
                                        &blob_table_list);
                if (ret)
                        goto out_cleanup;
        }

        /* Write blob table, XML data, and (optional) integrity table.  */
        ret = finish_write(wim, image, write_flags, &blob_table_list);
out_cleanup:
        (void)close_wim_writable(wim, write_flags);
        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)
{
        return write_wim_part(wim, path_or_fd, image, write_flags,
                              num_threads, 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)
{
        if (write_flags & ~WIMLIB_WRITE_MASK_PUBLIC)
                return WIMLIB_ERR_INVALID_PARAM;

        if (path == NULL || path[0] == T('\0'))
                return WIMLIB_ERR_INVALID_PARAM;

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

/* API function documented in wimlib.h  */
WIMLIBAPI int
wimlib_write_to_fd(WIMStruct *wim, int fd,
                   int image, int write_flags, unsigned num_threads)
{
        if (write_flags & ~WIMLIB_WRITE_MASK_PUBLIC)
                return WIMLIB_ERR_INVALID_PARAM;

        if (fd < 0)
                return WIMLIB_ERR_INVALID_PARAM;

        write_flags |= WIMLIB_WRITE_FLAG_FILE_DESCRIPTOR;

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

/* Have there been any changes to images in the specified WIM, including updates
 * as well as deletions and additions of entire images, but excluding changes to
 * the XML document?  */
static bool
any_images_changed(WIMStruct *wim)
{
        if (wim->image_deletion_occurred)
                return true;
        for (int i = 0; i < wim->hdr.image_count; i++)
                if (!is_image_unchanged_from_wim(wim->image_metadata[i], wim))
                        return true;
        return false;
}

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

        if (blob->blob_location == BLOB_IN_WIM &&
            blob->rdesc->wim == wim &&
            blob->rdesc->offset_in_wim + blob->rdesc->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 append to the WIM
 * file 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_blob_in_table(wim->blob_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_blob, wim);
                if (ret)
                        return ret;
        }
        return 0;
}

/*
 * Overwrite a WIM, possibly appending new resources to it.
 *
 * A WIM looks like (or is supposed to look like) the following:
 *
 *                   Header (212 bytes)
 *                   Resources for metadata and files (variable size)
 *                   Blob table (variable size)
 *                   XML data (variable size)
 *                   Integrity table (optional) (variable size)
 *
 * If we are not adding any new files or metadata, then the blob 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,
 * we write a temporary header 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 blobs, including new file data as well as any metadata
 * for any new images, then the blob table needs to be changed, and those blobs
 * need to be written.  In this case, we try to perform a safe update of the WIM
 * file by writing the blobs *after* the end of the previous WIM, then writing
 * the new blob table, XML data, and (optionally) integrity table following the
 * new blobs.  This will produce a layout like the following:
 *
 *                   Header (212 bytes)
 *                   (OLD) Resources for metadata and files (variable size)
 *                   (OLD) Blob table (variable size)
 *                   (OLD) XML data (variable size)
 *                   (OLD) Integrity table (optional) (variable size)
 *                   (NEW) Resources for metadata and files (variable size)
 *                   (NEW) Blob 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 blob table, XML data, and
 * integrity table, to produce the following layout:
 *
 *                   Header (212 bytes)
 *                   Resources for metadata and files (variable size)
 *                   Nothing (variable size)
 *                   Resources for metadata and files (variable size)
 *                   Blob table (variable size)
 *                   XML data (variable size)
 *                   Integrity table (optional) (variable size)
 *
 * This function allows an image to be appended to a large WIM very quickly, and
 * is crash-safe except in the case of write re-ordering, but the disadvantage
 * is that a small hole is left in the WIM where the old blob table, xml data,
 * and integrity table were.  (These usually only take up a small amount of
 * space compared to the blobs, however.)
 *
 * Finally, this function also supports "compaction" overwrites as an
 * alternative to the normal "append" overwrites described above.  In a
 * compaction, data is written starting immediately from the end of the header.
 * All existing resources are written first, in order by file offset.  New
 * resources are written afterwards, and at the end any extra data is truncated
 * from the file.  The advantage of this approach is that is that the WIM file
 * ends up fully optimized, without any holes remaining.  The main disadavantage
 * is that this operation is fundamentally unsafe and cannot be interrupted
 * without data corruption.  Consequently, compactions are only ever done when
 * explicitly requested by the library user with the flag
 * WIMLIB_WRITE_FLAG_UNSAFE_COMPACT.  (Another disadvantage is that a compaction
 * can be much slower than an append.)
 */
static int
overwrite_wim_inplace(WIMStruct *wim, int write_flags, unsigned num_threads)
{
        int ret;
        off_t old_wim_end;
        struct list_head blob_list;
        struct list_head blob_table_list;
        struct filter_context filter_ctx;

        /* Include an integrity table by default if no preference was given and
         * the WIM already had an integrity table.  */
        if (!(write_flags & (WIMLIB_WRITE_FLAG_CHECK_INTEGRITY |
                             WIMLIB_WRITE_FLAG_NO_CHECK_INTEGRITY)))
                if (wim_has_integrity_table(wim))
                        write_flags |= WIMLIB_WRITE_FLAG_CHECK_INTEGRITY;

        /* Start preparing the updated file header.  */
        memcpy(&wim->out_hdr, &wim->hdr, sizeof(wim->out_hdr));

        /* If using solid compression, the version number must be set to
         * WIM_VERSION_SOLID.  */
        if (write_flags & WIMLIB_WRITE_FLAG_SOLID)
                wim->out_hdr.wim_version = WIM_VERSION_SOLID;

        /* Default to solid compression if it is valid in the chosen WIM file
         * format and the WIMStruct references any solid resources.  This is
         * useful when updating a solid WIM.  */
        if (should_default_to_solid_compression(wim, write_flags))
                write_flags |= WIMLIB_WRITE_FLAG_SOLID;

        if (unlikely(write_flags & WIMLIB_WRITE_FLAG_UNSAFE_COMPACT)) {

                /* In-place compaction  */

                WARNING("The WIM file \"%"TS"\" is being compacted in place.\n"
                        "          Do *not* interrupt the operation, or else "
                        "the WIM file will be\n"
                        "          corrupted!", wim->filename);
                wim->being_compacted = 1;
                old_wim_end = WIM_HEADER_DISK_SIZE;

                ret = prepare_blob_list_for_write(wim, WIMLIB_ALL_IMAGES,
                                                  write_flags, &blob_list,
                                                  &blob_table_list, &filter_ctx);
                if (ret)
                        goto out;

                if (wim_has_metadata(wim)) {
                        /* Add existing metadata resources to be compacted along
                         * with the file resources.  */
                        for (int i = 0; i < wim->hdr.image_count; i++) {
                                struct wim_image_metadata *imd = wim->image_metadata[i];
                                if (is_image_unchanged_from_wim(imd, wim)) {
                                        fully_reference_blob_for_write(imd->metadata_blob,
                                                                       &blob_list);
                                }
                        }
                }
        } else {
                u64 old_blob_table_end, old_xml_begin, old_xml_end;

                /* Set additional flags for append.  */
                write_flags |= WIMLIB_WRITE_FLAG_APPEND |
                               WIMLIB_WRITE_FLAG_STREAMS_OK;

                /* Make sure there is no data after the XML data, except
                 * possibily an integrity table.  If this were the case, then
                 * this data would be overwritten.  */
                old_xml_begin = wim->hdr.xml_data_reshdr.offset_in_wim;
                old_xml_end = old_xml_begin + wim->hdr.xml_data_reshdr.size_in_wim;
                old_blob_table_end = wim->hdr.blob_table_reshdr.offset_in_wim +
                                     wim->hdr.blob_table_reshdr.size_in_wim;
                if (wim_has_integrity_table(wim) &&
                    wim->hdr.integrity_table_reshdr.offset_in_wim < old_xml_end) {
                        WARNING("Didn't expect the integrity table to be "
                                "before the XML data");
                        ret = WIMLIB_ERR_RESOURCE_ORDER;
                        goto out;
                }

                if (old_blob_table_end > old_xml_begin) {
                        WARNING("Didn't expect the blob table to be after "
                                "the XML data");
                        ret = WIMLIB_ERR_RESOURCE_ORDER;
                        goto out;
                }
                /* Set @old_wim_end, which indicates the point beyond which we
                 * don't allow any file and metadata resources to appear without
                 * returning WIMLIB_ERR_RESOURCE_ORDER (due to the fact that we
                 * would otherwise overwrite these resources). */
                if (!any_images_changed(wim)) {
                        /* If no images have been modified, added, or deleted,
                         * then a new blob table does not need to be written.
                         * We shall write the new XML data and optional
                         * integrity table immediately after the blob table.
                         * Note that this may overwrite an existing integrity
                         * table.  */
                        old_wim_end = old_blob_table_end;
                        write_flags |= WIMLIB_WRITE_FLAG_NO_NEW_BLOBS;
                } else if (wim_has_integrity_table(wim)) {
                        /* Old WIM has an integrity table; begin writing new
                         * blobs after it. */
                        old_wim_end = wim->hdr.integrity_table_reshdr.offset_in_wim +
                                      wim->hdr.integrity_table_reshdr.size_in_wim;
                } else {
                        /* No existing integrity table; begin writing new blobs
                         * after the old XML data. */
                        old_wim_end = old_xml_end;
                }

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

                ret = prepare_blob_list_for_write(wim, WIMLIB_ALL_IMAGES,
                                                  write_flags, &blob_list,
                                                  &blob_table_list, &filter_ctx);
                if (ret)
                        goto out;

                if (write_flags & WIMLIB_WRITE_FLAG_NO_NEW_BLOBS)
                        wimlib_assert(list_empty(&blob_list));
        }

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

        ret = lock_wim_for_append(wim);
        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);
        wim->hdr.flags &= ~WIM_HDR_FLAG_WRITE_IN_PROGRESS;
        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_hdr;
        }

        ret = write_file_data_blobs(wim, &blob_list, write_flags,
                                    num_threads, &filter_ctx);
        if (ret)
                goto out_truncate;

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

        ret = finish_write(wim, WIMLIB_ALL_IMAGES, write_flags,
                           &blob_table_list);
        if (ret)
                goto out_truncate;

        unlock_wim_for_append(wim);
        return 0;

out_truncate:
        if (!(write_flags & (WIMLIB_WRITE_FLAG_NO_NEW_BLOBS |
                             WIMLIB_WRITE_FLAG_UNSAFE_COMPACT))) {
                WARNING("Truncating \"%"TS"\" to its original size "
                        "(%"PRIu64" bytes)", wim->filename, old_wim_end);
                /* Return value of ftruncate() is ignored because this is
                 * already an error path.  */
                (void)ftruncate(wim->out_fd.fd, old_wim_end);
        }
out_restore_hdr:
        (void)write_wim_header_flags(wim->hdr.flags, &wim->out_fd);
out_unlock_wim:
        unlock_wim_for_append(wim);
out_close_wim:
        (void)close_wim_writable(wim, write_flags);
out:
        wim->being_compacted = 0;
        return ret;
}

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

        /* 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 |
                                WIMLIB_WRITE_FLAG_RETAIN_GUID,
                           num_threads);
        if (ret) {
                tunlink(tmpfile);
                return ret;
        }

        if (filedes_valid(&wim->in_fd)) {
                filedes_close(&wim->in_fd);
                filedes_invalidate(&wim->in_fd);
        }

        /* 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.  */
        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;
        }

        union wimlib_progress_info progress;
        progress.rename.from = tmpfile;
        progress.rename.to = wim->filename;
        return call_progress(wim->progfunc, WIMLIB_PROGRESS_MSG_RENAME,
                             &progress, wim->progctx);
}

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

        /* Image deletions cause full rebuild by default.  */
        if (wim->image_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;

        /* 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)
{
        int ret;
        u32 orig_hdr_flags;

        if (write_flags & ~WIMLIB_WRITE_MASK_PUBLIC)
                return WIMLIB_ERR_INVALID_PARAM;

        if (!wim->filename)
                return WIMLIB_ERR_NO_FILENAME;

        if (unlikely(write_flags & WIMLIB_WRITE_FLAG_UNSAFE_COMPACT)) {
                /*
                 * In UNSAFE_COMPACT mode:
                 *      - RECOMPRESS is forbidden
                 *      - REBUILD is ignored
                 *      - SOFT_DELETE and NO_SOLID_SORT are implied
                 */
                if (write_flags & WIMLIB_WRITE_FLAG_RECOMPRESS)
                        return WIMLIB_ERR_COMPACTION_NOT_POSSIBLE;
                write_flags &= ~WIMLIB_WRITE_FLAG_REBUILD;
                write_flags |= WIMLIB_WRITE_FLAG_SOFT_DELETE;
                write_flags |= WIMLIB_WRITE_FLAG_NO_SOLID_SORT;
        }

        orig_hdr_flags = wim->hdr.flags;
        if (write_flags & WIMLIB_WRITE_FLAG_IGNORE_READONLY_FLAG)
                wim->hdr.flags &= ~WIM_HDR_FLAG_READONLY;
        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);
                if (ret != WIMLIB_ERR_RESOURCE_ORDER)
                        return ret;
                WARNING("Falling back to re-building entire WIM");
        }
        if (write_flags & WIMLIB_WRITE_FLAG_UNSAFE_COMPACT)
                return WIMLIB_ERR_COMPACTION_NOT_POSSIBLE;
        return overwrite_wim_via_tmpfile(wim, write_flags, num_threads);
}