Cleanup the block processor file structure

A cleaner separation between common code, frontend code and backend
code is made.

The "is this byte blob zero" function is moved out to libutil (with
test case and everything) with a more optimized implementation.

Signed-off-by: David Oberhollenzer <david.oberhollenzer@sigma-star.at>

8 files changed, 624 insertions, 644 deletions

diff --git a/lib/sqfs/Makemodule.am b/lib/sqfs/Makemodule.am
index 5a62894..72eb6bc 100644
--- a/lib/sqfs/Makemodule.am
+++ b/lib/sqfs/Makemodule.am
@@ -25,8 +25,9 @@ libsquashfs_la_SOURCES += lib/sqfs/xattr/xattr_writer_record.c
 libsquashfs_la_SOURCES += lib/sqfs/xattr/xattr_writer.h
 libsquashfs_la_SOURCES += lib/sqfs/write_super.c lib/sqfs/data_reader.c
 libsquashfs_la_SOURCES += lib/sqfs/block_processor/internal.h
-libsquashfs_la_SOURCES += lib/sqfs/block_processor/common.c
 libsquashfs_la_SOURCES += lib/sqfs/block_processor/frontend.c
+libsquashfs_la_SOURCES += lib/sqfs/block_processor/block_processor.c
+libsquashfs_la_SOURCES += lib/sqfs/block_processor/backend.c
 libsquashfs_la_SOURCES += lib/sqfs/frag_table.c include/sqfs/frag_table.h
 libsquashfs_la_SOURCES += lib/sqfs/block_writer.c include/sqfs/block_writer.h
 libsquashfs_la_CPPFLAGS = $(AM_CPPFLAGS)
@@ -43,6 +44,7 @@ libsquashfs_la_SOURCES += lib/util/xxhash.c
 libsquashfs_la_SOURCES += lib/util/hash_table.c include/hash_table.h
 libsquashfs_la_SOURCES += lib/util/rbtree.c include/rbtree.h
 libsquashfs_la_SOURCES += lib/util/array.c include/array.h
+libsquashfs_la_SOURCES += lib/util/is_memory_zero.c
 libsquashfs_la_SOURCES += include/threadpool.h
 
 if CUSTOM_ALLOC
diff --git a/lib/sqfs/block_processor/backend.c b/lib/sqfs/block_processor/backend.c
new file mode 100644
index 0000000..ff142c9
--- /dev/null
+++ b/lib/sqfs/block_processor/backend.c
@@ -0,0 +1,288 @@
+/* SPDX-License-Identifier: LGPL-3.0-or-later */
+/*
+ * backend.c
+ *
+ * Copyright (C) 2019 David Oberhollenzer <goliath@infraroot.at>
+ */
+#define SQFS_BUILDING_DLL
+#include "internal.h"
+
+static int set_block_size(sqfs_inode_generic_t **inode,
+			  sqfs_u32 index, sqfs_u32 size)
+{
+	size_t min_size = (index + 1) * sizeof(sqfs_u32);
+	size_t avail = (*inode)->payload_bytes_available;
+	sqfs_inode_generic_t *new;
+	size_t newsz;
+
+	if (avail < min_size) {
+		newsz = avail ? avail : (sizeof(sqfs_u32) * 4);
+		while (newsz < min_size)
+			newsz *= 2;
+
+		if (SZ_ADD_OV(newsz, sizeof(**inode), &newsz))
+			return SQFS_ERROR_OVERFLOW;
+
+		if (sizeof(size_t) > sizeof(sqfs_u32)) {
+			if ((newsz - sizeof(**inode)) > 0x0FFFFFFFFUL)
+				return SQFS_ERROR_OVERFLOW;
+		}
+
+		new = realloc((*inode), newsz);
+		if (new == NULL)
+			return SQFS_ERROR_ALLOC;
+
+		(*inode) = new;
+		(*inode)->payload_bytes_available = newsz - sizeof(**inode);
+	}
+
+	(*inode)->extra[index] = size;
+
+	if (min_size >= (*inode)->payload_bytes_used)
+		(*inode)->payload_bytes_used = min_size;
+
+	return 0;
+}
+
+static void release_old_block(sqfs_block_processor_t *proc, sqfs_block_t *blk)
+{
+	blk->next = proc->free_list;
+	proc->free_list = blk;
+}
+
+static int process_completed_block(sqfs_block_processor_t *proc, sqfs_block_t *blk)
+{
+	sqfs_u64 location;
+	sqfs_u32 size;
+	int err;
+
+	err = proc->wr->write_data_block(proc->wr, blk->user, blk->size,
+					 blk->checksum,
+					 blk->flags & ~BLK_FLAG_INTERNAL,
+					 blk->data, &location);
+	if (err)
+		goto out;
+
+	proc->stats.output_bytes_generated += blk->size;
+
+	if (blk->flags & SQFS_BLK_IS_SPARSE) {
+		if (blk->inode != NULL) {
+			sqfs_inode_make_extended(*(blk->inode));
+			(*(blk->inode))->data.file_ext.sparse += blk->size;
+
+			err = set_block_size(blk->inode, blk->index, 0);
+			if (err)
+				goto out;
+		}
+		proc->stats.sparse_block_count += 1;
+	} else if (blk->size != 0) {
+		size = blk->size;
+		if (!(blk->flags & SQFS_BLK_IS_COMPRESSED))
+			size |= 1 << 24;
+
+		if (blk->flags & SQFS_BLK_FRAGMENT_BLOCK) {
+			if (proc->frag_tbl != NULL) {
+				err = sqfs_frag_table_set(proc->frag_tbl,
+							  blk->index, location,
+							  size);
+				if (err)
+					goto out;
+			}
+			proc->stats.frag_block_count += 1;
+		} else {
+			if (blk->inode != NULL) {
+				err = set_block_size(blk->inode, blk->index,
+						     size);
+				if (err)
+					goto out;
+			}
+			proc->stats.data_block_count += 1;
+		}
+	}
+
+	if (blk->flags & SQFS_BLK_LAST_BLOCK && blk->inode != NULL)
+		sqfs_inode_set_file_block_start(*(blk->inode), location);
+out:
+	release_old_block(proc, blk);
+	return err;
+}
+
+static int process_completed_fragment(sqfs_block_processor_t *proc,
+				      sqfs_block_t *frag)
+{
+	chunk_info_t *chunk = NULL, search;
+	struct hash_entry *entry;
+	sqfs_u32 index, offset;
+	int err;
+
+	if (frag->flags & SQFS_BLK_IS_SPARSE) {
+		if (frag->inode != NULL) {
+			sqfs_inode_make_extended(*(frag->inode));
+			set_block_size(frag->inode, frag->index, 0);
+			(*(frag->inode))->data.file_ext.sparse += frag->size;
+		}
+		proc->stats.sparse_block_count += 1;
+		release_old_block(proc, frag);
+		return 0;
+	}
+
+	proc->stats.total_frag_count += 1;
+
+	if (!(frag->flags & SQFS_BLK_DONT_DEDUPLICATE)) {
+		search.hash = frag->checksum;
+		search.size = frag->size;
+
+		entry = hash_table_search_pre_hashed(proc->frag_ht,
+						     search.hash, &search);
+
+		if (entry != NULL) {
+			if (frag->inode != NULL) {
+				chunk = entry->data;
+				sqfs_inode_set_frag_location(*(frag->inode),
+							     chunk->index,
+							     chunk->offset);
+			}
+			release_old_block(proc, frag);
+			return 0;
+		}
+	}
+
+	if (proc->frag_block != NULL) {
+		size_t size = proc->frag_block->size + frag->size;
+
+		if (size > proc->max_block_size) {
+			proc->frag_block->io_seq_num = proc->io_seq_num++;
+
+			err = enqueue_block(proc, proc->frag_block);
+			proc->frag_block = NULL;
+
+			if (err)
+				goto fail;
+		}
+	}
+
+	if (proc->frag_block == NULL) {
+		if (proc->frag_tbl == NULL) {
+			index = 0;
+		} else {
+			err = sqfs_frag_table_append(proc->frag_tbl,
+						     0, 0, &index);
+			if (err)
+				goto fail;
+		}
+
+		offset = 0;
+		proc->frag_block = frag;
+		proc->frag_block->index = index;
+		proc->frag_block->flags &= SQFS_BLK_DONT_COMPRESS;
+		proc->frag_block->flags |= SQFS_BLK_FRAGMENT_BLOCK;
+	} else {
+		index = proc->frag_block->index;
+		offset = proc->frag_block->size;
+
+		memcpy(proc->frag_block->data + proc->frag_block->size,
+		       frag->data, frag->size);
+
+		proc->frag_block->size += frag->size;
+		proc->frag_block->flags |=
+			(frag->flags & SQFS_BLK_DONT_COMPRESS);
+	}
+
+	if (proc->frag_tbl != NULL) {
+		err = SQFS_ERROR_ALLOC;
+		chunk = calloc(1, sizeof(*chunk));
+		if (chunk == NULL)
+			goto fail;
+
+		chunk->index = index;
+		chunk->offset = offset;
+		chunk->size = frag->size;
+		chunk->hash = frag->checksum;
+
+		entry = hash_table_insert_pre_hashed(proc->frag_ht, chunk->hash,
+						     chunk, chunk);
+
+		if (entry == NULL)
+			goto fail;
+	}
+
+	if (frag->inode != NULL)
+		sqfs_inode_set_frag_location(*(frag->inode), index, offset);
+
+	if (frag != proc->frag_block)
+		release_old_block(proc, frag);
+
+	proc->stats.actual_frag_count += 1;
+	return 0;
+fail:
+	free(chunk);
+	free(frag);
+	return err;
+}
+
+static void store_io_block(sqfs_block_processor_t *proc, sqfs_block_t *blk)
+{
+	sqfs_block_t *prev = NULL, *it = proc->io_queue;
+
+	while (it != NULL && (it->io_seq_num < blk->io_seq_num)) {
+		prev = it;
+		it = it->next;
+	}
+
+	if (prev == NULL) {
+		proc->io_queue = blk;
+	} else {
+		prev->next = blk;
+	}
+
+	blk->next = it;
+	proc->backlog += 1;
+}
+
+int dequeue_block(sqfs_block_processor_t *proc)
+{
+	size_t backlog_old = proc->backlog;
+	sqfs_block_t *blk;
+	int status;
+
+	do {
+		while (proc->io_queue != NULL) {
+			if (proc->io_queue->io_seq_num != proc->io_deq_seq_num)
+				break;
+
+			blk = proc->io_queue;
+			proc->io_queue = blk->next;
+			proc->io_deq_seq_num += 1;
+			proc->backlog -= 1;
+
+			status = process_completed_block(proc, blk);
+			if (status != 0)
+				return status;
+		}
+
+		if (proc->backlog < backlog_old)
+			break;
+
+		blk = proc->pool->dequeue(proc->pool);
+
+		if (blk == NULL) {
+			status = proc->pool->get_status(proc->pool);
+			return status ? status : SQFS_ERROR_INTERNAL;
+		}
+
+		proc->backlog -= 1;
+
+		if (blk->flags & SQFS_BLK_IS_FRAGMENT) {
+			status = process_completed_fragment(proc, blk);
+			if (status != 0)
+				return status;
+		} else {
+			if (!(blk->flags & SQFS_BLK_FRAGMENT_BLOCK))
+				blk->io_seq_num = proc->io_seq_num++;
+
+			store_io_block(proc, blk);
+		}
+	} while (proc->backlog >= backlog_old);
+
+	return 0;
+}
diff --git a/lib/sqfs/block_processor/block_processor.c b/lib/sqfs/block_processor/block_processor.c
new file mode 100644
index 0000000..f9313db
--- /dev/null
+++ b/lib/sqfs/block_processor/block_processor.c
@@ -0,0 +1,234 @@
+/* SPDX-License-Identifier: LGPL-3.0-or-later */
+/*
+ * block_processor.c
+ *
+ * Copyright (C) 2019 David Oberhollenzer <goliath@infraroot.at>
+ */
+#define SQFS_BUILDING_DLL
+#include "internal.h"
+
+static int process_block(void *userptr, void *workitem)
+{
+	worker_data_t *worker = userptr;
+	sqfs_block_t *block = workitem;
+	sqfs_s32 ret;
+
+	if (block->size == 0)
+		return 0;
+
+	if (!(block->flags & SQFS_BLK_IGNORE_SPARSE) &&
+	    is_memory_zero(block->data, block->size)) {
+		block->flags |= SQFS_BLK_IS_SPARSE;
+		return 0;
+	}
+
+	if (block->flags & SQFS_BLK_DONT_HASH) {
+		block->checksum = 0;
+	} else {
+		block->checksum = xxh32(block->data, block->size);
+	}
+
+	if (block->flags & (SQFS_BLK_IS_FRAGMENT | SQFS_BLK_DONT_COMPRESS))
+		return 0;
+
+	ret = worker->cmp->do_block(worker->cmp, block->data, block->size,
+				    worker->scratch, worker->scratch_size);
+	if (ret < 0)
+		return ret;
+
+	if (ret > 0) {
+		memcpy(block->data, worker->scratch, ret);
+		block->size = ret;
+		block->flags |= SQFS_BLK_IS_COMPRESSED;
+	}
+	return 0;
+}
+
+static bool chunk_info_equals(void *user, const void *k, const void *c)
+{
+	const chunk_info_t *key = k, *cmp = c;
+	(void)user;
+	return key->size == cmp->size && key->hash == cmp->hash;
+}
+
+static void ht_delete_function(struct hash_entry *entry)
+{
+	free(entry->data);
+}
+
+static void block_processor_destroy(sqfs_object_t *base)
+{
+	sqfs_block_processor_t *proc = (sqfs_block_processor_t *)base;
+	sqfs_block_t *it;
+
+	free(proc->frag_block);
+	free(proc->blk_current);
+
+	while (proc->free_list != NULL) {
+		it = proc->free_list;
+		proc->free_list = it->next;
+		free(it);
+	}
+
+	while (proc->io_queue != NULL) {
+		it = proc->io_queue;
+		proc->io_queue = it->next;
+		free(it);
+	}
+
+	if (proc->frag_ht != NULL)
+		hash_table_destroy(proc->frag_ht, ht_delete_function);
+
+	/* XXX: shut down the pool first before cleaning up the worker data */
+	if (proc->pool != NULL)
+		proc->pool->destroy(proc->pool);
+
+	while (proc->workers != NULL) {
+		worker_data_t *worker = proc->workers;
+		proc->workers = worker->next;
+
+		sqfs_destroy(worker->cmp);
+		free(worker);
+	}
+
+	free(proc);
+}
+
+int sqfs_block_processor_sync(sqfs_block_processor_t *proc)
+{
+	int ret;
+
+	while (proc->backlog > 0) {
+		ret = dequeue_block(proc);
+		if (ret != 0)
+			return ret;
+	}
+
+	return 0;
+}
+
+int sqfs_block_processor_finish(sqfs_block_processor_t *proc)
+{
+	sqfs_block_t *blk;
+	int status;
+
+	status = sqfs_block_processor_sync(proc);
+	if (status != 0)
+		return status;
+
+	if (proc->frag_block != NULL) {
+		blk = proc->frag_block;
+		blk->next = NULL;
+		proc->frag_block = NULL;
+
+		blk->io_seq_num = proc->io_seq_num++;
+
+		status = enqueue_block(proc, blk);
+		if (status != 0)
+			return status;
+
+		status = sqfs_block_processor_sync(proc);
+	}
+
+	return status;
+}
+
+const sqfs_block_processor_stats_t
+*sqfs_block_processor_get_stats(const sqfs_block_processor_t *proc)
+{
+	return &proc->stats;
+}
+
+int sqfs_block_processor_create_ex(const sqfs_block_processor_desc_t *desc,
+				   sqfs_block_processor_t **out)
+{
+	sqfs_block_processor_t *proc;
+	size_t i, count;
+	int ret;
+
+	if (desc->size != sizeof(sqfs_block_processor_desc_t))
+		return SQFS_ERROR_ARG_INVALID;
+
+	proc = calloc(1, sizeof(*proc));
+	if (proc == NULL)
+		return SQFS_ERROR_ALLOC;
+
+	proc->max_backlog = desc->max_backlog;
+	proc->max_block_size = desc->max_block_size;
+	proc->frag_tbl = desc->tbl;
+	proc->wr = desc->wr;
+	proc->file = desc->file;
+	proc->uncmp = desc->uncmp;
+	proc->stats.size = sizeof(proc->stats);
+	((sqfs_object_t *)proc)->destroy = block_processor_destroy;
+
+	/* create the thread pool */
+	proc->pool = thread_pool_create(desc->num_workers, process_block);
+	if (proc->pool == NULL) {
+		free(proc);
+		return SQFS_ERROR_INTERNAL;
+	}
+
+	/* create the worker compressors & scratch buffer */
+	count = proc->pool->get_worker_count(proc->pool);
+
+	for (i = 0; i < count; ++i) {
+		worker_data_t *worker = alloc_flex(sizeof(*worker), 1,
+						   desc->max_block_size);
+		if (worker == NULL) {
+			ret = SQFS_ERROR_ALLOC;
+			goto fail_pool;
+		}
+
+		worker->scratch_size = desc->max_block_size;
+		worker->next = proc->workers;
+		proc->workers = worker;
+
+		worker->cmp = sqfs_copy(desc->cmp);
+		if (worker->cmp == NULL) {
+			ret = SQFS_ERROR_ALLOC;
+			goto fail_pool;
+		}
+
+		proc->pool->set_worker_ptr(proc->pool, i, worker);
+	}
+
+	/* create the fragment hash table */
+	proc->frag_ht = hash_table_create(NULL, chunk_info_equals);
+	if (proc->frag_ht == NULL) {
+		ret = SQFS_ERROR_ALLOC;
+		goto fail_pool;
+	}
+
+	proc->frag_ht->user = proc;
+	*out = proc;
+	return 0;
+fail_pool:
+	block_processor_destroy((sqfs_object_t *)proc);
+	return ret;
+}
+
+sqfs_block_processor_t *sqfs_block_processor_create(size_t max_block_size,
+						    sqfs_compressor_t *cmp,
+						    unsigned int num_workers,
+						    size_t max_backlog,
+						    sqfs_block_writer_t *wr,
+						    sqfs_frag_table_t *tbl)
+{
+	sqfs_block_processor_desc_t desc;
+	sqfs_block_processor_t *out;
+
+	memset(&desc, 0, sizeof(desc));
+	desc.size = sizeof(desc);
+	desc.max_block_size = max_block_size;
+	desc.num_workers = num_workers;
+	desc.max_backlog = max_backlog;
+	desc.cmp = cmp;
+	desc.wr = wr;
+	desc.tbl = tbl;
+
+	if (sqfs_block_processor_create_ex(&desc, &out) != 0)
+		return NULL;
+
+	return out;
+}
diff --git a/lib/sqfs/block_processor/common.c b/lib/sqfs/block_processor/common.c
deleted file mode 100644
index 6a0015b..0000000
--- a/lib/sqfs/block_processor/common.c
+++ /dev/null
@@ -1,421 +0,0 @@
-/* SPDX-License-Identifier: LGPL-3.0-or-later */
-/*
- * common.c
- *
- * Copyright (C) 2019 David Oberhollenzer <goliath@infraroot.at>
- */
-#define SQFS_BUILDING_DLL
-#include "internal.h"
-
-static int set_block_size(sqfs_inode_generic_t **inode,
-			  sqfs_u32 index, sqfs_u32 size)
-{
-	size_t min_size = (index + 1) * sizeof(sqfs_u32);
-	size_t avail = (*inode)->payload_bytes_available;
-	sqfs_inode_generic_t *new;
-	size_t newsz;
-
-	if (avail < min_size) {
-		newsz = avail ? avail : (sizeof(sqfs_u32) * 4);
-		while (newsz < min_size)
-			newsz *= 2;
-
-		if (SZ_ADD_OV(newsz, sizeof(**inode), &newsz))
-			return SQFS_ERROR_OVERFLOW;
-
-		if (sizeof(size_t) > sizeof(sqfs_u32)) {
-			if ((newsz - sizeof(**inode)) > 0x0FFFFFFFFUL)
-				return SQFS_ERROR_OVERFLOW;
-		}
-
-		new = realloc((*inode), newsz);
-		if (new == NULL)
-			return SQFS_ERROR_ALLOC;
-
-		(*inode) = new;
-		(*inode)->payload_bytes_available = newsz - sizeof(**inode);
-	}
-
-	(*inode)->extra[index] = size;
-
-	if (min_size >= (*inode)->payload_bytes_used)
-		(*inode)->payload_bytes_used = min_size;
-
-	return 0;
-}
-
-static void release_old_block(sqfs_block_processor_t *proc, sqfs_block_t *blk)
-{
-	blk->next = proc->free_list;
-	proc->free_list = blk;
-}
-
-int process_completed_block(sqfs_block_processor_t *proc, sqfs_block_t *blk)
-{
-	sqfs_u64 location;
-	sqfs_u32 size;
-	int err;
-
-	err = proc->wr->write_data_block(proc->wr, blk->user, blk->size,
-					 blk->checksum,
-					 blk->flags & ~BLK_FLAG_INTERNAL,
-					 blk->data, &location);
-	if (err)
-		goto out;
-
-	proc->stats.output_bytes_generated += blk->size;
-
-	if (blk->flags & SQFS_BLK_IS_SPARSE) {
-		if (blk->inode != NULL) {
-			sqfs_inode_make_extended(*(blk->inode));
-			(*(blk->inode))->data.file_ext.sparse += blk->size;
-
-			err = set_block_size(blk->inode, blk->index, 0);
-			if (err)
-				goto out;
-		}
-		proc->stats.sparse_block_count += 1;
-	} else if (blk->size != 0) {
-		size = blk->size;
-		if (!(blk->flags & SQFS_BLK_IS_COMPRESSED))
-			size |= 1 << 24;
-
-		if (blk->flags & SQFS_BLK_FRAGMENT_BLOCK) {
-			if (proc->frag_tbl != NULL) {
-				err = sqfs_frag_table_set(proc->frag_tbl,
-							  blk->index, location,
-							  size);
-				if (err)
-					goto out;
-			}
-			proc->stats.frag_block_count += 1;
-		} else {
-			if (blk->inode != NULL) {
-				err = set_block_size(blk->inode, blk->index,
-						     size);
-				if (err)
-					goto out;
-			}
-			proc->stats.data_block_count += 1;
-		}
-	}
-
-	if (blk->flags & SQFS_BLK_LAST_BLOCK && blk->inode != NULL)
-		sqfs_inode_set_file_block_start(*(blk->inode), location);
-out:
-	release_old_block(proc, blk);
-	return err;
-}
-
-static bool is_zero_block(unsigned char *ptr, size_t size)
-{
-	return ptr[0] == 0 && memcmp(ptr, ptr + 1, size - 1) == 0;
-}
-
-static int process_block(void *userptr, void *workitem)
-{
-	sqfs_compressor_t *cmp = ((worker_data_t *)userptr)->cmp;
-	sqfs_u8 *scratch = ((worker_data_t *)userptr)->scratch;
-	size_t scratch_size = ((worker_data_t *)userptr)->scratch_size;
-	sqfs_block_t *block = workitem;
-	sqfs_s32 ret;
-
-	if (block->size == 0)
-		return 0;
-
-	if (!(block->flags & SQFS_BLK_IGNORE_SPARSE) &&
-	    is_zero_block(block->data, block->size)) {
-		block->flags |= SQFS_BLK_IS_SPARSE;
-		return 0;
-	}
-
-	if (block->flags & SQFS_BLK_DONT_HASH) {
-		block->checksum = 0;
-	} else {
-		block->checksum = xxh32(block->data, block->size);
-	}
-
-	if (block->flags & (SQFS_BLK_IS_FRAGMENT | SQFS_BLK_DONT_COMPRESS))
-		return 0;
-
-	ret = cmp->do_block(cmp, block->data, block->size,
-			    scratch, scratch_size);
-	if (ret < 0)
-		return ret;
-
-	if (ret > 0) {
-		memcpy(block->data, scratch, ret);
-		block->size = ret;
-		block->flags |= SQFS_BLK_IS_COMPRESSED;
-	}
-	return 0;
-}
-
-int process_completed_fragment(sqfs_block_processor_t *proc,
-			       sqfs_block_t *frag,
-			       sqfs_block_t **blk_out)
-{
-	chunk_info_t *chunk, search;
-	struct hash_entry *entry;
-	sqfs_u32 index, offset;
-	size_t size;
-	int err;
-
-	if (frag->flags & SQFS_BLK_IS_SPARSE) {
-		if (frag->inode != NULL) {
-			sqfs_inode_make_extended(*(frag->inode));
-			set_block_size(frag->inode, frag->index, 0);
-			(*(frag->inode))->data.file_ext.sparse += frag->size;
-		}
-		proc->stats.sparse_block_count += 1;
-		release_old_block(proc, frag);
-		return 0;
-	}
-
-	proc->stats.total_frag_count += 1;
-
-	if (!(frag->flags & SQFS_BLK_DONT_DEDUPLICATE)) {
-		search.hash = frag->checksum;
-		search.size = frag->size;
-
-		entry = hash_table_search_pre_hashed(proc->frag_ht,
-						     search.hash, &search);
-
-		if (entry != NULL) {
-			if (frag->inode != NULL) {
-				chunk = entry->data;
-				sqfs_inode_set_frag_location(*(frag->inode),
-							     chunk->index,
-							     chunk->offset);
-			}
-			release_old_block(proc, frag);
-			return 0;
-		}
-	}
-
-	if (proc->frag_block != NULL) {
-		size = proc->frag_block->size + frag->size;
-
-		if (size > proc->max_block_size) {
-			*blk_out = proc->frag_block;
-			proc->frag_block = NULL;
-		}
-	}
-
-	if (proc->frag_block == NULL) {
-		if (proc->frag_tbl == NULL) {
-			index = 0;
-		} else {
-			err = sqfs_frag_table_append(proc->frag_tbl,
-						     0, 0, &index);
-			if (err)
-				goto fail;
-		}
-
-		offset = 0;
-		proc->frag_block = frag;
-		proc->frag_block->index = index;
-		proc->frag_block->flags &= SQFS_BLK_DONT_COMPRESS;
-		proc->frag_block->flags |= SQFS_BLK_FRAGMENT_BLOCK;
-	} else {
-		index = proc->frag_block->index;
-		offset = proc->frag_block->size;
-
-		memcpy(proc->frag_block->data + proc->frag_block->size,
-		       frag->data, frag->size);
-
-		proc->frag_block->size += frag->size;
-		proc->frag_block->flags |=
-			(frag->flags & SQFS_BLK_DONT_COMPRESS);
-		release_old_block(proc, frag);
-	}
-
-	if (proc->frag_tbl != NULL) {
-		err = SQFS_ERROR_ALLOC;
-		chunk = calloc(1, sizeof(*chunk));
-		if (chunk == NULL)
-			goto fail_outblk;
-
-		chunk->index = index;
-		chunk->offset = offset;
-		chunk->size = frag->size;
-		chunk->hash = frag->checksum;
-
-		entry = hash_table_insert_pre_hashed(proc->frag_ht, chunk->hash,
-						     chunk, chunk);
-
-		if (entry == NULL) {
-			free(chunk);
-			goto fail_outblk;
-		}
-	}
-
-	if (frag->inode != NULL)
-		sqfs_inode_set_frag_location(*(frag->inode), index, offset);
-
-	proc->stats.actual_frag_count += 1;
-	return 0;
-fail:
-	release_old_block(proc, frag);
-fail_outblk:
-	if (*blk_out != NULL) {
-		release_old_block(proc, *blk_out);
-		*blk_out = NULL;
-	}
-	return err;
-}
-
-static uint32_t chunk_info_hash(void *user, const void *key)
-{
-	const chunk_info_t *chunk = key;
-	(void)user;
-	return chunk->hash;
-}
-
-static bool chunk_info_equals(void *user, const void *k, const void *c)
-{
-	const chunk_info_t *key = k, *cmp = c;
-	(void)user;
-	return key->size == cmp->size && key->hash == cmp->hash;
-}
-
-static void ht_delete_function(struct hash_entry *entry)
-{
-	free(entry->data);
-}
-
-static void block_processor_destroy(sqfs_object_t *base)
-{
-	sqfs_block_processor_t *proc = (sqfs_block_processor_t *)base;
-	sqfs_block_t *it;
-
-	if (proc->frag_block != NULL)
-		release_old_block(proc, proc->frag_block);
-
-	free(proc->blk_current);
-
-	while (proc->free_list != NULL) {
-		it = proc->free_list;
-		proc->free_list = it->next;
-		free(it);
-	}
-
-	hash_table_destroy(proc->frag_ht, ht_delete_function);
-
-	/* XXX: shut down the pool first before cleaning up the worker data */
-	proc->pool->destroy(proc->pool);
-
-	while (proc->workers != NULL) {
-		worker_data_t *worker = proc->workers;
-		proc->workers = worker->next;
-
-		sqfs_destroy(worker->cmp);
-		free(worker);
-	}
-
-	free(proc);
-}
-
-int sqfs_block_processor_create_ex(const sqfs_block_processor_desc_t *desc,
-				   sqfs_block_processor_t **out)
-{
-	sqfs_block_processor_t *proc;
-	size_t i, count;
-	int ret;
-
-	if (desc->size != sizeof(sqfs_block_processor_desc_t))
-		return SQFS_ERROR_ARG_INVALID;
-
-	proc = calloc(1, sizeof(*proc));
-	if (proc == NULL)
-		return SQFS_ERROR_ALLOC;
-
-	proc->max_backlog = desc->max_backlog;
-	proc->max_block_size = desc->max_block_size;
-	proc->frag_tbl = desc->tbl;
-	proc->wr = desc->wr;
-	proc->file = desc->file;
-	proc->uncmp = desc->uncmp;
-	proc->stats.size = sizeof(proc->stats);
-	((sqfs_object_t *)proc)->destroy = block_processor_destroy;
-
-	/* create the thread pool */
-	proc->pool = thread_pool_create(desc->num_workers, process_block);
-	if (proc->pool == NULL) {
-		free(proc);
-		return SQFS_ERROR_INTERNAL;
-	}
-
-	/* create the worker compressors & scratch buffer */
-	count = proc->pool->get_worker_count(proc->pool);
-
-	for (i = 0; i < count; ++i) {
-		worker_data_t *worker = alloc_flex(sizeof(*worker), 1,
-						   desc->max_block_size);
-		if (worker == NULL) {
-			ret = SQFS_ERROR_ALLOC;
-			goto fail_pool;
-		}
-
-		worker->scratch_size = desc->max_block_size;
-		worker->next = proc->workers;
-		proc->workers = worker;
-
-		worker->cmp = sqfs_copy(desc->cmp);
-		if (worker->cmp == NULL) {
-			ret = SQFS_ERROR_ALLOC;
-			goto fail_pool;
-		}
-
-		proc->pool->set_worker_ptr(proc->pool, i, worker);
-	}
-
-	/* create the fragment hash table */
-	proc->frag_ht = hash_table_create(chunk_info_hash, chunk_info_equals);
-	if (proc->frag_ht == NULL) {
-		ret = SQFS_ERROR_ALLOC;
-		goto fail_pool;
-	}
-
-	proc->frag_ht->user = proc;
-	*out = proc;
-	return 0;
-fail_pool:
-	proc->pool->destroy(proc->pool);
-	while (proc->workers != NULL) {
-		worker_data_t *worker = proc->workers;
-		proc->workers = worker->next;
-
-		if (worker->cmp != NULL)
-			sqfs_destroy(worker->cmp);
-
-		free(worker);
-	}
-	free(proc);
-	return ret;
-}
-
-sqfs_block_processor_t *sqfs_block_processor_create(size_t max_block_size,
-						    sqfs_compressor_t *cmp,
-						    unsigned int num_workers,
-						    size_t max_backlog,
-						    sqfs_block_writer_t *wr,
-						    sqfs_frag_table_t *tbl)
-{
-	sqfs_block_processor_desc_t desc;
-	sqfs_block_processor_t *out;
-
-	memset(&desc, 0, sizeof(desc));
-	desc.size = sizeof(desc);
-	desc.max_block_size = max_block_size;
-	desc.num_workers = num_workers;
-	desc.max_backlog = max_backlog;
-	desc.cmp = cmp;
-	desc.wr = wr;
-	desc.tbl = tbl;
-
-	if (sqfs_block_processor_create_ex(&desc, &out) != 0)
-		return NULL;
-
-	return out;
-}
diff --git a/lib/sqfs/block_processor/frontend.c b/lib/sqfs/block_processor/frontend.c
index 8bd6cf2..ccf54c0 100644
--- a/lib/sqfs/block_processor/frontend.c
+++ b/lib/sqfs/block_processor/frontend.c
@@ -7,123 +7,46 @@
 #define SQFS_BUILDING_DLL
 #include "internal.h"
 
-static sqfs_block_t *get_new_block(sqfs_block_processor_t *proc)
+static int get_new_block(sqfs_block_processor_t *proc, sqfs_block_t **out)
 {
 	sqfs_block_t *blk;
 
+	while (proc->backlog >= proc->max_backlog) {
+		int ret = dequeue_block(proc);
+		if (ret != 0)
+			return ret;
+	}
+
 	if (proc->free_list != NULL) {
 		blk = proc->free_list;
 		proc->free_list = blk->next;
 	} else {
 		blk = malloc(sizeof(*blk) + proc->max_block_size);
+		if (blk == NULL)
+			return SQFS_ERROR_ALLOC;
 	}
 
-	if (blk != NULL)
-		memset(blk, 0, sizeof(*blk));
-
-	return blk;
+	memset(blk, 0, sizeof(*blk));
+	*out = blk;
+	return 0;
 }
 
-static int dequeue_block(sqfs_block_processor_t *proc)
+static int add_sentinel_block(sqfs_block_processor_t *proc)
 {
-	sqfs_block_t *blk, *fragblk, *it, *prev;
-	bool have_dequeued = false;
-	int status;
-retry:
-	while (proc->io_queue != NULL) {
-		if (proc->io_queue->io_seq_num != proc->io_deq_seq_num)
-			break;
-
-		blk = proc->io_queue;
-		proc->io_queue = blk->next;
-		proc->io_deq_seq_num += 1;
-		proc->backlog -= 1;
-		have_dequeued = true;
-
-		status = process_completed_block(proc, blk);
-		if (status != 0)
-			return status;
-	}
-
-	if (have_dequeued)
-		return 0;
-
-	blk = proc->pool->dequeue(proc->pool);
-
-	if (blk == NULL) {
-		status = proc->pool->get_status(proc->pool);
-		if (status == 0)
-			status = SQFS_ERROR_INTERNAL;
-
-		return status;
-	}
-
-	proc->backlog -= 1;
-	have_dequeued = true;
-
-	if (blk->flags & SQFS_BLK_IS_FRAGMENT) {
-		fragblk = NULL;
-		status = process_completed_fragment(proc, blk, &fragblk);
-
-		if (status != 0) {
-			free(fragblk);
-			return status;
-		}
-
-		if (fragblk != NULL) {
-			fragblk->io_seq_num = proc->io_seq_num++;
-
-			if (proc->pool->submit(proc->pool, fragblk) != 0) {
-				free(fragblk);
-
-				if (status == 0) {
-					status = proc->pool->
-						get_status(proc->pool);
-
-					if (status == 0)
-						status = SQFS_ERROR_ALLOC;
-				}
-
-				return status;
-			}
-
-			proc->backlog += 1;
-			have_dequeued = false;
-		}
-	} else {
-		if (!(blk->flags & SQFS_BLK_FRAGMENT_BLOCK))
-			blk->io_seq_num = proc->io_seq_num++;
-
-		prev = NULL;
-		it = proc->io_queue;
-
-		while (it != NULL) {
-			if (it->io_seq_num >= blk->io_seq_num)
-				break;
-
-			prev = it;
-			it = it->next;
-		}
-
-		if (prev == NULL) {
-			blk->next = proc->io_queue;
-			proc->io_queue = blk;
-		} else {
-			blk->next = prev->next;
-			prev->next = blk;
-		}
+	sqfs_block_t *blk;
+	int ret;
 
-		proc->backlog += 1;
-		have_dequeued = false;
-	}
+	ret = get_new_block(proc, &blk);
+	if (ret != 0)
+		return ret;
 
-	if (!have_dequeued)
-		goto retry;
+	blk->inode = proc->inode;
+	blk->flags = proc->blk_flags | SQFS_BLK_LAST_BLOCK;
 
-	return 0;
+	return enqueue_block(proc, blk);
 }
 
-static int enqueue_block(sqfs_block_processor_t *proc, sqfs_block_t *blk)
+int enqueue_block(sqfs_block_processor_t *proc, sqfs_block_t *blk)
 {
 	int status;
 
@@ -141,44 +64,6 @@ static int enqueue_block(sqfs_block_processor_t *proc, sqfs_block_t *blk)
 	return 0;
 }
 
-static int add_sentinel_block(sqfs_block_processor_t *proc)
-{
-	sqfs_block_t *blk;
-	int ret;
-
-	if (proc->backlog == proc->max_backlog) {
-		ret = dequeue_block(proc);
-		if (ret != 0)
-			return ret;
-	}
-
-	blk = get_new_block(proc);
-	if (blk == NULL)
-		return SQFS_ERROR_ALLOC;
-
-	blk->inode = proc->inode;
-	blk->flags = proc->blk_flags | SQFS_BLK_LAST_BLOCK;
-
-	return enqueue_block(proc, blk);
-}
-
-static int flush_block(sqfs_block_processor_t *proc)
-{
-	sqfs_block_t *block;
-	int ret;
-
-	if (proc->backlog == proc->max_backlog) {
-		ret = dequeue_block(proc);
-		if (ret != 0)
-			return ret;
-	}
-
-	block = proc->blk_current;
-	proc->blk_current = NULL;
-
-	return enqueue_block(proc, block);
-}
-
 int sqfs_block_processor_begin_file(sqfs_block_processor_t *proc,
 				    sqfs_inode_generic_t **inode,
 				    void *user, sqfs_u32 flags)
@@ -224,9 +109,9 @@ int sqfs_block_processor_append(sqfs_block_processor_t *proc, const void *data,
 
 	while (size > 0) {
 		if (proc->blk_current == NULL) {
-			new = get_new_block(proc);
-			if (new == NULL)
-				return SQFS_ERROR_ALLOC;
+			err = get_new_block(proc, &new);
+			if (err != 0)
+				return err;
 
 			proc->blk_current = new;
 			proc->blk_current->flags = proc->blk_flags;
@@ -239,7 +124,9 @@ int sqfs_block_processor_append(sqfs_block_processor_t *proc, const void *data,
 		diff = proc->max_block_size - proc->blk_current->size;
 
 		if (diff == 0) {
-			err = flush_block(proc);
+			err = enqueue_block(proc, proc->blk_current);
+			proc->blk_current = NULL;
+
 			if (err)
 				return err;
 			continue;
@@ -258,9 +145,12 @@ int sqfs_block_processor_append(sqfs_block_processor_t *proc, const void *data,
 		proc->stats.input_bytes_read += diff;
 	}
 
-	if (proc->blk_current != NULL &&
-	    proc->blk_current->size == proc->max_block_size) {
-		return flush_block(proc);
+	if (proc->blk_current->size == proc->max_block_size) {
+		err = enqueue_block(proc, proc->blk_current);
+		proc->blk_current = NULL;
+
+		if (err)
+			return err;
 	}
 
 	return 0;
@@ -293,7 +183,9 @@ int sqfs_block_processor_end_file(sqfs_block_processor_t *proc)
 			proc->blk_current->flags |= SQFS_BLK_IS_FRAGMENT;
 		}
 
-		err = flush_block(proc);
+		err = enqueue_block(proc, proc->blk_current);
+		proc->blk_current = NULL;
+
 		if (err)
 			return err;
 	}
@@ -321,78 +213,14 @@ int sqfs_block_processor_submit_block(sqfs_block_processor_t *proc, void *user,
 	if (flags & ~SQFS_BLK_FLAGS_ALL)
 		return SQFS_ERROR_UNSUPPORTED;
 
-	if (proc->backlog == proc->max_backlog) {
-		ret = dequeue_block(proc);
-		if (ret != 0)
-			return ret;
-	}
-
-	blk = get_new_block(proc);
-	if (blk == NULL)
-		return SQFS_ERROR_ALLOC;
+	ret = get_new_block(proc, &blk);
+	if (ret != 0)
+		return ret;
 
 	blk->flags = flags | BLK_FLAG_MANUAL_SUBMISSION;
 	blk->user = user;
 	blk->size = size;
 	memcpy(blk->data, data, size);
 
-	ret = proc->pool->submit(proc->pool, blk);
-	if (ret != 0)
-		free(blk);
-
-	proc->backlog += 1;
-	return ret;
-}
-
-int sqfs_block_processor_sync(sqfs_block_processor_t *proc)
-{
-	int ret;
-
-	while (proc->backlog > 0) {
-		ret = dequeue_block(proc);
-		if (ret != 0)
-			return ret;
-	}
-
-	return 0;
-}
-
-int sqfs_block_processor_finish(sqfs_block_processor_t *proc)
-{
-	sqfs_block_t *blk;
-	int status;
-
-	status = sqfs_block_processor_sync(proc);
-	if (status != 0)
-		return status;
-
-	if (proc->frag_block != NULL) {
-		blk = proc->frag_block;
-		blk->next = NULL;
-		proc->frag_block = NULL;
-
-		blk->io_seq_num = proc->io_seq_num++;
-
-		status = proc->pool->submit(proc->pool, blk);
-		if (status != 0) {
-			status = proc->pool->get_status(proc->pool);
-
-			if (status == 0)
-				status = SQFS_ERROR_ALLOC;
-
-			free(blk);
-			return status;
-		}
-
-		proc->backlog += 1;
-		status = sqfs_block_processor_sync(proc);
-	}
-
-	return status;
-}
-
-const sqfs_block_processor_stats_t
-*sqfs_block_processor_get_stats(const sqfs_block_processor_t *proc)
-{
-	return &proc->stats;
+	return enqueue_block(proc, blk);
 }
diff --git a/lib/sqfs/block_processor/internal.h b/lib/sqfs/block_processor/internal.h
index 2393380..ef8ff0f 100644
--- a/lib/sqfs/block_processor/internal.h
+++ b/lib/sqfs/block_processor/internal.h
@@ -25,7 +25,6 @@
 
 #include <string.h>
 #include <stdlib.h>
-#include <assert.h>
 
 typedef struct {
 	sqfs_u32 index;
@@ -96,19 +95,14 @@ struct sqfs_block_processor_t {
 	thread_pool_t *pool;
 	worker_data_t *workers;
 
-
-
 	sqfs_block_t *io_queue;
 	sqfs_u32 io_seq_num;
 	sqfs_u32 io_deq_seq_num;
 };
 
-SQFS_INTERNAL
-int process_completed_block(sqfs_block_processor_t *proc, sqfs_block_t *blk);
+SQFS_INTERNAL int enqueue_block(sqfs_block_processor_t *proc,
+				sqfs_block_t *blk);
 
-SQFS_INTERNAL
-int process_completed_fragment(sqfs_block_processor_t *proc,
-			       sqfs_block_t *frag,
-			       sqfs_block_t **blk_out);
+SQFS_INTERNAL int dequeue_block(sqfs_block_processor_t *proc);
 
 #endif /* INTERNAL_H */
diff --git a/lib/util/Makemodule.am b/lib/util/Makemodule.am
index 113855c..c66c786 100644
--- a/lib/util/Makemodule.am
+++ b/lib/util/Makemodule.am
@@ -7,6 +7,7 @@ libutil_a_SOURCES += lib/util/fast_urem_by_const.h
 libutil_a_SOURCES += include/threadpool.h
 libutil_a_SOURCES += include/w32threadwrap.h
 libutil_a_SOURCES += lib/util/threadpool_serial.c
+libutil_a_SOURCES += lib/util/is_memory_zero.c
 libutil_a_CFLAGS = $(AM_CFLAGS)
 libutil_a_CPPFLAGS = $(AM_CPPFLAGS)
 
diff --git a/lib/util/is_memory_zero.c b/lib/util/is_memory_zero.c
new file mode 100644
index 0000000..3974ee2
--- /dev/null
+++ b/lib/util/is_memory_zero.c
@@ -0,0 +1,54 @@
+/* SPDX-License-Identifier: LGPL-3.0-or-later */
+/*
+ * is_memory_zero.c
+ *
+ * Copyright (C) 2021 David Oberhollenzer <goliath@infraroot.at>
+ */
+#include "config.h"
+#include "util.h"
+
+#include <stdint.h>
+
+#define U64THRESHOLD (128)
+
+static bool test_u8(const unsigned char *blob, size_t size)
+{
+	while (size--) {
+		if (*(blob++) != 0)
+			return false;
+	}
+
+	return true;
+}
+
+bool is_memory_zero(const void *blob, size_t size)
+{
+	const sqfs_u64 *u64ptr;
+	size_t diff;
+
+	if (size < U64THRESHOLD)
+		return test_u8(blob, size);
+
+	diff = (uintptr_t)blob % sizeof(sqfs_u64);
+
+	if (diff != 0) {
+		diff = sizeof(sqfs_u64) - diff;
+
+		if (!test_u8(blob, diff))
+			return false;
+
+		blob = (const char *)blob + diff;
+		size -= diff;
+	}
+
+	u64ptr = blob;
+
+	while (size >= sizeof(sqfs_u64)) {
+		if (*(u64ptr++) != 0)
+			return false;
+
+		size -= sizeof(sqfs_u64);
+	}
+
+	return test_u8((const unsigned char *)u64ptr, size);
+}