1 files changed, 161 insertions, 0 deletions
diff --git a/lib/fstree/optimize_unpack_order.c b/lib/fstree/optimize_unpack_order.c
new file mode 100644
index 0000000..ad036e8
--- /dev/null
+++ b/lib/fstree/optimize_unpack_order.c
@@ -0,0 +1,161 @@
+/* SPDX-License-Identifier: GPL-3.0-or-later */
+/*
+ * optimize_unpack_order.c
+ *
+ * Copyright (C) 2019 David Oberhollenzer <goliath@infraroot.at>
+ */
+#include "config.h"
+#include "fstree.h"
+
+static int compare_files(const fstree_t *fs, const file_info_t *lhs,
+			 const file_info_t *rhs)
+{
+	/* NOOP < everything else */
+	if (lhs->input_file == NULL)
+		return rhs->input_file == NULL ? 0 : -1;
+
+	if (rhs->input_file == NULL)
+		return 1;
+
+	/* Files with fragments come first, ordered by ID.
+	   In case of tie, files without data blocks come first,
+	   and the others are ordered by start block. */
+	if (lhs->flags & FILE_FLAG_HAS_FRAGMENT) {
+		if (!(rhs->flags & FILE_FLAG_HAS_FRAGMENT))
+			return -1;
+
+		if (lhs->fragment < rhs->fragment)
+			return -1;
+		if (lhs->fragment > rhs->fragment)
+			return 1;
+
+		if (lhs->size < fs->block_size)
+			return (rhs->size < fs->block_size) ? 0 : -1;
+		if (rhs->size < fs->block_size)
+			return 1;
+		goto order_by_start;
+	}
+
+	if (rhs->flags & FILE_FLAG_HAS_FRAGMENT)
+		return 1;
+
+	/* order the rest by start block */
+order_by_start:
+	return lhs->startblock < rhs->startblock ? -1 :
+		lhs->startblock > rhs->startblock ? 1 : 0;
+}
+
+/* TODO: unify ad-hoc merge sort with the one in fstree_sort */
+static file_info_t *merge(const fstree_t *fs, file_info_t *lhs,
+			  file_info_t *rhs)
+{
+	file_info_t *it;
+	file_info_t *head = NULL;
+	file_info_t **next_ptr = &head;
+
+	while (lhs != NULL && rhs != NULL) {
+		if (compare_files(fs, lhs, rhs) <= 0) {
+			it = lhs;
+			lhs = lhs->next;
+		} else {
+			it = rhs;
+			rhs = rhs->next;
+		}
+
+		*next_ptr = it;
+		next_ptr = &it->next;
+	}
+
+	it = (lhs != NULL ? lhs : rhs);
+	*next_ptr = it;
+	return head;
+}
+
+static file_info_t *list_sort(const fstree_t *fs, file_info_t *head)
+{
+	file_info_t *it, *half, *prev;
+
+	it = half = prev = head;
+	while (it != NULL) {
+		prev = half;
+		half = half->next;
+		it = it->next;
+		if (it != NULL) {
+			it = it->next;
+		}
+	}
+
+	// half refers to the (count/2)'th element ROUNDED UP.
+	// It will be null therefore only in the empty and the
+	// single element list
+	if (half == NULL) {
+		return head;
+	}
+
+	prev->next = NULL;
+
+	return merge(fs, list_sort(fs, head), list_sort(fs, half));
+}
+
+static file_info_t *split_list(file_info_t *list, uint64_t threashold)
+{
+	file_info_t *it, *new = NULL;
+	uint64_t size = 0;
+
+	for (it = list; it != NULL; it = it->next) {
+		size += it->size - it->sparse;
+
+		if (size >= threashold) {
+			new = it->next;
+			it->next = NULL;
+			break;
+		}
+	}
+
+	return new;
+}
+
+static uint64_t total_size(file_info_t *list)
+{
+	uint64_t size = 0;
+	file_info_t *it;
+
+	for (it = list; it != NULL; it = it->next)
+		size += it->size - it->sparse;
+
+	return size;
+}
+
+void optimize_unpack_order(fstree_t *fs, size_t num_jobs,
+			   file_info_t *out[num_jobs])
+{
+	file_info_t *file_list;
+	uint64_t threshold;
+	size_t i;
+
+	if (num_jobs < 1)
+		return;
+
+	for (i = 0; i < num_jobs; ++i)
+		out[i] = NULL;
+
+	file_list = list_sort(fs, fs->files);
+	while (file_list != NULL && file_list->input_file == NULL)
+		file_list = file_list->next;
+
+	fs->files = NULL;
+
+	if (num_jobs < 2) {
+		out[0] = file_list;
+		return;
+	}
+
+	threshold = total_size(file_list) / num_jobs;
+
+	for (i = 0; i < (num_jobs - 1); ++i) {
+		out[i] = file_list;
+		file_list = split_list(file_list, threshold);
+	}
+
+	out[i] = file_list;
+}