Adding upstream version 1:2.43.0.upstream/1%2.43.0

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 845 insertions, 0 deletions

diff --git a/pack-bitmap-write.c b/pack-bitmap-write.c
new file mode 100644
index 0000000..f4ecdf8
--- /dev/null
+++ b/pack-bitmap-write.c
@@ -0,0 +1,845 @@
+#include "git-compat-util.h"
+#include "environment.h"
+#include "gettext.h"
+#include "hex.h"
+#include "object-store-ll.h"
+#include "commit.h"
+#include "tag.h"
+#include "diff.h"
+#include "revision.h"
+#include "list-objects.h"
+#include "progress.h"
+#include "pack-revindex.h"
+#include "pack.h"
+#include "pack-bitmap.h"
+#include "hash-lookup.h"
+#include "pack-objects.h"
+#include "path.h"
+#include "commit-reach.h"
+#include "prio-queue.h"
+#include "trace2.h"
+#include "tree.h"
+#include "tree-walk.h"
+
+struct bitmapped_commit {
+	struct commit *commit;
+	struct ewah_bitmap *bitmap;
+	struct ewah_bitmap *write_as;
+	int flags;
+	int xor_offset;
+	uint32_t commit_pos;
+};
+
+struct bitmap_writer {
+	struct ewah_bitmap *commits;
+	struct ewah_bitmap *trees;
+	struct ewah_bitmap *blobs;
+	struct ewah_bitmap *tags;
+
+	kh_oid_map_t *bitmaps;
+	struct packing_data *to_pack;
+
+	struct bitmapped_commit *selected;
+	unsigned int selected_nr, selected_alloc;
+
+	struct progress *progress;
+	int show_progress;
+	unsigned char pack_checksum[GIT_MAX_RAWSZ];
+};
+
+static struct bitmap_writer writer;
+
+void bitmap_writer_show_progress(int show)
+{
+	writer.show_progress = show;
+}
+
+/**
+ * Build the initial type index for the packfile or multi-pack-index
+ */
+void bitmap_writer_build_type_index(struct packing_data *to_pack,
+				    struct pack_idx_entry **index,
+				    uint32_t index_nr)
+{
+	uint32_t i;
+
+	writer.commits = ewah_new();
+	writer.trees = ewah_new();
+	writer.blobs = ewah_new();
+	writer.tags = ewah_new();
+	ALLOC_ARRAY(to_pack->in_pack_pos, to_pack->nr_objects);
+
+	for (i = 0; i < index_nr; ++i) {
+		struct object_entry *entry = (struct object_entry *)index[i];
+		enum object_type real_type;
+
+		oe_set_in_pack_pos(to_pack, entry, i);
+
+		switch (oe_type(entry)) {
+		case OBJ_COMMIT:
+		case OBJ_TREE:
+		case OBJ_BLOB:
+		case OBJ_TAG:
+			real_type = oe_type(entry);
+			break;
+
+		default:
+			real_type = oid_object_info(to_pack->repo,
+						    &entry->idx.oid, NULL);
+			break;
+		}
+
+		switch (real_type) {
+		case OBJ_COMMIT:
+			ewah_set(writer.commits, i);
+			break;
+
+		case OBJ_TREE:
+			ewah_set(writer.trees, i);
+			break;
+
+		case OBJ_BLOB:
+			ewah_set(writer.blobs, i);
+			break;
+
+		case OBJ_TAG:
+			ewah_set(writer.tags, i);
+			break;
+
+		default:
+			die("Missing type information for %s (%d/%d)",
+			    oid_to_hex(&entry->idx.oid), real_type,
+			    oe_type(entry));
+		}
+	}
+}
+
+/**
+ * Compute the actual bitmaps
+ */
+
+static inline void push_bitmapped_commit(struct commit *commit)
+{
+	if (writer.selected_nr >= writer.selected_alloc) {
+		writer.selected_alloc = (writer.selected_alloc + 32) * 2;
+		REALLOC_ARRAY(writer.selected, writer.selected_alloc);
+	}
+
+	writer.selected[writer.selected_nr].commit = commit;
+	writer.selected[writer.selected_nr].bitmap = NULL;
+	writer.selected[writer.selected_nr].flags = 0;
+
+	writer.selected_nr++;
+}
+
+static uint32_t find_object_pos(const struct object_id *oid, int *found)
+{
+	struct object_entry *entry = packlist_find(writer.to_pack, oid);
+
+	if (!entry) {
+		if (found)
+			*found = 0;
+		warning("Failed to write bitmap index. Packfile doesn't have full closure "
+			"(object %s is missing)", oid_to_hex(oid));
+		return 0;
+	}
+
+	if (found)
+		*found = 1;
+	return oe_in_pack_pos(writer.to_pack, entry);
+}
+
+static void compute_xor_offsets(void)
+{
+	static const int MAX_XOR_OFFSET_SEARCH = 10;
+
+	int i, next = 0;
+
+	while (next < writer.selected_nr) {
+		struct bitmapped_commit *stored = &writer.selected[next];
+
+		int best_offset = 0;
+		struct ewah_bitmap *best_bitmap = stored->bitmap;
+		struct ewah_bitmap *test_xor;
+
+		for (i = 1; i <= MAX_XOR_OFFSET_SEARCH; ++i) {
+			int curr = next - i;
+
+			if (curr < 0)
+				break;
+
+			test_xor = ewah_pool_new();
+			ewah_xor(writer.selected[curr].bitmap, stored->bitmap, test_xor);
+
+			if (test_xor->buffer_size < best_bitmap->buffer_size) {
+				if (best_bitmap != stored->bitmap)
+					ewah_pool_free(best_bitmap);
+
+				best_bitmap = test_xor;
+				best_offset = i;
+			} else {
+				ewah_pool_free(test_xor);
+			}
+		}
+
+		stored->xor_offset = best_offset;
+		stored->write_as = best_bitmap;
+
+		next++;
+	}
+}
+
+struct bb_commit {
+	struct commit_list *reverse_edges;
+	struct bitmap *commit_mask;
+	struct bitmap *bitmap;
+	unsigned selected:1,
+		 maximal:1;
+	unsigned idx; /* within selected array */
+};
+
+define_commit_slab(bb_data, struct bb_commit);
+
+struct bitmap_builder {
+	struct bb_data data;
+	struct commit **commits;
+	size_t commits_nr, commits_alloc;
+};
+
+static void bitmap_builder_init(struct bitmap_builder *bb,
+				struct bitmap_writer *writer,
+				struct bitmap_index *old_bitmap)
+{
+	struct rev_info revs;
+	struct commit *commit;
+	struct commit_list *reusable = NULL;
+	struct commit_list *r;
+	unsigned int i, num_maximal = 0;
+
+	memset(bb, 0, sizeof(*bb));
+	init_bb_data(&bb->data);
+
+	reset_revision_walk();
+	repo_init_revisions(writer->to_pack->repo, &revs, NULL);
+	revs.topo_order = 1;
+	revs.first_parent_only = 1;
+
+	for (i = 0; i < writer->selected_nr; i++) {
+		struct commit *c = writer->selected[i].commit;
+		struct bb_commit *ent = bb_data_at(&bb->data, c);
+
+		ent->selected = 1;
+		ent->maximal = 1;
+		ent->idx = i;
+
+		ent->commit_mask = bitmap_new();
+		bitmap_set(ent->commit_mask, i);
+
+		add_pending_object(&revs, &c->object, "");
+	}
+
+	if (prepare_revision_walk(&revs))
+		die("revision walk setup failed");
+
+	while ((commit = get_revision(&revs))) {
+		struct commit_list *p = commit->parents;
+		struct bb_commit *c_ent;
+
+		parse_commit_or_die(commit);
+
+		c_ent = bb_data_at(&bb->data, commit);
+
+		/*
+		 * If there is no commit_mask, there is no reason to iterate
+		 * over this commit; it is not selected (if it were, it would
+		 * not have a blank commit mask) and all its children have
+		 * existing bitmaps (see the comment starting with "This commit
+		 * has an existing bitmap" below), so it does not contribute
+		 * anything to the final bitmap file or its descendants.
+		 */
+		if (!c_ent->commit_mask)
+			continue;
+
+		if (old_bitmap && bitmap_for_commit(old_bitmap, commit)) {
+			/*
+			 * This commit has an existing bitmap, so we can
+			 * get its bits immediately without an object
+			 * walk. That is, it is reusable as-is and there is no
+			 * need to continue walking beyond it.
+			 *
+			 * Mark it as such and add it to bb->commits separately
+			 * to avoid allocating a position in the commit mask.
+			 */
+			commit_list_insert(commit, &reusable);
+			goto next;
+		}
+
+		if (c_ent->maximal) {
+			num_maximal++;
+			ALLOC_GROW(bb->commits, bb->commits_nr + 1, bb->commits_alloc);
+			bb->commits[bb->commits_nr++] = commit;
+		}
+
+		if (p) {
+			struct bb_commit *p_ent = bb_data_at(&bb->data, p->item);
+			int c_not_p, p_not_c;
+
+			if (!p_ent->commit_mask) {
+				p_ent->commit_mask = bitmap_new();
+				c_not_p = 1;
+				p_not_c = 0;
+			} else {
+				c_not_p = bitmap_is_subset(c_ent->commit_mask, p_ent->commit_mask);
+				p_not_c = bitmap_is_subset(p_ent->commit_mask, c_ent->commit_mask);
+			}
+
+			if (!c_not_p)
+				continue;
+
+			bitmap_or(p_ent->commit_mask, c_ent->commit_mask);
+
+			if (p_not_c)
+				p_ent->maximal = 1;
+			else {
+				p_ent->maximal = 0;
+				free_commit_list(p_ent->reverse_edges);
+				p_ent->reverse_edges = NULL;
+			}
+
+			if (c_ent->maximal) {
+				commit_list_insert(commit, &p_ent->reverse_edges);
+			} else {
+				struct commit_list *cc = c_ent->reverse_edges;
+
+				for (; cc; cc = cc->next) {
+					if (!commit_list_contains(cc->item, p_ent->reverse_edges))
+						commit_list_insert(cc->item, &p_ent->reverse_edges);
+				}
+			}
+		}
+
+next:
+		bitmap_free(c_ent->commit_mask);
+		c_ent->commit_mask = NULL;
+	}
+
+	for (r = reusable; r; r = r->next) {
+		ALLOC_GROW(bb->commits, bb->commits_nr + 1, bb->commits_alloc);
+		bb->commits[bb->commits_nr++] = r->item;
+	}
+
+	trace2_data_intmax("pack-bitmap-write", the_repository,
+			   "num_selected_commits", writer->selected_nr);
+	trace2_data_intmax("pack-bitmap-write", the_repository,
+			   "num_maximal_commits", num_maximal);
+
+	release_revisions(&revs);
+	free_commit_list(reusable);
+}
+
+static void bitmap_builder_clear(struct bitmap_builder *bb)
+{
+	clear_bb_data(&bb->data);
+	free(bb->commits);
+	bb->commits_nr = bb->commits_alloc = 0;
+}
+
+static int fill_bitmap_tree(struct bitmap *bitmap,
+			    struct tree *tree)
+{
+	int found;
+	uint32_t pos;
+	struct tree_desc desc;
+	struct name_entry entry;
+
+	/*
+	 * If our bit is already set, then there is nothing to do. Both this
+	 * tree and all of its children will be set.
+	 */
+	pos = find_object_pos(&tree->object.oid, &found);
+	if (!found)
+		return -1;
+	if (bitmap_get(bitmap, pos))
+		return 0;
+	bitmap_set(bitmap, pos);
+
+	if (parse_tree(tree) < 0)
+		die("unable to load tree object %s",
+		    oid_to_hex(&tree->object.oid));
+	init_tree_desc(&desc, tree->buffer, tree->size);
+
+	while (tree_entry(&desc, &entry)) {
+		switch (object_type(entry.mode)) {
+		case OBJ_TREE:
+			if (fill_bitmap_tree(bitmap,
+					     lookup_tree(the_repository, &entry.oid)) < 0)
+				return -1;
+			break;
+		case OBJ_BLOB:
+			pos = find_object_pos(&entry.oid, &found);
+			if (!found)
+				return -1;
+			bitmap_set(bitmap, pos);
+			break;
+		default:
+			/* Gitlink, etc; not reachable */
+			break;
+		}
+	}
+
+	free_tree_buffer(tree);
+	return 0;
+}
+
+static int reused_bitmaps_nr;
+
+static int fill_bitmap_commit(struct bb_commit *ent,
+			      struct commit *commit,
+			      struct prio_queue *queue,
+			      struct prio_queue *tree_queue,
+			      struct bitmap_index *old_bitmap,
+			      const uint32_t *mapping)
+{
+	int found;
+	uint32_t pos;
+	if (!ent->bitmap)
+		ent->bitmap = bitmap_new();
+
+	prio_queue_put(queue, commit);
+
+	while (queue->nr) {
+		struct commit_list *p;
+		struct commit *c = prio_queue_get(queue);
+
+		if (old_bitmap && mapping) {
+			struct ewah_bitmap *old = bitmap_for_commit(old_bitmap, c);
+			struct bitmap *remapped = bitmap_new();
+			/*
+			 * If this commit has an old bitmap, then translate that
+			 * bitmap and add its bits to this one. No need to walk
+			 * parents or the tree for this commit.
+			 */
+			if (old && !rebuild_bitmap(mapping, old, remapped)) {
+				bitmap_or(ent->bitmap, remapped);
+				bitmap_free(remapped);
+				reused_bitmaps_nr++;
+				continue;
+			}
+			bitmap_free(remapped);
+		}
+
+		/*
+		 * Mark ourselves and queue our tree. The commit
+		 * walk ensures we cover all parents.
+		 */
+		pos = find_object_pos(&c->object.oid, &found);
+		if (!found)
+			return -1;
+		bitmap_set(ent->bitmap, pos);
+		prio_queue_put(tree_queue,
+			       repo_get_commit_tree(the_repository, c));
+
+		for (p = c->parents; p; p = p->next) {
+			pos = find_object_pos(&p->item->object.oid, &found);
+			if (!found)
+				return -1;
+			if (!bitmap_get(ent->bitmap, pos)) {
+				bitmap_set(ent->bitmap, pos);
+				prio_queue_put(queue, p->item);
+			}
+		}
+	}
+
+	while (tree_queue->nr) {
+		if (fill_bitmap_tree(ent->bitmap,
+				     prio_queue_get(tree_queue)) < 0)
+			return -1;
+	}
+	return 0;
+}
+
+static void store_selected(struct bb_commit *ent, struct commit *commit)
+{
+	struct bitmapped_commit *stored = &writer.selected[ent->idx];
+	khiter_t hash_pos;
+	int hash_ret;
+
+	stored->bitmap = bitmap_to_ewah(ent->bitmap);
+
+	hash_pos = kh_put_oid_map(writer.bitmaps, commit->object.oid, &hash_ret);
+	if (hash_ret == 0)
+		die("Duplicate entry when writing index: %s",
+		    oid_to_hex(&commit->object.oid));
+	kh_value(writer.bitmaps, hash_pos) = stored;
+}
+
+int bitmap_writer_build(struct packing_data *to_pack)
+{
+	struct bitmap_builder bb;
+	size_t i;
+	int nr_stored = 0; /* for progress */
+	struct prio_queue queue = { compare_commits_by_gen_then_commit_date };
+	struct prio_queue tree_queue = { NULL };
+	struct bitmap_index *old_bitmap;
+	uint32_t *mapping;
+	int closed = 1; /* until proven otherwise */
+
+	writer.bitmaps = kh_init_oid_map();
+	writer.to_pack = to_pack;
+
+	if (writer.show_progress)
+		writer.progress = start_progress("Building bitmaps", writer.selected_nr);
+	trace2_region_enter("pack-bitmap-write", "building_bitmaps_total",
+			    the_repository);
+
+	old_bitmap = prepare_bitmap_git(to_pack->repo);
+	if (old_bitmap)
+		mapping = create_bitmap_mapping(old_bitmap, to_pack);
+	else
+		mapping = NULL;
+
+	bitmap_builder_init(&bb, &writer, old_bitmap);
+	for (i = bb.commits_nr; i > 0; i--) {
+		struct commit *commit = bb.commits[i-1];
+		struct bb_commit *ent = bb_data_at(&bb.data, commit);
+		struct commit *child;
+		int reused = 0;
+
+		if (fill_bitmap_commit(ent, commit, &queue, &tree_queue,
+				       old_bitmap, mapping) < 0) {
+			closed = 0;
+			break;
+		}
+
+		if (ent->selected) {
+			store_selected(ent, commit);
+			nr_stored++;
+			display_progress(writer.progress, nr_stored);
+		}
+
+		while ((child = pop_commit(&ent->reverse_edges))) {
+			struct bb_commit *child_ent =
+				bb_data_at(&bb.data, child);
+
+			if (child_ent->bitmap)
+				bitmap_or(child_ent->bitmap, ent->bitmap);
+			else if (reused)
+				child_ent->bitmap = bitmap_dup(ent->bitmap);
+			else {
+				child_ent->bitmap = ent->bitmap;
+				reused = 1;
+			}
+		}
+		if (!reused)
+			bitmap_free(ent->bitmap);
+		ent->bitmap = NULL;
+	}
+	clear_prio_queue(&queue);
+	clear_prio_queue(&tree_queue);
+	bitmap_builder_clear(&bb);
+	free_bitmap_index(old_bitmap);
+	free(mapping);
+
+	trace2_region_leave("pack-bitmap-write", "building_bitmaps_total",
+			    the_repository);
+	trace2_data_intmax("pack-bitmap-write", the_repository,
+			   "building_bitmaps_reused", reused_bitmaps_nr);
+
+	stop_progress(&writer.progress);
+
+	if (closed)
+		compute_xor_offsets();
+	return closed ? 0 : -1;
+}
+
+/**
+ * Select the commits that will be bitmapped
+ */
+static inline unsigned int next_commit_index(unsigned int idx)
+{
+	static const unsigned int MIN_COMMITS = 100;
+	static const unsigned int MAX_COMMITS = 5000;
+
+	static const unsigned int MUST_REGION = 100;
+	static const unsigned int MIN_REGION = 20000;
+
+	unsigned int offset, next;
+
+	if (idx <= MUST_REGION)
+		return 0;
+
+	if (idx <= MIN_REGION) {
+		offset = idx - MUST_REGION;
+		return (offset < MIN_COMMITS) ? offset : MIN_COMMITS;
+	}
+
+	offset = idx - MIN_REGION;
+	next = (offset < MAX_COMMITS) ? offset : MAX_COMMITS;
+
+	return (next > MIN_COMMITS) ? next : MIN_COMMITS;
+}
+
+static int date_compare(const void *_a, const void *_b)
+{
+	struct commit *a = *(struct commit **)_a;
+	struct commit *b = *(struct commit **)_b;
+	return (long)b->date - (long)a->date;
+}
+
+void bitmap_writer_select_commits(struct commit **indexed_commits,
+				  unsigned int indexed_commits_nr,
+				  int max_bitmaps)
+{
+	unsigned int i = 0, j, next;
+
+	QSORT(indexed_commits, indexed_commits_nr, date_compare);
+
+	if (indexed_commits_nr < 100) {
+		for (i = 0; i < indexed_commits_nr; ++i)
+			push_bitmapped_commit(indexed_commits[i]);
+		return;
+	}
+
+	if (writer.show_progress)
+		writer.progress = start_progress("Selecting bitmap commits", 0);
+
+	for (;;) {
+		struct commit *chosen = NULL;
+
+		next = next_commit_index(i);
+
+		if (i + next >= indexed_commits_nr)
+			break;
+
+		if (max_bitmaps > 0 && writer.selected_nr >= max_bitmaps) {
+			writer.selected_nr = max_bitmaps;
+			break;
+		}
+
+		if (next == 0) {
+			chosen = indexed_commits[i];
+		} else {
+			chosen = indexed_commits[i + next];
+
+			for (j = 0; j <= next; ++j) {
+				struct commit *cm = indexed_commits[i + j];
+
+				if ((cm->object.flags & NEEDS_BITMAP) != 0) {
+					chosen = cm;
+					break;
+				}
+
+				if (cm->parents && cm->parents->next)
+					chosen = cm;
+			}
+		}
+
+		push_bitmapped_commit(chosen);
+
+		i += next + 1;
+		display_progress(writer.progress, i);
+	}
+
+	stop_progress(&writer.progress);
+}
+
+
+static int hashwrite_ewah_helper(void *f, const void *buf, size_t len)
+{
+	/* hashwrite will die on error */
+	hashwrite(f, buf, len);
+	return len;
+}
+
+/**
+ * Write the bitmap index to disk
+ */
+static inline void dump_bitmap(struct hashfile *f, struct ewah_bitmap *bitmap)
+{
+	if (ewah_serialize_to(bitmap, hashwrite_ewah_helper, f) < 0)
+		die("Failed to write bitmap index");
+}
+
+static const struct object_id *oid_access(size_t pos, const void *table)
+{
+	const struct pack_idx_entry * const *index = table;
+	return &index[pos]->oid;
+}
+
+static void write_selected_commits_v1(struct hashfile *f,
+				      uint32_t *commit_positions,
+				      off_t *offsets)
+{
+	int i;
+
+	for (i = 0; i < writer.selected_nr; ++i) {
+		struct bitmapped_commit *stored = &writer.selected[i];
+
+		if (offsets)
+			offsets[i] = hashfile_total(f);
+
+		hashwrite_be32(f, commit_positions[i]);
+		hashwrite_u8(f, stored->xor_offset);
+		hashwrite_u8(f, stored->flags);
+
+		dump_bitmap(f, stored->write_as);
+	}
+}
+
+static int table_cmp(const void *_va, const void *_vb, void *_data)
+{
+	uint32_t *commit_positions = _data;
+	uint32_t a = commit_positions[*(uint32_t *)_va];
+	uint32_t b = commit_positions[*(uint32_t *)_vb];
+
+	if (a > b)
+		return 1;
+	else if (a < b)
+		return -1;
+
+	return 0;
+}
+
+static void write_lookup_table(struct hashfile *f,
+			       uint32_t *commit_positions,
+			       off_t *offsets)
+{
+	uint32_t i;
+	uint32_t *table, *table_inv;
+
+	ALLOC_ARRAY(table, writer.selected_nr);
+	ALLOC_ARRAY(table_inv, writer.selected_nr);
+
+	for (i = 0; i < writer.selected_nr; i++)
+		table[i] = i;
+
+	/*
+	 * At the end of this sort table[j] = i means that the i'th
+	 * bitmap corresponds to j'th bitmapped commit (among the selected
+	 * commits) in lex order of OIDs.
+	 */
+	QSORT_S(table, writer.selected_nr, table_cmp, commit_positions);
+
+	/* table_inv helps us discover that relationship (i'th bitmap
+	 * to j'th commit by j = table_inv[i])
+	 */
+	for (i = 0; i < writer.selected_nr; i++)
+		table_inv[table[i]] = i;
+
+	trace2_region_enter("pack-bitmap-write", "writing_lookup_table", the_repository);
+	for (i = 0; i < writer.selected_nr; i++) {
+		struct bitmapped_commit *selected = &writer.selected[table[i]];
+		uint32_t xor_offset = selected->xor_offset;
+		uint32_t xor_row;
+
+		if (xor_offset) {
+			/*
+			 * xor_index stores the index (in the bitmap entries)
+			 * of the corresponding xor bitmap. But we need to convert
+			 * this index into lookup table's index. So, table_inv[xor_index]
+			 * gives us the index position w.r.t. the lookup table.
+			 *
+			 * If "k = table[i] - xor_offset" then the xor base is the k'th
+			 * bitmap. `table_inv[k]` gives us the position of that bitmap
+			 * in the lookup table.
+			 */
+			uint32_t xor_index = table[i] - xor_offset;
+			xor_row = table_inv[xor_index];
+		} else {
+			xor_row = 0xffffffff;
+		}
+
+		hashwrite_be32(f, commit_positions[table[i]]);
+		hashwrite_be64(f, (uint64_t)offsets[table[i]]);
+		hashwrite_be32(f, xor_row);
+	}
+	trace2_region_leave("pack-bitmap-write", "writing_lookup_table", the_repository);
+
+	free(table);
+	free(table_inv);
+}
+
+static void write_hash_cache(struct hashfile *f,
+			     struct pack_idx_entry **index,
+			     uint32_t index_nr)
+{
+	uint32_t i;
+
+	for (i = 0; i < index_nr; ++i) {
+		struct object_entry *entry = (struct object_entry *)index[i];
+		hashwrite_be32(f, entry->hash);
+	}
+}
+
+void bitmap_writer_set_checksum(const unsigned char *sha1)
+{
+	hashcpy(writer.pack_checksum, sha1);
+}
+
+void bitmap_writer_finish(struct pack_idx_entry **index,
+			  uint32_t index_nr,
+			  const char *filename,
+			  uint16_t options)
+{
+	static uint16_t default_version = 1;
+	static uint16_t flags = BITMAP_OPT_FULL_DAG;
+	struct strbuf tmp_file = STRBUF_INIT;
+	struct hashfile *f;
+	uint32_t *commit_positions = NULL;
+	off_t *offsets = NULL;
+	uint32_t i;
+
+	struct bitmap_disk_header header;
+
+	int fd = odb_mkstemp(&tmp_file, "pack/tmp_bitmap_XXXXXX");
+
+	f = hashfd(fd, tmp_file.buf);
+
+	memcpy(header.magic, BITMAP_IDX_SIGNATURE, sizeof(BITMAP_IDX_SIGNATURE));
+	header.version = htons(default_version);
+	header.options = htons(flags | options);
+	header.entry_count = htonl(writer.selected_nr);
+	hashcpy(header.checksum, writer.pack_checksum);
+
+	hashwrite(f, &header, sizeof(header) - GIT_MAX_RAWSZ + the_hash_algo->rawsz);
+	dump_bitmap(f, writer.commits);
+	dump_bitmap(f, writer.trees);
+	dump_bitmap(f, writer.blobs);
+	dump_bitmap(f, writer.tags);
+
+	if (options & BITMAP_OPT_LOOKUP_TABLE)
+		CALLOC_ARRAY(offsets, index_nr);
+
+	ALLOC_ARRAY(commit_positions, writer.selected_nr);
+
+	for (i = 0; i < writer.selected_nr; i++) {
+		struct bitmapped_commit *stored = &writer.selected[i];
+		int commit_pos = oid_pos(&stored->commit->object.oid, index, index_nr, oid_access);
+
+		if (commit_pos < 0)
+			BUG(_("trying to write commit not in index"));
+
+		commit_positions[i] = commit_pos;
+	}
+
+	write_selected_commits_v1(f, commit_positions, offsets);
+
+	if (options & BITMAP_OPT_LOOKUP_TABLE)
+		write_lookup_table(f, commit_positions, offsets);
+
+	if (options & BITMAP_OPT_HASH_CACHE)
+		write_hash_cache(f, index, index_nr);
+
+	finalize_hashfile(f, NULL, FSYNC_COMPONENT_PACK_METADATA,
+			  CSUM_HASH_IN_STREAM | CSUM_FSYNC | CSUM_CLOSE);
+
+	if (adjust_shared_perm(tmp_file.buf))
+		die_errno("unable to make temporary bitmap file readable");
+
+	if (rename(tmp_file.buf, filename))
+		die_errno("unable to rename temporary bitmap file to '%s'", filename);
+
+	strbuf_release(&tmp_file);
+	free(commit_positions);
+	free(offsets);
+}