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#include "git-compat-util.h"
#include "cache.h"
#include "dir.h"
#include "csum-file.h"
#include "lockfile.h"
#include "object-store.h"
#include "packfile.h"
#include "midx.h"

#define MIDX_SIGNATURE 0x4d494458 /* "MIDX" */
#define MIDX_VERSION 1
#define MIDX_HASH_VERSION 1 /* SHA-1 */
#define MIDX_HEADER_SIZE 12
#define MIDX_HASH_LEN 20
#define MIDX_MIN_SIZE (MIDX_HEADER_SIZE + MIDX_HASH_LEN)

#define MIDX_MAX_CHUNKS 2
#define MIDX_CHUNK_ALIGNMENT 4
#define MIDX_CHUNKID_PACKLOOKUP 0x504c4f4f /* "PLOO" */
#define MIDX_CHUNKID_PACKNAMES 0x504e414d /* "PNAM" */
#define MIDX_CHUNKLOOKUP_WIDTH (sizeof(uint32_t) + sizeof(uint64_t))

static char *get_midx_filename(const char *object_dir)
{
	struct strbuf midx_name = STRBUF_INIT;
	strbuf_addstr(&midx_name, object_dir);
	strbuf_addstr(&midx_name, "/pack/multi-pack-index");
	return strbuf_detach(&midx_name, NULL);
}

struct midxed_git *load_midxed_git(const char *object_dir)
{
	struct midxed_git *m;
	int fd;
	struct stat st;
	size_t midx_size;
	void *midx_map;
	const char *midx_name = get_midx_filename(object_dir);
	uint32_t i;

	fd = git_open(midx_name);
	if (fd < 0)
		return NULL;
	if (fstat(fd, &st)) {
		close(fd);
		return NULL;
	}
	midx_size = xsize_t(st.st_size);

	if (midx_size < MIDX_MIN_SIZE) {
		close(fd);
		die("multi-pack-index file %s is too small", midx_name);
	}

	midx_map = xmmap(NULL, midx_size, PROT_READ, MAP_PRIVATE, fd, 0);

	m = xcalloc(1, sizeof(*m) + strlen(object_dir) + 1);
	strcpy(m->object_dir, object_dir);
	m->data = midx_map;

	m->signature = get_be32(m->data);
	if (m->signature != MIDX_SIGNATURE) {
		error("multi-pack-index signature %X does not match signature %X",
		      m->signature, MIDX_SIGNATURE);
		goto cleanup_fail;
	}

	m->version = *(m->data + 4);
	if (m->version != MIDX_VERSION) {
		error("multi-pack-index version %d not recognized",
		      m->version);
		goto cleanup_fail;
	}

	m->hash_version = *(m->data + 5);
	if (m->hash_version != MIDX_HASH_VERSION) {
		error("hash version %d not recognized", m->hash_version);
		goto cleanup_fail;
	}
	m->hash_len = MIDX_HASH_LEN;

	m->num_chunks = *(m->data + 6);
	m->num_packs = get_be32(m->data + 8);

	for (i = 0; i < m->num_chunks; i++) {
		uint32_t chunk_id = get_be32(m->data + 12 + MIDX_CHUNKLOOKUP_WIDTH * i);
		uint64_t chunk_offset = get_be64(m->data + 16 + MIDX_CHUNKLOOKUP_WIDTH * i);

		switch (chunk_id) {
			case MIDX_CHUNKID_PACKLOOKUP:
				m->chunk_pack_lookup = (uint32_t *)(m->data + chunk_offset);
				break;

			case MIDX_CHUNKID_PACKNAMES:
				m->chunk_pack_names = m->data + chunk_offset;
				break;

			case 0:
				die("terminating MIDX chunk id appears earlier than expected");
				break;

			default:
				/*
				 * Do nothing on unrecognized chunks, allowing future
				 * extensions to add optional chunks.
				 */
				break;
		}
	}

	if (!m->chunk_pack_lookup)
		die("MIDX missing required pack lookup chunk");
	if (!m->chunk_pack_names)
		die("MIDX missing required pack-name chunk");

	m->pack_names = xcalloc(m->num_packs, sizeof(const char *));
	for (i = 0; i < m->num_packs; i++) {
		if (i) {
			if (ntohl(m->chunk_pack_lookup[i]) <= ntohl(m->chunk_pack_lookup[i - 1])) {
				error("MIDX pack lookup value %d before %d",
				      ntohl(m->chunk_pack_lookup[i - 1]),
				      ntohl(m->chunk_pack_lookup[i]));
				goto cleanup_fail;
			}
		}

		m->pack_names[i] = (const char *)(m->chunk_pack_names + ntohl(m->chunk_pack_lookup[i]));

		if (i && strcmp(m->pack_names[i], m->pack_names[i - 1]) <= 0) {
			error("MIDX pack names out of order: '%s' before '%s'",
			      m->pack_names[i - 1],
			      m->pack_names[i]);
			goto cleanup_fail;
		}
	}

	return m;

cleanup_fail:
	FREE_AND_NULL(m);
	munmap(midx_map, midx_size);
	close(fd);
	exit(1);
}

static size_t write_midx_header(struct hashfile *f,
				unsigned char num_chunks,
				uint32_t num_packs)
{
	char byte_values[4];
	hashwrite_be32(f, MIDX_SIGNATURE);
	byte_values[0] = MIDX_VERSION;
	byte_values[1] = MIDX_HASH_VERSION;
	byte_values[2] = num_chunks;
	byte_values[3] = 0; /* unused */
	hashwrite(f, byte_values, sizeof(byte_values));
	hashwrite_be32(f, num_packs);

	return MIDX_HEADER_SIZE;
}

struct pack_pair {
	uint32_t pack_int_id;
	char *pack_name;
};

static int pack_pair_compare(const void *_a, const void *_b)
{
	struct pack_pair *a = (struct pack_pair *)_a;
	struct pack_pair *b = (struct pack_pair *)_b;
	return strcmp(a->pack_name, b->pack_name);
}

static void sort_packs_by_name(char **pack_names, uint32_t nr_packs, uint32_t *perm)
{
	uint32_t i;
	struct pack_pair *pairs;

	ALLOC_ARRAY(pairs, nr_packs);

	for (i = 0; i < nr_packs; i++) {
		pairs[i].pack_int_id = i;
		pairs[i].pack_name = pack_names[i];
	}

	QSORT(pairs, nr_packs, pack_pair_compare);

	for (i = 0; i < nr_packs; i++) {
		pack_names[i] = pairs[i].pack_name;
		perm[pairs[i].pack_int_id] = i;
	}
}

static uint32_t get_pack_fanout(struct packed_git *p, uint32_t value)
{
	const uint32_t *level1_ofs = p->index_data;

	if (!level1_ofs) {
		if (open_pack_index(p))
			return 0;
		level1_ofs = p->index_data;
	}

	if (p->index_version > 1) {
		level1_ofs += 2;
	}

	return ntohl(level1_ofs[value]);
}

struct pack_midx_entry {
	struct object_id oid;
	uint32_t pack_int_id;
	time_t pack_mtime;
	uint64_t offset;
};

static int midx_oid_compare(const void *_a, const void *_b)
{
	struct pack_midx_entry *a = (struct pack_midx_entry *)_a;
	struct pack_midx_entry *b = (struct pack_midx_entry *)_b;
	int cmp = oidcmp(&a->oid, &b->oid);

	if (cmp)
		return cmp;

	if (a->pack_mtime > b->pack_mtime)
		return -1;
	else if (a->pack_mtime < b->pack_mtime)
		return 1;

	return a->pack_int_id - b->pack_int_id;
}

static void fill_pack_entry(uint32_t pack_int_id,
			    struct packed_git *p,
			    uint32_t cur_object,
			    struct pack_midx_entry *entry)
{
	if (!nth_packed_object_oid(&entry->oid, p, cur_object))
		die("failed to located object %d in packfile", cur_object);

	entry->pack_int_id = pack_int_id;
	entry->pack_mtime = p->mtime;

	entry->offset = nth_packed_object_offset(p, cur_object);
}

/*
 * It is possible to artificially get into a state where there are many
 * duplicate copies of objects. That can create high memory pressure if
 * we are to create a list of all objects before de-duplication. To reduce
 * this memory pressure without a significant performance drop, automatically
 * group objects by the first byte of their object id. Use the IDX fanout
 * tables to group the data, copy to a local array, then sort.
 *
 * Copy only the de-duplicated entries (selected by most-recent modified time
 * of a packfile containing the object).
 */
static struct pack_midx_entry *get_sorted_entries(struct packed_git **p,
						  uint32_t *perm,
						  uint32_t nr_packs,
						  uint32_t *nr_objects)
{
	uint32_t cur_fanout, cur_pack, cur_object;
	uint32_t nr_fanout, alloc_fanout, alloc_objects, total_objects = 0;
	struct pack_midx_entry *entries_by_fanout = NULL;
	struct pack_midx_entry *deduplicated_entries = NULL;

	for (cur_pack = 0; cur_pack < nr_packs; cur_pack++) {
		if (open_pack_index(p[cur_pack]))
			continue;

		total_objects += p[cur_pack]->num_objects;
	}

	/*
	 * As we de-duplicate by fanout value, we expect the fanout
	 * slices to be evenly distributed, with some noise. Hence,
	 * allocate slightly more than one 256th.
	 */
	alloc_objects = alloc_fanout = total_objects > 3200 ? total_objects / 200 : 16;

	ALLOC_ARRAY(entries_by_fanout, alloc_fanout);
	ALLOC_ARRAY(deduplicated_entries, alloc_objects);
	*nr_objects = 0;

	for (cur_fanout = 0; cur_fanout < 256; cur_fanout++) {
		nr_fanout = 0;

		for (cur_pack = 0; cur_pack < nr_packs; cur_pack++) {
			uint32_t start = 0, end;

			if (cur_fanout)
				start = get_pack_fanout(p[cur_pack], cur_fanout - 1);
			end = get_pack_fanout(p[cur_pack], cur_fanout);

			for (cur_object = start; cur_object < end; cur_object++) {
				ALLOC_GROW(entries_by_fanout, nr_fanout + 1, alloc_fanout);
				fill_pack_entry(perm[cur_pack], p[cur_pack], cur_object, &entries_by_fanout[nr_fanout]);
				nr_fanout++;
			}
		}

		QSORT(entries_by_fanout, nr_fanout, midx_oid_compare);

		/*
		 * The batch is now sorted by OID and then mtime (descending).
		 * Take only the first duplicate.
		 */
		for (cur_object = 0; cur_object < nr_fanout; cur_object++) {
			if (cur_object && !oidcmp(&entries_by_fanout[cur_object - 1].oid,
						  &entries_by_fanout[cur_object].oid))
				continue;

			ALLOC_GROW(deduplicated_entries, *nr_objects + 1, alloc_objects);
			memcpy(&deduplicated_entries[*nr_objects],
			       &entries_by_fanout[cur_object],
			       sizeof(struct pack_midx_entry));
			(*nr_objects)++;
		}
	}

	FREE_AND_NULL(entries_by_fanout);
	return deduplicated_entries;
}

static size_t write_midx_pack_lookup(struct hashfile *f,
				     char **pack_names,
				     uint32_t nr_packs)
{
	uint32_t i, cur_len = 0;

	for (i = 0; i < nr_packs; i++) {
		hashwrite_be32(f, cur_len);
		cur_len += strlen(pack_names[i]) + 1;
	}

	return sizeof(uint32_t) * (size_t)nr_packs;
}

static size_t write_midx_pack_names(struct hashfile *f,
				    char **pack_names,
				    uint32_t num_packs)
{
	uint32_t i;
	unsigned char padding[MIDX_CHUNK_ALIGNMENT];
	size_t written = 0;

	for (i = 0; i < num_packs; i++) {
		size_t writelen = strlen(pack_names[i]) + 1;

		if (i && strcmp(pack_names[i], pack_names[i - 1]) <= 0)
			BUG("incorrect pack-file order: %s before %s",
			    pack_names[i - 1],
			    pack_names[i]);

		hashwrite(f, pack_names[i], writelen);
		written += writelen;
	}

	/* add padding to be aligned */
	i = MIDX_CHUNK_ALIGNMENT - (written % MIDX_CHUNK_ALIGNMENT);
	if (i < MIDX_CHUNK_ALIGNMENT) {
		bzero(padding, sizeof(padding));
		hashwrite(f, padding, i);
		written += i;
	}

	return written;
}

int write_midx_file(const char *object_dir)
{
	unsigned char cur_chunk, num_chunks = 0;
	char *midx_name;
	struct hashfile *f;
	struct lock_file lk;
	struct packed_git **packs = NULL;
	char **pack_names = NULL;
	uint32_t *pack_perm;
	uint32_t i, nr_packs = 0, alloc_packs = 0;
	uint32_t alloc_pack_names = 0;
	DIR *dir;
	struct dirent *de;
	struct strbuf pack_dir = STRBUF_INIT;
	size_t pack_dir_len;
	uint64_t pack_name_concat_len = 0;
	uint64_t written = 0;
	uint32_t chunk_ids[MIDX_MAX_CHUNKS + 1];
	uint64_t chunk_offsets[MIDX_MAX_CHUNKS + 1];
	uint32_t nr_entries;

	midx_name = get_midx_filename(object_dir);
	if (safe_create_leading_directories(midx_name)) {
		UNLEAK(midx_name);
		die_errno(_("unable to create leading directories of %s"),
			  midx_name);
	}

	strbuf_addf(&pack_dir, "%s/pack", object_dir);
	dir = opendir(pack_dir.buf);

	if (!dir) {
		error_errno("unable to open pack directory: %s",
			    pack_dir.buf);
		strbuf_release(&pack_dir);
		return 1;
	}

	strbuf_addch(&pack_dir, '/');
	pack_dir_len = pack_dir.len;
	ALLOC_ARRAY(packs, alloc_packs);
	ALLOC_ARRAY(pack_names, alloc_pack_names);
	while ((de = readdir(dir)) != NULL) {
		if (is_dot_or_dotdot(de->d_name))
			continue;

		if (ends_with(de->d_name, ".idx")) {
			ALLOC_GROW(packs, nr_packs + 1, alloc_packs);
			ALLOC_GROW(pack_names, nr_packs + 1, alloc_pack_names);

			strbuf_setlen(&pack_dir, pack_dir_len);
			strbuf_addstr(&pack_dir, de->d_name);

			packs[nr_packs] = add_packed_git(pack_dir.buf,
							 pack_dir.len,
							 0);
			if (!packs[nr_packs]) {
				warning("failed to add packfile '%s'",
					pack_dir.buf);
				continue;
			}

			pack_names[nr_packs] = xstrdup(de->d_name);
			pack_name_concat_len += strlen(de->d_name) + 1;
			nr_packs++;
		}
	}

	closedir(dir);
	strbuf_release(&pack_dir);

	if (pack_name_concat_len % MIDX_CHUNK_ALIGNMENT)
		pack_name_concat_len += MIDX_CHUNK_ALIGNMENT -
					(pack_name_concat_len % MIDX_CHUNK_ALIGNMENT);

	ALLOC_ARRAY(pack_perm, nr_packs);
	sort_packs_by_name(pack_names, nr_packs, pack_perm);

	get_sorted_entries(packs, pack_perm, nr_packs, &nr_entries);

	hold_lock_file_for_update(&lk, midx_name, LOCK_DIE_ON_ERROR);
	f = hashfd(lk.tempfile->fd, lk.tempfile->filename.buf);
	FREE_AND_NULL(midx_name);

	cur_chunk = 0;
	num_chunks = 2;

	written = write_midx_header(f, num_chunks, nr_packs);

	chunk_ids[cur_chunk] = MIDX_CHUNKID_PACKLOOKUP;
	chunk_offsets[cur_chunk] = written + (num_chunks + 1) * MIDX_CHUNKLOOKUP_WIDTH;

	cur_chunk++;
	chunk_ids[cur_chunk] = MIDX_CHUNKID_PACKNAMES;
	chunk_offsets[cur_chunk] = chunk_offsets[cur_chunk - 1] + nr_packs * sizeof(uint32_t);

	cur_chunk++;
	chunk_ids[cur_chunk] = 0;
	chunk_offsets[cur_chunk] = chunk_offsets[cur_chunk - 1] + pack_name_concat_len;

	for (i = 0; i <= num_chunks; i++) {
		if (i && chunk_offsets[i] < chunk_offsets[i - 1])
			BUG("incorrect chunk offsets: %"PRIu64" before %"PRIu64,
			    chunk_offsets[i - 1],
			    chunk_offsets[i]);

		if (chunk_offsets[i] % MIDX_CHUNK_ALIGNMENT)
			BUG("chunk offset %"PRIu64" is not properly aligned",
			    chunk_offsets[i]);

		hashwrite_be32(f, chunk_ids[i]);
		hashwrite_be32(f, chunk_offsets[i] >> 32);
		hashwrite_be32(f, chunk_offsets[i]);

		written += MIDX_CHUNKLOOKUP_WIDTH;
	}

	for (i = 0; i < num_chunks; i++) {
		if (written != chunk_offsets[i])
			BUG("inccrrect chunk offset (%"PRIu64" != %"PRIu64") for chunk id %"PRIx32,
			    chunk_offsets[i],
			    written,
			    chunk_ids[i]);

		switch (chunk_ids[i]) {
			case MIDX_CHUNKID_PACKLOOKUP:
				written += write_midx_pack_lookup(f, pack_names, nr_packs);
				break;

			case MIDX_CHUNKID_PACKNAMES:
				written += write_midx_pack_names(f, pack_names, nr_packs);
				break;

			default:
				BUG("trying to write unknown chunk id %"PRIx32,
				    chunk_ids[i]);
		}
	}

	if (written != chunk_offsets[num_chunks])
		BUG("incorrect final offset %"PRIu64" != %"PRIu64,
		    written,
		    chunk_offsets[num_chunks]);

	finalize_hashfile(f, NULL, CSUM_FSYNC | CSUM_HASH_IN_STREAM);
	commit_lock_file(&lk);

	for (i = 0; i < nr_packs; i++) {
		close_pack(packs[i]);
		FREE_AND_NULL(packs[i]);
	}

	FREE_AND_NULL(packs);
	FREE_AND_NULL(pack_names);
	return 0;
}
debug log:

solving b20d52713c ...
found b20d52713c in https://public-inbox.org/git/20180607140338.32440-12-dstolee@microsoft.com/
found 923acda72e in https://public-inbox.org/git/20180607140338.32440-11-dstolee@microsoft.com/
found d4f4a01a51 in https://public-inbox.org/git/20180607140338.32440-10-dstolee@microsoft.com/
found 9fb89c80a2 in https://public-inbox.org/git/20180607140338.32440-9-dstolee@microsoft.com/
found fa18770f1d in https://public-inbox.org/git/20180607140338.32440-7-dstolee@microsoft.com/
found 3e55422a21 in https://public-inbox.org/git/20180607140338.32440-6-dstolee@microsoft.com/
found 616af66b13 in https://public-inbox.org/git/20180607140338.32440-5-dstolee@microsoft.com/

applying [1/7] https://public-inbox.org/git/20180607140338.32440-5-dstolee@microsoft.com/
diff --git a/midx.c b/midx.c
new file mode 100644
index 0000000000..616af66b13


applying [2/7] https://public-inbox.org/git/20180607140338.32440-6-dstolee@microsoft.com/
diff --git a/midx.c b/midx.c
index 616af66b13..3e55422a21 100644


applying [3/7] https://public-inbox.org/git/20180607140338.32440-7-dstolee@microsoft.com/
diff --git a/midx.c b/midx.c
index 3e55422a21..fa18770f1d 100644


applying [4/7] https://public-inbox.org/git/20180607140338.32440-9-dstolee@microsoft.com/
diff --git a/midx.c b/midx.c
index fa18770f1d..9fb89c80a2 100644


applying [5/7] https://public-inbox.org/git/20180607140338.32440-10-dstolee@microsoft.com/
diff --git a/midx.c b/midx.c
index 9fb89c80a2..d4f4a01a51 100644


applying [6/7] https://public-inbox.org/git/20180607140338.32440-11-dstolee@microsoft.com/
diff --git a/midx.c b/midx.c
index d4f4a01a51..923acda72e 100644


applying [7/7] https://public-inbox.org/git/20180607140338.32440-12-dstolee@microsoft.com/
diff --git a/midx.c b/midx.c
index 923acda72e..b20d52713c 100644

Checking patch midx.c...
Applied patch midx.c cleanly.
Checking patch midx.c...
Applied patch midx.c cleanly.
Checking patch midx.c...
Applied patch midx.c cleanly.
Checking patch midx.c...
Applied patch midx.c cleanly.
Checking patch midx.c...
Applied patch midx.c cleanly.
Checking patch midx.c...
Applied patch midx.c cleanly.
Checking patch midx.c...
Applied patch midx.c cleanly.

index at:
100644 b20d52713c2a6201553d05f9a976bbf886d01a55	midx.c

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