/src/git/midx.c

Source (jump to first uncovered line)
#include "git-compat-util.h"
#include "abspath.h"
#include "config.h"
#include "csum-file.h"
#include "dir.h"
#include "gettext.h"
#include "hex.h"
#include "lockfile.h"
#include "packfile.h"
#include "object-file.h"
#include "object-store-ll.h"
#include "hash-lookup.h"
#include "midx.h"
#include "progress.h"
#include "trace2.h"
#include "run-command.h"
#include "repository.h"
#include "chunk-format.h"
#include "pack.h"
#include "pack-bitmap.h"
#include "refs.h"
#include "revision.h"
#include "list-objects.h"

#define MIDX_SIGNATURE 0x4d494458 /* "MIDX" */
#define MIDX_VERSION 1
#define MIDX_BYTE_FILE_VERSION 4
#define MIDX_BYTE_HASH_VERSION 5
#define MIDX_BYTE_NUM_CHUNKS 6
#define MIDX_BYTE_NUM_PACKS 8
#define MIDX_HEADER_SIZE 12
#define MIDX_MIN_SIZE (MIDX_HEADER_SIZE + the_hash_algo->rawsz)

#define MIDX_CHUNK_ALIGNMENT 4
#define MIDX_CHUNKID_PACKNAMES 0x504e414d /* "PNAM" */
#define MIDX_CHUNKID_OIDFANOUT 0x4f494446 /* "OIDF" */
#define MIDX_CHUNKID_OIDLOOKUP 0x4f49444c /* "OIDL" */
#define MIDX_CHUNKID_OBJECTOFFSETS 0x4f4f4646 /* "OOFF" */
#define MIDX_CHUNKID_LARGEOFFSETS 0x4c4f4646 /* "LOFF" */
#define MIDX_CHUNKID_REVINDEX 0x52494458 /* "RIDX" */
#define MIDX_CHUNK_FANOUT_SIZE (sizeof(uint32_t) * 256)
#define MIDX_CHUNK_OFFSET_WIDTH (2 * sizeof(uint32_t))
#define MIDX_CHUNK_LARGE_OFFSET_WIDTH (sizeof(uint64_t))
#define MIDX_LARGE_OFFSET_NEEDED 0x80000000

#define PACK_EXPIRED UINT_MAX

const unsigned char *get_midx_checksum(struct multi_pack_index *m)
{
  return m->data + m->data_len - the_hash_algo->rawsz;
}

void get_midx_filename(struct strbuf *out, const char *object_dir)
{
  strbuf_addf(out, "%s/pack/multi-pack-index", object_dir);
}

void get_midx_rev_filename(struct strbuf *out, struct multi_pack_index *m)
{
  get_midx_filename(out, m->object_dir);
  strbuf_addf(out, "-%s.rev", hash_to_hex(get_midx_checksum(m)));
}

static int midx_read_oid_fanout(const unsigned char *chunk_start,
        size_t chunk_size, void *data)
{
  int i;
  struct multi_pack_index *m = data;
  m->chunk_oid_fanout = (uint32_t *)chunk_start;

  if (chunk_size != 4 * 256) {
    error(_("multi-pack-index OID fanout is of the wrong size"));
    return 1;
  }
  for (i = 0; i < 255; i++) {
    uint32_t oid_fanout1 = ntohl(m->chunk_oid_fanout[i]);
    uint32_t oid_fanout2 = ntohl(m->chunk_oid_fanout[i+1]);

    if (oid_fanout1 > oid_fanout2) {
      error(_("oid fanout out of order: fanout[%d] = %"PRIx32" > %"PRIx32" = fanout[%d]"),
            i, oid_fanout1, oid_fanout2, i + 1);
      return 1;
    }
  }
  m->num_objects = ntohl(m->chunk_oid_fanout[255]);
  return 0;
}

static int midx_read_oid_lookup(const unsigned char *chunk_start,
        size_t chunk_size, void *data)
{
  struct multi_pack_index *m = data;
  m->chunk_oid_lookup = chunk_start;

  if (chunk_size != st_mult(m->hash_len, m->num_objects)) {
    error(_("multi-pack-index OID lookup chunk is the wrong size"));
    return 1;
  }
  return 0;
}

static int midx_read_object_offsets(const unsigned char *chunk_start,
            size_t chunk_size, void *data)
{
  struct multi_pack_index *m = data;
  m->chunk_object_offsets = chunk_start;

  if (chunk_size != st_mult(m->num_objects, MIDX_CHUNK_OFFSET_WIDTH)) {
    error(_("multi-pack-index object offset chunk is the wrong size"));
    return 1;
  }
  return 0;
}

struct multi_pack_index *load_multi_pack_index(const char *object_dir, int local)
{
  struct multi_pack_index *m = NULL;
  int fd;
  struct stat st;
  size_t midx_size;
  void *midx_map = NULL;
  uint32_t hash_version;
  struct strbuf midx_name = STRBUF_INIT;
  uint32_t i;
  const char *cur_pack_name;
  struct chunkfile *cf = NULL;

  get_midx_filename(&midx_name, object_dir);

  fd = git_open(midx_name.buf);

  if (fd < 0)
    goto cleanup_fail;
  if (fstat(fd, &st)) {
    error_errno(_("failed to read %s"), midx_name.buf);
    goto cleanup_fail;
  }

  midx_size = xsize_t(st.st_size);

  if (midx_size < MIDX_MIN_SIZE) {
    error(_("multi-pack-index file %s is too small"), midx_name.buf);
    goto cleanup_fail;
  }

  strbuf_release(&midx_name);

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

  FLEX_ALLOC_STR(m, object_dir, object_dir);
  m->data = midx_map;
  m->data_len = midx_size;
  m->local = local;

  m->signature = get_be32(m->data);
  if (m->signature != MIDX_SIGNATURE)
    die(_("multi-pack-index signature 0x%08x does not match signature 0x%08x"),
          m->signature, MIDX_SIGNATURE);

  m->version = m->data[MIDX_BYTE_FILE_VERSION];
  if (m->version != MIDX_VERSION)
    die(_("multi-pack-index version %d not recognized"),
          m->version);

  hash_version = m->data[MIDX_BYTE_HASH_VERSION];
  if (hash_version != oid_version(the_hash_algo)) {
    error(_("multi-pack-index hash version %u does not match version %u"),
          hash_version, oid_version(the_hash_algo));
    goto cleanup_fail;
  }
  m->hash_len = the_hash_algo->rawsz;

  m->num_chunks = m->data[MIDX_BYTE_NUM_CHUNKS];

  m->num_packs = get_be32(m->data + MIDX_BYTE_NUM_PACKS);

  cf = init_chunkfile(NULL);

  if (read_table_of_contents(cf, m->data, midx_size,
           MIDX_HEADER_SIZE, m->num_chunks,
           MIDX_CHUNK_ALIGNMENT))
    goto cleanup_fail;

  if (pair_chunk(cf, MIDX_CHUNKID_PACKNAMES, &m->chunk_pack_names, &m->chunk_pack_names_len))
    die(_("multi-pack-index required pack-name chunk missing or corrupted"));
  if (read_chunk(cf, MIDX_CHUNKID_OIDFANOUT, midx_read_oid_fanout, m))
    die(_("multi-pack-index required OID fanout chunk missing or corrupted"));
  if (read_chunk(cf, MIDX_CHUNKID_OIDLOOKUP, midx_read_oid_lookup, m))
    die(_("multi-pack-index required OID lookup chunk missing or corrupted"));
  if (read_chunk(cf, MIDX_CHUNKID_OBJECTOFFSETS, midx_read_object_offsets, m))
    die(_("multi-pack-index required object offsets chunk missing or corrupted"));

  pair_chunk(cf, MIDX_CHUNKID_LARGEOFFSETS, &m->chunk_large_offsets,
       &m->chunk_large_offsets_len);

  if (git_env_bool("GIT_TEST_MIDX_READ_RIDX", 1))
    pair_chunk(cf, MIDX_CHUNKID_REVINDEX, &m->chunk_revindex,
         &m->chunk_revindex_len);

  CALLOC_ARRAY(m->pack_names, m->num_packs);
  CALLOC_ARRAY(m->packs, m->num_packs);

  cur_pack_name = (const char *)m->chunk_pack_names;
  for (i = 0; i < m->num_packs; i++) {
    const char *end;
    size_t avail = m->chunk_pack_names_len -
        (cur_pack_name - (const char *)m->chunk_pack_names);

    m->pack_names[i] = cur_pack_name;

    end = memchr(cur_pack_name, '\0', avail);
    if (!end)
      die(_("multi-pack-index pack-name chunk is too short"));
    cur_pack_name = end + 1;

    if (i && strcmp(m->pack_names[i], m->pack_names[i - 1]) <= 0)
      die(_("multi-pack-index pack names out of order: '%s' before '%s'"),
            m->pack_names[i - 1],
            m->pack_names[i]);
  }

  trace2_data_intmax("midx", the_repository, "load/num_packs", m->num_packs);
  trace2_data_intmax("midx", the_repository, "load/num_objects", m->num_objects);

  free_chunkfile(cf);
  return m;

cleanup_fail:
  free(m);
  strbuf_release(&midx_name);
  free_chunkfile(cf);
  if (midx_map)
    munmap(midx_map, midx_size);
  if (0 <= fd)
    close(fd);
  return NULL;
}

void close_midx(struct multi_pack_index *m)
{
  uint32_t i;

  if (!m)
    return;

  close_midx(m->next);

  munmap((unsigned char *)m->data, m->data_len);

  for (i = 0; i < m->num_packs; i++) {
    if (m->packs[i])
      m->packs[i]->multi_pack_index = 0;
  }
  FREE_AND_NULL(m->packs);
  FREE_AND_NULL(m->pack_names);
  free(m);
}

int prepare_midx_pack(struct repository *r, struct multi_pack_index *m, uint32_t pack_int_id)
{
  struct strbuf pack_name = STRBUF_INIT;
  struct packed_git *p;

  if (pack_int_id >= m->num_packs)
    die(_("bad pack-int-id: %u (%u total packs)"),
        pack_int_id, m->num_packs);

  if (m->packs[pack_int_id])
    return 0;

  strbuf_addf(&pack_name, "%s/pack/%s", m->object_dir,
        m->pack_names[pack_int_id]);

  p = add_packed_git(pack_name.buf, pack_name.len, m->local);
  strbuf_release(&pack_name);

  if (!p)
    return 1;

  p->multi_pack_index = 1;
  m->packs[pack_int_id] = p;
  install_packed_git(r, p);
  list_add_tail(&p->mru, &r->objects->packed_git_mru);

  return 0;
}

int bsearch_midx(const struct object_id *oid, struct multi_pack_index *m, uint32_t *result)
{
  return bsearch_hash(oid->hash, m->chunk_oid_fanout, m->chunk_oid_lookup,
          the_hash_algo->rawsz, result);
}

struct object_id *nth_midxed_object_oid(struct object_id *oid,
          struct multi_pack_index *m,
          uint32_t n)
{
  if (n >= m->num_objects)
    return NULL;

  oidread(oid, m->chunk_oid_lookup + st_mult(m->hash_len, n));
  return oid;
}

off_t nth_midxed_offset(struct multi_pack_index *m, uint32_t pos)
{
  const unsigned char *offset_data;
  uint32_t offset32;

  offset_data = m->chunk_object_offsets + (off_t)pos * MIDX_CHUNK_OFFSET_WIDTH;
  offset32 = get_be32(offset_data + sizeof(uint32_t));

  if (m->chunk_large_offsets && offset32 & MIDX_LARGE_OFFSET_NEEDED) {
    if (sizeof(off_t) < sizeof(uint64_t))
      die(_("multi-pack-index stores a 64-bit offset, but off_t is too small"));

    offset32 ^= MIDX_LARGE_OFFSET_NEEDED;
    if (offset32 >= m->chunk_large_offsets_len / sizeof(uint64_t))
      die(_("multi-pack-index large offset out of bounds"));
    return get_be64(m->chunk_large_offsets + sizeof(uint64_t) * offset32);
  }

  return offset32;
}

uint32_t nth_midxed_pack_int_id(struct multi_pack_index *m, uint32_t pos)
{
  return get_be32(m->chunk_object_offsets +
      (off_t)pos * MIDX_CHUNK_OFFSET_WIDTH);
}

int fill_midx_entry(struct repository *r,
        const struct object_id *oid,
        struct pack_entry *e,
        struct multi_pack_index *m)
{
  uint32_t pos;
  uint32_t pack_int_id;
  struct packed_git *p;

  if (!bsearch_midx(oid, m, &pos))
    return 0;

  if (pos >= m->num_objects)
    return 0;

  pack_int_id = nth_midxed_pack_int_id(m, pos);

  if (prepare_midx_pack(r, m, pack_int_id))
    return 0;
  p = m->packs[pack_int_id];

  /*
  * We are about to tell the caller where they can locate the
  * requested object.  We better make sure the packfile is
  * still here and can be accessed before supplying that
  * answer, as it may have been deleted since the MIDX was
  * loaded!
  */
  if (!is_pack_valid(p))
    return 0;

  if (oidset_size(&p->bad_objects) &&
      oidset_contains(&p->bad_objects, oid))
    return 0;

  e->offset = nth_midxed_offset(m, pos);
  e->p = p;

  return 1;
}

/* Match "foo.idx" against either "foo.pack" _or_ "foo.idx". */
static int cmp_idx_or_pack_name(const char *idx_or_pack_name,
        const char *idx_name)
{
  /* Skip past any initial matching prefix. */
  while (*idx_name && *idx_name == *idx_or_pack_name) {
    idx_name++;
    idx_or_pack_name++;
  }

  /*
   * If we didn't match completely, we may have matched "pack-1234." and
   * be left with "idx" and "pack" respectively, which is also OK. We do
   * not have to check for "idx" and "idx", because that would have been
   * a complete match (and in that case these strcmps will be false, but
   * we'll correctly return 0 from the final strcmp() below.
   *
   * Technically this matches "fooidx" and "foopack", but we'd never have
   * such names in the first place.
   */
  if (!strcmp(idx_name, "idx") && !strcmp(idx_or_pack_name, "pack"))
    return 0;

  /*
   * This not only checks for a complete match, but also orders based on
   * the first non-identical character, which means our ordering will
   * match a raw strcmp(). That makes it OK to use this to binary search
   * a naively-sorted list.
   */
  return strcmp(idx_or_pack_name, idx_name);
}

int midx_contains_pack(struct multi_pack_index *m, const char *idx_or_pack_name)
{
  uint32_t first = 0, last = m->num_packs;

  while (first < last) {
    uint32_t mid = first + (last - first) / 2;
    const char *current;
    int cmp;

    current = m->pack_names[mid];
    cmp = cmp_idx_or_pack_name(idx_or_pack_name, current);
    if (!cmp)
      return 1;
    if (cmp > 0) {
      first = mid + 1;
      continue;
    }
    last = mid;
  }

  return 0;
}

int prepare_multi_pack_index_one(struct repository *r, const char *object_dir, int local)
{
  struct multi_pack_index *m;
  struct multi_pack_index *m_search;

  prepare_repo_settings(r);
  if (!r->settings.core_multi_pack_index)
    return 0;

  for (m_search = r->objects->multi_pack_index; m_search; m_search = m_search->next)
    if (!strcmp(object_dir, m_search->object_dir))
      return 1;

  m = load_multi_pack_index(object_dir, local);

  if (m) {
    struct multi_pack_index *mp = r->objects->multi_pack_index;
    if (mp) {
      m->next = mp->next;
      mp->next = m;
    } else
      r->objects->multi_pack_index = m;
    return 1;
  }

  return 0;
}

static size_t write_midx_header(struct hashfile *f,
        unsigned char num_chunks,
        uint32_t num_packs)
{
  hashwrite_be32(f, MIDX_SIGNATURE);
  hashwrite_u8(f, MIDX_VERSION);
  hashwrite_u8(f, oid_version(the_hash_algo));
  hashwrite_u8(f, num_chunks);
  hashwrite_u8(f, 0); /* unused */
  hashwrite_be32(f, num_packs);

  return MIDX_HEADER_SIZE;
}

struct pack_info {
  uint32_t orig_pack_int_id;
  char *pack_name;
  struct packed_git *p;
  unsigned expired : 1;
};

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

static int idx_or_pack_name_cmp(const void *_va, const void *_vb)
{
  const char *pack_name = _va;
  const struct pack_info *compar = _vb;

  return cmp_idx_or_pack_name(pack_name, compar->pack_name);
}

struct write_midx_context {
  struct pack_info *info;
  size_t nr;
  size_t alloc;
  struct multi_pack_index *m;
  struct progress *progress;
  unsigned pack_paths_checked;

  struct pack_midx_entry *entries;
  size_t entries_nr;

  uint32_t *pack_perm;
  uint32_t *pack_order;
  unsigned large_offsets_needed:1;
  uint32_t num_large_offsets;

  int preferred_pack_idx;

  struct string_list *to_include;
};

static void add_pack_to_midx(const char *full_path, size_t full_path_len,
           const char *file_name, void *data)
{
  struct write_midx_context *ctx = data;

  if (ends_with(file_name, ".idx")) {
    display_progress(ctx->progress, ++ctx->pack_paths_checked);
    /*
     * Note that at most one of ctx->m and ctx->to_include are set,
     * so we are testing midx_contains_pack() and
     * string_list_has_string() independently (guarded by the
     * appropriate NULL checks).
     *
     * We could support passing to_include while reusing an existing
     * MIDX, but don't currently since the reuse process drags
     * forward all packs from an existing MIDX (without checking
     * whether or not they appear in the to_include list).
     *
     * If we added support for that, these next two conditional
     * should be performed independently (likely checking
     * to_include before the existing MIDX).
     */
    if (ctx->m && midx_contains_pack(ctx->m, file_name))
      return;
    else if (ctx->to_include &&
       !string_list_has_string(ctx->to_include, file_name))
      return;

    ALLOC_GROW(ctx->info, ctx->nr + 1, ctx->alloc);

    ctx->info[ctx->nr].p = add_packed_git(full_path,
                  full_path_len,
                  0);

    if (!ctx->info[ctx->nr].p) {
      warning(_("failed to add packfile '%s'"),
        full_path);
      return;
    }

    if (open_pack_index(ctx->info[ctx->nr].p)) {
      warning(_("failed to open pack-index '%s'"),
        full_path);
      close_pack(ctx->info[ctx->nr].p);
      FREE_AND_NULL(ctx->info[ctx->nr].p);
      return;
    }

    ctx->info[ctx->nr].pack_name = xstrdup(file_name);
    ctx->info[ctx->nr].orig_pack_int_id = ctx->nr;
    ctx->info[ctx->nr].expired = 0;
    ctx->nr++;
  }
}

struct pack_midx_entry {
  struct object_id oid;
  uint32_t pack_int_id;
  time_t pack_mtime;
  uint64_t offset;
  unsigned preferred : 1;
};

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

  if (cmp)
    return cmp;

  /* Sort objects in a preferred pack first when multiple copies exist. */
  if (a->preferred > b->preferred)
    return -1;
  if (a->preferred < b->preferred)
    return 1;

  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 int nth_midxed_pack_midx_entry(struct multi_pack_index *m,
              struct pack_midx_entry *e,
              uint32_t pos)
{
  if (pos >= m->num_objects)
    return 1;

  nth_midxed_object_oid(&e->oid, m, pos);
  e->pack_int_id = nth_midxed_pack_int_id(m, pos);
  e->offset = nth_midxed_offset(m, pos);

  /* consider objects in midx to be from "old" packs */
  e->pack_mtime = 0;
  return 0;
}

static void fill_pack_entry(uint32_t pack_int_id,
          struct packed_git *p,
          uint32_t cur_object,
          struct pack_midx_entry *entry,
          int preferred)
{
  if (nth_packed_object_id(&entry->oid, p, cur_object) < 0)
    die(_("failed to locate 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);
  entry->preferred = !!preferred;
}

struct midx_fanout {
  struct pack_midx_entry *entries;
  size_t nr, alloc;
};

static void midx_fanout_grow(struct midx_fanout *fanout, size_t nr)
{
  if (nr < fanout->nr)
    BUG("negative growth in midx_fanout_grow() (%"PRIuMAX" < %"PRIuMAX")",
        (uintmax_t)nr, (uintmax_t)fanout->nr);
  ALLOC_GROW(fanout->entries, nr, fanout->alloc);
}

static void midx_fanout_sort(struct midx_fanout *fanout)
{
  QSORT(fanout->entries, fanout->nr, midx_oid_compare);
}

static void midx_fanout_add_midx_fanout(struct midx_fanout *fanout,
          struct multi_pack_index *m,
          uint32_t cur_fanout,
          int preferred_pack)
{
  uint32_t start = 0, end;
  uint32_t cur_object;

  if (cur_fanout)
    start = ntohl(m->chunk_oid_fanout[cur_fanout - 1]);
  end = ntohl(m->chunk_oid_fanout[cur_fanout]);

  for (cur_object = start; cur_object < end; cur_object++) {
    if ((preferred_pack > -1) &&
        (preferred_pack == nth_midxed_pack_int_id(m, cur_object))) {
      /*
       * Objects from preferred packs are added
       * separately.
       */
      continue;
    }

    midx_fanout_grow(fanout, fanout->nr + 1);
    nth_midxed_pack_midx_entry(m,
             &fanout->entries[fanout->nr],
             cur_object);
    fanout->entries[fanout->nr].preferred = 0;
    fanout->nr++;
  }
}

static void midx_fanout_add_pack_fanout(struct midx_fanout *fanout,
          struct pack_info *info,
          uint32_t cur_pack,
          int preferred,
          uint32_t cur_fanout)
{
  struct packed_git *pack = info[cur_pack].p;
  uint32_t start = 0, end;
  uint32_t cur_object;

  if (cur_fanout)
    start = get_pack_fanout(pack, cur_fanout - 1);
  end = get_pack_fanout(pack, cur_fanout);

  for (cur_object = start; cur_object < end; cur_object++) {
    midx_fanout_grow(fanout, fanout->nr + 1);
    fill_pack_entry(cur_pack,
        info[cur_pack].p,
        cur_object,
        &fanout->entries[fanout->nr],
        preferred);
    fanout->nr++;
  }
}

/*
 * 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 multi_pack_index *m,
              struct pack_info *info,
              uint32_t nr_packs,
              size_t *nr_objects,
              int preferred_pack)
{
  uint32_t cur_fanout, cur_pack, cur_object;
  size_t alloc_objects, total_objects = 0;
  struct midx_fanout fanout = { 0 };
  struct pack_midx_entry *deduplicated_entries = NULL;
  uint32_t start_pack = m ? m->num_packs : 0;

  for (cur_pack = start_pack; cur_pack < nr_packs; cur_pack++)
    total_objects = st_add(total_objects,
               info[cur_pack].p->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 = fanout.alloc = total_objects > 3200 ? total_objects / 200 : 16;

  ALLOC_ARRAY(fanout.entries, fanout.alloc);
  ALLOC_ARRAY(deduplicated_entries, alloc_objects);
  *nr_objects = 0;

  for (cur_fanout = 0; cur_fanout < 256; cur_fanout++) {
    fanout.nr = 0;

    if (m)
      midx_fanout_add_midx_fanout(&fanout, m, cur_fanout,
                preferred_pack);

    for (cur_pack = start_pack; cur_pack < nr_packs; cur_pack++) {
      int preferred = cur_pack == preferred_pack;
      midx_fanout_add_pack_fanout(&fanout,
                info, cur_pack,
                preferred, cur_fanout);
    }

    if (-1 < preferred_pack && preferred_pack < start_pack)
      midx_fanout_add_pack_fanout(&fanout, info,
                preferred_pack, 1,
                cur_fanout);

    midx_fanout_sort(&fanout);

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

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

  free(fanout.entries);
  return deduplicated_entries;
}

static int write_midx_pack_names(struct hashfile *f, void *data)
{
  struct write_midx_context *ctx = data;
  uint32_t i;
  unsigned char padding[MIDX_CHUNK_ALIGNMENT];
  size_t written = 0;

  for (i = 0; i < ctx->nr; i++) {
    size_t writelen;

    if (ctx->info[i].expired)
      continue;

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

    writelen = strlen(ctx->info[i].pack_name) + 1;
    hashwrite(f, ctx->info[i].pack_name, writelen);
    written += writelen;
  }

  /* add padding to be aligned */
  i = MIDX_CHUNK_ALIGNMENT - (written % MIDX_CHUNK_ALIGNMENT);
  if (i < MIDX_CHUNK_ALIGNMENT) {
    memset(padding, 0, sizeof(padding));
    hashwrite(f, padding, i);
  }

  return 0;
}

static int write_midx_oid_fanout(struct hashfile *f,
         void *data)
{
  struct write_midx_context *ctx = data;
  struct pack_midx_entry *list = ctx->entries;
  struct pack_midx_entry *last = ctx->entries + ctx->entries_nr;
  uint32_t count = 0;
  uint32_t i;

  /*
  * Write the first-level table (the list is sorted,
  * but we use a 256-entry lookup to be able to avoid
  * having to do eight extra binary search iterations).
  */
  for (i = 0; i < 256; i++) {
    struct pack_midx_entry *next = list;

    while (next < last && next->oid.hash[0] == i) {
      count++;
      next++;
    }

    hashwrite_be32(f, count);
    list = next;
  }

  return 0;
}

static int write_midx_oid_lookup(struct hashfile *f,
         void *data)
{
  struct write_midx_context *ctx = data;
  unsigned char hash_len = the_hash_algo->rawsz;
  struct pack_midx_entry *list = ctx->entries;
  uint32_t i;

  for (i = 0; i < ctx->entries_nr; i++) {
    struct pack_midx_entry *obj = list++;

    if (i < ctx->entries_nr - 1) {
      struct pack_midx_entry *next = list;
      if (oidcmp(&obj->oid, &next->oid) >= 0)
        BUG("OIDs not in order: %s >= %s",
            oid_to_hex(&obj->oid),
            oid_to_hex(&next->oid));
    }

    hashwrite(f, obj->oid.hash, (int)hash_len);
  }

  return 0;
}

static int write_midx_object_offsets(struct hashfile *f,
             void *data)
{
  struct write_midx_context *ctx = data;
  struct pack_midx_entry *list = ctx->entries;
  uint32_t i, nr_large_offset = 0;

  for (i = 0; i < ctx->entries_nr; i++) {
    struct pack_midx_entry *obj = list++;

    if (ctx->pack_perm[obj->pack_int_id] == PACK_EXPIRED)
      BUG("object %s is in an expired pack with int-id %d",
          oid_to_hex(&obj->oid),
          obj->pack_int_id);

    hashwrite_be32(f, ctx->pack_perm[obj->pack_int_id]);

    if (ctx->large_offsets_needed && obj->offset >> 31)
      hashwrite_be32(f, MIDX_LARGE_OFFSET_NEEDED | nr_large_offset++);
    else if (!ctx->large_offsets_needed && obj->offset >> 32)
      BUG("object %s requires a large offset (%"PRIx64") but the MIDX is not writing large offsets!",
          oid_to_hex(&obj->oid),
          obj->offset);
    else
      hashwrite_be32(f, (uint32_t)obj->offset);
  }

  return 0;
}

static int write_midx_large_offsets(struct hashfile *f,
            void *data)
{
  struct write_midx_context *ctx = data;
  struct pack_midx_entry *list = ctx->entries;
  struct pack_midx_entry *end = ctx->entries + ctx->entries_nr;
  uint32_t nr_large_offset = ctx->num_large_offsets;

  while (nr_large_offset) {
    struct pack_midx_entry *obj;
    uint64_t offset;

    if (list >= end)
      BUG("too many large-offset objects");

    obj = list++;
    offset = obj->offset;

    if (!(offset >> 31))
      continue;

    hashwrite_be64(f, offset);

    nr_large_offset--;
  }

  return 0;
}

static int write_midx_revindex(struct hashfile *f,
             void *data)
{
  struct write_midx_context *ctx = data;
  uint32_t i;

  for (i = 0; i < ctx->entries_nr; i++)
    hashwrite_be32(f, ctx->pack_order[i]);

  return 0;
}

struct midx_pack_order_data {
  uint32_t nr;
  uint32_t pack;
  off_t offset;
};

static int midx_pack_order_cmp(const void *va, const void *vb)
{
  const struct midx_pack_order_data *a = va, *b = vb;
  if (a->pack < b->pack)
    return -1;
  else if (a->pack > b->pack)
    return 1;
  else if (a->offset < b->offset)
    return -1;
  else if (a->offset > b->offset)
    return 1;
  else
    return 0;
}

static uint32_t *midx_pack_order(struct write_midx_context *ctx)
{
  struct midx_pack_order_data *data;
  uint32_t *pack_order;
  uint32_t i;

  trace2_region_enter("midx", "midx_pack_order", the_repository);

  ALLOC_ARRAY(data, ctx->entries_nr);
  for (i = 0; i < ctx->entries_nr; i++) {
    struct pack_midx_entry *e = &ctx->entries[i];
    data[i].nr = i;
    data[i].pack = ctx->pack_perm[e->pack_int_id];
    if (!e->preferred)
      data[i].pack |= (1U << 31);
    data[i].offset = e->offset;
  }

  QSORT(data, ctx->entries_nr, midx_pack_order_cmp);

  ALLOC_ARRAY(pack_order, ctx->entries_nr);
  for (i = 0; i < ctx->entries_nr; i++)
    pack_order[i] = data[i].nr;
  free(data);

  trace2_region_leave("midx", "midx_pack_order", the_repository);

  return pack_order;
}

static void write_midx_reverse_index(char *midx_name, unsigned char *midx_hash,
             struct write_midx_context *ctx)
{
  struct strbuf buf = STRBUF_INIT;
  const char *tmp_file;

  trace2_region_enter("midx", "write_midx_reverse_index", the_repository);

  strbuf_addf(&buf, "%s-%s.rev", midx_name, hash_to_hex(midx_hash));

  tmp_file = write_rev_file_order(NULL, ctx->pack_order, ctx->entries_nr,
          midx_hash, WRITE_REV);

  if (finalize_object_file(tmp_file, buf.buf))
    die(_("cannot store reverse index file"));

  strbuf_release(&buf);

  trace2_region_leave("midx", "write_midx_reverse_index", the_repository);
}

static void clear_midx_files_ext(const char *object_dir, const char *ext,
         unsigned char *keep_hash);

static int midx_checksum_valid(struct multi_pack_index *m)
{
  return hashfile_checksum_valid(m->data, m->data_len);
}

static void prepare_midx_packing_data(struct packing_data *pdata,
              struct write_midx_context *ctx)
{
  uint32_t i;

  trace2_region_enter("midx", "prepare_midx_packing_data", the_repository);

  memset(pdata, 0, sizeof(struct packing_data));
  prepare_packing_data(the_repository, pdata);

  for (i = 0; i < ctx->entries_nr; i++) {
    struct pack_midx_entry *from = &ctx->entries[ctx->pack_order[i]];
    struct object_entry *to = packlist_alloc(pdata, &from->oid);

    oe_set_in_pack(pdata, to,
             ctx->info[ctx->pack_perm[from->pack_int_id]].p);
  }

  trace2_region_leave("midx", "prepare_midx_packing_data", the_repository);
}

static int add_ref_to_pending(const char *refname,
            const struct object_id *oid,
            int flag, void *cb_data)
{
  struct rev_info *revs = (struct rev_info*)cb_data;
  struct object_id peeled;
  struct object *object;

  if ((flag & REF_ISSYMREF) && (flag & REF_ISBROKEN)) {
    warning("symbolic ref is dangling: %s", refname);
    return 0;
  }

  if (!peel_iterated_oid(oid, &peeled))
    oid = &peeled;

  object = parse_object_or_die(oid, refname);
  if (object->type != OBJ_COMMIT)
    return 0;

  add_pending_object(revs, object, "");
  if (bitmap_is_preferred_refname(revs->repo, refname))
    object->flags |= NEEDS_BITMAP;
  return 0;
}

struct bitmap_commit_cb {
  struct commit **commits;
  size_t commits_nr, commits_alloc;

  struct write_midx_context *ctx;
};

static const struct object_id *bitmap_oid_access(size_t index,
             const void *_entries)
{
  const struct pack_midx_entry *entries = _entries;
  return &entries[index].oid;
}

static void bitmap_show_commit(struct commit *commit, void *_data)
{
  struct bitmap_commit_cb *data = _data;
  int pos = oid_pos(&commit->object.oid, data->ctx->entries,
        data->ctx->entries_nr,
        bitmap_oid_access);
  if (pos < 0)
    return;

  ALLOC_GROW(data->commits, data->commits_nr + 1, data->commits_alloc);
  data->commits[data->commits_nr++] = commit;
}

static int read_refs_snapshot(const char *refs_snapshot,
            struct rev_info *revs)
{
  struct strbuf buf = STRBUF_INIT;
  struct object_id oid;
  FILE *f = xfopen(refs_snapshot, "r");

  while (strbuf_getline(&buf, f) != EOF) {
    struct object *object;
    int preferred = 0;
    char *hex = buf.buf;
    const char *end = NULL;

    if (buf.len && *buf.buf == '+') {
      preferred = 1;
      hex = &buf.buf[1];
    }

    if (parse_oid_hex(hex, &oid, &end) < 0)
      die(_("could not parse line: %s"), buf.buf);
    if (*end)
      die(_("malformed line: %s"), buf.buf);

    object = parse_object_or_die(&oid, NULL);
    if (preferred)
      object->flags |= NEEDS_BITMAP;

    add_pending_object(revs, object, "");
  }

  fclose(f);
  strbuf_release(&buf);
  return 0;
}

static struct commit **find_commits_for_midx_bitmap(uint32_t *indexed_commits_nr_p,
                const char *refs_snapshot,
                struct write_midx_context *ctx)
{
  struct rev_info revs;
  struct bitmap_commit_cb cb = {0};

  trace2_region_enter("midx", "find_commits_for_midx_bitmap",
          the_repository);

  cb.ctx = ctx;

  repo_init_revisions(the_repository, &revs, NULL);
  if (refs_snapshot) {
    read_refs_snapshot(refs_snapshot, &revs);
  } else {
    setup_revisions(0, NULL, &revs, NULL);
    for_each_ref(add_ref_to_pending, &revs);
  }

  /*
   * Skipping promisor objects here is intentional, since it only excludes
   * them from the list of reachable commits that we want to select from
   * when computing the selection of MIDX'd commits to receive bitmaps.
   *
   * Reachability bitmaps do require that their objects be closed under
   * reachability, but fetching any objects missing from promisors at this
   * point is too late. But, if one of those objects can be reached from
   * an another object that is included in the bitmap, then we will
   * complain later that we don't have reachability closure (and fail
   * appropriately).
   */
  fetch_if_missing = 0;
  revs.exclude_promisor_objects = 1;

  if (prepare_revision_walk(&revs))
    die(_("revision walk setup failed"));

  traverse_commit_list(&revs, bitmap_show_commit, NULL, &cb);
  if (indexed_commits_nr_p)
    *indexed_commits_nr_p = cb.commits_nr;

  release_revisions(&revs);

  trace2_region_leave("midx", "find_commits_for_midx_bitmap",
          the_repository);

  return cb.commits;
}

static int write_midx_bitmap(const char *midx_name,
           const unsigned char *midx_hash,
           struct packing_data *pdata,
           struct commit **commits,
           uint32_t commits_nr,
           uint32_t *pack_order,
           unsigned flags)
{
  int ret, i;
  uint16_t options = 0;
  struct pack_idx_entry **index;
  char *bitmap_name = xstrfmt("%s-%s.bitmap", midx_name,
          hash_to_hex(midx_hash));

  trace2_region_enter("midx", "write_midx_bitmap", the_repository);

  if (flags & MIDX_WRITE_BITMAP_HASH_CACHE)
    options |= BITMAP_OPT_HASH_CACHE;

  if (flags & MIDX_WRITE_BITMAP_LOOKUP_TABLE)
    options |= BITMAP_OPT_LOOKUP_TABLE;

  /*
   * Build the MIDX-order index based on pdata.objects (which is already
   * in MIDX order; c.f., 'midx_pack_order_cmp()' for the definition of
   * this order).
   */
  ALLOC_ARRAY(index, pdata->nr_objects);
  for (i = 0; i < pdata->nr_objects; i++)
    index[i] = &pdata->objects[i].idx;

  bitmap_writer_show_progress(flags & MIDX_PROGRESS);
  bitmap_writer_build_type_index(pdata, index, pdata->nr_objects);

  /*
   * bitmap_writer_finish expects objects in lex order, but pack_order
   * gives us exactly that. use it directly instead of re-sorting the
   * array.
   *
   * This changes the order of objects in 'index' between
   * bitmap_writer_build_type_index and bitmap_writer_finish.
   *
   * The same re-ordering takes place in the single-pack bitmap code via
   * write_idx_file(), which is called by finish_tmp_packfile(), which
   * happens between bitmap_writer_build_type_index() and
   * bitmap_writer_finish().
   */
  for (i = 0; i < pdata->nr_objects; i++)
    index[pack_order[i]] = &pdata->objects[i].idx;

  bitmap_writer_select_commits(commits, commits_nr, -1);
  ret = bitmap_writer_build(pdata);
  if (ret < 0)
    goto cleanup;

  bitmap_writer_set_checksum(midx_hash);
  bitmap_writer_finish(index, pdata->nr_objects, bitmap_name, options);

cleanup:
  free(index);
  free(bitmap_name);

  trace2_region_leave("midx", "write_midx_bitmap", the_repository);

  return ret;
}

static struct multi_pack_index *lookup_multi_pack_index(struct repository *r,
              const char *object_dir)
{
  struct multi_pack_index *result = NULL;
  struct multi_pack_index *cur;
  char *obj_dir_real = real_pathdup(object_dir, 1);
  struct strbuf cur_path_real = STRBUF_INIT;

  /* Ensure the given object_dir is local, or a known alternate. */
  find_odb(r, obj_dir_real);

  for (cur = get_multi_pack_index(r); cur; cur = cur->next) {
    strbuf_realpath(&cur_path_real, cur->object_dir, 1);
    if (!strcmp(obj_dir_real, cur_path_real.buf)) {
      result = cur;
      goto cleanup;
    }
  }

cleanup:
  free(obj_dir_real);
  strbuf_release(&cur_path_real);
  return result;
}

static int write_midx_internal(const char *object_dir,
             struct string_list *packs_to_include,
             struct string_list *packs_to_drop,
             const char *preferred_pack_name,
             const char *refs_snapshot,
             unsigned flags)
{
  struct strbuf midx_name = STRBUF_INIT;
  unsigned char midx_hash[GIT_MAX_RAWSZ];
  uint32_t i;
  struct hashfile *f = NULL;
  struct lock_file lk;
  struct write_midx_context ctx = { 0 };
  int pack_name_concat_len = 0;
  int dropped_packs = 0;
  int result = 0;
  struct chunkfile *cf;

  trace2_region_enter("midx", "write_midx_internal", the_repository);

  get_midx_filename(&midx_name, object_dir);
  if (safe_create_leading_directories(midx_name.buf))
    die_errno(_("unable to create leading directories of %s"),
        midx_name.buf);

  if (!packs_to_include) {
    /*
     * Only reference an existing MIDX when not filtering which
     * packs to include, since all packs and objects are copied
     * blindly from an existing MIDX if one is present.
     */
    ctx.m = lookup_multi_pack_index(the_repository, object_dir);
  }

  if (ctx.m && !midx_checksum_valid(ctx.m)) {
    warning(_("ignoring existing multi-pack-index; checksum mismatch"));
    ctx.m = NULL;
  }

  ctx.nr = 0;
  ctx.alloc = ctx.m ? ctx.m->num_packs : 16;
  ctx.info = NULL;
  ALLOC_ARRAY(ctx.info, ctx.alloc);

  if (ctx.m) {
    for (i = 0; i < ctx.m->num_packs; i++) {
      ALLOC_GROW(ctx.info, ctx.nr + 1, ctx.alloc);

      ctx.info[ctx.nr].orig_pack_int_id = i;
      ctx.info[ctx.nr].pack_name = xstrdup(ctx.m->pack_names[i]);
      ctx.info[ctx.nr].p = ctx.m->packs[i];
      ctx.info[ctx.nr].expired = 0;

      if (flags & MIDX_WRITE_REV_INDEX) {
        /*
         * If generating a reverse index, need to have
         * packed_git's loaded to compare their
         * mtimes and object count.
         */
        if (prepare_midx_pack(the_repository, ctx.m, i)) {
          error(_("could not load pack"));
          result = 1;
          goto cleanup;
        }

        if (open_pack_index(ctx.m->packs[i]))
          die(_("could not open index for %s"),
              ctx.m->packs[i]->pack_name);
        ctx.info[ctx.nr].p = ctx.m->packs[i];
      }

      ctx.nr++;
    }
  }

  ctx.pack_paths_checked = 0;
  if (flags & MIDX_PROGRESS)
    ctx.progress = start_delayed_progress(_("Adding packfiles to multi-pack-index"), 0);
  else
    ctx.progress = NULL;

  ctx.to_include = packs_to_include;

  for_each_file_in_pack_dir(object_dir, add_pack_to_midx, &ctx);
  stop_progress(&ctx.progress);

  if ((ctx.m && ctx.nr == ctx.m->num_packs) &&
      !(packs_to_include || packs_to_drop)) {
    struct bitmap_index *bitmap_git;
    int bitmap_exists;
    int want_bitmap = flags & MIDX_WRITE_BITMAP;

    bitmap_git = prepare_midx_bitmap_git(ctx.m);
    bitmap_exists = bitmap_git && bitmap_is_midx(bitmap_git);
    free_bitmap_index(bitmap_git);

    if (bitmap_exists || !want_bitmap) {
      /*
       * The correct MIDX already exists, and so does a
       * corresponding bitmap (or one wasn't requested).
       */
      if (!want_bitmap)
        clear_midx_files_ext(object_dir, ".bitmap",
                 NULL);
      goto cleanup;
    }
  }

  if (preferred_pack_name) {
    ctx.preferred_pack_idx = -1;

    for (i = 0; i < ctx.nr; i++) {
      if (!cmp_idx_or_pack_name(preferred_pack_name,
              ctx.info[i].pack_name)) {
        ctx.preferred_pack_idx = i;
        break;
      }
    }

    if (ctx.preferred_pack_idx == -1)
      warning(_("unknown preferred pack: '%s'"),
        preferred_pack_name);
  } else if (ctx.nr &&
       (flags & (MIDX_WRITE_REV_INDEX | MIDX_WRITE_BITMAP))) {
    struct packed_git *oldest = ctx.info[ctx.preferred_pack_idx].p;
    ctx.preferred_pack_idx = 0;

    if (packs_to_drop && packs_to_drop->nr)
      BUG("cannot write a MIDX bitmap during expiration");

    /*
     * set a preferred pack when writing a bitmap to ensure that
     * the pack from which the first object is selected in pseudo
     * pack-order has all of its objects selected from that pack
     * (and not another pack containing a duplicate)
     */
    for (i = 1; i < ctx.nr; i++) {
      struct packed_git *p = ctx.info[i].p;

      if (!oldest->num_objects || p->mtime < oldest->mtime) {
        oldest = p;
        ctx.preferred_pack_idx = i;
      }
    }

    if (!oldest->num_objects) {
      /*
       * If all packs are empty; unset the preferred index.
       * This is acceptable since there will be no duplicate
       * objects to resolve, so the preferred value doesn't
       * matter.
       */
      ctx.preferred_pack_idx = -1;
    }
  } else {
    /*
     * otherwise don't mark any pack as preferred to avoid
     * interfering with expiration logic below
     */
    ctx.preferred_pack_idx = -1;
  }

  if (ctx.preferred_pack_idx > -1) {
    struct packed_git *preferred = ctx.info[ctx.preferred_pack_idx].p;
    if (!preferred->num_objects) {
      error(_("cannot select preferred pack %s with no objects"),
            preferred->pack_name);
      result = 1;
      goto cleanup;
    }
  }

  ctx.entries = get_sorted_entries(ctx.m, ctx.info, ctx.nr, &ctx.entries_nr,
           ctx.preferred_pack_idx);

  ctx.large_offsets_needed = 0;
  for (i = 0; i < ctx.entries_nr; i++) {
    if (ctx.entries[i].offset > 0x7fffffff)
      ctx.num_large_offsets++;
    if (ctx.entries[i].offset > 0xffffffff)
      ctx.large_offsets_needed = 1;
  }

  QSORT(ctx.info, ctx.nr, pack_info_compare);

  if (packs_to_drop && packs_to_drop->nr) {
    int drop_index = 0;
    int missing_drops = 0;

    for (i = 0; i < ctx.nr && drop_index < packs_to_drop->nr; i++) {
      int cmp = strcmp(ctx.info[i].pack_name,
           packs_to_drop->items[drop_index].string);

      if (!cmp) {
        drop_index++;
        ctx.info[i].expired = 1;
      } else if (cmp > 0) {
        error(_("did not see pack-file %s to drop"),
              packs_to_drop->items[drop_index].string);
        drop_index++;
        missing_drops++;
        i--;
      } else {
        ctx.info[i].expired = 0;
      }
    }

    if (missing_drops) {
      result = 1;
      goto cleanup;
    }
  }

  /*
   * pack_perm stores a permutation between pack-int-ids from the
   * previous multi-pack-index to the new one we are writing:
   *
   * pack_perm[old_id] = new_id
   */
  ALLOC_ARRAY(ctx.pack_perm, ctx.nr);
  for (i = 0; i < ctx.nr; i++) {
    if (ctx.info[i].expired) {
      dropped_packs++;
      ctx.pack_perm[ctx.info[i].orig_pack_int_id] = PACK_EXPIRED;
    } else {
      ctx.pack_perm[ctx.info[i].orig_pack_int_id] = i - dropped_packs;
    }
  }

  for (i = 0; i < ctx.nr; i++) {
    if (!ctx.info[i].expired)
      pack_name_concat_len += strlen(ctx.info[i].pack_name) + 1;
  }

  /* Check that the preferred pack wasn't expired (if given). */
  if (preferred_pack_name) {
    struct pack_info *preferred = bsearch(preferred_pack_name,
                  ctx.info, ctx.nr,
                  sizeof(*ctx.info),
                  idx_or_pack_name_cmp);
    if (preferred) {
      uint32_t perm = ctx.pack_perm[preferred->orig_pack_int_id];
      if (perm == PACK_EXPIRED)
        warning(_("preferred pack '%s' is expired"),
          preferred_pack_name);
    }
  }

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

  hold_lock_file_for_update(&lk, midx_name.buf, LOCK_DIE_ON_ERROR);
  f = hashfd(get_lock_file_fd(&lk), get_lock_file_path(&lk));

  if (ctx.nr - dropped_packs == 0) {
    error(_("no pack files to index."));
    result = 1;
    goto cleanup;
  }

  if (!ctx.entries_nr) {
    if (flags & MIDX_WRITE_BITMAP)
      warning(_("refusing to write multi-pack .bitmap without any objects"));
    flags &= ~(MIDX_WRITE_REV_INDEX | MIDX_WRITE_BITMAP);
  }

  cf = init_chunkfile(f);

  add_chunk(cf, MIDX_CHUNKID_PACKNAMES, pack_name_concat_len,
      write_midx_pack_names);
  add_chunk(cf, MIDX_CHUNKID_OIDFANOUT, MIDX_CHUNK_FANOUT_SIZE,
      write_midx_oid_fanout);
  add_chunk(cf, MIDX_CHUNKID_OIDLOOKUP,
      st_mult(ctx.entries_nr, the_hash_algo->rawsz),
      write_midx_oid_lookup);
  add_chunk(cf, MIDX_CHUNKID_OBJECTOFFSETS,
      st_mult(ctx.entries_nr, MIDX_CHUNK_OFFSET_WIDTH),
      write_midx_object_offsets);

  if (ctx.large_offsets_needed)
    add_chunk(cf, MIDX_CHUNKID_LARGEOFFSETS,
      st_mult(ctx.num_large_offsets,
        MIDX_CHUNK_LARGE_OFFSET_WIDTH),
      write_midx_large_offsets);

  if (flags & (MIDX_WRITE_REV_INDEX | MIDX_WRITE_BITMAP)) {
    ctx.pack_order = midx_pack_order(&ctx);
    add_chunk(cf, MIDX_CHUNKID_REVINDEX,
        st_mult(ctx.entries_nr, sizeof(uint32_t)),
        write_midx_revindex);
  }

  write_midx_header(f, get_num_chunks(cf), ctx.nr - dropped_packs);
  write_chunkfile(cf, &ctx);

  finalize_hashfile(f, midx_hash, FSYNC_COMPONENT_PACK_METADATA,
        CSUM_FSYNC | CSUM_HASH_IN_STREAM);
  free_chunkfile(cf);

  if (flags & MIDX_WRITE_REV_INDEX &&
      git_env_bool("GIT_TEST_MIDX_WRITE_REV", 0))
    write_midx_reverse_index(midx_name.buf, midx_hash, &ctx);

  if (flags & MIDX_WRITE_BITMAP) {
    struct packing_data pdata;
    struct commit **commits;
    uint32_t commits_nr;

    if (!ctx.entries_nr)
      BUG("cannot write a bitmap without any objects");

    prepare_midx_packing_data(&pdata, &ctx);

    commits = find_commits_for_midx_bitmap(&commits_nr, refs_snapshot, &ctx);

    /*
     * The previous steps translated the information from
     * 'entries' into information suitable for constructing
     * bitmaps. We no longer need that array, so clear it to
     * reduce memory pressure.
     */
    FREE_AND_NULL(ctx.entries);
    ctx.entries_nr = 0;

    if (write_midx_bitmap(midx_name.buf, midx_hash, &pdata,
              commits, commits_nr, ctx.pack_order,
              flags) < 0) {
      error(_("could not write multi-pack bitmap"));
      result = 1;
      goto cleanup;
    }
  }
  /*
   * NOTE: Do not use ctx.entries beyond this point, since it might
   * have been freed in the previous if block.
   */

  if (ctx.m)
    close_object_store(the_repository->objects);

  if (commit_lock_file(&lk) < 0)
    die_errno(_("could not write multi-pack-index"));

  clear_midx_files_ext(object_dir, ".bitmap", midx_hash);
  clear_midx_files_ext(object_dir, ".rev", midx_hash);

cleanup:
  for (i = 0; i < ctx.nr; i++) {
    if (ctx.info[i].p) {
      close_pack(ctx.info[i].p);
      free(ctx.info[i].p);
    }
    free(ctx.info[i].pack_name);
  }

  free(ctx.info);
  free(ctx.entries);
  free(ctx.pack_perm);
  free(ctx.pack_order);
  strbuf_release(&midx_name);

  trace2_region_leave("midx", "write_midx_internal", the_repository);

  return result;
}

int write_midx_file(const char *object_dir,
        const char *preferred_pack_name,
        const char *refs_snapshot,
        unsigned flags)
{
  return write_midx_internal(object_dir, NULL, NULL, preferred_pack_name,
           refs_snapshot, flags);
}

int write_midx_file_only(const char *object_dir,
       struct string_list *packs_to_include,
       const char *preferred_pack_name,
       const char *refs_snapshot,
       unsigned flags)
{
  return write_midx_internal(object_dir, packs_to_include, NULL,
           preferred_pack_name, refs_snapshot, flags);
}

struct clear_midx_data {
  char *keep;
  const char *ext;
};

static void clear_midx_file_ext(const char *full_path, size_t full_path_len UNUSED,
        const char *file_name, void *_data)
{
  struct clear_midx_data *data = _data;

  if (!(starts_with(file_name, "multi-pack-index-") &&
        ends_with(file_name, data->ext)))
    return;
  if (data->keep && !strcmp(data->keep, file_name))
    return;

  if (unlink(full_path))
    die_errno(_("failed to remove %s"), full_path);
}

static void clear_midx_files_ext(const char *object_dir, const char *ext,
         unsigned char *keep_hash)
{
  struct clear_midx_data data;
  memset(&data, 0, sizeof(struct clear_midx_data));

  if (keep_hash)
    data.keep = xstrfmt("multi-pack-index-%s%s",
            hash_to_hex(keep_hash), ext);
  data.ext = ext;

  for_each_file_in_pack_dir(object_dir,
          clear_midx_file_ext,
          &data);

  free(data.keep);
}

void clear_midx_file(struct repository *r)
{
  struct strbuf midx = STRBUF_INIT;

  get_midx_filename(&midx, r->objects->odb->path);

  if (r->objects && r->objects->multi_pack_index) {
    close_midx(r->objects->multi_pack_index);
    r->objects->multi_pack_index = NULL;
  }

  if (remove_path(midx.buf))
    die(_("failed to clear multi-pack-index at %s"), midx.buf);

  clear_midx_files_ext(r->objects->odb->path, ".bitmap", NULL);
  clear_midx_files_ext(r->objects->odb->path, ".rev", NULL);

  strbuf_release(&midx);
}

static int verify_midx_error;

__attribute__((format (printf, 1, 2)))
static void midx_report(const char *fmt, ...)
{
  va_list ap;
  verify_midx_error = 1;
  va_start(ap, fmt);
  vfprintf(stderr, fmt, ap);
  fprintf(stderr, "\n");
  va_end(ap);
}

struct pair_pos_vs_id
{
  uint32_t pos;
  uint32_t pack_int_id;
};

static int compare_pair_pos_vs_id(const void *_a, const void *_b)
{
  struct pair_pos_vs_id *a = (struct pair_pos_vs_id *)_a;
  struct pair_pos_vs_id *b = (struct pair_pos_vs_id *)_b;

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

/*
 * Limit calls to display_progress() for performance reasons.
 * The interval here was arbitrarily chosen.
 */
#define SPARSE_PROGRESS_INTERVAL (1 << 12)
#define midx_display_sparse_progress(progress, n) \
  do { \
    uint64_t _n = (n); \
    if ((_n & (SPARSE_PROGRESS_INTERVAL - 1)) == 0) \
      display_progress(progress, _n); \
  } while (0)

int verify_midx_file(struct repository *r, const char *object_dir, unsigned flags)
{
  struct pair_pos_vs_id *pairs = NULL;
  uint32_t i;
  struct progress *progress = NULL;
  struct multi_pack_index *m = load_multi_pack_index(object_dir, 1);
  verify_midx_error = 0;

  if (!m) {
    int result = 0;
    struct stat sb;
    struct strbuf filename = STRBUF_INIT;

    get_midx_filename(&filename, object_dir);

    if (!stat(filename.buf, &sb)) {
      error(_("multi-pack-index file exists, but failed to parse"));
      result = 1;
    }
    strbuf_release(&filename);
    return result;
  }

  if (!midx_checksum_valid(m))
    midx_report(_("incorrect checksum"));

  if (flags & MIDX_PROGRESS)
    progress = start_delayed_progress(_("Looking for referenced packfiles"),
            m->num_packs);
  for (i = 0; i < m->num_packs; i++) {
    if (prepare_midx_pack(r, m, i))
      midx_report("failed to load pack in position %d", i);

    display_progress(progress, i + 1);
  }
  stop_progress(&progress);

  if (m->num_objects == 0) {
    midx_report(_("the midx contains no oid"));
    /*
     * Remaining tests assume that we have objects, so we can
     * return here.
     */
    goto cleanup;
  }

  if (flags & MIDX_PROGRESS)
    progress = start_sparse_progress(_("Verifying OID order in multi-pack-index"),
             m->num_objects - 1);
  for (i = 0; i < m->num_objects - 1; i++) {
    struct object_id oid1, oid2;

    nth_midxed_object_oid(&oid1, m, i);
    nth_midxed_object_oid(&oid2, m, i + 1);

    if (oidcmp(&oid1, &oid2) >= 0)
      midx_report(_("oid lookup out of order: oid[%d] = %s >= %s = oid[%d]"),
            i, oid_to_hex(&oid1), oid_to_hex(&oid2), i + 1);

    midx_display_sparse_progress(progress, i + 1);
  }
  stop_progress(&progress);

  /*
   * Create an array mapping each object to its packfile id.  Sort it
   * to group the objects by packfile.  Use this permutation to visit
   * each of the objects and only require 1 packfile to be open at a
   * time.
   */
  ALLOC_ARRAY(pairs, m->num_objects);
  for (i = 0; i < m->num_objects; i++) {
    pairs[i].pos = i;
    pairs[i].pack_int_id = nth_midxed_pack_int_id(m, i);
  }

  if (flags & MIDX_PROGRESS)
    progress = start_sparse_progress(_("Sorting objects by packfile"),
             m->num_objects);
  display_progress(progress, 0); /* TODO: Measure QSORT() progress */
  QSORT(pairs, m->num_objects, compare_pair_pos_vs_id);
  stop_progress(&progress);

  if (flags & MIDX_PROGRESS)
    progress = start_sparse_progress(_("Verifying object offsets"), m->num_objects);
  for (i = 0; i < m->num_objects; i++) {
    struct object_id oid;
    struct pack_entry e;
    off_t m_offset, p_offset;

    if (i > 0 && pairs[i-1].pack_int_id != pairs[i].pack_int_id &&
        m->packs[pairs[i-1].pack_int_id])
    {
      close_pack_fd(m->packs[pairs[i-1].pack_int_id]);
      close_pack_index(m->packs[pairs[i-1].pack_int_id]);
    }

    nth_midxed_object_oid(&oid, m, pairs[i].pos);

    if (!fill_midx_entry(r, &oid, &e, m)) {
      midx_report(_("failed to load pack entry for oid[%d] = %s"),
            pairs[i].pos, oid_to_hex(&oid));
      continue;
    }

    if (open_pack_index(e.p)) {
      midx_report(_("failed to load pack-index for packfile %s"),
            e.p->pack_name);
      break;
    }

    m_offset = e.offset;
    p_offset = find_pack_entry_one(oid.hash, e.p);

    if (m_offset != p_offset)
      midx_report(_("incorrect object offset for oid[%d] = %s: %"PRIx64" != %"PRIx64),
            pairs[i].pos, oid_to_hex(&oid), m_offset, p_offset);

    midx_display_sparse_progress(progress, i + 1);
  }
  stop_progress(&progress);

cleanup:
  free(pairs);
  close_midx(m);

  return verify_midx_error;
}

int expire_midx_packs(struct repository *r, const char *object_dir, unsigned flags)
{
  uint32_t i, *count, result = 0;
  struct string_list packs_to_drop = STRING_LIST_INIT_DUP;
  struct multi_pack_index *m = lookup_multi_pack_index(r, object_dir);
  struct progress *progress = NULL;

  if (!m)
    return 0;

  CALLOC_ARRAY(count, m->num_packs);

  if (flags & MIDX_PROGRESS)
    progress = start_delayed_progress(_("Counting referenced objects"),
            m->num_objects);
  for (i = 0; i < m->num_objects; i++) {
    int pack_int_id = nth_midxed_pack_int_id(m, i);
    count[pack_int_id]++;
    display_progress(progress, i + 1);
  }
  stop_progress(&progress);

  if (flags & MIDX_PROGRESS)
    progress = start_delayed_progress(_("Finding and deleting unreferenced packfiles"),
            m->num_packs);
  for (i = 0; i < m->num_packs; i++) {
    char *pack_name;
    display_progress(progress, i + 1);

    if (count[i])
      continue;

    if (prepare_midx_pack(r, m, i))
      continue;

    if (m->packs[i]->pack_keep || m->packs[i]->is_cruft)
      continue;

    pack_name = xstrdup(m->packs[i]->pack_name);
    close_pack(m->packs[i]);

    string_list_insert(&packs_to_drop, m->pack_names[i]);
    unlink_pack_path(pack_name, 0);
    free(pack_name);
  }
  stop_progress(&progress);

  free(count);

  if (packs_to_drop.nr)
    result = write_midx_internal(object_dir, NULL, &packs_to_drop, NULL, NULL, flags);

  string_list_clear(&packs_to_drop, 0);

  return result;
}

struct repack_info {
  timestamp_t mtime;
  uint32_t referenced_objects;
  uint32_t pack_int_id;
};

static int compare_by_mtime(const void *a_, const void *b_)
{
  const struct repack_info *a, *b;

  a = (const struct repack_info *)a_;
  b = (const struct repack_info *)b_;

  if (a->mtime < b->mtime)
    return -1;
  if (a->mtime > b->mtime)
    return 1;
  return 0;
}

static int fill_included_packs_all(struct repository *r,
           struct multi_pack_index *m,
           unsigned char *include_pack)
{
  uint32_t i, count = 0;
  int pack_kept_objects = 0;

  repo_config_get_bool(r, "repack.packkeptobjects", &pack_kept_objects);

  for (i = 0; i < m->num_packs; i++) {
    if (prepare_midx_pack(r, m, i))
      continue;
    if (!pack_kept_objects && m->packs[i]->pack_keep)
      continue;
    if (m->packs[i]->is_cruft)
      continue;

    include_pack[i] = 1;
    count++;
  }

  return count < 2;
}

static int fill_included_packs_batch(struct repository *r,
             struct multi_pack_index *m,
             unsigned char *include_pack,
             size_t batch_size)
{
  uint32_t i, packs_to_repack;
  size_t total_size;
  struct repack_info *pack_info;
  int pack_kept_objects = 0;

  CALLOC_ARRAY(pack_info, m->num_packs);

  repo_config_get_bool(r, "repack.packkeptobjects", &pack_kept_objects);

  for (i = 0; i < m->num_packs; i++) {
    pack_info[i].pack_int_id = i;

    if (prepare_midx_pack(r, m, i))
      continue;

    pack_info[i].mtime = m->packs[i]->mtime;
  }

  for (i = 0; i < m->num_objects; i++) {
    uint32_t pack_int_id = nth_midxed_pack_int_id(m, i);
    pack_info[pack_int_id].referenced_objects++;
  }

  QSORT(pack_info, m->num_packs, compare_by_mtime);

  total_size = 0;
  packs_to_repack = 0;
  for (i = 0; total_size < batch_size && i < m->num_packs; i++) {
    int pack_int_id = pack_info[i].pack_int_id;
    struct packed_git *p = m->packs[pack_int_id];
    size_t expected_size;

    if (!p)
      continue;
    if (!pack_kept_objects && p->pack_keep)
      continue;
    if (p->is_cruft)
      continue;
    if (open_pack_index(p) || !p->num_objects)
      continue;

    expected_size = st_mult(p->pack_size,
          pack_info[i].referenced_objects);
    expected_size /= p->num_objects;

    if (expected_size >= batch_size)
      continue;

    packs_to_repack++;
    total_size += expected_size;
    include_pack[pack_int_id] = 1;
  }

  free(pack_info);

  if (packs_to_repack < 2)
    return 1;

  return 0;
}

int midx_repack(struct repository *r, const char *object_dir, size_t batch_size, unsigned flags)
{
  int result = 0;
  uint32_t i;
  unsigned char *include_pack;
  struct child_process cmd = CHILD_PROCESS_INIT;
  FILE *cmd_in;
  struct strbuf base_name = STRBUF_INIT;
  struct multi_pack_index *m = lookup_multi_pack_index(r, object_dir);

  /*
   * When updating the default for these configuration
   * variables in builtin/repack.c, these must be adjusted
   * to match.
   */
  int delta_base_offset = 1;
  int use_delta_islands = 0;

  if (!m)
    return 0;

  CALLOC_ARRAY(include_pack, m->num_packs);

  if (batch_size) {
    if (fill_included_packs_batch(r, m, include_pack, batch_size))
      goto cleanup;
  } else if (fill_included_packs_all(r, m, include_pack))
    goto cleanup;

  repo_config_get_bool(r, "repack.usedeltabaseoffset", &delta_base_offset);
  repo_config_get_bool(r, "repack.usedeltaislands", &use_delta_islands);

  strvec_push(&cmd.args, "pack-objects");

  strbuf_addstr(&base_name, object_dir);
  strbuf_addstr(&base_name, "/pack/pack");
  strvec_push(&cmd.args, base_name.buf);

  if (delta_base_offset)
    strvec_push(&cmd.args, "--delta-base-offset");
  if (use_delta_islands)
    strvec_push(&cmd.args, "--delta-islands");

  if (flags & MIDX_PROGRESS)
    strvec_push(&cmd.args, "--progress");
  else
    strvec_push(&cmd.args, "-q");

  strbuf_release(&base_name);

  cmd.git_cmd = 1;
  cmd.in = cmd.out = -1;

  if (start_command(&cmd)) {
    error(_("could not start pack-objects"));
    result = 1;
    goto cleanup;
  }

  cmd_in = xfdopen(cmd.in, "w");

  for (i = 0; i < m->num_objects; i++) {
    struct object_id oid;
    uint32_t pack_int_id = nth_midxed_pack_int_id(m, i);

    if (!include_pack[pack_int_id])
      continue;

    nth_midxed_object_oid(&oid, m, i);
    fprintf(cmd_in, "%s\n", oid_to_hex(&oid));
  }
  fclose(cmd_in);

  if (finish_command(&cmd)) {
    error(_("could not finish pack-objects"));
    result = 1;
    goto cleanup;
  }

  result = write_midx_internal(object_dir, NULL, NULL, NULL, NULL, flags);

cleanup:
  free(include_pack);
  return result;
}

Coverage Report

Created: 2023-11-19 07:08