/src/git/read-cache.c

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/*
 * GIT - The information manager from hell
 *
 * Copyright (C) Linus Torvalds, 2005
 */
#include "cache.h"
#include "config.h"
#include "diff.h"
#include "diffcore.h"
#include "tempfile.h"
#include "lockfile.h"
#include "cache-tree.h"
#include "refs.h"
#include "dir.h"
#include "object-store.h"
#include "tree.h"
#include "commit.h"
#include "blob.h"
#include "resolve-undo.h"
#include "run-command.h"
#include "strbuf.h"
#include "varint.h"
#include "split-index.h"
#include "utf8.h"
#include "fsmonitor.h"
#include "thread-utils.h"
#include "progress.h"
#include "sparse-index.h"
#include "csum-file.h"
#include "promisor-remote.h"
#include "hook.h"

/* Mask for the name length in ce_flags in the on-disk index */

#define CE_NAMEMASK  (0x0fff)

/* Index extensions.
 *
 * The first letter should be 'A'..'Z' for extensions that are not
 * necessary for a correct operation (i.e. optimization data).
 * When new extensions are added that _needs_ to be understood in
 * order to correctly interpret the index file, pick character that
 * is outside the range, to cause the reader to abort.
 */

#define CACHE_EXT(s) ( (s[0]<<24)|(s[1]<<16)|(s[2]<<8)|(s[3]) )
#define CACHE_EXT_TREE 0x54524545  /* "TREE" */
#define CACHE_EXT_RESOLVE_UNDO 0x52455543 /* "REUC" */
#define CACHE_EXT_LINK 0x6c696e6b    /* "link" */
#define CACHE_EXT_UNTRACKED 0x554E5452    /* "UNTR" */
#define CACHE_EXT_FSMONITOR 0x46534D4E    /* "FSMN" */
#define CACHE_EXT_ENDOFINDEXENTRIES 0x454F4945  /* "EOIE" */
#define CACHE_EXT_INDEXENTRYOFFSETTABLE 0x49454F54 /* "IEOT" */
#define CACHE_EXT_SPARSE_DIRECTORIES 0x73646972 /* "sdir" */

/* changes that can be kept in $GIT_DIR/index (basically all extensions) */
#define EXTMASK (RESOLVE_UNDO_CHANGED | CACHE_TREE_CHANGED | \
     CE_ENTRY_ADDED | CE_ENTRY_REMOVED | CE_ENTRY_CHANGED | \
     SPLIT_INDEX_ORDERED | UNTRACKED_CHANGED | FSMONITOR_CHANGED)


/*
 * This is an estimate of the pathname length in the index.  We use
 * this for V4 index files to guess the un-deltafied size of the index
 * in memory because of pathname deltafication.  This is not required
 * for V2/V3 index formats because their pathnames are not compressed.
 * If the initial amount of memory set aside is not sufficient, the
 * mem pool will allocate extra memory.
 */
#define CACHE_ENTRY_PATH_LENGTH 80

enum index_search_mode {
  NO_EXPAND_SPARSE = 0,
  EXPAND_SPARSE = 1
};

static inline struct cache_entry *mem_pool__ce_alloc(struct mem_pool *mem_pool, size_t len)
{
  struct cache_entry *ce;
  ce = mem_pool_alloc(mem_pool, cache_entry_size(len));
  ce->mem_pool_allocated = 1;
  return ce;
}

static inline struct cache_entry *mem_pool__ce_calloc(struct mem_pool *mem_pool, size_t len)
{
  struct cache_entry * ce;
  ce = mem_pool_calloc(mem_pool, 1, cache_entry_size(len));
  ce->mem_pool_allocated = 1;
  return ce;
}

static struct mem_pool *find_mem_pool(struct index_state *istate)
{
  struct mem_pool **pool_ptr;

  if (istate->split_index && istate->split_index->base)
    pool_ptr = &istate->split_index->base->ce_mem_pool;
  else
    pool_ptr = &istate->ce_mem_pool;

  if (!*pool_ptr) {
    *pool_ptr = xmalloc(sizeof(**pool_ptr));
    mem_pool_init(*pool_ptr, 0);
  }

  return *pool_ptr;
}

static const char *alternate_index_output;

static void set_index_entry(struct index_state *istate, int nr, struct cache_entry *ce)
{
  if (S_ISSPARSEDIR(ce->ce_mode))
    istate->sparse_index = INDEX_COLLAPSED;

  istate->cache[nr] = ce;
  add_name_hash(istate, ce);
}

static void replace_index_entry(struct index_state *istate, int nr, struct cache_entry *ce)
{
  struct cache_entry *old = istate->cache[nr];

  replace_index_entry_in_base(istate, old, ce);
  remove_name_hash(istate, old);
  discard_cache_entry(old);
  ce->ce_flags &= ~CE_HASHED;
  set_index_entry(istate, nr, ce);
  ce->ce_flags |= CE_UPDATE_IN_BASE;
  mark_fsmonitor_invalid(istate, ce);
  istate->cache_changed |= CE_ENTRY_CHANGED;
}

void rename_index_entry_at(struct index_state *istate, int nr, const char *new_name)
{
  struct cache_entry *old_entry = istate->cache[nr], *new_entry, *refreshed;
  int namelen = strlen(new_name);

  new_entry = make_empty_cache_entry(istate, namelen);
  copy_cache_entry(new_entry, old_entry);
  new_entry->ce_flags &= ~CE_HASHED;
  new_entry->ce_namelen = namelen;
  new_entry->index = 0;
  memcpy(new_entry->name, new_name, namelen + 1);

  cache_tree_invalidate_path(istate, old_entry->name);
  untracked_cache_remove_from_index(istate, old_entry->name);
  remove_index_entry_at(istate, nr);

  /*
   * Refresh the new index entry. Using 'refresh_cache_entry' ensures
   * we only update stat info if the entry is otherwise up-to-date (i.e.,
   * the contents/mode haven't changed). This ensures that we reflect the
   * 'ctime' of the rename in the index without (incorrectly) updating
   * the cached stat info to reflect unstaged changes on disk.
   */
  refreshed = refresh_cache_entry(istate, new_entry, CE_MATCH_REFRESH);
  if (refreshed && refreshed != new_entry) {
    add_index_entry(istate, refreshed, ADD_CACHE_OK_TO_ADD|ADD_CACHE_OK_TO_REPLACE);
    discard_cache_entry(new_entry);
  } else
    add_index_entry(istate, new_entry, ADD_CACHE_OK_TO_ADD|ADD_CACHE_OK_TO_REPLACE);
}

void fill_stat_data(struct stat_data *sd, struct stat *st)
{
  sd->sd_ctime.sec = (unsigned int)st->st_ctime;
  sd->sd_mtime.sec = (unsigned int)st->st_mtime;
  sd->sd_ctime.nsec = ST_CTIME_NSEC(*st);
  sd->sd_mtime.nsec = ST_MTIME_NSEC(*st);
  sd->sd_dev = st->st_dev;
  sd->sd_ino = st->st_ino;
  sd->sd_uid = st->st_uid;
  sd->sd_gid = st->st_gid;
  sd->sd_size = st->st_size;
}

int match_stat_data(const struct stat_data *sd, struct stat *st)
{
  int changed = 0;

  if (sd->sd_mtime.sec != (unsigned int)st->st_mtime)
    changed |= MTIME_CHANGED;
  if (trust_ctime && check_stat &&
      sd->sd_ctime.sec != (unsigned int)st->st_ctime)
    changed |= CTIME_CHANGED;

#ifdef USE_NSEC
  if (check_stat && sd->sd_mtime.nsec != ST_MTIME_NSEC(*st))
    changed |= MTIME_CHANGED;
  if (trust_ctime && check_stat &&
      sd->sd_ctime.nsec != ST_CTIME_NSEC(*st))
    changed |= CTIME_CHANGED;
#endif

  if (check_stat) {
    if (sd->sd_uid != (unsigned int) st->st_uid ||
      sd->sd_gid != (unsigned int) st->st_gid)
      changed |= OWNER_CHANGED;
    if (sd->sd_ino != (unsigned int) st->st_ino)
      changed |= INODE_CHANGED;
  }

#ifdef USE_STDEV
  /*
   * st_dev breaks on network filesystems where different
   * clients will have different views of what "device"
   * the filesystem is on
   */
  if (check_stat && sd->sd_dev != (unsigned int) st->st_dev)
      changed |= INODE_CHANGED;
#endif

  if (sd->sd_size != (unsigned int) st->st_size)
    changed |= DATA_CHANGED;

  return changed;
}

/*
 * This only updates the "non-critical" parts of the directory
 * cache, ie the parts that aren't tracked by GIT, and only used
 * to validate the cache.
 */
void fill_stat_cache_info(struct index_state *istate, struct cache_entry *ce, struct stat *st)
{
  fill_stat_data(&ce->ce_stat_data, st);

  if (assume_unchanged)
    ce->ce_flags |= CE_VALID;

  if (S_ISREG(st->st_mode)) {
    ce_mark_uptodate(ce);
    mark_fsmonitor_valid(istate, ce);
  }
}

static int ce_compare_data(struct index_state *istate,
         const struct cache_entry *ce,
         struct stat *st)
{
  int match = -1;
  int fd = git_open_cloexec(ce->name, O_RDONLY);

  if (fd >= 0) {
    struct object_id oid;
    if (!index_fd(istate, &oid, fd, st, OBJ_BLOB, ce->name, 0))
      match = !oideq(&oid, &ce->oid);
    /* index_fd() closed the file descriptor already */
  }
  return match;
}

static int ce_compare_link(const struct cache_entry *ce, size_t expected_size)
{
  int match = -1;
  void *buffer;
  unsigned long size;
  enum object_type type;
  struct strbuf sb = STRBUF_INIT;

  if (strbuf_readlink(&sb, ce->name, expected_size))
    return -1;

  buffer = read_object_file(&ce->oid, &type, &size);
  if (buffer) {
    if (size == sb.len)
      match = memcmp(buffer, sb.buf, size);
    free(buffer);
  }
  strbuf_release(&sb);
  return match;
}

static int ce_compare_gitlink(const struct cache_entry *ce)
{
  struct object_id oid;

  /*
   * We don't actually require that the .git directory
   * under GITLINK directory be a valid git directory. It
   * might even be missing (in case nobody populated that
   * sub-project).
   *
   * If so, we consider it always to match.
   */
  if (resolve_gitlink_ref(ce->name, "HEAD", &oid) < 0)
    return 0;
  return !oideq(&oid, &ce->oid);
}

static int ce_modified_check_fs(struct index_state *istate,
        const struct cache_entry *ce,
        struct stat *st)
{
  switch (st->st_mode & S_IFMT) {
  case S_IFREG:
    if (ce_compare_data(istate, ce, st))
      return DATA_CHANGED;
    break;
  case S_IFLNK:
    if (ce_compare_link(ce, xsize_t(st->st_size)))
      return DATA_CHANGED;
    break;
  case S_IFDIR:
    if (S_ISGITLINK(ce->ce_mode))
      return ce_compare_gitlink(ce) ? DATA_CHANGED : 0;
    /* else fallthrough */
  default:
    return TYPE_CHANGED;
  }
  return 0;
}

static int ce_match_stat_basic(const struct cache_entry *ce, struct stat *st)
{
  unsigned int changed = 0;

  if (ce->ce_flags & CE_REMOVE)
    return MODE_CHANGED | DATA_CHANGED | TYPE_CHANGED;

  switch (ce->ce_mode & S_IFMT) {
  case S_IFREG:
    changed |= !S_ISREG(st->st_mode) ? TYPE_CHANGED : 0;
    /* We consider only the owner x bit to be relevant for
     * "mode changes"
     */
    if (trust_executable_bit &&
        (0100 & (ce->ce_mode ^ st->st_mode)))
      changed |= MODE_CHANGED;
    break;
  case S_IFLNK:
    if (!S_ISLNK(st->st_mode) &&
        (has_symlinks || !S_ISREG(st->st_mode)))
      changed |= TYPE_CHANGED;
    break;
  case S_IFGITLINK:
    /* We ignore most of the st_xxx fields for gitlinks */
    if (!S_ISDIR(st->st_mode))
      changed |= TYPE_CHANGED;
    else if (ce_compare_gitlink(ce))
      changed |= DATA_CHANGED;
    return changed;
  default:
    BUG("unsupported ce_mode: %o", ce->ce_mode);
  }

  changed |= match_stat_data(&ce->ce_stat_data, st);

  /* Racily smudged entry? */
  if (!ce->ce_stat_data.sd_size) {
    if (!is_empty_blob_sha1(ce->oid.hash))
      changed |= DATA_CHANGED;
  }

  return changed;
}

static int is_racy_stat(const struct index_state *istate,
      const struct stat_data *sd)
{
  return (istate->timestamp.sec &&
#ifdef USE_NSEC
     /* nanosecond timestamped files can also be racy! */
    (istate->timestamp.sec < sd->sd_mtime.sec ||
     (istate->timestamp.sec == sd->sd_mtime.sec &&
      istate->timestamp.nsec <= sd->sd_mtime.nsec))
#else
    istate->timestamp.sec <= sd->sd_mtime.sec
#endif
    );
}

int is_racy_timestamp(const struct index_state *istate,
           const struct cache_entry *ce)
{
  return (!S_ISGITLINK(ce->ce_mode) &&
    is_racy_stat(istate, &ce->ce_stat_data));
}

int match_stat_data_racy(const struct index_state *istate,
       const struct stat_data *sd, struct stat *st)
{
  if (is_racy_stat(istate, sd))
    return MTIME_CHANGED;
  return match_stat_data(sd, st);
}

int ie_match_stat(struct index_state *istate,
      const struct cache_entry *ce, struct stat *st,
      unsigned int options)
{
  unsigned int changed;
  int ignore_valid = options & CE_MATCH_IGNORE_VALID;
  int ignore_skip_worktree = options & CE_MATCH_IGNORE_SKIP_WORKTREE;
  int assume_racy_is_modified = options & CE_MATCH_RACY_IS_DIRTY;
  int ignore_fsmonitor = options & CE_MATCH_IGNORE_FSMONITOR;

  if (!ignore_fsmonitor)
    refresh_fsmonitor(istate);
  /*
   * If it's marked as always valid in the index, it's
   * valid whatever the checked-out copy says.
   *
   * skip-worktree has the same effect with higher precedence
   */
  if (!ignore_skip_worktree && ce_skip_worktree(ce))
    return 0;
  if (!ignore_valid && (ce->ce_flags & CE_VALID))
    return 0;
  if (!ignore_fsmonitor && (ce->ce_flags & CE_FSMONITOR_VALID))
    return 0;

  /*
   * Intent-to-add entries have not been added, so the index entry
   * by definition never matches what is in the work tree until it
   * actually gets added.
   */
  if (ce_intent_to_add(ce))
    return DATA_CHANGED | TYPE_CHANGED | MODE_CHANGED;

  changed = ce_match_stat_basic(ce, st);

  /*
   * Within 1 second of this sequence:
   *  echo xyzzy >file && git-update-index --add file
   * running this command:
   *  echo frotz >file
   * would give a falsely clean cache entry.  The mtime and
   * length match the cache, and other stat fields do not change.
   *
   * We could detect this at update-index time (the cache entry
   * being registered/updated records the same time as "now")
   * and delay the return from git-update-index, but that would
   * effectively mean we can make at most one commit per second,
   * which is not acceptable.  Instead, we check cache entries
   * whose mtime are the same as the index file timestamp more
   * carefully than others.
   */
  if (!changed && is_racy_timestamp(istate, ce)) {
    if (assume_racy_is_modified)
      changed |= DATA_CHANGED;
    else
      changed |= ce_modified_check_fs(istate, ce, st);
  }

  return changed;
}

int ie_modified(struct index_state *istate,
    const struct cache_entry *ce,
    struct stat *st, unsigned int options)
{
  int changed, changed_fs;

  changed = ie_match_stat(istate, ce, st, options);
  if (!changed)
    return 0;
  /*
   * If the mode or type has changed, there's no point in trying
   * to refresh the entry - it's not going to match
   */
  if (changed & (MODE_CHANGED | TYPE_CHANGED))
    return changed;

  /*
   * Immediately after read-tree or update-index --cacheinfo,
   * the length field is zero, as we have never even read the
   * lstat(2) information once, and we cannot trust DATA_CHANGED
   * returned by ie_match_stat() which in turn was returned by
   * ce_match_stat_basic() to signal that the filesize of the
   * blob changed.  We have to actually go to the filesystem to
   * see if the contents match, and if so, should answer "unchanged".
   *
   * The logic does not apply to gitlinks, as ce_match_stat_basic()
   * already has checked the actual HEAD from the filesystem in the
   * subproject.  If ie_match_stat() already said it is different,
   * then we know it is.
   */
  if ((changed & DATA_CHANGED) &&
      (S_ISGITLINK(ce->ce_mode) || ce->ce_stat_data.sd_size != 0))
    return changed;

  changed_fs = ce_modified_check_fs(istate, ce, st);
  if (changed_fs)
    return changed | changed_fs;
  return 0;
}

int base_name_compare(const char *name1, size_t len1, int mode1,
          const char *name2, size_t len2, int mode2)
{
  unsigned char c1, c2;
  size_t len = len1 < len2 ? len1 : len2;
  int cmp;

  cmp = memcmp(name1, name2, len);
  if (cmp)
    return cmp;
  c1 = name1[len];
  c2 = name2[len];
  if (!c1 && S_ISDIR(mode1))
    c1 = '/';
  if (!c2 && S_ISDIR(mode2))
    c2 = '/';
  return (c1 < c2) ? -1 : (c1 > c2) ? 1 : 0;
}

/*
 * df_name_compare() is identical to base_name_compare(), except it
 * compares conflicting directory/file entries as equal. Note that
 * while a directory name compares as equal to a regular file, they
 * then individually compare _differently_ to a filename that has
 * a dot after the basename (because '\0' < '.' < '/').
 *
 * This is used by routines that want to traverse the git namespace
 * but then handle conflicting entries together when possible.
 */
int df_name_compare(const char *name1, size_t len1, int mode1,
        const char *name2, size_t len2, int mode2)
{
  unsigned char c1, c2;
  size_t len = len1 < len2 ? len1 : len2;
  int cmp;

  cmp = memcmp(name1, name2, len);
  if (cmp)
    return cmp;
  /* Directories and files compare equal (same length, same name) */
  if (len1 == len2)
    return 0;
  c1 = name1[len];
  if (!c1 && S_ISDIR(mode1))
    c1 = '/';
  c2 = name2[len];
  if (!c2 && S_ISDIR(mode2))
    c2 = '/';
  if (c1 == '/' && !c2)
    return 0;
  if (c2 == '/' && !c1)
    return 0;
  return c1 - c2;
}

int name_compare(const char *name1, size_t len1, const char *name2, size_t len2)
{
  size_t min_len = (len1 < len2) ? len1 : len2;
  int cmp = memcmp(name1, name2, min_len);
  if (cmp)
    return cmp;
  if (len1 < len2)
    return -1;
  if (len1 > len2)
    return 1;
  return 0;
}

int cache_name_stage_compare(const char *name1, int len1, int stage1, const char *name2, int len2, int stage2)
{
  int cmp;

  cmp = name_compare(name1, len1, name2, len2);
  if (cmp)
    return cmp;

  if (stage1 < stage2)
    return -1;
  if (stage1 > stage2)
    return 1;
  return 0;
}

static int index_name_stage_pos(struct index_state *istate,
        const char *name, int namelen,
        int stage,
        enum index_search_mode search_mode)
{
  int first, last;

  first = 0;
  last = istate->cache_nr;
  while (last > first) {
    int next = first + ((last - first) >> 1);
    struct cache_entry *ce = istate->cache[next];
    int cmp = cache_name_stage_compare(name, namelen, stage, ce->name, ce_namelen(ce), ce_stage(ce));
    if (!cmp)
      return next;
    if (cmp < 0) {
      last = next;
      continue;
    }
    first = next+1;
  }

  if (search_mode == EXPAND_SPARSE && istate->sparse_index &&
      first > 0) {
    /* Note: first <= istate->cache_nr */
    struct cache_entry *ce = istate->cache[first - 1];

    /*
     * If we are in a sparse-index _and_ the entry before the
     * insertion position is a sparse-directory entry that is
     * an ancestor of 'name', then we need to expand the index
     * and search again. This will only trigger once, because
     * thereafter the index is fully expanded.
     */
    if (S_ISSPARSEDIR(ce->ce_mode) &&
        ce_namelen(ce) < namelen &&
        !strncmp(name, ce->name, ce_namelen(ce))) {
      ensure_full_index(istate);
      return index_name_stage_pos(istate, name, namelen, stage, search_mode);
    }
  }

  return -first-1;
}

int index_name_pos(struct index_state *istate, const char *name, int namelen)
{
  return index_name_stage_pos(istate, name, namelen, 0, EXPAND_SPARSE);
}

int index_name_pos_sparse(struct index_state *istate, const char *name, int namelen)
{
  return index_name_stage_pos(istate, name, namelen, 0, NO_EXPAND_SPARSE);
}

int index_entry_exists(struct index_state *istate, const char *name, int namelen)
{
  return index_name_stage_pos(istate, name, namelen, 0, NO_EXPAND_SPARSE) >= 0;
}

int remove_index_entry_at(struct index_state *istate, int pos)
{
  struct cache_entry *ce = istate->cache[pos];

  record_resolve_undo(istate, ce);
  remove_name_hash(istate, ce);
  save_or_free_index_entry(istate, ce);
  istate->cache_changed |= CE_ENTRY_REMOVED;
  istate->cache_nr--;
  if (pos >= istate->cache_nr)
    return 0;
  MOVE_ARRAY(istate->cache + pos, istate->cache + pos + 1,
       istate->cache_nr - pos);
  return 1;
}

/*
 * Remove all cache entries marked for removal, that is where
 * CE_REMOVE is set in ce_flags.  This is much more effective than
 * calling remove_index_entry_at() for each entry to be removed.
 */
void remove_marked_cache_entries(struct index_state *istate, int invalidate)
{
  struct cache_entry **ce_array = istate->cache;
  unsigned int i, j;

  for (i = j = 0; i < istate->cache_nr; i++) {
    if (ce_array[i]->ce_flags & CE_REMOVE) {
      if (invalidate) {
        cache_tree_invalidate_path(istate,
                 ce_array[i]->name);
        untracked_cache_remove_from_index(istate,
                  ce_array[i]->name);
      }
      remove_name_hash(istate, ce_array[i]);
      save_or_free_index_entry(istate, ce_array[i]);
    }
    else
      ce_array[j++] = ce_array[i];
  }
  if (j == istate->cache_nr)
    return;
  istate->cache_changed |= CE_ENTRY_REMOVED;
  istate->cache_nr = j;
}

int remove_file_from_index(struct index_state *istate, const char *path)
{
  int pos = index_name_pos(istate, path, strlen(path));
  if (pos < 0)
    pos = -pos-1;
  cache_tree_invalidate_path(istate, path);
  untracked_cache_remove_from_index(istate, path);
  while (pos < istate->cache_nr && !strcmp(istate->cache[pos]->name, path))
    remove_index_entry_at(istate, pos);
  return 0;
}

static int compare_name(struct cache_entry *ce, const char *path, int namelen)
{
  return namelen != ce_namelen(ce) || memcmp(path, ce->name, namelen);
}

static int index_name_pos_also_unmerged(struct index_state *istate,
  const char *path, int namelen)
{
  int pos = index_name_pos(istate, path, namelen);
  struct cache_entry *ce;

  if (pos >= 0)
    return pos;

  /* maybe unmerged? */
  pos = -1 - pos;
  if (pos >= istate->cache_nr ||
      compare_name((ce = istate->cache[pos]), path, namelen))
    return -1;

  /* order of preference: stage 2, 1, 3 */
  if (ce_stage(ce) == 1 && pos + 1 < istate->cache_nr &&
      ce_stage((ce = istate->cache[pos + 1])) == 2 &&
      !compare_name(ce, path, namelen))
    pos++;
  return pos;
}

static int different_name(struct cache_entry *ce, struct cache_entry *alias)
{
  int len = ce_namelen(ce);
  return ce_namelen(alias) != len || memcmp(ce->name, alias->name, len);
}

/*
 * If we add a filename that aliases in the cache, we will use the
 * name that we already have - but we don't want to update the same
 * alias twice, because that implies that there were actually two
 * different files with aliasing names!
 *
 * So we use the CE_ADDED flag to verify that the alias was an old
 * one before we accept it as
 */
static struct cache_entry *create_alias_ce(struct index_state *istate,
             struct cache_entry *ce,
             struct cache_entry *alias)
{
  int len;
  struct cache_entry *new_entry;

  if (alias->ce_flags & CE_ADDED)
    die(_("will not add file alias '%s' ('%s' already exists in index)"),
        ce->name, alias->name);

  /* Ok, create the new entry using the name of the existing alias */
  len = ce_namelen(alias);
  new_entry = make_empty_cache_entry(istate, len);
  memcpy(new_entry->name, alias->name, len);
  copy_cache_entry(new_entry, ce);
  save_or_free_index_entry(istate, ce);
  return new_entry;
}

void set_object_name_for_intent_to_add_entry(struct cache_entry *ce)
{
  struct object_id oid;
  if (write_object_file("", 0, OBJ_BLOB, &oid))
    die(_("cannot create an empty blob in the object database"));
  oidcpy(&ce->oid, &oid);
}

int add_to_index(struct index_state *istate, const char *path, struct stat *st, int flags)
{
  int namelen, was_same;
  mode_t st_mode = st->st_mode;
  struct cache_entry *ce, *alias = NULL;
  unsigned ce_option = CE_MATCH_IGNORE_VALID|CE_MATCH_IGNORE_SKIP_WORKTREE|CE_MATCH_RACY_IS_DIRTY;
  int verbose = flags & (ADD_CACHE_VERBOSE | ADD_CACHE_PRETEND);
  int pretend = flags & ADD_CACHE_PRETEND;
  int intent_only = flags & ADD_CACHE_INTENT;
  int add_option = (ADD_CACHE_OK_TO_ADD|ADD_CACHE_OK_TO_REPLACE|
        (intent_only ? ADD_CACHE_NEW_ONLY : 0));
  unsigned hash_flags = pretend ? 0 : HASH_WRITE_OBJECT;
  struct object_id oid;

  if (flags & ADD_CACHE_RENORMALIZE)
    hash_flags |= HASH_RENORMALIZE;

  if (!S_ISREG(st_mode) && !S_ISLNK(st_mode) && !S_ISDIR(st_mode))
    return error(_("%s: can only add regular files, symbolic links or git-directories"), path);

  namelen = strlen(path);
  if (S_ISDIR(st_mode)) {
    if (resolve_gitlink_ref(path, "HEAD", &oid) < 0)
      return error(_("'%s' does not have a commit checked out"), path);
    while (namelen && path[namelen-1] == '/')
      namelen--;
  }
  ce = make_empty_cache_entry(istate, namelen);
  memcpy(ce->name, path, namelen);
  ce->ce_namelen = namelen;
  if (!intent_only)
    fill_stat_cache_info(istate, ce, st);
  else
    ce->ce_flags |= CE_INTENT_TO_ADD;


  if (trust_executable_bit && has_symlinks) {
    ce->ce_mode = create_ce_mode(st_mode);
  } else {
    /* If there is an existing entry, pick the mode bits and type
     * from it, otherwise assume unexecutable regular file.
     */
    struct cache_entry *ent;
    int pos = index_name_pos_also_unmerged(istate, path, namelen);

    ent = (0 <= pos) ? istate->cache[pos] : NULL;
    ce->ce_mode = ce_mode_from_stat(ent, st_mode);
  }

  /* When core.ignorecase=true, determine if a directory of the same name but differing
   * case already exists within the Git repository.  If it does, ensure the directory
   * case of the file being added to the repository matches (is folded into) the existing
   * entry's directory case.
   */
  if (ignore_case) {
    adjust_dirname_case(istate, ce->name);
  }
  if (!(flags & ADD_CACHE_RENORMALIZE)) {
    alias = index_file_exists(istate, ce->name,
            ce_namelen(ce), ignore_case);
    if (alias &&
        !ce_stage(alias) &&
        !ie_match_stat(istate, alias, st, ce_option)) {
      /* Nothing changed, really */
      if (!S_ISGITLINK(alias->ce_mode))
        ce_mark_uptodate(alias);
      alias->ce_flags |= CE_ADDED;

      discard_cache_entry(ce);
      return 0;
    }
  }
  if (!intent_only) {
    if (index_path(istate, &ce->oid, path, st, hash_flags)) {
      discard_cache_entry(ce);
      return error(_("unable to index file '%s'"), path);
    }
  } else
    set_object_name_for_intent_to_add_entry(ce);

  if (ignore_case && alias && different_name(ce, alias))
    ce = create_alias_ce(istate, ce, alias);
  ce->ce_flags |= CE_ADDED;

  /* It was suspected to be racily clean, but it turns out to be Ok */
  was_same = (alias &&
        !ce_stage(alias) &&
        oideq(&alias->oid, &ce->oid) &&
        ce->ce_mode == alias->ce_mode);

  if (pretend)
    discard_cache_entry(ce);
  else if (add_index_entry(istate, ce, add_option)) {
    discard_cache_entry(ce);
    return error(_("unable to add '%s' to index"), path);
  }
  if (verbose && !was_same)
    printf("add '%s'\n", path);
  return 0;
}

int add_file_to_index(struct index_state *istate, const char *path, int flags)
{
  struct stat st;
  if (lstat(path, &st))
    die_errno(_("unable to stat '%s'"), path);
  return add_to_index(istate, path, &st, flags);
}

struct cache_entry *make_empty_cache_entry(struct index_state *istate, size_t len)
{
  return mem_pool__ce_calloc(find_mem_pool(istate), len);
}

struct cache_entry *make_empty_transient_cache_entry(size_t len,
                 struct mem_pool *ce_mem_pool)
{
  if (ce_mem_pool)
    return mem_pool__ce_calloc(ce_mem_pool, len);
  return xcalloc(1, cache_entry_size(len));
}

enum verify_path_result {
  PATH_OK,
  PATH_INVALID,
  PATH_DIR_WITH_SEP,
};

static enum verify_path_result verify_path_internal(const char *, unsigned);

int verify_path(const char *path, unsigned mode)
{
  return verify_path_internal(path, mode) == PATH_OK;
}

struct cache_entry *make_cache_entry(struct index_state *istate,
             unsigned int mode,
             const struct object_id *oid,
             const char *path,
             int stage,
             unsigned int refresh_options)
{
  struct cache_entry *ce, *ret;
  int len;

  if (verify_path_internal(path, mode) == PATH_INVALID) {
    error(_("invalid path '%s'"), path);
    return NULL;
  }

  len = strlen(path);
  ce = make_empty_cache_entry(istate, len);

  oidcpy(&ce->oid, oid);
  memcpy(ce->name, path, len);
  ce->ce_flags = create_ce_flags(stage);
  ce->ce_namelen = len;
  ce->ce_mode = create_ce_mode(mode);

  ret = refresh_cache_entry(istate, ce, refresh_options);
  if (ret != ce)
    discard_cache_entry(ce);
  return ret;
}

struct cache_entry *make_transient_cache_entry(unsigned int mode,
                 const struct object_id *oid,
                 const char *path,
                 int stage,
                 struct mem_pool *ce_mem_pool)
{
  struct cache_entry *ce;
  int len;

  if (!verify_path(path, mode)) {
    error(_("invalid path '%s'"), path);
    return NULL;
  }

  len = strlen(path);
  ce = make_empty_transient_cache_entry(len, ce_mem_pool);

  oidcpy(&ce->oid, oid);
  memcpy(ce->name, path, len);
  ce->ce_flags = create_ce_flags(stage);
  ce->ce_namelen = len;
  ce->ce_mode = create_ce_mode(mode);

  return ce;
}

/*
 * Chmod an index entry with either +x or -x.
 *
 * Returns -1 if the chmod for the particular cache entry failed (if it's
 * not a regular file), -2 if an invalid flip argument is passed in, 0
 * otherwise.
 */
int chmod_index_entry(struct index_state *istate, struct cache_entry *ce,
          char flip)
{
  if (!S_ISREG(ce->ce_mode))
    return -1;
  switch (flip) {
  case '+':
    ce->ce_mode |= 0111;
    break;
  case '-':
    ce->ce_mode &= ~0111;
    break;
  default:
    return -2;
  }
  cache_tree_invalidate_path(istate, ce->name);
  ce->ce_flags |= CE_UPDATE_IN_BASE;
  mark_fsmonitor_invalid(istate, ce);
  istate->cache_changed |= CE_ENTRY_CHANGED;

  return 0;
}

int ce_same_name(const struct cache_entry *a, const struct cache_entry *b)
{
  int len = ce_namelen(a);
  return ce_namelen(b) == len && !memcmp(a->name, b->name, len);
}

/*
 * We fundamentally don't like some paths: we don't want
 * dot or dot-dot anywhere, and for obvious reasons don't
 * want to recurse into ".git" either.
 *
 * Also, we don't want double slashes or slashes at the
 * end that can make pathnames ambiguous.
 */
static int verify_dotfile(const char *rest, unsigned mode)
{
  /*
   * The first character was '.', but that
   * has already been discarded, we now test
   * the rest.
   */

  /* "." is not allowed */
  if (*rest == '\0' || is_dir_sep(*rest))
    return 0;

  switch (*rest) {
  /*
   * ".git" followed by NUL or slash is bad. Note that we match
   * case-insensitively here, even if ignore_case is not set.
   * This outlaws ".GIT" everywhere out of an abundance of caution,
   * since there's really no good reason to allow it.
   *
   * Once we've seen ".git", we can also find ".gitmodules", etc (also
   * case-insensitively).
   */
  case 'g':
  case 'G':
    if (rest[1] != 'i' && rest[1] != 'I')
      break;
    if (rest[2] != 't' && rest[2] != 'T')
      break;
    if (rest[3] == '\0' || is_dir_sep(rest[3]))
      return 0;
    if (S_ISLNK(mode)) {
      rest += 3;
      if (skip_iprefix(rest, "modules", &rest) &&
          (*rest == '\0' || is_dir_sep(*rest)))
        return 0;
    }
    break;
  case '.':
    if (rest[1] == '\0' || is_dir_sep(rest[1]))
      return 0;
  }
  return 1;
}

static enum verify_path_result verify_path_internal(const char *path,
                unsigned mode)
{
  char c = 0;

  if (has_dos_drive_prefix(path))
    return PATH_INVALID;

  if (!is_valid_path(path))
    return PATH_INVALID;

  goto inside;
  for (;;) {
    if (!c)
      return PATH_OK;
    if (is_dir_sep(c)) {
inside:
      if (protect_hfs) {

        if (is_hfs_dotgit(path))
          return PATH_INVALID;
        if (S_ISLNK(mode)) {
          if (is_hfs_dotgitmodules(path))
            return PATH_INVALID;
        }
      }
      if (protect_ntfs) {
#if defined GIT_WINDOWS_NATIVE || defined __CYGWIN__
        if (c == '\\')
          return PATH_INVALID;
#endif
        if (is_ntfs_dotgit(path))
          return PATH_INVALID;
        if (S_ISLNK(mode)) {
          if (is_ntfs_dotgitmodules(path))
            return PATH_INVALID;
        }
      }

      c = *path++;
      if ((c == '.' && !verify_dotfile(path, mode)) ||
          is_dir_sep(c))
        return PATH_INVALID;
      /*
       * allow terminating directory separators for
       * sparse directory entries.
       */
      if (c == '\0')
        return S_ISDIR(mode) ? PATH_DIR_WITH_SEP :
                   PATH_INVALID;
    } else if (c == '\\' && protect_ntfs) {
      if (is_ntfs_dotgit(path))
        return PATH_INVALID;
      if (S_ISLNK(mode)) {
        if (is_ntfs_dotgitmodules(path))
          return PATH_INVALID;
      }
    }

    c = *path++;
  }
}

/*
 * Do we have another file that has the beginning components being a
 * proper superset of the name we're trying to add?
 */
static int has_file_name(struct index_state *istate,
       const struct cache_entry *ce, int pos, int ok_to_replace)
{
  int retval = 0;
  int len = ce_namelen(ce);
  int stage = ce_stage(ce);
  const char *name = ce->name;

  while (pos < istate->cache_nr) {
    struct cache_entry *p = istate->cache[pos++];

    if (len >= ce_namelen(p))
      break;
    if (memcmp(name, p->name, len))
      break;
    if (ce_stage(p) != stage)
      continue;
    if (p->name[len] != '/')
      continue;
    if (p->ce_flags & CE_REMOVE)
      continue;
    retval = -1;
    if (!ok_to_replace)
      break;
    remove_index_entry_at(istate, --pos);
  }
  return retval;
}


/*
 * Like strcmp(), but also return the offset of the first change.
 * If strings are equal, return the length.
 */
int strcmp_offset(const char *s1, const char *s2, size_t *first_change)
{
  size_t k;

  if (!first_change)
    return strcmp(s1, s2);

  for (k = 0; s1[k] == s2[k]; k++)
    if (s1[k] == '\0')
      break;

  *first_change = k;
  return (unsigned char)s1[k] - (unsigned char)s2[k];
}

/*
 * Do we have another file with a pathname that is a proper
 * subset of the name we're trying to add?
 *
 * That is, is there another file in the index with a path
 * that matches a sub-directory in the given entry?
 */
static int has_dir_name(struct index_state *istate,
      const struct cache_entry *ce, int pos, int ok_to_replace)
{
  int retval = 0;
  int stage = ce_stage(ce);
  const char *name = ce->name;
  const char *slash = name + ce_namelen(ce);
  size_t len_eq_last;
  int cmp_last = 0;

  /*
   * We are frequently called during an iteration on a sorted
   * list of pathnames and while building a new index.  Therefore,
   * there is a high probability that this entry will eventually
   * be appended to the index, rather than inserted in the middle.
   * If we can confirm that, we can avoid binary searches on the
   * components of the pathname.
   *
   * Compare the entry's full path with the last path in the index.
   */
  if (istate->cache_nr > 0) {
    cmp_last = strcmp_offset(name,
      istate->cache[istate->cache_nr - 1]->name,
      &len_eq_last);
    if (cmp_last > 0) {
      if (len_eq_last == 0) {
        /*
         * The entry sorts AFTER the last one in the
         * index and their paths have no common prefix,
         * so there cannot be a F/D conflict.
         */
        return retval;
      } else {
        /*
         * The entry sorts AFTER the last one in the
         * index, but has a common prefix.  Fall through
         * to the loop below to disect the entry's path
         * and see where the difference is.
         */
      }
    } else if (cmp_last == 0) {
      /*
       * The entry exactly matches the last one in the
       * index, but because of multiple stage and CE_REMOVE
       * items, we fall through and let the regular search
       * code handle it.
       */
    }
  }

  for (;;) {
    size_t len;

    for (;;) {
      if (*--slash == '/')
        break;
      if (slash <= ce->name)
        return retval;
    }
    len = slash - name;

    if (cmp_last > 0) {
      /*
       * (len + 1) is a directory boundary (including
       * the trailing slash).  And since the loop is
       * decrementing "slash", the first iteration is
       * the longest directory prefix; subsequent
       * iterations consider parent directories.
       */

      if (len + 1 <= len_eq_last) {
        /*
         * The directory prefix (including the trailing
         * slash) also appears as a prefix in the last
         * entry, so the remainder cannot collide (because
         * strcmp said the whole path was greater).
         *
         * EQ: last: xxx/A
         *     this: xxx/B
         *
         * LT: last: xxx/file_A
         *     this: xxx/file_B
         */
        return retval;
      }

      if (len > len_eq_last) {
        /*
         * This part of the directory prefix (excluding
         * the trailing slash) is longer than the known
         * equal portions, so this sub-directory cannot
         * collide with a file.
         *
         * GT: last: xxxA
         *     this: xxxB/file
         */
        return retval;
      }

      /*
       * This is a possible collision. Fall through and
       * let the regular search code handle it.
       *
       * last: xxx
       * this: xxx/file
       */
    }

    pos = index_name_stage_pos(istate, name, len, stage, EXPAND_SPARSE);
    if (pos >= 0) {
      /*
       * Found one, but not so fast.  This could
       * be a marker that says "I was here, but
       * I am being removed".  Such an entry is
       * not a part of the resulting tree, and
       * it is Ok to have a directory at the same
       * path.
       */
      if (!(istate->cache[pos]->ce_flags & CE_REMOVE)) {
        retval = -1;
        if (!ok_to_replace)
          break;
        remove_index_entry_at(istate, pos);
        continue;
      }
    }
    else
      pos = -pos-1;

    /*
     * Trivial optimization: if we find an entry that
     * already matches the sub-directory, then we know
     * we're ok, and we can exit.
     */
    while (pos < istate->cache_nr) {
      struct cache_entry *p = istate->cache[pos];
      if ((ce_namelen(p) <= len) ||
          (p->name[len] != '/') ||
          memcmp(p->name, name, len))
        break; /* not our subdirectory */
      if (ce_stage(p) == stage && !(p->ce_flags & CE_REMOVE))
        /*
         * p is at the same stage as our entry, and
         * is a subdirectory of what we are looking
         * at, so we cannot have conflicts at our
         * level or anything shorter.
         */
        return retval;
      pos++;
    }
  }
  return retval;
}

/* We may be in a situation where we already have path/file and path
 * is being added, or we already have path and path/file is being
 * added.  Either one would result in a nonsense tree that has path
 * twice when git-write-tree tries to write it out.  Prevent it.
 *
 * If ok-to-replace is specified, we remove the conflicting entries
 * from the cache so the caller should recompute the insert position.
 * When this happens, we return non-zero.
 */
static int check_file_directory_conflict(struct index_state *istate,
           const struct cache_entry *ce,
           int pos, int ok_to_replace)
{
  int retval;

  /*
   * When ce is an "I am going away" entry, we allow it to be added
   */
  if (ce->ce_flags & CE_REMOVE)
    return 0;

  /*
   * We check if the path is a sub-path of a subsequent pathname
   * first, since removing those will not change the position
   * in the array.
   */
  retval = has_file_name(istate, ce, pos, ok_to_replace);

  /*
   * Then check if the path might have a clashing sub-directory
   * before it.
   */
  return retval + has_dir_name(istate, ce, pos, ok_to_replace);
}

static int add_index_entry_with_check(struct index_state *istate, struct cache_entry *ce, int option)
{
  int pos;
  int ok_to_add = option & ADD_CACHE_OK_TO_ADD;
  int ok_to_replace = option & ADD_CACHE_OK_TO_REPLACE;
  int skip_df_check = option & ADD_CACHE_SKIP_DFCHECK;
  int new_only = option & ADD_CACHE_NEW_ONLY;

  /*
   * If this entry's path sorts after the last entry in the index,
   * we can avoid searching for it.
   */
  if (istate->cache_nr > 0 &&
    strcmp(ce->name, istate->cache[istate->cache_nr - 1]->name) > 0)
    pos = index_pos_to_insert_pos(istate->cache_nr);
  else
    pos = index_name_stage_pos(istate, ce->name, ce_namelen(ce), ce_stage(ce), EXPAND_SPARSE);

  /*
   * Cache tree path should be invalidated only after index_name_stage_pos,
   * in case it expands a sparse index.
   */
  if (!(option & ADD_CACHE_KEEP_CACHE_TREE))
    cache_tree_invalidate_path(istate, ce->name);

  /* existing match? Just replace it. */
  if (pos >= 0) {
    if (!new_only)
      replace_index_entry(istate, pos, ce);
    return 0;
  }
  pos = -pos-1;

  if (!(option & ADD_CACHE_KEEP_CACHE_TREE))
    untracked_cache_add_to_index(istate, ce->name);

  /*
   * Inserting a merged entry ("stage 0") into the index
   * will always replace all non-merged entries..
   */
  if (pos < istate->cache_nr && ce_stage(ce) == 0) {
    while (ce_same_name(istate->cache[pos], ce)) {
      ok_to_add = 1;
      if (!remove_index_entry_at(istate, pos))
        break;
    }
  }

  if (!ok_to_add)
    return -1;
  if (verify_path_internal(ce->name, ce->ce_mode) == PATH_INVALID)
    return error(_("invalid path '%s'"), ce->name);

  if (!skip_df_check &&
      check_file_directory_conflict(istate, ce, pos, ok_to_replace)) {
    if (!ok_to_replace)
      return error(_("'%s' appears as both a file and as a directory"),
             ce->name);
    pos = index_name_stage_pos(istate, ce->name, ce_namelen(ce), ce_stage(ce), EXPAND_SPARSE);
    pos = -pos-1;
  }
  return pos + 1;
}

int add_index_entry(struct index_state *istate, struct cache_entry *ce, int option)
{
  int pos;

  if (option & ADD_CACHE_JUST_APPEND)
    pos = istate->cache_nr;
  else {
    int ret;
    ret = add_index_entry_with_check(istate, ce, option);
    if (ret <= 0)
      return ret;
    pos = ret - 1;
  }

  /* Make sure the array is big enough .. */
  ALLOC_GROW(istate->cache, istate->cache_nr + 1, istate->cache_alloc);

  /* Add it in.. */
  istate->cache_nr++;
  if (istate->cache_nr > pos + 1)
    MOVE_ARRAY(istate->cache + pos + 1, istate->cache + pos,
         istate->cache_nr - pos - 1);
  set_index_entry(istate, pos, ce);
  istate->cache_changed |= CE_ENTRY_ADDED;
  return 0;
}

/*
 * "refresh" does not calculate a new sha1 file or bring the
 * cache up-to-date for mode/content changes. But what it
 * _does_ do is to "re-match" the stat information of a file
 * with the cache, so that you can refresh the cache for a
 * file that hasn't been changed but where the stat entry is
 * out of date.
 *
 * For example, you'd want to do this after doing a "git-read-tree",
 * to link up the stat cache details with the proper files.
 */
static struct cache_entry *refresh_cache_ent(struct index_state *istate,
               struct cache_entry *ce,
               unsigned int options, int *err,
               int *changed_ret,
               int *t2_did_lstat,
               int *t2_did_scan)
{
  struct stat st;
  struct cache_entry *updated;
  int changed;
  int refresh = options & CE_MATCH_REFRESH;
  int ignore_valid = options & CE_MATCH_IGNORE_VALID;
  int ignore_skip_worktree = options & CE_MATCH_IGNORE_SKIP_WORKTREE;
  int ignore_missing = options & CE_MATCH_IGNORE_MISSING;
  int ignore_fsmonitor = options & CE_MATCH_IGNORE_FSMONITOR;

  if (!refresh || ce_uptodate(ce))
    return ce;

  if (!ignore_fsmonitor)
    refresh_fsmonitor(istate);
  /*
   * CE_VALID or CE_SKIP_WORKTREE means the user promised us
   * that the change to the work tree does not matter and told
   * us not to worry.
   */
  if (!ignore_skip_worktree && ce_skip_worktree(ce)) {
    ce_mark_uptodate(ce);
    return ce;
  }
  if (!ignore_valid && (ce->ce_flags & CE_VALID)) {
    ce_mark_uptodate(ce);
    return ce;
  }
  if (!ignore_fsmonitor && (ce->ce_flags & CE_FSMONITOR_VALID)) {
    ce_mark_uptodate(ce);
    return ce;
  }

  if (has_symlink_leading_path(ce->name, ce_namelen(ce))) {
    if (ignore_missing)
      return ce;
    if (err)
      *err = ENOENT;
    return NULL;
  }

  if (t2_did_lstat)
    *t2_did_lstat = 1;
  if (lstat(ce->name, &st) < 0) {
    if (ignore_missing && errno == ENOENT)
      return ce;
    if (err)
      *err = errno;
    return NULL;
  }

  changed = ie_match_stat(istate, ce, &st, options);
  if (changed_ret)
    *changed_ret = changed;
  if (!changed) {
    /*
     * The path is unchanged.  If we were told to ignore
     * valid bit, then we did the actual stat check and
     * found that the entry is unmodified.  If the entry
     * is not marked VALID, this is the place to mark it
     * valid again, under "assume unchanged" mode.
     */
    if (ignore_valid && assume_unchanged &&
        !(ce->ce_flags & CE_VALID))
      ; /* mark this one VALID again */
    else {
      /*
       * We do not mark the index itself "modified"
       * because CE_UPTODATE flag is in-core only;
       * we are not going to write this change out.
       */
      if (!S_ISGITLINK(ce->ce_mode)) {
        ce_mark_uptodate(ce);
        mark_fsmonitor_valid(istate, ce);
      }
      return ce;
    }
  }

  if (t2_did_scan)
    *t2_did_scan = 1;
  if (ie_modified(istate, ce, &st, options)) {
    if (err)
      *err = EINVAL;
    return NULL;
  }

  updated = make_empty_cache_entry(istate, ce_namelen(ce));
  copy_cache_entry(updated, ce);
  memcpy(updated->name, ce->name, ce->ce_namelen + 1);
  fill_stat_cache_info(istate, updated, &st);
  /*
   * If ignore_valid is not set, we should leave CE_VALID bit
   * alone.  Otherwise, paths marked with --no-assume-unchanged
   * (i.e. things to be edited) will reacquire CE_VALID bit
   * automatically, which is not really what we want.
   */
  if (!ignore_valid && assume_unchanged &&
      !(ce->ce_flags & CE_VALID))
    updated->ce_flags &= ~CE_VALID;

  /* istate->cache_changed is updated in the caller */
  return updated;
}

static void show_file(const char * fmt, const char * name, int in_porcelain,
          int * first, const char *header_msg)
{
  if (in_porcelain && *first && header_msg) {
    printf("%s\n", header_msg);
    *first = 0;
  }
  printf(fmt, name);
}

int repo_refresh_and_write_index(struct repository *repo,
         unsigned int refresh_flags,
         unsigned int write_flags,
         int gentle,
         const struct pathspec *pathspec,
         char *seen, const char *header_msg)
{
  struct lock_file lock_file = LOCK_INIT;
  int fd, ret = 0;

  fd = repo_hold_locked_index(repo, &lock_file, 0);
  if (!gentle && fd < 0)
    return -1;
  if (refresh_index(repo->index, refresh_flags, pathspec, seen, header_msg))
    ret = 1;
  if (0 <= fd && write_locked_index(repo->index, &lock_file, COMMIT_LOCK | write_flags))
    ret = -1;
  return ret;
}


int refresh_index(struct index_state *istate, unsigned int flags,
      const struct pathspec *pathspec,
      char *seen, const char *header_msg)
{
  int i;
  int has_errors = 0;
  int really = (flags & REFRESH_REALLY) != 0;
  int allow_unmerged = (flags & REFRESH_UNMERGED) != 0;
  int quiet = (flags & REFRESH_QUIET) != 0;
  int not_new = (flags & REFRESH_IGNORE_MISSING) != 0;
  int ignore_submodules = (flags & REFRESH_IGNORE_SUBMODULES) != 0;
  int ignore_skip_worktree = (flags & REFRESH_IGNORE_SKIP_WORKTREE) != 0;
  int first = 1;
  int in_porcelain = (flags & REFRESH_IN_PORCELAIN);
  unsigned int options = (CE_MATCH_REFRESH |
        (really ? CE_MATCH_IGNORE_VALID : 0) |
        (not_new ? CE_MATCH_IGNORE_MISSING : 0));
  const char *modified_fmt;
  const char *deleted_fmt;
  const char *typechange_fmt;
  const char *added_fmt;
  const char *unmerged_fmt;
  struct progress *progress = NULL;
  int t2_sum_lstat = 0;
  int t2_sum_scan = 0;

  if (flags & REFRESH_PROGRESS && isatty(2))
    progress = start_delayed_progress(_("Refresh index"),
              istate->cache_nr);

  trace_performance_enter();
  modified_fmt   = in_porcelain ? "M\t%s\n" : "%s: needs update\n";
  deleted_fmt    = in_porcelain ? "D\t%s\n" : "%s: needs update\n";
  typechange_fmt = in_porcelain ? "T\t%s\n" : "%s: needs update\n";
  added_fmt      = in_porcelain ? "A\t%s\n" : "%s: needs update\n";
  unmerged_fmt   = in_porcelain ? "U\t%s\n" : "%s: needs merge\n";
  /*
   * Use the multi-threaded preload_index() to refresh most of the
   * cache entries quickly then in the single threaded loop below,
   * we only have to do the special cases that are left.
   */
  preload_index(istate, pathspec, 0);
  trace2_region_enter("index", "refresh", NULL);

  for (i = 0; i < istate->cache_nr; i++) {
    struct cache_entry *ce, *new_entry;
    int cache_errno = 0;
    int changed = 0;
    int filtered = 0;
    int t2_did_lstat = 0;
    int t2_did_scan = 0;

    ce = istate->cache[i];
    if (ignore_submodules && S_ISGITLINK(ce->ce_mode))
      continue;
    if (ignore_skip_worktree && ce_skip_worktree(ce))
      continue;

    /*
     * If this entry is a sparse directory, then there isn't
     * any stat() information to update. Ignore the entry.
     */
    if (S_ISSPARSEDIR(ce->ce_mode))
      continue;

    if (pathspec && !ce_path_match(istate, ce, pathspec, seen))
      filtered = 1;

    if (ce_stage(ce)) {
      while ((i < istate->cache_nr) &&
             ! strcmp(istate->cache[i]->name, ce->name))
        i++;
      i--;
      if (allow_unmerged)
        continue;
      if (!filtered)
        show_file(unmerged_fmt, ce->name, in_porcelain,
            &first, header_msg);
      has_errors = 1;
      continue;
    }

    if (filtered)
      continue;

    new_entry = refresh_cache_ent(istate, ce, options,
                &cache_errno, &changed,
                &t2_did_lstat, &t2_did_scan);
    t2_sum_lstat += t2_did_lstat;
    t2_sum_scan += t2_did_scan;
    if (new_entry == ce)
      continue;
    display_progress(progress, i);
    if (!new_entry) {
      const char *fmt;

      if (really && cache_errno == EINVAL) {
        /* If we are doing --really-refresh that
         * means the index is not valid anymore.
         */
        ce->ce_flags &= ~CE_VALID;
        ce->ce_flags |= CE_UPDATE_IN_BASE;
        mark_fsmonitor_invalid(istate, ce);
        istate->cache_changed |= CE_ENTRY_CHANGED;
      }
      if (quiet)
        continue;

      if (cache_errno == ENOENT)
        fmt = deleted_fmt;
      else if (ce_intent_to_add(ce))
        fmt = added_fmt; /* must be before other checks */
      else if (changed & TYPE_CHANGED)
        fmt = typechange_fmt;
      else
        fmt = modified_fmt;
      show_file(fmt,
          ce->name, in_porcelain, &first, header_msg);
      has_errors = 1;
      continue;
    }

    replace_index_entry(istate, i, new_entry);
  }
  trace2_data_intmax("index", NULL, "refresh/sum_lstat", t2_sum_lstat);
  trace2_data_intmax("index", NULL, "refresh/sum_scan", t2_sum_scan);
  trace2_region_leave("index", "refresh", NULL);
  display_progress(progress, istate->cache_nr);
  stop_progress(&progress);
  trace_performance_leave("refresh index");
  return has_errors;
}

struct cache_entry *refresh_cache_entry(struct index_state *istate,
          struct cache_entry *ce,
          unsigned int options)
{
  return refresh_cache_ent(istate, ce, options, NULL, NULL, NULL, NULL);
}


/*****************************************************************
 * Index File I/O
 *****************************************************************/

#define INDEX_FORMAT_DEFAULT 3

static unsigned int get_index_format_default(struct repository *r)
{
  char *envversion = getenv("GIT_INDEX_VERSION");
  char *endp;
  unsigned int version = INDEX_FORMAT_DEFAULT;

  if (!envversion) {
    prepare_repo_settings(r);

    if (r->settings.index_version >= 0)
      version = r->settings.index_version;
    if (version < INDEX_FORMAT_LB || INDEX_FORMAT_UB < version) {
      warning(_("index.version set, but the value is invalid.\n"
          "Using version %i"), INDEX_FORMAT_DEFAULT);
      return INDEX_FORMAT_DEFAULT;
    }
    return version;
  }

  version = strtoul(envversion, &endp, 10);
  if (*endp ||
      version < INDEX_FORMAT_LB || INDEX_FORMAT_UB < version) {
    warning(_("GIT_INDEX_VERSION set, but the value is invalid.\n"
        "Using version %i"), INDEX_FORMAT_DEFAULT);
    version = INDEX_FORMAT_DEFAULT;
  }
  return version;
}

/*
 * dev/ino/uid/gid/size are also just tracked to the low 32 bits
 * Again - this is just a (very strong in practice) heuristic that
 * the inode hasn't changed.
 *
 * We save the fields in big-endian order to allow using the
 * index file over NFS transparently.
 */
struct ondisk_cache_entry {
  struct cache_time ctime;
  struct cache_time mtime;
  uint32_t dev;
  uint32_t ino;
  uint32_t mode;
  uint32_t uid;
  uint32_t gid;
  uint32_t size;
  /*
   * unsigned char hash[hashsz];
   * uint16_t flags;
   * if (flags & CE_EXTENDED)
   *  uint16_t flags2;
   */
  unsigned char data[GIT_MAX_RAWSZ + 2 * sizeof(uint16_t)];
  char name[FLEX_ARRAY];
};

/* These are only used for v3 or lower */
#define align_padding_size(size, len) ((size + (len) + 8) & ~7) - (size + len)
#define align_flex_name(STRUCT,len) ((offsetof(struct STRUCT,data) + (len) + 8) & ~7)
#define ondisk_cache_entry_size(len) align_flex_name(ondisk_cache_entry,len)
#define ondisk_data_size(flags, len) (the_hash_algo->rawsz + \
             ((flags & CE_EXTENDED) ? 2 : 1) * sizeof(uint16_t) + len)
#define ondisk_data_size_max(len) (ondisk_data_size(CE_EXTENDED, len))
#define ondisk_ce_size(ce) (ondisk_cache_entry_size(ondisk_data_size((ce)->ce_flags, ce_namelen(ce))))

/* Allow fsck to force verification of the index checksum. */
int verify_index_checksum;

/* Allow fsck to force verification of the cache entry order. */
int verify_ce_order;

static int verify_hdr(const struct cache_header *hdr, unsigned long size)
{
  git_hash_ctx c;
  unsigned char hash[GIT_MAX_RAWSZ];
  int hdr_version;
  unsigned char *start, *end;
  struct object_id oid;

  if (hdr->hdr_signature != htonl(CACHE_SIGNATURE))
    return error(_("bad signature 0x%08x"), hdr->hdr_signature);
  hdr_version = ntohl(hdr->hdr_version);
  if (hdr_version < INDEX_FORMAT_LB || INDEX_FORMAT_UB < hdr_version)
    return error(_("bad index version %d"), hdr_version);

  if (!verify_index_checksum)
    return 0;

  end = (unsigned char *)hdr + size;
  start = end - the_hash_algo->rawsz;
  oidread(&oid, start);
  if (oideq(&oid, null_oid()))
    return 0;

  the_hash_algo->init_fn(&c);
  the_hash_algo->update_fn(&c, hdr, size - the_hash_algo->rawsz);
  the_hash_algo->final_fn(hash, &c);
  if (!hasheq(hash, start))
    return error(_("bad index file sha1 signature"));
  return 0;
}

static int read_index_extension(struct index_state *istate,
        const char *ext, const char *data, unsigned long sz)
{
  switch (CACHE_EXT(ext)) {
  case CACHE_EXT_TREE:
    istate->cache_tree = cache_tree_read(data, sz);
    break;
  case CACHE_EXT_RESOLVE_UNDO:
    istate->resolve_undo = resolve_undo_read(data, sz);
    break;
  case CACHE_EXT_LINK:
    if (read_link_extension(istate, data, sz))
      return -1;
    break;
  case CACHE_EXT_UNTRACKED:
    istate->untracked = read_untracked_extension(data, sz);
    break;
  case CACHE_EXT_FSMONITOR:
    read_fsmonitor_extension(istate, data, sz);
    break;
  case CACHE_EXT_ENDOFINDEXENTRIES:
  case CACHE_EXT_INDEXENTRYOFFSETTABLE:
    /* already handled in do_read_index() */
    break;
  case CACHE_EXT_SPARSE_DIRECTORIES:
    /* no content, only an indicator */
    istate->sparse_index = INDEX_COLLAPSED;
    break;
  default:
    if (*ext < 'A' || 'Z' < *ext)
      return error(_("index uses %.4s extension, which we do not understand"),
             ext);
    fprintf_ln(stderr, _("ignoring %.4s extension"), ext);
    break;
  }
  return 0;
}

/*
 * Parses the contents of the cache entry contained within the 'ondisk' buffer
 * into a new incore 'cache_entry'.
 *
 * Note that 'char *ondisk' may not be aligned to a 4-byte address interval in
 * index v4, so we cannot cast it to 'struct ondisk_cache_entry *' and access
 * its members. Instead, we use the byte offsets of members within the struct to
 * identify where 'get_be16()', 'get_be32()', and 'oidread()' (which can all
 * read from an unaligned memory buffer) should read from the 'ondisk' buffer
 * into the corresponding incore 'cache_entry' members.
 */
static struct cache_entry *create_from_disk(struct mem_pool *ce_mem_pool,
              unsigned int version,
              const char *ondisk,
              unsigned long *ent_size,
              const struct cache_entry *previous_ce)
{
  struct cache_entry *ce;
  size_t len;
  const char *name;
  const unsigned hashsz = the_hash_algo->rawsz;
  const char *flagsp = ondisk + offsetof(struct ondisk_cache_entry, data) + hashsz;
  unsigned int flags;
  size_t copy_len = 0;
  /*
   * Adjacent cache entries tend to share the leading paths, so it makes
   * sense to only store the differences in later entries.  In the v4
   * on-disk format of the index, each on-disk cache entry stores the
   * number of bytes to be stripped from the end of the previous name,
   * and the bytes to append to the result, to come up with its name.
   */
  int expand_name_field = version == 4;

  /* On-disk flags are just 16 bits */
  flags = get_be16(flagsp);
  len = flags & CE_NAMEMASK;

  if (flags & CE_EXTENDED) {
    int extended_flags;
    extended_flags = get_be16(flagsp + sizeof(uint16_t)) << 16;
    /* We do not yet understand any bit out of CE_EXTENDED_FLAGS */
    if (extended_flags & ~CE_EXTENDED_FLAGS)
      die(_("unknown index entry format 0x%08x"), extended_flags);
    flags |= extended_flags;
    name = (const char *)(flagsp + 2 * sizeof(uint16_t));
  }
  else
    name = (const char *)(flagsp + sizeof(uint16_t));

  if (expand_name_field) {
    const unsigned char *cp = (const unsigned char *)name;
    size_t strip_len, previous_len;

    /* If we're at the beginning of a block, ignore the previous name */
    strip_len = decode_varint(&cp);
    if (previous_ce) {
      previous_len = previous_ce->ce_namelen;
      if (previous_len < strip_len)
        die(_("malformed name field in the index, near path '%s'"),
          previous_ce->name);
      copy_len = previous_len - strip_len;
    }
    name = (const char *)cp;
  }

  if (len == CE_NAMEMASK) {
    len = strlen(name);
    if (expand_name_field)
      len += copy_len;
  }

  ce = mem_pool__ce_alloc(ce_mem_pool, len);

  /*
   * NEEDSWORK: using 'offsetof()' is cumbersome and should be replaced
   * with something more akin to 'load_bitmap_entries_v1()'s use of
   * 'read_be16'/'read_be32'. For consistency with the corresponding
   * ondisk entry write function ('copy_cache_entry_to_ondisk()'), this
   * should be done at the same time as removing references to
   * 'ondisk_cache_entry' there.
   */
  ce->ce_stat_data.sd_ctime.sec = get_be32(ondisk + offsetof(struct ondisk_cache_entry, ctime)
              + offsetof(struct cache_time, sec));
  ce->ce_stat_data.sd_mtime.sec = get_be32(ondisk + offsetof(struct ondisk_cache_entry, mtime)
              + offsetof(struct cache_time, sec));
  ce->ce_stat_data.sd_ctime.nsec = get_be32(ondisk + offsetof(struct ondisk_cache_entry, ctime)
               + offsetof(struct cache_time, nsec));
  ce->ce_stat_data.sd_mtime.nsec = get_be32(ondisk + offsetof(struct ondisk_cache_entry, mtime)
               + offsetof(struct cache_time, nsec));
  ce->ce_stat_data.sd_dev   = get_be32(ondisk + offsetof(struct ondisk_cache_entry, dev));
  ce->ce_stat_data.sd_ino   = get_be32(ondisk + offsetof(struct ondisk_cache_entry, ino));
  ce->ce_mode  = get_be32(ondisk + offsetof(struct ondisk_cache_entry, mode));
  ce->ce_stat_data.sd_uid   = get_be32(ondisk + offsetof(struct ondisk_cache_entry, uid));
  ce->ce_stat_data.sd_gid   = get_be32(ondisk + offsetof(struct ondisk_cache_entry, gid));
  ce->ce_stat_data.sd_size  = get_be32(ondisk + offsetof(struct ondisk_cache_entry, size));
  ce->ce_flags = flags & ~CE_NAMEMASK;
  ce->ce_namelen = len;
  ce->index = 0;
  oidread(&ce->oid, (const unsigned char *)ondisk + offsetof(struct ondisk_cache_entry, data));

  if (expand_name_field) {
    if (copy_len)
      memcpy(ce->name, previous_ce->name, copy_len);
    memcpy(ce->name + copy_len, name, len + 1 - copy_len);
    *ent_size = (name - ((char *)ondisk)) + len + 1 - copy_len;
  } else {
    memcpy(ce->name, name, len + 1);
    *ent_size = ondisk_ce_size(ce);
  }
  return ce;
}

static void check_ce_order(struct index_state *istate)
{
  unsigned int i;

  if (!verify_ce_order)
    return;

  for (i = 1; i < istate->cache_nr; i++) {
    struct cache_entry *ce = istate->cache[i - 1];
    struct cache_entry *next_ce = istate->cache[i];
    int name_compare = strcmp(ce->name, next_ce->name);

    if (0 < name_compare)
      die(_("unordered stage entries in index"));
    if (!name_compare) {
      if (!ce_stage(ce))
        die(_("multiple stage entries for merged file '%s'"),
            ce->name);
      if (ce_stage(ce) > ce_stage(next_ce))
        die(_("unordered stage entries for '%s'"),
            ce->name);
    }
  }
}

static void tweak_untracked_cache(struct index_state *istate)
{
  struct repository *r = the_repository;

  prepare_repo_settings(r);

  switch (r->settings.core_untracked_cache) {
  case UNTRACKED_CACHE_REMOVE:
    remove_untracked_cache(istate);
    break;
  case UNTRACKED_CACHE_WRITE:
    add_untracked_cache(istate);
    break;
  case UNTRACKED_CACHE_KEEP:
    /*
     * Either an explicit "core.untrackedCache=keep", the
     * default if "core.untrackedCache" isn't configured,
     * or a fallback on an unknown "core.untrackedCache"
     * value.
     */
    break;
  }
}

static void tweak_split_index(struct index_state *istate)
{
  switch (git_config_get_split_index()) {
  case -1: /* unset: do nothing */
    break;
  case 0: /* false */
    remove_split_index(istate);
    break;
  case 1: /* true */
    add_split_index(istate);
    break;
  default: /* unknown value: do nothing */
    break;
  }
}

static void post_read_index_from(struct index_state *istate)
{
  check_ce_order(istate);
  tweak_untracked_cache(istate);
  tweak_split_index(istate);
  tweak_fsmonitor(istate);
}

static size_t estimate_cache_size_from_compressed(unsigned int entries)
{
  return entries * (sizeof(struct cache_entry) + CACHE_ENTRY_PATH_LENGTH);
}

static size_t estimate_cache_size(size_t ondisk_size, unsigned int entries)
{
  long per_entry = sizeof(struct cache_entry) - sizeof(struct ondisk_cache_entry);

  /*
   * Account for potential alignment differences.
   */
  per_entry += align_padding_size(per_entry, 0);
  return ondisk_size + entries * per_entry;
}

struct index_entry_offset
{
  /* starting byte offset into index file, count of index entries in this block */
  int offset, nr;
};

struct index_entry_offset_table
{
  int nr;
  struct index_entry_offset entries[FLEX_ARRAY];
};

static struct index_entry_offset_table *read_ieot_extension(const char *mmap, size_t mmap_size, size_t offset);
static void write_ieot_extension(struct strbuf *sb, struct index_entry_offset_table *ieot);

static size_t read_eoie_extension(const char *mmap, size_t mmap_size);
static void write_eoie_extension(struct strbuf *sb, git_hash_ctx *eoie_context, size_t offset);

struct load_index_extensions
{
  pthread_t pthread;
  struct index_state *istate;
  const char *mmap;
  size_t mmap_size;
  unsigned long src_offset;
};

static void *load_index_extensions(void *_data)
{
  struct load_index_extensions *p = _data;
  unsigned long src_offset = p->src_offset;

  while (src_offset <= p->mmap_size - the_hash_algo->rawsz - 8) {
    /* After an array of active_nr index entries,
     * there can be arbitrary number of extended
     * sections, each of which is prefixed with
     * extension name (4-byte) and section length
     * in 4-byte network byte order.
     */
    uint32_t extsize = get_be32(p->mmap + src_offset + 4);
    if (read_index_extension(p->istate,
           p->mmap + src_offset,
           p->mmap + src_offset + 8,
           extsize) < 0) {
      munmap((void *)p->mmap, p->mmap_size);
      die(_("index file corrupt"));
    }
    src_offset += 8;
    src_offset += extsize;
  }

  return NULL;
}

/*
 * A helper function that will load the specified range of cache entries
 * from the memory mapped file and add them to the given index.
 */
static unsigned long load_cache_entry_block(struct index_state *istate,
      struct mem_pool *ce_mem_pool, int offset, int nr, const char *mmap,
      unsigned long start_offset, const struct cache_entry *previous_ce)
{
  int i;
  unsigned long src_offset = start_offset;

  for (i = offset; i < offset + nr; i++) {
    struct cache_entry *ce;
    unsigned long consumed;

    ce = create_from_disk(ce_mem_pool, istate->version,
              mmap + src_offset,
              &consumed, previous_ce);
    set_index_entry(istate, i, ce);

    src_offset += consumed;
    previous_ce = ce;
  }
  return src_offset - start_offset;
}

static unsigned long load_all_cache_entries(struct index_state *istate,
      const char *mmap, size_t mmap_size, unsigned long src_offset)
{
  unsigned long consumed;

  istate->ce_mem_pool = xmalloc(sizeof(*istate->ce_mem_pool));
  if (istate->version == 4) {
    mem_pool_init(istate->ce_mem_pool,
        estimate_cache_size_from_compressed(istate->cache_nr));
  } else {
    mem_pool_init(istate->ce_mem_pool,
        estimate_cache_size(mmap_size, istate->cache_nr));
  }

  consumed = load_cache_entry_block(istate, istate->ce_mem_pool,
          0, istate->cache_nr, mmap, src_offset, NULL);
  return consumed;
}

/*
 * Mostly randomly chosen maximum thread counts: we
 * cap the parallelism to online_cpus() threads, and we want
 * to have at least 10000 cache entries per thread for it to
 * be worth starting a thread.
 */

#define THREAD_COST   (10000)

struct load_cache_entries_thread_data
{
  pthread_t pthread;
  struct index_state *istate;
  struct mem_pool *ce_mem_pool;
  int offset;
  const char *mmap;
  struct index_entry_offset_table *ieot;
  int ieot_start;   /* starting index into the ieot array */
  int ieot_blocks;  /* count of ieot entries to process */
  unsigned long consumed; /* return # of bytes in index file processed */
};

/*
 * A thread proc to run the load_cache_entries() computation
 * across multiple background threads.
 */
static void *load_cache_entries_thread(void *_data)
{
  struct load_cache_entries_thread_data *p = _data;
  int i;

  /* iterate across all ieot blocks assigned to this thread */
  for (i = p->ieot_start; i < p->ieot_start + p->ieot_blocks; i++) {
    p->consumed += load_cache_entry_block(p->istate, p->ce_mem_pool,
      p->offset, p->ieot->entries[i].nr, p->mmap, p->ieot->entries[i].offset, NULL);
    p->offset += p->ieot->entries[i].nr;
  }
  return NULL;
}

static unsigned long load_cache_entries_threaded(struct index_state *istate, const char *mmap, size_t mmap_size,
             int nr_threads, struct index_entry_offset_table *ieot)
{
  int i, offset, ieot_blocks, ieot_start, err;
  struct load_cache_entries_thread_data *data;
  unsigned long consumed = 0;

  /* a little sanity checking */
  if (istate->name_hash_initialized)
    BUG("the name hash isn't thread safe");

  istate->ce_mem_pool = xmalloc(sizeof(*istate->ce_mem_pool));
  mem_pool_init(istate->ce_mem_pool, 0);

  /* ensure we have no more threads than we have blocks to process */
  if (nr_threads > ieot->nr)
    nr_threads = ieot->nr;
  CALLOC_ARRAY(data, nr_threads);

  offset = ieot_start = 0;
  ieot_blocks = DIV_ROUND_UP(ieot->nr, nr_threads);
  for (i = 0; i < nr_threads; i++) {
    struct load_cache_entries_thread_data *p = &data[i];
    int nr, j;

    if (ieot_start + ieot_blocks > ieot->nr)
      ieot_blocks = ieot->nr - ieot_start;

    p->istate = istate;
    p->offset = offset;
    p->mmap = mmap;
    p->ieot = ieot;
    p->ieot_start = ieot_start;
    p->ieot_blocks = ieot_blocks;

    /* create a mem_pool for each thread */
    nr = 0;
    for (j = p->ieot_start; j < p->ieot_start + p->ieot_blocks; j++)
      nr += p->ieot->entries[j].nr;
    p->ce_mem_pool = xmalloc(sizeof(*istate->ce_mem_pool));
    if (istate->version == 4) {
      mem_pool_init(p->ce_mem_pool,
        estimate_cache_size_from_compressed(nr));
    } else {
      mem_pool_init(p->ce_mem_pool,
        estimate_cache_size(mmap_size, nr));
    }

    err = pthread_create(&p->pthread, NULL, load_cache_entries_thread, p);
    if (err)
      die(_("unable to create load_cache_entries thread: %s"), strerror(err));

    /* increment by the number of cache entries in the ieot block being processed */
    for (j = 0; j < ieot_blocks; j++)
      offset += ieot->entries[ieot_start + j].nr;
    ieot_start += ieot_blocks;
  }

  for (i = 0; i < nr_threads; i++) {
    struct load_cache_entries_thread_data *p = &data[i];

    err = pthread_join(p->pthread, NULL);
    if (err)
      die(_("unable to join load_cache_entries thread: %s"), strerror(err));
    mem_pool_combine(istate->ce_mem_pool, p->ce_mem_pool);
    consumed += p->consumed;
  }

  free(data);

  return consumed;
}

static void set_new_index_sparsity(struct index_state *istate)
{
  /*
   * If the index's repo exists, mark it sparse according to
   * repo settings.
   */
  prepare_repo_settings(istate->repo);
  if (!istate->repo->settings.command_requires_full_index &&
      is_sparse_index_allowed(istate, 0))
    istate->sparse_index = 1;
}

/* remember to discard_cache() before reading a different cache! */
int do_read_index(struct index_state *istate, const char *path, int must_exist)
{
  int fd;
  struct stat st;
  unsigned long src_offset;
  const struct cache_header *hdr;
  const char *mmap;
  size_t mmap_size;
  struct load_index_extensions p;
  size_t extension_offset = 0;
  int nr_threads, cpus;
  struct index_entry_offset_table *ieot = NULL;

  if (istate->initialized)
    return istate->cache_nr;

  istate->timestamp.sec = 0;
  istate->timestamp.nsec = 0;
  fd = open(path, O_RDONLY);
  if (fd < 0) {
    if (!must_exist && errno == ENOENT) {
      set_new_index_sparsity(istate);
      return 0;
    }
    die_errno(_("%s: index file open failed"), path);
  }

  if (fstat(fd, &st))
    die_errno(_("%s: cannot stat the open index"), path);

  mmap_size = xsize_t(st.st_size);
  if (mmap_size < sizeof(struct cache_header) + the_hash_algo->rawsz)
    die(_("%s: index file smaller than expected"), path);

  mmap = xmmap_gently(NULL, mmap_size, PROT_READ, MAP_PRIVATE, fd, 0);
  if (mmap == MAP_FAILED)
    die_errno(_("%s: unable to map index file%s"), path,
      mmap_os_err());
  close(fd);

  hdr = (const struct cache_header *)mmap;
  if (verify_hdr(hdr, mmap_size) < 0)
    goto unmap;

  oidread(&istate->oid, (const unsigned char *)hdr + mmap_size - the_hash_algo->rawsz);
  istate->version = ntohl(hdr->hdr_version);
  istate->cache_nr = ntohl(hdr->hdr_entries);
  istate->cache_alloc = alloc_nr(istate->cache_nr);
  CALLOC_ARRAY(istate->cache, istate->cache_alloc);
  istate->initialized = 1;

  p.istate = istate;
  p.mmap = mmap;
  p.mmap_size = mmap_size;

  src_offset = sizeof(*hdr);

  if (git_config_get_index_threads(&nr_threads))
    nr_threads = 1;

  /* TODO: does creating more threads than cores help? */
  if (!nr_threads) {
    nr_threads = istate->cache_nr / THREAD_COST;
    cpus = online_cpus();
    if (nr_threads > cpus)
      nr_threads = cpus;
  }

  if (!HAVE_THREADS)
    nr_threads = 1;

  if (nr_threads > 1) {
    extension_offset = read_eoie_extension(mmap, mmap_size);
    if (extension_offset) {
      int err;

      p.src_offset = extension_offset;
      err = pthread_create(&p.pthread, NULL, load_index_extensions, &p);
      if (err)
        die(_("unable to create load_index_extensions thread: %s"), strerror(err));

      nr_threads--;
    }
  }

  /*
   * Locate and read the index entry offset table so that we can use it
   * to multi-thread the reading of the cache entries.
   */
  if (extension_offset && nr_threads > 1)
    ieot = read_ieot_extension(mmap, mmap_size, extension_offset);

  if (ieot) {
    src_offset += load_cache_entries_threaded(istate, mmap, mmap_size, nr_threads, ieot);
    free(ieot);
  } else {
    src_offset += load_all_cache_entries(istate, mmap, mmap_size, src_offset);
  }

  istate->timestamp.sec = st.st_mtime;
  istate->timestamp.nsec = ST_MTIME_NSEC(st);

  /* if we created a thread, join it otherwise load the extensions on the primary thread */
  if (extension_offset) {
    int ret = pthread_join(p.pthread, NULL);
    if (ret)
      die(_("unable to join load_index_extensions thread: %s"), strerror(ret));
  } else {
    p.src_offset = src_offset;
    load_index_extensions(&p);
  }
  munmap((void *)mmap, mmap_size);

  /*
   * TODO trace2: replace "the_repository" with the actual repo instance
   * that is associated with the given "istate".
   */
  trace2_data_intmax("index", the_repository, "read/version",
         istate->version);
  trace2_data_intmax("index", the_repository, "read/cache_nr",
         istate->cache_nr);

  /*
   * If the command explicitly requires a full index, force it
   * to be full. Otherwise, correct the sparsity based on repository
   * settings and other properties of the index (if necessary).
   */
  prepare_repo_settings(istate->repo);
  if (istate->repo->settings.command_requires_full_index)
    ensure_full_index(istate);
  else
    ensure_correct_sparsity(istate);

  return istate->cache_nr;

unmap:
  munmap((void *)mmap, mmap_size);
  die(_("index file corrupt"));
}

/*
 * Signal that the shared index is used by updating its mtime.
 *
 * This way, shared index can be removed if they have not been used
 * for some time.
 */
static void freshen_shared_index(const char *shared_index, int warn)
{
  if (!check_and_freshen_file(shared_index, 1) && warn)
    warning(_("could not freshen shared index '%s'"), shared_index);
}

int read_index_from(struct index_state *istate, const char *path,
        const char *gitdir)
{
  struct split_index *split_index;
  int ret;
  char *base_oid_hex;
  char *base_path;

  /* istate->initialized covers both .git/index and .git/sharedindex.xxx */
  if (istate->initialized)
    return istate->cache_nr;

  /*
   * TODO trace2: replace "the_repository" with the actual repo instance
   * that is associated with the given "istate".
   */
  trace2_region_enter_printf("index", "do_read_index", the_repository,
           "%s", path);
  trace_performance_enter();
  ret = do_read_index(istate, path, 0);
  trace_performance_leave("read cache %s", path);
  trace2_region_leave_printf("index", "do_read_index", the_repository,
           "%s", path);

  split_index = istate->split_index;
  if (!split_index || is_null_oid(&split_index->base_oid)) {
    post_read_index_from(istate);
    return ret;
  }

  trace_performance_enter();
  if (split_index->base)
    release_index(split_index->base);
  else
    ALLOC_ARRAY(split_index->base, 1);
  index_state_init(split_index->base, istate->repo);

  base_oid_hex = oid_to_hex(&split_index->base_oid);
  base_path = xstrfmt("%s/sharedindex.%s", gitdir, base_oid_hex);
  trace2_region_enter_printf("index", "shared/do_read_index",
           the_repository, "%s", base_path);
  ret = do_read_index(split_index->base, base_path, 0);
  trace2_region_leave_printf("index", "shared/do_read_index",
           the_repository, "%s", base_path);
  if (!ret) {
    char *path_copy = xstrdup(path);
    char *base_path2 = xstrfmt("%s/sharedindex.%s",
             dirname(path_copy), base_oid_hex);
    free(path_copy);
    trace2_region_enter_printf("index", "shared/do_read_index",
             the_repository, "%s", base_path2);
    ret = do_read_index(split_index->base, base_path2, 1);
    trace2_region_leave_printf("index", "shared/do_read_index",
             the_repository, "%s", base_path2);
    free(base_path2);
  }
  if (!oideq(&split_index->base_oid, &split_index->base->oid))
    die(_("broken index, expect %s in %s, got %s"),
        base_oid_hex, base_path,
        oid_to_hex(&split_index->base->oid));

  freshen_shared_index(base_path, 0);
  merge_base_index(istate);
  post_read_index_from(istate);
  trace_performance_leave("read cache %s", base_path);
  free(base_path);
  return ret;
}

int is_index_unborn(struct index_state *istate)
{
  return (!istate->cache_nr && !istate->timestamp.sec);
}

void index_state_init(struct index_state *istate, struct repository *r)
{
  struct index_state blank = INDEX_STATE_INIT(r);
  memcpy(istate, &blank, sizeof(*istate));
}

void release_index(struct index_state *istate)
{
  /*
   * Cache entries in istate->cache[] should have been allocated
   * from the memory pool associated with this index, or from an
   * associated split_index. There is no need to free individual
   * cache entries. validate_cache_entries can detect when this
   * assertion does not hold.
   */
  validate_cache_entries(istate);

  resolve_undo_clear_index(istate);
  free_name_hash(istate);
  cache_tree_free(&(istate->cache_tree));
  free(istate->fsmonitor_last_update);
  free(istate->cache);
  discard_split_index(istate);
  free_untracked_cache(istate->untracked);

  if (istate->sparse_checkout_patterns) {
    clear_pattern_list(istate->sparse_checkout_patterns);
    FREE_AND_NULL(istate->sparse_checkout_patterns);
  }

  if (istate->ce_mem_pool) {
    mem_pool_discard(istate->ce_mem_pool, should_validate_cache_entries());
    FREE_AND_NULL(istate->ce_mem_pool);
  }
}

void discard_index(struct index_state *istate)
{
  release_index(istate);
  index_state_init(istate, istate->repo);
}

/*
 * Validate the cache entries of this index.
 * All cache entries associated with this index
 * should have been allocated by the memory pool
 * associated with this index, or by a referenced
 * split index.
 */
void validate_cache_entries(const struct index_state *istate)
{
  int i;

  if (!should_validate_cache_entries() ||!istate || !istate->initialized)
    return;

  for (i = 0; i < istate->cache_nr; i++) {
    if (!istate) {
      BUG("cache entry is not allocated from expected memory pool");
    } else if (!istate->ce_mem_pool ||
      !mem_pool_contains(istate->ce_mem_pool, istate->cache[i])) {
      if (!istate->split_index ||
        !istate->split_index->base ||
        !istate->split_index->base->ce_mem_pool ||
        !mem_pool_contains(istate->split_index->base->ce_mem_pool, istate->cache[i])) {
        BUG("cache entry is not allocated from expected memory pool");
      }
    }
  }

  if (istate->split_index)
    validate_cache_entries(istate->split_index->base);
}

int unmerged_index(const struct index_state *istate)
{
  int i;
  for (i = 0; i < istate->cache_nr; i++) {
    if (ce_stage(istate->cache[i]))
      return 1;
  }
  return 0;
}

int repo_index_has_changes(struct repository *repo,
         struct tree *tree,
         struct strbuf *sb)
{
  struct index_state *istate = repo->index;
  struct object_id cmp;
  int i;

  if (tree)
    cmp = tree->object.oid;
  if (tree || !get_oid_tree("HEAD", &cmp)) {
    struct diff_options opt;

    repo_diff_setup(repo, &opt);
    opt.flags.exit_with_status = 1;
    if (!sb)
      opt.flags.quick = 1;
    diff_setup_done(&opt);
    do_diff_cache(&cmp, &opt);
    diffcore_std(&opt);
    for (i = 0; sb && i < diff_queued_diff.nr; i++) {
      if (i)
        strbuf_addch(sb, ' ');
      strbuf_addstr(sb, diff_queued_diff.queue[i]->two->path);
    }
    diff_flush(&opt);
    return opt.flags.has_changes != 0;
  } else {
    /* TODO: audit for interaction with sparse-index. */
    ensure_full_index(istate);
    for (i = 0; sb && i < istate->cache_nr; i++) {
      if (i)
        strbuf_addch(sb, ' ');
      strbuf_addstr(sb, istate->cache[i]->name);
    }
    return !!istate->cache_nr;
  }
}

static int write_index_ext_header(struct hashfile *f,
          git_hash_ctx *eoie_f,
          unsigned int ext,
          unsigned int sz)
{
  hashwrite_be32(f, ext);
  hashwrite_be32(f, sz);

  if (eoie_f) {
    ext = htonl(ext);
    sz = htonl(sz);
    the_hash_algo->update_fn(eoie_f, &ext, sizeof(ext));
    the_hash_algo->update_fn(eoie_f, &sz, sizeof(sz));
  }
  return 0;
}

static void ce_smudge_racily_clean_entry(struct index_state *istate,
           struct cache_entry *ce)
{
  /*
   * The only thing we care about in this function is to smudge the
   * falsely clean entry due to touch-update-touch race, so we leave
   * everything else as they are.  We are called for entries whose
   * ce_stat_data.sd_mtime match the index file mtime.
   *
   * Note that this actually does not do much for gitlinks, for
   * which ce_match_stat_basic() always goes to the actual
   * contents.  The caller checks with is_racy_timestamp() which
   * always says "no" for gitlinks, so we are not called for them ;-)
   */
  struct stat st;

  if (lstat(ce->name, &st) < 0)
    return;
  if (ce_match_stat_basic(ce, &st))
    return;
  if (ce_modified_check_fs(istate, ce, &st)) {
    /* This is "racily clean"; smudge it.  Note that this
     * is a tricky code.  At first glance, it may appear
     * that it can break with this sequence:
     *
     * $ echo xyzzy >frotz
     * $ git-update-index --add frotz
     * $ : >frotz
     * $ sleep 3
     * $ echo filfre >nitfol
     * $ git-update-index --add nitfol
     *
     * but it does not.  When the second update-index runs,
     * it notices that the entry "frotz" has the same timestamp
     * as index, and if we were to smudge it by resetting its
     * size to zero here, then the object name recorded
     * in index is the 6-byte file but the cached stat information
     * becomes zero --- which would then match what we would
     * obtain from the filesystem next time we stat("frotz").
     *
     * However, the second update-index, before calling
     * this function, notices that the cached size is 6
     * bytes and what is on the filesystem is an empty
     * file, and never calls us, so the cached size information
     * for "frotz" stays 6 which does not match the filesystem.
     */
    ce->ce_stat_data.sd_size = 0;
  }
}

/* Copy miscellaneous fields but not the name */
static void copy_cache_entry_to_ondisk(struct ondisk_cache_entry *ondisk,
               struct cache_entry *ce)
{
  short flags;
  const unsigned hashsz = the_hash_algo->rawsz;
  uint16_t *flagsp = (uint16_t *)(ondisk->data + hashsz);

  ondisk->ctime.sec = htonl(ce->ce_stat_data.sd_ctime.sec);
  ondisk->mtime.sec = htonl(ce->ce_stat_data.sd_mtime.sec);
  ondisk->ctime.nsec = htonl(ce->ce_stat_data.sd_ctime.nsec);
  ondisk->mtime.nsec = htonl(ce->ce_stat_data.sd_mtime.nsec);
  ondisk->dev  = htonl(ce->ce_stat_data.sd_dev);
  ondisk->ino  = htonl(ce->ce_stat_data.sd_ino);
  ondisk->mode = htonl(ce->ce_mode);
  ondisk->uid  = htonl(ce->ce_stat_data.sd_uid);
  ondisk->gid  = htonl(ce->ce_stat_data.sd_gid);
  ondisk->size = htonl(ce->ce_stat_data.sd_size);
  hashcpy(ondisk->data, ce->oid.hash);

  flags = ce->ce_flags & ~CE_NAMEMASK;
  flags |= (ce_namelen(ce) >= CE_NAMEMASK ? CE_NAMEMASK : ce_namelen(ce));
  flagsp[0] = htons(flags);
  if (ce->ce_flags & CE_EXTENDED) {
    flagsp[1] = htons((ce->ce_flags & CE_EXTENDED_FLAGS) >> 16);
  }
}

static int ce_write_entry(struct hashfile *f, struct cache_entry *ce,
        struct strbuf *previous_name, struct ondisk_cache_entry *ondisk)
{
  int size;
  unsigned int saved_namelen;
  int stripped_name = 0;
  static unsigned char padding[8] = { 0x00 };

  if (ce->ce_flags & CE_STRIP_NAME) {
    saved_namelen = ce_namelen(ce);
    ce->ce_namelen = 0;
    stripped_name = 1;
  }

  size = offsetof(struct ondisk_cache_entry,data) + ondisk_data_size(ce->ce_flags, 0);

  if (!previous_name) {
    int len = ce_namelen(ce);
    copy_cache_entry_to_ondisk(ondisk, ce);
    hashwrite(f, ondisk, size);
    hashwrite(f, ce->name, len);
    hashwrite(f, padding, align_padding_size(size, len));
  } else {
    int common, to_remove, prefix_size;
    unsigned char to_remove_vi[16];
    for (common = 0;
         (ce->name[common] &&
          common < previous_name->len &&
          ce->name[common] == previous_name->buf[common]);
         common++)
      ; /* still matching */
    to_remove = previous_name->len - common;
    prefix_size = encode_varint(to_remove, to_remove_vi);

    copy_cache_entry_to_ondisk(ondisk, ce);
    hashwrite(f, ondisk, size);
    hashwrite(f, to_remove_vi, prefix_size);
    hashwrite(f, ce->name + common, ce_namelen(ce) - common);
    hashwrite(f, padding, 1);

    strbuf_splice(previous_name, common, to_remove,
            ce->name + common, ce_namelen(ce) - common);
  }
  if (stripped_name) {
    ce->ce_namelen = saved_namelen;
    ce->ce_flags &= ~CE_STRIP_NAME;
  }

  return 0;
}

/*
 * This function verifies if index_state has the correct sha1 of the
 * index file.  Don't die if we have any other failure, just return 0.
 */
static int verify_index_from(const struct index_state *istate, const char *path)
{
  int fd;
  ssize_t n;
  struct stat st;
  unsigned char hash[GIT_MAX_RAWSZ];

  if (!istate->initialized)
    return 0;

  fd = open(path, O_RDONLY);
  if (fd < 0)
    return 0;

  if (fstat(fd, &st))
    goto out;

  if (st.st_size < sizeof(struct cache_header) + the_hash_algo->rawsz)
    goto out;

  n = pread_in_full(fd, hash, the_hash_algo->rawsz, st.st_size - the_hash_algo->rawsz);
  if (n != the_hash_algo->rawsz)
    goto out;

  if (!hasheq(istate->oid.hash, hash))
    goto out;

  close(fd);
  return 1;

out:
  close(fd);
  return 0;
}

static int repo_verify_index(struct repository *repo)
{
  return verify_index_from(repo->index, repo->index_file);
}

int has_racy_timestamp(struct index_state *istate)
{
  int entries = istate->cache_nr;
  int i;

  for (i = 0; i < entries; i++) {
    struct cache_entry *ce = istate->cache[i];
    if (is_racy_timestamp(istate, ce))
      return 1;
  }
  return 0;
}

void repo_update_index_if_able(struct repository *repo,
             struct lock_file *lockfile)
{
  if ((repo->index->cache_changed ||
       has_racy_timestamp(repo->index)) &&
      repo_verify_index(repo))
    write_locked_index(repo->index, lockfile, COMMIT_LOCK);
  else
    rollback_lock_file(lockfile);
}

static int record_eoie(void)
{
  int val;

  if (!git_config_get_bool("index.recordendofindexentries", &val))
    return val;

  /*
   * As a convenience, the end of index entries extension
   * used for threading is written by default if the user
   * explicitly requested threaded index reads.
   */
  return !git_config_get_index_threads(&val) && val != 1;
}

static int record_ieot(void)
{
  int val;

  if (!git_config_get_bool("index.recordoffsettable", &val))
    return val;

  /*
   * As a convenience, the offset table used for threading is
   * written by default if the user explicitly requested
   * threaded index reads.
   */
  return !git_config_get_index_threads(&val) && val != 1;
}

/*
 * On success, `tempfile` is closed. If it is the temporary file
 * of a `struct lock_file`, we will therefore effectively perform
 * a 'close_lock_file_gently()`. Since that is an implementation
 * detail of lockfiles, callers of `do_write_index()` should not
 * rely on it.
 */
static int do_write_index(struct index_state *istate, struct tempfile *tempfile,
        int strip_extensions, unsigned flags)
{
  uint64_t start = getnanotime();
  struct hashfile *f;
  git_hash_ctx *eoie_c = NULL;
  struct cache_header hdr;
  int i, err = 0, removed, extended, hdr_version;
  struct cache_entry **cache = istate->cache;
  int entries = istate->cache_nr;
  struct stat st;
  struct ondisk_cache_entry ondisk;
  struct strbuf previous_name_buf = STRBUF_INIT, *previous_name;
  int drop_cache_tree = istate->drop_cache_tree;
  off_t offset;
  int csum_fsync_flag;
  int ieot_entries = 1;
  struct index_entry_offset_table *ieot = NULL;
  int nr, nr_threads;
  struct repository *r = istate->repo;

  f = hashfd(tempfile->fd, tempfile->filename.buf);

  prepare_repo_settings(r);
  f->skip_hash = r->settings.index_skip_hash;

  for (i = removed = extended = 0; i < entries; i++) {
    if (cache[i]->ce_flags & CE_REMOVE)
      removed++;

    /* reduce extended entries if possible */
    cache[i]->ce_flags &= ~CE_EXTENDED;
    if (cache[i]->ce_flags & CE_EXTENDED_FLAGS) {
      extended++;
      cache[i]->ce_flags |= CE_EXTENDED;
    }
  }

  if (!istate->version)
    istate->version = get_index_format_default(the_repository);

  /* demote version 3 to version 2 when the latter suffices */
  if (istate->version == 3 || istate->version == 2)
    istate->version = extended ? 3 : 2;

  hdr_version = istate->version;

  hdr.hdr_signature = htonl(CACHE_SIGNATURE);
  hdr.hdr_version = htonl(hdr_version);
  hdr.hdr_entries = htonl(entries - removed);

  hashwrite(f, &hdr, sizeof(hdr));

  if (!HAVE_THREADS || git_config_get_index_threads(&nr_threads))
    nr_threads = 1;

  if (nr_threads != 1 && record_ieot()) {
    int ieot_blocks, cpus;

    /*
     * ensure default number of ieot blocks maps evenly to the
     * default number of threads that will process them leaving
     * room for the thread to load the index extensions.
     */
    if (!nr_threads) {
      ieot_blocks = istate->cache_nr / THREAD_COST;
      cpus = online_cpus();
      if (ieot_blocks > cpus - 1)
        ieot_blocks = cpus - 1;
    } else {
      ieot_blocks = nr_threads;
      if (ieot_blocks > istate->cache_nr)
        ieot_blocks = istate->cache_nr;
    }

    /*
     * no reason to write out the IEOT extension if we don't
     * have enough blocks to utilize multi-threading
     */
    if (ieot_blocks > 1) {
      ieot = xcalloc(1, sizeof(struct index_entry_offset_table)
        + (ieot_blocks * sizeof(struct index_entry_offset)));
      ieot_entries = DIV_ROUND_UP(entries, ieot_blocks);
    }
  }

  offset = hashfile_total(f);

  nr = 0;
  previous_name = (hdr_version == 4) ? &previous_name_buf : NULL;

  for (i = 0; i < entries; i++) {
    struct cache_entry *ce = cache[i];
    if (ce->ce_flags & CE_REMOVE)
      continue;
    if (!ce_uptodate(ce) && is_racy_timestamp(istate, ce))
      ce_smudge_racily_clean_entry(istate, ce);
    if (is_null_oid(&ce->oid)) {
      static const char msg[] = "cache entry has null sha1: %s";
      static int allow = -1;

      if (allow < 0)
        allow = git_env_bool("GIT_ALLOW_NULL_SHA1", 0);
      if (allow)
        warning(msg, ce->name);
      else
        err = error(msg, ce->name);

      drop_cache_tree = 1;
    }
    if (ieot && i && (i % ieot_entries == 0)) {
      ieot->entries[ieot->nr].nr = nr;
      ieot->entries[ieot->nr].offset = offset;
      ieot->nr++;
      /*
       * If we have a V4 index, set the first byte to an invalid
       * character to ensure there is nothing common with the previous
       * entry
       */
      if (previous_name)
        previous_name->buf[0] = 0;
      nr = 0;

      offset = hashfile_total(f);
    }
    if (ce_write_entry(f, ce, previous_name, (struct ondisk_cache_entry *)&ondisk) < 0)
      err = -1;

    if (err)
      break;
    nr++;
  }
  if (ieot && nr) {
    ieot->entries[ieot->nr].nr = nr;
    ieot->entries[ieot->nr].offset = offset;
    ieot->nr++;
  }
  strbuf_release(&previous_name_buf);

  if (err) {
    free(ieot);
    return err;
  }

  offset = hashfile_total(f);

  /*
   * The extension headers must be hashed on their own for the
   * EOIE extension. Create a hashfile here to compute that hash.
   */
  if (offset && record_eoie()) {
    CALLOC_ARRAY(eoie_c, 1);
    the_hash_algo->init_fn(eoie_c);
  }

  /*
   * Lets write out CACHE_EXT_INDEXENTRYOFFSETTABLE first so that we
   * can minimize the number of extensions we have to scan through to
   * find it during load.  Write it out regardless of the
   * strip_extensions parameter as we need it when loading the shared
   * index.
   */
  if (ieot) {
    struct strbuf sb = STRBUF_INIT;

    write_ieot_extension(&sb, ieot);
    err = write_index_ext_header(f, eoie_c, CACHE_EXT_INDEXENTRYOFFSETTABLE, sb.len) < 0;
    hashwrite(f, sb.buf, sb.len);
    strbuf_release(&sb);
    free(ieot);
    if (err)
      return -1;
  }

  if (!strip_extensions && istate->split_index &&
      !is_null_oid(&istate->split_index->base_oid)) {
    struct strbuf sb = STRBUF_INIT;

    if (istate->sparse_index)
      die(_("cannot write split index for a sparse index"));

    err = write_link_extension(&sb, istate) < 0 ||
      write_index_ext_header(f, eoie_c, CACHE_EXT_LINK,
                 sb.len) < 0;
    hashwrite(f, sb.buf, sb.len);
    strbuf_release(&sb);
    if (err)
      return -1;
  }
  if (!strip_extensions && !drop_cache_tree && istate->cache_tree) {
    struct strbuf sb = STRBUF_INIT;

    cache_tree_write(&sb, istate->cache_tree);
    err = write_index_ext_header(f, eoie_c, CACHE_EXT_TREE, sb.len) < 0;
    hashwrite(f, sb.buf, sb.len);
    strbuf_release(&sb);
    if (err)
      return -1;
  }
  if (!strip_extensions && istate->resolve_undo) {
    struct strbuf sb = STRBUF_INIT;

    resolve_undo_write(&sb, istate->resolve_undo);
    err = write_index_ext_header(f, eoie_c, CACHE_EXT_RESOLVE_UNDO,
               sb.len) < 0;
    hashwrite(f, sb.buf, sb.len);
    strbuf_release(&sb);
    if (err)
      return -1;
  }
  if (!strip_extensions && istate->untracked) {
    struct strbuf sb = STRBUF_INIT;

    write_untracked_extension(&sb, istate->untracked);
    err = write_index_ext_header(f, eoie_c, CACHE_EXT_UNTRACKED,
               sb.len) < 0;
    hashwrite(f, sb.buf, sb.len);
    strbuf_release(&sb);
    if (err)
      return -1;
  }
  if (!strip_extensions && istate->fsmonitor_last_update) {
    struct strbuf sb = STRBUF_INIT;

    write_fsmonitor_extension(&sb, istate);
    err = write_index_ext_header(f, eoie_c, CACHE_EXT_FSMONITOR, sb.len) < 0;
    hashwrite(f, sb.buf, sb.len);
    strbuf_release(&sb);
    if (err)
      return -1;
  }
  if (istate->sparse_index) {
    if (write_index_ext_header(f, eoie_c, CACHE_EXT_SPARSE_DIRECTORIES, 0) < 0)
      return -1;
  }

  /*
   * CACHE_EXT_ENDOFINDEXENTRIES must be written as the last entry before the SHA1
   * so that it can be found and processed before all the index entries are
   * read.  Write it out regardless of the strip_extensions parameter as we need it
   * when loading the shared index.
   */
  if (eoie_c) {
    struct strbuf sb = STRBUF_INIT;

    write_eoie_extension(&sb, eoie_c, offset);
    err = write_index_ext_header(f, NULL, CACHE_EXT_ENDOFINDEXENTRIES, sb.len) < 0;
    hashwrite(f, sb.buf, sb.len);
    strbuf_release(&sb);
    if (err)
      return -1;
  }

  csum_fsync_flag = 0;
  if (!alternate_index_output && (flags & COMMIT_LOCK))
    csum_fsync_flag = CSUM_FSYNC;

  finalize_hashfile(f, istate->oid.hash, FSYNC_COMPONENT_INDEX,
        CSUM_HASH_IN_STREAM | csum_fsync_flag);

  if (close_tempfile_gently(tempfile)) {
    error(_("could not close '%s'"), get_tempfile_path(tempfile));
    return -1;
  }
  if (stat(get_tempfile_path(tempfile), &st))
    return -1;
  istate->timestamp.sec = (unsigned int)st.st_mtime;
  istate->timestamp.nsec = ST_MTIME_NSEC(st);
  trace_performance_since(start, "write index, changed mask = %x", istate->cache_changed);

  /*
   * TODO trace2: replace "the_repository" with the actual repo instance
   * that is associated with the given "istate".
   */
  trace2_data_intmax("index", the_repository, "write/version",
         istate->version);
  trace2_data_intmax("index", the_repository, "write/cache_nr",
         istate->cache_nr);

  return 0;
}

void set_alternate_index_output(const char *name)
{
  alternate_index_output = name;
}

static int commit_locked_index(struct lock_file *lk)
{
  if (alternate_index_output)
    return commit_lock_file_to(lk, alternate_index_output);
  else
    return commit_lock_file(lk);
}

static int do_write_locked_index(struct index_state *istate, struct lock_file *lock,
         unsigned flags)
{
  int ret;
  int was_full = istate->sparse_index == INDEX_EXPANDED;

  ret = convert_to_sparse(istate, 0);

  if (ret) {
    warning(_("failed to convert to a sparse-index"));
    return ret;
  }

  /*
   * TODO trace2: replace "the_repository" with the actual repo instance
   * that is associated with the given "istate".
   */
  trace2_region_enter_printf("index", "do_write_index", the_repository,
           "%s", get_lock_file_path(lock));
  ret = do_write_index(istate, lock->tempfile, 0, flags);
  trace2_region_leave_printf("index", "do_write_index", the_repository,
           "%s", get_lock_file_path(lock));

  if (was_full)
    ensure_full_index(istate);

  if (ret)
    return ret;
  if (flags & COMMIT_LOCK)
    ret = commit_locked_index(lock);
  else
    ret = close_lock_file_gently(lock);

  run_hooks_l("post-index-change",
      istate->updated_workdir ? "1" : "0",
      istate->updated_skipworktree ? "1" : "0", NULL);
  istate->updated_workdir = 0;
  istate->updated_skipworktree = 0;

  return ret;
}

static int write_split_index(struct index_state *istate,
           struct lock_file *lock,
           unsigned flags)
{
  int ret;
  prepare_to_write_split_index(istate);
  ret = do_write_locked_index(istate, lock, flags);
  finish_writing_split_index(istate);
  return ret;
}

static const char *shared_index_expire = "2.weeks.ago";

static unsigned long get_shared_index_expire_date(void)
{
  static unsigned long shared_index_expire_date;
  static int shared_index_expire_date_prepared;

  if (!shared_index_expire_date_prepared) {
    git_config_get_expiry("splitindex.sharedindexexpire",
              &shared_index_expire);
    shared_index_expire_date = approxidate(shared_index_expire);
    shared_index_expire_date_prepared = 1;
  }

  return shared_index_expire_date;
}

static int should_delete_shared_index(const char *shared_index_path)
{
  struct stat st;
  unsigned long expiration;

  /* Check timestamp */
  expiration = get_shared_index_expire_date();
  if (!expiration)
    return 0;
  if (stat(shared_index_path, &st))
    return error_errno(_("could not stat '%s'"), shared_index_path);
  if (st.st_mtime > expiration)
    return 0;

  return 1;
}

static int clean_shared_index_files(const char *current_hex)
{
  struct dirent *de;
  DIR *dir = opendir(get_git_dir());

  if (!dir)
    return error_errno(_("unable to open git dir: %s"), get_git_dir());

  while ((de = readdir(dir)) != NULL) {
    const char *sha1_hex;
    const char *shared_index_path;
    if (!skip_prefix(de->d_name, "sharedindex.", &sha1_hex))
      continue;
    if (!strcmp(sha1_hex, current_hex))
      continue;
    shared_index_path = git_path("%s", de->d_name);
    if (should_delete_shared_index(shared_index_path) > 0 &&
        unlink(shared_index_path))
      warning_errno(_("unable to unlink: %s"), shared_index_path);
  }
  closedir(dir);

  return 0;
}

static int write_shared_index(struct index_state *istate,
            struct tempfile **temp, unsigned flags)
{
  struct split_index *si = istate->split_index;
  int ret, was_full = !istate->sparse_index;

  move_cache_to_base_index(istate);
  convert_to_sparse(istate, 0);

  trace2_region_enter_printf("index", "shared/do_write_index",
           the_repository, "%s", get_tempfile_path(*temp));
  ret = do_write_index(si->base, *temp, 1, flags);
  trace2_region_leave_printf("index", "shared/do_write_index",
           the_repository, "%s", get_tempfile_path(*temp));

  if (was_full)
    ensure_full_index(istate);

  if (ret)
    return ret;
  ret = adjust_shared_perm(get_tempfile_path(*temp));
  if (ret) {
    error(_("cannot fix permission bits on '%s'"), get_tempfile_path(*temp));
    return ret;
  }
  ret = rename_tempfile(temp,
            git_path("sharedindex.%s", oid_to_hex(&si->base->oid)));
  if (!ret) {
    oidcpy(&si->base_oid, &si->base->oid);
    clean_shared_index_files(oid_to_hex(&si->base->oid));
  }

  return ret;
}

static const int default_max_percent_split_change = 20;

static int too_many_not_shared_entries(struct index_state *istate)
{
  int i, not_shared = 0;
  int max_split = git_config_get_max_percent_split_change();

  switch (max_split) {
  case -1:
    /* not or badly configured: use the default value */
    max_split = default_max_percent_split_change;
    break;
  case 0:
    return 1; /* 0% means always write a new shared index */
  case 100:
    return 0; /* 100% means never write a new shared index */
  default:
    break; /* just use the configured value */
  }

  /* Count not shared entries */
  for (i = 0; i < istate->cache_nr; i++) {
    struct cache_entry *ce = istate->cache[i];
    if (!ce->index)
      not_shared++;
  }

  return (int64_t)istate->cache_nr * max_split < (int64_t)not_shared * 100;
}

int write_locked_index(struct index_state *istate, struct lock_file *lock,
           unsigned flags)
{
  int new_shared_index, ret, test_split_index_env;
  struct split_index *si = istate->split_index;

  if (git_env_bool("GIT_TEST_CHECK_CACHE_TREE", 0))
    cache_tree_verify(the_repository, istate);

  if ((flags & SKIP_IF_UNCHANGED) && !istate->cache_changed) {
    if (flags & COMMIT_LOCK)
      rollback_lock_file(lock);
    return 0;
  }

  if (istate->fsmonitor_last_update)
    fill_fsmonitor_bitmap(istate);

  test_split_index_env = git_env_bool("GIT_TEST_SPLIT_INDEX", 0);

  if ((!si && !test_split_index_env) ||
      alternate_index_output ||
      (istate->cache_changed & ~EXTMASK)) {
    if (si)
      oidclr(&si->base_oid);
    ret = do_write_locked_index(istate, lock, flags);
    goto out;
  }

  if (test_split_index_env) {
    if (!si) {
      si = init_split_index(istate);
      istate->cache_changed |= SPLIT_INDEX_ORDERED;
    } else {
      int v = si->base_oid.hash[0];
      if ((v & 15) < 6)
        istate->cache_changed |= SPLIT_INDEX_ORDERED;
    }
  }
  if (too_many_not_shared_entries(istate))
    istate->cache_changed |= SPLIT_INDEX_ORDERED;

  new_shared_index = istate->cache_changed & SPLIT_INDEX_ORDERED;

  if (new_shared_index) {
    struct tempfile *temp;
    int saved_errno;

    /* Same initial permissions as the main .git/index file */
    temp = mks_tempfile_sm(git_path("sharedindex_XXXXXX"), 0, 0666);
    if (!temp) {
      oidclr(&si->base_oid);
      ret = do_write_locked_index(istate, lock, flags);
      goto out;
    }
    ret = write_shared_index(istate, &temp, flags);

    saved_errno = errno;
    if (is_tempfile_active(temp))
      delete_tempfile(&temp);
    errno = saved_errno;

    if (ret)
      goto out;
  }

  ret = write_split_index(istate, lock, flags);

  /* Freshen the shared index only if the split-index was written */
  if (!ret && !new_shared_index && !is_null_oid(&si->base_oid)) {
    const char *shared_index = git_path("sharedindex.%s",
                oid_to_hex(&si->base_oid));
    freshen_shared_index(shared_index, 1);
  }

out:
  if (flags & COMMIT_LOCK)
    rollback_lock_file(lock);
  return ret;
}

/*
 * Read the index file that is potentially unmerged into given
 * index_state, dropping any unmerged entries to stage #0 (potentially
 * resulting in a path appearing as both a file and a directory in the
 * index; the caller is responsible to clear out the extra entries
 * before writing the index to a tree).  Returns true if the index is
 * unmerged.  Callers who want to refuse to work from an unmerged
 * state can call this and check its return value, instead of calling
 * read_cache().
 */
int repo_read_index_unmerged(struct repository *repo)
{
  struct index_state *istate;
  int i;
  int unmerged = 0;

  repo_read_index(repo);
  istate = repo->index;
  for (i = 0; i < istate->cache_nr; i++) {
    struct cache_entry *ce = istate->cache[i];
    struct cache_entry *new_ce;
    int len;

    if (!ce_stage(ce))
      continue;
    unmerged = 1;
    len = ce_namelen(ce);
    new_ce = make_empty_cache_entry(istate, len);
    memcpy(new_ce->name, ce->name, len);
    new_ce->ce_flags = create_ce_flags(0) | CE_CONFLICTED;
    new_ce->ce_namelen = len;
    new_ce->ce_mode = ce->ce_mode;
    if (add_index_entry(istate, new_ce, ADD_CACHE_SKIP_DFCHECK))
      return error(_("%s: cannot drop to stage #0"),
             new_ce->name);
  }
  return unmerged;
}

/*
 * Returns 1 if the path is an "other" path with respect to
 * the index; that is, the path is not mentioned in the index at all,
 * either as a file, a directory with some files in the index,
 * or as an unmerged entry.
 *
 * We helpfully remove a trailing "/" from directories so that
 * the output of read_directory can be used as-is.
 */
int index_name_is_other(struct index_state *istate, const char *name,
      int namelen)
{
  int pos;
  if (namelen && name[namelen - 1] == '/')
    namelen--;
  pos = index_name_pos(istate, name, namelen);
  if (0 <= pos)
    return 0; /* exact match */
  pos = -pos - 1;
  if (pos < istate->cache_nr) {
    struct cache_entry *ce = istate->cache[pos];
    if (ce_namelen(ce) == namelen &&
        !memcmp(ce->name, name, namelen))
      return 0; /* Yup, this one exists unmerged */
  }
  return 1;
}

void *read_blob_data_from_index(struct index_state *istate,
        const char *path, unsigned long *size)
{
  int pos, len;
  unsigned long sz;
  enum object_type type;
  void *data;

  len = strlen(path);
  pos = index_name_pos(istate, path, len);
  if (pos < 0) {
    /*
     * We might be in the middle of a merge, in which
     * case we would read stage #2 (ours).
     */
    int i;
    for (i = -pos - 1;
         (pos < 0 && i < istate->cache_nr &&
          !strcmp(istate->cache[i]->name, path));
         i++)
      if (ce_stage(istate->cache[i]) == 2)
        pos = i;
  }
  if (pos < 0)
    return NULL;
  data = read_object_file(&istate->cache[pos]->oid, &type, &sz);
  if (!data || type != OBJ_BLOB) {
    free(data);
    return NULL;
  }
  if (size)
    *size = sz;
  return data;
}

void stat_validity_clear(struct stat_validity *sv)
{
  FREE_AND_NULL(sv->sd);
}

int stat_validity_check(struct stat_validity *sv, const char *path)
{
  struct stat st;

  if (stat(path, &st) < 0)
    return sv->sd == NULL;
  if (!sv->sd)
    return 0;
  return S_ISREG(st.st_mode) && !match_stat_data(sv->sd, &st);
}

void stat_validity_update(struct stat_validity *sv, int fd)
{
  struct stat st;

  if (fstat(fd, &st) < 0 || !S_ISREG(st.st_mode))
    stat_validity_clear(sv);
  else {
    if (!sv->sd)
      CALLOC_ARRAY(sv->sd, 1);
    fill_stat_data(sv->sd, &st);
  }
}

void move_index_extensions(struct index_state *dst, struct index_state *src)
{
  dst->untracked = src->untracked;
  src->untracked = NULL;
  dst->cache_tree = src->cache_tree;
  src->cache_tree = NULL;
}

struct cache_entry *dup_cache_entry(const struct cache_entry *ce,
            struct index_state *istate)
{
  unsigned int size = ce_size(ce);
  int mem_pool_allocated;
  struct cache_entry *new_entry = make_empty_cache_entry(istate, ce_namelen(ce));
  mem_pool_allocated = new_entry->mem_pool_allocated;

  memcpy(new_entry, ce, size);
  new_entry->mem_pool_allocated = mem_pool_allocated;
  return new_entry;
}

void discard_cache_entry(struct cache_entry *ce)
{
  if (ce && should_validate_cache_entries())
    memset(ce, 0xCD, cache_entry_size(ce->ce_namelen));

  if (ce && ce->mem_pool_allocated)
    return;

  free(ce);
}

int should_validate_cache_entries(void)
{
  static int validate_index_cache_entries = -1;

  if (validate_index_cache_entries < 0) {
    if (getenv("GIT_TEST_VALIDATE_INDEX_CACHE_ENTRIES"))
      validate_index_cache_entries = 1;
    else
      validate_index_cache_entries = 0;
  }

  return validate_index_cache_entries;
}

#define EOIE_SIZE (4 + GIT_SHA1_RAWSZ) /* <4-byte offset> + <20-byte hash> */
#define EOIE_SIZE_WITH_HEADER (4 + 4 + EOIE_SIZE) /* <4-byte signature> + <4-byte length> + EOIE_SIZE */

static size_t read_eoie_extension(const char *mmap, size_t mmap_size)
{
  /*
   * The end of index entries (EOIE) extension is guaranteed to be last
   * so that it can be found by scanning backwards from the EOF.
   *
   * "EOIE"
   * <4-byte length>
   * <4-byte offset>
   * <20-byte hash>
   */
  const char *index, *eoie;
  uint32_t extsize;
  size_t offset, src_offset;
  unsigned char hash[GIT_MAX_RAWSZ];
  git_hash_ctx c;

  /* ensure we have an index big enough to contain an EOIE extension */
  if (mmap_size < sizeof(struct cache_header) + EOIE_SIZE_WITH_HEADER + the_hash_algo->rawsz)
    return 0;

  /* validate the extension signature */
  index = eoie = mmap + mmap_size - EOIE_SIZE_WITH_HEADER - the_hash_algo->rawsz;
  if (CACHE_EXT(index) != CACHE_EXT_ENDOFINDEXENTRIES)
    return 0;
  index += sizeof(uint32_t);

  /* validate the extension size */
  extsize = get_be32(index);
  if (extsize != EOIE_SIZE)
    return 0;
  index += sizeof(uint32_t);

  /*
   * Validate the offset we're going to look for the first extension
   * signature is after the index header and before the eoie extension.
   */
  offset = get_be32(index);
  if (mmap + offset < mmap + sizeof(struct cache_header))
    return 0;
  if (mmap + offset >= eoie)
    return 0;
  index += sizeof(uint32_t);

  /*
   * The hash is computed over extension types and their sizes (but not
   * their contents).  E.g. if we have "TREE" extension that is N-bytes
   * long, "REUC" extension that is M-bytes long, followed by "EOIE",
   * then the hash would be:
   *
   * SHA-1("TREE" + <binary representation of N> +
   *   "REUC" + <binary representation of M>)
   */
  src_offset = offset;
  the_hash_algo->init_fn(&c);
  while (src_offset < mmap_size - the_hash_algo->rawsz - EOIE_SIZE_WITH_HEADER) {
    /* After an array of active_nr index entries,
     * there can be arbitrary number of extended
     * sections, each of which is prefixed with
     * extension name (4-byte) and section length
     * in 4-byte network byte order.
     */
    uint32_t extsize;
    memcpy(&extsize, mmap + src_offset + 4, 4);
    extsize = ntohl(extsize);

    /* verify the extension size isn't so large it will wrap around */
    if (src_offset + 8 + extsize < src_offset)
      return 0;

    the_hash_algo->update_fn(&c, mmap + src_offset, 8);

    src_offset += 8;
    src_offset += extsize;
  }
  the_hash_algo->final_fn(hash, &c);
  if (!hasheq(hash, (const unsigned char *)index))
    return 0;

  /* Validate that the extension offsets returned us back to the eoie extension. */
  if (src_offset != mmap_size - the_hash_algo->rawsz - EOIE_SIZE_WITH_HEADER)
    return 0;

  return offset;
}

static void write_eoie_extension(struct strbuf *sb, git_hash_ctx *eoie_context, size_t offset)
{
  uint32_t buffer;
  unsigned char hash[GIT_MAX_RAWSZ];

  /* offset */
  put_be32(&buffer, offset);
  strbuf_add(sb, &buffer, sizeof(uint32_t));

  /* hash */
  the_hash_algo->final_fn(hash, eoie_context);
  strbuf_add(sb, hash, the_hash_algo->rawsz);
}

#define IEOT_VERSION  (1)

static struct index_entry_offset_table *read_ieot_extension(const char *mmap, size_t mmap_size, size_t offset)
{
  const char *index = NULL;
  uint32_t extsize, ext_version;
  struct index_entry_offset_table *ieot;
  int i, nr;

  /* find the IEOT extension */
  if (!offset)
    return NULL;
  while (offset <= mmap_size - the_hash_algo->rawsz - 8) {
    extsize = get_be32(mmap + offset + 4);
    if (CACHE_EXT((mmap + offset)) == CACHE_EXT_INDEXENTRYOFFSETTABLE) {
      index = mmap + offset + 4 + 4;
      break;
    }
    offset += 8;
    offset += extsize;
  }
  if (!index)
    return NULL;

  /* validate the version is IEOT_VERSION */
  ext_version = get_be32(index);
  if (ext_version != IEOT_VERSION) {
    error("invalid IEOT version %d", ext_version);
    return NULL;
  }
  index += sizeof(uint32_t);

  /* extension size - version bytes / bytes per entry */
  nr = (extsize - sizeof(uint32_t)) / (sizeof(uint32_t) + sizeof(uint32_t));
  if (!nr) {
    error("invalid number of IEOT entries %d", nr);
    return NULL;
  }
  ieot = xmalloc(sizeof(struct index_entry_offset_table)
           + (nr * sizeof(struct index_entry_offset)));
  ieot->nr = nr;
  for (i = 0; i < nr; i++) {
    ieot->entries[i].offset = get_be32(index);
    index += sizeof(uint32_t);
    ieot->entries[i].nr = get_be32(index);
    index += sizeof(uint32_t);
  }

  return ieot;
}

static void write_ieot_extension(struct strbuf *sb, struct index_entry_offset_table *ieot)
{
  uint32_t buffer;
  int i;

  /* version */
  put_be32(&buffer, IEOT_VERSION);
  strbuf_add(sb, &buffer, sizeof(uint32_t));

  /* ieot */
  for (i = 0; i < ieot->nr; i++) {

    /* offset */
    put_be32(&buffer, ieot->entries[i].offset);
    strbuf_add(sb, &buffer, sizeof(uint32_t));

    /* count */
    put_be32(&buffer, ieot->entries[i].nr);
    strbuf_add(sb, &buffer, sizeof(uint32_t));
  }
}

void prefetch_cache_entries(const struct index_state *istate,
          must_prefetch_predicate must_prefetch)
{
  int i;
  struct oid_array to_fetch = OID_ARRAY_INIT;

  for (i = 0; i < istate->cache_nr; i++) {
    struct cache_entry *ce = istate->cache[i];

    if (S_ISGITLINK(ce->ce_mode) || !must_prefetch(ce))
      continue;
    if (!oid_object_info_extended(the_repository, &ce->oid,
                NULL,
                OBJECT_INFO_FOR_PREFETCH))
      continue;
    oid_array_append(&to_fetch, &ce->oid);
  }
  promisor_remote_get_direct(the_repository,
           to_fetch.oid, to_fetch.nr);
  oid_array_clear(&to_fetch);
}

Coverage Report

Created: 2023-02-27 06:33