merge(third_party/git): Merge squashed git subtree at v2.23.0 r/373

Merge commit '1b593e1ea4d2af0f6444d9a7788d5d99abd6fde5' as 'third_party/git'

1 files changed, 3609 insertions, 0 deletions

diff --git a/third_party/git/read-cache.c b/third_party/git/read-cache.c
new file mode 100644
index 0000000000..52ffa8a313
--- /dev/null
+++ b/third_party/git/read-cache.c
@@ -0,0 +1,3609 @@
+/*
+ * 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"
+
+/* 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" */
+
+/* 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
+
+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)
+		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)
+{
+	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;
+	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);
+	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, int len1, int mode1,
+		      const char *name2, int len2, int mode2)
+{
+	unsigned char c1, c2;
+	int 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, int len1, int mode1,
+		    const char *name2, int len2, int mode2)
+{
+	int len = len1 < len2 ? len1 : len2, cmp;
+	unsigned char c1, c2;
+
+	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(const struct index_state *istate, const char *name, int namelen, int stage)
+{
+	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;
+	}
+	return -first-1;
+}
+
+int index_name_pos(const struct index_state *istate, const char *name, int namelen)
+{
+	return index_name_stage_pos(istate, name, namelen, 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, blob_type, &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));
+	int hash_flags = 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)
+{
+	return xcalloc(1, cache_entry_size(len));
+}
+
+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(path, mode)) {
+		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 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);
+
+	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;
+}
+
+int verify_path(const char *path, unsigned mode)
+{
+	char c;
+
+	if (has_dos_drive_prefix(path))
+		return 0;
+
+	goto inside;
+	for (;;) {
+		if (!c)
+			return 1;
+		if (is_dir_sep(c)) {
+inside:
+			if (protect_hfs) {
+				if (is_hfs_dotgit(path))
+					return 0;
+				if (S_ISLNK(mode)) {
+					if (is_hfs_dotgitmodules(path))
+						return 0;
+				}
+			}
+			if (protect_ntfs) {
+				if (is_ntfs_dotgit(path))
+					return 0;
+				if (S_ISLNK(mode)) {
+					if (is_ntfs_dotgitmodules(path))
+						return 0;
+				}
+			}
+
+			c = *path++;
+			if ((c == '.' && !verify_dotfile(path, mode)) ||
+			    is_dir_sep(c) || c == '\0')
+				return 0;
+		}
+		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;
+			}
+
+			if (istate->cache_nr > 0 &&
+				ce_namelen(istate->cache[istate->cache_nr - 1]) > len) {
+				/*
+				 * The directory prefix lines up with part of
+				 * a longer file or directory name, but sorts
+				 * after it, so this sub-directory cannot
+				 * collide with a file.
+				 *
+				 * last: xxx/yy-file (because '-' sorts before '/')
+				 * this: xxx/yy/abc
+				 */
+				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);
+		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 (!(option & ADD_CACHE_KEEP_CACHE_TREE))
+		cache_tree_invalidate_path(istate, ce->name);
+
+	/*
+	 * 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 = -istate->cache_nr - 1;
+	else
+		pos = index_name_stage_pos(istate, ce->name, ce_namelen(ce), ce_stage(ce));
+
+	/* 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(ce->name, ce->ce_mode))
+		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));
+		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)
+{
+	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 (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 (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 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 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;
+
+	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);
+	for (i = 0; i < istate->cache_nr; i++) {
+		struct cache_entry *ce, *new_entry;
+		int cache_errno = 0;
+		int changed = 0;
+		int filtered = 0;
+
+		ce = istate->cache[i];
+		if (ignore_submodules && S_ISGITLINK(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);
+		if (new_entry == ce)
+			continue;
+		if (progress)
+			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);
+	}
+	if (progress) {
+		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);
+}
+
+
+/*****************************************************************
+ * Index File I/O
+ *****************************************************************/
+
+#define INDEX_FORMAT_DEFAULT 3
+
+static unsigned int get_index_format_default(void)
+{
+	char *envversion = getenv("GIT_INDEX_VERSION");
+	char *endp;
+	int value;
+	unsigned int version = INDEX_FORMAT_DEFAULT;
+
+	if (!envversion) {
+		if (!git_config_get_int("index.version", &value))
+			version = value;
+		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;
+
+	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;
+
+	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, (unsigned char *)hdr + size - the_hash_algo->rawsz))
+		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;
+	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;
+}
+
+static struct cache_entry *create_from_disk(struct mem_pool *ce_mem_pool,
+					    unsigned int version,
+					    struct ondisk_cache_entry *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 uint16_t *flagsp = (const uint16_t *)(ondisk->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 + 1) << 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);
+	}
+	else
+		name = (const char *)(flagsp + 1);
+
+	if (expand_name_field) {
+		const unsigned char *cp = (const unsigned char *)name;
+		size_t strip_len, previous_len;
+
+		/* If we're at the begining 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);
+
+	ce->ce_stat_data.sd_ctime.sec = get_be32(&ondisk->ctime.sec);
+	ce->ce_stat_data.sd_mtime.sec = get_be32(&ondisk->mtime.sec);
+	ce->ce_stat_data.sd_ctime.nsec = get_be32(&ondisk->ctime.nsec);
+	ce->ce_stat_data.sd_mtime.nsec = get_be32(&ondisk->mtime.nsec);
+	ce->ce_stat_data.sd_dev   = get_be32(&ondisk->dev);
+	ce->ce_stat_data.sd_ino   = get_be32(&ondisk->ino);
+	ce->ce_mode  = get_be32(&ondisk->mode);
+	ce->ce_stat_data.sd_uid   = get_be32(&ondisk->uid);
+	ce->ce_stat_data.sd_gid   = get_be32(&ondisk->gid);
+	ce->ce_stat_data.sd_size  = get_be32(&ondisk->size);
+	ce->ce_flags = flags & ~CE_NAMEMASK;
+	ce->ce_namelen = len;
+	ce->index = 0;
+	hashcpy(ce->oid.hash, ondisk->data);
+	memcpy(ce->name, name, len);
+	ce->name[len] = '\0';
+
+	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)
+{
+	switch (git_config_get_untracked_cache()) {
+	case -1: /* keep: do nothing */
+		break;
+	case 0: /* false */
+		remove_untracked_cache(istate);
+		break;
+	case 1: /* true */
+		add_untracked_cache(istate);
+		break;
+	default: /* unknown value: do nothing */
+		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(sizeof(struct cache_entry), -sizeof(struct ondisk_cache_entry));
+	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 ondisk_cache_entry *disk_ce;
+		struct cache_entry *ce;
+		unsigned long consumed;
+
+		disk_ce = (struct ondisk_cache_entry *)(mmap + src_offset);
+		ce = create_from_disk(ce_mem_pool, istate->version, disk_ce, &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;
+
+	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");
+
+	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;
+	data = xcalloc(nr_threads, sizeof(*data));
+
+	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;
+		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;
+}
+
+/* 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)
+			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"), path);
+	close(fd);
+
+	hdr = (const struct cache_header *)mmap;
+	if (verify_hdr(hdr, mmap_size) < 0)
+		goto unmap;
+
+	hashcpy(istate->oid.hash, (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);
+	istate->cache = xcalloc(istate->cache_alloc, sizeof(*istate->cache));
+	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);
+
+	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)
+		discard_index(split_index->base);
+	else
+		split_index->base = xcalloc(1, sizeof(*split_index->base));
+
+	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, 1);
+	trace2_region_leave_printf("index", "shared/do_read_index",
+				   the_repository, "%s", base_path);
+	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);
+}
+
+int discard_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);
+	istate->cache_nr = 0;
+	istate->cache_changed = 0;
+	istate->timestamp.sec = 0;
+	istate->timestamp.nsec = 0;
+	free_name_hash(istate);
+	cache_tree_free(&(istate->cache_tree));
+	istate->initialized = 0;
+	istate->fsmonitor_has_run_once = 0;
+	FREE_AND_NULL(istate->cache);
+	istate->cache_alloc = 0;
+	discard_split_index(istate);
+	free_untracked_cache(istate->untracked);
+	istate->untracked = NULL;
+
+	if (istate->ce_mem_pool) {
+		mem_pool_discard(istate->ce_mem_pool, should_validate_cache_entries());
+		istate->ce_mem_pool = NULL;
+	}
+
+	return 0;
+}
+
+/*
+ * 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;
+		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 {
+		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;
+	}
+}
+
+#define WRITE_BUFFER_SIZE 8192
+static unsigned char write_buffer[WRITE_BUFFER_SIZE];
+static unsigned long write_buffer_len;
+
+static int ce_write_flush(git_hash_ctx *context, int fd)
+{
+	unsigned int buffered = write_buffer_len;
+	if (buffered) {
+		the_hash_algo->update_fn(context, write_buffer, buffered);
+		if (write_in_full(fd, write_buffer, buffered) < 0)
+			return -1;
+		write_buffer_len = 0;
+	}
+	return 0;
+}
+
+static int ce_write(git_hash_ctx *context, int fd, void *data, unsigned int len)
+{
+	while (len) {
+		unsigned int buffered = write_buffer_len;
+		unsigned int partial = WRITE_BUFFER_SIZE - buffered;
+		if (partial > len)
+			partial = len;
+		memcpy(write_buffer + buffered, data, partial);
+		buffered += partial;
+		if (buffered == WRITE_BUFFER_SIZE) {
+			write_buffer_len = buffered;
+			if (ce_write_flush(context, fd))
+				return -1;
+			buffered = 0;
+		}
+		write_buffer_len = buffered;
+		len -= partial;
+		data = (char *) data + partial;
+	}
+	return 0;
+}
+
+static int write_index_ext_header(git_hash_ctx *context, git_hash_ctx *eoie_context,
+				  int fd, unsigned int ext, unsigned int sz)
+{
+	ext = htonl(ext);
+	sz = htonl(sz);
+	if (eoie_context) {
+		the_hash_algo->update_fn(eoie_context, &ext, 4);
+		the_hash_algo->update_fn(eoie_context, &sz, 4);
+	}
+	return ((ce_write(context, fd, &ext, 4) < 0) ||
+		(ce_write(context, fd, &sz, 4) < 0)) ? -1 : 0;
+}
+
+static int ce_flush(git_hash_ctx *context, int fd, unsigned char *hash)
+{
+	unsigned int left = write_buffer_len;
+
+	if (left) {
+		write_buffer_len = 0;
+		the_hash_algo->update_fn(context, write_buffer, left);
+	}
+
+	/* Flush first if not enough space for hash signature */
+	if (left + the_hash_algo->rawsz > WRITE_BUFFER_SIZE) {
+		if (write_in_full(fd, write_buffer, left) < 0)
+			return -1;
+		left = 0;
+	}
+
+	/* Append the hash signature at the end */
+	the_hash_algo->final_fn(write_buffer + left, context);
+	hashcpy(hash, write_buffer + left);
+	left += the_hash_algo->rawsz;
+	return (write_in_full(fd, write_buffer, left) < 0) ? -1 : 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(git_hash_ctx *c, int fd, struct cache_entry *ce,
+			  struct strbuf *previous_name, struct ondisk_cache_entry *ondisk)
+{
+	int size;
+	int result;
+	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);
+		result = ce_write(c, fd, ondisk, size);
+		if (!result)
+			result = ce_write(c, fd, ce->name, len);
+		if (!result)
+			result = ce_write(c, fd, 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);
+		result = ce_write(c, fd, ondisk, size);
+		if (!result)
+			result = ce_write(c, fd, to_remove_vi, prefix_size);
+		if (!result)
+			result = ce_write(c, fd, ce->name + common, ce_namelen(ce) - common);
+		if (!result)
+			result = ce_write(c, fd, 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 result;
+}
+
+/*
+ * 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);
+}
+
+static 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)
+{
+	uint64_t start = getnanotime();
+	int newfd = tempfile->fd;
+	git_hash_ctx c, eoie_c;
+	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 ieot_entries = 1;
+	struct index_entry_offset_table *ieot = NULL;
+	int nr, nr_threads;
+
+	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();
+		if (git_env_bool("GIT_TEST_SPLIT_INDEX", 0))
+			init_split_index(istate);
+	}
+
+	/* 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);
+
+	the_hash_algo->init_fn(&c);
+	if (ce_write(&c, newfd, &hdr, sizeof(hdr)) < 0)
+		return -1;
+
+	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 = lseek(newfd, 0, SEEK_CUR);
+	if (offset < 0) {
+		free(ieot);
+		return -1;
+	}
+	offset += write_buffer_len;
+	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 = lseek(newfd, 0, SEEK_CUR);
+			if (offset < 0) {
+				free(ieot);
+				return -1;
+			}
+			offset += write_buffer_len;
+		}
+		if (ce_write_entry(&c, newfd, 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;
+	}
+
+	/* Write extension data here */
+	offset = lseek(newfd, 0, SEEK_CUR);
+	if (offset < 0) {
+		free(ieot);
+		return -1;
+	}
+	offset += write_buffer_len;
+	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(&c, &eoie_c, newfd, CACHE_EXT_INDEXENTRYOFFSETTABLE, sb.len) < 0
+			|| ce_write(&c, newfd, sb.buf, sb.len) < 0;
+		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;
+
+		err = write_link_extension(&sb, istate) < 0 ||
+			write_index_ext_header(&c, &eoie_c, newfd, CACHE_EXT_LINK,
+					       sb.len) < 0 ||
+			ce_write(&c, newfd, sb.buf, sb.len) < 0;
+		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(&c, &eoie_c, newfd, CACHE_EXT_TREE, sb.len) < 0
+			|| ce_write(&c, newfd, sb.buf, sb.len) < 0;
+		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(&c, &eoie_c, newfd, CACHE_EXT_RESOLVE_UNDO,
+					     sb.len) < 0
+			|| ce_write(&c, newfd, sb.buf, sb.len) < 0;
+		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(&c, &eoie_c, newfd, CACHE_EXT_UNTRACKED,
+					     sb.len) < 0 ||
+			ce_write(&c, newfd, sb.buf, sb.len) < 0;
+		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(&c, &eoie_c, newfd, CACHE_EXT_FSMONITOR, sb.len) < 0
+			|| ce_write(&c, newfd, sb.buf, sb.len) < 0;
+		strbuf_release(&sb);
+		if (err)
+			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 (offset && record_eoie()) {
+		struct strbuf sb = STRBUF_INIT;
+
+		write_eoie_extension(&sb, &eoie_c, offset);
+		err = write_index_ext_header(&c, NULL, newfd, CACHE_EXT_ENDOFINDEXENTRIES, sb.len) < 0
+			|| ce_write(&c, newfd, sb.buf, sb.len) < 0;
+		strbuf_release(&sb);
+		if (err)
+			return -1;
+	}
+
+	if (ce_flush(&c, newfd, istate->oid.hash))
+		return -1;
+	if (close_tempfile_gently(tempfile)) {
+		error(_("could not close '%s'"), tempfile->filename.buf);
+		return -1;
+	}
+	if (stat(tempfile->filename.buf, &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;
+
+	/*
+	 * 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", lock->tempfile->filename.buf);
+	ret = do_write_index(istate, lock->tempfile, 0);
+	trace2_region_leave_printf("index", "do_write_index", the_repository,
+				   "%s", lock->tempfile->filename.buf);
+
+	if (ret)
+		return ret;
+	if (flags & COMMIT_LOCK)
+		ret = commit_locked_index(lock);
+	else
+		ret = close_lock_file_gently(lock);
+
+	run_hook_le(NULL, "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)
+{
+	struct split_index *si = istate->split_index;
+	int ret;
+
+	move_cache_to_base_index(istate);
+
+	trace2_region_enter_printf("index", "shared/do_write_index",
+				   the_repository, "%s", (*temp)->filename.buf);
+	ret = do_write_index(si->base, *temp, 1);
+	trace2_region_leave_printf("index", "shared/do_write_index",
+				   the_repository, "%s", (*temp)->filename.buf);
+
+	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;
+	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);
+
+	if (!si || alternate_index_output ||
+	    (istate->cache_changed & ~EXTMASK)) {
+		if (si)
+			oidclr(&si->base_oid);
+		ret = do_write_locked_index(istate, lock, flags);
+		goto out;
+	}
+
+	if (git_env_bool("GIT_TEST_SPLIT_INDEX", 0)) {
+		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);
+
+		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(const 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(const 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)
+			sv->sd = xcalloc(1, sizeof(struct stat_data));
+		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));
+	}
+}