Merge branch 'ds/reachable-first-parent-fix'
[gitweb.git] / read-cache.c
index 4b35e87847f0c346f4968765fa8dc64a863a8047..d57958233e82df6551fdc890f1238ae65beb8940 100644 (file)
@@ -6,11 +6,14 @@
 #define NO_THE_INDEX_COMPATIBILITY_MACROS
 #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"
@@ -20,6 +23,8 @@
 #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 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;
+}
+
 struct index_state the_index;
 static const char *alternate_index_output;
 
@@ -61,7 +110,7 @@ static void replace_index_entry(struct index_state *istate, int nr, struct cache
 
        replace_index_entry_in_base(istate, old, ce);
        remove_name_hash(istate, old);
-       free(old);
+       discard_cache_entry(old);
        ce->ce_flags &= ~CE_HASHED;
        set_index_entry(istate, nr, ce);
        ce->ce_flags |= CE_UPDATE_IN_BASE;
@@ -74,7 +123,7 @@ void rename_index_entry_at(struct index_state *istate, int nr, const char *new_n
        struct cache_entry *old_entry = istate->cache[nr], *new_entry;
        int namelen = strlen(new_name);
 
-       new_entry = xmalloc(cache_entry_size(namelen));
+       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;
@@ -160,15 +209,17 @@ void fill_stat_cache_info(struct cache_entry *ce, struct stat *st)
        }
 }
 
-static int ce_compare_data(const struct cache_entry *ce, struct stat *st)
+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(&oid, fd, st, OBJ_BLOB, ce->name, 0))
-                       match = oidcmp(&oid, &ce->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;
@@ -185,7 +236,7 @@ static int ce_compare_link(const struct cache_entry *ce, size_t expected_size)
        if (strbuf_readlink(&sb, ce->name, expected_size))
                return -1;
 
-       buffer = read_sha1_file(ce->oid.hash, &type, &size);
+       buffer = read_object_file(&ce->oid, &type, &size);
        if (buffer) {
                if (size == sb.len)
                        match = memcmp(buffer, sb.buf, size);
@@ -209,14 +260,16 @@ static int ce_compare_gitlink(const struct cache_entry *ce)
         */
        if (resolve_gitlink_ref(ce->name, "HEAD", &oid) < 0)
                return 0;
-       return oidcmp(&oid, &ce->oid);
+       return !oideq(&oid, &ce->oid);
 }
 
-static int ce_modified_check_fs(const struct cache_entry *ce, struct stat *st)
+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(ce, st))
+               if (ce_compare_data(istate, ce, st))
                        return DATA_CHANGED;
                break;
        case S_IFLNK:
@@ -292,7 +345,7 @@ static int is_racy_stat(const struct index_state *istate,
                );
 }
 
-static int is_racy_timestamp(const struct index_state *istate,
+int is_racy_timestamp(const struct index_state *istate,
                             const struct cache_entry *ce)
 {
        return (!S_ISGITLINK(ce->ce_mode) &&
@@ -362,7 +415,7 @@ int ie_match_stat(struct index_state *istate,
                if (assume_racy_is_modified)
                        changed |= DATA_CHANGED;
                else
-                       changed |= ce_modified_check_fs(ce, st);
+                       changed |= ce_modified_check_fs(istate, ce, st);
        }
 
        return changed;
@@ -402,7 +455,7 @@ int ie_modified(struct index_state *istate,
            (S_ISGITLINK(ce->ce_mode) || ce->ce_stat_data.sd_size != 0))
                return changed;
 
-       changed_fs = ce_modified_check_fs(ce, st);
+       changed_fs = ce_modified_check_fs(istate, ce, st);
        if (changed_fs)
                return changed | changed_fs;
        return 0;
@@ -623,7 +676,7 @@ static struct cache_entry *create_alias_ce(struct index_state *istate,
 
        /* Ok, create the new entry using the name of the existing alias */
        len = ce_namelen(alias);
-       new_entry = xcalloc(1, cache_entry_size(len));
+       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);
@@ -640,7 +693,7 @@ void set_object_name_for_intent_to_add_entry(struct cache_entry *ce)
 
 int add_to_index(struct index_state *istate, const char *path, struct stat *st, int flags)
 {
-       int size, namelen, was_same;
+       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;
@@ -662,8 +715,7 @@ int add_to_index(struct index_state *istate, const char *path, struct stat *st,
                while (namelen && path[namelen-1] == '/')
                        namelen--;
        }
-       size = cache_entry_size(namelen);
-       ce = xcalloc(1, size);
+       ce = make_empty_cache_entry(istate, namelen);
        memcpy(ce->name, path, namelen);
        ce->ce_namelen = namelen;
        if (!intent_only)
@@ -704,13 +756,13 @@ int add_to_index(struct index_state *istate, const char *path, struct stat *st,
                                ce_mark_uptodate(alias);
                        alias->ce_flags |= CE_ADDED;
 
-                       free(ce);
+                       discard_cache_entry(ce);
                        return 0;
                }
        }
        if (!intent_only) {
-               if (index_path(&ce->oid, path, st, newflags)) {
-                       free(ce);
+               if (index_path(istate, &ce->oid, path, st, newflags)) {
+                       discard_cache_entry(ce);
                        return error("unable to index file %s", path);
                }
        } else
@@ -723,13 +775,13 @@ int add_to_index(struct index_state *istate, const char *path, struct stat *st,
        /* It was suspected to be racily clean, but it turns out to be Ok */
        was_same = (alias &&
                    !ce_stage(alias) &&
-                   !oidcmp(&alias->oid, &ce->oid) &&
+                   oideq(&alias->oid, &ce->oid) &&
                    ce->ce_mode == alias->ce_mode);
 
        if (pretend)
-               free(ce);
+               discard_cache_entry(ce);
        else if (add_index_entry(istate, ce, add_option)) {
-               free(ce);
+               discard_cache_entry(ce);
                return error("unable to add %s to index", path);
        }
        if (verbose && !was_same)
@@ -745,12 +797,25 @@ int add_file_to_index(struct index_state *istate, const char *path, int flags)
        return add_to_index(istate, path, &st, flags);
 }
 
-struct cache_entry *make_cache_entry(unsigned int mode,
-               const unsigned char *sha1, const char *path, int stage,
-               unsigned int refresh_options)
+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)
 {
-       int size, len;
        struct cache_entry *ce, *ret;
+       int len;
 
        if (!verify_path(path, mode)) {
                error("Invalid path '%s'", path);
@@ -758,21 +823,43 @@ struct cache_entry *make_cache_entry(unsigned int mode,
        }
 
        len = strlen(path);
-       size = cache_entry_size(len);
-       ce = xcalloc(1, size);
+       ce = make_empty_cache_entry(istate, len);
 
-       hashcpy(ce->oid.hash, sha1);
+       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(ce, refresh_options);
+       ret = refresh_cache_entry(istate, ce, refresh_options);
        if (ret != ce)
-               free(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.
  *
@@ -1268,7 +1355,7 @@ static struct cache_entry *refresh_cache_ent(struct index_state *istate,
 {
        struct stat st;
        struct cache_entry *updated;
-       int changed, size;
+       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;
@@ -1348,8 +1435,7 @@ static struct cache_entry *refresh_cache_ent(struct index_state *istate,
                return NULL;
        }
 
-       size = ce_size(ce);
-       updated = xmalloc(size);
+       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(updated, &st);
@@ -1398,8 +1484,13 @@ int refresh_index(struct index_state *istate, unsigned int flags,
        const char *typechange_fmt;
        const char *added_fmt;
        const char *unmerged_fmt;
-       uint64_t start = getnanotime();
+       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");
@@ -1415,7 +1506,7 @@ int refresh_index(struct index_state *istate, unsigned int flags,
                if (ignore_submodules && S_ISGITLINK(ce->ce_mode))
                        continue;
 
-               if (pathspec && !ce_path_match(ce, pathspec, seen))
+               if (pathspec && !ce_path_match(istate, ce, pathspec, seen))
                        filtered = 1;
 
                if (ce_stage(ce)) {
@@ -1438,6 +1529,8 @@ int refresh_index(struct index_state *istate, unsigned int flags,
                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;
 
@@ -1469,14 +1562,19 @@ int refresh_index(struct index_state *istate, unsigned int flags,
 
                replace_index_entry(istate, i, new_entry);
        }
-       trace_performance_since(start, "refresh index");
+       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 cache_entry *ce,
-                                              unsigned int options)
+struct cache_entry *refresh_cache_entry(struct index_state *istate,
+                                       struct cache_entry *ce,
+                                       unsigned int options)
 {
-       return refresh_cache_ent(&the_index, ce, options, NULL, NULL);
+       return refresh_cache_ent(istate, ce, options, NULL, NULL);
 }
 
 
@@ -1571,7 +1669,7 @@ int verify_index_checksum;
 /* Allow fsck to force verification of the cache entry order. */
 int verify_ce_order;
 
-static int verify_hdr(struct cache_header *hdr, unsigned long size)
+static int verify_hdr(const struct cache_header *hdr, unsigned long size)
 {
        git_hash_ctx c;
        unsigned char hash[GIT_MAX_RAWSZ];
@@ -1589,13 +1687,13 @@ static int verify_hdr(struct cache_header *hdr, unsigned long size)
        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 (hashcmp(hash, (unsigned char *)hdr + size - the_hash_algo->rawsz))
+       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, void *data, unsigned long sz)
+                               const char *ext, const char *data, unsigned long sz)
 {
        switch (CACHE_EXT(ext)) {
        case CACHE_EXT_TREE:
@@ -1614,6 +1712,10 @@ static int read_index_extension(struct index_state *istate,
        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",
@@ -1634,61 +1736,25 @@ int read_index(struct index_state *istate)
        return read_index_from(istate, get_index_file(), get_git_dir());
 }
 
-static struct cache_entry *cache_entry_from_ondisk(struct ondisk_cache_entry *ondisk,
-                                                  unsigned int flags,
-                                                  const char *name,
-                                                  size_t len)
-{
-       struct cache_entry *ce = xmalloc(cache_entry_size(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->sha1);
-       memcpy(ce->name, name, len);
-       ce->name[len] = '\0';
-       return ce;
-}
-
-/*
- * 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.
- */
-static unsigned long expand_name_field(struct strbuf *name, const char *cp_)
-{
-       const unsigned char *ep, *cp = (const unsigned char *)cp_;
-       size_t len = decode_varint(&cp);
-
-       if (name->len < len)
-               die("malformed name field in the index");
-       strbuf_remove(name, name->len - len, len);
-       for (ep = cp; *ep; ep++)
-               ; /* find the end */
-       strbuf_add(name, cp, ep - cp);
-       return (const char *)ep + 1 - cp_;
-}
-
-static struct cache_entry *create_from_disk(struct ondisk_cache_entry *ondisk,
+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,
-                                           struct strbuf *previous_name)
+                                           const struct cache_entry *previous_ce)
 {
        struct cache_entry *ce;
        size_t len;
        const char *name;
        unsigned int flags;
+       size_t copy_len;
+       /*
+        * 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(&ondisk->flags);
@@ -1708,21 +1774,55 @@ static struct cache_entry *create_from_disk(struct ondisk_cache_entry *ondisk,
        else
                name = ondisk->name;
 
-       if (!previous_name) {
-               /* v3 and earlier */
-               if (len == CE_NAMEMASK)
-                       len = strlen(name);
-               ce = cache_entry_from_ondisk(ondisk, flags, name, len);
+       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;
+               } else {
+                       copy_len = 0;
+               }
+               name = (const char *)cp;
+       }
 
-               *ent_size = ondisk_ce_size(ce);
-       } else {
-               unsigned long consumed;
-               consumed = expand_name_field(previous_name, name);
-               ce = cache_entry_from_ondisk(ondisk, flags,
-                                            previous_name->buf,
-                                            previous_name->len);
+       if (len == CE_NAMEMASK) {
+               len = strlen(name);
+               if (expand_name_field)
+                       len += copy_len;
+       }
 
-               *ent_size = (name - ((char *)ondisk)) + consumed;
+       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->sha1);
+
+       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;
 }
@@ -1792,16 +1892,253 @@ static void post_read_index_from(struct index_state *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];
+};
+
+#ifndef NO_PTHREADS
+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);
+#endif
+
+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
+{
+#ifndef NO_PTHREADS
+       pthread_t pthread;
+#endif
+       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;
+}
+
+#ifndef NO_PTHREADS
+
+/*
+ * 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,
+                       unsigned long src_offset, 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;
+}
+#endif
+
 /* 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, i;
+       int fd;
        struct stat st;
        unsigned long src_offset;
-       struct cache_header *hdr;
-       void *mmap;
+       const struct cache_header *hdr;
+       const char *mmap;
        size_t mmap_size;
-       struct strbuf previous_name_buf = STRBUF_INIT, *previous_name;
+       struct load_index_extensions p;
+       size_t extension_offset = 0;
+#ifndef NO_PTHREADS
+       int nr_threads, cpus;
+       struct index_entry_offset_table *ieot = NULL;
+#endif
 
        if (istate->initialized)
                return istate->cache_nr;
@@ -1827,61 +2164,85 @@ int do_read_index(struct index_state *istate, const char *path, int must_exist)
                die_errno("unable to map index file");
        close(fd);
 
-       hdr = mmap;
+       hdr = (const struct cache_header *)mmap;
        if (verify_hdr(hdr, mmap_size) < 0)
                goto unmap;
 
-       hashcpy(istate->sha1, (const unsigned char *)hdr + mmap_size - the_hash_algo->rawsz);
+       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;
 
-       if (istate->version == 4)
-               previous_name = &previous_name_buf;
-       else
-               previous_name = NULL;
+       p.istate = istate;
+       p.mmap = mmap;
+       p.mmap_size = mmap_size;
 
        src_offset = sizeof(*hdr);
-       for (i = 0; i < istate->cache_nr; i++) {
-               struct ondisk_cache_entry *disk_ce;
-               struct cache_entry *ce;
-               unsigned long consumed;
 
-               disk_ce = (struct ondisk_cache_entry *)((char *)mmap + src_offset);
-               ce = create_from_disk(disk_ce, &consumed, previous_name);
-               set_index_entry(istate, i, ce);
+#ifndef NO_PTHREADS
+       nr_threads = git_config_get_index_threads();
 
-               src_offset += consumed;
+       /* 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;
        }
-       strbuf_release(&previous_name_buf);
+
+       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, src_offset, nr_threads, ieot);
+               free(ieot);
+       } else {
+               src_offset += load_all_cache_entries(istate, mmap, mmap_size, src_offset);
+       }
+#else
+       src_offset += load_all_cache_entries(istate, mmap, mmap_size, src_offset);
+#endif
+
        istate->timestamp.sec = st.st_mtime;
        istate->timestamp.nsec = ST_MTIME_NSEC(st);
 
-       while (src_offset <= 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;
-               memcpy(&extsize, (char *)mmap + src_offset + 4, 4);
-               extsize = ntohl(extsize);
-               if (read_index_extension(istate,
-                                        (const char *) mmap + src_offset,
-                                        (char *) mmap + src_offset + 8,
-                                        extsize) < 0)
-                       goto unmap;
-               src_offset += 8;
-               src_offset += extsize;
+       /* if we created a thread, join it otherwise load the extensions on the primary thread */
+#ifndef NO_PTHREADS
+       if (extension_offset) {
+               int ret = pthread_join(p.pthread, NULL);
+               if (ret)
+                       die(_("unable to join load_index_extensions thread: %s"), strerror(ret));
+       }
+#endif
+       if (!extension_offset) {
+               p.src_offset = src_offset;
+               load_index_extensions(&p);
        }
-       munmap(mmap, mmap_size);
+       munmap((void *)mmap, mmap_size);
        return istate->cache_nr;
 
 unmap:
-       munmap(mmap, mmap_size);
+       munmap((void *)mmap, mmap_size);
        die("index file corrupt");
 }
 
@@ -1900,43 +2261,44 @@ static void freshen_shared_index(const char *shared_index, int warn)
 int read_index_from(struct index_state *istate, const char *path,
                    const char *gitdir)
 {
-       uint64_t start = getnanotime();
        struct split_index *split_index;
        int ret;
-       char *base_sha1_hex;
+       char *base_oid_hex;
        char *base_path;
 
        /* istate->initialized covers both .git/index and .git/sharedindex.xxx */
        if (istate->initialized)
                return istate->cache_nr;
 
+       trace_performance_enter();
        ret = do_read_index(istate, path, 0);
-       trace_performance_since(start, "read cache %s", path);
+       trace_performance_leave("read cache %s", path);
 
        split_index = istate->split_index;
-       if (!split_index || is_null_sha1(split_index->base_sha1)) {
+       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_sha1_hex = sha1_to_hex(split_index->base_sha1);
-       base_path = xstrfmt("%s/sharedindex.%s", gitdir, base_sha1_hex);
+       base_oid_hex = oid_to_hex(&split_index->base_oid);
+       base_path = xstrfmt("%s/sharedindex.%s", gitdir, base_oid_hex);
        ret = do_read_index(split_index->base, base_path, 1);
-       if (hashcmp(split_index->base_sha1, split_index->base->sha1))
+       if (!oideq(&split_index->base_oid, &split_index->base->oid))
                die("broken index, expect %s in %s, got %s",
-                   base_sha1_hex, base_path,
-                   sha1_to_hex(split_index->base->sha1));
+                   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_since(start, "read cache %s", base_path);
        free(base_path);
+       trace_performance_leave("read cache %s", base_path);
        return ret;
 }
 
@@ -1947,17 +2309,15 @@ int is_index_unborn(struct index_state *istate)
 
 int discard_index(struct index_state *istate)
 {
-       int i;
+       /*
+        * 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);
 
-       for (i = 0; i < istate->cache_nr; i++) {
-               if (istate->cache[i]->index &&
-                   istate->split_index &&
-                   istate->split_index->base &&
-                   istate->cache[i]->index <= istate->split_index->base->cache_nr &&
-                   istate->cache[i] == istate->split_index->base->cache[istate->cache[i]->index - 1])
-                       continue;
-               free(istate->cache[i]);
-       }
        resolve_undo_clear_index(istate);
        istate->cache_nr = 0;
        istate->cache_changed = 0;
@@ -1971,9 +2331,47 @@ int discard_index(struct index_state *istate)
        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) {
+                       die("internal error: 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])) {
+                               die("internal error: 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;
@@ -1984,6 +2382,44 @@ int unmerged_index(const struct index_state *istate)
        return 0;
 }
 
+int index_has_changes(struct index_state *istate,
+                     struct tree *tree,
+                     struct strbuf *sb)
+{
+       struct object_id cmp;
+       int i;
+
+       if (istate != &the_index) {
+               BUG("index_has_changes cannot yet accept istate != &the_index; do_diff_cache needs updating first.");
+       }
+       if (tree)
+               cmp = tree->object.oid;
+       if (tree || !get_oid_tree("HEAD", &cmp)) {
+               struct diff_options opt;
+
+               repo_diff_setup(the_repository, &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;
@@ -2022,11 +2458,15 @@ static int ce_write(git_hash_ctx *context, int fd, void *data, unsigned int len)
        return 0;
 }
 
-static int write_index_ext_header(git_hash_ctx *context, int fd,
-                                 unsigned int ext, unsigned int sz)
+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;
 }
@@ -2054,7 +2494,8 @@ static int ce_flush(git_hash_ctx *context, int fd, unsigned char *hash)
        return (write_in_full(fd, write_buffer, left) < 0) ? -1 : 0;
 }
 
-static void ce_smudge_racily_clean_entry(struct cache_entry *ce)
+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
@@ -2073,7 +2514,7 @@ static void ce_smudge_racily_clean_entry(struct cache_entry *ce)
                return;
        if (ce_match_stat_basic(ce, &st))
                return;
-       if (ce_modified_check_fs(ce, &st)) {
+       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:
@@ -2219,7 +2660,7 @@ static int verify_index_from(const struct index_state *istate, const char *path)
        if (n != the_hash_algo->rawsz)
                goto out;
 
-       if (hashcmp(istate->sha1, hash))
+       if (!hasheq(istate->oid.hash, hash))
                goto out;
 
        close(fd);
@@ -2269,7 +2710,7 @@ static int do_write_index(struct index_state *istate, struct tempfile *tempfile,
 {
        uint64_t start = getnanotime();
        int newfd = tempfile->fd;
-       git_hash_ctx c;
+       git_hash_ctx c, eoie_c;
        struct cache_header hdr;
        int i, err = 0, removed, extended, hdr_version;
        struct cache_entry **cache = istate->cache;
@@ -2278,6 +2719,10 @@ static int do_write_index(struct index_state *istate, struct tempfile *tempfile,
        struct ondisk_cache_entry_extended 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)
@@ -2293,7 +2738,7 @@ static int do_write_index(struct index_state *istate, struct tempfile *tempfile,
 
        if (!istate->version) {
                istate->version = get_index_format_default();
-               if (getenv("GIT_TEST_SPLIT_INDEX"))
+               if (git_env_bool("GIT_TEST_SPLIT_INDEX", 0))
                        init_split_index(istate);
        }
 
@@ -2311,6 +2756,46 @@ static int do_write_index(struct index_state *istate, struct tempfile *tempfile,
        if (ce_write(&c, newfd, &hdr, sizeof(hdr)) < 0)
                return -1;
 
+#ifndef NO_PTHREADS
+       nr_threads = git_config_get_index_threads();
+       if (nr_threads != 1) {
+               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);
+               }
+       }
+#endif
+
+       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++) {
@@ -2318,7 +2803,7 @@ static int do_write_index(struct index_state *istate, struct tempfile *tempfile,
                if (ce->ce_flags & CE_REMOVE)
                        continue;
                if (!ce_uptodate(ce) && is_racy_timestamp(istate, ce))
-                       ce_smudge_racily_clean_entry(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;
@@ -2332,23 +2817,79 @@ static int do_write_index(struct index_state *istate, struct tempfile *tempfile,
 
                        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)
+       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.
+        */
+#ifndef NO_PTHREADS
+       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;
+       }
+#endif
+
        if (!strip_extensions && istate->split_index) {
                struct strbuf sb = STRBUF_INIT;
 
                err = write_link_extension(&sb, istate) < 0 ||
-                       write_index_ext_header(&c, newfd, CACHE_EXT_LINK,
+                       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);
@@ -2359,7 +2900,7 @@ static int do_write_index(struct index_state *istate, struct tempfile *tempfile,
                struct strbuf sb = STRBUF_INIT;
 
                cache_tree_write(&sb, istate->cache_tree);
-               err = write_index_ext_header(&c, newfd, CACHE_EXT_TREE, sb.len) < 0
+               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)
@@ -2369,7 +2910,7 @@ static int do_write_index(struct index_state *istate, struct tempfile *tempfile,
                struct strbuf sb = STRBUF_INIT;
 
                resolve_undo_write(&sb, istate->resolve_undo);
-               err = write_index_ext_header(&c, newfd, CACHE_EXT_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);
@@ -2380,7 +2921,7 @@ static int do_write_index(struct index_state *istate, struct tempfile *tempfile,
                struct strbuf sb = STRBUF_INIT;
 
                write_untracked_extension(&sb, istate->untracked);
-               err = write_index_ext_header(&c, newfd, CACHE_EXT_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);
@@ -2391,14 +2932,31 @@ static int do_write_index(struct index_state *istate, struct tempfile *tempfile,
                struct strbuf sb = STRBUF_INIT;
 
                write_fsmonitor_extension(&sb, istate);
-               err = write_index_ext_header(&c, newfd, CACHE_EXT_FSMONITOR, sb.len) < 0
+               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) {
+               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->sha1))
+       if (ce_flush(&c, newfd, istate->oid.hash))
                return -1;
        if (close_tempfile_gently(tempfile)) {
                error(_("could not close '%s'"), tempfile->filename.buf);
@@ -2522,10 +3080,10 @@ static int write_shared_index(struct index_state *istate,
                return ret;
        }
        ret = rename_tempfile(temp,
-                             git_path("sharedindex.%s", sha1_to_hex(si->base->sha1)));
+                             git_path("sharedindex.%s", oid_to_hex(&si->base->oid)));
        if (!ret) {
-               hashcpy(si->base_sha1, si->base->sha1);
-               clean_shared_index_files(sha1_to_hex(si->base->sha1));
+               oidcpy(&si->base_oid, &si->base->oid);
+               clean_shared_index_files(oid_to_hex(&si->base->oid));
        }
 
        return ret;
@@ -2567,6 +3125,9 @@ int write_locked_index(struct index_state *istate, struct lock_file *lock,
        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(istate);
+
        if ((flags & SKIP_IF_UNCHANGED) && !istate->cache_changed) {
                if (flags & COMMIT_LOCK)
                        rollback_lock_file(lock);
@@ -2579,13 +3140,13 @@ int write_locked_index(struct index_state *istate, struct lock_file *lock,
        if (!si || alternate_index_output ||
            (istate->cache_changed & ~EXTMASK)) {
                if (si)
-                       hashclr(si->base_sha1);
+                       oidclr(&si->base_oid);
                ret = do_write_locked_index(istate, lock, flags);
                goto out;
        }
 
-       if (getenv("GIT_TEST_SPLIT_INDEX")) {
-               int v = si->base_sha1[0];
+       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;
        }
@@ -2600,7 +3161,7 @@ int write_locked_index(struct index_state *istate, struct lock_file *lock,
 
                temp = mks_tempfile(git_path("sharedindex_XXXXXX"));
                if (!temp) {
-                       hashclr(si->base_sha1);
+                       oidclr(&si->base_oid);
                        ret = do_write_locked_index(istate, lock, flags);
                        goto out;
                }
@@ -2620,7 +3181,7 @@ int write_locked_index(struct index_state *istate, struct lock_file *lock,
        /* Freshen the shared index only if the split-index was written */
        if (!ret && !new_shared_index) {
                const char *shared_index = git_path("sharedindex.%s",
-                                                   sha1_to_hex(si->base_sha1));
+                                                   oid_to_hex(&si->base_oid));
                freshen_shared_index(shared_index, 1);
        }
 
@@ -2632,10 +3193,13 @@ int write_locked_index(struct index_state *istate, struct lock_file *lock,
 
 /*
  * Read the index file that is potentially unmerged into given
- * index_state, dropping any unmerged entries.  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().
+ * 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 read_index_unmerged(struct index_state *istate)
 {
@@ -2646,19 +3210,18 @@ int read_index_unmerged(struct index_state *istate)
        for (i = 0; i < istate->cache_nr; i++) {
                struct cache_entry *ce = istate->cache[i];
                struct cache_entry *new_ce;
-               int size, len;
+               int len;
 
                if (!ce_stage(ce))
                        continue;
                unmerged = 1;
                len = ce_namelen(ce);
-               size = cache_entry_size(len);
-               new_ce = xcalloc(1, size);
+               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, 0))
+               if (add_index_entry(istate, new_ce, ADD_CACHE_SKIP_DFCHECK))
                        return error("%s: cannot drop to stage #0",
                                     new_ce->name);
        }
@@ -2718,7 +3281,7 @@ void *read_blob_data_from_index(const struct index_state *istate,
        }
        if (pos < 0)
                return NULL;
-       data = read_sha1_file(istate->cache[pos]->oid.hash, &type, &sz);
+       data = read_object_file(&istate->cache[pos]->oid, &type, &sz);
        if (!data || type != OBJ_BLOB) {
                free(data);
                return NULL;
@@ -2761,4 +3324,222 @@ 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);
+}
+
+#ifndef NO_PTHREADS
+#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));
+       }
+}
+#endif