Squashed 'third_party/git/' content from commit cb71568594

git-subtree-dir: third_party/git
git-subtree-split: cb715685942260375e1eb8153b0768a376e4ece7

1 files changed, 3201 insertions, 0 deletions

diff --git a/refs/files-backend.c b/refs/files-backend.c
new file mode 100644
index 000000000000..d60767ab739f
--- /dev/null
+++ b/refs/files-backend.c
@@ -0,0 +1,3201 @@
+#include "../cache.h"
+#include "../config.h"
+#include "../refs.h"
+#include "refs-internal.h"
+#include "ref-cache.h"
+#include "packed-backend.h"
+#include "../iterator.h"
+#include "../dir-iterator.h"
+#include "../lockfile.h"
+#include "../object.h"
+#include "../dir.h"
+#include "../chdir-notify.h"
+#include "worktree.h"
+
+/*
+ * This backend uses the following flags in `ref_update::flags` for
+ * internal bookkeeping purposes. Their numerical values must not
+ * conflict with REF_NO_DEREF, REF_FORCE_CREATE_REFLOG, REF_HAVE_NEW,
+ * REF_HAVE_OLD, or REF_IS_PRUNING, which are also stored in
+ * `ref_update::flags`.
+ */
+
+/*
+ * Used as a flag in ref_update::flags when a loose ref is being
+ * pruned. This flag must only be used when REF_NO_DEREF is set.
+ */
+#define REF_IS_PRUNING (1 << 4)
+
+/*
+ * Flag passed to lock_ref_sha1_basic() telling it to tolerate broken
+ * refs (i.e., because the reference is about to be deleted anyway).
+ */
+#define REF_DELETING (1 << 5)
+
+/*
+ * Used as a flag in ref_update::flags when the lockfile needs to be
+ * committed.
+ */
+#define REF_NEEDS_COMMIT (1 << 6)
+
+/*
+ * Used as a flag in ref_update::flags when we want to log a ref
+ * update but not actually perform it.  This is used when a symbolic
+ * ref update is split up.
+ */
+#define REF_LOG_ONLY (1 << 7)
+
+/*
+ * Used as a flag in ref_update::flags when the ref_update was via an
+ * update to HEAD.
+ */
+#define REF_UPDATE_VIA_HEAD (1 << 8)
+
+/*
+ * Used as a flag in ref_update::flags when the loose reference has
+ * been deleted.
+ */
+#define REF_DELETED_LOOSE (1 << 9)
+
+struct ref_lock {
+	char *ref_name;
+	struct lock_file lk;
+	struct object_id old_oid;
+};
+
+struct files_ref_store {
+	struct ref_store base;
+	unsigned int store_flags;
+
+	char *gitdir;
+	char *gitcommondir;
+
+	struct ref_cache *loose;
+
+	struct ref_store *packed_ref_store;
+};
+
+static void clear_loose_ref_cache(struct files_ref_store *refs)
+{
+	if (refs->loose) {
+		free_ref_cache(refs->loose);
+		refs->loose = NULL;
+	}
+}
+
+/*
+ * Create a new submodule ref cache and add it to the internal
+ * set of caches.
+ */
+static struct ref_store *files_ref_store_create(const char *gitdir,
+						unsigned int flags)
+{
+	struct files_ref_store *refs = xcalloc(1, sizeof(*refs));
+	struct ref_store *ref_store = (struct ref_store *)refs;
+	struct strbuf sb = STRBUF_INIT;
+
+	base_ref_store_init(ref_store, &refs_be_files);
+	refs->store_flags = flags;
+
+	refs->gitdir = xstrdup(gitdir);
+	get_common_dir_noenv(&sb, gitdir);
+	refs->gitcommondir = strbuf_detach(&sb, NULL);
+	strbuf_addf(&sb, "%s/packed-refs", refs->gitcommondir);
+	refs->packed_ref_store = packed_ref_store_create(sb.buf, flags);
+	strbuf_release(&sb);
+
+	chdir_notify_reparent("files-backend $GIT_DIR",
+			      &refs->gitdir);
+	chdir_notify_reparent("files-backend $GIT_COMMONDIR",
+			      &refs->gitcommondir);
+
+	return ref_store;
+}
+
+/*
+ * Die if refs is not the main ref store. caller is used in any
+ * necessary error messages.
+ */
+static void files_assert_main_repository(struct files_ref_store *refs,
+					 const char *caller)
+{
+	if (refs->store_flags & REF_STORE_MAIN)
+		return;
+
+	BUG("operation %s only allowed for main ref store", caller);
+}
+
+/*
+ * Downcast ref_store to files_ref_store. Die if ref_store is not a
+ * files_ref_store. required_flags is compared with ref_store's
+ * store_flags to ensure the ref_store has all required capabilities.
+ * "caller" is used in any necessary error messages.
+ */
+static struct files_ref_store *files_downcast(struct ref_store *ref_store,
+					      unsigned int required_flags,
+					      const char *caller)
+{
+	struct files_ref_store *refs;
+
+	if (ref_store->be != &refs_be_files)
+		BUG("ref_store is type \"%s\" not \"files\" in %s",
+		    ref_store->be->name, caller);
+
+	refs = (struct files_ref_store *)ref_store;
+
+	if ((refs->store_flags & required_flags) != required_flags)
+		BUG("operation %s requires abilities 0x%x, but only have 0x%x",
+		    caller, required_flags, refs->store_flags);
+
+	return refs;
+}
+
+static void files_reflog_path_other_worktrees(struct files_ref_store *refs,
+					      struct strbuf *sb,
+					      const char *refname)
+{
+	const char *real_ref;
+	const char *worktree_name;
+	int length;
+
+	if (parse_worktree_ref(refname, &worktree_name, &length, &real_ref))
+		BUG("refname %s is not a other-worktree ref", refname);
+
+	if (worktree_name)
+		strbuf_addf(sb, "%s/worktrees/%.*s/logs/%s", refs->gitcommondir,
+			    length, worktree_name, real_ref);
+	else
+		strbuf_addf(sb, "%s/logs/%s", refs->gitcommondir,
+			    real_ref);
+}
+
+static void files_reflog_path(struct files_ref_store *refs,
+			      struct strbuf *sb,
+			      const char *refname)
+{
+	switch (ref_type(refname)) {
+	case REF_TYPE_PER_WORKTREE:
+	case REF_TYPE_PSEUDOREF:
+		strbuf_addf(sb, "%s/logs/%s", refs->gitdir, refname);
+		break;
+	case REF_TYPE_OTHER_PSEUDOREF:
+	case REF_TYPE_MAIN_PSEUDOREF:
+		files_reflog_path_other_worktrees(refs, sb, refname);
+		break;
+	case REF_TYPE_NORMAL:
+		strbuf_addf(sb, "%s/logs/%s", refs->gitcommondir, refname);
+		break;
+	default:
+		BUG("unknown ref type %d of ref %s",
+		    ref_type(refname), refname);
+	}
+}
+
+static void files_ref_path(struct files_ref_store *refs,
+			   struct strbuf *sb,
+			   const char *refname)
+{
+	switch (ref_type(refname)) {
+	case REF_TYPE_PER_WORKTREE:
+	case REF_TYPE_PSEUDOREF:
+		strbuf_addf(sb, "%s/%s", refs->gitdir, refname);
+		break;
+	case REF_TYPE_MAIN_PSEUDOREF:
+		if (!skip_prefix(refname, "main-worktree/", &refname))
+			BUG("ref %s is not a main pseudoref", refname);
+		/* fallthrough */
+	case REF_TYPE_OTHER_PSEUDOREF:
+	case REF_TYPE_NORMAL:
+		strbuf_addf(sb, "%s/%s", refs->gitcommondir, refname);
+		break;
+	default:
+		BUG("unknown ref type %d of ref %s",
+		    ref_type(refname), refname);
+	}
+}
+
+/*
+ * Manually add refs/bisect, refs/rewritten and refs/worktree, which, being
+ * per-worktree, might not appear in the directory listing for
+ * refs/ in the main repo.
+ */
+static void add_per_worktree_entries_to_dir(struct ref_dir *dir, const char *dirname)
+{
+	const char *prefixes[] = { "refs/bisect/", "refs/worktree/", "refs/rewritten/" };
+	int ip;
+
+	if (strcmp(dirname, "refs/"))
+		return;
+
+	for (ip = 0; ip < ARRAY_SIZE(prefixes); ip++) {
+		const char *prefix = prefixes[ip];
+		int prefix_len = strlen(prefix);
+		struct ref_entry *child_entry;
+		int pos;
+
+		pos = search_ref_dir(dir, prefix, prefix_len);
+		if (pos >= 0)
+			continue;
+		child_entry = create_dir_entry(dir->cache, prefix, prefix_len, 1);
+		add_entry_to_dir(dir, child_entry);
+	}
+}
+
+/*
+ * Read the loose references from the namespace dirname into dir
+ * (without recursing).  dirname must end with '/'.  dir must be the
+ * directory entry corresponding to dirname.
+ */
+static void loose_fill_ref_dir(struct ref_store *ref_store,
+			       struct ref_dir *dir, const char *dirname)
+{
+	struct files_ref_store *refs =
+		files_downcast(ref_store, REF_STORE_READ, "fill_ref_dir");
+	DIR *d;
+	struct dirent *de;
+	int dirnamelen = strlen(dirname);
+	struct strbuf refname;
+	struct strbuf path = STRBUF_INIT;
+	size_t path_baselen;
+
+	files_ref_path(refs, &path, dirname);
+	path_baselen = path.len;
+
+	d = opendir(path.buf);
+	if (!d) {
+		strbuf_release(&path);
+		return;
+	}
+
+	strbuf_init(&refname, dirnamelen + 257);
+	strbuf_add(&refname, dirname, dirnamelen);
+
+	while ((de = readdir(d)) != NULL) {
+		struct object_id oid;
+		struct stat st;
+		int flag;
+
+		if (de->d_name[0] == '.')
+			continue;
+		if (ends_with(de->d_name, ".lock"))
+			continue;
+		strbuf_addstr(&refname, de->d_name);
+		strbuf_addstr(&path, de->d_name);
+		if (stat(path.buf, &st) < 0) {
+			; /* silently ignore */
+		} else if (S_ISDIR(st.st_mode)) {
+			strbuf_addch(&refname, '/');
+			add_entry_to_dir(dir,
+					 create_dir_entry(dir->cache, refname.buf,
+							  refname.len, 1));
+		} else {
+			if (!refs_resolve_ref_unsafe(&refs->base,
+						     refname.buf,
+						     RESOLVE_REF_READING,
+						     &oid, &flag)) {
+				oidclr(&oid);
+				flag |= REF_ISBROKEN;
+			} else if (is_null_oid(&oid)) {
+				/*
+				 * It is so astronomically unlikely
+				 * that null_oid is the OID of an
+				 * actual object that we consider its
+				 * appearance in a loose reference
+				 * file to be repo corruption
+				 * (probably due to a software bug).
+				 */
+				flag |= REF_ISBROKEN;
+			}
+
+			if (check_refname_format(refname.buf,
+						 REFNAME_ALLOW_ONELEVEL)) {
+				if (!refname_is_safe(refname.buf))
+					die("loose refname is dangerous: %s", refname.buf);
+				oidclr(&oid);
+				flag |= REF_BAD_NAME | REF_ISBROKEN;
+			}
+			add_entry_to_dir(dir,
+					 create_ref_entry(refname.buf, &oid, flag));
+		}
+		strbuf_setlen(&refname, dirnamelen);
+		strbuf_setlen(&path, path_baselen);
+	}
+	strbuf_release(&refname);
+	strbuf_release(&path);
+	closedir(d);
+
+	add_per_worktree_entries_to_dir(dir, dirname);
+}
+
+static struct ref_cache *get_loose_ref_cache(struct files_ref_store *refs)
+{
+	if (!refs->loose) {
+		/*
+		 * Mark the top-level directory complete because we
+		 * are about to read the only subdirectory that can
+		 * hold references:
+		 */
+		refs->loose = create_ref_cache(&refs->base, loose_fill_ref_dir);
+
+		/* We're going to fill the top level ourselves: */
+		refs->loose->root->flag &= ~REF_INCOMPLETE;
+
+		/*
+		 * Add an incomplete entry for "refs/" (to be filled
+		 * lazily):
+		 */
+		add_entry_to_dir(get_ref_dir(refs->loose->root),
+				 create_dir_entry(refs->loose, "refs/", 5, 1));
+	}
+	return refs->loose;
+}
+
+static int files_read_raw_ref(struct ref_store *ref_store,
+			      const char *refname, struct object_id *oid,
+			      struct strbuf *referent, unsigned int *type)
+{
+	struct files_ref_store *refs =
+		files_downcast(ref_store, REF_STORE_READ, "read_raw_ref");
+	struct strbuf sb_contents = STRBUF_INIT;
+	struct strbuf sb_path = STRBUF_INIT;
+	const char *path;
+	const char *buf;
+	const char *p;
+	struct stat st;
+	int fd;
+	int ret = -1;
+	int save_errno;
+	int remaining_retries = 3;
+
+	*type = 0;
+	strbuf_reset(&sb_path);
+
+	files_ref_path(refs, &sb_path, refname);
+
+	path = sb_path.buf;
+
+stat_ref:
+	/*
+	 * We might have to loop back here to avoid a race
+	 * condition: first we lstat() the file, then we try
+	 * to read it as a link or as a file.  But if somebody
+	 * changes the type of the file (file <-> directory
+	 * <-> symlink) between the lstat() and reading, then
+	 * we don't want to report that as an error but rather
+	 * try again starting with the lstat().
+	 *
+	 * We'll keep a count of the retries, though, just to avoid
+	 * any confusing situation sending us into an infinite loop.
+	 */
+
+	if (remaining_retries-- <= 0)
+		goto out;
+
+	if (lstat(path, &st) < 0) {
+		if (errno != ENOENT)
+			goto out;
+		if (refs_read_raw_ref(refs->packed_ref_store, refname,
+				      oid, referent, type)) {
+			errno = ENOENT;
+			goto out;
+		}
+		ret = 0;
+		goto out;
+	}
+
+	/* Follow "normalized" - ie "refs/.." symlinks by hand */
+	if (S_ISLNK(st.st_mode)) {
+		strbuf_reset(&sb_contents);
+		if (strbuf_readlink(&sb_contents, path, st.st_size) < 0) {
+			if (errno == ENOENT || errno == EINVAL)
+				/* inconsistent with lstat; retry */
+				goto stat_ref;
+			else
+				goto out;
+		}
+		if (starts_with(sb_contents.buf, "refs/") &&
+		    !check_refname_format(sb_contents.buf, 0)) {
+			strbuf_swap(&sb_contents, referent);
+			*type |= REF_ISSYMREF;
+			ret = 0;
+			goto out;
+		}
+		/*
+		 * It doesn't look like a refname; fall through to just
+		 * treating it like a non-symlink, and reading whatever it
+		 * points to.
+		 */
+	}
+
+	/* Is it a directory? */
+	if (S_ISDIR(st.st_mode)) {
+		/*
+		 * Even though there is a directory where the loose
+		 * ref is supposed to be, there could still be a
+		 * packed ref:
+		 */
+		if (refs_read_raw_ref(refs->packed_ref_store, refname,
+				      oid, referent, type)) {
+			errno = EISDIR;
+			goto out;
+		}
+		ret = 0;
+		goto out;
+	}
+
+	/*
+	 * Anything else, just open it and try to use it as
+	 * a ref
+	 */
+	fd = open(path, O_RDONLY);
+	if (fd < 0) {
+		if (errno == ENOENT && !S_ISLNK(st.st_mode))
+			/* inconsistent with lstat; retry */
+			goto stat_ref;
+		else
+			goto out;
+	}
+	strbuf_reset(&sb_contents);
+	if (strbuf_read(&sb_contents, fd, 256) < 0) {
+		int save_errno = errno;
+		close(fd);
+		errno = save_errno;
+		goto out;
+	}
+	close(fd);
+	strbuf_rtrim(&sb_contents);
+	buf = sb_contents.buf;
+	if (starts_with(buf, "ref:")) {
+		buf += 4;
+		while (isspace(*buf))
+			buf++;
+
+		strbuf_reset(referent);
+		strbuf_addstr(referent, buf);
+		*type |= REF_ISSYMREF;
+		ret = 0;
+		goto out;
+	}
+
+	/*
+	 * Please note that FETCH_HEAD has additional
+	 * data after the sha.
+	 */
+	if (parse_oid_hex(buf, oid, &p) ||
+	    (*p != '\0' && !isspace(*p))) {
+		*type |= REF_ISBROKEN;
+		errno = EINVAL;
+		goto out;
+	}
+
+	ret = 0;
+
+out:
+	save_errno = errno;
+	strbuf_release(&sb_path);
+	strbuf_release(&sb_contents);
+	errno = save_errno;
+	return ret;
+}
+
+static void unlock_ref(struct ref_lock *lock)
+{
+	rollback_lock_file(&lock->lk);
+	free(lock->ref_name);
+	free(lock);
+}
+
+/*
+ * Lock refname, without following symrefs, and set *lock_p to point
+ * at a newly-allocated lock object. Fill in lock->old_oid, referent,
+ * and type similarly to read_raw_ref().
+ *
+ * The caller must verify that refname is a "safe" reference name (in
+ * the sense of refname_is_safe()) before calling this function.
+ *
+ * If the reference doesn't already exist, verify that refname doesn't
+ * have a D/F conflict with any existing references. extras and skip
+ * are passed to refs_verify_refname_available() for this check.
+ *
+ * If mustexist is not set and the reference is not found or is
+ * broken, lock the reference anyway but clear old_oid.
+ *
+ * Return 0 on success. On failure, write an error message to err and
+ * return TRANSACTION_NAME_CONFLICT or TRANSACTION_GENERIC_ERROR.
+ *
+ * Implementation note: This function is basically
+ *
+ *     lock reference
+ *     read_raw_ref()
+ *
+ * but it includes a lot more code to
+ * - Deal with possible races with other processes
+ * - Avoid calling refs_verify_refname_available() when it can be
+ *   avoided, namely if we were successfully able to read the ref
+ * - Generate informative error messages in the case of failure
+ */
+static int lock_raw_ref(struct files_ref_store *refs,
+			const char *refname, int mustexist,
+			const struct string_list *extras,
+			const struct string_list *skip,
+			struct ref_lock **lock_p,
+			struct strbuf *referent,
+			unsigned int *type,
+			struct strbuf *err)
+{
+	struct ref_lock *lock;
+	struct strbuf ref_file = STRBUF_INIT;
+	int attempts_remaining = 3;
+	int ret = TRANSACTION_GENERIC_ERROR;
+
+	assert(err);
+	files_assert_main_repository(refs, "lock_raw_ref");
+
+	*type = 0;
+
+	/* First lock the file so it can't change out from under us. */
+
+	*lock_p = lock = xcalloc(1, sizeof(*lock));
+
+	lock->ref_name = xstrdup(refname);
+	files_ref_path(refs, &ref_file, refname);
+
+retry:
+	switch (safe_create_leading_directories(ref_file.buf)) {
+	case SCLD_OK:
+		break; /* success */
+	case SCLD_EXISTS:
+		/*
+		 * Suppose refname is "refs/foo/bar". We just failed
+		 * to create the containing directory, "refs/foo",
+		 * because there was a non-directory in the way. This
+		 * indicates a D/F conflict, probably because of
+		 * another reference such as "refs/foo". There is no
+		 * reason to expect this error to be transitory.
+		 */
+		if (refs_verify_refname_available(&refs->base, refname,
+						  extras, skip, err)) {
+			if (mustexist) {
+				/*
+				 * To the user the relevant error is
+				 * that the "mustexist" reference is
+				 * missing:
+				 */
+				strbuf_reset(err);
+				strbuf_addf(err, "unable to resolve reference '%s'",
+					    refname);
+			} else {
+				/*
+				 * The error message set by
+				 * refs_verify_refname_available() is
+				 * OK.
+				 */
+				ret = TRANSACTION_NAME_CONFLICT;
+			}
+		} else {
+			/*
+			 * The file that is in the way isn't a loose
+			 * reference. Report it as a low-level
+			 * failure.
+			 */
+			strbuf_addf(err, "unable to create lock file %s.lock; "
+				    "non-directory in the way",
+				    ref_file.buf);
+		}
+		goto error_return;
+	case SCLD_VANISHED:
+		/* Maybe another process was tidying up. Try again. */
+		if (--attempts_remaining > 0)
+			goto retry;
+		/* fall through */
+	default:
+		strbuf_addf(err, "unable to create directory for %s",
+			    ref_file.buf);
+		goto error_return;
+	}
+
+	if (hold_lock_file_for_update_timeout(
+			    &lock->lk, ref_file.buf, LOCK_NO_DEREF,
+			    get_files_ref_lock_timeout_ms()) < 0) {
+		if (errno == ENOENT && --attempts_remaining > 0) {
+			/*
+			 * Maybe somebody just deleted one of the
+			 * directories leading to ref_file.  Try
+			 * again:
+			 */
+			goto retry;
+		} else {
+			unable_to_lock_message(ref_file.buf, errno, err);
+			goto error_return;
+		}
+	}
+
+	/*
+	 * Now we hold the lock and can read the reference without
+	 * fear that its value will change.
+	 */
+
+	if (files_read_raw_ref(&refs->base, refname,
+			       &lock->old_oid, referent, type)) {
+		if (errno == ENOENT) {
+			if (mustexist) {
+				/* Garden variety missing reference. */
+				strbuf_addf(err, "unable to resolve reference '%s'",
+					    refname);
+				goto error_return;
+			} else {
+				/*
+				 * Reference is missing, but that's OK. We
+				 * know that there is not a conflict with
+				 * another loose reference because
+				 * (supposing that we are trying to lock
+				 * reference "refs/foo/bar"):
+				 *
+				 * - We were successfully able to create
+				 *   the lockfile refs/foo/bar.lock, so we
+				 *   know there cannot be a loose reference
+				 *   named "refs/foo".
+				 *
+				 * - We got ENOENT and not EISDIR, so we
+				 *   know that there cannot be a loose
+				 *   reference named "refs/foo/bar/baz".
+				 */
+			}
+		} else if (errno == EISDIR) {
+			/*
+			 * There is a directory in the way. It might have
+			 * contained references that have been deleted. If
+			 * we don't require that the reference already
+			 * exists, try to remove the directory so that it
+			 * doesn't cause trouble when we want to rename the
+			 * lockfile into place later.
+			 */
+			if (mustexist) {
+				/* Garden variety missing reference. */
+				strbuf_addf(err, "unable to resolve reference '%s'",
+					    refname);
+				goto error_return;
+			} else if (remove_dir_recursively(&ref_file,
+							  REMOVE_DIR_EMPTY_ONLY)) {
+				if (refs_verify_refname_available(
+						    &refs->base, refname,
+						    extras, skip, err)) {
+					/*
+					 * The error message set by
+					 * verify_refname_available() is OK.
+					 */
+					ret = TRANSACTION_NAME_CONFLICT;
+					goto error_return;
+				} else {
+					/*
+					 * We can't delete the directory,
+					 * but we also don't know of any
+					 * references that it should
+					 * contain.
+					 */
+					strbuf_addf(err, "there is a non-empty directory '%s' "
+						    "blocking reference '%s'",
+						    ref_file.buf, refname);
+					goto error_return;
+				}
+			}
+		} else if (errno == EINVAL && (*type & REF_ISBROKEN)) {
+			strbuf_addf(err, "unable to resolve reference '%s': "
+				    "reference broken", refname);
+			goto error_return;
+		} else {
+			strbuf_addf(err, "unable to resolve reference '%s': %s",
+				    refname, strerror(errno));
+			goto error_return;
+		}
+
+		/*
+		 * If the ref did not exist and we are creating it,
+		 * make sure there is no existing packed ref that
+		 * conflicts with refname:
+		 */
+		if (refs_verify_refname_available(
+				    refs->packed_ref_store, refname,
+				    extras, skip, err))
+			goto error_return;
+	}
+
+	ret = 0;
+	goto out;
+
+error_return:
+	unlock_ref(lock);
+	*lock_p = NULL;
+
+out:
+	strbuf_release(&ref_file);
+	return ret;
+}
+
+struct files_ref_iterator {
+	struct ref_iterator base;
+
+	struct ref_iterator *iter0;
+	unsigned int flags;
+};
+
+static int files_ref_iterator_advance(struct ref_iterator *ref_iterator)
+{
+	struct files_ref_iterator *iter =
+		(struct files_ref_iterator *)ref_iterator;
+	int ok;
+
+	while ((ok = ref_iterator_advance(iter->iter0)) == ITER_OK) {
+		if (iter->flags & DO_FOR_EACH_PER_WORKTREE_ONLY &&
+		    ref_type(iter->iter0->refname) != REF_TYPE_PER_WORKTREE)
+			continue;
+
+		if (!(iter->flags & DO_FOR_EACH_INCLUDE_BROKEN) &&
+		    !ref_resolves_to_object(iter->iter0->refname,
+					    iter->iter0->oid,
+					    iter->iter0->flags))
+			continue;
+
+		iter->base.refname = iter->iter0->refname;
+		iter->base.oid = iter->iter0->oid;
+		iter->base.flags = iter->iter0->flags;
+		return ITER_OK;
+	}
+
+	iter->iter0 = NULL;
+	if (ref_iterator_abort(ref_iterator) != ITER_DONE)
+		ok = ITER_ERROR;
+
+	return ok;
+}
+
+static int files_ref_iterator_peel(struct ref_iterator *ref_iterator,
+				   struct object_id *peeled)
+{
+	struct files_ref_iterator *iter =
+		(struct files_ref_iterator *)ref_iterator;
+
+	return ref_iterator_peel(iter->iter0, peeled);
+}
+
+static int files_ref_iterator_abort(struct ref_iterator *ref_iterator)
+{
+	struct files_ref_iterator *iter =
+		(struct files_ref_iterator *)ref_iterator;
+	int ok = ITER_DONE;
+
+	if (iter->iter0)
+		ok = ref_iterator_abort(iter->iter0);
+
+	base_ref_iterator_free(ref_iterator);
+	return ok;
+}
+
+static struct ref_iterator_vtable files_ref_iterator_vtable = {
+	files_ref_iterator_advance,
+	files_ref_iterator_peel,
+	files_ref_iterator_abort
+};
+
+static struct ref_iterator *files_ref_iterator_begin(
+		struct ref_store *ref_store,
+		const char *prefix, unsigned int flags)
+{
+	struct files_ref_store *refs;
+	struct ref_iterator *loose_iter, *packed_iter, *overlay_iter;
+	struct files_ref_iterator *iter;
+	struct ref_iterator *ref_iterator;
+	unsigned int required_flags = REF_STORE_READ;
+
+	if (!(flags & DO_FOR_EACH_INCLUDE_BROKEN))
+		required_flags |= REF_STORE_ODB;
+
+	refs = files_downcast(ref_store, required_flags, "ref_iterator_begin");
+
+	/*
+	 * We must make sure that all loose refs are read before
+	 * accessing the packed-refs file; this avoids a race
+	 * condition if loose refs are migrated to the packed-refs
+	 * file by a simultaneous process, but our in-memory view is
+	 * from before the migration. We ensure this as follows:
+	 * First, we call start the loose refs iteration with its
+	 * `prime_ref` argument set to true. This causes the loose
+	 * references in the subtree to be pre-read into the cache.
+	 * (If they've already been read, that's OK; we only need to
+	 * guarantee that they're read before the packed refs, not
+	 * *how much* before.) After that, we call
+	 * packed_ref_iterator_begin(), which internally checks
+	 * whether the packed-ref cache is up to date with what is on
+	 * disk, and re-reads it if not.
+	 */
+
+	loose_iter = cache_ref_iterator_begin(get_loose_ref_cache(refs),
+					      prefix, 1);
+
+	/*
+	 * The packed-refs file might contain broken references, for
+	 * example an old version of a reference that points at an
+	 * object that has since been garbage-collected. This is OK as
+	 * long as there is a corresponding loose reference that
+	 * overrides it, and we don't want to emit an error message in
+	 * this case. So ask the packed_ref_store for all of its
+	 * references, and (if needed) do our own check for broken
+	 * ones in files_ref_iterator_advance(), after we have merged
+	 * the packed and loose references.
+	 */
+	packed_iter = refs_ref_iterator_begin(
+			refs->packed_ref_store, prefix, 0,
+			DO_FOR_EACH_INCLUDE_BROKEN);
+
+	overlay_iter = overlay_ref_iterator_begin(loose_iter, packed_iter);
+
+	iter = xcalloc(1, sizeof(*iter));
+	ref_iterator = &iter->base;
+	base_ref_iterator_init(ref_iterator, &files_ref_iterator_vtable,
+			       overlay_iter->ordered);
+	iter->iter0 = overlay_iter;
+	iter->flags = flags;
+
+	return ref_iterator;
+}
+
+/*
+ * Verify that the reference locked by lock has the value old_oid
+ * (unless it is NULL).  Fail if the reference doesn't exist and
+ * mustexist is set. Return 0 on success. On error, write an error
+ * message to err, set errno, and return a negative value.
+ */
+static int verify_lock(struct ref_store *ref_store, struct ref_lock *lock,
+		       const struct object_id *old_oid, int mustexist,
+		       struct strbuf *err)
+{
+	assert(err);
+
+	if (refs_read_ref_full(ref_store, lock->ref_name,
+			       mustexist ? RESOLVE_REF_READING : 0,
+			       &lock->old_oid, NULL)) {
+		if (old_oid) {
+			int save_errno = errno;
+			strbuf_addf(err, "can't verify ref '%s'", lock->ref_name);
+			errno = save_errno;
+			return -1;
+		} else {
+			oidclr(&lock->old_oid);
+			return 0;
+		}
+	}
+	if (old_oid && !oideq(&lock->old_oid, old_oid)) {
+		strbuf_addf(err, "ref '%s' is at %s but expected %s",
+			    lock->ref_name,
+			    oid_to_hex(&lock->old_oid),
+			    oid_to_hex(old_oid));
+		errno = EBUSY;
+		return -1;
+	}
+	return 0;
+}
+
+static int remove_empty_directories(struct strbuf *path)
+{
+	/*
+	 * we want to create a file but there is a directory there;
+	 * if that is an empty directory (or a directory that contains
+	 * only empty directories), remove them.
+	 */
+	return remove_dir_recursively(path, REMOVE_DIR_EMPTY_ONLY);
+}
+
+static int create_reflock(const char *path, void *cb)
+{
+	struct lock_file *lk = cb;
+
+	return hold_lock_file_for_update_timeout(
+			lk, path, LOCK_NO_DEREF,
+			get_files_ref_lock_timeout_ms()) < 0 ? -1 : 0;
+}
+
+/*
+ * Locks a ref returning the lock on success and NULL on failure.
+ * On failure errno is set to something meaningful.
+ */
+static struct ref_lock *lock_ref_oid_basic(struct files_ref_store *refs,
+					   const char *refname,
+					   const struct object_id *old_oid,
+					   const struct string_list *extras,
+					   const struct string_list *skip,
+					   unsigned int flags, int *type,
+					   struct strbuf *err)
+{
+	struct strbuf ref_file = STRBUF_INIT;
+	struct ref_lock *lock;
+	int last_errno = 0;
+	int mustexist = (old_oid && !is_null_oid(old_oid));
+	int resolve_flags = RESOLVE_REF_NO_RECURSE;
+	int resolved;
+
+	files_assert_main_repository(refs, "lock_ref_oid_basic");
+	assert(err);
+
+	lock = xcalloc(1, sizeof(struct ref_lock));
+
+	if (mustexist)
+		resolve_flags |= RESOLVE_REF_READING;
+	if (flags & REF_DELETING)
+		resolve_flags |= RESOLVE_REF_ALLOW_BAD_NAME;
+
+	files_ref_path(refs, &ref_file, refname);
+	resolved = !!refs_resolve_ref_unsafe(&refs->base,
+					     refname, resolve_flags,
+					     &lock->old_oid, type);
+	if (!resolved && errno == EISDIR) {
+		/*
+		 * we are trying to lock foo but we used to
+		 * have foo/bar which now does not exist;
+		 * it is normal for the empty directory 'foo'
+		 * to remain.
+		 */
+		if (remove_empty_directories(&ref_file)) {
+			last_errno = errno;
+			if (!refs_verify_refname_available(
+					    &refs->base,
+					    refname, extras, skip, err))
+				strbuf_addf(err, "there are still refs under '%s'",
+					    refname);
+			goto error_return;
+		}
+		resolved = !!refs_resolve_ref_unsafe(&refs->base,
+						     refname, resolve_flags,
+						     &lock->old_oid, type);
+	}
+	if (!resolved) {
+		last_errno = errno;
+		if (last_errno != ENOTDIR ||
+		    !refs_verify_refname_available(&refs->base, refname,
+						   extras, skip, err))
+			strbuf_addf(err, "unable to resolve reference '%s': %s",
+				    refname, strerror(last_errno));
+
+		goto error_return;
+	}
+
+	/*
+	 * If the ref did not exist and we are creating it, make sure
+	 * there is no existing packed ref whose name begins with our
+	 * refname, nor a packed ref whose name is a proper prefix of
+	 * our refname.
+	 */
+	if (is_null_oid(&lock->old_oid) &&
+	    refs_verify_refname_available(refs->packed_ref_store, refname,
+					  extras, skip, err)) {
+		last_errno = ENOTDIR;
+		goto error_return;
+	}
+
+	lock->ref_name = xstrdup(refname);
+
+	if (raceproof_create_file(ref_file.buf, create_reflock, &lock->lk)) {
+		last_errno = errno;
+		unable_to_lock_message(ref_file.buf, errno, err);
+		goto error_return;
+	}
+
+	if (verify_lock(&refs->base, lock, old_oid, mustexist, err)) {
+		last_errno = errno;
+		goto error_return;
+	}
+	goto out;
+
+ error_return:
+	unlock_ref(lock);
+	lock = NULL;
+
+ out:
+	strbuf_release(&ref_file);
+	errno = last_errno;
+	return lock;
+}
+
+struct ref_to_prune {
+	struct ref_to_prune *next;
+	struct object_id oid;
+	char name[FLEX_ARRAY];
+};
+
+enum {
+	REMOVE_EMPTY_PARENTS_REF = 0x01,
+	REMOVE_EMPTY_PARENTS_REFLOG = 0x02
+};
+
+/*
+ * Remove empty parent directories associated with the specified
+ * reference and/or its reflog, but spare [logs/]refs/ and immediate
+ * subdirs. flags is a combination of REMOVE_EMPTY_PARENTS_REF and/or
+ * REMOVE_EMPTY_PARENTS_REFLOG.
+ */
+static void try_remove_empty_parents(struct files_ref_store *refs,
+				     const char *refname,
+				     unsigned int flags)
+{
+	struct strbuf buf = STRBUF_INIT;
+	struct strbuf sb = STRBUF_INIT;
+	char *p, *q;
+	int i;
+
+	strbuf_addstr(&buf, refname);
+	p = buf.buf;
+	for (i = 0; i < 2; i++) { /* refs/{heads,tags,...}/ */
+		while (*p && *p != '/')
+			p++;
+		/* tolerate duplicate slashes; see check_refname_format() */
+		while (*p == '/')
+			p++;
+	}
+	q = buf.buf + buf.len;
+	while (flags & (REMOVE_EMPTY_PARENTS_REF | REMOVE_EMPTY_PARENTS_REFLOG)) {
+		while (q > p && *q != '/')
+			q--;
+		while (q > p && *(q-1) == '/')
+			q--;
+		if (q == p)
+			break;
+		strbuf_setlen(&buf, q - buf.buf);
+
+		strbuf_reset(&sb);
+		files_ref_path(refs, &sb, buf.buf);
+		if ((flags & REMOVE_EMPTY_PARENTS_REF) && rmdir(sb.buf))
+			flags &= ~REMOVE_EMPTY_PARENTS_REF;
+
+		strbuf_reset(&sb);
+		files_reflog_path(refs, &sb, buf.buf);
+		if ((flags & REMOVE_EMPTY_PARENTS_REFLOG) && rmdir(sb.buf))
+			flags &= ~REMOVE_EMPTY_PARENTS_REFLOG;
+	}
+	strbuf_release(&buf);
+	strbuf_release(&sb);
+}
+
+/* make sure nobody touched the ref, and unlink */
+static void prune_ref(struct files_ref_store *refs, struct ref_to_prune *r)
+{
+	struct ref_transaction *transaction;
+	struct strbuf err = STRBUF_INIT;
+	int ret = -1;
+
+	if (check_refname_format(r->name, 0))
+		return;
+
+	transaction = ref_store_transaction_begin(&refs->base, &err);
+	if (!transaction)
+		goto cleanup;
+	ref_transaction_add_update(
+			transaction, r->name,
+			REF_NO_DEREF | REF_HAVE_NEW | REF_HAVE_OLD | REF_IS_PRUNING,
+			&null_oid, &r->oid, NULL);
+	if (ref_transaction_commit(transaction, &err))
+		goto cleanup;
+
+	ret = 0;
+
+cleanup:
+	if (ret)
+		error("%s", err.buf);
+	strbuf_release(&err);
+	ref_transaction_free(transaction);
+	return;
+}
+
+/*
+ * Prune the loose versions of the references in the linked list
+ * `*refs_to_prune`, freeing the entries in the list as we go.
+ */
+static void prune_refs(struct files_ref_store *refs, struct ref_to_prune **refs_to_prune)
+{
+	while (*refs_to_prune) {
+		struct ref_to_prune *r = *refs_to_prune;
+		*refs_to_prune = r->next;
+		prune_ref(refs, r);
+		free(r);
+	}
+}
+
+/*
+ * Return true if the specified reference should be packed.
+ */
+static int should_pack_ref(const char *refname,
+			   const struct object_id *oid, unsigned int ref_flags,
+			   unsigned int pack_flags)
+{
+	/* Do not pack per-worktree refs: */
+	if (ref_type(refname) != REF_TYPE_NORMAL)
+		return 0;
+
+	/* Do not pack non-tags unless PACK_REFS_ALL is set: */
+	if (!(pack_flags & PACK_REFS_ALL) && !starts_with(refname, "refs/tags/"))
+		return 0;
+
+	/* Do not pack symbolic refs: */
+	if (ref_flags & REF_ISSYMREF)
+		return 0;
+
+	/* Do not pack broken refs: */
+	if (!ref_resolves_to_object(refname, oid, ref_flags))
+		return 0;
+
+	return 1;
+}
+
+static int files_pack_refs(struct ref_store *ref_store, unsigned int flags)
+{
+	struct files_ref_store *refs =
+		files_downcast(ref_store, REF_STORE_WRITE | REF_STORE_ODB,
+			       "pack_refs");
+	struct ref_iterator *iter;
+	int ok;
+	struct ref_to_prune *refs_to_prune = NULL;
+	struct strbuf err = STRBUF_INIT;
+	struct ref_transaction *transaction;
+
+	transaction = ref_store_transaction_begin(refs->packed_ref_store, &err);
+	if (!transaction)
+		return -1;
+
+	packed_refs_lock(refs->packed_ref_store, LOCK_DIE_ON_ERROR, &err);
+
+	iter = cache_ref_iterator_begin(get_loose_ref_cache(refs), NULL, 0);
+	while ((ok = ref_iterator_advance(iter)) == ITER_OK) {
+		/*
+		 * If the loose reference can be packed, add an entry
+		 * in the packed ref cache. If the reference should be
+		 * pruned, also add it to refs_to_prune.
+		 */
+		if (!should_pack_ref(iter->refname, iter->oid, iter->flags,
+				     flags))
+			continue;
+
+		/*
+		 * Add a reference creation for this reference to the
+		 * packed-refs transaction:
+		 */
+		if (ref_transaction_update(transaction, iter->refname,
+					   iter->oid, NULL,
+					   REF_NO_DEREF, NULL, &err))
+			die("failure preparing to create packed reference %s: %s",
+			    iter->refname, err.buf);
+
+		/* Schedule the loose reference for pruning if requested. */
+		if ((flags & PACK_REFS_PRUNE)) {
+			struct ref_to_prune *n;
+			FLEX_ALLOC_STR(n, name, iter->refname);
+			oidcpy(&n->oid, iter->oid);
+			n->next = refs_to_prune;
+			refs_to_prune = n;
+		}
+	}
+	if (ok != ITER_DONE)
+		die("error while iterating over references");
+
+	if (ref_transaction_commit(transaction, &err))
+		die("unable to write new packed-refs: %s", err.buf);
+
+	ref_transaction_free(transaction);
+
+	packed_refs_unlock(refs->packed_ref_store);
+
+	prune_refs(refs, &refs_to_prune);
+	strbuf_release(&err);
+	return 0;
+}
+
+static int files_delete_refs(struct ref_store *ref_store, const char *msg,
+			     struct string_list *refnames, unsigned int flags)
+{
+	struct files_ref_store *refs =
+		files_downcast(ref_store, REF_STORE_WRITE, "delete_refs");
+	struct strbuf err = STRBUF_INIT;
+	int i, result = 0;
+
+	if (!refnames->nr)
+		return 0;
+
+	if (packed_refs_lock(refs->packed_ref_store, 0, &err))
+		goto error;
+
+	if (refs_delete_refs(refs->packed_ref_store, msg, refnames, flags)) {
+		packed_refs_unlock(refs->packed_ref_store);
+		goto error;
+	}
+
+	packed_refs_unlock(refs->packed_ref_store);
+
+	for (i = 0; i < refnames->nr; i++) {
+		const char *refname = refnames->items[i].string;
+
+		if (refs_delete_ref(&refs->base, msg, refname, NULL, flags))
+			result |= error(_("could not remove reference %s"), refname);
+	}
+
+	strbuf_release(&err);
+	return result;
+
+error:
+	/*
+	 * If we failed to rewrite the packed-refs file, then it is
+	 * unsafe to try to remove loose refs, because doing so might
+	 * expose an obsolete packed value for a reference that might
+	 * even point at an object that has been garbage collected.
+	 */
+	if (refnames->nr == 1)
+		error(_("could not delete reference %s: %s"),
+		      refnames->items[0].string, err.buf);
+	else
+		error(_("could not delete references: %s"), err.buf);
+
+	strbuf_release(&err);
+	return -1;
+}
+
+/*
+ * People using contrib's git-new-workdir have .git/logs/refs ->
+ * /some/other/path/.git/logs/refs, and that may live on another device.
+ *
+ * IOW, to avoid cross device rename errors, the temporary renamed log must
+ * live into logs/refs.
+ */
+#define TMP_RENAMED_LOG  "refs/.tmp-renamed-log"
+
+struct rename_cb {
+	const char *tmp_renamed_log;
+	int true_errno;
+};
+
+static int rename_tmp_log_callback(const char *path, void *cb_data)
+{
+	struct rename_cb *cb = cb_data;
+
+	if (rename(cb->tmp_renamed_log, path)) {
+		/*
+		 * rename(a, b) when b is an existing directory ought
+		 * to result in ISDIR, but Solaris 5.8 gives ENOTDIR.
+		 * Sheesh. Record the true errno for error reporting,
+		 * but report EISDIR to raceproof_create_file() so
+		 * that it knows to retry.
+		 */
+		cb->true_errno = errno;
+		if (errno == ENOTDIR)
+			errno = EISDIR;
+		return -1;
+	} else {
+		return 0;
+	}
+}
+
+static int rename_tmp_log(struct files_ref_store *refs, const char *newrefname)
+{
+	struct strbuf path = STRBUF_INIT;
+	struct strbuf tmp = STRBUF_INIT;
+	struct rename_cb cb;
+	int ret;
+
+	files_reflog_path(refs, &path, newrefname);
+	files_reflog_path(refs, &tmp, TMP_RENAMED_LOG);
+	cb.tmp_renamed_log = tmp.buf;
+	ret = raceproof_create_file(path.buf, rename_tmp_log_callback, &cb);
+	if (ret) {
+		if (errno == EISDIR)
+			error("directory not empty: %s", path.buf);
+		else
+			error("unable to move logfile %s to %s: %s",
+			      tmp.buf, path.buf,
+			      strerror(cb.true_errno));
+	}
+
+	strbuf_release(&path);
+	strbuf_release(&tmp);
+	return ret;
+}
+
+static int write_ref_to_lockfile(struct ref_lock *lock,
+				 const struct object_id *oid, struct strbuf *err);
+static int commit_ref_update(struct files_ref_store *refs,
+			     struct ref_lock *lock,
+			     const struct object_id *oid, const char *logmsg,
+			     struct strbuf *err);
+
+static int files_copy_or_rename_ref(struct ref_store *ref_store,
+			    const char *oldrefname, const char *newrefname,
+			    const char *logmsg, int copy)
+{
+	struct files_ref_store *refs =
+		files_downcast(ref_store, REF_STORE_WRITE, "rename_ref");
+	struct object_id oid, orig_oid;
+	int flag = 0, logmoved = 0;
+	struct ref_lock *lock;
+	struct stat loginfo;
+	struct strbuf sb_oldref = STRBUF_INIT;
+	struct strbuf sb_newref = STRBUF_INIT;
+	struct strbuf tmp_renamed_log = STRBUF_INIT;
+	int log, ret;
+	struct strbuf err = STRBUF_INIT;
+
+	files_reflog_path(refs, &sb_oldref, oldrefname);
+	files_reflog_path(refs, &sb_newref, newrefname);
+	files_reflog_path(refs, &tmp_renamed_log, TMP_RENAMED_LOG);
+
+	log = !lstat(sb_oldref.buf, &loginfo);
+	if (log && S_ISLNK(loginfo.st_mode)) {
+		ret = error("reflog for %s is a symlink", oldrefname);
+		goto out;
+	}
+
+	if (!refs_resolve_ref_unsafe(&refs->base, oldrefname,
+				     RESOLVE_REF_READING | RESOLVE_REF_NO_RECURSE,
+				&orig_oid, &flag)) {
+		ret = error("refname %s not found", oldrefname);
+		goto out;
+	}
+
+	if (flag & REF_ISSYMREF) {
+		if (copy)
+			ret = error("refname %s is a symbolic ref, copying it is not supported",
+				    oldrefname);
+		else
+			ret = error("refname %s is a symbolic ref, renaming it is not supported",
+				    oldrefname);
+		goto out;
+	}
+	if (!refs_rename_ref_available(&refs->base, oldrefname, newrefname)) {
+		ret = 1;
+		goto out;
+	}
+
+	if (!copy && log && rename(sb_oldref.buf, tmp_renamed_log.buf)) {
+		ret = error("unable to move logfile logs/%s to logs/"TMP_RENAMED_LOG": %s",
+			    oldrefname, strerror(errno));
+		goto out;
+	}
+
+	if (copy && log && copy_file(tmp_renamed_log.buf, sb_oldref.buf, 0644)) {
+		ret = error("unable to copy logfile logs/%s to logs/"TMP_RENAMED_LOG": %s",
+			    oldrefname, strerror(errno));
+		goto out;
+	}
+
+	if (!copy && refs_delete_ref(&refs->base, logmsg, oldrefname,
+			    &orig_oid, REF_NO_DEREF)) {
+		error("unable to delete old %s", oldrefname);
+		goto rollback;
+	}
+
+	/*
+	 * Since we are doing a shallow lookup, oid is not the
+	 * correct value to pass to delete_ref as old_oid. But that
+	 * doesn't matter, because an old_oid check wouldn't add to
+	 * the safety anyway; we want to delete the reference whatever
+	 * its current value.
+	 */
+	if (!copy && !refs_read_ref_full(&refs->base, newrefname,
+				RESOLVE_REF_READING | RESOLVE_REF_NO_RECURSE,
+				&oid, NULL) &&
+	    refs_delete_ref(&refs->base, NULL, newrefname,
+			    NULL, REF_NO_DEREF)) {
+		if (errno == EISDIR) {
+			struct strbuf path = STRBUF_INIT;
+			int result;
+
+			files_ref_path(refs, &path, newrefname);
+			result = remove_empty_directories(&path);
+			strbuf_release(&path);
+
+			if (result) {
+				error("Directory not empty: %s", newrefname);
+				goto rollback;
+			}
+		} else {
+			error("unable to delete existing %s", newrefname);
+			goto rollback;
+		}
+	}
+
+	if (log && rename_tmp_log(refs, newrefname))
+		goto rollback;
+
+	logmoved = log;
+
+	lock = lock_ref_oid_basic(refs, newrefname, NULL, NULL, NULL,
+				  REF_NO_DEREF, NULL, &err);
+	if (!lock) {
+		if (copy)
+			error("unable to copy '%s' to '%s': %s", oldrefname, newrefname, err.buf);
+		else
+			error("unable to rename '%s' to '%s': %s", oldrefname, newrefname, err.buf);
+		strbuf_release(&err);
+		goto rollback;
+	}
+	oidcpy(&lock->old_oid, &orig_oid);
+
+	if (write_ref_to_lockfile(lock, &orig_oid, &err) ||
+	    commit_ref_update(refs, lock, &orig_oid, logmsg, &err)) {
+		error("unable to write current sha1 into %s: %s", newrefname, err.buf);
+		strbuf_release(&err);
+		goto rollback;
+	}
+
+	ret = 0;
+	goto out;
+
+ rollback:
+	lock = lock_ref_oid_basic(refs, oldrefname, NULL, NULL, NULL,
+				  REF_NO_DEREF, NULL, &err);
+	if (!lock) {
+		error("unable to lock %s for rollback: %s", oldrefname, err.buf);
+		strbuf_release(&err);
+		goto rollbacklog;
+	}
+
+	flag = log_all_ref_updates;
+	log_all_ref_updates = LOG_REFS_NONE;
+	if (write_ref_to_lockfile(lock, &orig_oid, &err) ||
+	    commit_ref_update(refs, lock, &orig_oid, NULL, &err)) {
+		error("unable to write current sha1 into %s: %s", oldrefname, err.buf);
+		strbuf_release(&err);
+	}
+	log_all_ref_updates = flag;
+
+ rollbacklog:
+	if (logmoved && rename(sb_newref.buf, sb_oldref.buf))
+		error("unable to restore logfile %s from %s: %s",
+			oldrefname, newrefname, strerror(errno));
+	if (!logmoved && log &&
+	    rename(tmp_renamed_log.buf, sb_oldref.buf))
+		error("unable to restore logfile %s from logs/"TMP_RENAMED_LOG": %s",
+			oldrefname, strerror(errno));
+	ret = 1;
+ out:
+	strbuf_release(&sb_newref);
+	strbuf_release(&sb_oldref);
+	strbuf_release(&tmp_renamed_log);
+
+	return ret;
+}
+
+static int files_rename_ref(struct ref_store *ref_store,
+			    const char *oldrefname, const char *newrefname,
+			    const char *logmsg)
+{
+	return files_copy_or_rename_ref(ref_store, oldrefname,
+				 newrefname, logmsg, 0);
+}
+
+static int files_copy_ref(struct ref_store *ref_store,
+			    const char *oldrefname, const char *newrefname,
+			    const char *logmsg)
+{
+	return files_copy_or_rename_ref(ref_store, oldrefname,
+				 newrefname, logmsg, 1);
+}
+
+static int close_ref_gently(struct ref_lock *lock)
+{
+	if (close_lock_file_gently(&lock->lk))
+		return -1;
+	return 0;
+}
+
+static int commit_ref(struct ref_lock *lock)
+{
+	char *path = get_locked_file_path(&lock->lk);
+	struct stat st;
+
+	if (!lstat(path, &st) && S_ISDIR(st.st_mode)) {
+		/*
+		 * There is a directory at the path we want to rename
+		 * the lockfile to. Hopefully it is empty; try to
+		 * delete it.
+		 */
+		size_t len = strlen(path);
+		struct strbuf sb_path = STRBUF_INIT;
+
+		strbuf_attach(&sb_path, path, len, len);
+
+		/*
+		 * If this fails, commit_lock_file() will also fail
+		 * and will report the problem.
+		 */
+		remove_empty_directories(&sb_path);
+		strbuf_release(&sb_path);
+	} else {
+		free(path);
+	}
+
+	if (commit_lock_file(&lock->lk))
+		return -1;
+	return 0;
+}
+
+static int open_or_create_logfile(const char *path, void *cb)
+{
+	int *fd = cb;
+
+	*fd = open(path, O_APPEND | O_WRONLY | O_CREAT, 0666);
+	return (*fd < 0) ? -1 : 0;
+}
+
+/*
+ * Create a reflog for a ref. If force_create = 0, only create the
+ * reflog for certain refs (those for which should_autocreate_reflog
+ * returns non-zero). Otherwise, create it regardless of the reference
+ * name. If the logfile already existed or was created, return 0 and
+ * set *logfd to the file descriptor opened for appending to the file.
+ * If no logfile exists and we decided not to create one, return 0 and
+ * set *logfd to -1. On failure, fill in *err, set *logfd to -1, and
+ * return -1.
+ */
+static int log_ref_setup(struct files_ref_store *refs,
+			 const char *refname, int force_create,
+			 int *logfd, struct strbuf *err)
+{
+	struct strbuf logfile_sb = STRBUF_INIT;
+	char *logfile;
+
+	files_reflog_path(refs, &logfile_sb, refname);
+	logfile = strbuf_detach(&logfile_sb, NULL);
+
+	if (force_create || should_autocreate_reflog(refname)) {
+		if (raceproof_create_file(logfile, open_or_create_logfile, logfd)) {
+			if (errno == ENOENT)
+				strbuf_addf(err, "unable to create directory for '%s': "
+					    "%s", logfile, strerror(errno));
+			else if (errno == EISDIR)
+				strbuf_addf(err, "there are still logs under '%s'",
+					    logfile);
+			else
+				strbuf_addf(err, "unable to append to '%s': %s",
+					    logfile, strerror(errno));
+
+			goto error;
+		}
+	} else {
+		*logfd = open(logfile, O_APPEND | O_WRONLY, 0666);
+		if (*logfd < 0) {
+			if (errno == ENOENT || errno == EISDIR) {
+				/*
+				 * The logfile doesn't already exist,
+				 * but that is not an error; it only
+				 * means that we won't write log
+				 * entries to it.
+				 */
+				;
+			} else {
+				strbuf_addf(err, "unable to append to '%s': %s",
+					    logfile, strerror(errno));
+				goto error;
+			}
+		}
+	}
+
+	if (*logfd >= 0)
+		adjust_shared_perm(logfile);
+
+	free(logfile);
+	return 0;
+
+error:
+	free(logfile);
+	return -1;
+}
+
+static int files_create_reflog(struct ref_store *ref_store,
+			       const char *refname, int force_create,
+			       struct strbuf *err)
+{
+	struct files_ref_store *refs =
+		files_downcast(ref_store, REF_STORE_WRITE, "create_reflog");
+	int fd;
+
+	if (log_ref_setup(refs, refname, force_create, &fd, err))
+		return -1;
+
+	if (fd >= 0)
+		close(fd);
+
+	return 0;
+}
+
+static int log_ref_write_fd(int fd, const struct object_id *old_oid,
+			    const struct object_id *new_oid,
+			    const char *committer, const char *msg)
+{
+	struct strbuf sb = STRBUF_INIT;
+	int ret = 0;
+
+	strbuf_addf(&sb, "%s %s %s", oid_to_hex(old_oid), oid_to_hex(new_oid), committer);
+	if (msg && *msg)
+		copy_reflog_msg(&sb, msg);
+	strbuf_addch(&sb, '\n');
+	if (write_in_full(fd, sb.buf, sb.len) < 0)
+		ret = -1;
+	strbuf_release(&sb);
+	return ret;
+}
+
+static int files_log_ref_write(struct files_ref_store *refs,
+			       const char *refname, const struct object_id *old_oid,
+			       const struct object_id *new_oid, const char *msg,
+			       int flags, struct strbuf *err)
+{
+	int logfd, result;
+
+	if (log_all_ref_updates == LOG_REFS_UNSET)
+		log_all_ref_updates = is_bare_repository() ? LOG_REFS_NONE : LOG_REFS_NORMAL;
+
+	result = log_ref_setup(refs, refname,
+			       flags & REF_FORCE_CREATE_REFLOG,
+			       &logfd, err);
+
+	if (result)
+		return result;
+
+	if (logfd < 0)
+		return 0;
+	result = log_ref_write_fd(logfd, old_oid, new_oid,
+				  git_committer_info(0), msg);
+	if (result) {
+		struct strbuf sb = STRBUF_INIT;
+		int save_errno = errno;
+
+		files_reflog_path(refs, &sb, refname);
+		strbuf_addf(err, "unable to append to '%s': %s",
+			    sb.buf, strerror(save_errno));
+		strbuf_release(&sb);
+		close(logfd);
+		return -1;
+	}
+	if (close(logfd)) {
+		struct strbuf sb = STRBUF_INIT;
+		int save_errno = errno;
+
+		files_reflog_path(refs, &sb, refname);
+		strbuf_addf(err, "unable to append to '%s': %s",
+			    sb.buf, strerror(save_errno));
+		strbuf_release(&sb);
+		return -1;
+	}
+	return 0;
+}
+
+/*
+ * Write oid into the open lockfile, then close the lockfile. On
+ * errors, rollback the lockfile, fill in *err and return -1.
+ */
+static int write_ref_to_lockfile(struct ref_lock *lock,
+				 const struct object_id *oid, struct strbuf *err)
+{
+	static char term = '\n';
+	struct object *o;
+	int fd;
+
+	o = parse_object(the_repository, oid);
+	if (!o) {
+		strbuf_addf(err,
+			    "trying to write ref '%s' with nonexistent object %s",
+			    lock->ref_name, oid_to_hex(oid));
+		unlock_ref(lock);
+		return -1;
+	}
+	if (o->type != OBJ_COMMIT && is_branch(lock->ref_name)) {
+		strbuf_addf(err,
+			    "trying to write non-commit object %s to branch '%s'",
+			    oid_to_hex(oid), lock->ref_name);
+		unlock_ref(lock);
+		return -1;
+	}
+	fd = get_lock_file_fd(&lock->lk);
+	if (write_in_full(fd, oid_to_hex(oid), the_hash_algo->hexsz) < 0 ||
+	    write_in_full(fd, &term, 1) < 0 ||
+	    close_ref_gently(lock) < 0) {
+		strbuf_addf(err,
+			    "couldn't write '%s'", get_lock_file_path(&lock->lk));
+		unlock_ref(lock);
+		return -1;
+	}
+	return 0;
+}
+
+/*
+ * Commit a change to a loose reference that has already been written
+ * to the loose reference lockfile. Also update the reflogs if
+ * necessary, using the specified lockmsg (which can be NULL).
+ */
+static int commit_ref_update(struct files_ref_store *refs,
+			     struct ref_lock *lock,
+			     const struct object_id *oid, const char *logmsg,
+			     struct strbuf *err)
+{
+	files_assert_main_repository(refs, "commit_ref_update");
+
+	clear_loose_ref_cache(refs);
+	if (files_log_ref_write(refs, lock->ref_name,
+				&lock->old_oid, oid,
+				logmsg, 0, err)) {
+		char *old_msg = strbuf_detach(err, NULL);
+		strbuf_addf(err, "cannot update the ref '%s': %s",
+			    lock->ref_name, old_msg);
+		free(old_msg);
+		unlock_ref(lock);
+		return -1;
+	}
+
+	if (strcmp(lock->ref_name, "HEAD") != 0) {
+		/*
+		 * Special hack: If a branch is updated directly and HEAD
+		 * points to it (may happen on the remote side of a push
+		 * for example) then logically the HEAD reflog should be
+		 * updated too.
+		 * A generic solution implies reverse symref information,
+		 * but finding all symrefs pointing to the given branch
+		 * would be rather costly for this rare event (the direct
+		 * update of a branch) to be worth it.  So let's cheat and
+		 * check with HEAD only which should cover 99% of all usage
+		 * scenarios (even 100% of the default ones).
+		 */
+		int head_flag;
+		const char *head_ref;
+
+		head_ref = refs_resolve_ref_unsafe(&refs->base, "HEAD",
+						   RESOLVE_REF_READING,
+						   NULL, &head_flag);
+		if (head_ref && (head_flag & REF_ISSYMREF) &&
+		    !strcmp(head_ref, lock->ref_name)) {
+			struct strbuf log_err = STRBUF_INIT;
+			if (files_log_ref_write(refs, "HEAD",
+						&lock->old_oid, oid,
+						logmsg, 0, &log_err)) {
+				error("%s", log_err.buf);
+				strbuf_release(&log_err);
+			}
+		}
+	}
+
+	if (commit_ref(lock)) {
+		strbuf_addf(err, "couldn't set '%s'", lock->ref_name);
+		unlock_ref(lock);
+		return -1;
+	}
+
+	unlock_ref(lock);
+	return 0;
+}
+
+static int create_ref_symlink(struct ref_lock *lock, const char *target)
+{
+	int ret = -1;
+#ifndef NO_SYMLINK_HEAD
+	char *ref_path = get_locked_file_path(&lock->lk);
+	unlink(ref_path);
+	ret = symlink(target, ref_path);
+	free(ref_path);
+
+	if (ret)
+		fprintf(stderr, "no symlink - falling back to symbolic ref\n");
+#endif
+	return ret;
+}
+
+static void update_symref_reflog(struct files_ref_store *refs,
+				 struct ref_lock *lock, const char *refname,
+				 const char *target, const char *logmsg)
+{
+	struct strbuf err = STRBUF_INIT;
+	struct object_id new_oid;
+	if (logmsg &&
+	    !refs_read_ref_full(&refs->base, target,
+				RESOLVE_REF_READING, &new_oid, NULL) &&
+	    files_log_ref_write(refs, refname, &lock->old_oid,
+				&new_oid, logmsg, 0, &err)) {
+		error("%s", err.buf);
+		strbuf_release(&err);
+	}
+}
+
+static int create_symref_locked(struct files_ref_store *refs,
+				struct ref_lock *lock, const char *refname,
+				const char *target, const char *logmsg)
+{
+	if (prefer_symlink_refs && !create_ref_symlink(lock, target)) {
+		update_symref_reflog(refs, lock, refname, target, logmsg);
+		return 0;
+	}
+
+	if (!fdopen_lock_file(&lock->lk, "w"))
+		return error("unable to fdopen %s: %s",
+			     lock->lk.tempfile->filename.buf, strerror(errno));
+
+	update_symref_reflog(refs, lock, refname, target, logmsg);
+
+	/* no error check; commit_ref will check ferror */
+	fprintf(lock->lk.tempfile->fp, "ref: %s\n", target);
+	if (commit_ref(lock) < 0)
+		return error("unable to write symref for %s: %s", refname,
+			     strerror(errno));
+	return 0;
+}
+
+static int files_create_symref(struct ref_store *ref_store,
+			       const char *refname, const char *target,
+			       const char *logmsg)
+{
+	struct files_ref_store *refs =
+		files_downcast(ref_store, REF_STORE_WRITE, "create_symref");
+	struct strbuf err = STRBUF_INIT;
+	struct ref_lock *lock;
+	int ret;
+
+	lock = lock_ref_oid_basic(refs, refname, NULL,
+				  NULL, NULL, REF_NO_DEREF, NULL,
+				  &err);
+	if (!lock) {
+		error("%s", err.buf);
+		strbuf_release(&err);
+		return -1;
+	}
+
+	ret = create_symref_locked(refs, lock, refname, target, logmsg);
+	unlock_ref(lock);
+	return ret;
+}
+
+static int files_reflog_exists(struct ref_store *ref_store,
+			       const char *refname)
+{
+	struct files_ref_store *refs =
+		files_downcast(ref_store, REF_STORE_READ, "reflog_exists");
+	struct strbuf sb = STRBUF_INIT;
+	struct stat st;
+	int ret;
+
+	files_reflog_path(refs, &sb, refname);
+	ret = !lstat(sb.buf, &st) && S_ISREG(st.st_mode);
+	strbuf_release(&sb);
+	return ret;
+}
+
+static int files_delete_reflog(struct ref_store *ref_store,
+			       const char *refname)
+{
+	struct files_ref_store *refs =
+		files_downcast(ref_store, REF_STORE_WRITE, "delete_reflog");
+	struct strbuf sb = STRBUF_INIT;
+	int ret;
+
+	files_reflog_path(refs, &sb, refname);
+	ret = remove_path(sb.buf);
+	strbuf_release(&sb);
+	return ret;
+}
+
+static int show_one_reflog_ent(struct strbuf *sb, each_reflog_ent_fn fn, void *cb_data)
+{
+	struct object_id ooid, noid;
+	char *email_end, *message;
+	timestamp_t timestamp;
+	int tz;
+	const char *p = sb->buf;
+
+	/* old SP new SP name <email> SP time TAB msg LF */
+	if (!sb->len || sb->buf[sb->len - 1] != '\n' ||
+	    parse_oid_hex(p, &ooid, &p) || *p++ != ' ' ||
+	    parse_oid_hex(p, &noid, &p) || *p++ != ' ' ||
+	    !(email_end = strchr(p, '>')) ||
+	    email_end[1] != ' ' ||
+	    !(timestamp = parse_timestamp(email_end + 2, &message, 10)) ||
+	    !message || message[0] != ' ' ||
+	    (message[1] != '+' && message[1] != '-') ||
+	    !isdigit(message[2]) || !isdigit(message[3]) ||
+	    !isdigit(message[4]) || !isdigit(message[5]))
+		return 0; /* corrupt? */
+	email_end[1] = '\0';
+	tz = strtol(message + 1, NULL, 10);
+	if (message[6] != '\t')
+		message += 6;
+	else
+		message += 7;
+	return fn(&ooid, &noid, p, timestamp, tz, message, cb_data);
+}
+
+static char *find_beginning_of_line(char *bob, char *scan)
+{
+	while (bob < scan && *(--scan) != '\n')
+		; /* keep scanning backwards */
+	/*
+	 * Return either beginning of the buffer, or LF at the end of
+	 * the previous line.
+	 */
+	return scan;
+}
+
+static int files_for_each_reflog_ent_reverse(struct ref_store *ref_store,
+					     const char *refname,
+					     each_reflog_ent_fn fn,
+					     void *cb_data)
+{
+	struct files_ref_store *refs =
+		files_downcast(ref_store, REF_STORE_READ,
+			       "for_each_reflog_ent_reverse");
+	struct strbuf sb = STRBUF_INIT;
+	FILE *logfp;
+	long pos;
+	int ret = 0, at_tail = 1;
+
+	files_reflog_path(refs, &sb, refname);
+	logfp = fopen(sb.buf, "r");
+	strbuf_release(&sb);
+	if (!logfp)
+		return -1;
+
+	/* Jump to the end */
+	if (fseek(logfp, 0, SEEK_END) < 0)
+		ret = error("cannot seek back reflog for %s: %s",
+			    refname, strerror(errno));
+	pos = ftell(logfp);
+	while (!ret && 0 < pos) {
+		int cnt;
+		size_t nread;
+		char buf[BUFSIZ];
+		char *endp, *scanp;
+
+		/* Fill next block from the end */
+		cnt = (sizeof(buf) < pos) ? sizeof(buf) : pos;
+		if (fseek(logfp, pos - cnt, SEEK_SET)) {
+			ret = error("cannot seek back reflog for %s: %s",
+				    refname, strerror(errno));
+			break;
+		}
+		nread = fread(buf, cnt, 1, logfp);
+		if (nread != 1) {
+			ret = error("cannot read %d bytes from reflog for %s: %s",
+				    cnt, refname, strerror(errno));
+			break;
+		}
+		pos -= cnt;
+
+		scanp = endp = buf + cnt;
+		if (at_tail && scanp[-1] == '\n')
+			/* Looking at the final LF at the end of the file */
+			scanp--;
+		at_tail = 0;
+
+		while (buf < scanp) {
+			/*
+			 * terminating LF of the previous line, or the beginning
+			 * of the buffer.
+			 */
+			char *bp;
+
+			bp = find_beginning_of_line(buf, scanp);
+
+			if (*bp == '\n') {
+				/*
+				 * The newline is the end of the previous line,
+				 * so we know we have complete line starting
+				 * at (bp + 1). Prefix it onto any prior data
+				 * we collected for the line and process it.
+				 */
+				strbuf_splice(&sb, 0, 0, bp + 1, endp - (bp + 1));
+				scanp = bp;
+				endp = bp + 1;
+				ret = show_one_reflog_ent(&sb, fn, cb_data);
+				strbuf_reset(&sb);
+				if (ret)
+					break;
+			} else if (!pos) {
+				/*
+				 * We are at the start of the buffer, and the
+				 * start of the file; there is no previous
+				 * line, and we have everything for this one.
+				 * Process it, and we can end the loop.
+				 */
+				strbuf_splice(&sb, 0, 0, buf, endp - buf);
+				ret = show_one_reflog_ent(&sb, fn, cb_data);
+				strbuf_reset(&sb);
+				break;
+			}
+
+			if (bp == buf) {
+				/*
+				 * We are at the start of the buffer, and there
+				 * is more file to read backwards. Which means
+				 * we are in the middle of a line. Note that we
+				 * may get here even if *bp was a newline; that
+				 * just means we are at the exact end of the
+				 * previous line, rather than some spot in the
+				 * middle.
+				 *
+				 * Save away what we have to be combined with
+				 * the data from the next read.
+				 */
+				strbuf_splice(&sb, 0, 0, buf, endp - buf);
+				break;
+			}
+		}
+
+	}
+	if (!ret && sb.len)
+		BUG("reverse reflog parser had leftover data");
+
+	fclose(logfp);
+	strbuf_release(&sb);
+	return ret;
+}
+
+static int files_for_each_reflog_ent(struct ref_store *ref_store,
+				     const char *refname,
+				     each_reflog_ent_fn fn, void *cb_data)
+{
+	struct files_ref_store *refs =
+		files_downcast(ref_store, REF_STORE_READ,
+			       "for_each_reflog_ent");
+	FILE *logfp;
+	struct strbuf sb = STRBUF_INIT;
+	int ret = 0;
+
+	files_reflog_path(refs, &sb, refname);
+	logfp = fopen(sb.buf, "r");
+	strbuf_release(&sb);
+	if (!logfp)
+		return -1;
+
+	while (!ret && !strbuf_getwholeline(&sb, logfp, '\n'))
+		ret = show_one_reflog_ent(&sb, fn, cb_data);
+	fclose(logfp);
+	strbuf_release(&sb);
+	return ret;
+}
+
+struct files_reflog_iterator {
+	struct ref_iterator base;
+
+	struct ref_store *ref_store;
+	struct dir_iterator *dir_iterator;
+	struct object_id oid;
+};
+
+static int files_reflog_iterator_advance(struct ref_iterator *ref_iterator)
+{
+	struct files_reflog_iterator *iter =
+		(struct files_reflog_iterator *)ref_iterator;
+	struct dir_iterator *diter = iter->dir_iterator;
+	int ok;
+
+	while ((ok = dir_iterator_advance(diter)) == ITER_OK) {
+		int flags;
+
+		if (!S_ISREG(diter->st.st_mode))
+			continue;
+		if (diter->basename[0] == '.')
+			continue;
+		if (ends_with(diter->basename, ".lock"))
+			continue;
+
+		if (refs_read_ref_full(iter->ref_store,
+				       diter->relative_path, 0,
+				       &iter->oid, &flags)) {
+			error("bad ref for %s", diter->path.buf);
+			continue;
+		}
+
+		iter->base.refname = diter->relative_path;
+		iter->base.oid = &iter->oid;
+		iter->base.flags = flags;
+		return ITER_OK;
+	}
+
+	iter->dir_iterator = NULL;
+	if (ref_iterator_abort(ref_iterator) == ITER_ERROR)
+		ok = ITER_ERROR;
+	return ok;
+}
+
+static int files_reflog_iterator_peel(struct ref_iterator *ref_iterator,
+				   struct object_id *peeled)
+{
+	BUG("ref_iterator_peel() called for reflog_iterator");
+}
+
+static int files_reflog_iterator_abort(struct ref_iterator *ref_iterator)
+{
+	struct files_reflog_iterator *iter =
+		(struct files_reflog_iterator *)ref_iterator;
+	int ok = ITER_DONE;
+
+	if (iter->dir_iterator)
+		ok = dir_iterator_abort(iter->dir_iterator);
+
+	base_ref_iterator_free(ref_iterator);
+	return ok;
+}
+
+static struct ref_iterator_vtable files_reflog_iterator_vtable = {
+	files_reflog_iterator_advance,
+	files_reflog_iterator_peel,
+	files_reflog_iterator_abort
+};
+
+static struct ref_iterator *reflog_iterator_begin(struct ref_store *ref_store,
+						  const char *gitdir)
+{
+	struct dir_iterator *diter;
+	struct files_reflog_iterator *iter;
+	struct ref_iterator *ref_iterator;
+	struct strbuf sb = STRBUF_INIT;
+
+	strbuf_addf(&sb, "%s/logs", gitdir);
+
+	diter = dir_iterator_begin(sb.buf, 0);
+	if (!diter) {
+		strbuf_release(&sb);
+		return empty_ref_iterator_begin();
+	}
+
+	iter = xcalloc(1, sizeof(*iter));
+	ref_iterator = &iter->base;
+
+	base_ref_iterator_init(ref_iterator, &files_reflog_iterator_vtable, 0);
+	iter->dir_iterator = diter;
+	iter->ref_store = ref_store;
+	strbuf_release(&sb);
+
+	return ref_iterator;
+}
+
+static enum iterator_selection reflog_iterator_select(
+	struct ref_iterator *iter_worktree,
+	struct ref_iterator *iter_common,
+	void *cb_data)
+{
+	if (iter_worktree) {
+		/*
+		 * We're a bit loose here. We probably should ignore
+		 * common refs if they are accidentally added as
+		 * per-worktree refs.
+		 */
+		return ITER_SELECT_0;
+	} else if (iter_common) {
+		if (ref_type(iter_common->refname) == REF_TYPE_NORMAL)
+			return ITER_SELECT_1;
+
+		/*
+		 * The main ref store may contain main worktree's
+		 * per-worktree refs, which should be ignored
+		 */
+		return ITER_SKIP_1;
+	} else
+		return ITER_DONE;
+}
+
+static struct ref_iterator *files_reflog_iterator_begin(struct ref_store *ref_store)
+{
+	struct files_ref_store *refs =
+		files_downcast(ref_store, REF_STORE_READ,
+			       "reflog_iterator_begin");
+
+	if (!strcmp(refs->gitdir, refs->gitcommondir)) {
+		return reflog_iterator_begin(ref_store, refs->gitcommondir);
+	} else {
+		return merge_ref_iterator_begin(
+			0,
+			reflog_iterator_begin(ref_store, refs->gitdir),
+			reflog_iterator_begin(ref_store, refs->gitcommondir),
+			reflog_iterator_select, refs);
+	}
+}
+
+/*
+ * If update is a direct update of head_ref (the reference pointed to
+ * by HEAD), then add an extra REF_LOG_ONLY update for HEAD.
+ */
+static int split_head_update(struct ref_update *update,
+			     struct ref_transaction *transaction,
+			     const char *head_ref,
+			     struct string_list *affected_refnames,
+			     struct strbuf *err)
+{
+	struct string_list_item *item;
+	struct ref_update *new_update;
+
+	if ((update->flags & REF_LOG_ONLY) ||
+	    (update->flags & REF_IS_PRUNING) ||
+	    (update->flags & REF_UPDATE_VIA_HEAD))
+		return 0;
+
+	if (strcmp(update->refname, head_ref))
+		return 0;
+
+	/*
+	 * First make sure that HEAD is not already in the
+	 * transaction. This check is O(lg N) in the transaction
+	 * size, but it happens at most once per transaction.
+	 */
+	if (string_list_has_string(affected_refnames, "HEAD")) {
+		/* An entry already existed */
+		strbuf_addf(err,
+			    "multiple updates for 'HEAD' (including one "
+			    "via its referent '%s') are not allowed",
+			    update->refname);
+		return TRANSACTION_NAME_CONFLICT;
+	}
+
+	new_update = ref_transaction_add_update(
+			transaction, "HEAD",
+			update->flags | REF_LOG_ONLY | REF_NO_DEREF,
+			&update->new_oid, &update->old_oid,
+			update->msg);
+
+	/*
+	 * Add "HEAD". This insertion is O(N) in the transaction
+	 * size, but it happens at most once per transaction.
+	 * Add new_update->refname instead of a literal "HEAD".
+	 */
+	if (strcmp(new_update->refname, "HEAD"))
+		BUG("%s unexpectedly not 'HEAD'", new_update->refname);
+	item = string_list_insert(affected_refnames, new_update->refname);
+	item->util = new_update;
+
+	return 0;
+}
+
+/*
+ * update is for a symref that points at referent and doesn't have
+ * REF_NO_DEREF set. Split it into two updates:
+ * - The original update, but with REF_LOG_ONLY and REF_NO_DEREF set
+ * - A new, separate update for the referent reference
+ * Note that the new update will itself be subject to splitting when
+ * the iteration gets to it.
+ */
+static int split_symref_update(struct ref_update *update,
+			       const char *referent,
+			       struct ref_transaction *transaction,
+			       struct string_list *affected_refnames,
+			       struct strbuf *err)
+{
+	struct string_list_item *item;
+	struct ref_update *new_update;
+	unsigned int new_flags;
+
+	/*
+	 * First make sure that referent is not already in the
+	 * transaction. This check is O(lg N) in the transaction
+	 * size, but it happens at most once per symref in a
+	 * transaction.
+	 */
+	if (string_list_has_string(affected_refnames, referent)) {
+		/* An entry already exists */
+		strbuf_addf(err,
+			    "multiple updates for '%s' (including one "
+			    "via symref '%s') are not allowed",
+			    referent, update->refname);
+		return TRANSACTION_NAME_CONFLICT;
+	}
+
+	new_flags = update->flags;
+	if (!strcmp(update->refname, "HEAD")) {
+		/*
+		 * Record that the new update came via HEAD, so that
+		 * when we process it, split_head_update() doesn't try
+		 * to add another reflog update for HEAD. Note that
+		 * this bit will be propagated if the new_update
+		 * itself needs to be split.
+		 */
+		new_flags |= REF_UPDATE_VIA_HEAD;
+	}
+
+	new_update = ref_transaction_add_update(
+			transaction, referent, new_flags,
+			&update->new_oid, &update->old_oid,
+			update->msg);
+
+	new_update->parent_update = update;
+
+	/*
+	 * Change the symbolic ref update to log only. Also, it
+	 * doesn't need to check its old OID value, as that will be
+	 * done when new_update is processed.
+	 */
+	update->flags |= REF_LOG_ONLY | REF_NO_DEREF;
+	update->flags &= ~REF_HAVE_OLD;
+
+	/*
+	 * Add the referent. This insertion is O(N) in the transaction
+	 * size, but it happens at most once per symref in a
+	 * transaction. Make sure to add new_update->refname, which will
+	 * be valid as long as affected_refnames is in use, and NOT
+	 * referent, which might soon be freed by our caller.
+	 */
+	item = string_list_insert(affected_refnames, new_update->refname);
+	if (item->util)
+		BUG("%s unexpectedly found in affected_refnames",
+		    new_update->refname);
+	item->util = new_update;
+
+	return 0;
+}
+
+/*
+ * Return the refname under which update was originally requested.
+ */
+static const char *original_update_refname(struct ref_update *update)
+{
+	while (update->parent_update)
+		update = update->parent_update;
+
+	return update->refname;
+}
+
+/*
+ * Check whether the REF_HAVE_OLD and old_oid values stored in update
+ * are consistent with oid, which is the reference's current value. If
+ * everything is OK, return 0; otherwise, write an error message to
+ * err and return -1.
+ */
+static int check_old_oid(struct ref_update *update, struct object_id *oid,
+			 struct strbuf *err)
+{
+	if (!(update->flags & REF_HAVE_OLD) ||
+		   oideq(oid, &update->old_oid))
+		return 0;
+
+	if (is_null_oid(&update->old_oid))
+		strbuf_addf(err, "cannot lock ref '%s': "
+			    "reference already exists",
+			    original_update_refname(update));
+	else if (is_null_oid(oid))
+		strbuf_addf(err, "cannot lock ref '%s': "
+			    "reference is missing but expected %s",
+			    original_update_refname(update),
+			    oid_to_hex(&update->old_oid));
+	else
+		strbuf_addf(err, "cannot lock ref '%s': "
+			    "is at %s but expected %s",
+			    original_update_refname(update),
+			    oid_to_hex(oid),
+			    oid_to_hex(&update->old_oid));
+
+	return -1;
+}
+
+/*
+ * Prepare for carrying out update:
+ * - Lock the reference referred to by update.
+ * - Read the reference under lock.
+ * - Check that its old OID value (if specified) is correct, and in
+ *   any case record it in update->lock->old_oid for later use when
+ *   writing the reflog.
+ * - If it is a symref update without REF_NO_DEREF, split it up into a
+ *   REF_LOG_ONLY update of the symref and add a separate update for
+ *   the referent to transaction.
+ * - If it is an update of head_ref, add a corresponding REF_LOG_ONLY
+ *   update of HEAD.
+ */
+static int lock_ref_for_update(struct files_ref_store *refs,
+			       struct ref_update *update,
+			       struct ref_transaction *transaction,
+			       const char *head_ref,
+			       struct string_list *affected_refnames,
+			       struct strbuf *err)
+{
+	struct strbuf referent = STRBUF_INIT;
+	int mustexist = (update->flags & REF_HAVE_OLD) &&
+		!is_null_oid(&update->old_oid);
+	int ret = 0;
+	struct ref_lock *lock;
+
+	files_assert_main_repository(refs, "lock_ref_for_update");
+
+	if ((update->flags & REF_HAVE_NEW) && is_null_oid(&update->new_oid))
+		update->flags |= REF_DELETING;
+
+	if (head_ref) {
+		ret = split_head_update(update, transaction, head_ref,
+					affected_refnames, err);
+		if (ret)
+			goto out;
+	}
+
+	ret = lock_raw_ref(refs, update->refname, mustexist,
+			   affected_refnames, NULL,
+			   &lock, &referent,
+			   &update->type, err);
+	if (ret) {
+		char *reason;
+
+		reason = strbuf_detach(err, NULL);
+		strbuf_addf(err, "cannot lock ref '%s': %s",
+			    original_update_refname(update), reason);
+		free(reason);
+		goto out;
+	}
+
+	update->backend_data = lock;
+
+	if (update->type & REF_ISSYMREF) {
+		if (update->flags & REF_NO_DEREF) {
+			/*
+			 * We won't be reading the referent as part of
+			 * the transaction, so we have to read it here
+			 * to record and possibly check old_oid:
+			 */
+			if (refs_read_ref_full(&refs->base,
+					       referent.buf, 0,
+					       &lock->old_oid, NULL)) {
+				if (update->flags & REF_HAVE_OLD) {
+					strbuf_addf(err, "cannot lock ref '%s': "
+						    "error reading reference",
+						    original_update_refname(update));
+					ret = TRANSACTION_GENERIC_ERROR;
+					goto out;
+				}
+			} else if (check_old_oid(update, &lock->old_oid, err)) {
+				ret = TRANSACTION_GENERIC_ERROR;
+				goto out;
+			}
+		} else {
+			/*
+			 * Create a new update for the reference this
+			 * symref is pointing at. Also, we will record
+			 * and verify old_oid for this update as part
+			 * of processing the split-off update, so we
+			 * don't have to do it here.
+			 */
+			ret = split_symref_update(update,
+						  referent.buf, transaction,
+						  affected_refnames, err);
+			if (ret)
+				goto out;
+		}
+	} else {
+		struct ref_update *parent_update;
+
+		if (check_old_oid(update, &lock->old_oid, err)) {
+			ret = TRANSACTION_GENERIC_ERROR;
+			goto out;
+		}
+
+		/*
+		 * If this update is happening indirectly because of a
+		 * symref update, record the old OID in the parent
+		 * update:
+		 */
+		for (parent_update = update->parent_update;
+		     parent_update;
+		     parent_update = parent_update->parent_update) {
+			struct ref_lock *parent_lock = parent_update->backend_data;
+			oidcpy(&parent_lock->old_oid, &lock->old_oid);
+		}
+	}
+
+	if ((update->flags & REF_HAVE_NEW) &&
+	    !(update->flags & REF_DELETING) &&
+	    !(update->flags & REF_LOG_ONLY)) {
+		if (!(update->type & REF_ISSYMREF) &&
+		    oideq(&lock->old_oid, &update->new_oid)) {
+			/*
+			 * The reference already has the desired
+			 * value, so we don't need to write it.
+			 */
+		} else if (write_ref_to_lockfile(lock, &update->new_oid,
+						 err)) {
+			char *write_err = strbuf_detach(err, NULL);
+
+			/*
+			 * The lock was freed upon failure of
+			 * write_ref_to_lockfile():
+			 */
+			update->backend_data = NULL;
+			strbuf_addf(err,
+				    "cannot update ref '%s': %s",
+				    update->refname, write_err);
+			free(write_err);
+			ret = TRANSACTION_GENERIC_ERROR;
+			goto out;
+		} else {
+			update->flags |= REF_NEEDS_COMMIT;
+		}
+	}
+	if (!(update->flags & REF_NEEDS_COMMIT)) {
+		/*
+		 * We didn't call write_ref_to_lockfile(), so
+		 * the lockfile is still open. Close it to
+		 * free up the file descriptor:
+		 */
+		if (close_ref_gently(lock)) {
+			strbuf_addf(err, "couldn't close '%s.lock'",
+				    update->refname);
+			ret = TRANSACTION_GENERIC_ERROR;
+			goto out;
+		}
+	}
+
+out:
+	strbuf_release(&referent);
+	return ret;
+}
+
+struct files_transaction_backend_data {
+	struct ref_transaction *packed_transaction;
+	int packed_refs_locked;
+};
+
+/*
+ * Unlock any references in `transaction` that are still locked, and
+ * mark the transaction closed.
+ */
+static void files_transaction_cleanup(struct files_ref_store *refs,
+				      struct ref_transaction *transaction)
+{
+	size_t i;
+	struct files_transaction_backend_data *backend_data =
+		transaction->backend_data;
+	struct strbuf err = STRBUF_INIT;
+
+	for (i = 0; i < transaction->nr; i++) {
+		struct ref_update *update = transaction->updates[i];
+		struct ref_lock *lock = update->backend_data;
+
+		if (lock) {
+			unlock_ref(lock);
+			update->backend_data = NULL;
+		}
+	}
+
+	if (backend_data->packed_transaction &&
+	    ref_transaction_abort(backend_data->packed_transaction, &err)) {
+		error("error aborting transaction: %s", err.buf);
+		strbuf_release(&err);
+	}
+
+	if (backend_data->packed_refs_locked)
+		packed_refs_unlock(refs->packed_ref_store);
+
+	free(backend_data);
+
+	transaction->state = REF_TRANSACTION_CLOSED;
+}
+
+static int files_transaction_prepare(struct ref_store *ref_store,
+				     struct ref_transaction *transaction,
+				     struct strbuf *err)
+{
+	struct files_ref_store *refs =
+		files_downcast(ref_store, REF_STORE_WRITE,
+			       "ref_transaction_prepare");
+	size_t i;
+	int ret = 0;
+	struct string_list affected_refnames = STRING_LIST_INIT_NODUP;
+	char *head_ref = NULL;
+	int head_type;
+	struct files_transaction_backend_data *backend_data;
+	struct ref_transaction *packed_transaction = NULL;
+
+	assert(err);
+
+	if (!transaction->nr)
+		goto cleanup;
+
+	backend_data = xcalloc(1, sizeof(*backend_data));
+	transaction->backend_data = backend_data;
+
+	/*
+	 * Fail if a refname appears more than once in the
+	 * transaction. (If we end up splitting up any updates using
+	 * split_symref_update() or split_head_update(), those
+	 * functions will check that the new updates don't have the
+	 * same refname as any existing ones.) Also fail if any of the
+	 * updates use REF_IS_PRUNING without REF_NO_DEREF.
+	 */
+	for (i = 0; i < transaction->nr; i++) {
+		struct ref_update *update = transaction->updates[i];
+		struct string_list_item *item =
+			string_list_append(&affected_refnames, update->refname);
+
+		if ((update->flags & REF_IS_PRUNING) &&
+		    !(update->flags & REF_NO_DEREF))
+			BUG("REF_IS_PRUNING set without REF_NO_DEREF");
+
+		/*
+		 * We store a pointer to update in item->util, but at
+		 * the moment we never use the value of this field
+		 * except to check whether it is non-NULL.
+		 */
+		item->util = update;
+	}
+	string_list_sort(&affected_refnames);
+	if (ref_update_reject_duplicates(&affected_refnames, err)) {
+		ret = TRANSACTION_GENERIC_ERROR;
+		goto cleanup;
+	}
+
+	/*
+	 * Special hack: If a branch is updated directly and HEAD
+	 * points to it (may happen on the remote side of a push
+	 * for example) then logically the HEAD reflog should be
+	 * updated too.
+	 *
+	 * A generic solution would require reverse symref lookups,
+	 * but finding all symrefs pointing to a given branch would be
+	 * rather costly for this rare event (the direct update of a
+	 * branch) to be worth it. So let's cheat and check with HEAD
+	 * only, which should cover 99% of all usage scenarios (even
+	 * 100% of the default ones).
+	 *
+	 * So if HEAD is a symbolic reference, then record the name of
+	 * the reference that it points to. If we see an update of
+	 * head_ref within the transaction, then split_head_update()
+	 * arranges for the reflog of HEAD to be updated, too.
+	 */
+	head_ref = refs_resolve_refdup(ref_store, "HEAD",
+				       RESOLVE_REF_NO_RECURSE,
+				       NULL, &head_type);
+
+	if (head_ref && !(head_type & REF_ISSYMREF)) {
+		FREE_AND_NULL(head_ref);
+	}
+
+	/*
+	 * Acquire all locks, verify old values if provided, check
+	 * that new values are valid, and write new values to the
+	 * lockfiles, ready to be activated. Only keep one lockfile
+	 * open at a time to avoid running out of file descriptors.
+	 * Note that lock_ref_for_update() might append more updates
+	 * to the transaction.
+	 */
+	for (i = 0; i < transaction->nr; i++) {
+		struct ref_update *update = transaction->updates[i];
+
+		ret = lock_ref_for_update(refs, update, transaction,
+					  head_ref, &affected_refnames, err);
+		if (ret)
+			goto cleanup;
+
+		if (update->flags & REF_DELETING &&
+		    !(update->flags & REF_LOG_ONLY) &&
+		    !(update->flags & REF_IS_PRUNING)) {
+			/*
+			 * This reference has to be deleted from
+			 * packed-refs if it exists there.
+			 */
+			if (!packed_transaction) {
+				packed_transaction = ref_store_transaction_begin(
+						refs->packed_ref_store, err);
+				if (!packed_transaction) {
+					ret = TRANSACTION_GENERIC_ERROR;
+					goto cleanup;
+				}
+
+				backend_data->packed_transaction =
+					packed_transaction;
+			}
+
+			ref_transaction_add_update(
+					packed_transaction, update->refname,
+					REF_HAVE_NEW | REF_NO_DEREF,
+					&update->new_oid, NULL,
+					NULL);
+		}
+	}
+
+	if (packed_transaction) {
+		if (packed_refs_lock(refs->packed_ref_store, 0, err)) {
+			ret = TRANSACTION_GENERIC_ERROR;
+			goto cleanup;
+		}
+		backend_data->packed_refs_locked = 1;
+
+		if (is_packed_transaction_needed(refs->packed_ref_store,
+						 packed_transaction)) {
+			ret = ref_transaction_prepare(packed_transaction, err);
+			/*
+			 * A failure during the prepare step will abort
+			 * itself, but not free. Do that now, and disconnect
+			 * from the files_transaction so it does not try to
+			 * abort us when we hit the cleanup code below.
+			 */
+			if (ret) {
+				ref_transaction_free(packed_transaction);
+				backend_data->packed_transaction = NULL;
+			}
+		} else {
+			/*
+			 * We can skip rewriting the `packed-refs`
+			 * file. But we do need to leave it locked, so
+			 * that somebody else doesn't pack a reference
+			 * that we are trying to delete.
+			 *
+			 * We need to disconnect our transaction from
+			 * backend_data, since the abort (whether successful or
+			 * not) will free it.
+			 */
+			backend_data->packed_transaction = NULL;
+			if (ref_transaction_abort(packed_transaction, err)) {
+				ret = TRANSACTION_GENERIC_ERROR;
+				goto cleanup;
+			}
+		}
+	}
+
+cleanup:
+	free(head_ref);
+	string_list_clear(&affected_refnames, 0);
+
+	if (ret)
+		files_transaction_cleanup(refs, transaction);
+	else
+		transaction->state = REF_TRANSACTION_PREPARED;
+
+	return ret;
+}
+
+static int files_transaction_finish(struct ref_store *ref_store,
+				    struct ref_transaction *transaction,
+				    struct strbuf *err)
+{
+	struct files_ref_store *refs =
+		files_downcast(ref_store, 0, "ref_transaction_finish");
+	size_t i;
+	int ret = 0;
+	struct strbuf sb = STRBUF_INIT;
+	struct files_transaction_backend_data *backend_data;
+	struct ref_transaction *packed_transaction;
+
+
+	assert(err);
+
+	if (!transaction->nr) {
+		transaction->state = REF_TRANSACTION_CLOSED;
+		return 0;
+	}
+
+	backend_data = transaction->backend_data;
+	packed_transaction = backend_data->packed_transaction;
+
+	/* Perform updates first so live commits remain referenced */
+	for (i = 0; i < transaction->nr; i++) {
+		struct ref_update *update = transaction->updates[i];
+		struct ref_lock *lock = update->backend_data;
+
+		if (update->flags & REF_NEEDS_COMMIT ||
+		    update->flags & REF_LOG_ONLY) {
+			if (files_log_ref_write(refs,
+						lock->ref_name,
+						&lock->old_oid,
+						&update->new_oid,
+						update->msg, update->flags,
+						err)) {
+				char *old_msg = strbuf_detach(err, NULL);
+
+				strbuf_addf(err, "cannot update the ref '%s': %s",
+					    lock->ref_name, old_msg);
+				free(old_msg);
+				unlock_ref(lock);
+				update->backend_data = NULL;
+				ret = TRANSACTION_GENERIC_ERROR;
+				goto cleanup;
+			}
+		}
+		if (update->flags & REF_NEEDS_COMMIT) {
+			clear_loose_ref_cache(refs);
+			if (commit_ref(lock)) {
+				strbuf_addf(err, "couldn't set '%s'", lock->ref_name);
+				unlock_ref(lock);
+				update->backend_data = NULL;
+				ret = TRANSACTION_GENERIC_ERROR;
+				goto cleanup;
+			}
+		}
+	}
+
+	/*
+	 * Now that updates are safely completed, we can perform
+	 * deletes. First delete the reflogs of any references that
+	 * will be deleted, since (in the unexpected event of an
+	 * error) leaving a reference without a reflog is less bad
+	 * than leaving a reflog without a reference (the latter is a
+	 * mildly invalid repository state):
+	 */
+	for (i = 0; i < transaction->nr; i++) {
+		struct ref_update *update = transaction->updates[i];
+		if (update->flags & REF_DELETING &&
+		    !(update->flags & REF_LOG_ONLY) &&
+		    !(update->flags & REF_IS_PRUNING)) {
+			strbuf_reset(&sb);
+			files_reflog_path(refs, &sb, update->refname);
+			if (!unlink_or_warn(sb.buf))
+				try_remove_empty_parents(refs, update->refname,
+							 REMOVE_EMPTY_PARENTS_REFLOG);
+		}
+	}
+
+	/*
+	 * Perform deletes now that updates are safely completed.
+	 *
+	 * First delete any packed versions of the references, while
+	 * retaining the packed-refs lock:
+	 */
+	if (packed_transaction) {
+		ret = ref_transaction_commit(packed_transaction, err);
+		ref_transaction_free(packed_transaction);
+		packed_transaction = NULL;
+		backend_data->packed_transaction = NULL;
+		if (ret)
+			goto cleanup;
+	}
+
+	/* Now delete the loose versions of the references: */
+	for (i = 0; i < transaction->nr; i++) {
+		struct ref_update *update = transaction->updates[i];
+		struct ref_lock *lock = update->backend_data;
+
+		if (update->flags & REF_DELETING &&
+		    !(update->flags & REF_LOG_ONLY)) {
+			if (!(update->type & REF_ISPACKED) ||
+			    update->type & REF_ISSYMREF) {
+				/* It is a loose reference. */
+				strbuf_reset(&sb);
+				files_ref_path(refs, &sb, lock->ref_name);
+				if (unlink_or_msg(sb.buf, err)) {
+					ret = TRANSACTION_GENERIC_ERROR;
+					goto cleanup;
+				}
+				update->flags |= REF_DELETED_LOOSE;
+			}
+		}
+	}
+
+	clear_loose_ref_cache(refs);
+
+cleanup:
+	files_transaction_cleanup(refs, transaction);
+
+	for (i = 0; i < transaction->nr; i++) {
+		struct ref_update *update = transaction->updates[i];
+
+		if (update->flags & REF_DELETED_LOOSE) {
+			/*
+			 * The loose reference was deleted. Delete any
+			 * empty parent directories. (Note that this
+			 * can only work because we have already
+			 * removed the lockfile.)
+			 */
+			try_remove_empty_parents(refs, update->refname,
+						 REMOVE_EMPTY_PARENTS_REF);
+		}
+	}
+
+	strbuf_release(&sb);
+	return ret;
+}
+
+static int files_transaction_abort(struct ref_store *ref_store,
+				   struct ref_transaction *transaction,
+				   struct strbuf *err)
+{
+	struct files_ref_store *refs =
+		files_downcast(ref_store, 0, "ref_transaction_abort");
+
+	files_transaction_cleanup(refs, transaction);
+	return 0;
+}
+
+static int ref_present(const char *refname,
+		       const struct object_id *oid, int flags, void *cb_data)
+{
+	struct string_list *affected_refnames = cb_data;
+
+	return string_list_has_string(affected_refnames, refname);
+}
+
+static int files_initial_transaction_commit(struct ref_store *ref_store,
+					    struct ref_transaction *transaction,
+					    struct strbuf *err)
+{
+	struct files_ref_store *refs =
+		files_downcast(ref_store, REF_STORE_WRITE,
+			       "initial_ref_transaction_commit");
+	size_t i;
+	int ret = 0;
+	struct string_list affected_refnames = STRING_LIST_INIT_NODUP;
+	struct ref_transaction *packed_transaction = NULL;
+
+	assert(err);
+
+	if (transaction->state != REF_TRANSACTION_OPEN)
+		BUG("commit called for transaction that is not open");
+
+	/* Fail if a refname appears more than once in the transaction: */
+	for (i = 0; i < transaction->nr; i++)
+		string_list_append(&affected_refnames,
+				   transaction->updates[i]->refname);
+	string_list_sort(&affected_refnames);
+	if (ref_update_reject_duplicates(&affected_refnames, err)) {
+		ret = TRANSACTION_GENERIC_ERROR;
+		goto cleanup;
+	}
+
+	/*
+	 * It's really undefined to call this function in an active
+	 * repository or when there are existing references: we are
+	 * only locking and changing packed-refs, so (1) any
+	 * simultaneous processes might try to change a reference at
+	 * the same time we do, and (2) any existing loose versions of
+	 * the references that we are setting would have precedence
+	 * over our values. But some remote helpers create the remote
+	 * "HEAD" and "master" branches before calling this function,
+	 * so here we really only check that none of the references
+	 * that we are creating already exists.
+	 */
+	if (refs_for_each_rawref(&refs->base, ref_present,
+				 &affected_refnames))
+		BUG("initial ref transaction called with existing refs");
+
+	packed_transaction = ref_store_transaction_begin(refs->packed_ref_store, err);
+	if (!packed_transaction) {
+		ret = TRANSACTION_GENERIC_ERROR;
+		goto cleanup;
+	}
+
+	for (i = 0; i < transaction->nr; i++) {
+		struct ref_update *update = transaction->updates[i];
+
+		if ((update->flags & REF_HAVE_OLD) &&
+		    !is_null_oid(&update->old_oid))
+			BUG("initial ref transaction with old_sha1 set");
+		if (refs_verify_refname_available(&refs->base, update->refname,
+						  &affected_refnames, NULL,
+						  err)) {
+			ret = TRANSACTION_NAME_CONFLICT;
+			goto cleanup;
+		}
+
+		/*
+		 * Add a reference creation for this reference to the
+		 * packed-refs transaction:
+		 */
+		ref_transaction_add_update(packed_transaction, update->refname,
+					   update->flags & ~REF_HAVE_OLD,
+					   &update->new_oid, &update->old_oid,
+					   NULL);
+	}
+
+	if (packed_refs_lock(refs->packed_ref_store, 0, err)) {
+		ret = TRANSACTION_GENERIC_ERROR;
+		goto cleanup;
+	}
+
+	if (initial_ref_transaction_commit(packed_transaction, err)) {
+		ret = TRANSACTION_GENERIC_ERROR;
+	}
+
+	packed_refs_unlock(refs->packed_ref_store);
+cleanup:
+	if (packed_transaction)
+		ref_transaction_free(packed_transaction);
+	transaction->state = REF_TRANSACTION_CLOSED;
+	string_list_clear(&affected_refnames, 0);
+	return ret;
+}
+
+struct expire_reflog_cb {
+	unsigned int flags;
+	reflog_expiry_should_prune_fn *should_prune_fn;
+	void *policy_cb;
+	FILE *newlog;
+	struct object_id last_kept_oid;
+};
+
+static int expire_reflog_ent(struct object_id *ooid, struct object_id *noid,
+			     const char *email, timestamp_t timestamp, int tz,
+			     const char *message, void *cb_data)
+{
+	struct expire_reflog_cb *cb = cb_data;
+	struct expire_reflog_policy_cb *policy_cb = cb->policy_cb;
+
+	if (cb->flags & EXPIRE_REFLOGS_REWRITE)
+		ooid = &cb->last_kept_oid;
+
+	if ((*cb->should_prune_fn)(ooid, noid, email, timestamp, tz,
+				   message, policy_cb)) {
+		if (!cb->newlog)
+			printf("would prune %s", message);
+		else if (cb->flags & EXPIRE_REFLOGS_VERBOSE)
+			printf("prune %s", message);
+	} else {
+		if (cb->newlog) {
+			fprintf(cb->newlog, "%s %s %s %"PRItime" %+05d\t%s",
+				oid_to_hex(ooid), oid_to_hex(noid),
+				email, timestamp, tz, message);
+			oidcpy(&cb->last_kept_oid, noid);
+		}
+		if (cb->flags & EXPIRE_REFLOGS_VERBOSE)
+			printf("keep %s", message);
+	}
+	return 0;
+}
+
+static int files_reflog_expire(struct ref_store *ref_store,
+			       const char *refname, const struct object_id *oid,
+			       unsigned int flags,
+			       reflog_expiry_prepare_fn prepare_fn,
+			       reflog_expiry_should_prune_fn should_prune_fn,
+			       reflog_expiry_cleanup_fn cleanup_fn,
+			       void *policy_cb_data)
+{
+	struct files_ref_store *refs =
+		files_downcast(ref_store, REF_STORE_WRITE, "reflog_expire");
+	struct lock_file reflog_lock = LOCK_INIT;
+	struct expire_reflog_cb cb;
+	struct ref_lock *lock;
+	struct strbuf log_file_sb = STRBUF_INIT;
+	char *log_file;
+	int status = 0;
+	int type;
+	struct strbuf err = STRBUF_INIT;
+
+	memset(&cb, 0, sizeof(cb));
+	cb.flags = flags;
+	cb.policy_cb = policy_cb_data;
+	cb.should_prune_fn = should_prune_fn;
+
+	/*
+	 * The reflog file is locked by holding the lock on the
+	 * reference itself, plus we might need to update the
+	 * reference if --updateref was specified:
+	 */
+	lock = lock_ref_oid_basic(refs, refname, oid,
+				  NULL, NULL, REF_NO_DEREF,
+				  &type, &err);
+	if (!lock) {
+		error("cannot lock ref '%s': %s", refname, err.buf);
+		strbuf_release(&err);
+		return -1;
+	}
+	if (!refs_reflog_exists(ref_store, refname)) {
+		unlock_ref(lock);
+		return 0;
+	}
+
+	files_reflog_path(refs, &log_file_sb, refname);
+	log_file = strbuf_detach(&log_file_sb, NULL);
+	if (!(flags & EXPIRE_REFLOGS_DRY_RUN)) {
+		/*
+		 * Even though holding $GIT_DIR/logs/$reflog.lock has
+		 * no locking implications, we use the lock_file
+		 * machinery here anyway because it does a lot of the
+		 * work we need, including cleaning up if the program
+		 * exits unexpectedly.
+		 */
+		if (hold_lock_file_for_update(&reflog_lock, log_file, 0) < 0) {
+			struct strbuf err = STRBUF_INIT;
+			unable_to_lock_message(log_file, errno, &err);
+			error("%s", err.buf);
+			strbuf_release(&err);
+			goto failure;
+		}
+		cb.newlog = fdopen_lock_file(&reflog_lock, "w");
+		if (!cb.newlog) {
+			error("cannot fdopen %s (%s)",
+			      get_lock_file_path(&reflog_lock), strerror(errno));
+			goto failure;
+		}
+	}
+
+	(*prepare_fn)(refname, oid, cb.policy_cb);
+	refs_for_each_reflog_ent(ref_store, refname, expire_reflog_ent, &cb);
+	(*cleanup_fn)(cb.policy_cb);
+
+	if (!(flags & EXPIRE_REFLOGS_DRY_RUN)) {
+		/*
+		 * It doesn't make sense to adjust a reference pointed
+		 * to by a symbolic ref based on expiring entries in
+		 * the symbolic reference's reflog. Nor can we update
+		 * a reference if there are no remaining reflog
+		 * entries.
+		 */
+		int update = (flags & EXPIRE_REFLOGS_UPDATE_REF) &&
+			!(type & REF_ISSYMREF) &&
+			!is_null_oid(&cb.last_kept_oid);
+
+		if (close_lock_file_gently(&reflog_lock)) {
+			status |= error("couldn't write %s: %s", log_file,
+					strerror(errno));
+			rollback_lock_file(&reflog_lock);
+		} else if (update &&
+			   (write_in_full(get_lock_file_fd(&lock->lk),
+				oid_to_hex(&cb.last_kept_oid), the_hash_algo->hexsz) < 0 ||
+			    write_str_in_full(get_lock_file_fd(&lock->lk), "\n") < 0 ||
+			    close_ref_gently(lock) < 0)) {
+			status |= error("couldn't write %s",
+					get_lock_file_path(&lock->lk));
+			rollback_lock_file(&reflog_lock);
+		} else if (commit_lock_file(&reflog_lock)) {
+			status |= error("unable to write reflog '%s' (%s)",
+					log_file, strerror(errno));
+		} else if (update && commit_ref(lock)) {
+			status |= error("couldn't set %s", lock->ref_name);
+		}
+	}
+	free(log_file);
+	unlock_ref(lock);
+	return status;
+
+ failure:
+	rollback_lock_file(&reflog_lock);
+	free(log_file);
+	unlock_ref(lock);
+	return -1;
+}
+
+static int files_init_db(struct ref_store *ref_store, struct strbuf *err)
+{
+	struct files_ref_store *refs =
+		files_downcast(ref_store, REF_STORE_WRITE, "init_db");
+	struct strbuf sb = STRBUF_INIT;
+
+	/*
+	 * Create .git/refs/{heads,tags}
+	 */
+	files_ref_path(refs, &sb, "refs/heads");
+	safe_create_dir(sb.buf, 1);
+
+	strbuf_reset(&sb);
+	files_ref_path(refs, &sb, "refs/tags");
+	safe_create_dir(sb.buf, 1);
+
+	strbuf_release(&sb);
+	return 0;
+}
+
+struct ref_storage_be refs_be_files = {
+	NULL,
+	"files",
+	files_ref_store_create,
+	files_init_db,
+	files_transaction_prepare,
+	files_transaction_finish,
+	files_transaction_abort,
+	files_initial_transaction_commit,
+
+	files_pack_refs,
+	files_create_symref,
+	files_delete_refs,
+	files_rename_ref,
+	files_copy_ref,
+
+	files_ref_iterator_begin,
+	files_read_raw_ref,
+
+	files_reflog_iterator_begin,
+	files_for_each_reflog_ent,
+	files_for_each_reflog_ent_reverse,
+	files_reflog_exists,
+	files_create_reflog,
+	files_delete_reflog,
+	files_reflog_expire
+};