Merging upstream version 1:2.45.1.

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

7 files changed, 2451 insertions, 254 deletions

diff --git a/refs/debug.c b/refs/debug.c
index b7ffc4c..c7531b1 100644
--- a/refs/debug.c
+++ b/refs/debug.c
@@ -33,10 +33,10 @@ struct ref_store *maybe_debug_wrap_ref_store(const char *gitdir, struct ref_stor
 	return (struct ref_store *)res;
 }
 
-static int debug_init_db(struct ref_store *refs, struct strbuf *err)
+static int debug_init_db(struct ref_store *refs, int flags, struct strbuf *err)
 {
 	struct debug_ref_store *drefs = (struct debug_ref_store *)refs;
-	int res = drefs->refs->be->init_db(drefs->refs, err);
+	int res = drefs->refs->be->init_db(drefs->refs, flags, err);
 	trace_printf_key(&trace_refs, "init_db: %d\n", res);
 	return res;
 }
@@ -143,20 +143,6 @@ static int debug_create_symref(struct ref_store *ref_store,
 	return res;
 }
 
-static int debug_delete_refs(struct ref_store *ref_store, const char *msg,
-			     struct string_list *refnames, unsigned int flags)
-{
-	struct debug_ref_store *drefs = (struct debug_ref_store *)ref_store;
-	int res =
-		drefs->refs->be->delete_refs(drefs->refs, msg, refnames, flags);
-	int i;
-	trace_printf_key(&trace_refs, "delete_refs {\n");
-	for (i = 0; i < refnames->nr; i++)
-		trace_printf_key(&trace_refs, "%s\n", refnames->items[i].string);
-	trace_printf_key(&trace_refs, "}: %d\n", res);
-	return res;
-}
-
 static int debug_rename_ref(struct ref_store *ref_store, const char *oldref,
 			    const char *newref, const char *logmsg)
 {
@@ -195,7 +181,6 @@ static int debug_ref_iterator_advance(struct ref_iterator *ref_iterator)
 		trace_printf_key(&trace_refs, "iterator_advance: %s (0)\n",
 			diter->iter->refname);
 
-	diter->base.ordered = diter->iter->ordered;
 	diter->base.refname = diter->iter->refname;
 	diter->base.oid = diter->iter->oid;
 	diter->base.flags = diter->iter->flags;
@@ -236,7 +221,7 @@ debug_ref_iterator_begin(struct ref_store *ref_store, const char *prefix,
 		drefs->refs->be->iterator_begin(drefs->refs, prefix,
 						exclude_patterns, flags);
 	struct debug_ref_iterator *diter = xcalloc(1, sizeof(*diter));
-	base_ref_iterator_init(&diter->base, &debug_ref_iterator_vtable, 1);
+	base_ref_iterator_init(&diter->base, &debug_ref_iterator_vtable);
 	diter->iter = res;
 	trace_printf_key(&trace_refs, "ref_iterator_begin: \"%s\" (0x%x)\n",
 			 prefix, flags);
@@ -440,7 +425,6 @@ static int debug_reflog_expire(struct ref_store *ref_store, const char *refname,
 }
 
 struct ref_storage_be refs_be_debug = {
-	.next = NULL,
 	.name = "debug",
 	.init = NULL,
 	.init_db = debug_init_db,
@@ -458,7 +442,6 @@ struct ref_storage_be refs_be_debug = {
 
 	.pack_refs = debug_pack_refs,
 	.create_symref = debug_create_symref,
-	.delete_refs = debug_delete_refs,
 	.rename_ref = debug_rename_ref,
 	.copy_ref = debug_copy_ref,
 
diff --git a/refs/files-backend.c b/refs/files-backend.c
index db5c0c7..a098d14 100644
--- a/refs/files-backend.c
+++ b/refs/files-backend.c
@@ -1,5 +1,4 @@
 #include "../git-compat-util.h"
-#include "../config.h"
 #include "../copy.h"
 #include "../environment.h"
 #include "../gettext.h"
@@ -19,7 +18,6 @@
 #include "../dir.h"
 #include "../chdir-notify.h"
 #include "../setup.h"
-#include "../worktree.h"
 #include "../wrapper.h"
 #include "../write-or-die.h"
 #include "../revision.h"
@@ -231,6 +229,38 @@ static void add_per_worktree_entries_to_dir(struct ref_dir *dir, const char *dir
 	}
 }
 
+static void loose_fill_ref_dir_regular_file(struct files_ref_store *refs,
+					    const char *refname,
+					    struct ref_dir *dir)
+{
+	struct object_id oid;
+	int flag;
+
+	if (!refs_resolve_ref_unsafe(&refs->base, refname, 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, REFNAME_ALLOW_ONELEVEL)) {
+		if (!refname_is_safe(refname))
+			die("loose refname is dangerous: %s", refname);
+		oidclr(&oid);
+		flag |= REF_BAD_NAME | REF_ISBROKEN;
+	}
+	add_entry_to_dir(dir, create_ref_entry(refname, &oid, flag));
+}
+
 /*
  * Read the loose references from the namespace dirname into dir
  * (without recursing).  dirname must end with '/'.  dir must be the
@@ -259,8 +289,6 @@ static void loose_fill_ref_dir(struct ref_store *ref_store,
 	strbuf_add(&refname, dirname, dirnamelen);
 
 	while ((de = readdir(d)) != NULL) {
-		struct object_id oid;
-		int flag;
 		unsigned char dtype;
 
 		if (de->d_name[0] == '.')
@@ -276,33 +304,7 @@ static void loose_fill_ref_dir(struct ref_store *ref_store,
 					 create_dir_entry(dir->cache, refname.buf,
 							  refname.len));
 		} else if (dtype == DT_REG) {
-			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));
+			loose_fill_ref_dir_regular_file(refs, refname.buf, dir);
 		}
 		strbuf_setlen(&refname, dirnamelen);
 	}
@@ -313,9 +315,59 @@ static void loose_fill_ref_dir(struct ref_store *ref_store,
 	add_per_worktree_entries_to_dir(dir, dirname);
 }
 
-static struct ref_cache *get_loose_ref_cache(struct files_ref_store *refs)
+/*
+ * Add pseudorefs to the ref dir by parsing the directory for any files
+ * which follow the pseudoref syntax.
+ */
+static void add_pseudoref_and_head_entries(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");
+	struct strbuf path = STRBUF_INIT, refname = STRBUF_INIT;
+	struct dirent *de;
+	size_t dirnamelen;
+	DIR *d;
+
+	files_ref_path(refs, &path, dirname);
+
+	d = opendir(path.buf);
+	if (!d) {
+		strbuf_release(&path);
+		return;
+	}
+
+	strbuf_addstr(&refname, dirname);
+	dirnamelen = refname.len;
+
+	while ((de = readdir(d)) != NULL) {
+		unsigned char dtype;
+
+		if (de->d_name[0] == '.')
+			continue;
+		if (ends_with(de->d_name, ".lock"))
+			continue;
+		strbuf_addstr(&refname, de->d_name);
+
+		dtype = get_dtype(de, &path, 1);
+		if (dtype == DT_REG && (is_pseudoref(ref_store, de->d_name) ||
+								is_headref(ref_store, de->d_name)))
+			loose_fill_ref_dir_regular_file(refs, refname.buf, dir);
+
+		strbuf_setlen(&refname, dirnamelen);
+	}
+	strbuf_release(&refname);
+	strbuf_release(&path);
+	closedir(d);
+}
+
+static struct ref_cache *get_loose_ref_cache(struct files_ref_store *refs,
+					     unsigned int flags)
 {
 	if (!refs->loose) {
+		struct ref_dir *dir;
+
 		/*
 		 * Mark the top-level directory complete because we
 		 * are about to read the only subdirectory that can
@@ -326,12 +378,17 @@ static struct ref_cache *get_loose_ref_cache(struct files_ref_store *refs)
 		/* We're going to fill the top level ourselves: */
 		refs->loose->root->flag &= ~REF_INCOMPLETE;
 
+		dir = get_ref_dir(refs->loose->root);
+
+		if (flags & DO_FOR_EACH_INCLUDE_ROOT_REFS)
+			add_pseudoref_and_head_entries(dir->cache->ref_store, dir,
+						       refs->loose->root->name);
+
 		/*
 		 * 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));
+		add_entry_to_dir(dir, create_dir_entry(refs->loose, "refs/", 5));
 	}
 	return refs->loose;
 }
@@ -859,7 +916,7 @@ static struct ref_iterator *files_ref_iterator_begin(
 	 * disk, and re-reads it if not.
 	 */
 
-	loose_iter = cache_ref_iterator_begin(get_loose_ref_cache(refs),
+	loose_iter = cache_ref_iterator_begin(get_loose_ref_cache(refs, flags),
 					      prefix, ref_store->repo, 1);
 
 	/*
@@ -881,8 +938,7 @@ static struct ref_iterator *files_ref_iterator_begin(
 
 	CALLOC_ARRAY(iter, 1);
 	ref_iterator = &iter->base;
-	base_ref_iterator_init(ref_iterator, &files_ref_iterator_vtable,
-			       overlay_iter->ordered);
+	base_ref_iterator_init(ref_iterator, &files_ref_iterator_vtable);
 	iter->iter0 = overlay_iter;
 	iter->repo = ref_store->repo;
 	iter->flags = flags;
@@ -1220,7 +1276,7 @@ static int files_pack_refs(struct ref_store *ref_store,
 
 	packed_refs_lock(refs->packed_ref_store, LOCK_DIE_ON_ERROR, &err);
 
-	iter = cache_ref_iterator_begin(get_loose_ref_cache(refs), NULL,
+	iter = cache_ref_iterator_begin(get_loose_ref_cache(refs, 0), NULL,
 					the_repository, 0);
 	while ((ok = ref_iterator_advance(iter)) == ITER_OK) {
 		/*
@@ -1265,54 +1321,6 @@ static int files_pack_refs(struct ref_store *ref_store,
 	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.
@@ -2166,10 +2174,8 @@ static int files_for_each_reflog_ent(struct ref_store *ref_store,
 
 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)
@@ -2180,25 +2186,13 @@ static int files_reflog_iterator_advance(struct ref_iterator *ref_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"))
+		if (check_refname_format(diter->basename,
+					 REFNAME_ALLOW_ONELEVEL))
 			continue;
 
-		if (!refs_resolve_ref_unsafe(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;
 	}
 
@@ -2243,7 +2237,7 @@ static struct ref_iterator *reflog_iterator_begin(struct ref_store *ref_store,
 
 	strbuf_addf(&sb, "%s/logs", gitdir);
 
-	diter = dir_iterator_begin(sb.buf, 0);
+	diter = dir_iterator_begin(sb.buf, DIR_ITERATOR_SORTED);
 	if (!diter) {
 		strbuf_release(&sb);
 		return empty_ref_iterator_begin();
@@ -2252,7 +2246,7 @@ static struct ref_iterator *reflog_iterator_begin(struct ref_store *ref_store,
 	CALLOC_ARRAY(iter, 1);
 	ref_iterator = &iter->base;
 
-	base_ref_iterator_init(ref_iterator, &files_reflog_iterator_vtable, 0);
+	base_ref_iterator_init(ref_iterator, &files_reflog_iterator_vtable);
 	iter->dir_iterator = diter;
 	iter->ref_store = ref_store;
 	strbuf_release(&sb);
@@ -2260,32 +2254,6 @@ static struct ref_iterator *reflog_iterator_begin(struct ref_store *ref_store,
 	return ref_iterator;
 }
 
-static enum iterator_selection reflog_iterator_select(
-	struct ref_iterator *iter_worktree,
-	struct ref_iterator *iter_common,
-	void *cb_data UNUSED)
-{
-	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 (parse_worktree_ref(iter_common->refname, NULL, NULL,
-				       NULL) == REF_WORKTREE_SHARED)
-			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 =
@@ -2296,9 +2264,9 @@ static struct ref_iterator *files_reflog_iterator_begin(struct ref_store *ref_st
 		return reflog_iterator_begin(ref_store, refs->gitcommondir);
 	} else {
 		return merge_ref_iterator_begin(
-			0, reflog_iterator_begin(ref_store, refs->base.gitdir),
+			reflog_iterator_begin(ref_store, refs->base.gitdir),
 			reflog_iterator_begin(ref_store, refs->gitcommondir),
-			reflog_iterator_select, refs);
+			ref_iterator_select, refs);
 	}
 }
 
@@ -3268,28 +3236,52 @@ static int files_reflog_expire(struct ref_store *ref_store,
 	return -1;
 }
 
-static int files_init_db(struct ref_store *ref_store, struct strbuf *err UNUSED)
+static int files_init_db(struct ref_store *ref_store,
+			 int flags,
+			 struct strbuf *err UNUSED)
 {
 	struct files_ref_store *refs =
 		files_downcast(ref_store, REF_STORE_WRITE, "init_db");
 	struct strbuf sb = STRBUF_INIT;
 
 	/*
-	 * Create .git/refs/{heads,tags}
+	 * We need to create a "refs" dir in any case so that older versions of
+	 * Git can tell that this is a repository. This serves two main purposes:
+	 *
+	 * - Clients will know to stop walking the parent-directory chain when
+	 *   detecting the Git repository. Otherwise they may end up detecting
+	 *   a Git repository in a parent directory instead.
+	 *
+	 * - Instead of failing to detect a repository with unknown reference
+	 *   format altogether, old clients will print an error saying that
+	 *   they do not understand the reference format extension.
 	 */
-	files_ref_path(refs, &sb, "refs/heads");
+	strbuf_addf(&sb, "%s/refs", ref_store->gitdir);
 	safe_create_dir(sb.buf, 1);
+	adjust_shared_perm(sb.buf);
 
-	strbuf_reset(&sb);
-	files_ref_path(refs, &sb, "refs/tags");
-	safe_create_dir(sb.buf, 1);
+	/*
+	 * There is no need to create directories for common refs when creating
+	 * a worktree ref store.
+	 */
+	if (!(flags & REFS_INIT_DB_IS_WORKTREE)) {
+		/*
+		 * Create .git/refs/{heads,tags}
+		 */
+		strbuf_reset(&sb);
+		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 = {
-	.next = NULL,
 	.name = "files",
 	.init = files_ref_store_create,
 	.init_db = files_init_db,
@@ -3300,7 +3292,6 @@ struct ref_storage_be refs_be_files = {
 
 	.pack_refs = files_pack_refs,
 	.create_symref = files_create_symref,
-	.delete_refs = files_delete_refs,
 	.rename_ref = files_rename_ref,
 	.copy_ref = files_copy_ref,
 
diff --git a/refs/iterator.c b/refs/iterator.c
index 6b680f6..9db8b05 100644
--- a/refs/iterator.c
+++ b/refs/iterator.c
@@ -25,11 +25,9 @@ int ref_iterator_abort(struct ref_iterator *ref_iterator)
 }
 
 void base_ref_iterator_init(struct ref_iterator *iter,
-			    struct ref_iterator_vtable *vtable,
-			    int ordered)
+			    struct ref_iterator_vtable *vtable)
 {
 	iter->vtable = vtable;
-	iter->ordered = !!ordered;
 	iter->refname = NULL;
 	iter->oid = NULL;
 	iter->flags = 0;
@@ -74,7 +72,7 @@ struct ref_iterator *empty_ref_iterator_begin(void)
 	struct empty_ref_iterator *iter = xcalloc(1, sizeof(*iter));
 	struct ref_iterator *ref_iterator = &iter->base;
 
-	base_ref_iterator_init(ref_iterator, &empty_ref_iterator_vtable, 1);
+	base_ref_iterator_init(ref_iterator, &empty_ref_iterator_vtable);
 	return ref_iterator;
 }
 
@@ -98,6 +96,49 @@ struct merge_ref_iterator {
 	struct ref_iterator **current;
 };
 
+enum iterator_selection ref_iterator_select(struct ref_iterator *iter_worktree,
+					    struct ref_iterator *iter_common,
+					    void *cb_data UNUSED)
+{
+	if (iter_worktree && !iter_common) {
+		/*
+		 * Return the worktree ref if there are no more common refs.
+		 */
+		return ITER_SELECT_0;
+	} else if (iter_common) {
+		/*
+		 * In case we have pending worktree and common refs we need to
+		 * yield them based on their lexicographical order. Worktree
+		 * refs that have the same name as common refs shadow the
+		 * latter.
+		 */
+		if (iter_worktree) {
+			int cmp = strcmp(iter_worktree->refname,
+					 iter_common->refname);
+			if (cmp < 0)
+				return ITER_SELECT_0;
+			else if (!cmp)
+				return ITER_SELECT_0_SKIP_1;
+		}
+
+		 /*
+		  * We now know that the lexicographically-next ref is a common
+		  * ref. When the common ref is a shared one we return it.
+		  */
+		if (parse_worktree_ref(iter_common->refname, NULL, NULL,
+				       NULL) == REF_WORKTREE_SHARED)
+			return ITER_SELECT_1;
+
+		/*
+		 * Otherwise, if the common ref is a per-worktree ref we skip
+		 * it because it would belong to the main worktree, not ours.
+		 */
+		return ITER_SKIP_1;
+	} else {
+		return ITER_DONE;
+	}
+}
+
 static int merge_ref_iterator_advance(struct ref_iterator *ref_iterator)
 {
 	struct merge_ref_iterator *iter =
@@ -207,7 +248,6 @@ static struct ref_iterator_vtable merge_ref_iterator_vtable = {
 };
 
 struct ref_iterator *merge_ref_iterator_begin(
-		int ordered,
 		struct ref_iterator *iter0, struct ref_iterator *iter1,
 		ref_iterator_select_fn *select, void *cb_data)
 {
@@ -222,7 +262,7 @@ struct ref_iterator *merge_ref_iterator_begin(
 	 * references through only if they exist in both iterators.
 	 */
 
-	base_ref_iterator_init(ref_iterator, &merge_ref_iterator_vtable, ordered);
+	base_ref_iterator_init(ref_iterator, &merge_ref_iterator_vtable);
 	iter->iter0 = iter0;
 	iter->iter1 = iter1;
 	iter->select = select;
@@ -271,12 +311,9 @@ struct ref_iterator *overlay_ref_iterator_begin(
 	} else if (is_empty_ref_iterator(back)) {
 		ref_iterator_abort(back);
 		return front;
-	} else if (!front->ordered || !back->ordered) {
-		BUG("overlay_ref_iterator requires ordered inputs");
 	}
 
-	return merge_ref_iterator_begin(1, front, back,
-					overlay_iterator_select, NULL);
+	return merge_ref_iterator_begin(front, back, overlay_iterator_select, NULL);
 }
 
 struct prefix_ref_iterator {
@@ -315,16 +352,12 @@ static int prefix_ref_iterator_advance(struct ref_iterator *ref_iterator)
 
 		if (cmp > 0) {
 			/*
-			 * If the source iterator is ordered, then we
+			 * As the source iterator is ordered, we
 			 * can stop the iteration as soon as we see a
 			 * refname that comes after the prefix:
 			 */
-			if (iter->iter0->ordered) {
-				ok = ref_iterator_abort(iter->iter0);
-				break;
-			} else {
-				continue;
-			}
+			ok = ref_iterator_abort(iter->iter0);
+			break;
 		}
 
 		if (iter->trim) {
@@ -396,7 +429,7 @@ struct ref_iterator *prefix_ref_iterator_begin(struct ref_iterator *iter0,
 	CALLOC_ARRAY(iter, 1);
 	ref_iterator = &iter->base;
 
-	base_ref_iterator_init(ref_iterator, &prefix_ref_iterator_vtable, iter0->ordered);
+	base_ref_iterator_init(ref_iterator, &prefix_ref_iterator_vtable);
 
 	iter->iter0 = iter0;
 	iter->prefix = xstrdup(prefix);
diff --git a/refs/packed-backend.c b/refs/packed-backend.c
index 59c78d7..4e826c0 100644
--- a/refs/packed-backend.c
+++ b/refs/packed-backend.c
@@ -1,5 +1,4 @@
 #include "../git-compat-util.h"
-#include "../alloc.h"
 #include "../config.h"
 #include "../gettext.h"
 #include "../hash.h"
@@ -1112,7 +1111,7 @@ static struct ref_iterator *packed_ref_iterator_begin(
 
 	CALLOC_ARRAY(iter, 1);
 	ref_iterator = &iter->base;
-	base_ref_iterator_init(ref_iterator, &packed_ref_iterator_vtable, 1);
+	base_ref_iterator_init(ref_iterator, &packed_ref_iterator_vtable);
 
 	if (exclude_patterns)
 		populate_excluded_jump_list(iter, snapshot, exclude_patterns);
@@ -1246,6 +1245,7 @@ static const char PACKED_REFS_HEADER[] =
 	"# pack-refs with: peeled fully-peeled sorted \n";
 
 static int packed_init_db(struct ref_store *ref_store UNUSED,
+			  int flags UNUSED,
 			  struct strbuf *err UNUSED)
 {
 	/* Nothing to do. */
@@ -1688,55 +1688,6 @@ static int packed_initial_transaction_commit(struct ref_store *ref_store UNUSED,
 	return ref_transaction_commit(transaction, err);
 }
 
-static int packed_delete_refs(struct ref_store *ref_store, const char *msg,
-			     struct string_list *refnames, unsigned int flags)
-{
-	struct packed_ref_store *refs =
-		packed_downcast(ref_store, REF_STORE_WRITE, "delete_refs");
-	struct strbuf err = STRBUF_INIT;
-	struct ref_transaction *transaction;
-	struct string_list_item *item;
-	int ret;
-
-	(void)refs; /* We need the check above, but don't use the variable */
-
-	if (!refnames->nr)
-		return 0;
-
-	/*
-	 * Since we don't check the references' old_oids, the
-	 * individual updates can't fail, so we can pack all of the
-	 * updates into a single transaction.
-	 */
-
-	transaction = ref_store_transaction_begin(ref_store, &err);
-	if (!transaction)
-		return -1;
-
-	for_each_string_list_item(item, refnames) {
-		if (ref_transaction_delete(transaction, item->string, NULL,
-					   flags, msg, &err)) {
-			warning(_("could not delete reference %s: %s"),
-				item->string, err.buf);
-			strbuf_reset(&err);
-		}
-	}
-
-	ret = ref_transaction_commit(transaction, &err);
-
-	if (ret) {
-		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);
-	}
-
-	ref_transaction_free(transaction);
-	strbuf_release(&err);
-	return ret;
-}
-
 static int packed_pack_refs(struct ref_store *ref_store UNUSED,
 			    struct pack_refs_opts *pack_opts UNUSED)
 {
@@ -1754,7 +1705,6 @@ static struct ref_iterator *packed_reflog_iterator_begin(struct ref_store *ref_s
 }
 
 struct ref_storage_be refs_be_packed = {
-	.next = NULL,
 	.name = "packed",
 	.init = packed_ref_store_create,
 	.init_db = packed_init_db,
@@ -1765,7 +1715,6 @@ struct ref_storage_be refs_be_packed = {
 
 	.pack_refs = packed_pack_refs,
 	.create_symref = NULL,
-	.delete_refs = packed_delete_refs,
 	.rename_ref = NULL,
 	.copy_ref = NULL,
 
diff --git a/refs/ref-cache.c b/refs/ref-cache.c
index 6e3b725..9f97972 100644
--- a/refs/ref-cache.c
+++ b/refs/ref-cache.c
@@ -1,5 +1,4 @@
 #include "../git-compat-util.h"
-#include "../alloc.h"
 #include "../hash.h"
 #include "../refs.h"
 #include "../repository.h"
@@ -487,7 +486,7 @@ struct ref_iterator *cache_ref_iterator_begin(struct ref_cache *cache,
 
 	CALLOC_ARRAY(iter, 1);
 	ref_iterator = &iter->base;
-	base_ref_iterator_init(ref_iterator, &cache_ref_iterator_vtable, 1);
+	base_ref_iterator_init(ref_iterator, &cache_ref_iterator_vtable);
 	ALLOC_GROW(iter->levels, 10, iter->levels_alloc);
 
 	iter->levels_nr = 1;
diff --git a/refs/refs-internal.h b/refs/refs-internal.h
index 9db8aec..56641aa 100644
--- a/refs/refs-internal.h
+++ b/refs/refs-internal.h
@@ -260,6 +260,12 @@ enum do_for_each_ref_flags {
 	 * INCLUDE_BROKEN, since they are otherwise not included at all.
 	 */
 	DO_FOR_EACH_OMIT_DANGLING_SYMREFS = (1 << 2),
+
+	/*
+	 * Include root refs i.e. HEAD and pseudorefs along with the regular
+	 * refs.
+	 */
+	DO_FOR_EACH_INCLUDE_ROOT_REFS = (1 << 3),
 };
 
 /*
@@ -312,13 +318,6 @@ enum do_for_each_ref_flags {
  */
 struct ref_iterator {
 	struct ref_iterator_vtable *vtable;
-
-	/*
-	 * Does this `ref_iterator` iterate over references in order
-	 * by refname?
-	 */
-	unsigned int ordered : 1;
-
 	const char *refname;
 	const struct object_id *oid;
 	unsigned int flags;
@@ -387,14 +386,21 @@ typedef enum iterator_selection ref_iterator_select_fn(
 		void *cb_data);
 
 /*
+ * An implementation of ref_iterator_select_fn that merges worktree and common
+ * refs. Per-worktree refs from the common iterator are ignored, worktree refs
+ * override common refs. Refs are selected lexicographically.
+ */
+enum iterator_selection ref_iterator_select(struct ref_iterator *iter_worktree,
+					    struct ref_iterator *iter_common,
+					    void *cb_data);
+
+/*
  * Iterate over the entries from iter0 and iter1, with the values
  * interleaved as directed by the select function. The iterator takes
  * ownership of iter0 and iter1 and frees them when the iteration is
- * over. A derived class should set `ordered` to 1 or 0 based on
- * whether it generates its output in order by reference name.
+ * over.
  */
 struct ref_iterator *merge_ref_iterator_begin(
-		int ordered,
 		struct ref_iterator *iter0, struct ref_iterator *iter1,
 		ref_iterator_select_fn *select, void *cb_data);
 
@@ -423,8 +429,6 @@ struct ref_iterator *overlay_ref_iterator_begin(
  * As an convenience to callers, if prefix is the empty string and
  * trim is zero, this function returns iter0 directly, without
  * wrapping it.
- *
- * The resulting ref_iterator is ordered if iter0 is.
  */
 struct ref_iterator *prefix_ref_iterator_begin(struct ref_iterator *iter0,
 					       const char *prefix,
@@ -435,14 +439,11 @@ struct ref_iterator *prefix_ref_iterator_begin(struct ref_iterator *iter0,
 /*
  * Base class constructor for ref_iterators. Initialize the
  * ref_iterator part of iter, setting its vtable pointer as specified.
- * `ordered` should be set to 1 if the iterator will iterate over
- * references in order by refname; otherwise it should be set to 0.
  * This is meant to be called only by the initializers of derived
  * classes.
  */
 void base_ref_iterator_init(struct ref_iterator *iter,
-			    struct ref_iterator_vtable *vtable,
-			    int ordered);
+			    struct ref_iterator_vtable *vtable);
 
 /*
  * Base class destructor for ref_iterators. Destroy the ref_iterator
@@ -529,7 +530,9 @@ typedef struct ref_store *ref_store_init_fn(struct repository *repo,
 					    const char *gitdir,
 					    unsigned int flags);
 
-typedef int ref_init_db_fn(struct ref_store *refs, struct strbuf *err);
+typedef int ref_init_db_fn(struct ref_store *refs,
+			   int flags,
+			   struct strbuf *err);
 
 typedef int ref_transaction_prepare_fn(struct ref_store *refs,
 				       struct ref_transaction *transaction,
@@ -553,8 +556,6 @@ typedef int create_symref_fn(struct ref_store *ref_store,
 			     const char *ref_target,
 			     const char *refs_heads_master,
 			     const char *logmsg);
-typedef int delete_refs_fn(struct ref_store *ref_store, const char *msg,
-			   struct string_list *refnames, unsigned int flags);
 typedef int rename_ref_fn(struct ref_store *ref_store,
 			  const char *oldref, const char *newref,
 			  const char *logmsg);
@@ -665,7 +666,6 @@ typedef int read_symbolic_ref_fn(struct ref_store *ref_store, const char *refnam
 				 struct strbuf *referent);
 
 struct ref_storage_be {
-	struct ref_storage_be *next;
 	const char *name;
 	ref_store_init_fn *init;
 	ref_init_db_fn *init_db;
@@ -677,7 +677,6 @@ struct ref_storage_be {
 
 	pack_refs_fn *pack_refs;
 	create_symref_fn *create_symref;
-	delete_refs_fn *delete_refs;
 	rename_ref_fn *rename_ref;
 	copy_ref_fn *copy_ref;
 
@@ -695,6 +694,7 @@ struct ref_storage_be {
 };
 
 extern struct ref_storage_be refs_be_files;
+extern struct ref_storage_be refs_be_reftable;
 extern struct ref_storage_be refs_be_packed;
 
 /*
diff --git a/refs/reftable-backend.c b/refs/reftable-backend.c
new file mode 100644
index 0000000..1cda48c
--- /dev/null
+++ b/refs/reftable-backend.c
@@ -0,0 +1,2242 @@
+#include "../git-compat-util.h"
+#include "../abspath.h"
+#include "../chdir-notify.h"
+#include "../environment.h"
+#include "../gettext.h"
+#include "../hash.h"
+#include "../hex.h"
+#include "../iterator.h"
+#include "../ident.h"
+#include "../lockfile.h"
+#include "../object.h"
+#include "../path.h"
+#include "../refs.h"
+#include "../reftable/reftable-stack.h"
+#include "../reftable/reftable-record.h"
+#include "../reftable/reftable-error.h"
+#include "../reftable/reftable-iterator.h"
+#include "../reftable/reftable-merged.h"
+#include "../setup.h"
+#include "../strmap.h"
+#include "parse.h"
+#include "refs-internal.h"
+
+/*
+ * 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)
+
+struct reftable_ref_store {
+	struct ref_store base;
+
+	/*
+	 * The main stack refers to the common dir and thus contains common
+	 * refs as well as refs of the main repository.
+	 */
+	struct reftable_stack *main_stack;
+	/*
+	 * The worktree stack refers to the gitdir in case the refdb is opened
+	 * via a worktree. It thus contains the per-worktree refs.
+	 */
+	struct reftable_stack *worktree_stack;
+	/*
+	 * Map of worktree stacks by their respective worktree names. The map
+	 * is populated lazily when we try to resolve `worktrees/$worktree` refs.
+	 */
+	struct strmap worktree_stacks;
+	struct reftable_write_options write_options;
+
+	unsigned int store_flags;
+	int err;
+};
+
+/*
+ * Downcast ref_store to reftable_ref_store. Die if ref_store is not a
+ * reftable_ref_store. required_flags is compared with ref_store's store_flags
+ * to ensure the ref_store has all required capabilities. "caller" is used in
+ * any necessary error messages.
+ */
+static struct reftable_ref_store *reftable_be_downcast(struct ref_store *ref_store,
+						       unsigned int required_flags,
+						       const char *caller)
+{
+	struct reftable_ref_store *refs;
+
+	if (ref_store->be != &refs_be_reftable)
+		BUG("ref_store is type \"%s\" not \"reftables\" in %s",
+		    ref_store->be->name, caller);
+
+	refs = (struct reftable_ref_store *)ref_store;
+
+	if ((refs->store_flags & required_flags) != required_flags)
+		BUG("operation %s requires abilities 0x%x, but only have 0x%x",
+		    caller, required_flags, refs->store_flags);
+
+	return refs;
+}
+
+/*
+ * Some refs are global to the repository (refs/heads/{*}), while others are
+ * local to the worktree (eg. HEAD, refs/bisect/{*}). We solve this by having
+ * multiple separate databases (ie. multiple reftable/ directories), one for
+ * the shared refs, one for the current worktree refs, and one for each
+ * additional worktree. For reading, we merge the view of both the shared and
+ * the current worktree's refs, when necessary.
+ *
+ * This function also optionally assigns the rewritten reference name that is
+ * local to the stack. This translation is required when using worktree refs
+ * like `worktrees/$worktree/refs/heads/foo` as worktree stacks will store
+ * those references in their normalized form.
+ */
+static struct reftable_stack *stack_for(struct reftable_ref_store *store,
+					const char *refname,
+					const char **rewritten_ref)
+{
+	const char *wtname;
+	int wtname_len;
+
+	if (!refname)
+		return store->main_stack;
+
+	switch (parse_worktree_ref(refname, &wtname, &wtname_len, rewritten_ref)) {
+	case REF_WORKTREE_OTHER: {
+		static struct strbuf wtname_buf = STRBUF_INIT;
+		struct strbuf wt_dir = STRBUF_INIT;
+		struct reftable_stack *stack;
+
+		/*
+		 * We're using a static buffer here so that we don't need to
+		 * allocate the worktree name whenever we look up a reference.
+		 * This could be avoided if the strmap interface knew how to
+		 * handle keys with a length.
+		 */
+		strbuf_reset(&wtname_buf);
+		strbuf_add(&wtname_buf, wtname, wtname_len);
+
+		/*
+		 * There is an edge case here: when the worktree references the
+		 * current worktree, then we set up the stack once via
+		 * `worktree_stacks` and once via `worktree_stack`. This is
+		 * wasteful, but in the reading case it shouldn't matter. And
+		 * in the writing case we would notice that the stack is locked
+		 * already and error out when trying to write a reference via
+		 * both stacks.
+		 */
+		stack = strmap_get(&store->worktree_stacks, wtname_buf.buf);
+		if (!stack) {
+			strbuf_addf(&wt_dir, "%s/worktrees/%s/reftable",
+				    store->base.repo->commondir, wtname_buf.buf);
+
+			store->err = reftable_new_stack(&stack, wt_dir.buf,
+							store->write_options);
+			assert(store->err != REFTABLE_API_ERROR);
+			strmap_put(&store->worktree_stacks, wtname_buf.buf, stack);
+		}
+
+		strbuf_release(&wt_dir);
+		return stack;
+	}
+	case REF_WORKTREE_CURRENT:
+		/*
+		 * If there is no worktree stack then we're currently in the
+		 * main worktree. We thus return the main stack in that case.
+		 */
+		if (!store->worktree_stack)
+			return store->main_stack;
+		return store->worktree_stack;
+	case REF_WORKTREE_MAIN:
+	case REF_WORKTREE_SHARED:
+		return store->main_stack;
+	default:
+		BUG("unhandled worktree reference type");
+	}
+}
+
+static int should_write_log(struct ref_store *refs, const char *refname)
+{
+	if (log_all_ref_updates == LOG_REFS_UNSET)
+		log_all_ref_updates = is_bare_repository() ? LOG_REFS_NONE : LOG_REFS_NORMAL;
+
+	switch (log_all_ref_updates) {
+	case LOG_REFS_NONE:
+		return refs_reflog_exists(refs, refname);
+	case LOG_REFS_ALWAYS:
+		return 1;
+	case LOG_REFS_NORMAL:
+		if (should_autocreate_reflog(refname))
+			return 1;
+		return refs_reflog_exists(refs, refname);
+	default:
+		BUG("unhandled core.logAllRefUpdates value %d", log_all_ref_updates);
+	}
+}
+
+static void fill_reftable_log_record(struct reftable_log_record *log)
+{
+	const char *info = git_committer_info(0);
+	struct ident_split split = {0};
+	int sign = 1;
+
+	if (split_ident_line(&split, info, strlen(info)))
+		BUG("failed splitting committer info");
+
+	reftable_log_record_release(log);
+	log->value_type = REFTABLE_LOG_UPDATE;
+	log->value.update.name =
+		xstrndup(split.name_begin, split.name_end - split.name_begin);
+	log->value.update.email =
+		xstrndup(split.mail_begin, split.mail_end - split.mail_begin);
+	log->value.update.time = atol(split.date_begin);
+	if (*split.tz_begin == '-') {
+		sign = -1;
+		split.tz_begin++;
+	}
+	if (*split.tz_begin == '+') {
+		sign = 1;
+		split.tz_begin++;
+	}
+
+	log->value.update.tz_offset = sign * atoi(split.tz_begin);
+}
+
+static int read_ref_without_reload(struct reftable_stack *stack,
+				   const char *refname,
+				   struct object_id *oid,
+				   struct strbuf *referent,
+				   unsigned int *type)
+{
+	struct reftable_ref_record ref = {0};
+	int ret;
+
+	ret = reftable_stack_read_ref(stack, refname, &ref);
+	if (ret)
+		goto done;
+
+	if (ref.value_type == REFTABLE_REF_SYMREF) {
+		strbuf_reset(referent);
+		strbuf_addstr(referent, ref.value.symref);
+		*type |= REF_ISSYMREF;
+	} else if (reftable_ref_record_val1(&ref)) {
+		oidread(oid, reftable_ref_record_val1(&ref));
+	} else {
+		/* We got a tombstone, which should not happen. */
+		BUG("unhandled reference value type %d", ref.value_type);
+	}
+
+done:
+	assert(ret != REFTABLE_API_ERROR);
+	reftable_ref_record_release(&ref);
+	return ret;
+}
+
+static struct ref_store *reftable_be_init(struct repository *repo,
+					  const char *gitdir,
+					  unsigned int store_flags)
+{
+	struct reftable_ref_store *refs = xcalloc(1, sizeof(*refs));
+	struct strbuf path = STRBUF_INIT;
+	int is_worktree;
+	mode_t mask;
+
+	mask = umask(0);
+	umask(mask);
+
+	base_ref_store_init(&refs->base, repo, gitdir, &refs_be_reftable);
+	strmap_init(&refs->worktree_stacks);
+	refs->store_flags = store_flags;
+	refs->write_options.block_size = 4096;
+	refs->write_options.hash_id = repo->hash_algo->format_id;
+	refs->write_options.default_permissions = calc_shared_perm(0666 & ~mask);
+	refs->write_options.disable_auto_compact =
+		!git_env_bool("GIT_TEST_REFTABLE_AUTOCOMPACTION", 1);
+
+	/*
+	 * Set up the main reftable stack that is hosted in GIT_COMMON_DIR.
+	 * This stack contains both the shared and the main worktree refs.
+	 *
+	 * Note that we don't try to resolve the path in case we have a
+	 * worktree because `get_common_dir_noenv()` already does it for us.
+	 */
+	is_worktree = get_common_dir_noenv(&path, gitdir);
+	if (!is_worktree) {
+		strbuf_reset(&path);
+		strbuf_realpath(&path, gitdir, 0);
+	}
+	strbuf_addstr(&path, "/reftable");
+	refs->err = reftable_new_stack(&refs->main_stack, path.buf,
+				       refs->write_options);
+	if (refs->err)
+		goto done;
+
+	/*
+	 * If we're in a worktree we also need to set up the worktree reftable
+	 * stack that is contained in the per-worktree GIT_DIR.
+	 *
+	 * Ideally, we would also add the stack to our worktree stack map. But
+	 * we have no way to figure out the worktree name here and thus can't
+	 * do it efficiently.
+	 */
+	if (is_worktree) {
+		strbuf_reset(&path);
+		strbuf_addf(&path, "%s/reftable", gitdir);
+
+		refs->err = reftable_new_stack(&refs->worktree_stack, path.buf,
+					       refs->write_options);
+		if (refs->err)
+			goto done;
+	}
+
+	chdir_notify_reparent("reftables-backend $GIT_DIR", &refs->base.gitdir);
+
+done:
+	assert(refs->err != REFTABLE_API_ERROR);
+	strbuf_release(&path);
+	return &refs->base;
+}
+
+static int reftable_be_init_db(struct ref_store *ref_store,
+			       int flags UNUSED,
+			       struct strbuf *err UNUSED)
+{
+	struct reftable_ref_store *refs =
+		reftable_be_downcast(ref_store, REF_STORE_WRITE, "init_db");
+	struct strbuf sb = STRBUF_INIT;
+
+	strbuf_addf(&sb, "%s/reftable", refs->base.gitdir);
+	safe_create_dir(sb.buf, 1);
+	strbuf_reset(&sb);
+
+	strbuf_addf(&sb, "%s/HEAD", refs->base.gitdir);
+	write_file(sb.buf, "ref: refs/heads/.invalid");
+	adjust_shared_perm(sb.buf);
+	strbuf_reset(&sb);
+
+	strbuf_addf(&sb, "%s/refs", refs->base.gitdir);
+	safe_create_dir(sb.buf, 1);
+	strbuf_reset(&sb);
+
+	strbuf_addf(&sb, "%s/refs/heads", refs->base.gitdir);
+	write_file(sb.buf, "this repository uses the reftable format");
+	adjust_shared_perm(sb.buf);
+
+	strbuf_release(&sb);
+	return 0;
+}
+
+struct reftable_ref_iterator {
+	struct ref_iterator base;
+	struct reftable_ref_store *refs;
+	struct reftable_iterator iter;
+	struct reftable_ref_record ref;
+	struct object_id oid;
+
+	const char *prefix;
+	size_t prefix_len;
+	unsigned int flags;
+	int err;
+};
+
+static int reftable_ref_iterator_advance(struct ref_iterator *ref_iterator)
+{
+	struct reftable_ref_iterator *iter =
+		(struct reftable_ref_iterator *)ref_iterator;
+	struct reftable_ref_store *refs = iter->refs;
+
+	while (!iter->err) {
+		int flags = 0;
+
+		iter->err = reftable_iterator_next_ref(&iter->iter, &iter->ref);
+		if (iter->err)
+			break;
+
+		/*
+		 * The files backend only lists references contained in "refs/" unless
+		 * the root refs are to be included. We emulate the same behaviour here.
+		 */
+		if (!starts_with(iter->ref.refname, "refs/") &&
+		    !(iter->flags & DO_FOR_EACH_INCLUDE_ROOT_REFS &&
+		     (is_pseudoref(&iter->refs->base, iter->ref.refname) ||
+		      is_headref(&iter->refs->base, iter->ref.refname)))) {
+			continue;
+		}
+
+		if (iter->prefix_len &&
+		    strncmp(iter->prefix, iter->ref.refname, iter->prefix_len)) {
+			iter->err = 1;
+			break;
+		}
+
+		if (iter->flags & DO_FOR_EACH_PER_WORKTREE_ONLY &&
+		    parse_worktree_ref(iter->ref.refname, NULL, NULL, NULL) !=
+			    REF_WORKTREE_CURRENT)
+			continue;
+
+		switch (iter->ref.value_type) {
+		case REFTABLE_REF_VAL1:
+			oidread(&iter->oid, iter->ref.value.val1);
+			break;
+		case REFTABLE_REF_VAL2:
+			oidread(&iter->oid, iter->ref.value.val2.value);
+			break;
+		case REFTABLE_REF_SYMREF:
+			if (!refs_resolve_ref_unsafe(&iter->refs->base, iter->ref.refname,
+						     RESOLVE_REF_READING, &iter->oid, &flags))
+				oidclr(&iter->oid);
+			break;
+		default:
+			BUG("unhandled reference value type %d", iter->ref.value_type);
+		}
+
+		if (is_null_oid(&iter->oid))
+			flags |= REF_ISBROKEN;
+
+		if (check_refname_format(iter->ref.refname, REFNAME_ALLOW_ONELEVEL)) {
+			if (!refname_is_safe(iter->ref.refname))
+				die(_("refname is dangerous: %s"), iter->ref.refname);
+			oidclr(&iter->oid);
+			flags |= REF_BAD_NAME | REF_ISBROKEN;
+		}
+
+		if (iter->flags & DO_FOR_EACH_OMIT_DANGLING_SYMREFS &&
+		    flags & REF_ISSYMREF &&
+		    flags & REF_ISBROKEN)
+			continue;
+
+		if (!(iter->flags & DO_FOR_EACH_INCLUDE_BROKEN) &&
+		    !ref_resolves_to_object(iter->ref.refname, refs->base.repo,
+					    &iter->oid, flags))
+				continue;
+
+		iter->base.refname = iter->ref.refname;
+		iter->base.oid = &iter->oid;
+		iter->base.flags = flags;
+
+		break;
+	}
+
+	if (iter->err > 0) {
+		if (ref_iterator_abort(ref_iterator) != ITER_DONE)
+			return ITER_ERROR;
+		return ITER_DONE;
+	}
+
+	if (iter->err < 0) {
+		ref_iterator_abort(ref_iterator);
+		return ITER_ERROR;
+	}
+
+	return ITER_OK;
+}
+
+static int reftable_ref_iterator_peel(struct ref_iterator *ref_iterator,
+				      struct object_id *peeled)
+{
+	struct reftable_ref_iterator *iter =
+		(struct reftable_ref_iterator *)ref_iterator;
+
+	if (iter->ref.value_type == REFTABLE_REF_VAL2) {
+		oidread(peeled, iter->ref.value.val2.target_value);
+		return 0;
+	}
+
+	return -1;
+}
+
+static int reftable_ref_iterator_abort(struct ref_iterator *ref_iterator)
+{
+	struct reftable_ref_iterator *iter =
+		(struct reftable_ref_iterator *)ref_iterator;
+	reftable_ref_record_release(&iter->ref);
+	reftable_iterator_destroy(&iter->iter);
+	free(iter);
+	return ITER_DONE;
+}
+
+static struct ref_iterator_vtable reftable_ref_iterator_vtable = {
+	.advance = reftable_ref_iterator_advance,
+	.peel = reftable_ref_iterator_peel,
+	.abort = reftable_ref_iterator_abort
+};
+
+static struct reftable_ref_iterator *ref_iterator_for_stack(struct reftable_ref_store *refs,
+							    struct reftable_stack *stack,
+							    const char *prefix,
+							    int flags)
+{
+	struct reftable_merged_table *merged_table;
+	struct reftable_ref_iterator *iter;
+	int ret;
+
+	iter = xcalloc(1, sizeof(*iter));
+	base_ref_iterator_init(&iter->base, &reftable_ref_iterator_vtable);
+	iter->prefix = prefix;
+	iter->prefix_len = prefix ? strlen(prefix) : 0;
+	iter->base.oid = &iter->oid;
+	iter->flags = flags;
+	iter->refs = refs;
+
+	ret = refs->err;
+	if (ret)
+		goto done;
+
+	ret = reftable_stack_reload(stack);
+	if (ret)
+		goto done;
+
+	merged_table = reftable_stack_merged_table(stack);
+
+	ret = reftable_merged_table_seek_ref(merged_table, &iter->iter, prefix);
+	if (ret)
+		goto done;
+
+done:
+	iter->err = ret;
+	return iter;
+}
+
+static struct ref_iterator *reftable_be_iterator_begin(struct ref_store *ref_store,
+						       const char *prefix,
+						       const char **exclude_patterns,
+						       unsigned int flags)
+{
+	struct reftable_ref_iterator *main_iter, *worktree_iter;
+	struct reftable_ref_store *refs;
+	unsigned int required_flags = REF_STORE_READ;
+
+	if (!(flags & DO_FOR_EACH_INCLUDE_BROKEN))
+		required_flags |= REF_STORE_ODB;
+	refs = reftable_be_downcast(ref_store, required_flags, "ref_iterator_begin");
+
+	main_iter = ref_iterator_for_stack(refs, refs->main_stack, prefix, flags);
+
+	/*
+	 * The worktree stack is only set when we're in an actual worktree
+	 * right now. If we aren't, then we return the common reftable
+	 * iterator, only.
+	 */
+	 if (!refs->worktree_stack)
+		return &main_iter->base;
+
+	/*
+	 * Otherwise we merge both the common and the per-worktree refs into a
+	 * single iterator.
+	 */
+	worktree_iter = ref_iterator_for_stack(refs, refs->worktree_stack, prefix, flags);
+	return merge_ref_iterator_begin(&worktree_iter->base, &main_iter->base,
+					ref_iterator_select, NULL);
+}
+
+static int reftable_be_read_raw_ref(struct ref_store *ref_store,
+				    const char *refname,
+				    struct object_id *oid,
+				    struct strbuf *referent,
+				    unsigned int *type,
+				    int *failure_errno)
+{
+	struct reftable_ref_store *refs =
+		reftable_be_downcast(ref_store, REF_STORE_READ, "read_raw_ref");
+	struct reftable_stack *stack = stack_for(refs, refname, &refname);
+	int ret;
+
+	if (refs->err < 0)
+		return refs->err;
+
+	ret = reftable_stack_reload(stack);
+	if (ret)
+		return ret;
+
+	ret = read_ref_without_reload(stack, refname, oid, referent, type);
+	if (ret < 0)
+		return ret;
+	if (ret > 0) {
+		*failure_errno = ENOENT;
+		return -1;
+	}
+
+	return 0;
+}
+
+static int reftable_be_read_symbolic_ref(struct ref_store *ref_store,
+					 const char *refname,
+					 struct strbuf *referent)
+{
+	struct reftable_ref_store *refs =
+		reftable_be_downcast(ref_store, REF_STORE_READ, "read_symbolic_ref");
+	struct reftable_stack *stack = stack_for(refs, refname, &refname);
+	struct reftable_ref_record ref = {0};
+	int ret;
+
+	ret = reftable_stack_reload(stack);
+	if (ret)
+		return ret;
+
+	ret = reftable_stack_read_ref(stack, refname, &ref);
+	if (ret == 0 && ref.value_type == REFTABLE_REF_SYMREF)
+		strbuf_addstr(referent, ref.value.symref);
+	else
+		ret = -1;
+
+	reftable_ref_record_release(&ref);
+	return ret;
+}
+
+/*
+ * 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;
+}
+
+struct reftable_transaction_update {
+	struct ref_update *update;
+	struct object_id current_oid;
+};
+
+struct write_transaction_table_arg {
+	struct reftable_ref_store *refs;
+	struct reftable_stack *stack;
+	struct reftable_addition *addition;
+	struct reftable_transaction_update *updates;
+	size_t updates_nr;
+	size_t updates_alloc;
+	size_t updates_expected;
+};
+
+struct reftable_transaction_data {
+	struct write_transaction_table_arg *args;
+	size_t args_nr, args_alloc;
+};
+
+static void free_transaction_data(struct reftable_transaction_data *tx_data)
+{
+	if (!tx_data)
+		return;
+	for (size_t i = 0; i < tx_data->args_nr; i++) {
+		reftable_addition_destroy(tx_data->args[i].addition);
+		free(tx_data->args[i].updates);
+	}
+	free(tx_data->args);
+	free(tx_data);
+}
+
+/*
+ * Prepare transaction update for the given reference update. This will cause
+ * us to lock the corresponding reftable stack for concurrent modification.
+ */
+static int prepare_transaction_update(struct write_transaction_table_arg **out,
+				      struct reftable_ref_store *refs,
+				      struct reftable_transaction_data *tx_data,
+				      struct ref_update *update,
+				      struct strbuf *err)
+{
+	struct reftable_stack *stack = stack_for(refs, update->refname, NULL);
+	struct write_transaction_table_arg *arg = NULL;
+	size_t i;
+	int ret;
+
+	/*
+	 * Search for a preexisting stack update. If there is one then we add
+	 * the update to it, otherwise we set up a new stack update.
+	 */
+	for (i = 0; !arg && i < tx_data->args_nr; i++)
+		if (tx_data->args[i].stack == stack)
+			arg = &tx_data->args[i];
+
+	if (!arg) {
+		struct reftable_addition *addition;
+
+		ret = reftable_stack_reload(stack);
+		if (ret)
+			return ret;
+
+		ret = reftable_stack_new_addition(&addition, stack);
+		if (ret) {
+			if (ret == REFTABLE_LOCK_ERROR)
+				strbuf_addstr(err, "cannot lock references");
+			return ret;
+		}
+
+		ALLOC_GROW(tx_data->args, tx_data->args_nr + 1,
+			   tx_data->args_alloc);
+		arg = &tx_data->args[tx_data->args_nr++];
+		arg->refs = refs;
+		arg->stack = stack;
+		arg->addition = addition;
+		arg->updates = NULL;
+		arg->updates_nr = 0;
+		arg->updates_alloc = 0;
+		arg->updates_expected = 0;
+	}
+
+	arg->updates_expected++;
+
+	if (out)
+		*out = arg;
+
+	return 0;
+}
+
+/*
+ * Queue a reference update for the correct stack. We potentially need to
+ * handle multiple stack updates in a single transaction when it spans across
+ * multiple worktrees.
+ */
+static int queue_transaction_update(struct reftable_ref_store *refs,
+				    struct reftable_transaction_data *tx_data,
+				    struct ref_update *update,
+				    struct object_id *current_oid,
+				    struct strbuf *err)
+{
+	struct write_transaction_table_arg *arg = NULL;
+	int ret;
+
+	if (update->backend_data)
+		BUG("reference update queued more than once");
+
+	ret = prepare_transaction_update(&arg, refs, tx_data, update, err);
+	if (ret < 0)
+		return ret;
+
+	ALLOC_GROW(arg->updates, arg->updates_nr + 1,
+		   arg->updates_alloc);
+	arg->updates[arg->updates_nr].update = update;
+	oidcpy(&arg->updates[arg->updates_nr].current_oid, current_oid);
+	update->backend_data = &arg->updates[arg->updates_nr++];
+
+	return 0;
+}
+
+static int reftable_be_transaction_prepare(struct ref_store *ref_store,
+					   struct ref_transaction *transaction,
+					   struct strbuf *err)
+{
+	struct reftable_ref_store *refs =
+		reftable_be_downcast(ref_store, REF_STORE_WRITE|REF_STORE_MAIN, "ref_transaction_prepare");
+	struct strbuf referent = STRBUF_INIT, head_referent = STRBUF_INIT;
+	struct string_list affected_refnames = STRING_LIST_INIT_NODUP;
+	struct reftable_transaction_data *tx_data = NULL;
+	struct object_id head_oid;
+	unsigned int head_type = 0;
+	size_t i;
+	int ret;
+
+	ret = refs->err;
+	if (ret < 0)
+		goto done;
+
+	tx_data = xcalloc(1, sizeof(*tx_data));
+
+	/*
+	 * Preprocess all updates. For one we check that there are no duplicate
+	 * reference updates in this transaction. Second, we lock all stacks
+	 * that will be modified during the transaction.
+	 */
+	for (i = 0; i < transaction->nr; i++) {
+		ret = prepare_transaction_update(NULL, refs, tx_data,
+						 transaction->updates[i], err);
+		if (ret)
+			goto done;
+
+		string_list_append(&affected_refnames,
+				   transaction->updates[i]->refname);
+	}
+
+	/*
+	 * Now that we have counted updates per stack we can preallocate their
+	 * arrays. This avoids having to reallocate many times.
+	 */
+	for (i = 0; i < tx_data->args_nr; i++) {
+		CALLOC_ARRAY(tx_data->args[i].updates, tx_data->args[i].updates_expected);
+		tx_data->args[i].updates_alloc = tx_data->args[i].updates_expected;
+	}
+
+	/*
+	 * Fail if a refname appears more than once in the transaction.
+	 * This code is taken from the files backend and is a good candidate to
+	 * be moved into the generic layer.
+	 */
+	string_list_sort(&affected_refnames);
+	if (ref_update_reject_duplicates(&affected_refnames, err)) {
+		ret = TRANSACTION_GENERIC_ERROR;
+		goto done;
+	}
+
+	ret = read_ref_without_reload(stack_for(refs, "HEAD", NULL), "HEAD", &head_oid,
+				      &head_referent, &head_type);
+	if (ret < 0)
+		goto done;
+	ret = 0;
+
+	for (i = 0; i < transaction->nr; i++) {
+		struct ref_update *u = transaction->updates[i];
+		struct object_id current_oid = {0};
+		struct reftable_stack *stack;
+		const char *rewritten_ref;
+
+		stack = stack_for(refs, u->refname, &rewritten_ref);
+
+		/* Verify that the new object ID is valid. */
+		if ((u->flags & REF_HAVE_NEW) && !is_null_oid(&u->new_oid) &&
+		    !(u->flags & REF_SKIP_OID_VERIFICATION) &&
+		    !(u->flags & REF_LOG_ONLY)) {
+			struct object *o = parse_object(refs->base.repo, &u->new_oid);
+			if (!o) {
+				strbuf_addf(err,
+					    _("trying to write ref '%s' with nonexistent object %s"),
+					    u->refname, oid_to_hex(&u->new_oid));
+				ret = -1;
+				goto done;
+			}
+
+			if (o->type != OBJ_COMMIT && is_branch(u->refname)) {
+				strbuf_addf(err, _("trying to write non-commit object %s to branch '%s'"),
+					    oid_to_hex(&u->new_oid), u->refname);
+				ret = -1;
+				goto done;
+			}
+		}
+
+		/*
+		 * When we update the reference that HEAD points to we enqueue
+		 * a second log-only update for HEAD so that its reflog is
+		 * updated accordingly.
+		 */
+		if (head_type == REF_ISSYMREF &&
+		    !(u->flags & REF_LOG_ONLY) &&
+		    !(u->flags & REF_UPDATE_VIA_HEAD) &&
+		    !strcmp(rewritten_ref, head_referent.buf)) {
+			struct ref_update *new_update;
+
+			/*
+			 * 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"),
+					    u->refname);
+				ret = TRANSACTION_NAME_CONFLICT;
+				goto done;
+			}
+
+			new_update = ref_transaction_add_update(
+					transaction, "HEAD",
+					u->flags | REF_LOG_ONLY | REF_NO_DEREF,
+					&u->new_oid, &u->old_oid, u->msg);
+			string_list_insert(&affected_refnames, new_update->refname);
+		}
+
+		ret = read_ref_without_reload(stack, rewritten_ref,
+					      &current_oid, &referent, &u->type);
+		if (ret < 0)
+			goto done;
+		if (ret > 0 && (!(u->flags & REF_HAVE_OLD) || is_null_oid(&u->old_oid))) {
+			/*
+			 * The reference does not exist, and we either have no
+			 * old object ID or expect the reference to not exist.
+			 * We can thus skip below safety checks as well as the
+			 * symref splitting. But we do want to verify that
+			 * there is no conflicting reference here so that we
+			 * can output a proper error message instead of failing
+			 * at a later point.
+			 */
+			ret = refs_verify_refname_available(ref_store, u->refname,
+							    &affected_refnames, NULL, err);
+			if (ret < 0)
+				goto done;
+
+			/*
+			 * There is no need to write the reference deletion
+			 * when the reference in question doesn't exist.
+			 */
+			 if (u->flags & REF_HAVE_NEW && !is_null_oid(&u->new_oid)) {
+				 ret = queue_transaction_update(refs, tx_data, u,
+								&current_oid, err);
+				 if (ret)
+					 goto done;
+			 }
+
+			continue;
+		}
+		if (ret > 0) {
+			/* The reference does not exist, but we expected it to. */
+			strbuf_addf(err, _("cannot lock ref '%s': "
+				    "unable to resolve reference '%s'"),
+				    original_update_refname(u), u->refname);
+			ret = -1;
+			goto done;
+		}
+
+		if (u->type & REF_ISSYMREF) {
+			/*
+			 * The reftable stack is locked at this point already,
+			 * so it is safe to call `refs_resolve_ref_unsafe()`
+			 * here without causing races.
+			 */
+			const char *resolved = refs_resolve_ref_unsafe(&refs->base, u->refname, 0,
+								       &current_oid, NULL);
+
+			if (u->flags & REF_NO_DEREF) {
+				if (u->flags & REF_HAVE_OLD && !resolved) {
+					strbuf_addf(err, _("cannot lock ref '%s': "
+						    "error reading reference"), u->refname);
+					ret = -1;
+					goto done;
+				}
+			} else {
+				struct ref_update *new_update;
+				int new_flags;
+
+				new_flags = u->flags;
+				if (!strcmp(rewritten_ref, "HEAD"))
+					new_flags |= REF_UPDATE_VIA_HEAD;
+
+				/*
+				 * If we are updating a symref (eg. HEAD), we should also
+				 * update the branch that the symref points to.
+				 *
+				 * This is generic functionality, and would be better
+				 * done in refs.c, but the current implementation is
+				 * intertwined with the locking in files-backend.c.
+				 */
+				new_update = ref_transaction_add_update(
+						transaction, referent.buf, new_flags,
+						&u->new_oid, &u->old_oid, u->msg);
+				new_update->parent_update = u;
+
+				/*
+				 * 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.
+				 */
+				u->flags |= REF_LOG_ONLY | REF_NO_DEREF;
+				u->flags &= ~REF_HAVE_OLD;
+
+				if (string_list_has_string(&affected_refnames, new_update->refname)) {
+					strbuf_addf(err,
+						    _("multiple updates for '%s' (including one "
+						    "via symref '%s') are not allowed"),
+						    referent.buf, u->refname);
+					ret = TRANSACTION_NAME_CONFLICT;
+					goto done;
+				}
+				string_list_insert(&affected_refnames, new_update->refname);
+			}
+		}
+
+		/*
+		 * Verify that the old object matches our expectations. Note
+		 * that the error messages here do not make a lot of sense in
+		 * the context of the reftable backend as we never lock
+		 * individual refs. But the error messages match what the files
+		 * backend returns, which keeps our tests happy.
+		 */
+		if (u->flags & REF_HAVE_OLD && !oideq(&current_oid, &u->old_oid)) {
+			if (is_null_oid(&u->old_oid))
+				strbuf_addf(err, _("cannot lock ref '%s': "
+					    "reference already exists"),
+					    original_update_refname(u));
+			else if (is_null_oid(&current_oid))
+				strbuf_addf(err, _("cannot lock ref '%s': "
+					    "reference is missing but expected %s"),
+					    original_update_refname(u),
+					    oid_to_hex(&u->old_oid));
+			else
+				strbuf_addf(err, _("cannot lock ref '%s': "
+					    "is at %s but expected %s"),
+					    original_update_refname(u),
+					    oid_to_hex(&current_oid),
+					    oid_to_hex(&u->old_oid));
+			ret = -1;
+			goto done;
+		}
+
+		/*
+		 * If all of the following conditions are true:
+		 *
+		 *   - We're not about to write a symref.
+		 *   - We're not about to write a log-only entry.
+		 *   - Old and new object ID are different.
+		 *
+		 * Then we're essentially doing a no-op update that can be
+		 * skipped. This is not only for the sake of efficiency, but
+		 * also skips writing unneeded reflog entries.
+		 */
+		if ((u->type & REF_ISSYMREF) ||
+		    (u->flags & REF_LOG_ONLY) ||
+		    (u->flags & REF_HAVE_NEW && !oideq(&current_oid, &u->new_oid))) {
+			ret = queue_transaction_update(refs, tx_data, u,
+						       &current_oid, err);
+			if (ret)
+				goto done;
+		}
+	}
+
+	transaction->backend_data = tx_data;
+	transaction->state = REF_TRANSACTION_PREPARED;
+
+done:
+	assert(ret != REFTABLE_API_ERROR);
+	if (ret < 0) {
+		free_transaction_data(tx_data);
+		transaction->state = REF_TRANSACTION_CLOSED;
+		if (!err->len)
+			strbuf_addf(err, _("reftable: transaction prepare: %s"),
+				    reftable_error_str(ret));
+	}
+	string_list_clear(&affected_refnames, 0);
+	strbuf_release(&referent);
+	strbuf_release(&head_referent);
+
+	return ret;
+}
+
+static int reftable_be_transaction_abort(struct ref_store *ref_store,
+					 struct ref_transaction *transaction,
+					 struct strbuf *err)
+{
+	struct reftable_transaction_data *tx_data = transaction->backend_data;
+	free_transaction_data(tx_data);
+	transaction->state = REF_TRANSACTION_CLOSED;
+	return 0;
+}
+
+static int transaction_update_cmp(const void *a, const void *b)
+{
+	return strcmp(((struct reftable_transaction_update *)a)->update->refname,
+		      ((struct reftable_transaction_update *)b)->update->refname);
+}
+
+static int write_transaction_table(struct reftable_writer *writer, void *cb_data)
+{
+	struct write_transaction_table_arg *arg = cb_data;
+	struct reftable_merged_table *mt =
+		reftable_stack_merged_table(arg->stack);
+	uint64_t ts = reftable_stack_next_update_index(arg->stack);
+	struct reftable_log_record *logs = NULL;
+	size_t logs_nr = 0, logs_alloc = 0, i;
+	int ret = 0;
+
+	QSORT(arg->updates, arg->updates_nr, transaction_update_cmp);
+
+	reftable_writer_set_limits(writer, ts, ts);
+
+	for (i = 0; i < arg->updates_nr; i++) {
+		struct reftable_transaction_update *tx_update = &arg->updates[i];
+		struct ref_update *u = tx_update->update;
+
+		/*
+		 * Write a reflog entry when updating a ref to point to
+		 * something new in either of the following cases:
+		 *
+		 * - The reference is about to be deleted. We always want to
+		 *   delete the reflog in that case.
+		 * - REF_FORCE_CREATE_REFLOG is set, asking us to always create
+		 *   the reflog entry.
+		 * - `core.logAllRefUpdates` tells us to create the reflog for
+		 *   the given ref.
+		 */
+		if (u->flags & REF_HAVE_NEW && !(u->type & REF_ISSYMREF) && is_null_oid(&u->new_oid)) {
+			struct reftable_log_record log = {0};
+			struct reftable_iterator it = {0};
+
+			/*
+			 * When deleting refs we also delete all reflog entries
+			 * with them. While it is not strictly required to
+			 * delete reflogs together with their refs, this
+			 * matches the behaviour of the files backend.
+			 *
+			 * Unfortunately, we have no better way than to delete
+			 * all reflog entries one by one.
+			 */
+			ret = reftable_merged_table_seek_log(mt, &it, u->refname);
+			while (ret == 0) {
+				struct reftable_log_record *tombstone;
+
+				ret = reftable_iterator_next_log(&it, &log);
+				if (ret < 0)
+					break;
+				if (ret > 0 || strcmp(log.refname, u->refname)) {
+					ret = 0;
+					break;
+				}
+
+				ALLOC_GROW(logs, logs_nr + 1, logs_alloc);
+				tombstone = &logs[logs_nr++];
+				tombstone->refname = xstrdup(u->refname);
+				tombstone->value_type = REFTABLE_LOG_DELETION;
+				tombstone->update_index = log.update_index;
+			}
+
+			reftable_log_record_release(&log);
+			reftable_iterator_destroy(&it);
+
+			if (ret)
+				goto done;
+		} else if (u->flags & REF_HAVE_NEW &&
+			   (u->flags & REF_FORCE_CREATE_REFLOG ||
+			    should_write_log(&arg->refs->base, u->refname))) {
+			struct reftable_log_record *log;
+
+			ALLOC_GROW(logs, logs_nr + 1, logs_alloc);
+			log = &logs[logs_nr++];
+			memset(log, 0, sizeof(*log));
+
+			fill_reftable_log_record(log);
+			log->update_index = ts;
+			log->refname = xstrdup(u->refname);
+			memcpy(log->value.update.new_hash, u->new_oid.hash, GIT_MAX_RAWSZ);
+			memcpy(log->value.update.old_hash, tx_update->current_oid.hash, GIT_MAX_RAWSZ);
+			log->value.update.message =
+				xstrndup(u->msg, arg->refs->write_options.block_size / 2);
+		}
+
+		if (u->flags & REF_LOG_ONLY)
+			continue;
+
+		if (u->flags & REF_HAVE_NEW && is_null_oid(&u->new_oid)) {
+			struct reftable_ref_record ref = {
+				.refname = (char *)u->refname,
+				.update_index = ts,
+				.value_type = REFTABLE_REF_DELETION,
+			};
+
+			ret = reftable_writer_add_ref(writer, &ref);
+			if (ret < 0)
+				goto done;
+		} else if (u->flags & REF_HAVE_NEW) {
+			struct reftable_ref_record ref = {0};
+			struct object_id peeled;
+			int peel_error;
+
+			ref.refname = (char *)u->refname;
+			ref.update_index = ts;
+
+			peel_error = peel_object(&u->new_oid, &peeled);
+			if (!peel_error) {
+				ref.value_type = REFTABLE_REF_VAL2;
+				memcpy(ref.value.val2.target_value, peeled.hash, GIT_MAX_RAWSZ);
+				memcpy(ref.value.val2.value, u->new_oid.hash, GIT_MAX_RAWSZ);
+			} else if (!is_null_oid(&u->new_oid)) {
+				ref.value_type = REFTABLE_REF_VAL1;
+				memcpy(ref.value.val1, u->new_oid.hash, GIT_MAX_RAWSZ);
+			}
+
+			ret = reftable_writer_add_ref(writer, &ref);
+			if (ret < 0)
+				goto done;
+		}
+	}
+
+	/*
+	 * Logs are written at the end so that we do not have intermixed ref
+	 * and log blocks.
+	 */
+	if (logs) {
+		ret = reftable_writer_add_logs(writer, logs, logs_nr);
+		if (ret < 0)
+			goto done;
+	}
+
+done:
+	assert(ret != REFTABLE_API_ERROR);
+	for (i = 0; i < logs_nr; i++)
+		reftable_log_record_release(&logs[i]);
+	free(logs);
+	return ret;
+}
+
+static int reftable_be_transaction_finish(struct ref_store *ref_store,
+					  struct ref_transaction *transaction,
+					  struct strbuf *err)
+{
+	struct reftable_transaction_data *tx_data = transaction->backend_data;
+	int ret = 0;
+
+	for (size_t i = 0; i < tx_data->args_nr; i++) {
+		ret = reftable_addition_add(tx_data->args[i].addition,
+					    write_transaction_table, &tx_data->args[i]);
+		if (ret < 0)
+			goto done;
+
+		ret = reftable_addition_commit(tx_data->args[i].addition);
+		if (ret < 0)
+			goto done;
+	}
+
+done:
+	assert(ret != REFTABLE_API_ERROR);
+	free_transaction_data(tx_data);
+	transaction->state = REF_TRANSACTION_CLOSED;
+
+	if (ret) {
+		strbuf_addf(err, _("reftable: transaction failure: %s"),
+			    reftable_error_str(ret));
+		return -1;
+	}
+	return ret;
+}
+
+static int reftable_be_initial_transaction_commit(struct ref_store *ref_store UNUSED,
+						  struct ref_transaction *transaction,
+						  struct strbuf *err)
+{
+	return ref_transaction_commit(transaction, err);
+}
+
+static int reftable_be_pack_refs(struct ref_store *ref_store,
+				 struct pack_refs_opts *opts)
+{
+	struct reftable_ref_store *refs =
+		reftable_be_downcast(ref_store, REF_STORE_WRITE | REF_STORE_ODB, "pack_refs");
+	struct reftable_stack *stack;
+	int ret;
+
+	if (refs->err)
+		return refs->err;
+
+	stack = refs->worktree_stack;
+	if (!stack)
+		stack = refs->main_stack;
+
+	if (opts->flags & PACK_REFS_AUTO)
+		ret = reftable_stack_auto_compact(stack);
+	else
+		ret = reftable_stack_compact_all(stack, NULL);
+	if (ret < 0) {
+		ret = error(_("unable to compact stack: %s"),
+			    reftable_error_str(ret));
+		goto out;
+	}
+
+	ret = reftable_stack_clean(stack);
+	if (ret)
+		goto out;
+
+out:
+	return ret;
+}
+
+struct write_create_symref_arg {
+	struct reftable_ref_store *refs;
+	struct reftable_stack *stack;
+	const char *refname;
+	const char *target;
+	const char *logmsg;
+};
+
+static int write_create_symref_table(struct reftable_writer *writer, void *cb_data)
+{
+	struct write_create_symref_arg *create = cb_data;
+	uint64_t ts = reftable_stack_next_update_index(create->stack);
+	struct reftable_ref_record ref = {
+		.refname = (char *)create->refname,
+		.value_type = REFTABLE_REF_SYMREF,
+		.value.symref = (char *)create->target,
+		.update_index = ts,
+	};
+	struct reftable_log_record log = {0};
+	struct object_id new_oid;
+	struct object_id old_oid;
+	int ret;
+
+	reftable_writer_set_limits(writer, ts, ts);
+
+	ret = reftable_writer_add_ref(writer, &ref);
+	if (ret)
+		return ret;
+
+	/*
+	 * Note that it is important to try and resolve the reference before we
+	 * write the log entry. This is because `should_write_log()` will munge
+	 * `core.logAllRefUpdates`, which is undesirable when we create a new
+	 * repository because it would be written into the config. As HEAD will
+	 * not resolve for new repositories this ordering will ensure that this
+	 * never happens.
+	 */
+	if (!create->logmsg ||
+	    !refs_resolve_ref_unsafe(&create->refs->base, create->target,
+				     RESOLVE_REF_READING, &new_oid, NULL) ||
+	    !should_write_log(&create->refs->base, create->refname))
+		return 0;
+
+	fill_reftable_log_record(&log);
+	log.refname = xstrdup(create->refname);
+	log.update_index = ts;
+	log.value.update.message = xstrndup(create->logmsg,
+					    create->refs->write_options.block_size / 2);
+	memcpy(log.value.update.new_hash, new_oid.hash, GIT_MAX_RAWSZ);
+	if (refs_resolve_ref_unsafe(&create->refs->base, create->refname,
+				    RESOLVE_REF_READING, &old_oid, NULL))
+		memcpy(log.value.update.old_hash, old_oid.hash, GIT_MAX_RAWSZ);
+
+	ret = reftable_writer_add_log(writer, &log);
+	reftable_log_record_release(&log);
+	return ret;
+}
+
+static int reftable_be_create_symref(struct ref_store *ref_store,
+				     const char *refname,
+				     const char *target,
+				     const char *logmsg)
+{
+	struct reftable_ref_store *refs =
+		reftable_be_downcast(ref_store, REF_STORE_WRITE, "create_symref");
+	struct reftable_stack *stack = stack_for(refs, refname, &refname);
+	struct write_create_symref_arg arg = {
+		.refs = refs,
+		.stack = stack,
+		.refname = refname,
+		.target = target,
+		.logmsg = logmsg,
+	};
+	int ret;
+
+	ret = refs->err;
+	if (ret < 0)
+		goto done;
+
+	ret = reftable_stack_reload(stack);
+	if (ret)
+		goto done;
+
+	ret = reftable_stack_add(stack, &write_create_symref_table, &arg);
+
+done:
+	assert(ret != REFTABLE_API_ERROR);
+	if (ret)
+		error("unable to write symref for %s: %s", refname,
+		      reftable_error_str(ret));
+	return ret;
+}
+
+struct write_copy_arg {
+	struct reftable_ref_store *refs;
+	struct reftable_stack *stack;
+	const char *oldname;
+	const char *newname;
+	const char *logmsg;
+	int delete_old;
+};
+
+static int write_copy_table(struct reftable_writer *writer, void *cb_data)
+{
+	struct write_copy_arg *arg = cb_data;
+	uint64_t deletion_ts, creation_ts;
+	struct reftable_merged_table *mt = reftable_stack_merged_table(arg->stack);
+	struct reftable_ref_record old_ref = {0}, refs[2] = {0};
+	struct reftable_log_record old_log = {0}, *logs = NULL;
+	struct reftable_iterator it = {0};
+	struct string_list skip = STRING_LIST_INIT_NODUP;
+	struct strbuf errbuf = STRBUF_INIT;
+	size_t logs_nr = 0, logs_alloc = 0, i;
+	int ret;
+
+	if (reftable_stack_read_ref(arg->stack, arg->oldname, &old_ref)) {
+		ret = error(_("refname %s not found"), arg->oldname);
+		goto done;
+	}
+	if (old_ref.value_type == REFTABLE_REF_SYMREF) {
+		ret = error(_("refname %s is a symbolic ref, copying it is not supported"),
+			    arg->oldname);
+		goto done;
+	}
+
+	/*
+	 * There's nothing to do in case the old and new name are the same, so
+	 * we exit early in that case.
+	 */
+	if (!strcmp(arg->oldname, arg->newname)) {
+		ret = 0;
+		goto done;
+	}
+
+	/*
+	 * Verify that the new refname is available.
+	 */
+	string_list_insert(&skip, arg->oldname);
+	ret = refs_verify_refname_available(&arg->refs->base, arg->newname,
+					    NULL, &skip, &errbuf);
+	if (ret < 0) {
+		error("%s", errbuf.buf);
+		goto done;
+	}
+
+	/*
+	 * When deleting the old reference we have to use two update indices:
+	 * once to delete the old ref and its reflog, and once to create the
+	 * new ref and its reflog. They need to be staged with two separate
+	 * indices because the new reflog needs to encode both the deletion of
+	 * the old branch and the creation of the new branch, and we cannot do
+	 * two changes to a reflog in a single update.
+	 */
+	deletion_ts = creation_ts = reftable_stack_next_update_index(arg->stack);
+	if (arg->delete_old)
+		creation_ts++;
+	reftable_writer_set_limits(writer, deletion_ts, creation_ts);
+
+	/*
+	 * Add the new reference. If this is a rename then we also delete the
+	 * old reference.
+	 */
+	refs[0] = old_ref;
+	refs[0].refname = (char *)arg->newname;
+	refs[0].update_index = creation_ts;
+	if (arg->delete_old) {
+		refs[1].refname = (char *)arg->oldname;
+		refs[1].value_type = REFTABLE_REF_DELETION;
+		refs[1].update_index = deletion_ts;
+	}
+	ret = reftable_writer_add_refs(writer, refs, arg->delete_old ? 2 : 1);
+	if (ret < 0)
+		goto done;
+
+	/*
+	 * When deleting the old branch we need to create a reflog entry on the
+	 * new branch name that indicates that the old branch has been deleted
+	 * and then recreated. This is a tad weird, but matches what the files
+	 * backend does.
+	 */
+	if (arg->delete_old) {
+		struct strbuf head_referent = STRBUF_INIT;
+		struct object_id head_oid;
+		int append_head_reflog;
+		unsigned head_type = 0;
+
+		ALLOC_GROW(logs, logs_nr + 1, logs_alloc);
+		memset(&logs[logs_nr], 0, sizeof(logs[logs_nr]));
+		fill_reftable_log_record(&logs[logs_nr]);
+		logs[logs_nr].refname = (char *)arg->newname;
+		logs[logs_nr].update_index = deletion_ts;
+		logs[logs_nr].value.update.message =
+			xstrndup(arg->logmsg, arg->refs->write_options.block_size / 2);
+		memcpy(logs[logs_nr].value.update.old_hash, old_ref.value.val1, GIT_MAX_RAWSZ);
+		logs_nr++;
+
+		ret = read_ref_without_reload(arg->stack, "HEAD", &head_oid, &head_referent, &head_type);
+		if (ret < 0)
+			goto done;
+		append_head_reflog = (head_type & REF_ISSYMREF) && !strcmp(head_referent.buf, arg->oldname);
+		strbuf_release(&head_referent);
+
+		/*
+		 * The files backend uses `refs_delete_ref()` to delete the old
+		 * branch name, which will append a reflog entry for HEAD in
+		 * case it points to the old branch.
+		 */
+		if (append_head_reflog) {
+			ALLOC_GROW(logs, logs_nr + 1, logs_alloc);
+			logs[logs_nr] = logs[logs_nr - 1];
+			logs[logs_nr].refname = "HEAD";
+			logs_nr++;
+		}
+	}
+
+	/*
+	 * Create the reflog entry for the newly created branch.
+	 */
+	ALLOC_GROW(logs, logs_nr + 1, logs_alloc);
+	memset(&logs[logs_nr], 0, sizeof(logs[logs_nr]));
+	fill_reftable_log_record(&logs[logs_nr]);
+	logs[logs_nr].refname = (char *)arg->newname;
+	logs[logs_nr].update_index = creation_ts;
+	logs[logs_nr].value.update.message =
+		xstrndup(arg->logmsg, arg->refs->write_options.block_size / 2);
+	memcpy(logs[logs_nr].value.update.new_hash, old_ref.value.val1, GIT_MAX_RAWSZ);
+	logs_nr++;
+
+	/*
+	 * In addition to writing the reflog entry for the new branch, we also
+	 * copy over all log entries from the old reflog. Last but not least,
+	 * when renaming we also have to delete all the old reflog entries.
+	 */
+	ret = reftable_merged_table_seek_log(mt, &it, arg->oldname);
+	if (ret < 0)
+		goto done;
+
+	while (1) {
+		ret = reftable_iterator_next_log(&it, &old_log);
+		if (ret < 0)
+			goto done;
+		if (ret > 0 || strcmp(old_log.refname, arg->oldname)) {
+			ret = 0;
+			break;
+		}
+
+		free(old_log.refname);
+
+		/*
+		 * Copy over the old reflog entry with the new refname.
+		 */
+		ALLOC_GROW(logs, logs_nr + 1, logs_alloc);
+		logs[logs_nr] = old_log;
+		logs[logs_nr].refname = (char *)arg->newname;
+		logs_nr++;
+
+		/*
+		 * Delete the old reflog entry in case we are renaming.
+		 */
+		if (arg->delete_old) {
+			ALLOC_GROW(logs, logs_nr + 1, logs_alloc);
+			memset(&logs[logs_nr], 0, sizeof(logs[logs_nr]));
+			logs[logs_nr].refname = (char *)arg->oldname;
+			logs[logs_nr].value_type = REFTABLE_LOG_DELETION;
+			logs[logs_nr].update_index = old_log.update_index;
+			logs_nr++;
+		}
+
+		/*
+		 * Transfer ownership of the log record we're iterating over to
+		 * the array of log records. Otherwise, the pointers would get
+		 * free'd or reallocated by the iterator.
+		 */
+		memset(&old_log, 0, sizeof(old_log));
+	}
+
+	ret = reftable_writer_add_logs(writer, logs, logs_nr);
+	if (ret < 0)
+		goto done;
+
+done:
+	assert(ret != REFTABLE_API_ERROR);
+	reftable_iterator_destroy(&it);
+	string_list_clear(&skip, 0);
+	strbuf_release(&errbuf);
+	for (i = 0; i < logs_nr; i++) {
+		if (!strcmp(logs[i].refname, "HEAD"))
+			continue;
+		logs[i].refname = NULL;
+		reftable_log_record_release(&logs[i]);
+	}
+	free(logs);
+	reftable_ref_record_release(&old_ref);
+	reftable_log_record_release(&old_log);
+	return ret;
+}
+
+static int reftable_be_rename_ref(struct ref_store *ref_store,
+				  const char *oldrefname,
+				  const char *newrefname,
+				  const char *logmsg)
+{
+	struct reftable_ref_store *refs =
+		reftable_be_downcast(ref_store, REF_STORE_WRITE, "rename_ref");
+	struct reftable_stack *stack = stack_for(refs, newrefname, &newrefname);
+	struct write_copy_arg arg = {
+		.refs = refs,
+		.stack = stack,
+		.oldname = oldrefname,
+		.newname = newrefname,
+		.logmsg = logmsg,
+		.delete_old = 1,
+	};
+	int ret;
+
+	ret = refs->err;
+	if (ret < 0)
+		goto done;
+
+	ret = reftable_stack_reload(stack);
+	if (ret)
+		goto done;
+	ret = reftable_stack_add(stack, &write_copy_table, &arg);
+
+done:
+	assert(ret != REFTABLE_API_ERROR);
+	return ret;
+}
+
+static int reftable_be_copy_ref(struct ref_store *ref_store,
+				const char *oldrefname,
+				const char *newrefname,
+				const char *logmsg)
+{
+	struct reftable_ref_store *refs =
+		reftable_be_downcast(ref_store, REF_STORE_WRITE, "copy_ref");
+	struct reftable_stack *stack = stack_for(refs, newrefname, &newrefname);
+	struct write_copy_arg arg = {
+		.refs = refs,
+		.stack = stack,
+		.oldname = oldrefname,
+		.newname = newrefname,
+		.logmsg = logmsg,
+	};
+	int ret;
+
+	ret = refs->err;
+	if (ret < 0)
+		goto done;
+
+	ret = reftable_stack_reload(stack);
+	if (ret)
+		goto done;
+	ret = reftable_stack_add(stack, &write_copy_table, &arg);
+
+done:
+	assert(ret != REFTABLE_API_ERROR);
+	return ret;
+}
+
+struct reftable_reflog_iterator {
+	struct ref_iterator base;
+	struct reftable_ref_store *refs;
+	struct reftable_iterator iter;
+	struct reftable_log_record log;
+	struct strbuf last_name;
+	int err;
+};
+
+static int reftable_reflog_iterator_advance(struct ref_iterator *ref_iterator)
+{
+	struct reftable_reflog_iterator *iter =
+		(struct reftable_reflog_iterator *)ref_iterator;
+
+	while (!iter->err) {
+		iter->err = reftable_iterator_next_log(&iter->iter, &iter->log);
+		if (iter->err)
+			break;
+
+		/*
+		 * We want the refnames that we have reflogs for, so we skip if
+		 * we've already produced this name. This could be faster by
+		 * seeking directly to reflog@update_index==0.
+		 */
+		if (!strcmp(iter->log.refname, iter->last_name.buf))
+			continue;
+
+		if (check_refname_format(iter->log.refname,
+					 REFNAME_ALLOW_ONELEVEL))
+			continue;
+
+		strbuf_reset(&iter->last_name);
+		strbuf_addstr(&iter->last_name, iter->log.refname);
+		iter->base.refname = iter->log.refname;
+
+		break;
+	}
+
+	if (iter->err > 0) {
+		if (ref_iterator_abort(ref_iterator) != ITER_DONE)
+			return ITER_ERROR;
+		return ITER_DONE;
+	}
+
+	if (iter->err < 0) {
+		ref_iterator_abort(ref_iterator);
+		return ITER_ERROR;
+	}
+
+	return ITER_OK;
+}
+
+static int reftable_reflog_iterator_peel(struct ref_iterator *ref_iterator,
+						 struct object_id *peeled)
+{
+	BUG("reftable reflog iterator cannot be peeled");
+	return -1;
+}
+
+static int reftable_reflog_iterator_abort(struct ref_iterator *ref_iterator)
+{
+	struct reftable_reflog_iterator *iter =
+		(struct reftable_reflog_iterator *)ref_iterator;
+	reftable_log_record_release(&iter->log);
+	reftable_iterator_destroy(&iter->iter);
+	strbuf_release(&iter->last_name);
+	free(iter);
+	return ITER_DONE;
+}
+
+static struct ref_iterator_vtable reftable_reflog_iterator_vtable = {
+	.advance = reftable_reflog_iterator_advance,
+	.peel = reftable_reflog_iterator_peel,
+	.abort = reftable_reflog_iterator_abort
+};
+
+static struct reftable_reflog_iterator *reflog_iterator_for_stack(struct reftable_ref_store *refs,
+								  struct reftable_stack *stack)
+{
+	struct reftable_merged_table *merged_table;
+	struct reftable_reflog_iterator *iter;
+	int ret;
+
+	iter = xcalloc(1, sizeof(*iter));
+	base_ref_iterator_init(&iter->base, &reftable_reflog_iterator_vtable);
+	strbuf_init(&iter->last_name, 0);
+	iter->refs = refs;
+
+	ret = refs->err;
+	if (ret)
+		goto done;
+
+	ret = reftable_stack_reload(stack);
+	if (ret < 0)
+		goto done;
+
+	merged_table = reftable_stack_merged_table(stack);
+
+	ret = reftable_merged_table_seek_log(merged_table, &iter->iter, "");
+	if (ret < 0)
+		goto done;
+
+done:
+	iter->err = ret;
+	return iter;
+}
+
+static struct ref_iterator *reftable_be_reflog_iterator_begin(struct ref_store *ref_store)
+{
+	struct reftable_ref_store *refs =
+		reftable_be_downcast(ref_store, REF_STORE_READ, "reflog_iterator_begin");
+	struct reftable_reflog_iterator *main_iter, *worktree_iter;
+
+	main_iter = reflog_iterator_for_stack(refs, refs->main_stack);
+	if (!refs->worktree_stack)
+		return &main_iter->base;
+
+	worktree_iter = reflog_iterator_for_stack(refs, refs->worktree_stack);
+
+	return merge_ref_iterator_begin(&worktree_iter->base, &main_iter->base,
+					ref_iterator_select, NULL);
+}
+
+static int yield_log_record(struct reftable_log_record *log,
+			    each_reflog_ent_fn fn,
+			    void *cb_data)
+{
+	struct object_id old_oid, new_oid;
+	const char *full_committer;
+
+	oidread(&old_oid, log->value.update.old_hash);
+	oidread(&new_oid, log->value.update.new_hash);
+
+	/*
+	 * When both the old object ID and the new object ID are null
+	 * then this is the reflog existence marker. The caller must
+	 * not be aware of it.
+	 */
+	if (is_null_oid(&old_oid) && is_null_oid(&new_oid))
+		return 0;
+
+	full_committer = fmt_ident(log->value.update.name, log->value.update.email,
+				   WANT_COMMITTER_IDENT, NULL, IDENT_NO_DATE);
+	return fn(&old_oid, &new_oid, full_committer,
+		  log->value.update.time, log->value.update.tz_offset,
+		  log->value.update.message, cb_data);
+}
+
+static int reftable_be_for_each_reflog_ent_reverse(struct ref_store *ref_store,
+						   const char *refname,
+						   each_reflog_ent_fn fn,
+						   void *cb_data)
+{
+	struct reftable_ref_store *refs =
+		reftable_be_downcast(ref_store, REF_STORE_READ, "for_each_reflog_ent_reverse");
+	struct reftable_stack *stack = stack_for(refs, refname, &refname);
+	struct reftable_merged_table *mt = NULL;
+	struct reftable_log_record log = {0};
+	struct reftable_iterator it = {0};
+	int ret;
+
+	if (refs->err < 0)
+		return refs->err;
+
+	mt = reftable_stack_merged_table(stack);
+	ret = reftable_merged_table_seek_log(mt, &it, refname);
+	while (!ret) {
+		ret = reftable_iterator_next_log(&it, &log);
+		if (ret < 0)
+			break;
+		if (ret > 0 || strcmp(log.refname, refname)) {
+			ret = 0;
+			break;
+		}
+
+		ret = yield_log_record(&log, fn, cb_data);
+		if (ret)
+			break;
+	}
+
+	reftable_log_record_release(&log);
+	reftable_iterator_destroy(&it);
+	return ret;
+}
+
+static int reftable_be_for_each_reflog_ent(struct ref_store *ref_store,
+					   const char *refname,
+					   each_reflog_ent_fn fn,
+					   void *cb_data)
+{
+	struct reftable_ref_store *refs =
+		reftable_be_downcast(ref_store, REF_STORE_READ, "for_each_reflog_ent");
+	struct reftable_stack *stack = stack_for(refs, refname, &refname);
+	struct reftable_merged_table *mt = NULL;
+	struct reftable_log_record *logs = NULL;
+	struct reftable_iterator it = {0};
+	size_t logs_alloc = 0, logs_nr = 0, i;
+	int ret;
+
+	if (refs->err < 0)
+		return refs->err;
+
+	mt = reftable_stack_merged_table(stack);
+	ret = reftable_merged_table_seek_log(mt, &it, refname);
+	while (!ret) {
+		struct reftable_log_record log = {0};
+
+		ret = reftable_iterator_next_log(&it, &log);
+		if (ret < 0)
+			goto done;
+		if (ret > 0 || strcmp(log.refname, refname)) {
+			reftable_log_record_release(&log);
+			ret = 0;
+			break;
+		}
+
+		ALLOC_GROW(logs, logs_nr + 1, logs_alloc);
+		logs[logs_nr++] = log;
+	}
+
+	for (i = logs_nr; i--;) {
+		ret = yield_log_record(&logs[i], fn, cb_data);
+		if (ret)
+			goto done;
+	}
+
+done:
+	reftable_iterator_destroy(&it);
+	for (i = 0; i < logs_nr; i++)
+		reftable_log_record_release(&logs[i]);
+	free(logs);
+	return ret;
+}
+
+static int reftable_be_reflog_exists(struct ref_store *ref_store,
+				     const char *refname)
+{
+	struct reftable_ref_store *refs =
+		reftable_be_downcast(ref_store, REF_STORE_READ, "reflog_exists");
+	struct reftable_stack *stack = stack_for(refs, refname, &refname);
+	struct reftable_merged_table *mt = reftable_stack_merged_table(stack);
+	struct reftable_log_record log = {0};
+	struct reftable_iterator it = {0};
+	int ret;
+
+	ret = refs->err;
+	if (ret < 0)
+		goto done;
+
+	ret = reftable_stack_reload(stack);
+	if (ret < 0)
+		goto done;
+
+	ret = reftable_merged_table_seek_log(mt, &it, refname);
+	if (ret < 0)
+		goto done;
+
+	/*
+	 * Check whether we get at least one log record for the given ref name.
+	 * If so, the reflog exists, otherwise it doesn't.
+	 */
+	ret = reftable_iterator_next_log(&it, &log);
+	if (ret < 0)
+		goto done;
+	if (ret > 0) {
+		ret = 0;
+		goto done;
+	}
+
+	ret = strcmp(log.refname, refname) == 0;
+
+done:
+	reftable_iterator_destroy(&it);
+	reftable_log_record_release(&log);
+	if (ret < 0)
+		ret = 0;
+	return ret;
+}
+
+struct write_reflog_existence_arg {
+	struct reftable_ref_store *refs;
+	const char *refname;
+	struct reftable_stack *stack;
+};
+
+static int write_reflog_existence_table(struct reftable_writer *writer,
+					void *cb_data)
+{
+	struct write_reflog_existence_arg *arg = cb_data;
+	uint64_t ts = reftable_stack_next_update_index(arg->stack);
+	struct reftable_log_record log = {0};
+	int ret;
+
+	ret = reftable_stack_read_log(arg->stack, arg->refname, &log);
+	if (ret <= 0)
+		goto done;
+
+	reftable_writer_set_limits(writer, ts, ts);
+
+	/*
+	 * The existence entry has both old and new object ID set to the the
+	 * null object ID. Our iterators are aware of this and will not present
+	 * them to their callers.
+	 */
+	log.refname = xstrdup(arg->refname);
+	log.update_index = ts;
+	log.value_type = REFTABLE_LOG_UPDATE;
+	ret = reftable_writer_add_log(writer, &log);
+
+done:
+	assert(ret != REFTABLE_API_ERROR);
+	reftable_log_record_release(&log);
+	return ret;
+}
+
+static int reftable_be_create_reflog(struct ref_store *ref_store,
+				     const char *refname,
+				     struct strbuf *errmsg)
+{
+	struct reftable_ref_store *refs =
+		reftable_be_downcast(ref_store, REF_STORE_WRITE, "create_reflog");
+	struct reftable_stack *stack = stack_for(refs, refname, &refname);
+	struct write_reflog_existence_arg arg = {
+		.refs = refs,
+		.stack = stack,
+		.refname = refname,
+	};
+	int ret;
+
+	ret = refs->err;
+	if (ret < 0)
+		goto done;
+
+	ret = reftable_stack_reload(stack);
+	if (ret)
+		goto done;
+
+	ret = reftable_stack_add(stack, &write_reflog_existence_table, &arg);
+
+done:
+	return ret;
+}
+
+struct write_reflog_delete_arg {
+	struct reftable_stack *stack;
+	const char *refname;
+};
+
+static int write_reflog_delete_table(struct reftable_writer *writer, void *cb_data)
+{
+	struct write_reflog_delete_arg *arg = cb_data;
+	struct reftable_merged_table *mt =
+		reftable_stack_merged_table(arg->stack);
+	struct reftable_log_record log = {0}, tombstone = {0};
+	struct reftable_iterator it = {0};
+	uint64_t ts = reftable_stack_next_update_index(arg->stack);
+	int ret;
+
+	reftable_writer_set_limits(writer, ts, ts);
+
+	/*
+	 * In order to delete a table we need to delete all reflog entries one
+	 * by one. This is inefficient, but the reftable format does not have a
+	 * better marker right now.
+	 */
+	ret = reftable_merged_table_seek_log(mt, &it, arg->refname);
+	while (ret == 0) {
+		ret = reftable_iterator_next_log(&it, &log);
+		if (ret < 0)
+			break;
+		if (ret > 0 || strcmp(log.refname, arg->refname)) {
+			ret = 0;
+			break;
+		}
+
+		tombstone.refname = (char *)arg->refname;
+		tombstone.value_type = REFTABLE_LOG_DELETION;
+		tombstone.update_index = log.update_index;
+
+		ret = reftable_writer_add_log(writer, &tombstone);
+	}
+
+	reftable_log_record_release(&log);
+	reftable_iterator_destroy(&it);
+	return ret;
+}
+
+static int reftable_be_delete_reflog(struct ref_store *ref_store,
+				     const char *refname)
+{
+	struct reftable_ref_store *refs =
+		reftable_be_downcast(ref_store, REF_STORE_WRITE, "delete_reflog");
+	struct reftable_stack *stack = stack_for(refs, refname, &refname);
+	struct write_reflog_delete_arg arg = {
+		.stack = stack,
+		.refname = refname,
+	};
+	int ret;
+
+	ret = reftable_stack_reload(stack);
+	if (ret)
+		return ret;
+	ret = reftable_stack_add(stack, &write_reflog_delete_table, &arg);
+
+	assert(ret != REFTABLE_API_ERROR);
+	return ret;
+}
+
+struct reflog_expiry_arg {
+	struct reftable_stack *stack;
+	struct reftable_log_record *records;
+	struct object_id update_oid;
+	const char *refname;
+	size_t len;
+};
+
+static int write_reflog_expiry_table(struct reftable_writer *writer, void *cb_data)
+{
+	struct reflog_expiry_arg *arg = cb_data;
+	uint64_t ts = reftable_stack_next_update_index(arg->stack);
+	uint64_t live_records = 0;
+	size_t i;
+	int ret;
+
+	for (i = 0; i < arg->len; i++)
+		if (arg->records[i].value_type == REFTABLE_LOG_UPDATE)
+			live_records++;
+
+	reftable_writer_set_limits(writer, ts, ts);
+
+	if (!is_null_oid(&arg->update_oid)) {
+		struct reftable_ref_record ref = {0};
+		struct object_id peeled;
+
+		ref.refname = (char *)arg->refname;
+		ref.update_index = ts;
+
+		if (!peel_object(&arg->update_oid, &peeled)) {
+			ref.value_type = REFTABLE_REF_VAL2;
+			memcpy(ref.value.val2.target_value, peeled.hash, GIT_MAX_RAWSZ);
+			memcpy(ref.value.val2.value, arg->update_oid.hash, GIT_MAX_RAWSZ);
+		} else {
+			ref.value_type = REFTABLE_REF_VAL1;
+			memcpy(ref.value.val1, arg->update_oid.hash, GIT_MAX_RAWSZ);
+		}
+
+		ret = reftable_writer_add_ref(writer, &ref);
+		if (ret < 0)
+			return ret;
+	}
+
+	/*
+	 * When there are no more entries left in the reflog we empty it
+	 * completely, but write a placeholder reflog entry that indicates that
+	 * the reflog still exists.
+	 */
+	if (!live_records) {
+		struct reftable_log_record log = {
+			.refname = (char *)arg->refname,
+			.value_type = REFTABLE_LOG_UPDATE,
+			.update_index = ts,
+		};
+
+		ret = reftable_writer_add_log(writer, &log);
+		if (ret)
+			return ret;
+	}
+
+	for (i = 0; i < arg->len; i++) {
+		ret = reftable_writer_add_log(writer, &arg->records[i]);
+		if (ret)
+			return ret;
+	}
+
+	return 0;
+}
+
+static int reftable_be_reflog_expire(struct ref_store *ref_store,
+				     const char *refname,
+				     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)
+{
+	/*
+	 * For log expiry, we write tombstones for every single reflog entry
+	 * that is to be expired. This means that the entries are still
+	 * retrievable by delving into the stack, and expiring entries
+	 * paradoxically takes extra memory. This memory is only reclaimed when
+	 * compacting the reftable stack.
+	 *
+	 * It would be better if the refs backend supported an API that sets a
+	 * criterion for all refs, passing the criterion to pack_refs().
+	 *
+	 * On the plus side, because we do the expiration per ref, we can easily
+	 * insert the reflog existence dummies.
+	 */
+	struct reftable_ref_store *refs =
+		reftable_be_downcast(ref_store, REF_STORE_WRITE, "reflog_expire");
+	struct reftable_stack *stack = stack_for(refs, refname, &refname);
+	struct reftable_merged_table *mt = reftable_stack_merged_table(stack);
+	struct reftable_log_record *logs = NULL;
+	struct reftable_log_record *rewritten = NULL;
+	struct reftable_ref_record ref_record = {0};
+	struct reftable_iterator it = {0};
+	struct reftable_addition *add = NULL;
+	struct reflog_expiry_arg arg = {0};
+	struct object_id oid = {0};
+	uint8_t *last_hash = NULL;
+	size_t logs_nr = 0, logs_alloc = 0, i;
+	int ret;
+
+	if (refs->err < 0)
+		return refs->err;
+
+	ret = reftable_stack_reload(stack);
+	if (ret < 0)
+		goto done;
+
+	ret = reftable_merged_table_seek_log(mt, &it, refname);
+	if (ret < 0)
+		goto done;
+
+	ret = reftable_stack_new_addition(&add, stack);
+	if (ret < 0)
+		goto done;
+
+	ret = reftable_stack_read_ref(stack, refname, &ref_record);
+	if (ret < 0)
+		goto done;
+	if (reftable_ref_record_val1(&ref_record))
+		oidread(&oid, reftable_ref_record_val1(&ref_record));
+	prepare_fn(refname, &oid, policy_cb_data);
+
+	while (1) {
+		struct reftable_log_record log = {0};
+		struct object_id old_oid, new_oid;
+
+		ret = reftable_iterator_next_log(&it, &log);
+		if (ret < 0)
+			goto done;
+		if (ret > 0 || strcmp(log.refname, refname)) {
+			reftable_log_record_release(&log);
+			break;
+		}
+
+		oidread(&old_oid, log.value.update.old_hash);
+		oidread(&new_oid, log.value.update.new_hash);
+
+		/*
+		 * Skip over the reflog existence marker. We will add it back
+		 * in when there are no live reflog records.
+		 */
+		if (is_null_oid(&old_oid) && is_null_oid(&new_oid)) {
+			reftable_log_record_release(&log);
+			continue;
+		}
+
+		ALLOC_GROW(logs, logs_nr + 1, logs_alloc);
+		logs[logs_nr++] = log;
+	}
+
+	/*
+	 * We need to rewrite all reflog entries according to the pruning
+	 * callback function:
+	 *
+	 *   - If a reflog entry shall be pruned we mark the record for
+	 *     deletion.
+	 *
+	 *   - Otherwise we may have to rewrite the chain of reflog entries so
+	 *     that gaps created by just-deleted records get backfilled.
+	 */
+	CALLOC_ARRAY(rewritten, logs_nr);
+	for (i = logs_nr; i--;) {
+		struct reftable_log_record *dest = &rewritten[i];
+		struct object_id old_oid, new_oid;
+
+		*dest = logs[i];
+		oidread(&old_oid, logs[i].value.update.old_hash);
+		oidread(&new_oid, logs[i].value.update.new_hash);
+
+		if (should_prune_fn(&old_oid, &new_oid, logs[i].value.update.email,
+				    (timestamp_t)logs[i].value.update.time,
+				    logs[i].value.update.tz_offset,
+				    logs[i].value.update.message,
+				    policy_cb_data)) {
+			dest->value_type = REFTABLE_LOG_DELETION;
+		} else {
+			if ((flags & EXPIRE_REFLOGS_REWRITE) && last_hash)
+				memcpy(dest->value.update.old_hash, last_hash, GIT_MAX_RAWSZ);
+			last_hash = logs[i].value.update.new_hash;
+		}
+	}
+
+	if (flags & EXPIRE_REFLOGS_UPDATE_REF && last_hash &&
+	    reftable_ref_record_val1(&ref_record))
+		oidread(&arg.update_oid, last_hash);
+
+	arg.records = rewritten;
+	arg.len = logs_nr;
+	arg.stack = stack,
+	arg.refname = refname,
+
+	ret = reftable_addition_add(add, &write_reflog_expiry_table, &arg);
+	if (ret < 0)
+		goto done;
+
+	/*
+	 * Future improvement: we could skip writing records that were
+	 * not changed.
+	 */
+	if (!(flags & EXPIRE_REFLOGS_DRY_RUN))
+		ret = reftable_addition_commit(add);
+
+done:
+	if (add)
+		cleanup_fn(policy_cb_data);
+	assert(ret != REFTABLE_API_ERROR);
+
+	reftable_ref_record_release(&ref_record);
+	reftable_iterator_destroy(&it);
+	reftable_addition_destroy(add);
+	for (i = 0; i < logs_nr; i++)
+		reftable_log_record_release(&logs[i]);
+	free(logs);
+	free(rewritten);
+	return ret;
+}
+
+struct ref_storage_be refs_be_reftable = {
+	.name = "reftable",
+	.init = reftable_be_init,
+	.init_db = reftable_be_init_db,
+	.transaction_prepare = reftable_be_transaction_prepare,
+	.transaction_finish = reftable_be_transaction_finish,
+	.transaction_abort = reftable_be_transaction_abort,
+	.initial_transaction_commit = reftable_be_initial_transaction_commit,
+
+	.pack_refs = reftable_be_pack_refs,
+	.create_symref = reftable_be_create_symref,
+	.rename_ref = reftable_be_rename_ref,
+	.copy_ref = reftable_be_copy_ref,
+
+	.iterator_begin = reftable_be_iterator_begin,
+	.read_raw_ref = reftable_be_read_raw_ref,
+	.read_symbolic_ref = reftable_be_read_symbolic_ref,
+
+	.reflog_iterator_begin = reftable_be_reflog_iterator_begin,
+	.for_each_reflog_ent = reftable_be_for_each_reflog_ent,
+	.for_each_reflog_ent_reverse = reftable_be_for_each_reflog_ent_reverse,
+	.reflog_exists = reftable_be_reflog_exists,
+	.create_reflog = reftable_be_create_reflog,
+	.delete_reflog = reftable_be_delete_reflog,
+	.reflog_expire = reftable_be_reflog_expire,
+};