[PATCH 5/5] Reftable support for git-core

["Han-Wen Nienhuys via GitGitGadget" <gitgitgadget@gmail.com>]

From: Han-Wen Nienhuys <hanwen@google.com>

$ ~/vc/git/git init
warning: templates not found in /usr/local/google/home/hanwen/share/git-core/templates
Initialized empty Git repository in /tmp/qz/.git/
$ echo q > a
$ ~/vc/git/git add a
$ ~/vc/git/git commit -mx
fatal: not a git repository (or any of the parent directories): .git
[master (root-commit) 373d969] x
 1 file changed, 1 insertion(+)
 create mode 100644 a
$ ~/vc/git/git show-ref
373d96972fca9b63595740bba3898a762778ba20 HEAD
373d96972fca9b63595740bba3898a762778ba20 refs/heads/master
$ ls -l .git/reftable/
total 12
-rw------- 1 hanwen primarygroup  126 Jan 23 20:08 000000000001-000000000001.ref
-rw------- 1 hanwen primarygroup 4277 Jan 23 20:08 000000000002-000000000002.ref
$ go run ~/vc/reftable/cmd/dump.go  -table /tmp/qz/.git/reftable/000000000002-000000000002.ref
** DEBUG **
name /tmp/qz/.git/reftable/000000000002-000000000002.ref, sz 4209: 'r' reftable.readerOffsets{Present:true, Offset:0x0, IndexOffset:0x0}, 'o' reftable.readerOffsets{Present:false, Offset:0x0, IndexOffset:0x0} 'g' reftable.readerOffsets{Present:true, Offset:0x1000, IndexOffset:0x0}
** REFS **
reftable.RefRecord{RefName:"refs/heads/master", UpdateIndex:0x2, Value:[]uint8{0x37, 0x3d, 0x96, 0x97, 0x2f, 0xca, 0x9b, 0x63, 0x59, 0x57, 0x40, 0xbb, 0xa3, 0x89, 0x8a, 0x76, 0x27, 0x78, 0xba, 0x20}, TargetValue:[]uint8(nil), Target:""}
** LOGS **
reftable.LogRecord{RefName:"HEAD", UpdateIndex:0x2, New:[]uint8{0x37, 0x3d, 0x96, 0x97, 0x2f, 0xca, 0x9b, 0x63, 0x59, 0x57, 0x40, 0xbb, 0xa3, 0x89, 0x8a, 0x76, 0x27, 0x78, 0xba, 0x20}, Old:[]uint8{0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0}, Name:"Han-Wen Nienhuys", Email:"hanwen@google.com", Time:0x5e29ef27, TZOffset:100, Message:"commit (initial): x\n"}

TODO:
 * resolve the design problem with reflog expiry.

Change-Id: I225ee6317b7911edf9aa95f43299f6c7c4511914
Signed-off-by: Han-Wen Nienhuys <hanwen@google.com>
---
 Makefile                |  23 +-
 refs.c                  |  18 +-
 refs.h                  |   2 +
 refs/refs-internal.h    |   1 +
 refs/reftable-backend.c | 780 ++++++++++++++++++++++++++++++++++++++++
 5 files changed, 820 insertions(+), 4 deletions(-)
 create mode 100644 refs/reftable-backend.c

diff --git a/Makefile b/Makefile
index 09f98b777c..4f0bcbfbcb 100644
--- a/Makefile
+++ b/Makefile
@@ -813,6 +813,7 @@ TEST_SHELL_PATH = $(SHELL_PATH)
 LIB_FILE = libgit.a
 XDIFF_LIB = xdiff/lib.a
 VCSSVN_LIB = vcs-svn/lib.a
+REFTABLE_LIB = reftable/libreftable.a
 
 GENERATED_H += command-list.h
 
@@ -958,6 +959,7 @@ LIB_OBJS += rebase-interactive.o
 LIB_OBJS += reflog-walk.o
 LIB_OBJS += refs.o
 LIB_OBJS += refs/files-backend.o
+LIB_OBJS += refs/reftable-backend.o
 LIB_OBJS += refs/iterator.o
 LIB_OBJS += refs/packed-backend.o
 LIB_OBJS += refs/ref-cache.o
@@ -1162,7 +1164,7 @@ THIRD_PARTY_SOURCES += compat/regex/%
 THIRD_PARTY_SOURCES += sha1collisiondetection/%
 THIRD_PARTY_SOURCES += sha1dc/%
 
-GITLIBS = common-main.o $(LIB_FILE) $(XDIFF_LIB)
+GITLIBS = common-main.o $(LIB_FILE) $(XDIFF_LIB) $(REFTABLE_LIB)
 EXTLIBS =
 
 GIT_USER_AGENT = git/$(GIT_VERSION)
@@ -2343,11 +2345,27 @@ VCSSVN_OBJS += vcs-svn/fast_export.o
 VCSSVN_OBJS += vcs-svn/svndiff.o
 VCSSVN_OBJS += vcs-svn/svndump.o
 
+REFTABLE_OBJS += reftable/basics.o
+REFTABLE_OBJS += reftable/block.o
+REFTABLE_OBJS += reftable/bytes.o
+REFTABLE_OBJS += reftable/file.o
+REFTABLE_OBJS += reftable/iter.o
+REFTABLE_OBJS += reftable/merged.o
+REFTABLE_OBJS += reftable/pq.o
+REFTABLE_OBJS += reftable/reader.o
+REFTABLE_OBJS += reftable/record.o
+REFTABLE_OBJS += reftable/slice.o
+REFTABLE_OBJS += reftable/stack.o
+REFTABLE_OBJS += reftable/tree.o
+REFTABLE_OBJS += reftable/writer.o
+
+
 TEST_OBJS := $(patsubst %$X,%.o,$(TEST_PROGRAMS)) $(patsubst %,t/helper/%,$(TEST_BUILTINS_OBJS))
 OBJECTS := $(LIB_OBJS) $(BUILTIN_OBJS) $(PROGRAM_OBJS) $(TEST_OBJS) \
 	$(XDIFF_OBJS) \
 	$(VCSSVN_OBJS) \
 	$(FUZZ_OBJS) \
+	$(REFTABLE_OBJS) \
 	common-main.o \
 	git.o
 ifndef NO_CURL
@@ -2484,6 +2502,9 @@ $(XDIFF_LIB): $(XDIFF_OBJS)
 $(VCSSVN_LIB): $(VCSSVN_OBJS)
 	$(QUIET_AR)$(RM) $@ && $(AR) $(ARFLAGS) $@ $^
 
+$(REFTABLE_LIB): $(REFTABLE_OBJS)
+	$(QUIET_AR)$(RM) $@ && $(AR) $(ARFLAGS) $@ $^
+
 export DEFAULT_EDITOR DEFAULT_PAGER
 
 Documentation/GIT-EXCLUDED-PROGRAMS: FORCE
diff --git a/refs.c b/refs.c
index 1ab0bb54d3..b4764c9a68 100644
--- a/refs.c
+++ b/refs.c
@@ -20,7 +20,7 @@
 /*
  * List of all available backends
  */
-static struct ref_storage_be *refs_backends = &refs_be_files;
+static struct ref_storage_be *refs_backends = &refs_be_reftable;
 
 static struct ref_storage_be *find_ref_storage_backend(const char *name)
 {
@@ -1839,10 +1839,22 @@ static struct ref_store *lookup_ref_store_map(struct hashmap *map,
 static struct ref_store *ref_store_init(const char *gitdir,
 					unsigned int flags)
 {
-	const char *be_name = "files";
-	struct ref_storage_be *be = find_ref_storage_backend(be_name);
+	struct strbuf refs_path = STRBUF_INIT;
+
+        // XXX this should probably come from a git config setting and not
+        // default to reftable.
+	const char *be_name = "reftable";
+	struct ref_storage_be *be;
 	struct ref_store *refs;
 
+	strbuf_addstr(&refs_path, gitdir);
+	strbuf_addstr(&refs_path, "/refs");
+
+	if (!is_directory(refs_path.buf)) {
+		be_name = "reftable";
+	}
+	strbuf_release(&refs_path);
+	be = find_ref_storage_backend(be_name);
 	if (!be)
 		BUG("reference backend %s is unknown", be_name);
 
diff --git a/refs.h b/refs.h
index 545029c6d8..4eedee37c9 100644
--- a/refs.h
+++ b/refs.h
@@ -456,6 +456,8 @@ int refs_for_each_reflog_ent_reverse(struct ref_store *refs,
 				     const char *refname,
 				     each_reflog_ent_fn fn,
 				     void *cb_data);
+
+// XXX which ordering are these? Newest or oldest first?
 int for_each_reflog_ent(const char *refname, each_reflog_ent_fn fn, void *cb_data);
 int for_each_reflog_ent_reverse(const char *refname, each_reflog_ent_fn fn, void *cb_data);
 
diff --git a/refs/refs-internal.h b/refs/refs-internal.h
index fc18b12340..2744aa57f2 100644
--- a/refs/refs-internal.h
+++ b/refs/refs-internal.h
@@ -659,6 +659,7 @@ 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 0000000000..6fcb72dd95
--- /dev/null
+++ b/refs/reftable-backend.c
@@ -0,0 +1,780 @@
+#include "../cache.h"
+#include "../config.h"
+#include "../refs.h"
+#include "refs-internal.h"
+#include "../iterator.h"
+#include "../lockfile.h"
+#include "../chdir-notify.h"
+
+#include "../reftable/reftable.h"
+
+extern struct ref_storage_be refs_be_reftable;
+
+struct reftable_ref_store {
+	struct ref_store base;
+	unsigned int store_flags;
+
+	int err;
+	char *reftable_dir;
+	char *table_list_file;
+	struct stack *stack;
+};
+
+static void clear_log_record(struct log_record* log) {
+        log->old_hash = NULL;
+        log->new_hash = NULL;
+        log->message = NULL;
+        log->ref_name = NULL;
+        log_record_clear(log);
+}
+
+static void fill_log_record(struct log_record* log) {
+        const char* info = git_committer_info(0);
+        struct ident_split split = {};
+        int result = split_ident_line(&split, info, strlen(info));
+        int sign = 1;
+        assert(0==result);
+
+        log_record_clear(log);
+        log->name = xstrndup(split.name_begin, split.name_end - split.name_begin);
+        log->email = xstrndup(split.mail_begin, split.mail_end - split.mail_begin);
+        log->time = atol(split.date_begin);
+        if (*split.tz_begin == '-') {
+                sign = -1;
+                split.tz_begin ++;
+        }
+        if (*split.tz_begin == '+') {
+                sign = 1;
+                split.tz_begin ++;
+        }
+
+        log->tz_offset = sign * atoi(split.tz_begin);
+}
+
+static struct ref_store *reftable_ref_store_create(const char *path,
+                                                   unsigned int store_flags) {
+  	struct reftable_ref_store *refs = xcalloc(1, sizeof(*refs));
+	struct ref_store *ref_store = (struct ref_store *)refs;
+	struct write_options cfg = {
+		.block_size = 4096,
+	};
+	struct strbuf sb = STRBUF_INIT;
+
+	base_ref_store_init(ref_store, &refs_be_reftable);
+	refs->store_flags = store_flags;
+
+	strbuf_addf(&sb, "%s/refs", path);
+	refs->table_list_file = xstrdup(sb.buf);
+	strbuf_reset(&sb);
+	strbuf_addf(&sb, "%s/reftable", path);
+	refs->reftable_dir = xstrdup(sb.buf);
+	strbuf_release(&sb);
+
+	refs->err = new_stack(&refs->stack, refs->reftable_dir, refs->table_list_file, cfg);
+
+	return ref_store;
+}
+
+static int reftable_init_db(struct ref_store *ref_store, struct strbuf *err)
+{
+	struct reftable_ref_store *refs = (struct reftable_ref_store*) ref_store;
+	FILE *f = fopen(refs->table_list_file, "a");
+	if (f == NULL) {
+	  return -1;
+	}
+	fclose(f);
+
+	safe_create_dir(refs->reftable_dir, 1);
+	return 0;
+}
+
+
+struct reftable_iterator {
+	struct ref_iterator base;
+	struct iterator iter;
+	struct ref_record ref;
+	struct object_id oid;
+        struct ref_store *ref_store;
+	char *prefix;
+};
+
+static int reftable_ref_iterator_advance(struct ref_iterator *ref_iterator)
+{
+        while (1) {
+                struct reftable_iterator *ri = (struct reftable_iterator*) ref_iterator;
+                int err = iterator_next_ref(ri->iter, &ri->ref);
+                if (err > 0) {
+                        return ITER_DONE;
+                }
+                if (err < 0) {
+                        return ITER_ERROR;
+                }
+
+                ri->base.refname = ri->ref.ref_name;
+                if (ri->prefix != NULL && 0 != strncmp(ri->prefix, ri->ref.ref_name, strlen(ri->prefix))) {
+                        return ITER_DONE;
+                }
+
+                ri->base.flags = 0;
+                if (ri->ref.value != NULL) {
+                        memcpy(ri->oid.hash, ri->ref.value, GIT_SHA1_RAWSZ);
+                } else if (ri->ref.target != NULL) {
+                        int out_flags = 0;
+                        const char *resolved =
+                                refs_resolve_ref_unsafe(ri->ref_store, ri->ref.ref_name, RESOLVE_REF_READING,
+                                                        &ri->oid, &out_flags);
+                        ri->base.flags = out_flags;
+                        if (resolved == NULL && !(ri->base.flags & DO_FOR_EACH_INCLUDE_BROKEN)
+                            && (ri->base.flags & REF_ISBROKEN)) {
+                                continue;
+                        }
+                }
+                ri->base.oid  = &ri->oid;
+                return ITER_OK;
+        }
+}
+
+static int reftable_ref_iterator_peel(struct ref_iterator *ref_iterator,
+				      struct object_id *peeled)
+{
+	struct reftable_iterator *ri = (struct reftable_iterator*) ref_iterator;
+	if (ri->ref.target_value != NULL) {
+		memcpy(peeled->hash, ri->ref.target_value, GIT_SHA1_RAWSZ);
+		return 0;
+	}
+
+	return -1;
+}
+
+static int reftable_ref_iterator_abort(struct ref_iterator *ref_iterator)
+{
+	struct reftable_iterator *ri = (struct reftable_iterator*) ref_iterator;
+	ref_record_clear(&ri->ref);
+	iterator_destroy(&ri->iter);
+	return 0;
+}
+
+static struct ref_iterator_vtable reftable_ref_iterator_vtable = {
+	reftable_ref_iterator_advance,
+	reftable_ref_iterator_peel,
+	reftable_ref_iterator_abort
+};
+
+static struct ref_iterator *reftable_ref_iterator_begin(
+		struct ref_store *ref_store,
+		const char *prefix, unsigned int flags)
+{
+	struct reftable_ref_store *refs = (struct reftable_ref_store*) ref_store;
+	struct reftable_iterator *ri = xcalloc(1, sizeof(*ri));
+	struct merged_table *mt = NULL;
+	int err = 0;
+	if (refs->err) {
+		// XXX ?
+		return NULL;
+	}
+
+	mt = stack_merged_table(refs->stack);
+
+	// XXX something with flags?
+	err = merged_table_seek_ref(mt, &ri->iter, prefix);
+	// XXX what to do with err?
+	assert(err == 0);
+	base_ref_iterator_init(&ri->base, &reftable_ref_iterator_vtable, 1);
+	ri->base.oid = &ri->oid;
+        ri->ref_store = ref_store;
+	return &ri->base;
+}
+
+static int reftable_transaction_prepare(struct ref_store *ref_store,
+					struct ref_transaction *transaction,
+					struct strbuf *err)
+{
+	return 0;
+}
+
+static int reftable_transaction_abort(struct ref_store *ref_store,
+				    struct ref_transaction *transaction,
+				    struct strbuf *err)
+{
+	struct reftable_ref_store *refs = (struct reftable_ref_store*) ref_store;
+	(void)refs;
+	return 0;
+}
+
+
+static int ref_update_cmp(const void *a, const void *b) {
+	return strcmp(((struct ref_update*)a)->refname, ((struct ref_update*)b)->refname);
+}
+
+static int reftable_check_old_oid(struct ref_store *refs, const char *refname, struct object_id *want_oid) {
+        struct object_id out_oid = {};
+        int out_flags = 0;
+        const char *resolved =
+                refs_resolve_ref_unsafe(refs, refname, RESOLVE_REF_READING,
+                                        &out_oid, &out_flags);
+        if (is_null_oid(want_oid) != (resolved == NULL)) {
+                return LOCK_ERROR;
+        }
+
+        if (resolved != NULL && !oideq(&out_oid, want_oid)) {
+                return LOCK_ERROR;
+        }
+
+        return 0;
+}
+
+static int write_transaction_table(struct writer *writer, void *arg) {
+	struct ref_transaction *transaction = (struct ref_transaction *)arg;
+	struct reftable_ref_store *refs
+		= (struct reftable_ref_store*)transaction->ref_store;
+	uint64_t ts = stack_next_update_index(refs->stack);
+	int err = 0;
+	// XXX - are we allowed to mutate the input data?
+	qsort(transaction->updates, transaction->nr, sizeof(struct ref_update*),
+	      ref_update_cmp);
+	writer_set_limits(writer, ts, ts);
+
+	for (int i = 0; i <  transaction->nr; i++) {
+		struct ref_update * u = transaction->updates[i];
+		if (u->flags & REF_HAVE_OLD) {
+			err = reftable_check_old_oid(transaction->ref_store, u->refname, &u->old_oid);
+			if (err < 0) {
+				goto exit;
+			}
+		}
+	}
+
+	for (int i = 0; i <  transaction->nr; i++) {
+		struct ref_update * u = transaction->updates[i];
+		if (u->flags & REF_HAVE_NEW) {
+                        struct object_id out_oid = {};
+                        int out_flags = 0;
+                        // XXX who owns the memory here?
+                        const char *resolved
+                                = refs_resolve_ref_unsafe(transaction->ref_store, u->refname, 0, &out_oid, &out_flags);
+                        struct ref_record ref = {};
+                        ref.ref_name = (char*)(resolved ? resolved : u->refname);
+                        ref.value = u->new_oid.hash;
+                        ref.update_index = ts;
+                        err = writer_add_ref(writer, &ref);
+                        if (err < 0) {
+                                goto exit;
+                        }
+		}
+	}
+
+
+	for (int i = 0; i <  transaction->nr; i++) {
+		struct ref_update * u = transaction->updates[i];
+                struct log_record log = {};
+                fill_log_record(&log);
+
+                log.ref_name = (char*)u->refname;
+                log.old_hash = u->old_oid.hash;
+                log.new_hash = u->new_oid.hash;
+                log.update_index = ts;
+                log.message = u->msg;
+
+                err = writer_add_log(writer, &log);
+                clear_log_record(&log);
+                if (err < 0) { return err; }
+        }
+exit:
+	return err;
+}
+
+static int reftable_transaction_commit(struct ref_store *ref_store,
+				       struct ref_transaction *transaction,
+				       struct strbuf *errmsg)
+{
+	struct reftable_ref_store *refs = (struct reftable_ref_store*) ref_store;
+	int err = stack_add(refs->stack,
+		  &write_transaction_table,
+		  transaction);
+	if (err < 0) {
+		strbuf_addf(errmsg, "reftable: transaction failure %s", error_str(err));
+		return -1;
+ 	}
+
+	return 0;
+}
+
+
+static int reftable_transaction_finish(struct ref_store *ref_store,
+				     struct ref_transaction *transaction,
+				     struct strbuf *err)
+{
+        return reftable_transaction_commit(ref_store, transaction, err);
+}
+
+
+
+struct write_delete_refs_arg {
+	struct stack *stack;
+	struct string_list *refnames;
+	const char *logmsg;
+        unsigned int flags;
+};
+
+static int write_delete_refs_table(struct writer *writer, void *argv) {
+	struct write_delete_refs_arg *arg = (struct write_delete_refs_arg*)argv;
+	uint64_t ts = stack_next_update_index(arg->stack);
+	int err = 0;
+
+        writer_set_limits(writer, ts, ts);
+        for (int i = 0; i < arg->refnames->nr; i++) {
+                struct ref_record ref = {
+                        .ref_name = (char*) arg->refnames->items[i].string,
+                        .update_index = ts,
+                };
+                err = writer_add_ref(writer, &ref);
+                if (err < 0) {
+                        return err;
+                }
+        }
+
+        for (int i = 0; i < arg->refnames->nr; i++) {
+                struct log_record log = {};
+                fill_log_record(&log);
+                log.message = xstrdup(arg->logmsg);
+                log.new_hash = NULL;
+
+                // XXX should lookup old oid.
+                log.old_hash = NULL;
+                log.update_index = ts;
+                log.ref_name = (char*) arg->refnames->items[i].string;
+
+                err = writer_add_log(writer, &log);
+                clear_log_record(&log);
+                if (err < 0) {
+                        return err;
+                }
+        }
+	return 0;
+}
+
+static int reftable_delete_refs(struct ref_store *ref_store, const char *msg,
+                                struct string_list *refnames, unsigned int flags)
+{
+	struct reftable_ref_store *refs = (struct reftable_ref_store*)ref_store;
+	struct write_delete_refs_arg arg = {
+		.stack = refs->stack,
+		.refnames = refnames,
+		.logmsg = msg,
+                .flags = flags,
+	};
+	return stack_add(refs->stack, &write_delete_refs_table, &arg);
+}
+
+static int reftable_pack_refs(struct ref_store *ref_store, unsigned int flags)
+{
+	struct reftable_ref_store *refs = (struct reftable_ref_store*)ref_store;
+        // XXX reflog expiry.
+	return stack_compact_all(refs->stack, NULL);
+}
+
+struct write_create_symref_arg {
+	struct stack *stack;
+	const char *refname;
+	const char *target;
+	const char *logmsg;
+};
+
+static int write_create_symref_table(struct writer *writer, void *arg) {
+	struct write_create_symref_arg *create = (struct write_create_symref_arg*)arg;
+	uint64_t ts = stack_next_update_index(create->stack);
+	int err = 0;
+
+	struct ref_record ref = {
+		.ref_name = (char*) create->refname,
+		.target = (char*) create->target,
+		.update_index = ts,
+	};
+	writer_set_limits(writer, ts, ts);
+	err = writer_add_ref(writer, &ref);
+	if (err < 0) {
+		return err;
+	}
+
+	// XXX reflog?
+
+	return 0;
+}
+
+static int reftable_create_symref(struct ref_store *ref_store,
+				  const char *refname, const char *target,
+				  const char *logmsg)
+{
+	struct reftable_ref_store *refs = (struct reftable_ref_store*)ref_store;
+	struct write_create_symref_arg arg = {
+		.stack = refs->stack,
+		.refname = refname,
+		.target = target,
+		.logmsg = logmsg
+	};
+	return stack_add(refs->stack, &write_create_symref_table, &arg);
+}
+
+
+struct write_rename_arg {
+	struct stack *stack;
+	const char *oldname;
+	const char *newname;
+	const char *logmsg;
+};
+
+static int write_rename_table(struct writer *writer, void *argv) {
+	struct write_rename_arg *arg = (struct write_rename_arg*)argv;
+	uint64_t ts = stack_next_update_index(arg->stack);
+	struct ref_record ref = {};
+	int err = stack_read_ref(arg->stack, arg->oldname, &ref);
+	if (err) {
+		goto exit;
+	}
+
+	// XXX should check that dest doesn't exist?
+	free(ref.ref_name);
+	ref.ref_name = strdup(arg->newname);
+	writer_set_limits(writer, ts, ts);
+	ref.update_index = ts;
+
+	{
+		struct ref_record todo[2]  = {};
+		todo[0].ref_name =  (char *) arg->oldname;
+		todo[0].update_index = ts;
+		todo[1] = ref;
+		todo[1].update_index = ts;
+
+		err = writer_add_refs(writer, todo, 2);
+		if (err < 0) {
+			goto exit;
+		}
+	}
+
+        if (ref.value != NULL) {
+                struct log_record todo[2] = {};
+                fill_log_record(&todo[0]);
+                fill_log_record(&todo[1]);
+
+                todo[0].ref_name = (char *) arg->oldname;
+                todo[0].update_index = ts;
+                todo[0].message = (char*)arg->logmsg;
+                todo[0].old_hash = ref.value;
+                todo[0].new_hash = NULL;
+
+                todo[1].ref_name = (char *) arg->newname;
+                todo[1].update_index = ts;
+                todo[1].old_hash = NULL;
+                todo[1].new_hash = ref.value;
+                todo[1].message = (char*) arg->logmsg;
+
+		err = writer_add_logs(writer, todo, 2);
+
+                clear_log_record(&todo[0]);
+                clear_log_record(&todo[1]);
+
+		if (err < 0) {
+			goto exit;
+		}
+
+        } else {
+                // symrefs?
+        }
+
+exit:
+	ref_record_clear(&ref);
+	return err;
+}
+
+
+static int reftable_rename_ref(struct ref_store *ref_store,
+			    const char *oldrefname, const char *newrefname,
+			    const char *logmsg)
+{
+	struct reftable_ref_store *refs = (struct reftable_ref_store*) ref_store;
+	struct write_rename_arg arg = {
+		.stack = refs->stack,
+		.oldname = oldrefname,
+		.newname = newrefname,
+		.logmsg = logmsg,
+	};
+	return stack_add(refs->stack, &write_rename_table, &arg);
+}
+
+static int reftable_copy_ref(struct ref_store *ref_store,
+			   const char *oldrefname, const char *newrefname,
+			   const char *logmsg)
+{
+	BUG("reftable reference store does not support copying references");
+}
+
+struct reftable_reflog_ref_iterator {
+        struct ref_iterator base;
+        struct iterator iter;
+        struct log_record log;
+        struct object_id oid;
+        char *last_name;
+};
+
+static int reftable_reflog_ref_iterator_advance(struct ref_iterator *ref_iterator)
+{
+        struct reftable_reflog_ref_iterator *ri = (struct reftable_reflog_ref_iterator*) ref_iterator;
+
+        while (1) {
+                int err = iterator_next_log(ri->iter, &ri->log);
+                if (err > 0) {
+                        return ITER_DONE;
+                }
+                if (err < 0) {
+                        return ITER_ERROR;
+                }
+
+                ri->base.refname = ri->log.ref_name;
+                if (ri->last_name != NULL && 0 == strcmp(ri->log.ref_name, ri->last_name)) {
+                        continue;
+                }
+
+                free(ri->last_name);
+                ri->last_name = xstrdup(ri->log.ref_name);
+                // XXX const?
+                memcpy(&ri->oid.hash, ri->log.new_hash, GIT_SHA1_RAWSZ);
+                return ITER_OK;
+        }
+}
+
+static int reftable_reflog_ref_iterator_peel(struct ref_iterator *ref_iterator,
+                                             struct object_id *peeled)
+{
+        BUG("not supported.");
+	return -1;
+}
+
+static int reftable_reflog_ref_iterator_abort(struct ref_iterator *ref_iterator)
+{
+	struct reftable_reflog_ref_iterator *ri = (struct reftable_reflog_ref_iterator*) ref_iterator;
+	log_record_clear(&ri->log);
+	iterator_destroy(&ri->iter);
+	return 0;
+}
+
+static struct ref_iterator_vtable reftable_reflog_ref_iterator_vtable = {
+	reftable_reflog_ref_iterator_advance,
+	reftable_reflog_ref_iterator_peel,
+	reftable_reflog_ref_iterator_abort
+};
+
+static struct ref_iterator *reftable_reflog_iterator_begin(struct ref_store *ref_store)
+{
+        struct reftable_reflog_ref_iterator *ri = xcalloc(sizeof(*ri), 1);
+        struct reftable_ref_store *refs = (struct reftable_ref_store*) ref_store;
+
+	struct merged_table *mt = stack_merged_table(refs->stack);
+        int err = merged_table_seek_log(mt, &ri->iter, "");
+        if (err < 0) {
+                free(ri);
+                return NULL;
+        }
+
+	base_ref_iterator_init(&ri->base, &reftable_reflog_ref_iterator_vtable, 1);
+	ri->base.oid = &ri->oid;
+
+	return empty_ref_iterator_begin();
+}
+
+static int reftable_for_each_reflog_ent_newest_first(struct ref_store *ref_store,
+                                        const char *refname,
+                                        each_reflog_ent_fn fn, void *cb_data)
+{
+        struct iterator it = { };
+        struct reftable_ref_store *refs = (struct reftable_ref_store*) ref_store;
+        struct merged_table *mt = stack_merged_table(refs->stack);
+        int err = merged_table_seek_log(mt, &it, refname);
+        struct log_record log = {};
+
+        while (err == 0)  {
+                err = iterator_next_log(it, &log);
+                if (err != 0) {
+                        break;
+                }
+
+                if (0 != strcmp(log.ref_name, refname)) {
+                        break;
+                }
+
+                {
+                        struct object_id old_oid = {};
+                        struct object_id new_oid = {};
+
+                        memcpy(&old_oid.hash, log.old_hash, GIT_SHA1_RAWSZ);
+                        memcpy(&new_oid.hash, log.new_hash, GIT_SHA1_RAWSZ);
+
+                        // XXX committer = email? name?
+                        if (fn(&old_oid, &new_oid, log.name, log.time, log.tz_offset, log.message, cb_data)) {
+                                err = -1;
+                                break;
+                        }
+                }
+        }
+
+        log_record_clear(&log);
+        iterator_destroy(&it);
+        if (err > 0) {
+                err = 0;
+        }
+	return err;
+}
+
+static int reftable_for_each_reflog_ent_oldest_first(struct ref_store *ref_store,
+                                                     const char *refname,
+                                                     each_reflog_ent_fn fn,
+                                                     void *cb_data)
+{
+        struct iterator it = { };
+        struct reftable_ref_store *refs = (struct reftable_ref_store*) ref_store;
+        struct merged_table *mt = stack_merged_table(refs->stack);
+        int err = merged_table_seek_log(mt, &it, refname);
+
+        struct log_record *logs = NULL;
+        int cap = 0;
+        int len = 0;
+
+        printf("oldest first\n");
+        while (err == 0)  {
+                struct log_record log = {};
+                err = iterator_next_log(it, &log);
+                if (err != 0) {
+                        break;
+                }
+
+                if (0 != strcmp(log.ref_name, refname)) {
+                        break;
+                }
+
+                if (len == cap) {
+                        cap  =2*cap + 1;
+                        logs = realloc(logs, cap * sizeof(*logs));
+                }
+
+                logs[len++] = log;
+        }
+
+        for (int i = len; i--; ) {
+                struct log_record *log = &logs[i];
+                struct object_id old_oid = {};
+                struct object_id new_oid = {};
+
+                memcpy(&old_oid.hash, log->old_hash, GIT_SHA1_RAWSZ);
+                memcpy(&new_oid.hash, log->new_hash, GIT_SHA1_RAWSZ);
+
+                // XXX committer = email? name?
+                if (!fn(&old_oid, &new_oid, log->name, log->time, log->tz_offset, log->message, cb_data)) {
+                        err = -1;
+                        break;
+                }
+        }
+
+        for (int i = 0; i < len; i++) {
+                log_record_clear(&logs[i]);
+        }
+        free(logs);
+
+        iterator_destroy(&it);
+        if (err > 0) {
+                err = 0;
+        }
+	return err;
+}
+
+static int reftable_reflog_exists(struct ref_store *ref_store,
+                                  const char *refname)
+{
+        // always exists.
+	return 1;
+}
+
+static int reftable_create_reflog(struct ref_store *ref_store,
+                                  const char *refname, int force_create,
+                                  struct strbuf *err)
+{
+        return 0;
+}
+
+static int reftable_delete_reflog(struct ref_store *ref_store,
+                                  const char *refname)
+{
+	return 0;
+}
+
+static int reftable_reflog_expire(struct ref_store *ref_store,
+				const char *refname, const struct object_id *oid,
+				unsigned int flags,
+				reflog_expiry_prepare_fn prepare_fn,
+				reflog_expiry_should_prune_fn should_prune_fn,
+				reflog_expiry_cleanup_fn cleanup_fn,
+				void *policy_cb_data)
+{
+        /*
+          XXX
+
+          This doesn't fit with the reftable API. If we are expiring for space
+          reasons, the expiry should be combined with a compaction, and there
+          should be a policy that can be called for all refnames, not for a
+          single ref name.
+
+          If this is for cleaning up individual entries, we'll have to write
+          extra data to create tombstones.
+         */
+	return 0;
+}
+
+
+static int reftable_read_raw_ref(struct ref_store *ref_store,
+				 const char *refname, struct object_id *oid,
+				 struct strbuf *referent, unsigned int *type)
+{
+	struct reftable_ref_store *refs = (struct reftable_ref_store*) ref_store;
+	struct ref_record ref = {};
+	int err = stack_read_ref(refs->stack, refname, &ref);
+	if (err) {
+		goto exit;
+	}
+	if (ref.target != NULL) {
+		strbuf_reset(referent);
+		strbuf_addstr(referent, ref.target);
+		*type |= REF_ISSYMREF;
+ 	} else  {
+		memcpy(oid->hash, ref.value, GIT_SHA1_RAWSZ);
+	}
+
+exit:
+	ref_record_clear(&ref);
+	return err;
+}
+
+struct ref_storage_be refs_be_reftable = {
+	&refs_be_files,
+	"reftable",
+	reftable_ref_store_create,
+	reftable_init_db,
+	reftable_transaction_prepare,
+	reftable_transaction_finish,
+	reftable_transaction_abort,
+	reftable_transaction_commit,
+
+	reftable_pack_refs,
+	reftable_create_symref,
+	reftable_delete_refs,
+	reftable_rename_ref,
+	reftable_copy_ref,
+
+	reftable_ref_iterator_begin,
+	reftable_read_raw_ref,
+
+	reftable_reflog_iterator_begin,
+	reftable_for_each_reflog_ent_newest_first,
+	reftable_for_each_reflog_ent_oldest_first,
+	reftable_reflog_exists,
+	reftable_create_reflog,
+	reftable_delete_reflog,
+	reftable_reflog_expire
+};
-- 
gitgitgadget