1 files changed, 634 insertions, 300 deletions
diff --git a/reftable/stack.c b/reftable/stack.c
index 737591125e..531660a49f 100644
--- a/reftable/stack.c
+++ b/reftable/stack.c
@@ -8,17 +8,14 @@ https://developers.google.com/open-source/licenses/bsd
 
 #include "stack.h"
 
-#include "../write-or-die.h"
 #include "system.h"
 #include "constants.h"
 #include "merged.h"
 #include "reader.h"
 #include "reftable-error.h"
-#include "reftable-generic.h"
 #include "reftable-record.h"
 #include "reftable-merged.h"
 #include "writer.h"
-#include "tempfile.h"
 
 static int stack_try_add(struct reftable_stack *st,
 			 int (*write_table)(struct reftable_writer *wr,
@@ -32,58 +29,87 @@ static void reftable_addition_close(struct reftable_addition *add);
 static int reftable_stack_reload_maybe_reuse(struct reftable_stack *st,
 					     int reuse_open);
 
-static void stack_filename(struct strbuf *dest, struct reftable_stack *st,
-			   const char *name)
+static int stack_filename(struct reftable_buf *dest, struct reftable_stack *st,
+			  const char *name)
 {
-	strbuf_reset(dest);
-	strbuf_addstr(dest, st->reftable_dir);
-	strbuf_addstr(dest, "/");
-	strbuf_addstr(dest, name);
+	int err;
+	reftable_buf_reset(dest);
+	if ((err = reftable_buf_addstr(dest, st->reftable_dir)) < 0 ||
+	    (err = reftable_buf_addstr(dest, "/")) < 0 ||
+	    (err = reftable_buf_addstr(dest, name)) < 0)
+		return err;
+	return 0;
 }
 
-static ssize_t reftable_fd_write(void *arg, const void *data, size_t sz)
+static int stack_fsync(const struct reftable_write_options *opts, int fd)
 {
-	int *fdp = (int *)arg;
-	return write_in_full(*fdp, data, sz);
+	if (opts->fsync)
+		return opts->fsync(fd);
+	return fsync(fd);
 }
 
-static int reftable_fd_flush(void *arg)
+struct fd_writer {
+	const struct reftable_write_options *opts;
+	int fd;
+};
+
+static ssize_t fd_writer_write(void *arg, const void *data, size_t sz)
 {
-	int *fdp = (int *)arg;
+	struct fd_writer *writer = arg;
+	return write_in_full(writer->fd, data, sz);
+}
 
-	return fsync_component(FSYNC_COMPONENT_REFERENCE, *fdp);
+static int fd_writer_flush(void *arg)
+{
+	struct fd_writer *writer = arg;
+	return stack_fsync(writer->opts, writer->fd);
 }
 
 int reftable_new_stack(struct reftable_stack **dest, const char *dir,
 		       const struct reftable_write_options *_opts)
 {
-	struct reftable_stack *p = reftable_calloc(1, sizeof(*p));
-	struct strbuf list_file_name = STRBUF_INIT;
-	struct reftable_write_options opts = {0};
-	int err = 0;
+	struct reftable_buf list_file_name = REFTABLE_BUF_INIT;
+	struct reftable_write_options opts = { 0 };
+	struct reftable_stack *p;
+	int err;
+
+	p = reftable_calloc(1, sizeof(*p));
+	if (!p) {
+		err = REFTABLE_OUT_OF_MEMORY_ERROR;
+		goto out;
+	}
 
 	if (_opts)
 		opts = *_opts;
 	if (opts.hash_id == 0)
-		opts.hash_id = GIT_SHA1_FORMAT_ID;
+		opts.hash_id = REFTABLE_HASH_SHA1;
 
 	*dest = NULL;
 
-	strbuf_reset(&list_file_name);
-	strbuf_addstr(&list_file_name, dir);
-	strbuf_addstr(&list_file_name, "/tables.list");
+	reftable_buf_reset(&list_file_name);
+	if ((err = reftable_buf_addstr(&list_file_name, dir)) < 0 ||
+	    (err = reftable_buf_addstr(&list_file_name, "/tables.list")) < 0)
+		goto out;
 
-	p->list_file = strbuf_detach(&list_file_name, NULL);
+	p->list_file = reftable_buf_detach(&list_file_name);
 	p->list_fd = -1;
-	p->reftable_dir = xstrdup(dir);
 	p->opts = opts;
+	p->reftable_dir = reftable_strdup(dir);
+	if (!p->reftable_dir) {
+		err = REFTABLE_OUT_OF_MEMORY_ERROR;
+		goto out;
+	}
 
 	err = reftable_stack_reload_maybe_reuse(p, 1);
-	if (err < 0) {
+	if (err < 0)
+		goto out;
+
+	*dest = p;
+	err = 0;
+
+out:
+	if (err < 0)
 		reftable_stack_destroy(p);
-	} else {
-		*dest = p;
-	}
 	return err;
 }
 
@@ -103,13 +129,22 @@ static int fd_read_lines(int fd, char ***namesp)
 	}
 
 	REFTABLE_ALLOC_ARRAY(buf, size + 1);
+	if (!buf) {
+		err = REFTABLE_OUT_OF_MEMORY_ERROR;
+		goto done;
+	}
+
 	if (read_in_full(fd, buf, size) != size) {
 		err = REFTABLE_IO_ERROR;
 		goto done;
 	}
 	buf[size] = 0;
 
-	parse_names(buf, size, namesp);
+	*namesp = parse_names(buf, size);
+	if (!*namesp) {
+		err = REFTABLE_OUT_OF_MEMORY_ERROR;
+		goto done;
+	}
 
 done:
 	reftable_free(buf);
@@ -123,6 +158,8 @@ int read_lines(const char *filename, char ***namesp)
 	if (fd < 0) {
 		if (errno == ENOENT) {
 			REFTABLE_CALLOC_ARRAY(*namesp, 1);
+			if (!*namesp)
+				return REFTABLE_OUT_OF_MEMORY_ERROR;
 			return 0;
 		}
 
@@ -133,18 +170,18 @@ int read_lines(const char *filename, char ***namesp)
 	return err;
 }
 
-void reftable_stack_init_ref_iterator(struct reftable_stack *st,
+int reftable_stack_init_ref_iterator(struct reftable_stack *st,
 				      struct reftable_iterator *it)
 {
-	merged_table_init_iter(reftable_stack_merged_table(st),
-			       it, BLOCK_TYPE_REF);
+	return merged_table_init_iter(reftable_stack_merged_table(st),
+				      it, BLOCK_TYPE_REF);
 }
 
-void reftable_stack_init_log_iterator(struct reftable_stack *st,
-				      struct reftable_iterator *it)
+int reftable_stack_init_log_iterator(struct reftable_stack *st,
+				     struct reftable_iterator *it)
 {
-	merged_table_init_iter(reftable_stack_merged_table(st),
-			       it, BLOCK_TYPE_LOG);
+	return merged_table_init_iter(reftable_stack_merged_table(st),
+				      it, BLOCK_TYPE_LOG);
 }
 
 struct reftable_merged_table *
@@ -168,6 +205,10 @@ void reftable_stack_destroy(struct reftable_stack *st)
 {
 	char **names = NULL;
 	int err = 0;
+
+	if (!st)
+		return;
+
 	if (st->merged) {
 		reftable_merged_table_free(st->merged);
 		st->merged = NULL;
@@ -175,28 +216,31 @@ void reftable_stack_destroy(struct reftable_stack *st)
 
 	err = read_lines(st->list_file, &names);
 	if (err < 0) {
-		FREE_AND_NULL(names);
+		REFTABLE_FREE_AND_NULL(names);
 	}
 
 	if (st->readers) {
 		int i = 0;
-		struct strbuf filename = STRBUF_INIT;
+		struct reftable_buf filename = REFTABLE_BUF_INIT;
 		for (i = 0; i < st->readers_len; i++) {
 			const char *name = reader_name(st->readers[i]);
-			strbuf_reset(&filename);
+			int try_unlinking = 1;
+
+			reftable_buf_reset(&filename);
 			if (names && !has_name(names, name)) {
-				stack_filename(&filename, st, name);
+				if (stack_filename(&filename, st, name) < 0)
+					try_unlinking = 0;
 			}
-			reftable_reader_free(st->readers[i]);
+			reftable_reader_decref(st->readers[i]);
 
-			if (filename.len) {
+			if (try_unlinking && filename.len) {
 				/* On Windows, can only unlink after closing. */
 				unlink(filename.buf);
 			}
 		}
-		strbuf_release(&filename);
+		reftable_buf_release(&filename);
 		st->readers_len = 0;
-		FREE_AND_NULL(st->readers);
+		REFTABLE_FREE_AND_NULL(st->readers);
 	}
 
 	if (st->list_fd >= 0) {
@@ -204,20 +248,20 @@ void reftable_stack_destroy(struct reftable_stack *st)
 		st->list_fd = -1;
 	}
 
-	FREE_AND_NULL(st->list_file);
-	FREE_AND_NULL(st->reftable_dir);
+	REFTABLE_FREE_AND_NULL(st->list_file);
+	REFTABLE_FREE_AND_NULL(st->reftable_dir);
 	reftable_free(st);
 	free_names(names);
 }
 
 static struct reftable_reader **stack_copy_readers(struct reftable_stack *st,
-						   int cur_len)
+						   size_t cur_len)
 {
 	struct reftable_reader **cur = reftable_calloc(cur_len, sizeof(*cur));
-	int i = 0;
-	for (i = 0; i < cur_len; i++) {
+	if (!cur)
+		return NULL;
+	for (size_t i = 0; i < cur_len; i++)
 		cur[i] = st->readers[i];
-	}
 	return cur;
 }
 
@@ -225,19 +269,35 @@ static int reftable_stack_reload_once(struct reftable_stack *st,
 				      const char **names,
 				      int reuse_open)
 {
-	size_t cur_len = !st->merged ? 0 : st->merged->stack_len;
-	struct reftable_reader **cur = stack_copy_readers(st, cur_len);
-	size_t names_len = names_length(names);
-	struct reftable_reader **new_readers =
-		reftable_calloc(names_len, sizeof(*new_readers));
-	struct reftable_table *new_tables =
-		reftable_calloc(names_len, sizeof(*new_tables));
+	size_t cur_len = !st->merged ? 0 : st->merged->readers_len;
+	struct reftable_reader **cur = NULL;
+	struct reftable_reader **reused = NULL;
+	struct reftable_reader **new_readers = NULL;
+	size_t reused_len = 0, reused_alloc = 0, names_len;
 	size_t new_readers_len = 0;
 	struct reftable_merged_table *new_merged = NULL;
-	struct strbuf table_path = STRBUF_INIT;
+	struct reftable_buf table_path = REFTABLE_BUF_INIT;
 	int err = 0;
 	size_t i;
 
+	if (cur_len) {
+		cur = stack_copy_readers(st, cur_len);
+		if (!cur) {
+			err = REFTABLE_OUT_OF_MEMORY_ERROR;
+			goto done;
+		}
+	}
+
+	names_len = names_length(names);
+
+	if (names_len) {
+		new_readers = reftable_calloc(names_len, sizeof(*new_readers));
+		if (!new_readers) {
+			err = REFTABLE_OUT_OF_MEMORY_ERROR;
+			goto done;
+		}
+	}
+
 	while (*names) {
 		struct reftable_reader *rd = NULL;
 		const char *name = *names++;
@@ -248,70 +308,102 @@ static int reftable_stack_reload_once(struct reftable_stack *st,
 			if (cur[i] && 0 == strcmp(cur[i]->name, name)) {
 				rd = cur[i];
 				cur[i] = NULL;
+
+				/*
+				 * When reloading the stack fails, we end up
+				 * releasing all new readers. This also
+				 * includes the reused readers, even though
+				 * they are still in used by the old stack. We
+				 * thus need to keep them alive here, which we
+				 * do by bumping their refcount.
+				 */
+				REFTABLE_ALLOC_GROW_OR_NULL(reused,
+							    reused_len + 1,
+							    reused_alloc);
+				if (!reused) {
+					err = REFTABLE_OUT_OF_MEMORY_ERROR;
+					goto done;
+				}
+				reused[reused_len++] = rd;
+				reftable_reader_incref(rd);
 				break;
 			}
 		}
 
 		if (!rd) {
 			struct reftable_block_source src = { NULL };
-			stack_filename(&table_path, st, name);
+
+			err = stack_filename(&table_path, st, name);
+			if (err < 0)
+				goto done;
 
 			err = reftable_block_source_from_file(&src,
 							      table_path.buf);
 			if (err < 0)
 				goto done;
 
-			err = reftable_new_reader(&rd, &src, name);
+			err = reftable_reader_new(&rd, &src, name);
 			if (err < 0)
 				goto done;
 		}
 
 		new_readers[new_readers_len] = rd;
-		reftable_table_from_reader(&new_tables[new_readers_len], rd);
 		new_readers_len++;
 	}
 
 	/* success! */
-	err = reftable_new_merged_table(&new_merged, new_tables,
+	err = reftable_merged_table_new(&new_merged, new_readers,
 					new_readers_len, st->opts.hash_id);
 	if (err < 0)
 		goto done;
 
-	new_tables = NULL;
-	st->readers_len = new_readers_len;
-	if (st->merged)
-		reftable_merged_table_free(st->merged);
-	if (st->readers) {
-		reftable_free(st->readers);
-	}
-	st->readers = new_readers;
-	new_readers = NULL;
-	new_readers_len = 0;
-
-	new_merged->suppress_deletions = 1;
-	st->merged = new_merged;
+	/*
+	 * Close the old, non-reused readers and proactively try to unlink
+	 * them. This is done for systems like Windows, where the underlying
+	 * file of such an open reader wouldn't have been possible to be
+	 * unlinked by the compacting process.
+	 */
 	for (i = 0; i < cur_len; i++) {
 		if (cur[i]) {
 			const char *name = reader_name(cur[i]);
-			stack_filename(&table_path, st, name);
 
-			reader_close(cur[i]);
-			reftable_reader_free(cur[i]);
+			err = stack_filename(&table_path, st, name);
+			if (err < 0)
+				goto done;
 
-			/* On Windows, can only unlink after closing. */
+			reftable_reader_decref(cur[i]);
 			unlink(table_path.buf);
 		}
 	}
 
+	/* Update the stack to point to the new tables. */
+	if (st->merged)
+		reftable_merged_table_free(st->merged);
+	new_merged->suppress_deletions = 1;
+	st->merged = new_merged;
+
+	if (st->readers)
+		reftable_free(st->readers);
+	st->readers = new_readers;
+	st->readers_len = new_readers_len;
+	new_readers = NULL;
+	new_readers_len = 0;
+
+	/*
+	 * Decrement the refcount of reused readers again. This only needs to
+	 * happen on the successful case, because on the unsuccessful one we
+	 * decrement their refcount via `new_readers`.
+	 */
+	for (i = 0; i < reused_len; i++)
+		reftable_reader_decref(reused[i]);
+
 done:
-	for (i = 0; i < new_readers_len; i++) {
-		reader_close(new_readers[i]);
-		reftable_reader_free(new_readers[i]);
-	}
+	for (i = 0; i < new_readers_len; i++)
+		reftable_reader_decref(new_readers[i]);
 	reftable_free(new_readers);
-	reftable_free(new_tables);
+	reftable_free(reused);
 	reftable_free(cur);
-	strbuf_release(&table_path);
+	reftable_buf_release(&table_path);
 	return err;
 }
 
@@ -364,6 +456,10 @@ static int reftable_stack_reload_maybe_reuse(struct reftable_stack *st,
 			}
 
 			REFTABLE_CALLOC_ARRAY(names, 1);
+			if (!names) {
+				err = REFTABLE_OUT_OF_MEMORY_ERROR;
+				goto out;
+			}
 		} else {
 			err = fd_read_lines(fd, &names);
 			if (err < 0)
@@ -458,6 +554,10 @@ out:
 		close(fd);
 	free_names(names);
 	free_names(names_after);
+
+	if (st->opts.on_reload)
+		st->opts.on_reload(st->opts.on_reload_payload);
+
 	return err;
 }
 
@@ -520,7 +620,7 @@ static int stack_uptodate(struct reftable_stack *st)
 		}
 	}
 
-	if (names[st->merged->stack_len]) {
+	if (names[st->merged->readers_len]) {
 		err = 1;
 		goto done;
 	}
@@ -556,18 +656,18 @@ int reftable_stack_add(struct reftable_stack *st,
 	return 0;
 }
 
-static void format_name(struct strbuf *dest, uint64_t min, uint64_t max)
+static int format_name(struct reftable_buf *dest, uint64_t min, uint64_t max)
 {
 	char buf[100];
 	uint32_t rnd = (uint32_t)git_rand();
 	snprintf(buf, sizeof(buf), "0x%012" PRIx64 "-0x%012" PRIx64 "-%08x",
 		 min, max, rnd);
-	strbuf_reset(dest);
-	strbuf_addstr(dest, buf);
+	reftable_buf_reset(dest);
+	return reftable_buf_addstr(dest, buf);
 }
 
 struct reftable_addition {
-	struct tempfile *lock_file;
+	struct reftable_flock tables_list_lock;
 	struct reftable_stack *stack;
 
 	char **new_tables;
@@ -578,16 +678,17 @@ struct reftable_addition {
 #define REFTABLE_ADDITION_INIT {0}
 
 static int reftable_stack_init_addition(struct reftable_addition *add,
-					struct reftable_stack *st)
+					struct reftable_stack *st,
+					unsigned int flags)
 {
-	struct strbuf lock_file_name = STRBUF_INIT;
-	int err = 0;
-	add->stack = st;
+	struct reftable_buf lock_file_name = REFTABLE_BUF_INIT;
+	int err;
 
-	strbuf_addf(&lock_file_name, "%s.lock", st->list_file);
+	add->stack = st;
 
-	add->lock_file = create_tempfile(lock_file_name.buf);
-	if (!add->lock_file) {
+	err = flock_acquire(&add->tables_list_lock, st->list_file,
+			    st->opts.lock_timeout_ms);
+	if (err < 0) {
 		if (errno == EEXIST) {
 			err = REFTABLE_LOCK_ERROR;
 		} else {
@@ -596,7 +697,8 @@ static int reftable_stack_init_addition(struct reftable_addition *add,
 		goto done;
 	}
 	if (st->opts.default_permissions) {
-		if (chmod(add->lock_file->filename.buf, st->opts.default_permissions) < 0) {
+		if (chmod(add->tables_list_lock.path,
+			  st->opts.default_permissions) < 0) {
 			err = REFTABLE_IO_ERROR;
 			goto done;
 		}
@@ -605,6 +707,11 @@ static int reftable_stack_init_addition(struct reftable_addition *add,
 	err = stack_uptodate(st);
 	if (err < 0)
 		goto done;
+	if (err > 0 && flags & REFTABLE_STACK_NEW_ADDITION_RELOAD) {
+		err = reftable_stack_reload_maybe_reuse(add->stack, 1);
+		if (err)
+			goto done;
+	}
 	if (err > 0) {
 		err = REFTABLE_OUTDATED_ERROR;
 		goto done;
@@ -612,21 +719,20 @@ static int reftable_stack_init_addition(struct reftable_addition *add,
 
 	add->next_update_index = reftable_stack_next_update_index(st);
 done:
-	if (err) {
+	if (err)
 		reftable_addition_close(add);
-	}
-	strbuf_release(&lock_file_name);
+	reftable_buf_release(&lock_file_name);
 	return err;
 }
 
 static void reftable_addition_close(struct reftable_addition *add)
 {
-	struct strbuf nm = STRBUF_INIT;
+	struct reftable_buf nm = REFTABLE_BUF_INIT;
 	size_t i;
 
 	for (i = 0; i < add->new_tables_len; i++) {
-		stack_filename(&nm, add->stack, add->new_tables[i]);
-		unlink(nm.buf);
+		if (!stack_filename(&nm, add->stack, add->new_tables[i]))
+			unlink(nm.buf);
 		reftable_free(add->new_tables[i]);
 		add->new_tables[i] = NULL;
 	}
@@ -635,8 +741,8 @@ static void reftable_addition_close(struct reftable_addition *add)
 	add->new_tables_len = 0;
 	add->new_tables_cap = 0;
 
-	delete_tempfile(&add->lock_file);
-	strbuf_release(&nm);
+	flock_release(&add->tables_list_lock);
+	reftable_buf_release(&nm);
 }
 
 void reftable_addition_destroy(struct reftable_addition *add)
@@ -650,34 +756,38 @@ void reftable_addition_destroy(struct reftable_addition *add)
 
 int reftable_addition_commit(struct reftable_addition *add)
 {
-	struct strbuf table_list = STRBUF_INIT;
-	int lock_file_fd = get_tempfile_fd(add->lock_file);
+	struct reftable_buf table_list = REFTABLE_BUF_INIT;
 	int err = 0;
 	size_t i;
 
 	if (add->new_tables_len == 0)
 		goto done;
 
-	for (i = 0; i < add->stack->merged->stack_len; i++) {
-		strbuf_addstr(&table_list, add->stack->readers[i]->name);
-		strbuf_addstr(&table_list, "\n");
+	for (i = 0; i < add->stack->merged->readers_len; i++) {
+		if ((err = reftable_buf_addstr(&table_list, add->stack->readers[i]->name)) < 0 ||
+		    (err = reftable_buf_addstr(&table_list, "\n")) < 0)
+			goto done;
 	}
 	for (i = 0; i < add->new_tables_len; i++) {
-		strbuf_addstr(&table_list, add->new_tables[i]);
-		strbuf_addstr(&table_list, "\n");
+		if ((err = reftable_buf_addstr(&table_list, add->new_tables[i])) < 0 ||
+		    (err = reftable_buf_addstr(&table_list, "\n")) < 0)
+			goto done;
 	}
 
-	err = write_in_full(lock_file_fd, table_list.buf, table_list.len);
-	strbuf_release(&table_list);
+	err = write_in_full(add->tables_list_lock.fd, table_list.buf, table_list.len);
+	reftable_buf_release(&table_list);
 	if (err < 0) {
 		err = REFTABLE_IO_ERROR;
 		goto done;
 	}
 
-	fsync_component_or_die(FSYNC_COMPONENT_REFERENCE, lock_file_fd,
-			       get_tempfile_path(add->lock_file));
+	err = stack_fsync(&add->stack->opts, add->tables_list_lock.fd);
+	if (err < 0) {
+		err = REFTABLE_IO_ERROR;
+		goto done;
+	}
 
-	err = rename_tempfile(&add->lock_file, add->stack->list_file);
+	err = flock_commit(&add->tables_list_lock);
 	if (err < 0) {
 		err = REFTABLE_IO_ERROR;
 		goto done;
@@ -715,13 +825,18 @@ done:
 }
 
 int reftable_stack_new_addition(struct reftable_addition **dest,
-				struct reftable_stack *st)
+				struct reftable_stack *st,
+				unsigned int flags)
 {
 	int err = 0;
 	struct reftable_addition empty = REFTABLE_ADDITION_INIT;
+
 	REFTABLE_CALLOC_ARRAY(*dest, 1);
+	if (!*dest)
+		return REFTABLE_OUT_OF_MEMORY_ERROR;
+
 	**dest = empty;
-	err = reftable_stack_init_addition(*dest, st);
+	err = reftable_stack_init_addition(*dest, st, flags);
 	if (err) {
 		reftable_free(*dest);
 		*dest = NULL;
@@ -735,7 +850,7 @@ static int stack_try_add(struct reftable_stack *st,
 			 void *arg)
 {
 	struct reftable_addition add = REFTABLE_ADDITION_INIT;
-	int err = reftable_stack_init_addition(&add, st);
+	int err = reftable_stack_init_addition(&add, st, 0);
 	if (err < 0)
 		goto done;
 
@@ -754,36 +869,47 @@ int reftable_addition_add(struct reftable_addition *add,
 					     void *arg),
 			  void *arg)
 {
-	struct strbuf temp_tab_file_name = STRBUF_INIT;
-	struct strbuf tab_file_name = STRBUF_INIT;
-	struct strbuf next_name = STRBUF_INIT;
+	struct reftable_buf temp_tab_file_name = REFTABLE_BUF_INIT;
+	struct reftable_buf tab_file_name = REFTABLE_BUF_INIT;
+	struct reftable_buf next_name = REFTABLE_BUF_INIT;
 	struct reftable_writer *wr = NULL;
-	struct tempfile *tab_file = NULL;
+	struct reftable_tmpfile tab_file = REFTABLE_TMPFILE_INIT;
+	struct fd_writer writer = {
+		.opts = &add->stack->opts,
+	};
 	int err = 0;
-	int tab_fd;
 
-	strbuf_reset(&next_name);
-	format_name(&next_name, add->next_update_index, add->next_update_index);
+	reftable_buf_reset(&next_name);
 
-	stack_filename(&temp_tab_file_name, add->stack, next_name.buf);
-	strbuf_addstr(&temp_tab_file_name, ".temp.XXXXXX");
+	err = format_name(&next_name, add->next_update_index, add->next_update_index);
+	if (err < 0)
+		goto done;
 
-	tab_file = mks_tempfile(temp_tab_file_name.buf);
-	if (!tab_file) {
-		err = REFTABLE_IO_ERROR;
+	err = stack_filename(&temp_tab_file_name, add->stack, next_name.buf);
+	if (err < 0)
+		goto done;
+
+	err = reftable_buf_addstr(&temp_tab_file_name, ".temp.XXXXXX");
+	if (err < 0)
+		goto done;
+
+	err = tmpfile_from_pattern(&tab_file, temp_tab_file_name.buf);
+	if (err < 0)
 		goto done;
-	}
 	if (add->stack->opts.default_permissions) {
-		if (chmod(get_tempfile_path(tab_file),
+		if (chmod(tab_file.path,
 			  add->stack->opts.default_permissions)) {
 			err = REFTABLE_IO_ERROR;
 			goto done;
 		}
 	}
-	tab_fd = get_tempfile_fd(tab_file);
 
-	wr = reftable_new_writer(reftable_fd_write, reftable_fd_flush, &tab_fd,
-				 &add->stack->opts);
+	writer.fd = tab_file.fd;
+	err = reftable_writer_new(&wr, fd_writer_write, fd_writer_flush,
+				  &writer, &add->stack->opts);
+	if (err < 0)
+		goto done;
+
 	err = write_table(wr, arg);
 	if (err < 0)
 		goto done;
@@ -796,46 +922,55 @@ int reftable_addition_add(struct reftable_addition *add,
 	if (err < 0)
 		goto done;
 
-	err = close_tempfile_gently(tab_file);
-	if (err < 0) {
-		err = REFTABLE_IO_ERROR;
+	err = tmpfile_close(&tab_file);
+	if (err < 0)
 		goto done;
-	}
 
 	if (wr->min_update_index < add->next_update_index) {
 		err = REFTABLE_API_ERROR;
 		goto done;
 	}
 
-	format_name(&next_name, wr->min_update_index, wr->max_update_index);
-	strbuf_addstr(&next_name, ".ref");
-	stack_filename(&tab_file_name, add->stack, next_name.buf);
+	err = format_name(&next_name, wr->min_update_index, wr->max_update_index);
+	if (err < 0)
+		goto done;
+
+	err = reftable_buf_addstr(&next_name, ".ref");
+	if (err < 0)
+		goto done;
+
+	err = stack_filename(&tab_file_name, add->stack, next_name.buf);
+	if (err < 0)
+		goto done;
 
 	/*
 	  On windows, this relies on rand() picking a unique destination name.
 	  Maybe we should do retry loop as well?
 	 */
-	err = rename_tempfile(&tab_file, tab_file_name.buf);
-	if (err < 0) {
-		err = REFTABLE_IO_ERROR;
+	err = tmpfile_rename(&tab_file, tab_file_name.buf);
+	if (err < 0)
+		goto done;
+
+	REFTABLE_ALLOC_GROW_OR_NULL(add->new_tables, add->new_tables_len + 1,
+				    add->new_tables_cap);
+	if (!add->new_tables) {
+		err = REFTABLE_OUT_OF_MEMORY_ERROR;
 		goto done;
 	}
+	add->new_tables[add->new_tables_len++] = reftable_buf_detach(&next_name);
 
-	REFTABLE_ALLOC_GROW(add->new_tables, add->new_tables_len + 1,
-			    add->new_tables_cap);
-	add->new_tables[add->new_tables_len++] = strbuf_detach(&next_name, NULL);
 done:
-	delete_tempfile(&tab_file);
-	strbuf_release(&temp_tab_file_name);
-	strbuf_release(&tab_file_name);
-	strbuf_release(&next_name);
+	tmpfile_delete(&tab_file);
+	reftable_buf_release(&temp_tab_file_name);
+	reftable_buf_release(&tab_file_name);
+	reftable_buf_release(&next_name);
 	reftable_writer_free(wr);
 	return err;
 }
 
 uint64_t reftable_stack_next_update_index(struct reftable_stack *st)
 {
-	int sz = st->merged->stack_len;
+	int sz = st->merged->readers_len;
 	if (sz > 0)
 		return reftable_reader_max_update_index(st->readers[sz - 1]) +
 		       1;
@@ -845,35 +980,46 @@ uint64_t reftable_stack_next_update_index(struct reftable_stack *st)
 static int stack_compact_locked(struct reftable_stack *st,
 				size_t first, size_t last,
 				struct reftable_log_expiry_config *config,
-				struct tempfile **tab_file_out)
+				struct reftable_tmpfile *tab_file_out)
 {
-	struct strbuf next_name = STRBUF_INIT;
-	struct strbuf tab_file_path = STRBUF_INIT;
+	struct reftable_buf next_name = REFTABLE_BUF_INIT;
+	struct reftable_buf tab_file_path = REFTABLE_BUF_INIT;
 	struct reftable_writer *wr = NULL;
-	struct tempfile *tab_file;
-	int tab_fd, err = 0;
+	struct fd_writer writer=  {
+		.opts = &st->opts,
+	};
+	struct reftable_tmpfile tab_file = REFTABLE_TMPFILE_INIT;
+	int err = 0;
+
+	err = format_name(&next_name, reftable_reader_min_update_index(st->readers[first]),
+			  reftable_reader_max_update_index(st->readers[last]));
+	if (err < 0)
+		goto done;
 
-	format_name(&next_name,
-		    reftable_reader_min_update_index(st->readers[first]),
-		    reftable_reader_max_update_index(st->readers[last]));
-	stack_filename(&tab_file_path, st, next_name.buf);
-	strbuf_addstr(&tab_file_path, ".temp.XXXXXX");
+	err = stack_filename(&tab_file_path, st, next_name.buf);
+	if (err < 0)
+		goto done;
 
-	tab_file = mks_tempfile(tab_file_path.buf);
-	if (!tab_file) {
-		err = REFTABLE_IO_ERROR;
+	err = reftable_buf_addstr(&tab_file_path, ".temp.XXXXXX");
+	if (err < 0)
+		goto done;
+
+	err = tmpfile_from_pattern(&tab_file, tab_file_path.buf);
+	if (err < 0)
 		goto done;
-	}
-	tab_fd = get_tempfile_fd(tab_file);
 
 	if (st->opts.default_permissions &&
-	    chmod(get_tempfile_path(tab_file), st->opts.default_permissions) < 0) {
+	    chmod(tab_file.path, st->opts.default_permissions) < 0) {
 		err = REFTABLE_IO_ERROR;
 		goto done;
 	}
 
-	wr = reftable_new_writer(reftable_fd_write, reftable_fd_flush,
-				 &tab_fd, &st->opts);
+	writer.fd = tab_file.fd;
+	err = reftable_writer_new(&wr, fd_writer_write, fd_writer_flush,
+				  &writer, &st->opts);
+	if (err < 0)
+		goto done;
+
 	err = stack_write_compact(st, wr, first, last, config);
 	if (err < 0)
 		goto done;
@@ -882,18 +1028,18 @@ static int stack_compact_locked(struct reftable_stack *st,
 	if (err < 0)
 		goto done;
 
-	err = close_tempfile_gently(tab_file);
+	err = tmpfile_close(&tab_file);
 	if (err < 0)
 		goto done;
 
 	*tab_file_out = tab_file;
-	tab_file = NULL;
+	tab_file = REFTABLE_TMPFILE_INIT;
 
 done:
-	delete_tempfile(&tab_file);
+	tmpfile_delete(&tab_file);
 	reftable_writer_free(wr);
-	strbuf_release(&next_name);
-	strbuf_release(&tab_file_path);
+	reftable_buf_release(&next_name);
+	reftable_buf_release(&tab_file_path);
 	return err;
 }
 
@@ -902,32 +1048,28 @@ static int stack_write_compact(struct reftable_stack *st,
 			       size_t first, size_t last,
 			       struct reftable_log_expiry_config *config)
 {
-	size_t subtabs_len = last - first + 1;
-	struct reftable_table *subtabs = reftable_calloc(
-		last - first + 1, sizeof(*subtabs));
 	struct reftable_merged_table *mt = NULL;
 	struct reftable_iterator it = { NULL };
 	struct reftable_ref_record ref = { NULL };
 	struct reftable_log_record log = { NULL };
+	size_t subtabs_len = last - first + 1;
 	uint64_t entries = 0;
 	int err = 0;
 
-	for (size_t i = first, j = 0; i <= last; i++) {
-		struct reftable_reader *t = st->readers[i];
-		reftable_table_from_reader(&subtabs[j++], t);
-		st->stats.bytes += t->size;
-	}
+	for (size_t i = first; i <= last; i++)
+		st->stats.bytes += st->readers[i]->size;
 	reftable_writer_set_limits(wr, st->readers[first]->min_update_index,
 				   st->readers[last]->max_update_index);
 
-	err = reftable_new_merged_table(&mt, subtabs, subtabs_len,
+	err = reftable_merged_table_new(&mt, st->readers + first, subtabs_len,
 					st->opts.hash_id);
-	if (err < 0) {
-		reftable_free(subtabs);
+	if (err < 0)
+		goto done;
+
+	err = merged_table_init_iter(mt, &it, BLOCK_TYPE_REF);
+	if (err < 0)
 		goto done;
-	}
 
-	merged_table_init_iter(mt, &it, BLOCK_TYPE_REF);
 	err = reftable_iterator_seek_ref(&it, "");
 	if (err < 0)
 		goto done;
@@ -952,7 +1094,10 @@ static int stack_write_compact(struct reftable_stack *st,
 	}
 	reftable_iterator_destroy(&it);
 
-	merged_table_init_iter(mt, &it, BLOCK_TYPE_LOG);
+	err = merged_table_init_iter(mt, &it, BLOCK_TYPE_LOG);
+	if (err < 0)
+		goto done;
+
 	err = reftable_iterator_seek_log(&it, "");
 	if (err < 0)
 		goto done;
@@ -995,6 +1140,15 @@ done:
 	return err;
 }
 
+enum stack_compact_range_flags {
+	/*
+	 * Perform a best-effort compaction. That is, even if we cannot lock
+	 * all tables in the specified range, we will try to compact the
+	 * remaining slice.
+	 */
+	STACK_COMPACT_RANGE_BEST_EFFORT = (1 << 0),
+};
+
 /*
  * Compact all tables in the range `[first, last)` into a single new table.
  *
@@ -1006,17 +1160,20 @@ done:
  */
 static int stack_compact_range(struct reftable_stack *st,
 			       size_t first, size_t last,
-			       struct reftable_log_expiry_config *expiry)
+			       struct reftable_log_expiry_config *expiry,
+			       unsigned int flags)
 {
-	struct strbuf tables_list_buf = STRBUF_INIT;
-	struct strbuf new_table_name = STRBUF_INIT;
-	struct strbuf new_table_path = STRBUF_INIT;
-	struct strbuf table_name = STRBUF_INIT;
-	struct lock_file tables_list_lock = LOCK_INIT;
-	struct lock_file *table_locks = NULL;
-	struct tempfile *new_table = NULL;
+	struct reftable_buf tables_list_buf = REFTABLE_BUF_INIT;
+	struct reftable_buf new_table_name = REFTABLE_BUF_INIT;
+	struct reftable_buf new_table_path = REFTABLE_BUF_INIT;
+	struct reftable_buf table_name = REFTABLE_BUF_INIT;
+	struct reftable_flock tables_list_lock = REFTABLE_FLOCK_INIT;
+	struct reftable_flock *table_locks = NULL;
+	struct reftable_tmpfile new_table = REFTABLE_TMPFILE_INIT;
 	int is_empty_table = 0, err = 0;
-	size_t i;
+	size_t first_to_replace, last_to_replace;
+	size_t i, nlocks = 0;
+	char **names = NULL;
 
 	if (first > last || (!expiry && first == last)) {
 		err = 0;
@@ -1029,8 +1186,7 @@ static int stack_compact_range(struct reftable_stack *st,
 	 * Hold the lock so that we can read "tables.list" and lock all tables
 	 * which are part of the user-specified range.
 	 */
-	err = hold_lock_file_for_update(&tables_list_lock, st->list_file,
-					LOCK_NO_DEREF);
+	err = flock_acquire(&tables_list_lock, st->list_file, st->opts.lock_timeout_ms);
 	if (err < 0) {
 		if (errno == EEXIST)
 			err = REFTABLE_LOCK_ERROR;
@@ -1046,19 +1202,55 @@ static int stack_compact_range(struct reftable_stack *st,
 	/*
 	 * Lock all tables in the user-provided range. This is the slice of our
 	 * stack which we'll compact.
+	 *
+	 * Note that we lock tables in reverse order from last to first. The
+	 * intent behind this is to allow a newer process to perform best
+	 * effort compaction of tables that it has added in the case where an
+	 * older process is still busy compacting tables which are preexisting
+	 * from the point of view of the newer process.
 	 */
-	REFTABLE_CALLOC_ARRAY(table_locks, last - first + 1);
-	for (i = first; i <= last; i++) {
-		stack_filename(&table_name, st, reader_name(st->readers[i]));
+	REFTABLE_ALLOC_ARRAY(table_locks, last - first + 1);
+	if (!table_locks) {
+		err = REFTABLE_OUT_OF_MEMORY_ERROR;
+		goto done;
+	}
+	for (i = 0; i < last - first + 1; i++)
+		table_locks[i] = REFTABLE_FLOCK_INIT;
+
+	for (i = last + 1; i > first; i--) {
+		err = stack_filename(&table_name, st, reader_name(st->readers[i - 1]));
+		if (err < 0)
+			goto done;
 
-		err = hold_lock_file_for_update(&table_locks[i - first],
-						table_name.buf, LOCK_NO_DEREF);
+		err = flock_acquire(&table_locks[nlocks], table_name.buf, 0);
 		if (err < 0) {
-			if (errno == EEXIST)
+			/*
+			 * When the table is locked already we may do a
+			 * best-effort compaction and compact only the tables
+			 * that we have managed to lock so far. This of course
+			 * requires that we have been able to lock at least two
+			 * tables, otherwise there would be nothing to compact.
+			 * In that case, we return a lock error to our caller.
+			 */
+			if (errno == EEXIST && last - (i - 1) >= 2 &&
+			    flags & STACK_COMPACT_RANGE_BEST_EFFORT) {
+				err = 0;
+				/*
+				 * The subtraction is to offset the index, the
+				 * addition is to only compact up to the table
+				 * of the preceding iteration. They obviously
+				 * cancel each other out, but that may be
+				 * non-obvious when it was omitted.
+				 */
+				first = (i - 1) + 1;
+				break;
+			} else if (errno == EEXIST) {
 				err = REFTABLE_LOCK_ERROR;
-			else
+				goto done;
+			} else {
 				err = REFTABLE_IO_ERROR;
-			goto done;
+				goto done;
+			}
 		}
 
 		/*
@@ -1066,7 +1258,7 @@ static int stack_compact_range(struct reftable_stack *st,
 		 * run into file descriptor exhaustion when we compress a lot
 		 * of tables.
 		 */
-		err = close_lock_file_gently(&table_locks[i - first]);
+		err = flock_close(&table_locks[nlocks++]);
 		if (err < 0) {
 			err = REFTABLE_IO_ERROR;
 			goto done;
@@ -1078,7 +1270,7 @@ static int stack_compact_range(struct reftable_stack *st,
 	 * "tables.list" lock while compacting the locked tables. This allows
 	 * concurrent updates to the stack to proceed.
 	 */
-	err = rollback_lock_file(&tables_list_lock);
+	err = flock_release(&tables_list_lock);
 	if (err < 0) {
 		err = REFTABLE_IO_ERROR;
 		goto done;
@@ -1101,8 +1293,7 @@ static int stack_compact_range(struct reftable_stack *st,
 	 * "tables.list". We'll then replace the compacted range of tables with
 	 * the new table.
 	 */
-	err = hold_lock_file_for_update(&tables_list_lock, st->list_file,
-					LOCK_NO_DEREF);
+	err = flock_acquire(&tables_list_lock, st->list_file, st->opts.lock_timeout_ms);
 	if (err < 0) {
 		if (errno == EEXIST)
 			err = REFTABLE_LOCK_ERROR;
@@ -1112,7 +1303,7 @@ static int stack_compact_range(struct reftable_stack *st,
 	}
 
 	if (st->opts.default_permissions) {
-		if (chmod(get_lock_file_path(&tables_list_lock),
+		if (chmod(tables_list_lock.path,
 			  st->opts.default_permissions) < 0) {
 			err = REFTABLE_IO_ERROR;
 			goto done;
@@ -1120,20 +1311,130 @@ static int stack_compact_range(struct reftable_stack *st,
 	}
 
 	/*
+	 * As we have unlocked the stack while compacting our slice of tables
+	 * it may have happened that a concurrently running process has updated
+	 * the stack while we were compacting. In that case, we need to check
+	 * whether the tables that we have just compacted still exist in the
+	 * stack in the exact same order as we have compacted them.
+	 *
+	 * If they do exist, then it is fine to continue and replace those
+	 * tables with our compacted version. If they don't, then we need to
+	 * abort.
+	 */
+	err = stack_uptodate(st);
+	if (err < 0)
+		goto done;
+	if (err > 0) {
+		ssize_t new_offset = -1;
+		int fd;
+
+		fd = open(st->list_file, O_RDONLY);
+		if (fd < 0) {
+			err = REFTABLE_IO_ERROR;
+			goto done;
+		}
+
+		err = fd_read_lines(fd, &names);
+		close(fd);
+		if (err < 0)
+			goto done;
+
+		/*
+		 * Search for the offset of the first table that we have
+		 * compacted in the updated "tables.list" file.
+		 */
+		for (size_t i = 0; names[i]; i++) {
+			if (strcmp(names[i], st->readers[first]->name))
+				continue;
+
+			/*
+			 * We have found the first entry. Verify that all the
+			 * subsequent tables we have compacted still exist in
+			 * the modified stack in the exact same order as we
+			 * have compacted them.
+			 */
+			for (size_t j = 1; j < last - first + 1; j++) {
+				const char *old = first + j < st->merged->readers_len ?
+					st->readers[first + j]->name : NULL;
+				const char *new = names[i + j];
+
+				/*
+				 * If some entries are missing or in case the tables
+				 * have changed then we need to bail out. Again, this
+				 * shouldn't ever happen because we have locked the
+				 * tables we are compacting.
+				 */
+				if (!old || !new || strcmp(old, new)) {
+					err = REFTABLE_OUTDATED_ERROR;
+					goto done;
+				}
+			}
+
+			new_offset = i;
+			break;
+		}
+
+		/*
+		 * In case we didn't find our compacted tables in the stack we
+		 * need to bail out. In theory, this should have never happened
+		 * because we locked the tables we are compacting.
+		 */
+		if (new_offset < 0) {
+			err = REFTABLE_OUTDATED_ERROR;
+			goto done;
+		}
+
+		/*
+		 * We have found the new range that we want to replace, so
+		 * let's update the range of tables that we want to replace.
+		 */
+		first_to_replace = new_offset;
+		last_to_replace = last + (new_offset - first);
+	} else {
+		/*
+		 * `fd_read_lines()` uses a `NULL` sentinel to indicate that
+		 * the array is at its end. As we use `free_names()` to free
+		 * the array, we need to include this sentinel value here and
+		 * thus have to allocate `readers_len + 1` many entries.
+		 */
+		REFTABLE_CALLOC_ARRAY(names, st->merged->readers_len + 1);
+		if (!names) {
+			err = REFTABLE_OUT_OF_MEMORY_ERROR;
+			goto done;
+		}
+
+		for (size_t i = 0; i < st->merged->readers_len; i++) {
+			names[i] = reftable_strdup(st->readers[i]->name);
+			if (!names[i]) {
+				err = REFTABLE_OUT_OF_MEMORY_ERROR;
+				goto done;
+			}
+		}
+		first_to_replace = first;
+		last_to_replace = last;
+	}
+
+	/*
 	 * If the resulting compacted table is not empty, then we need to move
 	 * it into place now.
 	 */
 	if (!is_empty_table) {
-		format_name(&new_table_name, st->readers[first]->min_update_index,
-			    st->readers[last]->max_update_index);
-		strbuf_addstr(&new_table_name, ".ref");
-		stack_filename(&new_table_path, st, new_table_name.buf);
+		err = format_name(&new_table_name, st->readers[first]->min_update_index,
+				  st->readers[last]->max_update_index);
+		if (err < 0)
+			goto done;
 
-		err = rename_tempfile(&new_table, new_table_path.buf);
-		if (err < 0) {
-			err = REFTABLE_IO_ERROR;
+		err = reftable_buf_addstr(&new_table_name, ".ref");
+		if (err < 0)
+			goto done;
+
+		err = stack_filename(&new_table_path, st, new_table_name.buf);
+		if (err < 0)
+			goto done;
+
+		err = tmpfile_rename(&new_table, new_table_path.buf);
+		if (err < 0)
 			goto done;
-		}
 	}
 
 	/*
@@ -1141,14 +1442,23 @@ static int stack_compact_range(struct reftable_stack *st,
 	 * have just written. In case the compacted table became empty we
 	 * simply skip writing it.
 	 */
-	for (i = 0; i < first; i++)
-		strbuf_addf(&tables_list_buf, "%s\n", st->readers[i]->name);
-	if (!is_empty_table)
-		strbuf_addf(&tables_list_buf, "%s\n", new_table_name.buf);
-	for (i = last + 1; i < st->merged->stack_len; i++)
-		strbuf_addf(&tables_list_buf, "%s\n", st->readers[i]->name);
-
-	err = write_in_full(get_lock_file_fd(&tables_list_lock),
+	for (i = 0; i < first_to_replace; i++) {
+		if ((err = reftable_buf_addstr(&tables_list_buf, names[i])) < 0 ||
+		    (err = reftable_buf_addstr(&tables_list_buf, "\n")) < 0)
+		      goto done;
+	}
+	if (!is_empty_table) {
+		if ((err = reftable_buf_addstr(&tables_list_buf, new_table_name.buf)) < 0 ||
+		    (err = reftable_buf_addstr(&tables_list_buf, "\n")) < 0)
+			goto done;
+	}
+	for (i = last_to_replace + 1; names[i]; i++) {
+		if ((err = reftable_buf_addstr(&tables_list_buf, names[i])) < 0 ||
+		    (err = reftable_buf_addstr(&tables_list_buf, "\n")) < 0)
+			goto done;
+	}
+
+	err = write_in_full(tables_list_lock.fd,
 			    tables_list_buf.buf, tables_list_buf.len);
 	if (err < 0) {
 		err = REFTABLE_IO_ERROR;
@@ -1156,14 +1466,14 @@ static int stack_compact_range(struct reftable_stack *st,
 		goto done;
 	}
 
-	err = fsync_component(FSYNC_COMPONENT_REFERENCE, get_lock_file_fd(&tables_list_lock));
+	err = stack_fsync(&st->opts, tables_list_lock.fd);
 	if (err < 0) {
 		err = REFTABLE_IO_ERROR;
 		unlink(new_table_path.buf);
 		goto done;
 	}
 
-	err = commit_lock_file(&tables_list_lock);
+	err = flock_commit(&tables_list_lock);
 	if (err < 0) {
 		err = REFTABLE_IO_ERROR;
 		unlink(new_table_path.buf);
@@ -1183,43 +1493,42 @@ static int stack_compact_range(struct reftable_stack *st,
 	 * Delete the old tables. They may still be in use by concurrent
 	 * readers, so it is expected that unlinking tables may fail.
 	 */
-	for (i = first; i <= last; i++) {
-		struct lock_file *table_lock = &table_locks[i - first];
-		char *table_path = get_locked_file_path(table_lock);
-		unlink(table_path);
-		free(table_path);
+	for (i = 0; i < nlocks; i++) {
+		struct reftable_flock *table_lock = &table_locks[i];
+
+		reftable_buf_reset(&table_name);
+		err = reftable_buf_add(&table_name, table_lock->path,
+				       strlen(table_lock->path) - strlen(".lock"));
+		if (err)
+			continue;
+
+		unlink(table_name.buf);
 	}
 
 done:
-	rollback_lock_file(&tables_list_lock);
-	for (i = first; table_locks && i <= last; i++)
-		rollback_lock_file(&table_locks[i - first]);
+	flock_release(&tables_list_lock);
+	for (i = 0; table_locks && i < nlocks; i++)
+		flock_release(&table_locks[i]);
 	reftable_free(table_locks);
 
-	delete_tempfile(&new_table);
-	strbuf_release(&new_table_name);
-	strbuf_release(&new_table_path);
+	tmpfile_delete(&new_table);
+	reftable_buf_release(&new_table_name);
+	reftable_buf_release(&new_table_path);
+	reftable_buf_release(&tables_list_buf);
+	reftable_buf_release(&table_name);
+	free_names(names);
+
+	if (err == REFTABLE_LOCK_ERROR)
+		st->stats.failures++;
 
-	strbuf_release(&tables_list_buf);
-	strbuf_release(&table_name);
 	return err;
 }
 
 int reftable_stack_compact_all(struct reftable_stack *st,
 			       struct reftable_log_expiry_config *config)
 {
-	return stack_compact_range(st, 0, st->merged->stack_len ?
-			st->merged->stack_len - 1 : 0, config);
-}
-
-static int stack_compact_range_stats(struct reftable_stack *st,
-				     size_t first, size_t last,
-				     struct reftable_log_expiry_config *config)
-{
-	int err = stack_compact_range(st, first, last, config);
-	if (err == REFTABLE_LOCK_ERROR)
-		st->stats.failures++;
-	return err;
+	size_t last = st->merged->readers_len ? st->merged->readers_len - 1 : 0;
+	return stack_compact_range(st, 0, last, config, 0);
 }
 
 static int segment_size(struct segment *s)
@@ -1305,27 +1614,39 @@ struct segment suggest_compaction_segment(uint64_t *sizes, size_t n,
 
 static uint64_t *stack_table_sizes_for_compaction(struct reftable_stack *st)
 {
-	uint64_t *sizes =
-		reftable_calloc(st->merged->stack_len, sizeof(*sizes));
-	int version = (st->opts.hash_id == GIT_SHA1_FORMAT_ID) ? 1 : 2;
+	int version = (st->opts.hash_id == REFTABLE_HASH_SHA1) ? 1 : 2;
 	int overhead = header_size(version) - 1;
-	int i = 0;
-	for (i = 0; i < st->merged->stack_len; i++) {
+	uint64_t *sizes;
+
+	REFTABLE_CALLOC_ARRAY(sizes, st->merged->readers_len);
+	if (!sizes)
+		return NULL;
+
+	for (size_t i = 0; i < st->merged->readers_len; i++)
 		sizes[i] = st->readers[i]->size - overhead;
-	}
+
 	return sizes;
 }
 
 int reftable_stack_auto_compact(struct reftable_stack *st)
 {
-	uint64_t *sizes = stack_table_sizes_for_compaction(st);
-	struct segment seg =
-		suggest_compaction_segment(sizes, st->merged->stack_len,
-					   st->opts.auto_compaction_factor);
+	struct segment seg;
+	uint64_t *sizes;
+
+	if (st->merged->readers_len < 2)
+		return 0;
+
+	sizes = stack_table_sizes_for_compaction(st);
+	if (!sizes)
+		return REFTABLE_OUT_OF_MEMORY_ERROR;
+
+	seg = suggest_compaction_segment(sizes, st->merged->readers_len,
+					 st->opts.auto_compaction_factor);
 	reftable_free(sizes);
+
 	if (segment_size(&seg) > 0)
-		return stack_compact_range_stats(st, seg.start, seg.end - 1,
-						 NULL);
+		return stack_compact_range(st, seg.start, seg.end - 1,
+					   NULL, STACK_COMPACT_RANGE_BEST_EFFORT);
 
 	return 0;
 }
@@ -1339,9 +1660,31 @@ reftable_stack_compaction_stats(struct reftable_stack *st)
 int reftable_stack_read_ref(struct reftable_stack *st, const char *refname,
 			    struct reftable_ref_record *ref)
 {
-	struct reftable_table tab = { NULL };
-	reftable_table_from_merged_table(&tab, reftable_stack_merged_table(st));
-	return reftable_table_read_ref(&tab, refname, ref);
+	struct reftable_iterator it = { 0 };
+	int ret;
+
+	ret = reftable_merged_table_init_ref_iterator(st->merged, &it);
+	if (ret)
+		goto out;
+
+	ret = reftable_iterator_seek_ref(&it, refname);
+	if (ret)
+		goto out;
+
+	ret = reftable_iterator_next_ref(&it, ref);
+	if (ret)
+		goto out;
+
+	if (strcmp(ref->refname, refname) ||
+	    reftable_ref_record_is_deletion(ref)) {
+		reftable_ref_record_release(ref);
+		ret = 1;
+		goto out;
+	}
+
+out:
+	reftable_iterator_destroy(&it);
+	return ret;
 }
 
 int reftable_stack_read_log(struct reftable_stack *st, const char *refname,
@@ -1350,7 +1693,10 @@ int reftable_stack_read_log(struct reftable_stack *st, const char *refname,
 	struct reftable_iterator it = {0};
 	int err;
 
-	reftable_stack_init_log_iterator(st, &it);
+	err = reftable_stack_init_log_iterator(st, &it);
+	if (err)
+		goto done;
+
 	err = reftable_iterator_seek_log(&it, refname);
 	if (err)
 		goto done;
@@ -1386,25 +1732,28 @@ static void remove_maybe_stale_table(struct reftable_stack *st, uint64_t max,
 	uint64_t update_idx = 0;
 	struct reftable_block_source src = { NULL };
 	struct reftable_reader *rd = NULL;
-	struct strbuf table_path = STRBUF_INIT;
-	stack_filename(&table_path, st, name);
+	struct reftable_buf table_path = REFTABLE_BUF_INIT;
+
+	err = stack_filename(&table_path, st, name);
+	if (err < 0)
+		goto done;
 
 	err = reftable_block_source_from_file(&src, table_path.buf);
 	if (err < 0)
 		goto done;
 
-	err = reftable_new_reader(&rd, &src, name);
+	err = reftable_reader_new(&rd, &src, name);
 	if (err < 0)
 		goto done;
 
 	update_idx = reftable_reader_max_update_index(rd);
-	reftable_reader_free(rd);
+	reftable_reader_decref(rd);
 
 	if (update_idx <= max) {
 		unlink(table_path.buf);
 	}
 done:
-	strbuf_release(&table_path);
+	reftable_buf_release(&table_path);
 }
 
 static int reftable_stack_clean_locked(struct reftable_stack *st)
@@ -1439,7 +1788,7 @@ static int reftable_stack_clean_locked(struct reftable_stack *st)
 int reftable_stack_clean(struct reftable_stack *st)
 {
 	struct reftable_addition *add = NULL;
-	int err = reftable_stack_new_addition(&add, st);
+	int err = reftable_stack_new_addition(&add, st, 0);
 	if (err < 0) {
 		goto done;
 	}
@@ -1456,22 +1805,7 @@ done:
 	return err;
 }
 
-int reftable_stack_print_directory(const char *stackdir, uint32_t hash_id)
+enum reftable_hash reftable_stack_hash_id(struct reftable_stack *st)
 {
-	struct reftable_stack *stack = NULL;
-	struct reftable_write_options opts = { .hash_id = hash_id };
-	struct reftable_merged_table *merged = NULL;
-	struct reftable_table table = { NULL };
-
-	int err = reftable_new_stack(&stack, stackdir, &opts);
-	if (err < 0)
-		goto done;
-
-	merged = reftable_stack_merged_table(stack);
-	reftable_table_from_merged_table(&table, merged);
-	err = reftable_table_print(&table);
-done:
-	if (stack)
-		reftable_stack_destroy(stack);
-	return err;
+	return reftable_merged_table_hash_id(st->merged);
 }