diff --git a/Makefile b/Makefile
index 549b24e7fd..2a7a0c9d10 100644
--- a/Makefile
+++ b/Makefile
@@ -2722,6 +2722,7 @@ REFTABLE_OBJS += reftable/pq.o
 REFTABLE_OBJS += reftable/reader.o
 REFTABLE_OBJS += reftable/record.o
 REFTABLE_OBJS += reftable/stack.o
+REFTABLE_OBJS += reftable/system.o
 REFTABLE_OBJS += reftable/tree.o
 REFTABLE_OBJS += reftable/writer.o
 
diff --git a/refs/reftable-backend.c b/refs/reftable-backend.c
index 647ef9b05b..97c2231eee 100644
--- a/refs/reftable-backend.c
+++ b/refs/reftable-backend.c
@@ -15,6 +15,7 @@
 #include "../object.h"
 #include "../path.h"
 #include "../refs.h"
+#include "../reftable/reftable-basics.h"
 #include "../reftable/reftable-stack.h"
 #include "../reftable/reftable-record.h"
 #include "../reftable/reftable-error.h"
@@ -23,6 +24,7 @@
 #include "../setup.h"
 #include "../strmap.h"
 #include "../trace2.h"
+#include "../write-or-die.h"
 #include "parse.h"
 #include "refs-internal.h"
 
@@ -272,6 +274,11 @@ static int reftable_be_config(const char *var, const char *value,
 	return 0;
 }
 
+static int reftable_be_fsync(int fd)
+{
+	return fsync_component(FSYNC_COMPONENT_REFERENCE, fd);
+}
+
 static struct ref_store *reftable_be_init(struct repository *repo,
 					  const char *gitdir,
 					  unsigned int store_flags)
@@ -289,11 +296,21 @@ static struct ref_store *reftable_be_init(struct repository *repo,
 	refs->store_flags = store_flags;
 	refs->log_all_ref_updates = repo_settings_get_log_all_ref_updates(repo);
 
-	refs->write_options.hash_id = repo->hash_algo->format_id;
+	switch (repo->hash_algo->format_id) {
+	case GIT_SHA1_FORMAT_ID:
+		refs->write_options.hash_id = REFTABLE_HASH_SHA1;
+		break;
+	case GIT_SHA256_FORMAT_ID:
+		refs->write_options.hash_id = REFTABLE_HASH_SHA256;
+		break;
+	default:
+		BUG("unknown hash algorithm %d", 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);
 	refs->write_options.lock_timeout_ms = 100;
+	refs->write_options.fsync = reftable_be_fsync;
 
 	git_config(reftable_be_config, &refs->write_options);
 
diff --git a/reftable/basics.c b/reftable/basics.c
index bc4fcc9144..7d84a5d62d 100644
--- a/reftable/basics.c
+++ b/reftable/basics.c
@@ -271,14 +271,15 @@ int common_prefix_size(struct reftable_buf *a, struct reftable_buf *b)
 	return p;
 }
 
-int hash_size(uint32_t id)
+int hash_size(enum reftable_hash id)
 {
+	if (!id)
+		return REFTABLE_HASH_SIZE_SHA1;
 	switch (id) {
-	case 0:
-	case GIT_SHA1_FORMAT_ID:
-		return GIT_SHA1_RAWSZ;
-	case GIT_SHA256_FORMAT_ID:
-		return GIT_SHA256_RAWSZ;
+	case REFTABLE_HASH_SHA1:
+		return REFTABLE_HASH_SIZE_SHA1;
+	case REFTABLE_HASH_SHA256:
+		return REFTABLE_HASH_SIZE_SHA256;
 	}
 	abort();
 }
diff --git a/reftable/basics.h b/reftable/basics.h
index 7aa46d7c30..36beda2c25 100644
--- a/reftable/basics.h
+++ b/reftable/basics.h
@@ -148,6 +148,14 @@ char *reftable_strdup(const char *str);
 /* Find the longest shared prefix size of `a` and `b` */
 int common_prefix_size(struct reftable_buf *a, struct reftable_buf *b);
 
-int hash_size(uint32_t id);
+int hash_size(enum reftable_hash id);
+
+/*
+ * Format IDs that identify the hash function used by a reftable. Note that
+ * these constants end up on disk and thus mustn't change. The format IDs are
+ * "sha1" and "s256" in big endian, respectively.
+ */
+#define REFTABLE_FORMAT_ID_SHA1   ((uint32_t) 0x73686131)
+#define REFTABLE_FORMAT_ID_SHA256 ((uint32_t) 0x73323536)
 
 #endif
diff --git a/reftable/merged.c b/reftable/merged.c
index 514d6facf4..5b93e20f42 100644
--- a/reftable/merged.c
+++ b/reftable/merged.c
@@ -181,7 +181,7 @@ static void iterator_from_merged_iter(struct reftable_iterator *it,
 
 int reftable_merged_table_new(struct reftable_merged_table **dest,
 			      struct reftable_reader **readers, size_t n,
-			      uint32_t hash_id)
+			      enum reftable_hash hash_id)
 {
 	struct reftable_merged_table *m = NULL;
 	uint64_t last_max = 0;
@@ -293,7 +293,7 @@ int reftable_merged_table_init_log_iterator(struct reftable_merged_table *mt,
 	return merged_table_init_iter(mt, it, BLOCK_TYPE_LOG);
 }
 
-uint32_t reftable_merged_table_hash_id(struct reftable_merged_table *mt)
+enum reftable_hash reftable_merged_table_hash_id(struct reftable_merged_table *mt)
 {
 	return mt->hash_id;
 }
diff --git a/reftable/merged.h b/reftable/merged.h
index 89bd0c4b35..0b7d939e92 100644
--- a/reftable/merged.h
+++ b/reftable/merged.h
@@ -10,11 +10,12 @@ https://developers.google.com/open-source/licenses/bsd
 #define MERGED_H
 
 #include "system.h"
+#include "reftable-basics.h"
 
 struct reftable_merged_table {
 	struct reftable_reader **readers;
 	size_t readers_len;
-	uint32_t hash_id;
+	enum reftable_hash hash_id;
 
 	/* If unset, produce deletions. This is useful for compaction. For the
 	 * full stack, deletions should be produced. */
diff --git a/reftable/reader.c b/reftable/reader.c
index 90dc950b57..ea82955c9b 100644
--- a/reftable/reader.c
+++ b/reftable/reader.c
@@ -67,7 +67,7 @@ static int reader_get_block(struct reftable_reader *r,
 	return block_source_read_block(&r->source, dest, off, sz);
 }
 
-uint32_t reftable_reader_hash_id(struct reftable_reader *r)
+enum reftable_hash reftable_reader_hash_id(struct reftable_reader *r)
 {
 	return r->hash_id;
 }
@@ -107,18 +107,20 @@ static int parse_footer(struct reftable_reader *r, uint8_t *footer,
 	f += 8;
 
 	if (r->version == 1) {
-		r->hash_id = GIT_SHA1_FORMAT_ID;
+		r->hash_id = REFTABLE_HASH_SHA1;
 	} else {
-		r->hash_id = get_be32(f);
-		switch (r->hash_id) {
-		case GIT_SHA1_FORMAT_ID:
+		switch (get_be32(f)) {
+		case REFTABLE_FORMAT_ID_SHA1:
+			r->hash_id = REFTABLE_HASH_SHA1;
 			break;
-		case GIT_SHA256_FORMAT_ID:
+		case REFTABLE_FORMAT_ID_SHA256:
+			r->hash_id = REFTABLE_HASH_SHA256;
 			break;
 		default:
 			err = REFTABLE_FORMAT_ERROR;
 			goto done;
 		}
+
 		f += 4;
 	}
 
diff --git a/reftable/reader.h b/reftable/reader.h
index 010fbfe851..d2b48a4849 100644
--- a/reftable/reader.h
+++ b/reftable/reader.h
@@ -37,8 +37,8 @@ struct reftable_reader {
 	/* Size of the file, excluding the footer. */
 	uint64_t size;
 
-	/* 'sha1' for SHA1, 's256' for SHA-256 */
-	uint32_t hash_id;
+	/* The hash function used for ref records. */
+	enum reftable_hash hash_id;
 
 	uint32_t block_size;
 	uint64_t min_update_index;
diff --git a/reftable/reftable-basics.h b/reftable/reftable-basics.h
index 6e8e636b71..e0397ed583 100644
--- a/reftable/reftable-basics.h
+++ b/reftable/reftable-basics.h
@@ -11,6 +11,19 @@
 
 #include <stddef.h>
 
+/*
+ * Hash functions understood by the reftable library. Note that the values are
+ * arbitrary and somewhat random such that we can easily detect cases where the
+ * hash hasn't been properly set up.
+ */
+enum reftable_hash {
+	REFTABLE_HASH_SHA1   = 89,
+	REFTABLE_HASH_SHA256 = 247,
+};
+#define REFTABLE_HASH_SIZE_SHA1   20
+#define REFTABLE_HASH_SIZE_SHA256 32
+#define REFTABLE_HASH_SIZE_MAX    REFTABLE_HASH_SIZE_SHA256
+
 /* Overrides the functions to use for memory management. */
 void reftable_set_alloc(void *(*malloc)(size_t),
 			void *(*realloc)(void *, size_t), void (*free)(void *));
diff --git a/reftable/reftable-merged.h b/reftable/reftable-merged.h
index a970d5dd89..f2d01c3ef8 100644
--- a/reftable/reftable-merged.h
+++ b/reftable/reftable-merged.h
@@ -34,7 +34,7 @@ struct reftable_reader;
  */
 int reftable_merged_table_new(struct reftable_merged_table **dest,
 			      struct reftable_reader **readers, size_t n,
-			      uint32_t hash_id);
+			      enum reftable_hash hash_id);
 
 /* Initialize a merged table iterator for reading refs. */
 int reftable_merged_table_init_ref_iterator(struct reftable_merged_table *mt,
@@ -56,6 +56,6 @@ reftable_merged_table_min_update_index(struct reftable_merged_table *mt);
 void reftable_merged_table_free(struct reftable_merged_table *m);
 
 /* return the hash ID of the merged table. */
-uint32_t reftable_merged_table_hash_id(struct reftable_merged_table *m);
+enum reftable_hash reftable_merged_table_hash_id(struct reftable_merged_table *m);
 
 #endif
diff --git a/reftable/reftable-reader.h b/reftable/reftable-reader.h
index 6a2d0b693f..0085fbb903 100644
--- a/reftable/reftable-reader.h
+++ b/reftable/reftable-reader.h
@@ -54,7 +54,7 @@ int reftable_reader_init_log_iterator(struct reftable_reader *r,
 				      struct reftable_iterator *it);
 
 /* returns the hash ID used in this table. */
-uint32_t reftable_reader_hash_id(struct reftable_reader *r);
+enum reftable_hash reftable_reader_hash_id(struct reftable_reader *r);
 
 /* return an iterator for the refs pointing to `oid`. */
 int reftable_reader_refs_for(struct reftable_reader *r,
diff --git a/reftable/reftable-record.h b/reftable/reftable-record.h
index 2d42463c58..ddd48eb579 100644
--- a/reftable/reftable-record.h
+++ b/reftable/reftable-record.h
@@ -9,7 +9,7 @@ https://developers.google.com/open-source/licenses/bsd
 #ifndef REFTABLE_RECORD_H
 #define REFTABLE_RECORD_H
 
-#include "hash.h"
+#include "reftable-basics.h"
 #include <stdint.h>
 
 /*
@@ -40,10 +40,10 @@ struct reftable_ref_record {
 #define REFTABLE_NR_REF_VALUETYPES 4
 	} value_type;
 	union {
-		unsigned char val1[GIT_MAX_RAWSZ];
+		unsigned char val1[REFTABLE_HASH_SIZE_MAX];
 		struct {
-			unsigned char value[GIT_MAX_RAWSZ]; /* first hash  */
-			unsigned char target_value[GIT_MAX_RAWSZ]; /* second hash */
+			unsigned char value[REFTABLE_HASH_SIZE_MAX]; /* first hash  */
+			unsigned char target_value[REFTABLE_HASH_SIZE_MAX]; /* second hash */
 		} val2;
 		char *symref; /* referent, malloced 0-terminated string */
 	} value;
@@ -85,8 +85,8 @@ struct reftable_log_record {
 
 	union {
 		struct {
-			unsigned char new_hash[GIT_MAX_RAWSZ];
-			unsigned char old_hash[GIT_MAX_RAWSZ];
+			unsigned char new_hash[REFTABLE_HASH_SIZE_MAX];
+			unsigned char old_hash[REFTABLE_HASH_SIZE_MAX];
 			char *name;
 			char *email;
 			uint64_t time;
diff --git a/reftable/reftable-writer.h b/reftable/reftable-writer.h
index e4fc953788..c85ef5a5bd 100644
--- a/reftable/reftable-writer.h
+++ b/reftable/reftable-writer.h
@@ -33,7 +33,7 @@ struct reftable_write_options {
 	/* 4-byte identifier ("sha1", "s256") of the hash.
 	 * Defaults to SHA1 if unset
 	 */
-	uint32_t hash_id;
+	enum reftable_hash hash_id;
 
 	/* Default mode for creating files. If unset, use 0666 (+umask) */
 	unsigned int default_permissions;
@@ -62,6 +62,12 @@ struct reftable_write_options {
 	 * negative value will cause us to block indefinitely.
 	 */
 	long lock_timeout_ms;
+
+	/*
+	 * Optional callback used to fsync files to disk. Falls back to using
+	 * fsync(3P) when unset.
+	 */
+	int (*fsync)(int fd);
 };
 
 /* reftable_block_stats holds statistics for a single block type */
diff --git a/reftable/stack.c b/reftable/stack.c
index c33979536e..10d45e89d0 100644
--- a/reftable/stack.c
+++ b/reftable/stack.c
@@ -8,7 +8,6 @@ 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"
@@ -17,7 +16,6 @@ https://developers.google.com/open-source/licenses/bsd
 #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,
@@ -43,17 +41,28 @@ static int stack_filename(struct reftable_buf *dest, struct reftable_stack *st,
 	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)
-{
-	int *fdp = (int *)arg;
+struct fd_writer {
+	const struct reftable_write_options *opts;
+	int fd;
+};
 
-	return fsync_component(FSYNC_COMPONENT_REFERENCE, *fdp);
+static ssize_t fd_writer_write(void *arg, const void *data, size_t sz)
+{
+	struct fd_writer *writer = arg;
+	return write_in_full(writer->fd, data, sz);
+}
+
+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,
@@ -73,7 +82,7 @@ int reftable_new_stack(struct reftable_stack **dest, const char *dir,
 	if (_opts)
 		opts = *_opts;
 	if (opts.hash_id == 0)
-		opts.hash_id = GIT_SHA1_FORMAT_ID;
+		opts.hash_id = REFTABLE_HASH_SHA1;
 
 	*dest = NULL;
 
@@ -648,7 +657,7 @@ static int format_name(struct reftable_buf *dest, uint64_t min, uint64_t max)
 }
 
 struct reftable_addition {
-	struct lock_file tables_list_lock;
+	struct reftable_flock tables_list_lock;
 	struct reftable_stack *stack;
 
 	char **new_tables;
@@ -667,10 +676,8 @@ static int reftable_stack_init_addition(struct reftable_addition *add,
 
 	add->stack = st;
 
-	err = hold_lock_file_for_update_timeout(&add->tables_list_lock,
-						st->list_file,
-						LOCK_NO_DEREF,
-						st->opts.lock_timeout_ms);
+	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;
@@ -680,7 +687,7 @@ static int reftable_stack_init_addition(struct reftable_addition *add,
 		goto done;
 	}
 	if (st->opts.default_permissions) {
-		if (chmod(get_lock_file_path(&add->tables_list_lock),
+		if (chmod(add->tables_list_lock.path,
 			  st->opts.default_permissions) < 0) {
 			err = REFTABLE_IO_ERROR;
 			goto done;
@@ -724,7 +731,7 @@ static void reftable_addition_close(struct reftable_addition *add)
 	add->new_tables_len = 0;
 	add->new_tables_cap = 0;
 
-	rollback_lock_file(&add->tables_list_lock);
+	flock_release(&add->tables_list_lock);
 	reftable_buf_release(&nm);
 }
 
@@ -740,7 +747,6 @@ void reftable_addition_destroy(struct reftable_addition *add)
 int reftable_addition_commit(struct reftable_addition *add)
 {
 	struct reftable_buf table_list = REFTABLE_BUF_INIT;
-	int lock_file_fd = get_lock_file_fd(&add->tables_list_lock);
 	int err = 0;
 	size_t i;
 
@@ -758,20 +764,20 @@ int reftable_addition_commit(struct reftable_addition *add)
 			goto done;
 	}
 
-	err = write_in_full(lock_file_fd, table_list.buf, table_list.len);
+	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;
 	}
 
-	err = fsync_component(FSYNC_COMPONENT_REFERENCE, lock_file_fd);
+	err = stack_fsync(&add->stack->opts, add->tables_list_lock.fd);
 	if (err < 0) {
 		err = REFTABLE_IO_ERROR;
 		goto done;
 	}
 
-	err = commit_lock_file(&add->tables_list_lock);
+	err = flock_commit(&add->tables_list_lock);
 	if (err < 0) {
 		err = REFTABLE_IO_ERROR;
 		goto done;
@@ -857,9 +863,11 @@ int reftable_addition_add(struct reftable_addition *add,
 	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;
 
 	reftable_buf_reset(&next_name);
 
@@ -875,22 +883,20 @@ int reftable_addition_add(struct reftable_addition *add,
 	if (err < 0)
 		goto done;
 
-	tab_file = mks_tempfile(temp_tab_file_name.buf);
-	if (!tab_file) {
-		err = REFTABLE_IO_ERROR;
+	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);
 
-	err = reftable_writer_new(&wr, 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;
 
@@ -906,11 +912,9 @@ 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;
@@ -933,11 +937,9 @@ int reftable_addition_add(struct reftable_addition *add,
 	  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(add->new_tables, add->new_tables_len + 1,
 			    add->new_tables_cap);
@@ -948,7 +950,7 @@ int reftable_addition_add(struct reftable_addition *add,
 	add->new_tables[add->new_tables_len++] = reftable_buf_detach(&next_name);
 
 done:
-	delete_tempfile(&tab_file);
+	tmpfile_delete(&tab_file);
 	reftable_buf_release(&temp_tab_file_name);
 	reftable_buf_release(&tab_file_name);
 	reftable_buf_release(&next_name);
@@ -968,13 +970,16 @@ 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 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]));
@@ -989,21 +994,19 @@ static int stack_compact_locked(struct reftable_stack *st,
 	if (err < 0)
 		goto done;
 
-	tab_file = mks_tempfile(tab_file_path.buf);
-	if (!tab_file) {
-		err = REFTABLE_IO_ERROR;
+	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;
 	}
 
-	err = reftable_writer_new(&wr, 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;
 
@@ -1015,15 +1018,15 @@ 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);
 	reftable_buf_release(&next_name);
 	reftable_buf_release(&tab_file_path);
@@ -1154,9 +1157,9 @@ static int stack_compact_range(struct reftable_stack *st,
 	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 lock_file tables_list_lock = LOCK_INIT;
-	struct lock_file *table_locks = NULL;
-	struct tempfile *new_table = NULL;
+	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 first_to_replace, last_to_replace;
 	size_t i, nlocks = 0;
@@ -1173,10 +1176,7 @@ 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_timeout(&tables_list_lock,
-						st->list_file,
-						LOCK_NO_DEREF,
-						st->opts.lock_timeout_ms);
+	err = flock_acquire(&tables_list_lock, st->list_file, st->opts.lock_timeout_ms);
 	if (err < 0) {
 		if (errno == EEXIST)
 			err = REFTABLE_LOCK_ERROR;
@@ -1199,19 +1199,20 @@ static int stack_compact_range(struct reftable_stack *st,
 	 * 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);
+	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[nlocks],
-						table_name.buf, LOCK_NO_DEREF);
+		err = flock_acquire(&table_locks[nlocks], table_name.buf, 0);
 		if (err < 0) {
 			/*
 			 * When the table is locked already we may do a
@@ -1247,7 +1248,7 @@ 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[nlocks++]);
+		err = flock_close(&table_locks[nlocks++]);
 		if (err < 0) {
 			err = REFTABLE_IO_ERROR;
 			goto done;
@@ -1259,7 +1260,7 @@ 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;
@@ -1282,10 +1283,7 @@ 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_timeout(&tables_list_lock,
-						st->list_file,
-						LOCK_NO_DEREF,
-						st->opts.lock_timeout_ms);
+	err = flock_acquire(&tables_list_lock, st->list_file, st->opts.lock_timeout_ms);
 	if (err < 0) {
 		if (errno == EEXIST)
 			err = REFTABLE_LOCK_ERROR;
@@ -1295,7 +1293,7 @@ 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;
@@ -1424,11 +1422,9 @@ static int stack_compact_range(struct reftable_stack *st,
 		if (err < 0)
 			goto done;
 
-		err = rename_tempfile(&new_table, new_table_path.buf);
-		if (err < 0) {
-			err = REFTABLE_IO_ERROR;
+		err = tmpfile_rename(&new_table, new_table_path.buf);
+		if (err < 0)
 			goto done;
-		}
 	}
 
 	/*
@@ -1452,7 +1448,7 @@ static int stack_compact_range(struct reftable_stack *st,
 			goto done;
 	}
 
-	err = write_in_full(get_lock_file_fd(&tables_list_lock),
+	err = write_in_full(tables_list_lock.fd,
 			    tables_list_buf.buf, tables_list_buf.len);
 	if (err < 0) {
 		err = REFTABLE_IO_ERROR;
@@ -1460,14 +1456,14 @@ 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);
@@ -1488,19 +1484,24 @@ static int stack_compact_range(struct reftable_stack *st,
 	 * readers, so it is expected that unlinking tables may fail.
 	 */
 	for (i = 0; i < nlocks; i++) {
-		struct lock_file *table_lock = &table_locks[i];
-		char *table_path = get_locked_file_path(table_lock);
-		unlink(table_path);
-		reftable_free(table_path);
+		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);
+	flock_release(&tables_list_lock);
 	for (i = 0; table_locks && i < nlocks; i++)
-		rollback_lock_file(&table_locks[i]);
+		flock_release(&table_locks[i]);
 	reftable_free(table_locks);
 
-	delete_tempfile(&new_table);
+	tmpfile_delete(&new_table);
 	reftable_buf_release(&new_table_name);
 	reftable_buf_release(&new_table_path);
 	reftable_buf_release(&tables_list_buf);
@@ -1603,7 +1604,7 @@ struct segment suggest_compaction_segment(uint64_t *sizes, size_t n,
 
 static uint64_t *stack_table_sizes_for_compaction(struct reftable_stack *st)
 {
-	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;
 	uint64_t *sizes;
 
diff --git a/reftable/system.c b/reftable/system.c
new file mode 100644
index 0000000000..adf8e4d30b
--- /dev/null
+++ b/reftable/system.c
@@ -0,0 +1,126 @@
+#include "system.h"
+#include "basics.h"
+#include "reftable-error.h"
+#include "../lockfile.h"
+#include "../tempfile.h"
+
+int tmpfile_from_pattern(struct reftable_tmpfile *out, const char *pattern)
+{
+	struct tempfile *tempfile;
+
+	tempfile = mks_tempfile(pattern);
+	if (!tempfile)
+		return REFTABLE_IO_ERROR;
+
+	out->path = tempfile->filename.buf;
+	out->fd = tempfile->fd;
+	out->priv = tempfile;
+
+	return 0;
+}
+
+int tmpfile_close(struct reftable_tmpfile *t)
+{
+	struct tempfile *tempfile = t->priv;
+	int ret = close_tempfile_gently(tempfile);
+	t->fd = -1;
+	if (ret < 0)
+		return REFTABLE_IO_ERROR;
+	return 0;
+}
+
+int tmpfile_delete(struct reftable_tmpfile *t)
+{
+	struct tempfile *tempfile = t->priv;
+	int ret = delete_tempfile(&tempfile);
+	*t = REFTABLE_TMPFILE_INIT;
+	if (ret < 0)
+		return REFTABLE_IO_ERROR;
+	return 0;
+}
+
+int tmpfile_rename(struct reftable_tmpfile *t, const char *path)
+{
+	struct tempfile *tempfile = t->priv;
+	int ret = rename_tempfile(&tempfile, path);
+	*t = REFTABLE_TMPFILE_INIT;
+	if (ret < 0)
+		return REFTABLE_IO_ERROR;
+	return 0;
+}
+
+int flock_acquire(struct reftable_flock *l, const char *target_path,
+		  long timeout_ms)
+{
+	struct lock_file *lockfile;
+	int err;
+
+	lockfile = reftable_malloc(sizeof(*lockfile));
+	if (!lockfile)
+		return REFTABLE_OUT_OF_MEMORY_ERROR;
+
+	err = hold_lock_file_for_update_timeout(lockfile, target_path, LOCK_NO_DEREF,
+						timeout_ms);
+	if (err < 0) {
+		reftable_free(lockfile);
+		if (errno == EEXIST)
+			return REFTABLE_LOCK_ERROR;
+		return -1;
+	}
+
+	l->fd = get_lock_file_fd(lockfile);
+	l->path = get_lock_file_path(lockfile);
+	l->priv = lockfile;
+
+	return 0;
+}
+
+int flock_close(struct reftable_flock *l)
+{
+	struct lock_file *lockfile = l->priv;
+	int ret;
+
+	if (!lockfile)
+		return REFTABLE_API_ERROR;
+
+	ret = close_lock_file_gently(lockfile);
+	l->fd = -1;
+	if (ret < 0)
+		return REFTABLE_IO_ERROR;
+
+	return 0;
+}
+
+int flock_release(struct reftable_flock *l)
+{
+	struct lock_file *lockfile = l->priv;
+	int ret;
+
+	if (!lockfile)
+		return 0;
+
+	ret = rollback_lock_file(lockfile);
+	reftable_free(lockfile);
+	*l = REFTABLE_FLOCK_INIT;
+	if (ret < 0)
+		return REFTABLE_IO_ERROR;
+
+	return 0;
+}
+
+int flock_commit(struct reftable_flock *l)
+{
+	struct lock_file *lockfile = l->priv;
+	int ret;
+
+	if (!lockfile)
+		return REFTABLE_API_ERROR;
+
+	ret = commit_lock_file(lockfile);
+	reftable_free(lockfile);
+	*l = REFTABLE_FLOCK_INIT;
+	if (ret < 0)
+		return REFTABLE_IO_ERROR;
+
+	return 0;
+}
diff --git a/reftable/system.h b/reftable/system.h
index 5ec8583343..7d5f803eeb 100644
--- a/reftable/system.h
+++ b/reftable/system.h
@@ -12,11 +12,90 @@ https://developers.google.com/open-source/licenses/bsd
 /* This header glues the reftable library to the rest of Git */
 
 #include "git-compat-util.h"
-#include "lockfile.h"
-#include "tempfile.h"
-#include "hash.h" /* hash ID, sizes.*/
-#include "dir.h" /* remove_dir_recursively, for tests.*/
 
-int hash_size(uint32_t id);
+/*
+ * An implementation-specific temporary file. By making this specific to the
+ * implementation it becomes possible to tie temporary files into any kind of
+ * signal or atexit handlers for cleanup on abnormal situations.
+ */
+struct reftable_tmpfile {
+	const char *path;
+	int fd;
+	void *priv;
+};
+#define REFTABLE_TMPFILE_INIT ((struct reftable_tmpfile) { .fd = -1, })
+
+/*
+ * Create a temporary file from a pattern similar to how mkstemp(3p) would.
+ * The `pattern` shall not be modified. On success, the structure at `out` has
+ * been initialized such that it is ready for use. Returns 0 on success, a
+ * reftable error code on error.
+ */
+int tmpfile_from_pattern(struct reftable_tmpfile *out, const char *pattern);
+
+/*
+ * Close the temporary file's file descriptor without removing the file itself.
+ * This is a no-op in case the file has already been closed beforehand. Returns
+ * 0 on success, a reftable error code on error.
+ */
+int tmpfile_close(struct reftable_tmpfile *t);
+
+/*
+ * Close the temporary file and delete it. This is a no-op in case the file has
+ * already been deleted or renamed beforehand. Returns 0 on success, a reftable
+ * error code on error.
+ */
+int tmpfile_delete(struct reftable_tmpfile *t);
+
+/*
+ * Rename the temporary file to the provided path. The temporary file must be
+ * active. Return 0 on success, a reftable error code on error. Deactivates the
+ * temporary file.
+ */
+int tmpfile_rename(struct reftable_tmpfile *t, const char *path);
+
+/*
+ * An implementation-specific file lock. Same as with `reftable_tmpfile`,
+ * making this specific to the implementation makes it possible to tie this
+ * into signal or atexit handlers such that we know to clean up stale locks on
+ * abnormal exits.
+ */
+struct reftable_flock {
+	const char *path;
+	int fd;
+	void *priv;
+};
+#define REFTABLE_FLOCK_INIT ((struct reftable_flock){ .fd = -1, })
+
+/*
+ * Acquire the lock for the given target path by exclusively creating a file
+ * with ".lock" appended to it. If that lock exists, we wait up to `timeout_ms`
+ * to acquire the lock. If `timeout_ms` is 0 we don't wait, if it is negative
+ * we block indefinitely.
+ *
+ * Retrun 0 on success, a reftable error code on error.
+ */
+int flock_acquire(struct reftable_flock *l, const char *target_path,
+		  long timeout_ms);
+
+/*
+ * Close the lockfile's file descriptor without removing the lock itself. This
+ * is a no-op in case the lockfile has already been closed beforehand. Returns
+ * 0 on success, a reftable error code on error.
+ */
+int flock_close(struct reftable_flock *l);
+
+/*
+ * Release the lock by unlinking the lockfile. This is a no-op in case the
+ * lockfile has already been released or committed beforehand. Returns 0 on
+ * success, a reftable error code on error.
+ */
+int flock_release(struct reftable_flock *l);
+
+/*
+ * Commit the lock by renaming the lockfile into place. Returns 0 on success, a
+ * reftable error code on error.
+ */
+int flock_commit(struct reftable_flock *l);
 
 #endif
diff --git a/reftable/writer.c b/reftable/writer.c
index be0fae6cb2..9efeab13e1 100644
--- a/reftable/writer.c
+++ b/reftable/writer.c
@@ -79,7 +79,7 @@ static void options_set_defaults(struct reftable_write_options *opts)
 	}
 
 	if (opts->hash_id == 0) {
-		opts->hash_id = GIT_SHA1_FORMAT_ID;
+		opts->hash_id = REFTABLE_HASH_SHA1;
 	}
 	if (opts->block_size == 0) {
 		opts->block_size = DEFAULT_BLOCK_SIZE;
@@ -88,7 +88,7 @@ static void options_set_defaults(struct reftable_write_options *opts)
 
 static int writer_version(struct reftable_writer *w)
 {
-	return (w->opts.hash_id == 0 || w->opts.hash_id == GIT_SHA1_FORMAT_ID) ?
+	return (w->opts.hash_id == 0 || w->opts.hash_id == REFTABLE_HASH_SHA1) ?
 			     1 :
 			     2;
 }
@@ -103,8 +103,22 @@ static int writer_write_header(struct reftable_writer *w, uint8_t *dest)
 	put_be64(dest + 8, w->min_update_index);
 	put_be64(dest + 16, w->max_update_index);
 	if (writer_version(w) == 2) {
-		put_be32(dest + 24, w->opts.hash_id);
+		uint32_t hash_id;
+
+		switch (w->opts.hash_id) {
+		case REFTABLE_HASH_SHA1:
+			hash_id = REFTABLE_FORMAT_ID_SHA1;
+			break;
+		case REFTABLE_HASH_SHA256:
+			hash_id = REFTABLE_FORMAT_ID_SHA256;
+			break;
+		default:
+			return -1;
+		}
+
+		put_be32(dest + 24, hash_id);
 	}
+
 	return header_size(writer_version(w));
 }
 
diff --git a/t/helper/test-reftable.c b/t/helper/test-reftable.c
index 5c8849d115..3c72ed985b 100644
--- a/t/helper/test-reftable.c
+++ b/t/helper/test-reftable.c
@@ -156,7 +156,7 @@ int cmd__dump_reftable(int argc, const char **argv)
 	int opt_dump_blocks = 0;
 	int opt_dump_table = 0;
 	int opt_dump_stack = 0;
-	uint32_t opt_hash_id = GIT_SHA1_FORMAT_ID;
+	uint32_t opt_hash_id = REFTABLE_HASH_SHA1;
 	const char *arg = NULL, *argv0 = argv[0];
 
 	for (; argc > 1; argv++, argc--)
@@ -167,7 +167,7 @@ int cmd__dump_reftable(int argc, const char **argv)
 		else if (!strcmp("-t", argv[1]))
 			opt_dump_table = 1;
 		else if (!strcmp("-6", argv[1]))
-			opt_hash_id = GIT_SHA256_FORMAT_ID;
+			opt_hash_id = REFTABLE_HASH_SHA256;
 		else if (!strcmp("-s", argv[1]))
 			opt_dump_stack = 1;
 		else if (!strcmp("-?", argv[1]) || !strcmp("-h", argv[1])) {
diff --git a/t/unit-tests/lib-reftable.c b/t/unit-tests/lib-reftable.c
index 2ddf480588..d795dfb7c9 100644
--- a/t/unit-tests/lib-reftable.c
+++ b/t/unit-tests/lib-reftable.c
@@ -2,8 +2,9 @@
 #include "test-lib.h"
 #include "reftable/constants.h"
 #include "reftable/writer.h"
+#include "strbuf.h"
 
-void t_reftable_set_hash(uint8_t *p, int i, uint32_t id)
+void t_reftable_set_hash(uint8_t *p, int i, enum reftable_hash id)
 {
 	memset(p, (uint8_t)i, hash_size(id));
 }
@@ -82,7 +83,7 @@ void t_reftable_write_to_buf(struct reftable_buf *buf,
 		size_t off = i * (opts.block_size ? opts.block_size
 						  : DEFAULT_BLOCK_SIZE);
 		if (!off)
-			off = header_size(opts.hash_id == GIT_SHA256_FORMAT_ID ? 2 : 1);
+			off = header_size(opts.hash_id == REFTABLE_HASH_SHA256 ? 2 : 1);
 		check_char(buf->buf[off], ==, 'r');
 	}
 
diff --git a/t/unit-tests/lib-reftable.h b/t/unit-tests/lib-reftable.h
index d4950fed3d..e4c360fa7e 100644
--- a/t/unit-tests/lib-reftable.h
+++ b/t/unit-tests/lib-reftable.h
@@ -6,7 +6,7 @@
 
 struct reftable_buf;
 
-void t_reftable_set_hash(uint8_t *p, int i, uint32_t id);
+void t_reftable_set_hash(uint8_t *p, int i, enum reftable_hash id);
 
 struct reftable_writer *t_reftable_strbuf_writer(struct reftable_buf *buf,
 						 struct reftable_write_options *opts);
diff --git a/t/unit-tests/t-reftable-block.c b/t/unit-tests/t-reftable-block.c
index f9af907117..22040aeefa 100644
--- a/t/unit-tests/t-reftable-block.c
+++ b/t/unit-tests/t-reftable-block.c
@@ -11,6 +11,7 @@ https://developers.google.com/open-source/licenses/bsd
 #include "reftable/blocksource.h"
 #include "reftable/constants.h"
 #include "reftable/reftable-error.h"
+#include "strbuf.h"
 
 static void t_ref_block_read_write(void)
 {
@@ -36,7 +37,7 @@ static void t_ref_block_read_write(void)
 	block.len = block_size;
 	block_source_from_buf(&block.source ,&buf);
 	ret = block_writer_init(&bw, BLOCK_TYPE_REF, block.data, block_size,
-				header_off, hash_size(GIT_SHA1_FORMAT_ID));
+				header_off, hash_size(REFTABLE_HASH_SHA1));
 	check(!ret);
 
 	rec.u.ref.refname = (char *) "";
@@ -47,7 +48,7 @@ static void t_ref_block_read_write(void)
 	for (i = 0; i < N; i++) {
 		rec.u.ref.refname = xstrfmt("branch%02"PRIuMAX, (uintmax_t)i);
 		rec.u.ref.value_type = REFTABLE_REF_VAL1;
-		memset(rec.u.ref.value.val1, i, GIT_SHA1_RAWSZ);
+		memset(rec.u.ref.value.val1, i, REFTABLE_HASH_SIZE_SHA1);
 
 		recs[i] = rec;
 		ret = block_writer_add(&bw, &rec);
@@ -61,7 +62,7 @@ static void t_ref_block_read_write(void)
 
 	block_writer_release(&bw);
 
-	block_reader_init(&br, &block, header_off, block_size, GIT_SHA1_RAWSZ);
+	block_reader_init(&br, &block, header_off, block_size, REFTABLE_HASH_SIZE_SHA1);
 
 	block_iter_seek_start(&it, &br);
 
@@ -72,7 +73,7 @@ static void t_ref_block_read_write(void)
 			check_int(i, ==, N);
 			break;
 		}
-		check(reftable_record_equal(&recs[i], &rec, GIT_SHA1_RAWSZ));
+		check(reftable_record_equal(&recs[i], &rec, REFTABLE_HASH_SIZE_SHA1));
 	}
 
 	for (i = 0; i < N; i++) {
@@ -85,7 +86,7 @@ static void t_ref_block_read_write(void)
 		ret = block_iter_next(&it, &rec);
 		check_int(ret, ==, 0);
 
-		check(reftable_record_equal(&recs[i], &rec, GIT_SHA1_RAWSZ));
+		check(reftable_record_equal(&recs[i], &rec, REFTABLE_HASH_SIZE_SHA1));
 
 		want.len--;
 		ret = block_iter_seek_key(&it, &br, &want);
@@ -93,7 +94,7 @@ static void t_ref_block_read_write(void)
 
 		ret = block_iter_next(&it, &rec);
 		check_int(ret, ==, 0);
-		check(reftable_record_equal(&recs[10 * (i / 10)], &rec, GIT_SHA1_RAWSZ));
+		check(reftable_record_equal(&recs[10 * (i / 10)], &rec, REFTABLE_HASH_SIZE_SHA1));
 	}
 
 	block_reader_release(&br);
@@ -130,7 +131,7 @@ static void t_log_block_read_write(void)
 	block.len = block_size;
 	block_source_from_buf(&block.source ,&buf);
 	ret = block_writer_init(&bw, BLOCK_TYPE_LOG, block.data, block_size,
-				header_off, hash_size(GIT_SHA1_FORMAT_ID));
+				header_off, hash_size(REFTABLE_HASH_SHA1));
 	check(!ret);
 
 	for (i = 0; i < N; i++) {
@@ -150,7 +151,7 @@ static void t_log_block_read_write(void)
 
 	block_writer_release(&bw);
 
-	block_reader_init(&br, &block, header_off, block_size, GIT_SHA1_RAWSZ);
+	block_reader_init(&br, &block, header_off, block_size, REFTABLE_HASH_SIZE_SHA1);
 
 	block_iter_seek_start(&it, &br);
 
@@ -161,7 +162,7 @@ static void t_log_block_read_write(void)
 			check_int(i, ==, N);
 			break;
 		}
-		check(reftable_record_equal(&recs[i], &rec, GIT_SHA1_RAWSZ));
+		check(reftable_record_equal(&recs[i], &rec, REFTABLE_HASH_SIZE_SHA1));
 	}
 
 	for (i = 0; i < N; i++) {
@@ -175,7 +176,7 @@ static void t_log_block_read_write(void)
 		ret = block_iter_next(&it, &rec);
 		check_int(ret, ==, 0);
 
-		check(reftable_record_equal(&recs[i], &rec, GIT_SHA1_RAWSZ));
+		check(reftable_record_equal(&recs[i], &rec, REFTABLE_HASH_SIZE_SHA1));
 
 		want.len--;
 		ret = block_iter_seek_key(&it, &br, &want);
@@ -183,7 +184,7 @@ static void t_log_block_read_write(void)
 
 		ret = block_iter_next(&it, &rec);
 		check_int(ret, ==, 0);
-		check(reftable_record_equal(&recs[10 * (i / 10)], &rec, GIT_SHA1_RAWSZ));
+		check(reftable_record_equal(&recs[10 * (i / 10)], &rec, REFTABLE_HASH_SIZE_SHA1));
 	}
 
 	block_reader_release(&br);
@@ -220,7 +221,7 @@ static void t_obj_block_read_write(void)
 	block.len = block_size;
 	block_source_from_buf(&block.source, &buf);
 	ret = block_writer_init(&bw, BLOCK_TYPE_OBJ, block.data, block_size,
-				header_off, hash_size(GIT_SHA1_FORMAT_ID));
+				header_off, hash_size(REFTABLE_HASH_SHA1));
 	check(!ret);
 
 	for (i = 0; i < N; i++) {
@@ -242,7 +243,7 @@ static void t_obj_block_read_write(void)
 
 	block_writer_release(&bw);
 
-	block_reader_init(&br, &block, header_off, block_size, GIT_SHA1_RAWSZ);
+	block_reader_init(&br, &block, header_off, block_size, REFTABLE_HASH_SIZE_SHA1);
 
 	block_iter_seek_start(&it, &br);
 
@@ -253,7 +254,7 @@ static void t_obj_block_read_write(void)
 			check_int(i, ==, N);
 			break;
 		}
-		check(reftable_record_equal(&recs[i], &rec, GIT_SHA1_RAWSZ));
+		check(reftable_record_equal(&recs[i], &rec, REFTABLE_HASH_SIZE_SHA1));
 	}
 
 	for (i = 0; i < N; i++) {
@@ -266,7 +267,7 @@ static void t_obj_block_read_write(void)
 		ret = block_iter_next(&it, &rec);
 		check_int(ret, ==, 0);
 
-		check(reftable_record_equal(&recs[i], &rec, GIT_SHA1_RAWSZ));
+		check(reftable_record_equal(&recs[i], &rec, REFTABLE_HASH_SIZE_SHA1));
 	}
 
 	block_reader_release(&br);
@@ -304,7 +305,7 @@ static void t_index_block_read_write(void)
 	block.len = block_size;
 	block_source_from_buf(&block.source, &buf);
 	ret = block_writer_init(&bw, BLOCK_TYPE_INDEX, block.data, block_size,
-				header_off, hash_size(GIT_SHA1_FORMAT_ID));
+				header_off, hash_size(REFTABLE_HASH_SHA1));
 	check(!ret);
 
 	for (i = 0; i < N; i++) {
@@ -326,7 +327,7 @@ static void t_index_block_read_write(void)
 
 	block_writer_release(&bw);
 
-	block_reader_init(&br, &block, header_off, block_size, GIT_SHA1_RAWSZ);
+	block_reader_init(&br, &block, header_off, block_size, REFTABLE_HASH_SIZE_SHA1);
 
 	block_iter_seek_start(&it, &br);
 
@@ -337,7 +338,7 @@ static void t_index_block_read_write(void)
 			check_int(i, ==, N);
 			break;
 		}
-		check(reftable_record_equal(&recs[i], &rec, GIT_SHA1_RAWSZ));
+		check(reftable_record_equal(&recs[i], &rec, REFTABLE_HASH_SIZE_SHA1));
 	}
 
 	for (i = 0; i < N; i++) {
@@ -350,7 +351,7 @@ static void t_index_block_read_write(void)
 		ret = block_iter_next(&it, &rec);
 		check_int(ret, ==, 0);
 
-		check(reftable_record_equal(&recs[i], &rec, GIT_SHA1_RAWSZ));
+		check(reftable_record_equal(&recs[i], &rec, REFTABLE_HASH_SIZE_SHA1));
 
 		want.len--;
 		ret = block_iter_seek_key(&it, &br, &want);
@@ -358,7 +359,7 @@ static void t_index_block_read_write(void)
 
 		ret = block_iter_next(&it, &rec);
 		check_int(ret, ==, 0);
-		check(reftable_record_equal(&recs[10 * (i / 10)], &rec, GIT_SHA1_RAWSZ));
+		check(reftable_record_equal(&recs[10 * (i / 10)], &rec, REFTABLE_HASH_SIZE_SHA1));
 	}
 
 	block_reader_release(&br);
diff --git a/t/unit-tests/t-reftable-merged.c b/t/unit-tests/t-reftable-merged.c
index 4c25ee5334..2591b5e597 100644
--- a/t/unit-tests/t-reftable-merged.c
+++ b/t/unit-tests/t-reftable-merged.c
@@ -42,7 +42,7 @@ merged_table_from_records(struct reftable_ref_record **refs,
 		check(!err);
 	}
 
-	err = reftable_merged_table_new(&mt, *readers, n, GIT_SHA1_FORMAT_ID);
+	err = reftable_merged_table_new(&mt, *readers, n, REFTABLE_HASH_SHA1);
 	check(!err);
 	return mt;
 }
@@ -91,7 +91,7 @@ static void t_merged_single_record(void)
 
 	err = reftable_iterator_next_ref(&it, &ref);
 	check(!err);
-	check(reftable_ref_record_equal(&r2[0], &ref, GIT_SHA1_RAWSZ));
+	check(reftable_ref_record_equal(&r2[0], &ref, REFTABLE_HASH_SIZE_SHA1));
 	reftable_ref_record_release(&ref);
 	reftable_iterator_destroy(&it);
 	readers_destroy(readers, 3);
@@ -168,7 +168,7 @@ static void t_merged_refs(void)
 	check(!err);
 	err = reftable_iterator_seek_ref(&it, "a");
 	check(!err);
-	check_int(reftable_merged_table_hash_id(mt), ==, GIT_SHA1_FORMAT_ID);
+	check_int(reftable_merged_table_hash_id(mt), ==, REFTABLE_HASH_SHA1);
 	check_int(reftable_merged_table_min_update_index(mt), ==, 1);
 	check_int(reftable_merged_table_max_update_index(mt), ==, 3);
 
@@ -186,7 +186,7 @@ static void t_merged_refs(void)
 	check_int(ARRAY_SIZE(want), ==, len);
 	for (i = 0; i < len; i++)
 		check(reftable_ref_record_equal(want[i], &out[i],
-						 GIT_SHA1_RAWSZ));
+						 REFTABLE_HASH_SIZE_SHA1));
 	for (i = 0; i < len; i++)
 		reftable_ref_record_release(&out[i]);
 	reftable_free(out);
@@ -252,12 +252,12 @@ static void t_merged_seek_multiple_times(void)
 
 		err = reftable_iterator_next_ref(&it, &rec);
 		check(!err);
-		err = reftable_ref_record_equal(&rec, &r1[1], GIT_SHA1_RAWSZ);
+		err = reftable_ref_record_equal(&rec, &r1[1], REFTABLE_HASH_SIZE_SHA1);
 		check(err == 1);
 
 		err = reftable_iterator_next_ref(&it, &rec);
 		check(!err);
-		err = reftable_ref_record_equal(&rec, &r2[1], GIT_SHA1_RAWSZ);
+		err = reftable_ref_record_equal(&rec, &r2[1], REFTABLE_HASH_SIZE_SHA1);
 		check(err == 1);
 
 		err = reftable_iterator_next_ref(&it, &rec);
@@ -300,7 +300,7 @@ merged_table_from_log_records(struct reftable_log_record **logs,
 		check(!err);
 	}
 
-	err = reftable_merged_table_new(&mt, *readers, n, GIT_SHA1_FORMAT_ID);
+	err = reftable_merged_table_new(&mt, *readers, n, REFTABLE_HASH_SHA1);
 	check(!err);
 	return mt;
 }
@@ -377,7 +377,7 @@ static void t_merged_logs(void)
 	check(!err);
 	err = reftable_iterator_seek_log(&it, "a");
 	check(!err);
-	check_int(reftable_merged_table_hash_id(mt), ==, GIT_SHA1_FORMAT_ID);
+	check_int(reftable_merged_table_hash_id(mt), ==, REFTABLE_HASH_SHA1);
 	check_int(reftable_merged_table_min_update_index(mt), ==, 1);
 	check_int(reftable_merged_table_max_update_index(mt), ==, 3);
 
@@ -395,7 +395,7 @@ static void t_merged_logs(void)
 	check_int(ARRAY_SIZE(want), ==, len);
 	for (i = 0; i < len; i++)
 		check(reftable_log_record_equal(want[i], &out[i],
-						 GIT_SHA1_RAWSZ));
+						 REFTABLE_HASH_SIZE_SHA1));
 
 	err = merged_table_init_iter(mt, &it, BLOCK_TYPE_LOG);
 	check(!err);
@@ -404,7 +404,7 @@ static void t_merged_logs(void)
 	reftable_log_record_release(&out[0]);
 	err = reftable_iterator_next_log(&it, &out[0]);
 	check(!err);
-	check(reftable_log_record_equal(&out[0], &r3[0], GIT_SHA1_RAWSZ));
+	check(reftable_log_record_equal(&out[0], &r3[0], REFTABLE_HASH_SIZE_SHA1));
 	reftable_iterator_destroy(&it);
 
 	for (i = 0; i < len; i++)
@@ -448,11 +448,11 @@ static void t_default_write_opts(void)
 	check(!err);
 
 	hash_id = reftable_reader_hash_id(rd);
-	check_int(hash_id, ==, GIT_SHA1_FORMAT_ID);
+	check_int(hash_id, ==, REFTABLE_HASH_SHA1);
 
-	err = reftable_merged_table_new(&merged, &rd, 1, GIT_SHA256_FORMAT_ID);
+	err = reftable_merged_table_new(&merged, &rd, 1, REFTABLE_HASH_SHA256);
 	check_int(err, ==, REFTABLE_FORMAT_ERROR);
-	err = reftable_merged_table_new(&merged, &rd, 1, GIT_SHA1_FORMAT_ID);
+	err = reftable_merged_table_new(&merged, &rd, 1, REFTABLE_HASH_SHA1);
 	check(!err);
 
 	reftable_reader_decref(rd);
diff --git a/t/unit-tests/t-reftable-pq.c b/t/unit-tests/t-reftable-pq.c
index ada4c19f18..f3f8a0cdf3 100644
--- a/t/unit-tests/t-reftable-pq.c
+++ b/t/unit-tests/t-reftable-pq.c
@@ -9,6 +9,7 @@ https://developers.google.com/open-source/licenses/bsd
 #include "test-lib.h"
 #include "reftable/constants.h"
 #include "reftable/pq.h"
+#include "strbuf.h"
 
 static void merged_iter_pqueue_check(const struct merged_iter_pqueue *pq)
 {
@@ -132,7 +133,7 @@ static void t_merged_iter_pqueue_top(void)
 
 		merged_iter_pqueue_check(&pq);
 		check(pq_entry_equal(&top, &e));
-		check(reftable_record_equal(top.rec, &recs[i], GIT_SHA1_RAWSZ));
+		check(reftable_record_equal(top.rec, &recs[i], REFTABLE_HASH_SIZE_SHA1));
 		for (size_t j = 0; i < pq.len; j++) {
 			check(pq_less(&top, &pq.heap[j]));
 			check_int(top.index, >, j);
diff --git a/t/unit-tests/t-reftable-reader.c b/t/unit-tests/t-reftable-reader.c
index 19cb53b641..546df6005e 100644
--- a/t/unit-tests/t-reftable-reader.c
+++ b/t/unit-tests/t-reftable-reader.c
@@ -31,7 +31,7 @@ static int t_reader_seek_once(void)
 	ret = reftable_iterator_next_ref(&it, &ref);
 	check(!ret);
 
-	ret = reftable_ref_record_equal(&ref, &records[0], GIT_SHA1_RAWSZ);
+	ret = reftable_ref_record_equal(&ref, &records[0], REFTABLE_HASH_SIZE_SHA1);
 	check_int(ret, ==, 1);
 
 	ret = reftable_iterator_next_ref(&it, &ref);
@@ -74,7 +74,7 @@ static int t_reader_reseek(void)
 		ret = reftable_iterator_next_ref(&it, &ref);
 		check(!ret);
 
-		ret = reftable_ref_record_equal(&ref, &records[0], GIT_SHA1_RAWSZ);
+		ret = reftable_ref_record_equal(&ref, &records[0], REFTABLE_HASH_SIZE_SHA1);
 		check_int(ret, ==, 1);
 
 		ret = reftable_iterator_next_ref(&it, &ref);
diff --git a/t/unit-tests/t-reftable-readwrite.c b/t/unit-tests/t-reftable-readwrite.c
index d279b86df0..91c881aedf 100644
--- a/t/unit-tests/t-reftable-readwrite.c
+++ b/t/unit-tests/t-reftable-readwrite.c
@@ -13,6 +13,7 @@ https://developers.google.com/open-source/licenses/bsd
 #include "reftable/reader.h"
 #include "reftable/reftable-error.h"
 #include "reftable/reftable-writer.h"
+#include "strbuf.h"
 
 static const int update_index = 5;
 
@@ -41,7 +42,7 @@ static void t_buffer(void)
 }
 
 static void write_table(char ***names, struct reftable_buf *buf, int N,
-			int block_size, uint32_t hash_id)
+			int block_size, enum reftable_hash hash_id)
 {
 	struct reftable_write_options opts = {
 		.block_size = block_size,
@@ -62,7 +63,7 @@ static void write_table(char ***names, struct reftable_buf *buf, int N,
 		refs[i].refname = (*names)[i] = xstrfmt("refs/heads/branch%02d", i);
 		refs[i].update_index = update_index;
 		refs[i].value_type = REFTABLE_REF_VAL1;
-		t_reftable_set_hash(refs[i].value.val1, i, GIT_SHA1_FORMAT_ID);
+		t_reftable_set_hash(refs[i].value.val1, i, REFTABLE_HASH_SHA1);
 	}
 
 	for (i = 0; i < N; i++) {
@@ -70,7 +71,7 @@ static void write_table(char ***names, struct reftable_buf *buf, int N,
 		logs[i].update_index = update_index;
 		logs[i].value_type = REFTABLE_LOG_UPDATE;
 		t_reftable_set_hash(logs[i].value.update.new_hash, i,
-				    GIT_SHA1_FORMAT_ID);
+				    REFTABLE_HASH_SHA1);
 		logs[i].value.update.message = (char *) "message";
 	}
 
@@ -104,7 +105,7 @@ static void t_log_buffer_size(void)
 	/* This tests buffer extension for log compression. Must use a random
 	   hash, to ensure that the compressed part is larger than the original.
 	*/
-	for (i = 0; i < GIT_SHA1_RAWSZ; i++) {
+	for (i = 0; i < REFTABLE_HASH_SIZE_SHA1; i++) {
 		log.value.update.old_hash[i] = (uint8_t)(git_rand() % 256);
 		log.value.update.new_hash[i] = (uint8_t)(git_rand() % 256);
 	}
@@ -191,9 +192,9 @@ static void t_log_write_read(void)
 		log.update_index = i;
 		log.value_type = REFTABLE_LOG_UPDATE;
 		t_reftable_set_hash(log.value.update.old_hash, i,
-				    GIT_SHA1_FORMAT_ID);
+				    REFTABLE_HASH_SHA1);
 		t_reftable_set_hash(log.value.update.new_hash, i + 1,
-				    GIT_SHA1_FORMAT_ID);
+				    REFTABLE_HASH_SHA1);
 
 		err = reftable_writer_add_log(w, &log);
 		check(!err);
@@ -326,7 +327,7 @@ static void t_table_read_write_sequential(void)
 	int err = 0;
 	int j = 0;
 
-	write_table(&names, &buf, N, 256, GIT_SHA1_FORMAT_ID);
+	write_table(&names, &buf, N, 256, REFTABLE_HASH_SHA1);
 
 	block_source_from_buf(&source, &buf);
 
@@ -361,7 +362,7 @@ static void t_table_write_small_table(void)
 	char **names;
 	struct reftable_buf buf = REFTABLE_BUF_INIT;
 	int N = 1;
-	write_table(&names, &buf, N, 4096, GIT_SHA1_FORMAT_ID);
+	write_table(&names, &buf, N, 4096, REFTABLE_HASH_SHA1);
 	check_int(buf.len, <, 200);
 	reftable_buf_release(&buf);
 	free_names(names);
@@ -378,7 +379,7 @@ static void t_table_read_api(void)
 	struct reftable_log_record log = { 0 };
 	struct reftable_iterator it = { 0 };
 
-	write_table(&names, &buf, N, 256, GIT_SHA1_FORMAT_ID);
+	write_table(&names, &buf, N, 256, REFTABLE_HASH_SHA1);
 
 	block_source_from_buf(&source, &buf);
 
@@ -400,7 +401,7 @@ static void t_table_read_api(void)
 	reftable_buf_release(&buf);
 }
 
-static void t_table_read_write_seek(int index, int hash_id)
+static void t_table_read_write_seek(int index, enum reftable_hash hash_id)
 {
 	char **names;
 	struct reftable_buf buf = REFTABLE_BUF_INIT;
@@ -467,24 +468,24 @@ static void t_table_read_write_seek(int index, int hash_id)
 
 static void t_table_read_write_seek_linear(void)
 {
-	t_table_read_write_seek(0, GIT_SHA1_FORMAT_ID);
+	t_table_read_write_seek(0, REFTABLE_HASH_SHA1);
 }
 
 static void t_table_read_write_seek_linear_sha256(void)
 {
-	t_table_read_write_seek(0, GIT_SHA256_FORMAT_ID);
+	t_table_read_write_seek(0, REFTABLE_HASH_SHA256);
 }
 
 static void t_table_read_write_seek_index(void)
 {
-	t_table_read_write_seek(1, GIT_SHA1_FORMAT_ID);
+	t_table_read_write_seek(1, REFTABLE_HASH_SHA1);
 }
 
 static void t_table_refs_for(int indexed)
 {
 	char **want_names;
 	int want_names_len = 0;
-	uint8_t want_hash[GIT_SHA1_RAWSZ];
+	uint8_t want_hash[REFTABLE_HASH_SIZE_SHA1];
 
 	struct reftable_write_options opts = {
 		.block_size = 256,
@@ -500,10 +501,10 @@ static void t_table_refs_for(int indexed)
 	want_names = reftable_calloc(N + 1, sizeof(*want_names));
 	check(want_names != NULL);
 
-	t_reftable_set_hash(want_hash, 4, GIT_SHA1_FORMAT_ID);
+	t_reftable_set_hash(want_hash, 4, REFTABLE_HASH_SHA1);
 
 	for (i = 0; i < N; i++) {
-		uint8_t hash[GIT_SHA1_RAWSZ];
+		uint8_t hash[REFTABLE_HASH_SIZE_SHA1];
 		char fill[51] = { 0 };
 		char name[100];
 		struct reftable_ref_record ref = { 0 };
@@ -517,9 +518,9 @@ static void t_table_refs_for(int indexed)
 
 		ref.value_type = REFTABLE_REF_VAL2;
 		t_reftable_set_hash(ref.value.val2.value, i / 4,
-				    GIT_SHA1_FORMAT_ID);
+				    REFTABLE_HASH_SHA1);
 		t_reftable_set_hash(ref.value.val2.target_value, 3 + i / 4,
-				    GIT_SHA1_FORMAT_ID);
+				    REFTABLE_HASH_SHA1);
 
 		/* 80 bytes / entry, so 3 entries per block. Yields 17
 		 */
@@ -527,8 +528,8 @@ static void t_table_refs_for(int indexed)
 		n = reftable_writer_add_ref(w, &ref);
 		check_int(n, ==, 0);
 
-		if (!memcmp(ref.value.val2.value, want_hash, GIT_SHA1_RAWSZ) ||
-		    !memcmp(ref.value.val2.target_value, want_hash, GIT_SHA1_RAWSZ))
+		if (!memcmp(ref.value.val2.value, want_hash, REFTABLE_HASH_SIZE_SHA1) ||
+		    !memcmp(ref.value.val2.target_value, want_hash, REFTABLE_HASH_SIZE_SHA1))
 			want_names[want_names_len++] = xstrdup(name);
 	}
 
diff --git a/t/unit-tests/t-reftable-record.c b/t/unit-tests/t-reftable-record.c
index eb98bf2da9..42bc64cec8 100644
--- a/t/unit-tests/t-reftable-record.c
+++ b/t/unit-tests/t-reftable-record.c
@@ -7,6 +7,7 @@
 */
 
 #include "test-lib.h"
+#include "reftable/basics.h"
 #include "reftable/constants.h"
 #include "reftable/record.h"
 
@@ -17,10 +18,10 @@ static void t_copy(struct reftable_record *rec)
 
 	typ = reftable_record_type(rec);
 	reftable_record_init(&copy, typ);
-	reftable_record_copy_from(&copy, rec, GIT_SHA1_RAWSZ);
+	reftable_record_copy_from(&copy, rec, REFTABLE_HASH_SIZE_SHA1);
 	/* do it twice to catch memory leaks */
-	reftable_record_copy_from(&copy, rec, GIT_SHA1_RAWSZ);
-	check(reftable_record_equal(rec, &copy, GIT_SHA1_RAWSZ));
+	reftable_record_copy_from(&copy, rec, REFTABLE_HASH_SIZE_SHA1);
+	check(reftable_record_equal(rec, &copy, REFTABLE_HASH_SIZE_SHA1));
 
 	reftable_record_release(&copy);
 }
@@ -59,7 +60,7 @@ static void t_varint_roundtrip(void)
 
 static void set_hash(uint8_t *h, int j)
 {
-	for (int i = 0; i < hash_size(GIT_SHA1_FORMAT_ID); i++)
+	for (int i = 0; i < hash_size(REFTABLE_HASH_SHA1); i++)
 		h[i] = (j >> i) & 0xff;
 }
 
@@ -84,14 +85,14 @@ static void t_reftable_ref_record_comparison(void)
 		},
 	};
 
-	check(!reftable_record_equal(&in[0], &in[1], GIT_SHA1_RAWSZ));
+	check(!reftable_record_equal(&in[0], &in[1], REFTABLE_HASH_SIZE_SHA1));
 	check(!reftable_record_cmp(&in[0], &in[1]));
 
-	check(!reftable_record_equal(&in[1], &in[2], GIT_SHA1_RAWSZ));
+	check(!reftable_record_equal(&in[1], &in[2], REFTABLE_HASH_SIZE_SHA1));
 	check_int(reftable_record_cmp(&in[1], &in[2]), >, 0);
 
 	in[1].u.ref.value_type = in[0].u.ref.value_type;
-	check(reftable_record_equal(&in[0], &in[1], GIT_SHA1_RAWSZ));
+	check(reftable_record_equal(&in[0], &in[1], REFTABLE_HASH_SIZE_SHA1));
 	check(!reftable_record_cmp(&in[0], &in[1]));
 }
 
@@ -155,15 +156,15 @@ static void t_reftable_ref_record_roundtrip(void)
 		check_int(reftable_record_is_deletion(&in), ==, i == REFTABLE_REF_DELETION);
 
 		reftable_record_key(&in, &key);
-		n = reftable_record_encode(&in, dest, GIT_SHA1_RAWSZ);
+		n = reftable_record_encode(&in, dest, REFTABLE_HASH_SIZE_SHA1);
 		check_int(n, >, 0);
 
 		/* decode into a non-zero reftable_record to test for leaks. */
-		m = reftable_record_decode(&out, key, i, dest, GIT_SHA1_RAWSZ, &scratch);
+		m = reftable_record_decode(&out, key, i, dest, REFTABLE_HASH_SIZE_SHA1, &scratch);
 		check_int(n, ==, m);
 
 		check(reftable_ref_record_equal(&in.u.ref, &out.u.ref,
-						 GIT_SHA1_RAWSZ));
+						 REFTABLE_HASH_SIZE_SHA1));
 		reftable_record_release(&in);
 
 		reftable_buf_release(&key);
@@ -193,15 +194,15 @@ static void t_reftable_log_record_comparison(void)
 		},
 	};
 
-	check(!reftable_record_equal(&in[0], &in[1], GIT_SHA1_RAWSZ));
-	check(!reftable_record_equal(&in[1], &in[2], GIT_SHA1_RAWSZ));
+	check(!reftable_record_equal(&in[0], &in[1], REFTABLE_HASH_SIZE_SHA1));
+	check(!reftable_record_equal(&in[1], &in[2], REFTABLE_HASH_SIZE_SHA1));
 	check_int(reftable_record_cmp(&in[1], &in[2]), >, 0);
 	/* comparison should be reversed for equal keys, because
 	 * comparison is now performed on the basis of update indices */
 	check_int(reftable_record_cmp(&in[0], &in[1]), <, 0);
 
 	in[1].u.log.update_index = in[0].u.log.update_index;
-	check(reftable_record_equal(&in[0], &in[1], GIT_SHA1_RAWSZ));
+	check(reftable_record_equal(&in[0], &in[1], REFTABLE_HASH_SIZE_SHA1));
 	check(!reftable_record_cmp(&in[0], &in[1]));
 }
 
@@ -303,15 +304,15 @@ static void t_reftable_log_record_roundtrip(void)
 
 		reftable_record_key(&rec, &key);
 
-		n = reftable_record_encode(&rec, dest, GIT_SHA1_RAWSZ);
+		n = reftable_record_encode(&rec, dest, REFTABLE_HASH_SIZE_SHA1);
 		check_int(n, >=, 0);
 		valtype = reftable_record_val_type(&rec);
 		m = reftable_record_decode(&out, key, valtype, dest,
-					   GIT_SHA1_RAWSZ, &scratch);
+					   REFTABLE_HASH_SIZE_SHA1, &scratch);
 		check_int(n, ==, m);
 
 		check(reftable_log_record_equal(&in[i], &out.u.log,
-						 GIT_SHA1_RAWSZ));
+						 REFTABLE_HASH_SIZE_SHA1));
 		reftable_log_record_release(&in[i]);
 		reftable_buf_release(&key);
 		reftable_record_release(&out);
@@ -380,20 +381,20 @@ static void t_reftable_obj_record_comparison(void)
 		},
 	};
 
-	check(!reftable_record_equal(&in[0], &in[1], GIT_SHA1_RAWSZ));
+	check(!reftable_record_equal(&in[0], &in[1], REFTABLE_HASH_SIZE_SHA1));
 	check(!reftable_record_cmp(&in[0], &in[1]));
 
-	check(!reftable_record_equal(&in[1], &in[2], GIT_SHA1_RAWSZ));
+	check(!reftable_record_equal(&in[1], &in[2], REFTABLE_HASH_SIZE_SHA1));
 	check_int(reftable_record_cmp(&in[1], &in[2]), >, 0);
 
 	in[1].u.obj.offset_len = in[0].u.obj.offset_len;
-	check(reftable_record_equal(&in[0], &in[1], GIT_SHA1_RAWSZ));
+	check(reftable_record_equal(&in[0], &in[1], REFTABLE_HASH_SIZE_SHA1));
 	check(!reftable_record_cmp(&in[0], &in[1]));
 }
 
 static void t_reftable_obj_record_roundtrip(void)
 {
-	uint8_t testHash1[GIT_SHA1_RAWSZ] = { 1, 2, 3, 4, 0 };
+	uint8_t testHash1[REFTABLE_HASH_SIZE_SHA1] = { 1, 2, 3, 4, 0 };
 	uint64_t till9[] = { 1, 2, 3, 4, 500, 600, 700, 800, 9000 };
 	struct reftable_obj_record recs[3] = {
 		{
@@ -435,14 +436,14 @@ static void t_reftable_obj_record_roundtrip(void)
 		check(!reftable_record_is_deletion(&in));
 		t_copy(&in);
 		reftable_record_key(&in, &key);
-		n = reftable_record_encode(&in, dest, GIT_SHA1_RAWSZ);
+		n = reftable_record_encode(&in, dest, REFTABLE_HASH_SIZE_SHA1);
 		check_int(n, >, 0);
 		extra = reftable_record_val_type(&in);
 		m = reftable_record_decode(&out, key, extra, dest,
-					   GIT_SHA1_RAWSZ, &scratch);
+					   REFTABLE_HASH_SIZE_SHA1, &scratch);
 		check_int(n, ==, m);
 
-		check(reftable_record_equal(&in, &out, GIT_SHA1_RAWSZ));
+		check(reftable_record_equal(&in, &out, REFTABLE_HASH_SIZE_SHA1));
 		reftable_buf_release(&key);
 		reftable_record_release(&out);
 	}
@@ -473,14 +474,14 @@ static void t_reftable_index_record_comparison(void)
 	check(!reftable_buf_addstr(&in[1].u.idx.last_key, "refs/heads/master"));
 	check(!reftable_buf_addstr(&in[2].u.idx.last_key, "refs/heads/branch"));
 
-	check(!reftable_record_equal(&in[0], &in[1], GIT_SHA1_RAWSZ));
+	check(!reftable_record_equal(&in[0], &in[1], REFTABLE_HASH_SIZE_SHA1));
 	check(!reftable_record_cmp(&in[0], &in[1]));
 
-	check(!reftable_record_equal(&in[1], &in[2], GIT_SHA1_RAWSZ));
+	check(!reftable_record_equal(&in[1], &in[2], REFTABLE_HASH_SIZE_SHA1));
 	check_int(reftable_record_cmp(&in[1], &in[2]), >, 0);
 
 	in[1].u.idx.offset = in[0].u.idx.offset;
-	check(reftable_record_equal(&in[0], &in[1], GIT_SHA1_RAWSZ));
+	check(reftable_record_equal(&in[0], &in[1], REFTABLE_HASH_SIZE_SHA1));
 	check(!reftable_record_cmp(&in[0], &in[1]));
 
 	for (size_t i = 0; i < ARRAY_SIZE(in); i++)
@@ -516,15 +517,15 @@ static void t_reftable_index_record_roundtrip(void)
 
 	check(!reftable_record_is_deletion(&in));
 	check(!reftable_buf_cmp(&key, &in.u.idx.last_key));
-	n = reftable_record_encode(&in, dest, GIT_SHA1_RAWSZ);
+	n = reftable_record_encode(&in, dest, REFTABLE_HASH_SIZE_SHA1);
 	check_int(n, >, 0);
 
 	extra = reftable_record_val_type(&in);
-	m = reftable_record_decode(&out, key, extra, dest, GIT_SHA1_RAWSZ,
+	m = reftable_record_decode(&out, key, extra, dest, REFTABLE_HASH_SIZE_SHA1,
 				   &scratch);
 	check_int(m, ==, n);
 
-	check(reftable_record_equal(&in, &out, GIT_SHA1_RAWSZ));
+	check(reftable_record_equal(&in, &out, REFTABLE_HASH_SIZE_SHA1));
 
 	reftable_record_release(&out);
 	reftable_buf_release(&key);
diff --git a/t/unit-tests/t-reftable-stack.c b/t/unit-tests/t-reftable-stack.c
index 72f6747064..b2f6c1c37e 100644
--- a/t/unit-tests/t-reftable-stack.c
+++ b/t/unit-tests/t-reftable-stack.c
@@ -8,10 +8,13 @@ https://developers.google.com/open-source/licenses/bsd
 
 #include "test-lib.h"
 #include "lib-reftable.h"
+#include "dir.h"
 #include "reftable/merged.h"
 #include "reftable/reader.h"
 #include "reftable/reftable-error.h"
 #include "reftable/stack.h"
+#include "strbuf.h"
+#include "tempfile.h"
 #include <dirent.h>
 
 static void clear_dir(const char *dirname)
@@ -120,7 +123,7 @@ static void write_n_ref_tables(struct reftable_stack *st,
 
 		snprintf(buf, sizeof(buf), "refs/heads/branch-%04"PRIuMAX, (uintmax_t)i);
 		ref.refname = buf;
-		t_reftable_set_hash(ref.value.val1, i, GIT_SHA1_FORMAT_ID);
+		t_reftable_set_hash(ref.value.val1, i, REFTABLE_HASH_SHA1);
 
 		err = reftable_stack_add(st, &write_test_ref, &ref);
 		check(!err);
@@ -168,7 +171,7 @@ static void t_reftable_stack_add_one(void)
 
 	err = reftable_stack_read_ref(st, ref.refname, &dest);
 	check(!err);
-	check(reftable_ref_record_equal(&ref, &dest, GIT_SHA1_RAWSZ));
+	check(reftable_ref_record_equal(&ref, &dest, REFTABLE_HASH_SIZE_SHA1));
 	check_int(st->readers_len, >, 0);
 
 #ifndef GIT_WINDOWS_NATIVE
@@ -279,7 +282,7 @@ static void t_reftable_stack_transaction_api(void)
 	err = reftable_stack_read_ref(st, ref.refname, &dest);
 	check(!err);
 	check_int(REFTABLE_REF_SYMREF, ==, dest.value_type);
-	check(reftable_ref_record_equal(&ref, &dest, GIT_SHA1_RAWSZ));
+	check(reftable_ref_record_equal(&ref, &dest, REFTABLE_HASH_SIZE_SHA1));
 
 	reftable_ref_record_release(&dest);
 	reftable_stack_destroy(st);
@@ -339,7 +342,7 @@ static void t_reftable_stack_transaction_with_reload(void)
 	for (size_t i = 0; i < ARRAY_SIZE(refs); i++) {
 		err = reftable_stack_read_ref(st2, refs[i].refname, &ref);
 		check(!err);
-		check(reftable_ref_record_equal(&refs[i], &ref, GIT_SHA1_RAWSZ));
+		check(reftable_ref_record_equal(&refs[i], &ref, REFTABLE_HASH_SIZE_SHA1));
 	}
 
 	reftable_ref_record_release(&ref);
@@ -529,13 +532,13 @@ static void t_reftable_stack_add(void)
 		refs[i].refname = xstrdup(buf);
 		refs[i].update_index = i + 1;
 		refs[i].value_type = REFTABLE_REF_VAL1;
-		t_reftable_set_hash(refs[i].value.val1, i, GIT_SHA1_FORMAT_ID);
+		t_reftable_set_hash(refs[i].value.val1, i, REFTABLE_HASH_SHA1);
 
 		logs[i].refname = xstrdup(buf);
 		logs[i].update_index = N + i + 1;
 		logs[i].value_type = REFTABLE_LOG_UPDATE;
 		logs[i].value.update.email = xstrdup("identity@invalid");
-		t_reftable_set_hash(logs[i].value.update.new_hash, i, GIT_SHA1_FORMAT_ID);
+		t_reftable_set_hash(logs[i].value.update.new_hash, i, REFTABLE_HASH_SHA1);
 	}
 
 	for (i = 0; i < N; i++) {
@@ -561,7 +564,7 @@ static void t_reftable_stack_add(void)
 		int err = reftable_stack_read_ref(st, refs[i].refname, &dest);
 		check(!err);
 		check(reftable_ref_record_equal(&dest, refs + i,
-						 GIT_SHA1_RAWSZ));
+						 REFTABLE_HASH_SIZE_SHA1));
 		reftable_ref_record_release(&dest);
 	}
 
@@ -570,7 +573,7 @@ static void t_reftable_stack_add(void)
 		int err = reftable_stack_read_log(st, refs[i].refname, &dest);
 		check(!err);
 		check(reftable_log_record_equal(&dest, logs + i,
-						 GIT_SHA1_RAWSZ));
+						 REFTABLE_HASH_SIZE_SHA1));
 		reftable_log_record_release(&dest);
 	}
 
@@ -621,14 +624,14 @@ static void t_reftable_stack_iterator(void)
 		refs[i].refname = xstrfmt("branch%02"PRIuMAX, (uintmax_t)i);
 		refs[i].update_index = i + 1;
 		refs[i].value_type = REFTABLE_REF_VAL1;
-		t_reftable_set_hash(refs[i].value.val1, i, GIT_SHA1_FORMAT_ID);
+		t_reftable_set_hash(refs[i].value.val1, i, REFTABLE_HASH_SHA1);
 
 		logs[i].refname = xstrfmt("branch%02"PRIuMAX, (uintmax_t)i);
 		logs[i].update_index = i + 1;
 		logs[i].value_type = REFTABLE_LOG_UPDATE;
 		logs[i].value.update.email = xstrdup("johndoe@invalid");
 		logs[i].value.update.message = xstrdup("commit\n");
-		t_reftable_set_hash(logs[i].value.update.new_hash, i, GIT_SHA1_FORMAT_ID);
+		t_reftable_set_hash(logs[i].value.update.new_hash, i, REFTABLE_HASH_SHA1);
 	}
 
 	for (i = 0; i < N; i++) {
@@ -655,7 +658,7 @@ static void t_reftable_stack_iterator(void)
 		if (err > 0)
 			break;
 		check(!err);
-		check(reftable_ref_record_equal(&ref, &refs[i], GIT_SHA1_RAWSZ));
+		check(reftable_ref_record_equal(&ref, &refs[i], REFTABLE_HASH_SIZE_SHA1));
 		reftable_ref_record_release(&ref);
 	}
 	check_int(i, ==, N);
@@ -673,7 +676,7 @@ static void t_reftable_stack_iterator(void)
 		if (err > 0)
 			break;
 		check(!err);
-		check(reftable_log_record_equal(&log, &logs[i], GIT_SHA1_RAWSZ));
+		check(reftable_log_record_equal(&log, &logs[i], REFTABLE_HASH_SIZE_SHA1));
 		reftable_log_record_release(&log);
 	}
 	check_int(i, ==, N);
@@ -766,7 +769,7 @@ static void t_reftable_stack_tombstone(void)
 		if (i % 2 == 0) {
 			refs[i].value_type = REFTABLE_REF_VAL1;
 			t_reftable_set_hash(refs[i].value.val1, i,
-					    GIT_SHA1_FORMAT_ID);
+					    REFTABLE_HASH_SHA1);
 		}
 
 		logs[i].refname = xstrdup(buf);
@@ -775,7 +778,7 @@ static void t_reftable_stack_tombstone(void)
 		if (i % 2 == 0) {
 			logs[i].value_type = REFTABLE_LOG_UPDATE;
 			t_reftable_set_hash(logs[i].value.update.new_hash, i,
-					    GIT_SHA1_FORMAT_ID);
+					    REFTABLE_HASH_SHA1);
 			logs[i].value.update.email =
 				xstrdup("identity@invalid");
 		}
@@ -835,7 +838,7 @@ static void t_reftable_stack_hash_id(void)
 		.value.symref = (char *) "target",
 		.update_index = 1,
 	};
-	struct reftable_write_options opts32 = { .hash_id = GIT_SHA256_FORMAT_ID };
+	struct reftable_write_options opts32 = { .hash_id = REFTABLE_HASH_SHA256 };
 	struct reftable_stack *st32 = NULL;
 	struct reftable_write_options opts_default = { 0 };
 	struct reftable_stack *st_default = NULL;
@@ -858,7 +861,7 @@ static void t_reftable_stack_hash_id(void)
 	err = reftable_stack_read_ref(st_default, "master", &dest);
 	check(!err);
 
-	check(reftable_ref_record_equal(&ref, &dest, GIT_SHA1_RAWSZ));
+	check(reftable_ref_record_equal(&ref, &dest, REFTABLE_HASH_SIZE_SHA1));
 	reftable_ref_record_release(&dest);
 	reftable_stack_destroy(st);
 	reftable_stack_destroy(st_default);
@@ -908,7 +911,7 @@ static void t_reflog_expire(void)
 		logs[i].value.update.time = i;
 		logs[i].value.update.email = xstrdup("identity@invalid");
 		t_reftable_set_hash(logs[i].value.update.new_hash, i,
-				    GIT_SHA1_FORMAT_ID);
+				    REFTABLE_HASH_SHA1);
 	}
 
 	for (i = 1; i <= N; i++) {