3 files changed, 45 insertions, 17 deletions
diff --git a/refs/reftable-backend.c b/refs/reftable-backend.c
index 7d86d92097..2e774176ed 100644
--- a/refs/reftable-backend.c
+++ b/refs/reftable-backend.c
@@ -24,6 +24,7 @@
 #include "../setup.h"
 #include "../strmap.h"
 #include "../trace2.h"
+#include "../write-or-die.h"
 #include "parse.h"
 #include "refs-internal.h"
 
@@ -273,6 +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)
@@ -304,6 +310,7 @@ static struct ref_store *reftable_be_init(struct repository *repo,
 	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/reftable-writer.h b/reftable/reftable-writer.h
index 211860d08a..c85ef5a5bd 100644
--- a/reftable/reftable-writer.h
+++ b/reftable/reftable-writer.h
@@ -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 9ae716ff37..c67bdd952c 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"
@@ -43,17 +42,28 @@ 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)
+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,
@@ -765,7 +775,7 @@ int reftable_addition_commit(struct reftable_addition *add)
 		goto done;
 	}
 
-	err = fsync_component(FSYNC_COMPONENT_REFERENCE, lock_file_fd);
+	err = stack_fsync(&add->stack->opts, lock_file_fd);
 	if (err < 0) {
 		err = REFTABLE_IO_ERROR;
 		goto done;
@@ -858,8 +868,10 @@ int reftable_addition_add(struct reftable_addition *add,
 	struct reftable_buf next_name = REFTABLE_BUF_INIT;
 	struct reftable_writer *wr = NULL;
 	struct tempfile *tab_file = NULL;
+	struct fd_writer writer = {
+		.opts = &add->stack->opts,
+	};
 	int err = 0;
-	int tab_fd;
 
 	reftable_buf_reset(&next_name);
 
@@ -887,10 +899,10 @@ int reftable_addition_add(struct reftable_addition *add,
 			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 = get_tempfile_fd(tab_file);
+	err = reftable_writer_new(&wr, fd_writer_write, fd_writer_flush,
+				  &writer, &add->stack->opts);
 	if (err < 0)
 		goto done;
 
@@ -973,8 +985,11 @@ static int stack_compact_locked(struct reftable_stack *st,
 	struct reftable_buf next_name = REFTABLE_BUF_INIT;
 	struct reftable_buf tab_file_path = REFTABLE_BUF_INIT;
 	struct reftable_writer *wr = NULL;
+	struct fd_writer writer=  {
+		.opts = &st->opts,
+	};
 	struct tempfile *tab_file;
-	int tab_fd, err = 0;
+	int err = 0;
 
 	err = format_name(&next_name, reftable_reader_min_update_index(st->readers[first]),
 			  reftable_reader_max_update_index(st->readers[last]));
@@ -994,7 +1009,6 @@ static int stack_compact_locked(struct reftable_stack *st,
 		err = REFTABLE_IO_ERROR;
 		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) {
@@ -1002,8 +1016,9 @@ static int stack_compact_locked(struct reftable_stack *st,
 		goto done;
 	}
 
-	err = reftable_writer_new(&wr, reftable_fd_write, reftable_fd_flush,
-				  &tab_fd, &st->opts);
+	writer.fd = get_tempfile_fd(tab_file);
+	err = reftable_writer_new(&wr, fd_writer_write, fd_writer_flush,
+				  &writer, &st->opts);
 	if (err < 0)
 		goto done;
 
@@ -1460,7 +1475,7 @@ 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, get_lock_file_fd(&tables_list_lock));
 	if (err < 0) {
 		err = REFTABLE_IO_ERROR;
 		unlink(new_table_path.buf);