git_filebuf: optionally fsync when committing

src/filebuf.c

@@ -291,6 +291,9 @@ int git_filebuf_open_withsize(git_filebuf *file, const char *path, int flags, mo
 	if (flags & GIT_FILEBUF_DO_NOT_BUFFER)
 		file->do_not_buffer = true;
 
+	if (flags & GIT_FILEBUF_FSYNC)
+		file->do_fsync = true;
+
 	file->buf_size = size;
 	file->buf_pos = 0;
 	file->fd = -1;
@@ -425,6 +428,11 @@ int git_filebuf_commit(git_filebuf *file)
 
 	file->fd_is_open = false;
 
+	if (file->do_fsync && p_fsync(file->fd) < 0) {
+		giterr_set(GITERR_OS, "failed to fsync '%s'", file->path_lock);
+		goto on_error;
+	}
+
 	if (p_close(file->fd) < 0) {
 		giterr_set(GITERR_OS, "failed to close file at '%s'", file->path_lock);
 		goto on_error;

src/filebuf.h

@@ -20,7 +20,8 @@
 #define GIT_FILEBUF_FORCE				(1 << 3)
 #define GIT_FILEBUF_TEMPORARY			(1 << 4)
 #define GIT_FILEBUF_DO_NOT_BUFFER		(1 << 5)
-#define GIT_FILEBUF_DEFLATE_SHIFT		(6)
+#define GIT_FILEBUF_FSYNC				(1 << 6)
+#define GIT_FILEBUF_DEFLATE_SHIFT		(7)
 
 #define GIT_FILELOCK_EXTENSION ".lock\0"
 #define GIT_FILELOCK_EXTLENGTH 6
@@ -47,6 +48,7 @@ struct git_filebuf {
 	bool created_lock;
 	bool did_rename;
 	bool do_not_buffer;
+	bool do_fsync;
 	int last_error;
 };