Add __weak sync_file_range()

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
diff --git a/helpers.c b/helpers.c
index 9b1f3e9..779f9fb 100644
--- a/helpers.c
+++ b/helpers.c
@@ -29,3 +29,9 @@
 
 	return ret;
 }
+
+int __weak sync_file_range(int fd, off64_t offset, off64_t nbytes,
+			   unsigned int flags)
+{
+	return 0;
+}
diff --git a/helpers.h b/helpers.h
index 4f8cc0c..8307c43 100644
--- a/helpers.h
+++ b/helpers.h
@@ -9,5 +9,7 @@
 extern int __weak posix_fallocate(int fd, off_t offset, off_t len);
 extern int __weak inet_aton(const char *cp, struct in_addr *inp);
 extern int __weak clock_gettime(clockid_t clk_id, struct timespec *ts);
+extern int __weak sync_file_range(int fd, off64_t offset, off64_t nbytes,
+					unsigned int flags);
 
 #endif