ext4_utils: export make_ext4fs_sparse_fd

Export a function to create a sparse image, writing the output to
an fd.  Useful for utilities that need to format a partition.

Change-Id: I3737c65c69b7df0a0bd25885ee70aaadef8a4ad5
diff --git a/ext4_utils/make_ext4fs.c b/ext4_utils/make_ext4fs.c
index 64fcc84..5717912 100644
--- a/ext4_utils/make_ext4fs.c
+++ b/ext4_utils/make_ext4fs.c
@@ -353,6 +353,15 @@
     }
 }
 
+int make_ext4fs_sparse_fd(int fd, s64 len,
+                const char *mountpoint, struct selabel_handle *sehnd)
+{
+	reset_ext4fs_info();
+	info.len = len;
+
+	return make_ext4fs_internal(fd, NULL, mountpoint, NULL, 0, 1, 0, 0, 0, sehnd);
+}
+
 int make_ext4fs(const char *filename, s64 len,
                 const char *mountpoint, struct selabel_handle *sehnd)
 {