Linux 5.1 (commit 6dc4f100c175dd0511ae8674786e7c9006cdfbfa) introduces
bvec_iter_all.

--- a/libcfs/libcfs/crypto/bio.c
+++ b/libcfs/libcfs/crypto/bio.c
@@ -29,7 +29,11 @@
 static void __llcrypt_decrypt_bio(struct bio *bio, bool done)
 {
 	struct bio_vec *bv;
+#ifdef HAVE_BVEC_ITER_ALL
 	struct bvec_iter_all iter_all;
+#else
+	int iter_all;
+#endif
 
 	bio_for_each_segment_all(bv, bio, iter_all) {
 		struct page *page = bv->bv_page;