ceph: don't reach into request header for readdir info

We already have a pointer to the argument struct in req->r_args. Use that
instead of groveling around in the ceph_mds_request_head.
Signed-off-by: Jeff Layton <jlayton@kernel.org>
Reviewed-by: Xiubo Li <xiubli@redhat.com>
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>

fs/ceph/inode.c

@@ -1594,8 +1594,7 @@ int ceph_readdir_prepopulate(struct ceph_mds_request *req,
 	struct dentry *dn;
 	struct inode *in;
 	int err = 0, skipped = 0, ret, i;
-	struct ceph_mds_request_head *rhead = req->r_request->front.iov_base;
-	u32 frag = le32_to_cpu(rhead->args.readdir.frag);
+	u32 frag = le32_to_cpu(req->r_args.readdir.frag);
 	u32 last_hash = 0;
 	u32 fpos_offset;
 	struct ceph_readdir_cache_control cache_ctl = {};
@@ -1612,7 +1611,7 @@ int ceph_readdir_prepopulate(struct ceph_mds_request *req,
 		} else if (rinfo->offset_hash) {
 			/* mds understands offset_hash */
 			WARN_ON_ONCE(req->r_readdir_offset != 2);
-			last_hash = le32_to_cpu(rhead->args.readdir.offset_hash);
+			last_hash = le32_to_cpu(req->r_args.readdir.offset_hash);
 		}
 	}