cifs: split out smb3_use_rdma_offload() helper

We should have the logic to decide if we want rdma offload
in a single spot in order to advance it in future.

Signed-off-by: Stefan Metzmacher <metze@samba.org>
Cc: Steve French <smfrench@gmail.com>
Cc: Tom Talpey <tom@talpey.com>
Cc: Long Li <longli@microsoft.com>
Cc: Namjae Jeon <linkinjeon@kernel.org>
Cc: David Howells <dhowells@redhat.com>
Cc: linux-cifs@vger.kernel.org
Cc: stable@vger.kernel.org
Signed-off-by: Steve French <stfrench@microsoft.com>

Author: metze-samba

fs/cifs/smb2pdu.c

@@ -4063,6 +4063,32 @@ SMB2_flush(const unsigned int xid, struct cifs_tcon *tcon, u64 persistent_fid,
 	return rc;
 }
 
+#ifdef CONFIG_CIFS_SMB_DIRECT
+static inline bool smb3_use_rdma_offload(struct cifs_io_parms *io_parms)
+{
+	struct TCP_Server_Info *server = io_parms->server;
+	struct cifs_tcon *tcon = io_parms->tcon;
+
+	/* we can only offload if we're connected */
+	if (!server || !tcon)
+		return false;
+
+	/* we can only offload on an rdma connection */
+	if (!server->rdma || !server->smbd_conn)
+		return false;
+
+	/* we don't support signed offload yet */
+	if (server->sign)
+		return false;
+
+	/* offload also has its overhead, so only do it if desired */
+	if (io_parms->length < server->smbd_conn->rdma_readwrite_threshold)
+		return false;
+
+	return true;
+}
+#endif /* CONFIG_CIFS_SMB_DIRECT */
+
 /*
  * To form a chain of read requests, any read requests after the first should
  * have the end_of_chain boolean set to true.
@@ -4106,9 +4132,7 @@ smb2_new_read_req(void **buf, unsigned int *total_len,
 	 * If we want to do a RDMA write, fill in and append
 	 * smbd_buffer_descriptor_v1 to the end of read request
 	 */
-	if (server->rdma && rdata && !server->sign &&
-		rdata->bytes >= server->smbd_conn->rdma_readwrite_threshold) {
-
+	if (smb3_use_rdma_offload(io_parms)) {
 		struct smbd_buffer_descriptor_v1 *v1;
 		bool need_invalidate = server->dialect == SMB30_PROT_ID;
 
@@ -4558,9 +4582,7 @@ smb2_async_writev(struct cifs_writedata *wdata,
 	 * If we want to do a server RDMA read, fill in and append
 	 * smbd_buffer_descriptor_v1 to the end of write request
 	 */
-	if (server->rdma && !server->sign && io_parms->length >=
-		server->smbd_conn->rdma_readwrite_threshold) {
-
+	if (smb3_use_rdma_offload(io_parms)) {
 		struct smbd_buffer_descriptor_v1 *v1;
 		bool need_invalidate = server->dialect == SMB30_PROT_ID;