CIFS: Add transform header handling callbacks

BugLink: http://bugs.launchpad.net/bugs/1670508

We need to recognize and parse transformed packets in demultiplex
thread to find a corresponsing mid and process it further.
Signed-off-by: Pavel Shilovsky <pshilov@microsoft.com>
(cherry picked from commit 9bb17e09)
Signed-off-by: Joseph Salisbury <joseph.salisbury@canonical.com>

fs/cifs/cifsglob.h

@@ -438,6 +438,9 @@ struct smb_version_operations {
 				 struct smb_rqst *);
 	/* free transform request */
 	void (*free_transform_rq)(struct smb_rqst *);
+	int (*is_transform_hdr)(void *buf);
+	int (*receive_transform)(struct TCP_Server_Info *,
+				 struct mid_q_entry **);
 };
 
 struct smb_version_values {

fs/cifs/connect.c

@@ -857,12 +857,19 @@ cifs_demultiplex_thread(void *p)
 			continue;
 		server->total_read += length;
 
-		mid_entry = server->ops->find_mid(server, buf);
+		if (server->ops->is_transform_hdr &&
+		    server->ops->receive_transform &&
+		    server->ops->is_transform_hdr(buf)) {
+			length = server->ops->receive_transform(server,
+								&mid_entry);
+		} else {
+			mid_entry = server->ops->find_mid(server, buf);
 
-		if (!mid_entry || !mid_entry->receive)
-			length = standard_receive3(server, mid_entry);
-		else
-			length = mid_entry->receive(server, mid_entry);
+			if (!mid_entry || !mid_entry->receive)
+				length = standard_receive3(server, mid_entry);
+			else
+				length = mid_entry->receive(server, mid_entry);
+		}
 
 		if (length < 0)
 			continue;