cifs: multichannel: try to rebind when reconnecting a channel

first steps in trying to make channels properly reconnect.

* add cifs_ses_find_chan() function to find the enclosing cifs_chan
  struct it belongs to
* while we have the session lock and are redoing negprot and
  sess.setup in smb2_reconnect() redo the binding of channels.
Signed-off-by: Aurelien Aptel <aaptel@suse.com>
Signed-off-by: Steve French <stfrench@microsoft.com>

fs/cifs/cifsproto.h

@@ -593,6 +593,8 @@ void cifs_free_hash(struct crypto_shash **shash, struct sdesc **sdesc);
 
 extern void rqst_page_get_length(struct smb_rqst *rqst, unsigned int page,
 				unsigned int *len, unsigned int *offset);
+struct cifs_chan *
+cifs_ses_find_chan(struct cifs_ses *ses, struct TCP_Server_Info *server);
 int cifs_try_adding_channels(struct cifs_ses *ses);
 int cifs_ses_add_channel(struct cifs_ses *ses,
 				struct cifs_server_iface *iface);

fs/cifs/sess.c

@@ -150,6 +150,22 @@ int cifs_try_adding_channels(struct cifs_ses *ses)
 	return ses->chan_count - old_chan_count;
 }
 
+/*
+ * If server is a channel of ses, return the corresponding enclosing
+ * cifs_chan otherwise return NULL.
+ */
+struct cifs_chan *
+cifs_ses_find_chan(struct cifs_ses *ses, struct TCP_Server_Info *server)
+{
+	int i;
+
+	for (i = 0; i < ses->chan_count; i++) {
+		if (ses->chans[i].server == server)
+			return &ses->chans[i];
+	}
+	return NULL;
+}
+
 int
 cifs_ses_add_channel(struct cifs_ses *ses, struct cifs_server_iface *iface)
 {

fs/cifs/smb2pdu.c

@@ -375,15 +375,31 @@ smb2_reconnect(__le16 smb2_command, struct cifs_tcon *tcon,
 		goto out;
 	}
 
+	/*
+	 * If we are reconnecting an extra channel, bind
+	 */
+	if (server->is_channel) {
+		ses->binding = true;
+		ses->binding_chan = cifs_ses_find_chan(ses, server);
+	}
+
 	rc = cifs_negotiate_protocol(0, tcon->ses);
 	if (!rc && tcon->ses->need_reconnect) {
 		rc = cifs_setup_session(0, tcon->ses, nls_codepage);
 		if ((rc == -EACCES) && !tcon->retry) {
 			rc = -EHOSTDOWN;
+			ses->binding = false;
+			ses->binding_chan = NULL;
 			mutex_unlock(&tcon->ses->session_mutex);
 			goto failed;
 		}
 	}
+	/*
+	 * End of channel binding
+	 */
+	ses->binding = false;
+	ses->binding_chan = NULL;
+
 	if (rc || !tcon->need_reconnect) {
 		mutex_unlock(&tcon->ses->session_mutex);
 		goto out;