smb: smbdirect: introduce smbdirect_mr_io.{kref,mutex} and SMBDIRECT_MR_DISABLED

This will be used in the next commits in order to improve the
client code.

A broken connection can just disable the smbdirect_mr_io while
keeping the memory arround for the caller.

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: linux-cifs@vger.kernel.org
Cc: samba-technical@lists.samba.org
Signed-off-by: Stefan Metzmacher <metze@samba.org>
Signed-off-by: Steve French <stfrench@microsoft.com>

Author: metze-samba

fs/smb/common/smbdirect/smbdirect_socket.h

@@ -437,13 +437,22 @@ enum smbdirect_mr_state {
 	SMBDIRECT_MR_READY,
 	SMBDIRECT_MR_REGISTERED,
 	SMBDIRECT_MR_INVALIDATED,
-	SMBDIRECT_MR_ERROR
+	SMBDIRECT_MR_ERROR,
+	SMBDIRECT_MR_DISABLED
 };
 
 struct smbdirect_mr_io {
 	struct smbdirect_socket *socket;
 	struct ib_cqe cqe;
 
+	/*
+	 * We can have up to two references:
+	 * 1. by the connection
+	 * 2. by the registration
+	 */
+	struct kref kref;
+	struct mutex mutex;
+
 	struct list_head list;
 
 	enum smbdirect_mr_state state;