when 'pb_status' = -ENOTCONN is returned in an RPC reply message. The
connection refered to by that status is the Lustre connection. That
connection is part of the shared state between Lustre clients and
-servers that gets established via MDS_CONNECT and OST_CONNECT RPCs,
-and can be lost due to an 'eviction'. So, even when that Lusre
-connection is lost (or has not been established, yet), RPC messages
-can be exchanged.
+servers that gets established via *_CONNECT RPCs,
+and can be lost due to an 'eviction' in the face of temporary connection
+failure or in case of an unresponsive client (from the server's point
+of view). So, even when that Lusre connection is lost (or has not been
+established, yet), RPC messages such as *_CONNECT can be exchanged.
The 'pb_version' identifies the version of the Lustre protocol and is
derived from the following constants. The lower two bytes give the
transactions. If 'pb_last_committed' is larger than, or equal to, any
of the client's uncommitted requests (see 'pb_transno' below) then the
server is confirming those requests have been committed to stable
-storage. At that point the client will free the request structures.
+storage. At that point the client may free those request structures
+as they will no longer be necessary for replay during recovery.
The 'pb_transno' value is always zero in a new request. It is also
zero for replies to operations that do not modify the file system. For
MGS_CONNECT_ASYNC is currently unused.
MSG_CONNECT_NEXT_VER indicates that the client can understand the next
-higher protocol version, and the server can reply to the connect with
-that RPC version if it is supported, otherwise it will reply with the
+higher protocol version in addition to the currently used protocol, and
+the server can reply to the connect with that higher RPC version if
+it is supported, otherwise it will reply with the
same RPC version as the request. This allows RPC protocol versions to
be negotiated during a transition period (e.g. upgrade from RPC from
LUSTRE_MSG_MAGIC_V1 to LUSTRE_MSG_MAGIC_V2).