+ * @seq: The sequence number of the message; must match the sequence
+ * number for the existing message context waiting for this
+ * response
+ *
+ * Processes a response message after sending an operation request to
+ * userspace. Some other process is awaiting this response. Before
+ * sending out its first communications, the other process allocated a
+ * msg_ctx from the ecryptfs_msg_ctx_arr at a particular index. The
+ * response message contains this index so that we can copy over the
+ * response message into the msg_ctx that the process holds a
+ * reference to. The other process is going to wake up, check to see
+ * that msg_ctx->state == ECRYPTFS_MSG_CTX_STATE_DONE, and then
+ * proceed to read off and process the response message. Returns zero
+ * upon delivery to desired context element; non-zero upon delivery
+ * failure or error.