claim append parf of bufferlist

Hi all, Does anyone know how to claim-append part of bufferlist? After the head part has been claim-appended, the left part can be still cliam-appended. I know there's bufferlist::claim_append API. However it will claim append the whole part of the bufferlist. The background is: I use one function handle_io_am_write_request to recevie the network data sent by peer node, then append it into the cache data space(e.g. bufferlist object recv_pending_bl). Then I trigger the up software layer to read the received the data in recv_pending_bl. The code is below (you can also click the above link to read the code, no more than 40 lines). There're several bugs in the below code. I'm looking for the high efficiency method to receive the data and trigger the up software layer to read the data in the right way. Any suggesion is welcome to supply the high efficiency method to do it. B.R. Changcheng