RPC 105: LDLM_CP_CALLBACK
~~~~~~~~~~~~~~~~~~~~~~~~~
[[ldlm-cp-callback-rpc]]

An RPC that notifies an entity that a requested lock is now available.

.LDLM_CP_CALLBACK Request Packet Structure
image::ldlm-cp-callback-request.png["LDLM_CP_CALLBACK Request Packet Structure",height=50]

//////////////////////////////////////////////////////////////////////
The ldlm-cp-callback-request.png diagram resembles this text
art:

       LDLM_CP_CALLBACK:
      --request-------------------------------
      | ptlrpc_body | ldlm_request | ost_lvb |
      ----------------------------------------
//////////////////////////////////////////////////////////////////////

The request RPC identifies the relevant resource that already had a
request pending. It notifies the original requester that it now has
the stated lock, along with attribute information the about the
resource.

'ptlrpc_body'::
RPC descriptor <<struct-ptlrpc-body>>.

'ldlm_request'::
Description of the lock being requested. Which resource is the target,
what lock is current, and what lock desired. <<struct-ldlm-request>>

'ost_lvb'::
Attribute data associated with a resource on an OST. <<struct-ost-lvb>>

.LDLM_CP_CALLBACK Reply Packet Structure
image::ldlm-cp-callback-reply.png["LDLM_CP_CALLBACK Reply Packet Structure",height=50]

//////////////////////////////////////////////////////////////////////
The ldlm-cp-callback-reply.png diagram resembles this text
art:

       LDLM_CP_CALLBACK:
      --reply--------
      | ptlrpc_body |
      ---------------
//////////////////////////////////////////////////////////////////////

The reply is just an acknowledgment of receipt, and doesn't
carry any further information about the lock or the resource.

'ptlrpc_body'::
RPC descriptor <<struct-ptlrpc-body>>.