RPC 104: LDLM_GL_CALLBACK
~~~~~~~~~~~~~~~~~~~~~~~~~
[[ldlm-gl-callback-rpc]]

An RPC that assists with getting a lock back from an entity that has
it.

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

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

       LDLM_GL_CALLBACK:
      --request---------------------
      | ptlrpc_body | ldlm_request |
      ------------------------------
//////////////////////////////////////////////////////////////////////

The request RPC resembles the simplest LDLM_ENQUEUE RPC, but only
identifies the relevant resource that the destination entity already
had a lock on. It asks the recipient to flush its dirty write cache,
and notify the requester of size and time attributes once that is
done.

'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>>

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

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

       LDLM_GL_CALLBACK:
      --reply------------------
      | ptlrpc_body | ost_lvb |
      -------------------------
//////////////////////////////////////////////////////////////////////

The reply updates the attributes on the requester.

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

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