RPC 8: OST CONNECT - Client connection to an OST
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
[[ost-connect-rpc]]

When a client initiates a connection to a specific target on an OSS,
it does so via an OST_CONNECT RPC ('pb_oc' = 8). From a previous
interaction with the MGS the client knows the UUID of the target OST,
and can fill that value into the 'obd_connect_client' message.

.OST_CONNECT Generic Packet Structure
image::ost-connect-generic.png["OST_CONNECT Generic Packet Structure",height=100]

//////////////////////////////////////////////////////////////////////
The ost-connect-generic.png diagram resembles this text art:

       OST_CONNECT:
      --request--------------------------------------------
      | ptlrpc_body | obd_uuid | obd_uuid | lustre_handle |
      -----------------------------------------------------
      |  obd_connect_data |
      ---------------------
      --reply---------------------------
      | ptlrpc_body | obd_connect_data |
      ----------------------------------
//////////////////////////////////////////////////////////////////////

'ptlrpc_body'::
RPC descriptor.

'obd_uuid'::
UUIDs of the target (first) and client (second) entities. See
<<struct-obd-uuid>>.

'lustre_handle'::
See <<struct-lustre-handle>>.

'obd_connect_data'::
See <<struct-obd-connect-data>>.

In the OST_CONNECT RPC reply from the server the 'ptlrpc_body' field
'pb__handle' is set to uniquely identify the connection for subsequent
communication. The client notes that handle in its import for the
given target.