IET (iSCSI Enterprise target) is extended for support of OSD devices using
OSD-iSCSI Module.

We are describing in brief about implementation about IET. This information
is obtained by analyzing the source code. Module names used are assigned by
us depending on their functionality. We will be describing modules and information related to exporting LUN and iSCSI command processing. Note that, this is not verified by IET developers.

IET consists of User mode and Kernel Mode modules which communicate using netlink.

 

User Mode Program :ietd daemon

This is iSCSI Target program management utility.

•  It is used to configure many parameters such as iSCSI target port,uid,gid.

• Information about this is available on iSCSI-target site.

• As far as working of ietd is concerned,it takes entry from iSCSI configuration file "/etc/ietd.conf" and submit it to Kernel mode module.

• Exporter module from OSD simulator makes entry for OSD LUN in iSCSI
  configuration file.ietd daemon submits this entry to kernel module.

 

Kernel Mode Program:(Module File : iscsi_tgt.ko)

There are various modules of this program. We are describing only related
modules.

IOTYPE

This module is responsible for creating iSCSI LUN that can be exported to
initiator. Device IOTypes can be registered to this module. User mode program
i.e.ietd daemon communicate to IOTYPE module. Communication includes passing
various configuration parameters, see /etc/ietd.conf for details.

For each entry in configuration file ietd daemon submits information containing target name,lun, device io-type,path. IOTYPE creates iSCSI LUN for each entry and initialize its access methods depending on its io-type.

We are registering new device IOTYPE as osd-io to this module.All callback functions for osd-io devices type are implemented.


NTHREAD (Network Thread)

• listens for iSCSI request from iSCSI Initiator.

• Accepts iSCSI request

• Initializes iSCSI command structure and corresponding LUN parameters.

• Allocates data buffers

• Handles Processing of r2t data, if any.

This module is extended for support of OSD commands which includes

• Accepting OSD commands and OSD SCSI AHS data

• Calculate r2t data size. Unlike other SCSI commands where r2t data field is  present in SCSI CDB, in OSD SCSI command it depends on OSD service action
  and GET/SET ATTR parameters in OSD request.So it need to be calculated.

• Send request to receive r2t data

WTHREAD (Worker Thread)

•  This does task of processing iSCSI Command. Commands are classified into two classes
      LUN io-type specific and  LUN io-type independent

• For each command a callback function need to be implemented. This will be
  called by WTHREAD module for processing of corresponding command.

• For LUN io-specific commands it invokes corresponding callback function
  registered for the LUN device IO-type.

This module is extended for support of OSD commands which includes calling
callback function for processing OSD command. Callback function handles
processing of OSD command depending on service action.

This function does following

• Communicate with OSD simulator

• Send OSD task request to OSD Task processor module which contains
  OSD SCSI CDB,OSD SCSI AHS, OSD LUN for iSCSI request, Data IN if any

• Receive OSD response, OSD response status, OSD Sense Data in case of error and  OSD DATA OUT, if any.

iSCSI RESPONSE Module

•  After processing of iSCSI command, WTHREAD passes processing to this module.

• Depending on status of command it generates corresponding response.

• If error while processing, it sends SCSI sense data depending on type of
  error.

• r2t data processing if there is any response data.

• This module is extended for support of OSD commands. In case of error,it
  transfers sense data generated by OSD simulator module.