Querry !

[Kaushik Datta <kdatta@npd.hcltech.com>]

Hello all,

       We are a group of Engineers working on an idea related to the
   scsi subsystem in FreeBSD.We have approached this project from the
   perspective of iscsi.The project revolves around using iscsi target
   stack on FreeBSD and the changes  that (we feel) can be made to the
   scsi subsystem in FreeBSD.As we all know that the FreeBSD scsi
   system adheres to the CAM architecture model, wherein we have an
   upper layer of driver pertaining to different kinds of devices, disk,
   tape etc.Now this upper layer drivers or Peripheral modules(PM) takes
   the task of forming the scsi CDB and passes it on to the CAM transport
   layer or the XPT layer.This transport layer then forms a CCB and
   passes it further on to the lower layer SIM HBA driver.
   Now iscsi pdu carry scsi cdb as a part of it.But in the existing
   scsi subsystem in FreeBSD, the PM layer takes care of forming the
   scsi pdu in case of a normal I/O operation.Now assuming iscsi
   target stack running on the machine, won't it be feasible if we
   can write a pseudo driver that takes care of the fetching the
   scsi cdb as such and passing it on to the SIM driver ? In a
   way we will get away from the PM functionality which forms the
   scsi CDB in case of a normal I/O.Now where exactly this driver
   should fit ? Should this use the xpt transport layer functionality
   which takes care of the routing decision and device initialization?
 
   Any ideas related to the design will be of great help.Also we would
   like to know if any group is working on implementing iscsi stack
   on FreeBSD.

   Thanks for your patience !
   Kaushik