Porting upper layer SCSI driver from Solaris to Linux

Hi,

We are porting an upper layer device driver of SCSI (sd ) from Solaris to Linux.

We want to develop an upper layer (for a block device) which can interact with the middle generic layer(scsi_mod).What are the list of API's exposed by the middle layer and where can I get a documentation of these i.e how does the upper layer interact with the middle layer?
Also what methods do the upper layer needs to expose to the user application?

Thanks nad Regards
Chandrasekhar