request_buffer - either contains data buffer or scatter gather list
depending on the setting of use_sg. Scatter gather
elements are defined by 'struct scatterlist' found
- in include/asm/scatterlist.h .
+ in include/linux/scatterlist.h .
done - function pointer that should be invoked by LLD when the
SCSI command is completed (successfully or otherwise).
Should only be called by an LLD if the LLD has accepted