This value points to user memory of at least 'mx_sb_len' bytes length
where the SCSI sense buffer will be output. Most successful commands
do not output a sense buffer and this will be indicated by
'sb_len_wr' being zero. Note that there are error conditions that
don't result in a sense buffer be generated. The sense buffer results
from the "auto-sense" mechanism in the SCSI mid-level driver. This
mechanism detects a CHECK_CONDITION status and issues a REQUEST SENSE
command and conveys its response back as the "sense buffer".
The type of sbp is unsigned char * .
