Logically: masked_status == ((status & 0x3e) >> 1) . So 'masked_status' strips the vendor information bits off 'status' and then shifts it right one position. This makes it easier to do things like "if (CHECK_CONDITION == masked_status) ..." using the definitions in <scsi/scsi.h>. The defined values in this file are:
Note that SCSI 3 defines some additional status codes.  The type of masked_status is unsigned char .
Some lower level drivers (e.g. ide-scsi) clear this masked_status field even when a CHECK_CONDITION or COMMAND_TERMINATED status has occurred. However they do set DRIVER_SENSE in driver_status field. Also a (sb_len_wr > 0) indicates there is a sense buffer.