Description

   The routine mrd_scsi_decode(3mrd) is used by the low level MRD
   routines to map SCSI device errors to MRD_STATUS codes. It
   uses the Additional Sense Code (asc) and Additional Sense Code
   Qualifier (ascq) of the status structure to find an appropriate
   MRD_STATUS code. If both the asc and ascq are zero (0), the Sense
   Key (key) will be used to determine the code. The resulting MRD_
   STATUS code will be copied to the code field and returned.

   The routine mrd_map_os_error(3mrd) is used to map operating
   system specific failures to MRD_STATUS codes. If the os_status
   isn't recognized, the routine will return MRD_STATUS_OS_ERROR.
   If the log_info argument is a valid pointer, a copy of the
   operating system text for the message will also copied to the
   space provided.

   This routine uses the dev_status_t structure for handing errors.
   The dev_status_t structure includes the code, os_status, and SCSI
   error fields. The following describes how to decode errors with
   the dev_status_t structure.

   SCSI Errors

   SCSI errors are indicated when the value of the valid field of
   the SCSI error is not equal to 0. The key, asc, and ascq fields
   provide additional information to help determine the cause of the
   error.

   The code usually maps the Additional Sense Code and Additional
   Sense Code Qualifier (ASC/ASCQ) values to an MRD error. The asc
   and ascq values are copied from the request sense data returned
   by the target.

   The Additional Sense Code (asc) indicates further information
   related to the error or exception condition reported in the sense
   key field. The Additional Sense Code Qualifier (ascq) indicates
   detailed information related to the additional sense code. For
   more information, consult the SCSI-2 Specification.

   Operating System Errors

   Operating system errors are indicated when the value of the valid
   field of the SCSI error is equal to 0 and the value of the os_
   status field is not equal to 0. This result is most likely caused
   by an operating system error, and probably has a mapped error in
   MRD.

   MRD Errors

   MRD errors are indicated when the value of the os_status field is
   0, and the value of the valid field of the SCSI error is 0. This
   result is most likely caused when MRD encounters its own failure.