[QUESTION]: Why did we clear the lowest bit of SCSI command's status in scsi_status_is_good

[Wenchao Hao <haowenchao@huawei.com>]

static inline bool scsi_status_is_good(int status)                                                                                                                                                             
{
        if (status < 0)
                return false;

        if (host_byte(status) == DID_NO_CONNECT)
                return false;

        /*  
         * FIXME: bit0 is listed as reserved in SCSI-2, but is
         * significant in SCSI-3.  For now, we follow the SCSI-2
         * behaviour and ignore reserved bits.
         */
        status &= 0xfe;
        return ((status == SAM_STAT_GOOD) ||
                (status == SAM_STAT_CONDITION_MET) ||
                /* Next two "intermediate" statuses are obsolete in SAM-4 */
                (status == SAM_STAT_INTERMEDIATE) ||
                (status == SAM_STAT_INTERMEDIATE_CONDITION_MET) ||
                /* FIXME: this is obsolete in SAM-3 */
                (status == SAM_STAT_COMMAND_TERMINATED));
}
We have function defined in include/scsi/scsi.h as above, which is used to check
if the status in result is good.

But the function cleared the lowest bit of SCSI command's status, which would
translate an undefined status to good in some condition, for example the status
is 0x1.

This code seems introduced in this patch:
https://lore.kernel.org/all/1052403312.2097.35.camel@mulgrave/

Is anyone who knows why did we clear the lowest bit? 

We found some firmware or drivers would return status which did not defined in
SAM. Now SCSI middle level do not have an uniform behavior for these undefined
status. I want to change the logic to return error for all status which did not
defined in SAM or define a method in host template to let drivers to judge
what to do in this condition.