On Thu, 2021-04-29 at 09:32 -0700, Bart Van Assche wrote:

On 4/29/21 8:50 AM, mwilck@suse.com wrote:

quoted

+       if (hdr.dxfer_len > (queue_max_hw_sectors(bdev->bd_disk-

quoted

queue) << 9))

+               return -EIO;

How about using SECTOR_SHIFT instead of the number 9?

no problem. That line was just copied from the scsi_ioctl code.

quoted

+               /*
+                * Errors resulting from invalid parameters
shouldn't be retried
+                * on another path.
+                */
+               switch (rc) {
+               case -ENOIOCTLCMD:
+               case -EFAULT:
+               case -EINVAL:
+               case -EPERM:
+                       goto out;
+               default:
+                       break;
+               }

Will -ENOMEM result in an immediate retry? Is that what's desired?

No, I overlooked that case. Thanks for pointing this out. 

quoted

+               if (rhdr.info & SG_INFO_CHECK) {
+                       int result;
+                       blk_status_t sts;
+
+                       __set_status_byte(&result, rhdr.status);
+                       __set_msg_byte(&result, rhdr.msg_status);
+                       __set_host_byte(&result, rhdr.host_status);
+                       __set_driver_byte(&result,
rhdr.driver_status);
+
+                       sts = __scsi_result_to_blk_status(&result,
result);
+                       rhdr.host_status = host_byte(result);
+
+                       /* See if this is a target or path error.
*/
+                       if (sts == BLK_STS_OK)
+                               rc = 0;
+                       else if (blk_path_error(sts))
+                               rc = -EIO;
+                       else {
+                               rc = blk_status_to_errno(sts);
+                               goto out;
+                       }
+               }

Will SAM_STAT_CHECK_CONDITION be treated as an I/O error? Is that
what's
desired? If not, does that mean that scsi_result_to_blk_status()
shouldn't be used but instead that a custom SCSI result conversion is
needed?

This mimics the logic for regular SCSI block I/O. By default, CHECK
CONDITION indeed maps to a BLK_STS_IO_ERR, and will be treated as a
path error. As you probably know, there are some exceptions that are
handled in the SCSI mid-layer beforehand. For example, check_sense()
sets DID_TARGET_FAILURE or DID_MEDIUM_ERROR for certain sense codes,
which map to target errors. So yes, I think this is correct.

If __scsi_result_to_blk_status() is the right function to call, how
about making that function accept the driver status, host status, msg
and SAM status as four separate arguments such that the
__set_*_byte()
calls can be left out?

quoted

+                       char *argv[2] = { "fail_path", bdbuf };

Can the above array be declared static?

How would that work? The function needs to be reentrant, and bdbuf is
on the stack. I don't see an issue here, it's really just two pointers
on the stack.

Regards,
Martin