[SCSI] sas_ata: sas_ata_qc_issue should return AC_ERR_*

The sas_ata_qc_issue function was incorrectly written to return error
codes such as -ENOMEM.  Since libata OR's qc->err_mask with the
return value, It is necessary to make my code return one of the
AC_ERR_ codes instead.  For now, use AC_ERR_SYSTEM because an error
here means that the OS couldn't send the command to the controller.

If anybody has a suggestion for a better AC_ERR_ code to use, please
suggest it.
Signed-off-by: Darrick J. Wong <djwong@us.ibm.com>
Signed-off-by: James Bottomley <James.Bottomley@SteelEye.com>

drivers/scsi/libsas/sas_ata.c

@@ -123,7 +123,7 @@ static void sas_ata_task_done(struct sas_task *task)
 
 static unsigned int sas_ata_qc_issue(struct ata_queued_cmd *qc)
 {
-	int res = -ENOMEM;
+	int res;
 	struct sas_task *task;
 	struct domain_device *dev = qc->ap->private_data;
 	struct sas_ha_struct *sas_ha = dev->port->ha;
@@ -135,7 +135,7 @@ static unsigned int sas_ata_qc_issue(struct ata_queued_cmd *qc)
 
 	task = sas_alloc_task(GFP_ATOMIC);
 	if (!task)
-		goto out;
+		return AC_ERR_SYSTEM;
 	task->dev = dev;
 	task->task_proto = SAS_PROTOCOL_STP;
 	task->task_done = sas_ata_task_done;
@@ -187,12 +187,10 @@ static unsigned int sas_ata_qc_issue(struct ata_queued_cmd *qc)
 		SAS_DPRINTK("lldd_execute_task returned: %d\n", res);
 
 		sas_free_task(task);
-		if (res == -SAS_QUEUE_FULL)
-			return -ENOMEM;
+		return AC_ERR_SYSTEM;
 	}
 
-out:
-	return res;
+	return 0;
 }
 
 static u8 sas_ata_check_status(struct ata_port *ap)