scsi: st: Modify st.c to use the new scsi_error counters

Compare the stored values of por_ctr and new_media_ctr against the values
in the device struct. In case of mismatch, the Unit Attention corresponding
to the counter has happened. This is a safeguard against another ULD
catching the Unit Attention sense data.

Macros scsi_get_ua_new_media_ctr and scsi_get_ua_por_ctr are added to read
the current values of the counters.

Signed-off-by: Kai Mäkisara <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Reviewed-by: John Meneghini <[e-mail]>
Tested-by: John Meneghini <[e-mail]>
Signed-off-by: Martin K. Petersen <[e-mail]>

drivers/scsi/st.c

···
 
 static int debugging = DEBUG;
 
+/* Setting these non-zero may risk recognizing resets */
 #define MAX_RETRIES 0
 #define MAX_WRITE_RETRIES 0
 #define MAX_READY_RETRIES 0
+
 #define NO_TAPE  NOT_READY
 
 #define ST_TIMEOUT (900 * HZ)
···
 {
 	int result = SRpnt->result;
 	u8 scode;
+	unsigned int ctr;
 	DEB(const char *stp;)
 	char *name = STp->name;
 	struct st_cmdstatus *cmdstatp;
+
+	ctr = scsi_get_ua_por_ctr(STp->device);
+	if (ctr != STp->por_ctr) {
+		STp->por_ctr = ctr;
+		STp->pos_unknown = 1; /* ASC => power on / reset */
+		st_printk(KERN_WARNING, STp, "Power on/reset recognized.");
+	}
 
 	if (!result)
 		return 0;
···
 	if (cmdstatp->have_sense &&
 	    cmdstatp->sense_hdr.asc == 0 && cmdstatp->sense_hdr.ascq == 0x17)
 		STp->cleaning_req = 1; /* ASC and ASCQ => cleaning requested */
-	if (cmdstatp->have_sense && scode == UNIT_ATTENTION && cmdstatp->sense_hdr.asc == 0x29)
+	if (cmdstatp->have_sense && scode == UNIT_ATTENTION &&
+		cmdstatp->sense_hdr.asc == 0x29 && !STp->pos_unknown) {
 		STp->pos_unknown = 1; /* ASC => power on / reset */
-
-	STp->pos_unknown |= STp->device->was_reset;
+		st_printk(KERN_WARNING, STp, "Power on/reset recognized.");
+	}
 
 	if (cmdstatp->have_sense &&
 	    scode == RECOVERED_ERROR
···
 {
 	int attentions, waits, max_wait, scode;
 	int retval = CHKRES_READY, new_session = 0;
+	unsigned int ctr;
 	unsigned char cmd[MAX_COMMAND_SIZE];
 	struct st_request *SRpnt = NULL;
 	struct st_cmdstatus *cmdstatp = &STp->buffer->cmdstat;
···
 					break;
 				}
 			}
+		}
+
+		ctr = scsi_get_ua_new_media_ctr(STp->device);
+		if (ctr != STp->new_media_ctr) {
+			STp->new_media_ctr = ctr;
+			new_session = 1;
+			DEBC_printk(STp, "New tape session.");
 		}
 
 		retval = (STp->buffer)->syscall_result;
···
 				goto out;
 			}
 			reset_state(STp); /* Clears pos_unknown */
-			/* remove this when the midlevel properly clears was_reset */
-			STp->device->was_reset = 0;
 
 			/* Fix the device settings after reset, ignore errors */
 			if (mtc.mt_op == MTREW || mtc.mt_op == MTSEEK ||
···
 			    "st: Can't allocate statistics.\n");
 		goto out_idr_remove;
 	}
+
+	tpnt->new_media_ctr = scsi_get_ua_new_media_ctr(SDp);
+	tpnt->por_ctr = scsi_get_ua_por_ctr(SDp);
 
 	dev_set_drvdata(dev, tpnt);
 

drivers/scsi/st.h

···
 	int recover_count;     /* From tape opening */
 	int recover_reg;       /* From last status call */
 
+	/* The saved values of midlevel counters */
+	unsigned int new_media_ctr;
+	unsigned int por_ctr;
+
 #if DEBUG
 	unsigned char write_pending;
 	int nbr_finished;

include/scsi/scsi_device.h

···
 	return sbitmap_weight(&sdev->budget_map);
 }
 
+/* Macros to access the UNIT ATTENTION counters */
+#define scsi_get_ua_new_media_ctr(sdev) \
+	((const unsigned int)(sdev->ua_new_media_ctr))
+#define scsi_get_ua_por_ctr(sdev) \
+	((const unsigned int)(sdev->ua_por_ctr))
+
 #define MODULE_ALIAS_SCSI_DEVICE(type) \
 	MODULE_ALIAS("scsi:t-" __stringify(type) "*")
 #define SCSI_DEVICE_MODALIAS_FMT "scsi:t-0x%02x"