scsi: scsi_dh_alua: Prevent duplicate pg info print in alua_rtpg()

Due to the frequency that alua_rtpg() is called, the path group info print
within can print the same info multiple times in the logs, subsequent
prints adding no new information or value.

To reproduce:

    # modprobe scsi_debug vpd_use_hostno=0
    # systemctl start multipathd.service

To fix, check stored values, only printing at alua attach/activate and if
any of the values change.

Link: https://lore.kernel.org/r/20210331181656.5046-1-jpittman@redhat.comReviewed-by: David Jeffery <djeffery@redhat.com>
Reviewed-by: Laurence Oberman <loberman@redhat.com>
Signed-off-by: John Pittman <jpittman@redhat.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

drivers/scsi/device_handler/scsi_dh_alua.c

@@ -515,6 +515,7 @@ static int alua_rtpg(struct scsi_device *sdev, struct alua_port_group *pg)
 	struct scsi_sense_hdr sense_hdr;
 	struct alua_port_group *tmp_pg;
 	int len, k, off, bufflen = ALUA_RTPG_SIZE;
+	int group_id_old, state_old, pref_old, valid_states_old;
 	unsigned char *desc, *buff;
 	unsigned err, retval;
 	unsigned int tpg_desc_tbl_off;
@@ -522,6 +523,11 @@ static int alua_rtpg(struct scsi_device *sdev, struct alua_port_group *pg)
 	unsigned long flags;
 	bool transitioning_sense = false;
 
+	group_id_old = pg->group_id;
+	state_old = pg->state;
+	pref_old = pg->pref;
+	valid_states_old = pg->valid_states;
+
 	if (!pg->expiry) {
 		unsigned long transition_tmo = ALUA_FAILOVER_TIMEOUT * HZ;
 
@@ -686,6 +692,8 @@ static int alua_rtpg(struct scsi_device *sdev, struct alua_port_group *pg)
 	if (transitioning_sense)
 		pg->state = SCSI_ACCESS_STATE_TRANSITIONING;
 
+	if (group_id_old != pg->group_id || state_old != pg->state ||
+		pref_old != pg->pref || valid_states_old != pg->valid_states)
 		sdev_printk(KERN_INFO, sdev,
 			"%s: port group %02x state %c %s supports %c%c%c%c%c%c%c\n",
 			ALUA_DH_NAME, pg->group_id, print_alua_state(pg->state),