scsi_dh_alua: Send TEST UNIT READY to poll for transitioning

Sending a 'REPORT TARGET PORT GROUP' command is a costly operation,
as the array has to gather information about all ports.
So instead of using RTPG to poll for a status update when a port
is in transitioning we should be sending a TEST UNIT READY, and
wait for the sense code to report success.

Reviewed-by: Bart Van Assche <bart.vanassche@sandisk.com>
Reviewed-by: Ewan Milne <emilne@redhat.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Hannes Reinecke <hare@suse.de>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

diff --git a/drivers/scsi/device_handler/scsi_dh_alua.c b/drivers/scsi/device_handler/scsi_dh_alua.c
index 98d87d9..3d8a254 100644 (file)
--- a/drivers/scsi/device_handler/scsi_dh_alua.c
+++ b/drivers/scsi/device_handler/scsi_dh_alua.c
@@ -465,6 +465,30 @@ static int alua_check_sense(struct scsi_device *sdev,
        return SCSI_RETURN_NOT_HANDLED;
 }
 
+/*
+ * alua_tur - Send a TEST UNIT READY
+ * @sdev: device to which the TEST UNIT READY command should be send
+ *
+ * Send a TEST UNIT READY to @sdev to figure out the device state
+ * Returns SCSI_DH_RETRY if the sense code is NOT READY/ALUA TRANSITIONING,
+ * SCSI_DH_OK if no error occurred, and SCSI_DH_IO otherwise.
+ */
+static int alua_tur(struct scsi_device *sdev)
+{
+       struct scsi_sense_hdr sense_hdr;
+       int retval;
+
+       retval = scsi_test_unit_ready(sdev, ALUA_FAILOVER_TIMEOUT * HZ,
+                                     ALUA_FAILOVER_RETRIES, &sense_hdr);
+       if (sense_hdr.sense_key == NOT_READY &&
+           sense_hdr.asc == 0x04 && sense_hdr.ascq == 0x0a)
+               return SCSI_DH_RETRY;
+       else if (retval)
+               return SCSI_DH_IO;
+       else
+               return SCSI_DH_OK;
+}
+
 /*
  * alua_rtpg - Evaluate REPORT TARGET GROUP STATES
  * @sdev: the device to be evaluated.
@@ -732,8 +756,22 @@ static void alua_rtpg_work(struct work_struct *work)
                alua_wq = kaluad_sync_wq;
        pg->flags |= ALUA_PG_RUNNING;
        if (pg->flags & ALUA_PG_RUN_RTPG) {
+               int state = pg->state;
+
                pg->flags &= ~ALUA_PG_RUN_RTPG;
                spin_unlock_irqrestore(&pg->lock, flags);
+               if (state == TPGS_STATE_TRANSITIONING) {
+                       if (alua_tur(sdev) == SCSI_DH_RETRY) {
+                               spin_lock_irqsave(&pg->lock, flags);
+                               pg->flags &= ~ALUA_PG_RUNNING;
+                               pg->flags |= ALUA_PG_RUN_RTPG;
+                               spin_unlock_irqrestore(&pg->lock, flags);
+                               queue_delayed_work(alua_wq, &pg->rtpg_work,
+                                                  pg->interval * HZ);
+                               return;
+                       }
+                       /* Send RTPG on failure or if TUR indicates SUCCESS */
+               }
                err = alua_rtpg(sdev, pg);
                spin_lock_irqsave(&pg->lock, flags);
                if (err == SCSI_DH_RETRY || pg->flags & ALUA_PG_RUN_RTPG) {