[PATCH 6/6] scsi: Handle reprobe for existing devices during SCSI scan

[Brian Bunker <brian@purestorage.com>]

Complement scsi_rescan_device() reprobe by handling the scan path.
Update INQUIRY data and reprobe existing devices when PQ or type changed.

Signed-off-by: Brian Bunker <brian@purestorage.com>
Signed-off-by: Krishna Kant <krishna.kant@purestorage.com>
---
 drivers/scsi/scsi_scan.c | 91 ++++++++++++++++++++++++++++++++++++----
 1 file changed, 83 insertions(+), 8 deletions(-)

diff --git a/drivers/scsi/scsi_scan.c b/drivers/scsi/scsi_scan.c
index d54f64ae80f61..514b633d7182e 100644
--- a/drivers/scsi/scsi_scan.c
+++ b/drivers/scsi/scsi_scan.c
@@ -1129,6 +1129,7 @@ static int scsi_probe_and_add_lun(struct scsi_target *starget,
 	blist_flags_t bflags;
 	int res = SCSI_SCAN_NO_RESPONSE, result_len = 256;
 	struct Scsi_Host *shost = dev_to_shost(starget->dev.parent);
+	bool is_reprobe = false;
 
 	/*
 	 * The rescan flag is used as an optimization, the first scan of a
@@ -1136,7 +1137,32 @@ static int scsi_probe_and_add_lun(struct scsi_target *starget,
 	 */
 	sdev = scsi_device_lookup_by_target(starget, lun);
 	if (sdev) {
-		if (rescan != SCSI_SCAN_INITIAL || !scsi_device_created(sdev)) {
+		if (rescan == SCSI_SCAN_INITIAL && scsi_device_created(sdev)) {
+			/*
+			 * Initial scan found device in CREATED state (being probed
+			 * by another thread). Drop reference and allocate new -
+			 * the other thread will complete setup of the original.
+			 */
+			scsi_device_put(sdev);
+			sdev = scsi_alloc_sdev(starget, lun, hostdata);
+			if (!sdev)
+				goto out;
+		} else if (rescan != SCSI_SCAN_INITIAL && !scsi_device_created(sdev)) {
+			/*
+			 * Manual rescan of fully initialized device.
+			 * Reprobe to detect peripheral qualifier or device type
+			 * changes (e.g., ALUA state transitions).
+			 */
+			SCSI_LOG_SCAN_BUS(3, sdev_printk(KERN_INFO, sdev,
+				"scsi scan: device exists (type %d, PQ %d), reprobing\n",
+				sdev->type, sdev->inq_periph_qual));
+			is_reprobe = true;
+		} else {
+			/*
+			 * Either initial scan with fully initialized device,
+			 * or manual rescan with device still in CREATED state.
+			 * Return that device exists.
+			 */
 			SCSI_LOG_SCAN_BUS(3, sdev_printk(KERN_INFO, sdev,
 				"scsi scan: device exists on %s\n",
 				dev_name(&sdev->sdev_gendev)));
@@ -1151,11 +1177,11 @@ static int scsi_probe_and_add_lun(struct scsi_target *starget,
 								 sdev->model);
 			return SCSI_SCAN_LUN_PRESENT;
 		}
-		scsi_device_put(sdev);
-	} else
+	} else {
 		sdev = scsi_alloc_sdev(starget, lun, hostdata);
-	if (!sdev)
-		goto out;
+		if (!sdev)
+			goto out;
+	}
 
 	if (scsi_device_is_pseudo_dev(sdev)) {
 		if (bflagsp)
@@ -1170,6 +1196,40 @@ static int scsi_probe_and_add_lun(struct scsi_target *starget,
 	if (scsi_probe_lun(sdev, result, result_len, &bflags))
 		goto out_free_result;
 
+	/*
+	 * For reprobe scenarios, update the inquiry data with fresh
+	 * INQUIRY results. The device already exists in sysfs, so we
+	 * don't call scsi_add_lun() which would try to add it again.
+	 */
+	if (is_reprobe) {
+		bool need_reprobe = false;
+		int update_ret = __scsi_reprobe_inquiry(sdev, result, result_len,
+							&need_reprobe);
+
+		if (update_ret < 0) {
+			res = SCSI_SCAN_NO_RESPONSE;
+			goto out_free_result;
+		}
+
+		if (bflagsp)
+			*bflagsp = bflags;
+
+		/*
+		 * If type or PQ changed, reprobe to update driver attachment.
+		 * Reprobe failure is not fatal - device exists, just may have
+		 * wrong driver attached.
+		 */
+		if (need_reprobe) {
+			if (device_reprobe(&sdev->sdev_gendev) < 0)
+				sdev_printk(KERN_WARNING, sdev,
+					    "device reprobe failed\n");
+		}
+
+		/* Device already exists, just return success */
+		res = SCSI_SCAN_LUN_PRESENT;
+		goto out_free_result;
+	}
+
 	if (bflagsp)
 		*bflagsp = bflags;
 	/*
@@ -1252,12 +1312,27 @@ static int scsi_probe_and_add_lun(struct scsi_target *starget,
 			if (scsi_device_get(sdev) == 0) {
 				*sdevp = sdev;
 			} else {
-				__scsi_remove_device(sdev);
+				if (!is_reprobe)
+					__scsi_remove_device(sdev);
 				res = SCSI_SCAN_NO_RESPONSE;
 			}
 		}
-	} else
-		__scsi_remove_device(sdev);
+		/*
+		 * For reprobe case, we held a reference from
+		 * scsi_device_lookup_by_target(), release it now.
+		 */
+		if (is_reprobe)
+			scsi_device_put(sdev);
+	} else {
+		/*
+		 * For reprobe, device already exists - don't remove it.
+		 * Just release the reference we got from lookup.
+		 */
+		if (is_reprobe)
+			scsi_device_put(sdev);
+		else
+			__scsi_remove_device(sdev);
+	}
  out:
 	return res;
 }
-- 
2.50.1 (Apple Git-155)