[PATCH v3 2/3] scsi: add shost helper to set max queue depth on all of its devices

[James Smart <jsmart2021@gmail.com>]

Create a helper routine to loop through all devices on an shost and
change their current and maximum queue depth. The helper is created
such that is lldd callable.

Signed-off-by: James Smart <jsmart2021@gmail.com>

---
v3:
 fix spaces
 change ENOTSUPP to ENXIO
---
 drivers/scsi/scsi.c        | 32 ++++++++++++++++++++++++++++++++
 include/scsi/scsi_device.h |  1 +
 2 files changed, 33 insertions(+)

diff --git a/drivers/scsi/scsi.c b/drivers/scsi/scsi.c
index 195c0b11260a..86db018bacb2 100644
--- a/drivers/scsi/scsi.c
+++ b/drivers/scsi/scsi.c
@@ -272,6 +272,38 @@ scsi_change_max_queue_depth(struct scsi_device *sdev, int depth)
 }
 
 /**
+ * shost_change_max_queue_depths - helper to walk all devices on a
+ *         shost and change their max queue depth.
+ * @shost: shost whose devices we want to iterate over.
+ * @depth: number of commands allowed to be queued to the driver
+ *
+ * Validates the shost allows a change of queue depth, the value is valid,
+ * then traverses over all devices and sets their maximum queue depth.
+ */
+int shost_change_max_queue_depths(struct Scsi_Host *shost, int depth)
+{
+	struct scsi_device *sdev;
+	int retval;
+
+	if (!shost->hostt->change_queue_depth)
+		return -ENXIO;
+
+	if (depth < 1 || depth > shost->can_queue)
+		return -EINVAL;
+
+	shost_for_each_device(sdev, shost) {
+		retval = scsi_change_max_queue_depth(sdev, depth);
+		if (retval != 0)
+			sdev_printk(KERN_INFO, sdev,
+				"failed to set queue depth to %d (err %d)",
+				depth, retval);
+	}
+
+	return 0;
+}
+EXPORT_SYMBOL(shost_change_max_queue_depths);
+
+/**
  * scsi_track_queue_full - track QUEUE_FULL events to adjust queue depth
  * @sdev: SCSI Device in question
  * @depth: Current number of outstanding SCSI commands on this device,
diff --git a/include/scsi/scsi_device.h b/include/scsi/scsi_device.h
index f8312a3e5b42..38c4b97fc1b8 100644
--- a/include/scsi/scsi_device.h
+++ b/include/scsi/scsi_device.h
@@ -392,6 +392,7 @@ extern struct scsi_device *__scsi_iterate_devices(struct Scsi_Host *,
 
 extern int scsi_change_queue_depth(struct scsi_device *, int);
 extern int scsi_track_queue_full(struct scsi_device *, int);
+extern int shost_change_max_queue_depths(struct Scsi_Host *shost, int depth);
 
 extern int scsi_set_medium_removal(struct scsi_device *, char);
 
-- 
2.13.7