From: Mike Christie <mchristi@redhat.com>
Subject: [PATCH RHEL5] make fc transport removal of target configurable
Date: Wed, 29 Nov 2006 12:36:57 -0600
Bugzilla: 215797
Message-Id: <456DD349.2020809@redhat.com>
Changelog: scsi: make fc transport removal of target configurable


This is for BZ 215797.

In RHEL5, if you pull a Fibre Channel cable and the dev_loss_tmo expires
the fc transport class will remove the attached scsi devices (/dev/sdX
is deleted). The problem with this is that if there is something layered
on top of the scsi device like software RAID or multipath, those apps
must be made hotplug aware so that when the cable is plugged back in the
new devices are added back to that app. Currently, only dm-multipath
partially handles this. With the dm queueing patches merged last month,
dm-multipath can better handle this situation, however if userspace
cannot handle the hotplug events quick enough we get the oops in the
bugzilla above.

The attached patch will make the device removal optional with the
default to not remove the devices when the dev_loss_tmo fires. This
patch will never be merged upstream. See here for reference:
http://marc.theaimsgroup.com/?l=linux-scsi&m=115015423722568&w=2

linux-scsi would prefer that apps be converted and like the userspace
firmware issue is using this as a chance to motivate us. Unfortunately,
SUSE added the same patch, so vendors working on testing and
qualification for SLES10 did not have any motivation to change their own
apps and we were only able to partially fix a couple of our apps in time.

I have tested the patch with lpfc and qla2xxx using multipath and
without multipath, by pulling cables and stopping the target. I was not
able to test zfcp or mpt_fc.

diff -aurp linux-2.6.18.noarch/drivers/scsi/scsi_transport_fc.c linux-2.6.18.noarch.work/drivers/scsi/scsi_transport_fc.c
--- linux-2.6.18.noarch/drivers/scsi/scsi_transport_fc.c	2006-11-27 14:10:59.000000000 -0600
+++ linux-2.6.18.noarch.work/drivers/scsi/scsi_transport_fc.c	2006-11-28 18:54:12.000000000 -0600
@@ -401,9 +401,29 @@ module_param_named(dev_loss_tmo, fc_dev_
 MODULE_PARM_DESC(dev_loss_tmo,
 		 "Maximum number of seconds that the FC transport should"
 		 " insulate the loss of a remote port. Once this value is"
-		 " exceeded, the scsi target is removed. Value should be"
+		 " exceeded, the scsi target may be removed. Reference the"
+		 " remove_on_dev_loss module parameter.  Value should be"
 		 " between 1 and SCSI_DEVICE_BLOCK_MAX_TIMEOUT.");
 
+/*
+ * remove_on_dev_loss: controls whether the transport will
+ *   remove a scsi target after the device loss timer expires.
+ *   Removal on disconnect is modeled after the USB subsystem
+ *   and expects subsystems layered on SCSI to be aware of
+ *   potential device loss and handle it appropriately. However,
+ *   many subsystems do not support device removal, leaving situations
+ *   where structure references may remain, causing new device
+ *   name assignments, etc., if the target returns.
+*/
+static unsigned int fc_remove_on_dev_loss = 0;
+module_param_named(remove_on_dev_loss, fc_remove_on_dev_loss,
+		   int, S_IRUGO|S_IWUSR);
+MODULE_PARM_DESC(remove_on_dev_loss,
+		 "Boolean.  When the device loss timer fires, this variable"
+		 " controls whether the scsi infrastructure for the target"
+		 " device is removed.  Values: zero means do not remove,"
+		 " non-zero means remove.  Default is zero.");
+
 /**
  * Netlink Infrastructure
  **/
@@ -1742,7 +1762,8 @@ fc_starget_delete(void *data)
 	}
 	spin_unlock_irqrestore(shost->host_lock, flags);
 
-	scsi_remove_target(&rport->dev);
+	if (fc_remove_on_dev_loss)
+		scsi_remove_target(&rport->dev);
 }
 
 
@@ -2311,9 +2332,13 @@ fc_timeout_deleted_rport(void  *data)
 		return;
 	}
 
-	dev_printk(KERN_ERR, &rport->dev,
-		"blocked FC remote port time out: removing target and "
-		"saving binding\n");
+	if (fc_remove_on_dev_loss)
+		dev_printk(KERN_ERR, &rport->dev,
+			"blocked FC remote port time out: removing target and "
+			"saving binding\n");
+	else
+		dev_printk(KERN_ERR, &rport->dev,
+			"blocked FC remote port time out: saving binding\n");
 
 	list_move_tail(&rport->peers, &fc_host->rport_bindings);