[SCSI] zfcp: No automatic port_rescan on events

In FC fabrics with large zones, the automatic port_rescan on incoming ELS
and any adapter recovery can cause quite some traffic at the very same
time, especially if lots of Linux images share an HBA, which is common on
s390. This can cause trouble and failures. Fix this by making such port
rescans dependent on a user configurable module parameter.

The following unconditional automatic port rescans remain as is:
On setting an adapter online and
on manual user-triggered writes to the sysfs attribute port_rescan.

Signed-off-by: Steffen Maier <maier@linux.vnet.ibm.com>
Signed-off-by: James Bottomley <JBottomley@Parallels.com>

1 files changed, 22 insertions, 1 deletions

diff --git a/drivers/s390/scsi/zfcp_fc.c b/drivers/s390/scsi/zfcp_fc.c
index 88688a8..ff598cd 100644
--- a/drivers/s390/scsi/zfcp_fc.c
+++ b/drivers/s390/scsi/zfcp_fc.c
@@ -26,6 +26,27 @@ static u32 zfcp_fc_rscn_range_mask[] = {
 	[ELS_ADDR_FMT_FAB]		= 0x000000,
 };
 
+static bool no_auto_port_rescan;
+module_param_named(no_auto_port_rescan, no_auto_port_rescan, bool, 0600);
+MODULE_PARM_DESC(no_auto_port_rescan,
+		 "no automatic port_rescan (default off)");
+
+void zfcp_fc_conditional_port_scan(struct zfcp_adapter *adapter)
+{
+	if (no_auto_port_rescan)
+		return;
+
+	queue_work(adapter->work_queue, &adapter->scan_work);
+}
+
+void zfcp_fc_inverse_conditional_port_scan(struct zfcp_adapter *adapter)
+{
+	if (!no_auto_port_rescan)
+		return;
+
+	queue_work(adapter->work_queue, &adapter->scan_work);
+}
+
 /**
  * zfcp_fc_post_event - post event to userspace via fc_transport
  * @work: work struct with enqueued events
@@ -206,7 +227,7 @@ static void zfcp_fc_incoming_rscn(struct zfcp_fsf_req *fsf_req)
 		zfcp_fc_enqueue_event(fsf_req->adapter, FCH_EVT_RSCN,
 				      *(u32 *)page);
 	}
-	queue_work(fsf_req->adapter->work_queue, &fsf_req->adapter->scan_work);
+	zfcp_fc_conditional_port_scan(fsf_req->adapter);
 }
 
 static void zfcp_fc_incoming_wwpn(struct zfcp_fsf_req *req, u64 wwpn)