[PATCH ] tcm_qla2xxx Add SCSI command jammer/discard capabilty to the tcm_qla2xxx module

[Laurence Oberman <loberman@redhat.com>]

Hello

I use target LIO for all my storage array test targets and customer problem resolution here at Red Hat.
This patch resulted from a requirement to mimic behaviour of an expensive hardware jammer for a customer.
I have used this for some time with good success to simulate and reproduce latency and slow drain fabric issues and
for testing and validating error handling behaviour in the Emulex, Qlogic and other F/C drivers.

Works by checking jammer_flag==1 and host # and discards SCSI command, controlled using echo to sys parameter.

I decided to share the patch, in the hope it may be useful for others but I do understand this is a special use case.
If this is useful and Nab wants to include it I will create a proper documentation patch as well.

filename:       /lib/modules/3.17.7-200.jammer.fc20.x86_64/kernel/drivers/scsi/qla2xxx/tcm_qla2xxx.ko
license:        GPL
description:    TCM QLA2XXX series NPIV enabled fabric driver
depends:        target_core_mod,qla2xxx,scsi_transport_fc
intree:         Y
vermagic:       3.17.7-200.jammer.fc20.x86_64 SMP mod_unload 
parm:           jammer_flag:Set to 1: Enable jammer (int)
parm:           host_flag:host number to match on (int)


Enable host 6 to be jammed
echo 6 > /sys/module/tcm_qla2xxx/parameters/host_flag

Usage example script:

#!/bin/bash
host=`cat /sys/module/tcm_qla2xxx/parameters/host_flag`
sleep_time=120  ### Time to jam for
echo "We start to discard commands on SCSI host $host"
logger "Jammer started"
echo 1 >  /sys/module/tcm_qla2xxx/parameters/jammer_flag
sleep $sleep_time
echo 0 >  /sys/module/tcm_qla2xxx/parameters/jammer_flag
echo "We stopped the jammer"
logger "Jammer stopped"

This Patch diff against 3.19.1

Tested by: Laurence Oberman <loberman@redhat.com>
Signed-off-by: Laurence Oberman <loberman@redhat.com>

diff -Nurp a/drivers/scsi/qla2xxx/tcm_qla2xxx.c b/drivers/scsi/qla2xxx/tcm_qla2xxx.c
--- a/drivers/scsi/qla2xxx/tcm_qla2xxx.c	2015-03-07 18:35:15.246737589 -0500
+++ b/drivers/scsi/qla2xxx/tcm_qla2xxx.c	2015-03-07 18:35:40.168599630 -0500
@@ -50,6 +50,14 @@
 #include "qla_target.h"
 #include "tcm_qla2xxx.h"
 
+int message_flag=0;
+int jammer_flag = 0;
+module_param(jammer_flag, int,0644);
+MODULE_PARM_DESC(jammer_flag, "If set to 1: Enable jammer");
+int host_flag=0;
+module_param(host_flag, int,0644);
+MODULE_PARM_DESC(host_flag, "host number to match on");
+
 static struct workqueue_struct *tcm_qla2xxx_free_wq;
 static struct workqueue_struct *tcm_qla2xxx_cmd_wq;
 
@@ -570,6 +578,22 @@ static int tcm_qla2xxx_handle_cmd(scsi_q
 		pr_err("Unable to locate active struct se_session\n");
 		return -EINVAL;
 	}
+	
+ 	// Control messaging here
+	message_flag += jammer_flag;
+	if(message_flag == 1)
+		printk("tcm_qla2xx:SCSI Jammer enabled on host %d\n",host_flag);
+	if((jammer_flag == 0) && (message_flag >=0)) {
+		printk("tcm_qla2xx:SCSI Jammer stopped, %d SCSI commands discarded for host %d\n",message_flag,host_flag);
+		message_flag=-1;
+	}
+		
+	if ((vha->host_no == host_flag) && (jammer_flag == 1))
+	{
+		// return, and don't run target_submit_cmd, effectively discarding command
+		return 0;
+	}
+
 
 	return target_submit_cmd(se_cmd, se_sess, cdb, &cmd->sense_buffer[0],
 				cmd->unpacked_lun, data_length, fcp_task_attr,
@@ -2165,6 +2189,7 @@ static void tcm_qla2xxx_deregister_confi
 static int __init tcm_qla2xxx_init(void)
 {
 	int ret;
+	jammer_flag = 0;
 
 	ret = tcm_qla2xxx_register_configfs();
 	if (ret < 0)