adding per scsi-host workqueues for defered processing

@@ -160,6 +160,9 @@ static void scsi_host_dev_release(struct
 		shost->eh_notify = NULL;
 	}
 
+	if (shost->create_work_queue)
+		destroy_workqueue(shost->work_q);
+
 	scsi_proc_hostdir_rm(shost->hostt);
 	scsi_destroy_command_freelist(shost);
 	kfree(shost->shost_data);

@@ -247,6 +250,7 @@ struct Scsi_Host *scsi_host_alloc(struct
 	shost->cmd_per_lun = sht->cmd_per_lun;
 	shost->unchecked_isa_dma = sht->unchecked_isa_dma;
 	shost->use_clustering = sht->use_clustering;
+	shost->create_work_queue = sht->create_work_queue;
 
 	if (sht->max_host_blocked)
 		shost->max_host_blocked = sht->max_host_blocked;

@@ -285,16 +289,27 @@ struct Scsi_Host *scsi_host_alloc(struct
 	snprintf(shost->shost_classdev.class_id, BUS_ID_SIZE, "host%d",
 		  shost->host_no);
 
+	if (shost->create_work_queue) {
+		snprintf(shost->work_q_name, KOBJ_NAME_LEN, "scsi_wq_%d",
+			shost->host_no);
+		shost->work_q = create_singlethread_workqueue(
+			shost->work_q_name);
+		if (!shost->work_q)
+			goto fail_destroy_freelist;
+	}
+
 	shost->eh_notify = &complete;
 	rval = kernel_thread(scsi_error_handler, shost, 0);
 	if (rval < 0)
-		goto fail_destroy_freelist;
+		goto fail_destroy_workqueue;
 	wait_for_completion(&complete);
 	shost->eh_notify = NULL;
 
 	scsi_proc_hostdir_add(shost->hostt);
 	return shost;
 
+ fail_destroy_workqueue:
+	destroy_workqueue(shost->work_q);
  fail_destroy_freelist:
 	scsi_destroy_command_freelist(shost);
  fail_kfree:

@@ -392,3 +407,26 @@ int scsi_is_host_device(const struct dev
 	return dev->release == scsi_host_dev_release;
 }
 EXPORT_SYMBOL(scsi_is_host_device);
+
+/**
+ * scsi_queue_work - Queue work to the Scsi_Host workqueue.
+ * @shost:	Pointer to Scsi_Host.
+ * @work:	Work to queue for execution.
+ *
+ * Return value: 
+ * 	0 on success / != 0 for error
+ **/
+int scsi_queue_work(struct Scsi_Host *shost, struct work_struct *work)
+{
+	if (unlikely(!shost->create_work_queue)) {
+		printk(KERN_ERR
+			"ERROR: Scsi host '%s' attempted to queue scsi-work, "
+			"when no workqueue created.\n", shost->hostt->name);
+		dump_stack();
+
+		return -EINVAL;
+	}
+
+	return queue_work(shost->work_q, work);
+}
+EXPORT_SYMBOL_GPL(scsi_queue_work);

@@ -4,6 +4,7 @@
 #include <linux/device.h>
 #include <linux/list.h>
 #include <linux/types.h>
+#include <linux/workqueue.h>
 
 struct block_device;
 struct module;

@@ -363,6 +364,11 @@ struct scsi_host_template {
 	unsigned skip_settle_delay:1;
 
 	/*
+	 * True if a work-queue should be created for shost processing.
+	 */
+	unsigned create_work_queue:1;
+
+	/*
 	 * Countdown for host blocking with no commands outstanding
 	 */
 	unsigned int max_host_blocked;

@@ -501,6 +507,11 @@ struct Scsi_Host {
 	 */
 	unsigned reverse_ordering:1;
 
+	unsigned create_work_queue:1;
+
+	char work_q_name[KOBJ_NAME_LEN];
+	struct workqueue_struct *work_q;
+
 	/*
 	 * Host has rejected a command because it was busy.
 	 */

@@ -598,6 +609,7 @@ extern void scsi_free_host_dev(struct sc
 extern struct scsi_device *scsi_get_host_dev(struct Scsi_Host *);
 int scsi_is_host_device(const struct device *);
 
+extern int scsi_queue_work(struct Scsi_Host *, struct work_struct *);
 
 /* legacy interfaces */
 extern struct Scsi_Host *scsi_register(struct scsi_host_template *, int);