From: mchristi@redhat.com <mchristi@redhat.com>
Date: Thu, 28 Aug 2008 13:43:33 -0500
Subject: [scsi] add infrastructure for SCSI Device Handlers
Message-id: 1219949016-15055-3-git-send-email-mchristi@redhat.com
O-Subject: [RHEL 5.3 PATCH 2/5] scsi: add infrastructure for SCSI Device Handlers
Bugzilla: 438761
RH-Acked-by: Doug Ledford <dledford@redhat.com>

From: Mike Christie <mchristi@redhat.com>

Some of the storage devices (that can be accessed through multiple paths),
do need some special handling for
        1. Activating the passive path of the storage access.
        2. Decode and handle the special sense codes returned by the devices.
        3. Handle the I/Os being sent to the passive path, especially
           during the device probe time.
when accessed through multiple paths.

As of today this special device handling is done at the dm-multipath
layer using dm-handlers. That works well for (1); for (2) to be handled
at dm layer, scsi sense information need to be exported from SCSI to dm-layer,
which is not very attractive; (3) cannot be done at all at the dm layer.

Device handler has been moved to SCSI mainly to handle (2) and (3) properly.

The base of this patch is upstream here:
http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commit;h=a6a8d9f87eb8510a8f53672ea87703f62185d75f

It has been modified to support our kabi (check-kabi has been run on this
patch without errors).

diff --git a/drivers/scsi/Kconfig b/drivers/scsi/Kconfig
index 99db502..766f648 100644
--- a/drivers/scsi/Kconfig
+++ b/drivers/scsi/Kconfig
@@ -1743,4 +1743,6 @@ endmenu
 
 source "drivers/scsi/pcmcia/Kconfig"
 
+source "drivers/scsi/device_handler/Kconfig"
+
 endmenu
diff --git a/drivers/scsi/Makefile b/drivers/scsi/Makefile
index bcca39c..7e0f83e 100644
--- a/drivers/scsi/Makefile
+++ b/drivers/scsi/Makefile
@@ -33,6 +33,7 @@ obj-$(CONFIG_SCSI_FC_ATTRS) 	+= scsi_transport_fc.o
 obj-$(CONFIG_SCSI_ISCSI_ATTRS)	+= scsi_transport_iscsi.o
 obj-$(CONFIG_SCSI_SAS_ATTRS)	+= scsi_transport_sas.o
 obj-$(CONFIG_SCSI_SAS_LIBSAS)	+= libsas/
+obj-y				+= device_handler/
 
 obj-$(CONFIG_ISCSI_TCP) 	+= libiscsi.o	iscsi_tcp.o
 obj-$(CONFIG_INFINIBAND_ISER) 	+= libiscsi.o
@@ -144,7 +145,7 @@ obj-$(CONFIG_SCSI_DEBUG)	+= scsi_debug.o
 scsi_mod-y			+= scsi.o hosts.o scsi_ioctl.o constants.o \
 				   scsicam.o scsi_error.o scsi_lib.o \
 				   scsi_scan.o scsi_sysfs.o \
-				   scsi_devinfo.o
+				   scsi_devinfo.o scsi_dh_export.o
 scsi_mod-$(CONFIG_SCSI_NETLINK)	+= scsi_netlink.o
 scsi_mod-$(CONFIG_SYSCTL)	+= scsi_sysctl.o
 scsi_mod-$(CONFIG_SCSI_PROC_FS)	+= scsi_proc.o
diff --git a/drivers/scsi/device_handler/Kconfig b/drivers/scsi/device_handler/Kconfig
new file mode 100644
index 0000000..228241d
--- /dev/null
+++ b/drivers/scsi/device_handler/Kconfig
@@ -0,0 +1,12 @@
+#
+# SCSI Device Handler configuration
+#
+
+menuconfig SCSI_DH
+	tristate "SCSI Device Handlers"
+	depends on SCSI
+	default n
+	help
+	  SCSI Device Handlers provide device specific support for
+	  devices utilized in multipath configurations. Say Y here to
+	  select support for specific hardware.
diff --git a/drivers/scsi/device_handler/Makefile b/drivers/scsi/device_handler/Makefile
new file mode 100644
index 0000000..f306e44
--- /dev/null
+++ b/drivers/scsi/device_handler/Makefile
@@ -0,0 +1,4 @@
+#
+# SCSI Device Handler
+#
+obj-$(CONFIG_SCSI_DH)		+= scsi_dh.o
diff --git a/drivers/scsi/device_handler/scsi_dh.c b/drivers/scsi/device_handler/scsi_dh.c
new file mode 100644
index 0000000..fcbf552
--- /dev/null
+++ b/drivers/scsi/device_handler/scsi_dh.c
@@ -0,0 +1,554 @@
+/*
+ * SCSI device handler infrastruture.
+ *
+ * This program is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License as published by the
+ * Free Software Foundation; either version 2 of the License, or (at your
+ * option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with this program; if not, write to the Free Software Foundation, Inc.,
+ * 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
+ *
+ * Copyright IBM Corporation, 2007
+ *      Authors:
+ *               Chandra Seetharaman <sekharan@us.ibm.com>
+ *               Mike Anderson <andmike@linux.vnet.ibm.com>
+ */
+
+#include <scsi/scsi_dh.h>
+#include "../scsi_priv.h"
+
+struct scsi_dh_devinfo_list {
+	struct list_head node;
+	char vendor[9];
+	char model[17];
+	struct scsi_device_handler *handler;
+};
+
+static DEFINE_SPINLOCK(list_lock);
+static LIST_HEAD(scsi_dh_list);
+static LIST_HEAD(scsi_dh_dev_list);
+
+static struct scsi_device_handler *get_device_handler(const char *name)
+{
+	struct scsi_device_handler *tmp, *found = NULL;
+
+	spin_lock(&list_lock);
+	list_for_each_entry(tmp, &scsi_dh_list, list) {
+		if (!strncmp(tmp->name, name, strlen(tmp->name))) {
+			found = tmp;
+			break;
+		}
+	}
+	spin_unlock(&list_lock);
+	return found;
+}
+
+
+static struct scsi_device_handler *
+scsi_dh_cache_lookup(struct scsi_device *sdev)
+{
+	struct scsi_dh_devinfo_list *tmp;
+	struct scsi_device_handler *found_dh = NULL;
+
+	spin_lock(&list_lock);
+	list_for_each_entry(tmp, &scsi_dh_dev_list, node) {
+		if (!strncmp(sdev->vendor, tmp->vendor, strlen(tmp->vendor)) &&
+		    !strncmp(sdev->model, tmp->model, strlen(tmp->model))) {
+			found_dh = tmp->handler;
+			break;
+		}
+	}
+	spin_unlock(&list_lock);
+
+	return found_dh;
+}
+
+static int scsi_dh_handler_lookup(struct scsi_device_handler *scsi_dh,
+				  struct scsi_device *sdev)
+{
+	int i, found = 0;
+
+	for(i = 0; scsi_dh->devlist[i].vendor; i++) {
+		if (!strncmp(sdev->vendor, scsi_dh->devlist[i].vendor,
+			     strlen(scsi_dh->devlist[i].vendor)) &&
+		    !strncmp(sdev->model, scsi_dh->devlist[i].model,
+			     strlen(scsi_dh->devlist[i].model))) {
+			found = 1;
+			break;
+		}
+	}
+	return found;
+}
+
+/*
+ * device_handler_match - Attach a device handler to a device
+ * @scsi_dh - The device handler to match against or NULL
+ * @sdev - SCSI device to be tested against @scsi_dh
+ *
+ * Tests @sdev against the device handler @scsi_dh or against
+ * all registered device_handler if @scsi_dh == NULL.
+ * Returns the found device handler or NULL if not found.
+ */
+static struct scsi_device_handler *
+device_handler_match(struct scsi_device_handler *scsi_dh,
+		     struct scsi_device *sdev)
+{
+	struct scsi_device_handler *found_dh = NULL;
+	struct scsi_dh_devinfo_list *tmp;
+
+	found_dh = scsi_dh_cache_lookup(sdev);
+	if (found_dh)
+		return found_dh;
+
+	if (scsi_dh) {
+		if (scsi_dh_handler_lookup(scsi_dh, sdev))
+			found_dh = scsi_dh;
+	} else {
+		struct scsi_device_handler *tmp_dh;
+
+		spin_lock(&list_lock);
+		list_for_each_entry(tmp_dh, &scsi_dh_list, list) {
+			if (scsi_dh_handler_lookup(tmp_dh, sdev))
+				found_dh = tmp_dh;
+		}
+		spin_unlock(&list_lock);
+	}
+
+	if (found_dh) { /* If device is found, add it to the cache */
+		tmp = kmalloc(sizeof(*tmp), GFP_KERNEL);
+		if (tmp) {
+			strncpy(tmp->vendor, sdev->vendor, 8);
+			strncpy(tmp->model, sdev->model, 16);
+			tmp->vendor[8] = '\0';
+			tmp->model[16] = '\0';
+			tmp->handler = found_dh;
+			spin_lock(&list_lock);
+			list_add(&tmp->node, &scsi_dh_dev_list);
+			spin_unlock(&list_lock);
+		} else {
+			found_dh = NULL;
+		}
+	}
+
+	return found_dh;
+}
+
+/*
+ * scsi_dh_handler_attach - Attach a device handler to a device
+ * @sdev - SCSI device the device handler should attach to
+ * @scsi_dh - The device handler to attach
+ */
+static int scsi_dh_handler_attach(struct scsi_device *sdev,
+				  struct scsi_device_handler *scsi_dh)
+{
+	int err = 0;
+	struct scsi_dh_data *scsi_dh_data = retrieve_scsi_dh_data(sdev);
+
+	if (scsi_dh_data) {
+		if (scsi_dh_data->scsi_dh != scsi_dh)
+			err = -EBUSY;
+	} else if (scsi_dh->attach)
+		err = scsi_dh->attach(sdev);
+
+	return err;
+}
+
+/*
+ * scsi_dh_handler_detach - Detach a device handler from a device
+ * @sdev - SCSI device the device handler should be detached from
+ * @scsi_dh - Device handler to be detached
+ *
+ * Detach from a device handler. If a device handler is specified,
+ * only detach if the currently attached handler matches @scsi_dh.
+ */
+static void scsi_dh_handler_detach(struct scsi_device *sdev,
+				   struct scsi_device_handler *scsi_dh)
+{
+	struct scsi_dh_data *scsi_dh_data = retrieve_scsi_dh_data(sdev);
+
+	if (!scsi_dh_data)
+		return;
+
+	if (scsi_dh && scsi_dh != scsi_dh_data->scsi_dh)
+		return;
+
+	if (!scsi_dh)
+		scsi_dh = scsi_dh_data->scsi_dh;
+
+	if (scsi_dh && scsi_dh->detach)
+		scsi_dh->detach(sdev);
+}
+
+/*
+ * Functions for sysfs attribute 'dh_state'
+ */
+static ssize_t
+store_dh_state(struct device *dev, struct device_attribute *attr,
+	       const char *buf, size_t count)
+{
+	struct scsi_device *sdev = to_scsi_device(dev);
+	struct scsi_dh_data *scsi_dh_data = retrieve_scsi_dh_data(sdev);
+	struct scsi_device_handler *scsi_dh;
+	int err = -EINVAL;
+
+	if (!scsi_dh_data) {
+		/*
+		 * Attach to a device handler
+		 */
+		if (!(scsi_dh = get_device_handler(buf)))
+			return err;
+		err = scsi_dh_handler_attach(sdev, scsi_dh);
+	} else {
+		scsi_dh = scsi_dh_data->scsi_dh;
+		if (!strncmp(buf, "detach", 6)) {
+			/*
+			 * Detach from a device handler
+			 */
+			scsi_dh_handler_detach(sdev, scsi_dh);
+			err = 0;
+		} else if (!strncmp(buf, "activate", 8)) {
+			/*
+			 * Activate a device handler
+			 */
+			if (scsi_dh->activate)
+				err = scsi_dh->activate(sdev);
+			else
+				err = 0;
+		}
+	}
+
+	return err<0?err:count;
+}
+
+static ssize_t
+show_dh_state(struct device *dev, struct device_attribute *attr, char *buf)
+{
+	struct scsi_device *sdev = to_scsi_device(dev);
+	struct scsi_dh_data *scsi_dh_data = retrieve_scsi_dh_data(sdev);
+
+	if (!scsi_dh_data)
+		return snprintf(buf, 20, "detached\n");
+
+	return snprintf(buf, 20, "%s\n", scsi_dh_data->scsi_dh->name);
+}
+
+static struct device_attribute scsi_dh_state_attr =
+	__ATTR(dh_state, S_IRUGO | S_IWUSR, show_dh_state,
+	       store_dh_state);
+
+/*
+ * scsi_dh_sysfs_attr_add - Callback for scsi_init_dh
+ */
+static int scsi_dh_sysfs_attr_add(struct device *dev, void *data)
+{
+	struct scsi_device *sdev;
+	int err;
+
+	if (!scsi_is_sdev_device(dev))
+		return 0;
+
+	sdev = to_scsi_device(dev);
+
+	err = device_create_file(&sdev->sdev_gendev,
+				 &scsi_dh_state_attr);
+
+	return 0;
+}
+
+/*
+ * scsi_dh_sysfs_attr_remove - Callback for scsi_exit_dh
+ */
+static int scsi_dh_sysfs_attr_remove(struct device *dev, void *data)
+{
+	struct scsi_device *sdev;
+
+	if (!scsi_is_sdev_device(dev))
+		return 0;
+
+	sdev = to_scsi_device(dev);
+
+	device_remove_file(&sdev->sdev_gendev,
+			   &scsi_dh_state_attr);
+
+	return 0;
+}
+
+/*
+ * scsi_dh_notifier - notifier chain callback
+ */
+static int scsi_dh_notifier(struct notifier_block *nb,
+			    unsigned long action, void *data)
+{
+	struct device *dev = data;
+	struct scsi_device *sdev;
+	int err = 0;
+	struct scsi_device_handler *devinfo = NULL;
+
+	if (!scsi_is_sdev_device(dev))
+		return 0;
+
+	sdev = to_scsi_device(dev);
+
+	if (action == BUS_NOTIFY_ADD_DEVICE) {
+		devinfo = device_handler_match(NULL, sdev);
+		if (!devinfo)
+			goto out;
+
+		err = scsi_dh_handler_attach(sdev, devinfo);
+		if (!err)
+			err = device_create_file(dev, &scsi_dh_state_attr);
+	} else if (action == BUS_NOTIFY_DEL_DEVICE) {
+		device_remove_file(dev, &scsi_dh_state_attr);
+		scsi_dh_handler_detach(sdev, NULL);
+	}
+out:
+	return err;
+}
+
+/*
+ * scsi_dh_notifier_add - Callback for scsi_register_device_handler
+ */
+static int scsi_dh_notifier_add(struct device *dev, void *data)
+{
+	struct scsi_device_handler *scsi_dh = data;
+	struct scsi_device *sdev;
+
+	if (!scsi_is_sdev_device(dev))
+		return 0;
+
+	if (!get_device(dev))
+		return 0;
+
+	sdev = to_scsi_device(dev);
+
+	if (device_handler_match(scsi_dh, sdev))
+		scsi_dh_handler_attach(sdev, scsi_dh);
+
+	put_device(dev);
+
+	return 0;
+}
+
+/*
+ * scsi_dh_notifier_remove - Callback for scsi_unregister_device_handler
+ */
+static int scsi_dh_notifier_remove(struct device *dev, void *data)
+{
+	struct scsi_device_handler *scsi_dh = data;
+	struct scsi_device *sdev;
+
+	if (!scsi_is_sdev_device(dev))
+		return 0;
+
+	if (!get_device(dev))
+		return 0;
+
+	sdev = to_scsi_device(dev);
+
+	scsi_dh_handler_detach(sdev, scsi_dh);
+
+	put_device(dev);
+
+	return 0;
+}
+
+/*
+ * scsi_register_device_handler - register a device handler personality
+ *      module.
+ * @scsi_dh - device handler to be registered.
+ *
+ * Returns 0 on success, -EBUSY if handler already registered.
+ */
+int scsi_register_device_handler(struct scsi_device_handler *scsi_dh)
+{
+	if (get_device_handler(scsi_dh->name))
+		return -EBUSY;
+
+	spin_lock(&list_lock);
+	list_add(&scsi_dh->list, &scsi_dh_list);
+	spin_unlock(&list_lock);
+	bus_for_each_dev(&scsi_bus_type, NULL, scsi_dh, scsi_dh_notifier_add);
+	printk(KERN_INFO "%s: device handler registered\n", scsi_dh->name);
+
+	return SCSI_DH_OK;
+}
+EXPORT_SYMBOL_GPL(scsi_register_device_handler);
+
+/*
+ * scsi_unregister_device_handler - register a device handler personality
+ *      module.
+ * @scsi_dh - device handler to be unregistered.
+ *
+ * Returns 0 on success, -ENODEV if handler not registered.
+ */
+int scsi_unregister_device_handler(struct scsi_device_handler *scsi_dh)
+{
+	struct scsi_dh_devinfo_list *tmp, *pos;
+
+	if (!get_device_handler(scsi_dh->name))
+		return -ENODEV;
+
+	bus_for_each_dev(&scsi_bus_type, NULL, scsi_dh,
+			 scsi_dh_notifier_remove);
+
+	spin_lock(&list_lock);
+	list_del(&scsi_dh->list);
+	list_for_each_entry_safe(pos, tmp, &scsi_dh_dev_list, node) {
+		if (pos->handler == scsi_dh) {
+			list_del(&pos->node);
+			kfree(pos);
+		}
+	}
+	spin_unlock(&list_lock);
+	printk(KERN_INFO "%s: device handler unregistered\n", scsi_dh->name);
+
+	return SCSI_DH_OK;
+}
+EXPORT_SYMBOL_GPL(scsi_unregister_device_handler);
+
+/*
+ * scsi_dh_activate - activate the path associated with the scsi_device
+ *      corresponding to the given request queue.
+ * @q - Request queue that is associated with the scsi_device to be
+ *      activated.
+ */
+int scsi_dh_activate(struct request_queue *q)
+{
+	int err = 0;
+	unsigned long flags;
+	struct scsi_device *sdev;
+	struct scsi_device_handler *scsi_dh = NULL;
+	struct scsi_dh_data *data;
+
+	spin_lock_irqsave(q->queue_lock, flags);
+	sdev = q->queuedata;
+	if (sdev && ((data = retrieve_scsi_dh_data(sdev)) != NULL))
+		scsi_dh = data->scsi_dh;
+	if (!scsi_dh || !get_device(&sdev->sdev_gendev))
+		err = SCSI_DH_NOSYS;
+	spin_unlock_irqrestore(q->queue_lock, flags);
+
+	if (err)
+		return err;
+
+	if (scsi_dh->activate)
+		err = scsi_dh->activate(sdev);
+	put_device(&sdev->sdev_gendev);
+	return err;
+}
+EXPORT_SYMBOL_GPL(scsi_dh_activate);
+
+/*
+ * scsi_dh_handler_exist - Return TRUE(1) if a device handler exists for
+ *	the given name. FALSE(0) otherwise.
+ * @name - name of the device handler.
+ */
+int scsi_dh_handler_exist(const char *name)
+{
+	return (get_device_handler(name) != NULL);
+}
+EXPORT_SYMBOL_GPL(scsi_dh_handler_exist);
+
+/*
+ * scsi_dh_handler_attach - Attach device handler
+ * @sdev - sdev the handler should be attached to
+ * @name - name of the handler to attach
+ */
+int scsi_dh_attach(struct request_queue *q, const char *name)
+{
+	unsigned long flags;
+	struct scsi_device *sdev;
+	struct scsi_device_handler *scsi_dh;
+	int err = 0;
+
+	scsi_dh = get_device_handler(name);
+	if (!scsi_dh)
+		return -EINVAL;
+
+	spin_lock_irqsave(q->queue_lock, flags);
+	sdev = q->queuedata;
+	if (!sdev || !get_device(&sdev->sdev_gendev))
+		err = -ENODEV;
+	spin_unlock_irqrestore(q->queue_lock, flags);
+
+	if (!err) {
+		err = scsi_dh_handler_attach(sdev, scsi_dh);
+
+		put_device(&sdev->sdev_gendev);
+	}
+	return err;
+}
+EXPORT_SYMBOL_GPL(scsi_dh_attach);
+
+/*
+ * scsi_dh_handler_detach - Detach device handler
+ * @sdev - sdev the handler should be detached from
+ *
+ * This function will detach the device handler only
+ * if the sdev is not part of the internal list, ie
+ * if it has been attached manually.
+ */
+void scsi_dh_detach(struct request_queue *q)
+{
+	unsigned long flags;
+	struct scsi_device *sdev;
+	struct scsi_device_handler *scsi_dh = NULL;
+	struct scsi_dh_data *scsi_dh_data;
+
+	spin_lock_irqsave(q->queue_lock, flags);
+	sdev = q->queuedata;
+	if (!sdev || !get_device(&sdev->sdev_gendev))
+		sdev = NULL;
+	spin_unlock_irqrestore(q->queue_lock, flags);
+
+	if (!sdev)
+		return;
+
+	scsi_dh_data = retrieve_scsi_dh_data(sdev);
+	if (scsi_dh_data) {
+		/* if sdev is not on internal list, detach */
+		scsi_dh = scsi_dh_data->scsi_dh;
+		if (!device_handler_match(scsi_dh, sdev))
+			scsi_dh_handler_detach(sdev, scsi_dh);
+	}
+	put_device(&sdev->sdev_gendev);
+}
+EXPORT_SYMBOL_GPL(scsi_dh_detach);
+
+static struct notifier_block scsi_dh_nb = {
+	.notifier_call = scsi_dh_notifier
+};
+
+static int __init scsi_dh_init(void)
+{
+	int r;
+
+	r = bus_register_notifier(&scsi_bus_type, &scsi_dh_nb);
+
+	if (!r)
+		bus_for_each_dev(&scsi_bus_type, NULL, NULL,
+				 scsi_dh_sysfs_attr_add);
+
+	return r;
+}
+
+static void __exit scsi_dh_exit(void)
+{
+	bus_for_each_dev(&scsi_bus_type, NULL, NULL,
+			 scsi_dh_sysfs_attr_remove);
+	bus_unregister_notifier(&scsi_bus_type, &scsi_dh_nb);
+}
+
+module_init(scsi_dh_init);
+module_exit(scsi_dh_exit);
+
+MODULE_DESCRIPTION("SCSI device handler");
+MODULE_AUTHOR("Chandra Seetharaman <sekharan@us.ibm.com>");
+MODULE_LICENSE("GPL");
diff --git a/drivers/scsi/scsi_dh_export.c b/drivers/scsi/scsi_dh_export.c
new file mode 100644
index 0000000..ec025c7
--- /dev/null
+++ b/drivers/scsi/scsi_dh_export.c
@@ -0,0 +1,40 @@
+/*
+ * SCSI device handler infrastruture - export symbols used by scsi generic
+ *
+ * This program is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License as published by the
+ * Free Software Foundation; either version 2 of the License, or (at your
+ * option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with this program; if not, write to the Free Software Foundation, Inc.,
+ * 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
+ *
+ * Copyright IBM Corporation, 2008
+ *      Authors:
+ *               Chandra Seetharaman <sekharan@us.ibm.com>
+ */
+
+#include <scsi/scsi_dh.h>
+
+void store_scsi_dh_data(struct scsi_device *sdev, struct scsi_dh_data *data)
+{
+	struct scsi_device_dh_data *s = container_of(sdev,
+					struct scsi_device_dh_data, sdev);
+	s->scsi_dh_data = data;
+}
+EXPORT_SYMBOL_GPL(store_scsi_dh_data);
+
+struct scsi_dh_data *retrieve_scsi_dh_data(struct scsi_device *sdev)
+{
+	struct scsi_device_dh_data *s = container_of(sdev,
+					struct scsi_device_dh_data, sdev);
+	return s->scsi_dh_data;
+}
+EXPORT_SYMBOL_GPL(retrieve_scsi_dh_data);
+
diff --git a/drivers/scsi/scsi_error.c b/drivers/scsi/scsi_error.c
index ab13c38..6cb4584 100644
--- a/drivers/scsi/scsi_error.c
+++ b/drivers/scsi/scsi_error.c
@@ -33,6 +33,7 @@
 #include <scsi/scsi_transport.h>
 #include <scsi/scsi_host.h>
 #include <scsi/scsi_ioctl.h>
+#include <scsi/scsi_dh.h>
 
 #include "scsi_priv.h"
 #include "scsi_logging.h"
@@ -298,7 +299,9 @@ static inline void scsi_eh_prt_fail_stats(struct Scsi_Host *shost,
  **/
 static int scsi_check_sense(struct scsi_cmnd *scmd)
 {
+	struct scsi_device *sdev = scmd->device;
 	struct scsi_sense_hdr sshdr;
+	struct scsi_dh_data *scsi_dh_data = retrieve_scsi_dh_data(sdev);
 
 	if (! scsi_command_normalize_sense(scmd, &sshdr))
 		return FAILED;	/* no valid sense data */
@@ -306,6 +309,16 @@ static int scsi_check_sense(struct scsi_cmnd *scmd)
 	if (scsi_sense_is_deferred(&sshdr))
 		return NEEDS_RETRY;
 
+	if (scsi_dh_data && scsi_dh_data->scsi_dh &&
+			scsi_dh_data->scsi_dh->check_sense) {
+		int rc;
+
+		rc = scsi_dh_data->scsi_dh->check_sense(sdev, &sshdr);
+		if (rc != SCSI_RETURN_NOT_HANDLED)
+			return rc;
+		/* handler does not care. Drop down to default handling */
+	}
+
 	/*
 	 * Previous logic looked for FILEMARK, EOM or ILI which are
 	 * mainly associated with tapes and returned SUCCESS.
diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c
index 9cd2d39..35332a4 100644
--- a/drivers/scsi/scsi_lib.c
+++ b/drivers/scsi/scsi_lib.c
@@ -25,6 +25,7 @@
 #include <scsi/scsi_driver.h>
 #include <scsi/scsi_eh.h>
 #include <scsi/scsi_host.h>
+#include <scsi/scsi_dh.h>
 
 #include "scsi_priv.h"
 #include "scsi_logging.h"
@@ -1104,6 +1105,7 @@ static int scsi_prep_fn(struct request_queue *q, struct request *req)
 	struct scsi_device *sdev = q->queuedata;
 	struct scsi_cmnd *cmd;
 	int specials_only = 0;
+	struct scsi_dh_data *scsi_dh_data = retrieve_scsi_dh_data(sdev);
 
 	/*
 	 * Just check to see if the device is online.  If it isn't, we
@@ -1131,6 +1133,18 @@ static int scsi_prep_fn(struct request_queue *q, struct request *req)
 	}
 
 	/*
+	 * If it is a filesystem cmd, call the prep_fn of the
+	 * hardware handler.
+	 */
+	if (blk_fs_request(req) &&
+		unlikely(scsi_dh_data && scsi_dh_data->scsi_dh
+			&& scsi_dh_data->scsi_dh->prep_fn)) {
+		int ret = scsi_dh_data->scsi_dh->prep_fn(sdev, req);
+		if (ret != BLKPREP_OK)
+			return ret;
+	}
+
+	/*
 	 * Find the actual device driver associated with this command.
 	 * The SPECIAL requests are things like character device or
 	 * ioctls, which did not originate from ll_rw_blk.  Note that
diff --git a/drivers/scsi/scsi_scan.c b/drivers/scsi/scsi_scan.c
index f7384c1..0be62ad 100644
--- a/drivers/scsi/scsi_scan.c
+++ b/drivers/scsi/scsi_scan.c
@@ -204,8 +204,8 @@ static struct scsi_device *scsi_alloc_sdev(struct scsi_target *starget,
 	int display_failure_msg = 1, ret;
 	struct Scsi_Host *shost = dev_to_shost(starget->dev.parent);
 
-	sdev = kzalloc(sizeof(*sdev) + shost->transportt->device_size,
-		       GFP_ATOMIC);
+	sdev = kzalloc(sizeof(*sdev) + shost->transportt->device_size
+			+ sizeof(struct scsi_dh_data *), GFP_ATOMIC);
 	if (!sdev)
 		goto out;
 
diff --git a/drivers/scsi/scsi_sysfs.c b/drivers/scsi/scsi_sysfs.c
index 48676b7..0a8eac3 100644
--- a/drivers/scsi/scsi_sysfs.c
+++ b/drivers/scsi/scsi_sysfs.c
@@ -313,6 +313,7 @@ struct bus_type scsi_bus_type = {
 	.suspend	= scsi_bus_suspend,
 	.resume		= scsi_bus_resume,
 };
+EXPORT_SYMBOL_GPL(scsi_bus_type);
 
 int scsi_sysfs_register(void)
 {
diff --git a/include/scsi/scsi.h b/include/scsi/scsi.h
index 583e2e7..2048abc 100644
--- a/include/scsi/scsi.h
+++ b/include/scsi/scsi.h
@@ -347,6 +347,7 @@ struct scsi_lun {
 #define SOFT_ERROR      0x2005
 #define ADD_TO_MLQUEUE  0x2006
 #define TIMEOUT_ERROR   0x2007
+#define SCSI_RETURN_NOT_HANDLED   0x2008
 
 /*
  * Midlevel queue return values.
diff --git a/include/scsi/scsi_device.h b/include/scsi/scsi_device.h
index af224bb..7fc5ac4 100644
--- a/include/scsi/scsi_device.h
+++ b/include/scsi/scsi_device.h
@@ -7,6 +7,7 @@
 #include <linux/workqueue.h>
 #include <asm/atomic.h>
 
+struct request;
 struct request_queue;
 struct scsi_cmnd;
 struct scsi_lun;
@@ -164,6 +165,38 @@ struct scsi_device {
 	enum scsi_device_state sdev_state;
 	unsigned long		sdev_data[0];
 } __attribute__((aligned(sizeof(unsigned long))));
+
+struct scsi_dh_devlist {
+	char *vendor;
+	char *model;
+};
+
+struct scsi_device_dh_data {
+	struct scsi_device	sdev;
+	struct scsi_dh_data	*scsi_dh_data;
+	unsigned long		sdev_data[0];
+} __attribute__((aligned(sizeof(unsigned long))));
+
+struct scsi_device_handler {
+	/* Used by the infrastructure */
+	struct list_head list; /* list of scsi_device_handlers */
+
+	/* Filled by the hardware handler */
+	struct module *module;
+	const char *name;
+	const struct scsi_dh_devlist *devlist;
+	int (*check_sense)(struct scsi_device *, struct scsi_sense_hdr *);
+	int (*attach)(struct scsi_device *);
+	void (*detach)(struct scsi_device *);
+	int (*activate)(struct scsi_device *);
+	int (*prep_fn)(struct scsi_device *, struct request *);
+};
+
+struct scsi_dh_data {
+	struct scsi_device_handler *scsi_dh;
+	char buf[0];
+};
+
 #define	to_scsi_device(d)	\
 	container_of(d, struct scsi_device, sdev_gendev)
 #define	class_to_sdev(d)	\
@@ -238,6 +271,9 @@ extern int scsi_add_device(struct Scsi_Host *host, uint channel,
 extern void scsi_remove_device(struct scsi_device *);
 extern int scsi_device_cancel(struct scsi_device *, int);
 
+extern int scsi_register_device_handler(struct scsi_device_handler *scsi_dh);
+extern int scsi_unregister_device_handler(struct scsi_device_handler *scsi_dh);
+
 extern int scsi_device_get(struct scsi_device *);
 extern void scsi_device_put(struct scsi_device *);
 extern struct scsi_device *scsi_device_lookup(struct Scsi_Host *,
diff --git a/include/scsi/scsi_dh.h b/include/scsi/scsi_dh.h
new file mode 100644
index 0000000..c901a9f
--- /dev/null
+++ b/include/scsi/scsi_dh.h
@@ -0,0 +1,91 @@
+/*
+ * Header file for SCSI device handler infrastruture.
+ *
+ * Modified version of patches posted by Mike Christie <michaelc@cs.wisc.edu>
+ *
+ * This program is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License as published by the
+ * Free Software Foundation; either version 2 of the License, or (at your
+ * option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with this program; if not, write to the Free Software Foundation, Inc.,
+ * 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
+ *
+ * Copyright IBM Corporation, 2007
+ *      Authors:
+ *               Chandra Seetharaman <sekharan@us.ibm.com>
+ *               Mike Anderson <andmike@linux.vnet.ibm.com>
+ */
+
+#include <linux/blkdev.h>
+#include <scsi/scsi_device.h>
+
+enum {
+	SCSI_DH_OK = 0,
+	/*
+	 * device errors
+	 */
+	SCSI_DH_DEV_FAILED,	/* generic device error */
+	SCSI_DH_DEV_TEMP_BUSY,
+	SCSI_DH_DEVICE_MAX,	/* max device blkerr definition */
+
+	/*
+	 * transport errors
+	 */
+	SCSI_DH_NOTCONN = SCSI_DH_DEVICE_MAX + 1,
+	SCSI_DH_CONN_FAILURE,
+	SCSI_DH_TRANSPORT_MAX,	/* max transport blkerr definition */
+
+	/*
+	 * driver and generic errors
+	 */
+	SCSI_DH_IO = SCSI_DH_TRANSPORT_MAX + 1,	/* generic error */
+	SCSI_DH_INVALID_IO,
+	SCSI_DH_RETRY,		/* retry the req, but not immediately */
+	SCSI_DH_IMM_RETRY,	/* immediately retry the req */
+	SCSI_DH_TIMED_OUT,
+	SCSI_DH_RES_TEMP_UNAVAIL,
+	SCSI_DH_DEV_OFFLINED,
+	SCSI_DH_NOSYS,
+	SCSI_DH_DRIVER_MAX,
+};
+
+#if defined(CONFIG_SCSI_DH) || defined(CONFIG_SCSI_DH_MODULE)
+extern int scsi_dh_activate(struct request_queue *);
+extern int scsi_dh_handler_exist(const char *);
+extern void store_scsi_dh_data(struct scsi_device *, struct scsi_dh_data *);
+extern struct scsi_dh_data *retrieve_scsi_dh_data(struct scsi_device *);
+extern int scsi_dh_attach(struct request_queue *, const char *);
+extern void scsi_dh_detach(struct request_queue *);
+#else
+static inline int scsi_dh_activate(struct request_queue *req)
+{
+	return 0;
+}
+static inline int scsi_dh_handler_exist(const char *name)
+{
+	return 0;
+}
+static inline void store_scsi_dh_data(struct scsi_device *sdev,
+				struct scsi_dh_data *scsi_dh_data)
+{
+}
+static inline struct scsi_dh_data *retrieve_scsi_dh_data(struct scsi_device *sdev)
+{
+	return NULL;
+}
+static inline int scsi_dh_attach(struct request_queue *req, const char *name)
+{
+	return SCSI_DH_NOSYS;
+}
+static inline void scsi_dh_detach(struct request_queue *q)
+{
+	return;
+}
+#endif
diff --git a/include/scsi/scsi_transport.h b/include/scsi/scsi_transport.h
index cca1d49..8dbe858 100644
--- a/include/scsi/scsi_transport.h
+++ b/include/scsi/scsi_transport.h
@@ -101,6 +101,7 @@ scsi_transport_device_data(struct scsi_device *sdev)
 {
 	struct Scsi_Host *shost = sdev->host;
 	return (u8 *)sdev->sdev_data
+		+ sizeof(struct scsi_dh_data *)
 		+ shost->transportt->device_private_offset;
 }