[SCSI] scsi_dh: add infrastructure for SCSI Device Handlers

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.

Signed-off-by: Chandra Seetharaman <sekharan@us.ibm.com>
Signed-off-by: Mike Anderson <andmike@linux.vnet.ibm.com>
Signed-off-by: Mike Christie <michaelc@cs.wisc.edu>
Signed-off-by: James Bottomley <James.Bottomley@HansenPartnership.com>

8 files changed, 201 insertions, 0 deletions

diff --git a/drivers/scsi/Kconfig b/drivers/scsi/Kconfig
index 81ccbd7f9e3..7886ec6e5f8 100644
--- a/drivers/scsi/Kconfig
+++ b/drivers/scsi/Kconfig
@@ -1771,4 +1771,6 @@ endif # SCSI_LOWLEVEL
 
 source "drivers/scsi/pcmcia/Kconfig"
 
+source "drivers/scsi/device_handler/Kconfig"
+
 endmenu
diff --git a/drivers/scsi/Makefile b/drivers/scsi/Makefile
index 6c775e350c9..aa8272e188e 100644
--- a/drivers/scsi/Makefile
+++ b/drivers/scsi/Makefile
@@ -34,6 +34,7 @@ obj-$(CONFIG_SCSI_ISCSI_ATTRS)	+= scsi_transport_iscsi.o
 obj-$(CONFIG_SCSI_SAS_ATTRS)	+= scsi_transport_sas.o
 obj-$(CONFIG_SCSI_SAS_LIBSAS)	+= libsas/
 obj-$(CONFIG_SCSI_SRP_ATTRS)	+= scsi_transport_srp.o
+obj-$(CONFIG_SCSI_DH)		+= device_handler/
 
 obj-$(CONFIG_ISCSI_TCP) 	+= libiscsi.o	iscsi_tcp.o
 obj-$(CONFIG_INFINIBAND_ISER) 	+= libiscsi.o
diff --git a/drivers/scsi/device_handler/Kconfig b/drivers/scsi/device_handler/Kconfig
new file mode 100644
index 00000000000..228241d1d98
--- /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 00000000000..f306e44e383
--- /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 00000000000..ab6c21cd968
--- /dev/null
+++ b/drivers/scsi/device_handler/scsi_dh.c
@@ -0,0 +1,162 @@
+/*
+ * 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"
+
+static DEFINE_SPINLOCK(list_lock);
+static LIST_HEAD(scsi_dh_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 (!strcmp(tmp->name, name)) {
+			found = tmp;
+			break;
+		}
+	}
+	spin_unlock(&list_lock);
+	return found;
+}
+
+static int scsi_dh_notifier_add(struct device *dev, void *data)
+{
+	struct scsi_device_handler *scsi_dh = data;
+
+	scsi_dh->nb.notifier_call(&scsi_dh->nb, BUS_NOTIFY_ADD_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)
+{
+	int ret = -EBUSY;
+	struct scsi_device_handler *tmp;
+
+	tmp = get_device_handler(scsi_dh->name);
+	if (tmp)
+		goto done;
+
+	ret = bus_register_notifier(&scsi_bus_type, &scsi_dh->nb);
+
+	bus_for_each_dev(&scsi_bus_type, NULL, scsi_dh, scsi_dh_notifier_add);
+	spin_lock(&list_lock);
+	list_add(&scsi_dh->list, &scsi_dh_list);
+	spin_unlock(&list_lock);
+
+done:
+	return ret;
+}
+EXPORT_SYMBOL_GPL(scsi_register_device_handler);
+
+static int scsi_dh_notifier_remove(struct device *dev, void *data)
+{
+	struct scsi_device_handler *scsi_dh = data;
+
+	scsi_dh->nb.notifier_call(&scsi_dh->nb, BUS_NOTIFY_DEL_DEVICE, dev);
+	return 0;
+}
+
+/*
+ * 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)
+{
+	int ret = -ENODEV;
+	struct scsi_device_handler *tmp;
+
+	tmp = get_device_handler(scsi_dh->name);
+	if (!tmp)
+		goto done;
+
+	ret = bus_unregister_notifier(&scsi_bus_type, &scsi_dh->nb);
+
+	bus_for_each_dev(&scsi_bus_type, NULL, scsi_dh,
+					scsi_dh_notifier_remove);
+	spin_lock(&list_lock);
+	list_del(&scsi_dh->list);
+	spin_unlock(&list_lock);
+
+done:
+	return ret;
+}
+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;
+
+	spin_lock_irqsave(q->queue_lock, flags);
+	sdev = q->queuedata;
+	if (sdev && sdev->scsi_dh_data)
+		scsi_dh = sdev->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);
+
+MODULE_DESCRIPTION("SCSI device handler");
+MODULE_AUTHOR("Chandra Seetharaman <sekharan@us.ibm.com>");
+MODULE_LICENSE("GPL");
diff --git a/drivers/scsi/scsi_error.c b/drivers/scsi/scsi_error.c
index eaf5a8add1b..006a95916f7 100644
--- a/drivers/scsi/scsi_error.c
+++ b/drivers/scsi/scsi_error.c
@@ -298,6 +298,7 @@ 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;
 
 	if (! scsi_command_normalize_sense(scmd, &sshdr))
@@ -306,6 +307,16 @@ static int scsi_check_sense(struct scsi_cmnd *scmd)
 	if (scsi_sense_is_deferred(&sshdr))
 		return NEEDS_RETRY;
 
+	if (sdev->scsi_dh_data && sdev->scsi_dh_data->scsi_dh &&
+			sdev->scsi_dh_data->scsi_dh->check_sense) {
+		int rc;
+
+		rc = sdev->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 a82d2fe80fb..033c58a65f5 100644
--- a/drivers/scsi/scsi_lib.c
+++ b/drivers/scsi/scsi_lib.c
@@ -1160,6 +1160,14 @@ int scsi_setup_fs_cmnd(struct scsi_device *sdev, struct request *req)
 
 	if (ret != BLKPREP_OK)
 		return ret;
+
+	if (unlikely(sdev->scsi_dh_data && sdev->scsi_dh_data->scsi_dh
+			 && sdev->scsi_dh_data->scsi_dh->prep_fn)) {
+		ret = sdev->scsi_dh_data->scsi_dh->prep_fn(sdev, req);
+		if (ret != BLKPREP_OK)
+			return ret;
+	}
+
 	/*
 	 * Filesystem requests must transfer data.
 	 */
diff --git a/drivers/scsi/scsi_sysfs.c b/drivers/scsi/scsi_sysfs.c
index 93d2b671445..b6e56105977 100644
--- a/drivers/scsi/scsi_sysfs.c
+++ b/drivers/scsi/scsi_sysfs.c
@@ -439,6 +439,7 @@ struct bus_type scsi_bus_type = {
 	.resume		= scsi_bus_resume,
 	.remove		= scsi_bus_remove,
 };
+EXPORT_SYMBOL_GPL(scsi_bus_type);
 
 int scsi_sysfs_register(void)
 {