drivers/block/xen-blkback/xenbus.c - kernel/msm-4.9 - Gitiles

 /*  Xenbus code for blkif backend
     Copyright (C) 2005 Rusty Russell <rusty@rustcorp.com.au>
     Copyright (C) 2005 XenSource Ltd

     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.

 */

 #include <stdarg.h>
 #include <linux/module.h>
 #include <linux/kthread.h>
 #include <xen/events.h>
 #include <xen/grant_table.h>
 #include "common.h"

 struct backend_info {
 	struct xenbus_device	*dev;
 	struct xen_blkif	*blkif;
 	struct xenbus_watch	backend_watch;
 	unsigned		major;
 	unsigned		minor;
 	char			*mode;
 };

 static struct kmem_cache *xen_blkif_cachep;
 static void connect(struct backend_info *);
 static int connect_ring(struct backend_info *);
 static void backend_changed(struct xenbus_watch *, const char **,
 			    unsigned int);

 struct xenbus_device *xen_blkbk_xenbus(struct backend_info *be)
 {
 	return be->dev;
 }

 static int blkback_name(struct xen_blkif *blkif, char *buf)
 {
 	char *devpath, *devname;
 	struct xenbus_device *dev = blkif->be->dev;

 	devpath = xenbus_read(XBT_NIL, dev->nodename, "dev", NULL);
 	if (IS_ERR(devpath))
 		return PTR_ERR(devpath);

 	devname = strstr(devpath, "/dev/");
 	if (devname != NULL)
 		devname += strlen("/dev/");
 	else
 		devname  = devpath;

 	snprintf(buf, TASK_COMM_LEN, "blkback.%d.%s", blkif->domid, devname);
 	kfree(devpath);

 	return 0;
 }

 static void xen_update_blkif_status(struct xen_blkif *blkif)
 {
 	int err;
 	char name[TASK_COMM_LEN];

 	/* Not ready to connect? */
 	if (!blkif->irq || !blkif->vbd.bdev)
 		return;

 	/* Already connected? */
 	if (blkif->be->dev->state == XenbusStateConnected)
 		return;

 	/* Attempt to connect: exit if we fail to. */
 	connect(blkif->be);
 	if (blkif->be->dev->state != XenbusStateConnected)
 		return;

 	err = blkback_name(blkif, name);
 	if (err) {
 		xenbus_dev_error(blkif->be->dev, err, "get blkback dev name");
 		return;
 	}

 	err = filemap_write_and_wait(blkif->vbd.bdev->bd_inode->i_mapping);
 	if (err) {
 		xenbus_dev_error(blkif->be->dev, err, "block flush");
 		return;
 	}
 	invalidate_inode_pages2(blkif->vbd.bdev->bd_inode->i_mapping);

 	blkif->xenblkd = kthread_run(xen_blkif_schedule, blkif, name);
 	if (IS_ERR(blkif->xenblkd)) {
 		err = PTR_ERR(blkif->xenblkd);
 		blkif->xenblkd = NULL;
 		xenbus_dev_error(blkif->be->dev, err, "start xenblkd");
 	}
 }

 static struct xen_blkif *xen_blkif_alloc(domid_t domid)
 {
 	struct xen_blkif *blkif;

 	blkif = kmem_cache_zalloc(xen_blkif_cachep, GFP_KERNEL);
 	if (!blkif)
 		return ERR_PTR(-ENOMEM);

 	blkif->domid = domid;
 	spin_lock_init(&blkif->blk_ring_lock);
 	atomic_set(&blkif->refcnt, 1);
 	init_waitqueue_head(&blkif->wq);
 	init_completion(&blkif->drain_complete);
 	atomic_set(&blkif->drain, 0);
 	blkif->st_print = jiffies;
 	init_waitqueue_head(&blkif->waiting_to_free);

 	return blkif;
 }

 static int xen_blkif_map(struct xen_blkif *blkif, unsigned long shared_page,
 			 unsigned int evtchn)
 {
 	int err;

 	/* Already connected through? */
 	if (blkif->irq)
 		return 0;

 	err = xenbus_map_ring_valloc(blkif->be->dev, shared_page, &blkif->blk_ring);
 	if (err < 0)
 		return err;

 	switch (blkif->blk_protocol) {
 	case BLKIF_PROTOCOL_NATIVE:
 	{
 		struct blkif_sring *sring;
 		sring = (struct blkif_sring *)blkif->blk_ring;
 		BACK_RING_INIT(&blkif->blk_rings.native, sring, PAGE_SIZE);
 		break;
 	}
 	case BLKIF_PROTOCOL_X86_32:
 	{
 		struct blkif_x86_32_sring *sring_x86_32;
 		sring_x86_32 = (struct blkif_x86_32_sring *)blkif->blk_ring;
 		BACK_RING_INIT(&blkif->blk_rings.x86_32, sring_x86_32, PAGE_SIZE);
 		break;
 	}
 	case BLKIF_PROTOCOL_X86_64:
 	{
 		struct blkif_x86_64_sring *sring_x86_64;
 		sring_x86_64 = (struct blkif_x86_64_sring *)blkif->blk_ring;
 		BACK_RING_INIT(&blkif->blk_rings.x86_64, sring_x86_64, PAGE_SIZE);
 		break;
 	}
 	default:
 		BUG();
 	}

 	err = bind_interdomain_evtchn_to_irqhandler(blkif->domid, evtchn,
 						    xen_blkif_be_int, 0,
 						    "blkif-backend", blkif);
 	if (err < 0) {
 		xenbus_unmap_ring_vfree(blkif->be->dev, blkif->blk_ring);
 		blkif->blk_rings.common.sring = NULL;
 		return err;
 	}
 	blkif->irq = err;

 	return 0;
 }

 static void xen_blkif_disconnect(struct xen_blkif *blkif)
 {
 	if (blkif->xenblkd) {
 		kthread_stop(blkif->xenblkd);
 		blkif->xenblkd = NULL;
 	}

 	atomic_dec(&blkif->refcnt);
 	wait_event(blkif->waiting_to_free, atomic_read(&blkif->refcnt) == 0);
 	atomic_inc(&blkif->refcnt);

 	if (blkif->irq) {
 		unbind_from_irqhandler(blkif->irq, blkif);
 		blkif->irq = 0;
 	}

 	if (blkif->blk_rings.common.sring) {
 		xenbus_unmap_ring_vfree(blkif->be->dev, blkif->blk_ring);
 		blkif->blk_rings.common.sring = NULL;
 	}
 }

 static void xen_blkif_free(struct xen_blkif *blkif)
 {
 	if (!atomic_dec_and_test(&blkif->refcnt))
 		BUG();
 	kmem_cache_free(xen_blkif_cachep, blkif);
 }

 int __init xen_blkif_interface_init(void)
 {
 	xen_blkif_cachep = kmem_cache_create("blkif_cache",
 					     sizeof(struct xen_blkif),
 					     0, 0, NULL);
 	if (!xen_blkif_cachep)
 		return -ENOMEM;

 	return 0;
 }

 /*
  *  sysfs interface for VBD I/O requests
  */

 #define VBD_SHOW(name, format, args...)					\
 	static ssize_t show_##name(struct device *_dev,			\
 				   struct device_attribute *attr,	\
 				   char *buf)				\
 	{								\
 		struct xenbus_device *dev = to_xenbus_device(_dev);	\
 		struct backend_info *be = dev_get_drvdata(&dev->dev);	\
 									\
 		return sprintf(buf, format, ##args);			\
 	}								\
 	static DEVICE_ATTR(name, S_IRUGO, show_##name, NULL)

 VBD_SHOW(oo_req,  "%d\n", be->blkif->st_oo_req);
 VBD_SHOW(rd_req,  "%d\n", be->blkif->st_rd_req);
 VBD_SHOW(wr_req,  "%d\n", be->blkif->st_wr_req);
 VBD_SHOW(f_req,  "%d\n", be->blkif->st_f_req);
 VBD_SHOW(ds_req,  "%d\n", be->blkif->st_ds_req);
 VBD_SHOW(rd_sect, "%d\n", be->blkif->st_rd_sect);
 VBD_SHOW(wr_sect, "%d\n", be->blkif->st_wr_sect);

 static struct attribute *xen_vbdstat_attrs[] = {
 	&dev_attr_oo_req.attr,
 	&dev_attr_rd_req.attr,
 	&dev_attr_wr_req.attr,
 	&dev_attr_f_req.attr,
 	&dev_attr_ds_req.attr,
 	&dev_attr_rd_sect.attr,
 	&dev_attr_wr_sect.attr,
 	NULL
 };

 static struct attribute_group xen_vbdstat_group = {
 	.name = "statistics",
 	.attrs = xen_vbdstat_attrs,
 };

 VBD_SHOW(physical_device, "%x:%x\n", be->major, be->minor);
 VBD_SHOW(mode, "%s\n", be->mode);

 static int xenvbd_sysfs_addif(struct xenbus_device *dev)
 {
 	int error;

 	error = device_create_file(&dev->dev, &dev_attr_physical_device);
 	if (error)
 		goto fail1;

 	error = device_create_file(&dev->dev, &dev_attr_mode);
 	if (error)
 		goto fail2;

 	error = sysfs_create_group(&dev->dev.kobj, &xen_vbdstat_group);
 	if (error)
 		goto fail3;

 	return 0;

 fail3:	sysfs_remove_group(&dev->dev.kobj, &xen_vbdstat_group);
 fail2:	device_remove_file(&dev->dev, &dev_attr_mode);
 fail1:	device_remove_file(&dev->dev, &dev_attr_physical_device);
 	return error;
 }

 static void xenvbd_sysfs_delif(struct xenbus_device *dev)
 {
 	sysfs_remove_group(&dev->dev.kobj, &xen_vbdstat_group);
 	device_remove_file(&dev->dev, &dev_attr_mode);
 	device_remove_file(&dev->dev, &dev_attr_physical_device);
 }


 static void xen_vbd_free(struct xen_vbd *vbd)
 {
 	if (vbd->bdev)
 		blkdev_put(vbd->bdev, vbd->readonly ? FMODE_READ : FMODE_WRITE);
 	vbd->bdev = NULL;
 }

 static int xen_vbd_create(struct xen_blkif *blkif, blkif_vdev_t handle,
 			  unsigned major, unsigned minor, int readonly,
 			  int cdrom)
 {
 	struct xen_vbd *vbd;
 	struct block_device *bdev;
 	struct request_queue *q;

 	vbd = &blkif->vbd;
 	vbd->handle   = handle;
 	vbd->readonly = readonly;
 	vbd->type     = 0;

 	vbd->pdevice  = MKDEV(major, minor);

 	bdev = blkdev_get_by_dev(vbd->pdevice, vbd->readonly ?
 				 FMODE_READ : FMODE_WRITE, NULL);

 	if (IS_ERR(bdev)) {
 		DPRINTK("xen_vbd_create: device %08x could not be opened.\n",
 			vbd->pdevice);
 		return -ENOENT;
 	}

 	vbd->bdev = bdev;
 	if (vbd->bdev->bd_disk == NULL) {
 		DPRINTK("xen_vbd_create: device %08x doesn't exist.\n",
 			vbd->pdevice);
 		xen_vbd_free(vbd);
 		return -ENOENT;
 	}
 	vbd->size = vbd_sz(vbd);

 	if (vbd->bdev->bd_disk->flags & GENHD_FL_CD || cdrom)
 		vbd->type |= VDISK_CDROM;
 	if (vbd->bdev->bd_disk->flags & GENHD_FL_REMOVABLE)
 		vbd->type |= VDISK_REMOVABLE;

 	q = bdev_get_queue(bdev);
 	if (q && q->flush_flags)
 		vbd->flush_support = true;

 	if (q && blk_queue_secdiscard(q))
 		vbd->discard_secure = true;

 	DPRINTK("Successful creation of handle=%04x (dom=%u)\n",
 		handle, blkif->domid);
 	return 0;
 }
 static int xen_blkbk_remove(struct xenbus_device *dev)
 {
 	struct backend_info *be = dev_get_drvdata(&dev->dev);

 	DPRINTK("");

 	if (be->major || be->minor)
 		xenvbd_sysfs_delif(dev);

 	if (be->backend_watch.node) {
 		unregister_xenbus_watch(&be->backend_watch);
 		kfree(be->backend_watch.node);
 		be->backend_watch.node = NULL;
 	}

 	if (be->blkif) {
 		xen_blkif_disconnect(be->blkif);
 		xen_vbd_free(&be->blkif->vbd);
 		xen_blkif_free(be->blkif);
 		be->blkif = NULL;
 	}

 	kfree(be);
 	dev_set_drvdata(&dev->dev, NULL);
 	return 0;
 }

 int xen_blkbk_flush_diskcache(struct xenbus_transaction xbt,
 			      struct backend_info *be, int state)
 {
 	struct xenbus_device *dev = be->dev;
 	int err;

 	err = xenbus_printf(xbt, dev->nodename, "feature-flush-cache",
 			    "%d", state);
 	if (err)
 		dev_warn(&dev->dev, "writing feature-flush-cache (%d)", err);

 	return err;
 }

 static void xen_blkbk_discard(struct xenbus_transaction xbt, struct backend_info *be)
 {
 	struct xenbus_device *dev = be->dev;
 	struct xen_blkif *blkif = be->blkif;
 	int err;
 	int state = 0;
 	struct block_device *bdev = be->blkif->vbd.bdev;
 	struct request_queue *q = bdev_get_queue(bdev);

 	if (blk_queue_discard(q)) {
 		err = xenbus_printf(xbt, dev->nodename,
 			"discard-granularity", "%u",
 			q->limits.discard_granularity);
 		if (err) {
 			dev_warn(&dev->dev, "writing discard-granularity (%d)", err);
 			return;
 		}
 		err = xenbus_printf(xbt, dev->nodename,
 			"discard-alignment", "%u",
 			q->limits.discard_alignment);
 		if (err) {
 			dev_warn(&dev->dev, "writing discard-alignment (%d)", err);
 			return;
 		}
 		state = 1;
 		/* Optional. */
 		err = xenbus_printf(xbt, dev->nodename,
 				    "discard-secure", "%d",
 				    blkif->vbd.discard_secure);
 		if (err) {
 			dev_warn(&dev->dev, "writing discard-secure (%d)", err);
 			return;
 		}
 	}
 	err = xenbus_printf(xbt, dev->nodename, "feature-discard",
 			    "%d", state);
 	if (err)
 		dev_warn(&dev->dev, "writing feature-discard (%d)", err);
 }
 int xen_blkbk_barrier(struct xenbus_transaction xbt,
 		      struct backend_info *be, int state)
 {
 	struct xenbus_device *dev = be->dev;
 	int err;

 	err = xenbus_printf(xbt, dev->nodename, "feature-barrier",
 			    "%d", state);
 	if (err)
 		dev_warn(&dev->dev, "writing feature-barrier (%d)", err);

 	return err;
 }

 /*
  * Entry point to this code when a new device is created.  Allocate the basic
  * structures, and watch the store waiting for the hotplug scripts to tell us
  * the device's physical major and minor numbers.  Switch to InitWait.
  */
 static int xen_blkbk_probe(struct xenbus_device *dev,
 			   const struct xenbus_device_id *id)
 {
 	int err;
 	struct backend_info *be = kzalloc(sizeof(struct backend_info),
 					  GFP_KERNEL);
 	if (!be) {
 		xenbus_dev_fatal(dev, -ENOMEM,
 				 "allocating backend structure");
 		return -ENOMEM;
 	}
 	be->dev = dev;
 	dev_set_drvdata(&dev->dev, be);

 	be->blkif = xen_blkif_alloc(dev->otherend_id);
 	if (IS_ERR(be->blkif)) {
 		err = PTR_ERR(be->blkif);
 		be->blkif = NULL;
 		xenbus_dev_fatal(dev, err, "creating block interface");
 		goto fail;
 	}

 	/* setup back pointer */
 	be->blkif->be = be;

 	err = xenbus_watch_pathfmt(dev, &be->backend_watch, backend_changed,
 				   "%s/%s", dev->nodename, "physical-device");
 	if (err)
 		goto fail;

 	err = xenbus_switch_state(dev, XenbusStateInitWait);
 	if (err)
 		goto fail;

 	return 0;

 fail:
 	DPRINTK("failed");
 	xen_blkbk_remove(dev);
 	return err;
 }


 /*
  * Callback received when the hotplug scripts have placed the physical-device
  * node.  Read it and the mode node, and create a vbd.  If the frontend is
  * ready, connect.
  */
 static void backend_changed(struct xenbus_watch *watch,
 			    const char **vec, unsigned int len)
 {
 	int err;
 	unsigned major;
 	unsigned minor;
 	struct backend_info *be
 		= container_of(watch, struct backend_info, backend_watch);
 	struct xenbus_device *dev = be->dev;
 	int cdrom = 0;
 	char *device_type;

 	DPRINTK("");

 	err = xenbus_scanf(XBT_NIL, dev->nodename, "physical-device", "%x:%x",
 			   &major, &minor);
 	if (XENBUS_EXIST_ERR(err)) {
 		/*
 		 * Since this watch will fire once immediately after it is
 		 * registered, we expect this.  Ignore it, and wait for the
 		 * hotplug scripts.
 		 */
 		return;
 	}
 	if (err != 2) {
 		xenbus_dev_fatal(dev, err, "reading physical-device");
 		return;
 	}

 	if ((be->major || be->minor) &&
 	    ((be->major != major) || (be->minor != minor))) {
 		pr_warn(DRV_PFX "changing physical device (from %x:%x to %x:%x) not supported.\n",
 			be->major, be->minor, major, minor);
 		return;
 	}

 	be->mode = xenbus_read(XBT_NIL, dev->nodename, "mode", NULL);
 	if (IS_ERR(be->mode)) {
 		err = PTR_ERR(be->mode);
 		be->mode = NULL;
 		xenbus_dev_fatal(dev, err, "reading mode");
 		return;
 	}

 	device_type = xenbus_read(XBT_NIL, dev->otherend, "device-type", NULL);
 	if (!IS_ERR(device_type)) {
 		cdrom = strcmp(device_type, "cdrom") == 0;
 		kfree(device_type);
 	}

 	if (be->major == 0 && be->minor == 0) {
 		/* Front end dir is a number, which is used as the handle. */

 		char *p = strrchr(dev->otherend, '/') + 1;
 		long handle;
 		err = strict_strtoul(p, 0, &handle);
 		if (err)
 			return;

 		be->major = major;
 		be->minor = minor;

 		err = xen_vbd_create(be->blkif, handle, major, minor,
 				 (NULL == strchr(be->mode, 'w')), cdrom);
 		if (err) {
 			be->major = 0;
 			be->minor = 0;
 			xenbus_dev_fatal(dev, err, "creating vbd structure");
 			return;
 		}

 		err = xenvbd_sysfs_addif(dev);
 		if (err) {
 			xen_vbd_free(&be->blkif->vbd);
 			be->major = 0;
 			be->minor = 0;
 			xenbus_dev_fatal(dev, err, "creating sysfs entries");
 			return;
 		}

 		/* We're potentially connected now */
 		xen_update_blkif_status(be->blkif);
 	}
 }


 /*
  * Callback received when the frontend's state changes.
  */
 static void frontend_changed(struct xenbus_device *dev,
 			     enum xenbus_state frontend_state)
 {
 	struct backend_info *be = dev_get_drvdata(&dev->dev);
 	int err;

 	DPRINTK("%s", xenbus_strstate(frontend_state));

 	switch (frontend_state) {
 	case XenbusStateInitialising:
 		if (dev->state == XenbusStateClosed) {
 			pr_info(DRV_PFX "%s: prepare for reconnect\n",
 				dev->nodename);
 			xenbus_switch_state(dev, XenbusStateInitWait);
 		}
 		break;

 	case XenbusStateInitialised:
 	case XenbusStateConnected:
 		/*
 		 * Ensure we connect even when two watches fire in
 		 * close succession and we miss the intermediate value
 		 * of frontend_state.
 		 */
 		if (dev->state == XenbusStateConnected)
 			break;

 		/*
 		 * Enforce precondition before potential leak point.
 		 * xen_blkif_disconnect() is idempotent.
 		 */
 		xen_blkif_disconnect(be->blkif);

 		err = connect_ring(be);
 		if (err)
 			break;
 		xen_update_blkif_status(be->blkif);
 		break;

 	case XenbusStateClosing:
 		xenbus_switch_state(dev, XenbusStateClosing);
 		break;

 	case XenbusStateClosed:
 		xen_blkif_disconnect(be->blkif);
 		xenbus_switch_state(dev, XenbusStateClosed);
 		if (xenbus_dev_is_online(dev))
 			break;
 		/* fall through if not online */
 	case XenbusStateUnknown:
 		/* implies xen_blkif_disconnect() via xen_blkbk_remove() */
 		device_unregister(&dev->dev);
 		break;

 	default:
 		xenbus_dev_fatal(dev, -EINVAL, "saw state %d at frontend",
 				 frontend_state);
 		break;
 	}
 }


 /* ** Connection ** */


 /*
  * Write the physical details regarding the block device to the store, and
  * switch to Connected state.
  */
 static void connect(struct backend_info *be)
 {
 	struct xenbus_transaction xbt;
 	int err;
 	struct xenbus_device *dev = be->dev;

 	DPRINTK("%s", dev->otherend);

 	/* Supply the information about the device the frontend needs */
 again:
 	err = xenbus_transaction_start(&xbt);
 	if (err) {
 		xenbus_dev_fatal(dev, err, "starting transaction");
 		return;
 	}

 	/* If we can't advertise it is OK. */
 	xen_blkbk_flush_diskcache(xbt, be, be->blkif->vbd.flush_support);

 	xen_blkbk_discard(xbt, be);

 	xen_blkbk_barrier(xbt, be, be->blkif->vbd.flush_support);

 	err = xenbus_printf(xbt, dev->nodename, "sectors", "%llu",
 			    (unsigned long long)vbd_sz(&be->blkif->vbd));
 	if (err) {
 		xenbus_dev_fatal(dev, err, "writing %s/sectors",
 				 dev->nodename);
 		goto abort;
 	}

 	/* FIXME: use a typename instead */
 	err = xenbus_printf(xbt, dev->nodename, "info", "%u",
 			    be->blkif->vbd.type |
 			    (be->blkif->vbd.readonly ? VDISK_READONLY : 0));
 	if (err) {
 		xenbus_dev_fatal(dev, err, "writing %s/info",
 				 dev->nodename);
 		goto abort;
 	}
 	err = xenbus_printf(xbt, dev->nodename, "sector-size", "%lu",
 			    (unsigned long)
 			    bdev_logical_block_size(be->blkif->vbd.bdev));
 	if (err) {
 		xenbus_dev_fatal(dev, err, "writing %s/sector-size",
 				 dev->nodename);
 		goto abort;
 	}

 	err = xenbus_transaction_end(xbt, 0);
 	if (err == -EAGAIN)
 		goto again;
 	if (err)
 		xenbus_dev_fatal(dev, err, "ending transaction");

 	err = xenbus_switch_state(dev, XenbusStateConnected);
 	if (err)
 		xenbus_dev_fatal(dev, err, "%s: switching to Connected state",
 				 dev->nodename);

 	return;
  abort:
 	xenbus_transaction_end(xbt, 1);
 }


 static int connect_ring(struct backend_info *be)
 {
 	struct xenbus_device *dev = be->dev;
 	unsigned long ring_ref;
 	unsigned int evtchn;
 	char protocol[64] = "";
 	int err;

 	DPRINTK("%s", dev->otherend);

 	err = xenbus_gather(XBT_NIL, dev->otherend, "ring-ref", "%lu",
 			    &ring_ref, "event-channel", "%u", &evtchn, NULL);
 	if (err) {
 		xenbus_dev_fatal(dev, err,
 				 "reading %s/ring-ref and event-channel",
 				 dev->otherend);
 		return err;
 	}

 	be->blkif->blk_protocol = BLKIF_PROTOCOL_NATIVE;
 	err = xenbus_gather(XBT_NIL, dev->otherend, "protocol",
 			    "%63s", protocol, NULL);
 	if (err)
 		strcpy(protocol, "unspecified, assuming native");
 	else if (0 == strcmp(protocol, XEN_IO_PROTO_ABI_NATIVE))
 		be->blkif->blk_protocol = BLKIF_PROTOCOL_NATIVE;
 	else if (0 == strcmp(protocol, XEN_IO_PROTO_ABI_X86_32))
 		be->blkif->blk_protocol = BLKIF_PROTOCOL_X86_32;
 	else if (0 == strcmp(protocol, XEN_IO_PROTO_ABI_X86_64))
 		be->blkif->blk_protocol = BLKIF_PROTOCOL_X86_64;
 	else {
 		xenbus_dev_fatal(dev, err, "unknown fe protocol %s", protocol);
 		return -1;
 	}
 	pr_info(DRV_PFX "ring-ref %ld, event-channel %d, protocol %d (%s)\n",
 		ring_ref, evtchn, be->blkif->blk_protocol, protocol);

 	/* Map the shared frame, irq etc. */
 	err = xen_blkif_map(be->blkif, ring_ref, evtchn);
 	if (err) {
 		xenbus_dev_fatal(dev, err, "mapping ring-ref %lu port %u",
 				 ring_ref, evtchn);
 		return err;
 	}

 	return 0;
 }


 /* ** Driver Registration ** */


 static const struct xenbus_device_id xen_blkbk_ids[] = {
 	{ "vbd" },
 	{ "" }
 };


 static DEFINE_XENBUS_DRIVER(xen_blkbk, ,
 	.probe = xen_blkbk_probe,
 	.remove = xen_blkbk_remove,
 	.otherend_changed = frontend_changed
 );


 int xen_blkif_xenbus_init(void)
 {
 	return xenbus_register_backend(&xen_blkbk_driver);
 }
	/* Xenbus code for blkif backend
	Copyright (C) 2005 Rusty Russell <rusty@rustcorp.com.au>
	Copyright (C) 2005 XenSource Ltd

	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.

	*/

	#include <stdarg.h>
	#include <linux/module.h>
	#include <linux/kthread.h>
	#include <xen/events.h>
	#include <xen/grant_table.h>
	#include "common.h"

	struct backend_info {
	struct xenbus_device *dev;
	struct xen_blkif *blkif;
	struct xenbus_watch backend_watch;
	unsigned major;
	unsigned minor;
	char *mode;
	};

	static struct kmem_cache *xen_blkif_cachep;
	static void connect(struct backend_info *);
	static int connect_ring(struct backend_info *);
	static void backend_changed(struct xenbus_watch , const char *,
	unsigned int);

	struct xenbus_device xen_blkbk_xenbus(struct backend_info be)
	{
	return be->dev;
	}

	static int blkback_name(struct xen_blkif blkif, char buf)
	{
	char devpath, devname;
	struct xenbus_device *dev = blkif->be->dev;

	devpath = xenbus_read(XBT_NIL, dev->nodename, "dev", NULL);
	if (IS_ERR(devpath))
	return PTR_ERR(devpath);

	devname = strstr(devpath, "/dev/");
	if (devname != NULL)
	devname += strlen("/dev/");
	else
	devname = devpath;

	snprintf(buf, TASK_COMM_LEN, "blkback.%d.%s", blkif->domid, devname);
	kfree(devpath);

	return 0;
	}

	static void xen_update_blkif_status(struct xen_blkif *blkif)
	{
	int err;
	char name[TASK_COMM_LEN];

	/* Not ready to connect? */
	if (!blkif->irq \|\| !blkif->vbd.bdev)
	return;

	/* Already connected? */
	if (blkif->be->dev->state == XenbusStateConnected)
	return;

	/* Attempt to connect: exit if we fail to. */
	connect(blkif->be);
	if (blkif->be->dev->state != XenbusStateConnected)
	return;

	err = blkback_name(blkif, name);
	if (err) {
	xenbus_dev_error(blkif->be->dev, err, "get blkback dev name");
	return;
	}

	err = filemap_write_and_wait(blkif->vbd.bdev->bd_inode->i_mapping);
	if (err) {
	xenbus_dev_error(blkif->be->dev, err, "block flush");
	return;
	}
	invalidate_inode_pages2(blkif->vbd.bdev->bd_inode->i_mapping);

	blkif->xenblkd = kthread_run(xen_blkif_schedule, blkif, name);
	if (IS_ERR(blkif->xenblkd)) {
	err = PTR_ERR(blkif->xenblkd);
	blkif->xenblkd = NULL;
	xenbus_dev_error(blkif->be->dev, err, "start xenblkd");
	}
	}

	static struct xen_blkif *xen_blkif_alloc(domid_t domid)
	{
	struct xen_blkif *blkif;

	blkif = kmem_cache_zalloc(xen_blkif_cachep, GFP_KERNEL);
	if (!blkif)
	return ERR_PTR(-ENOMEM);

	blkif->domid = domid;
	spin_lock_init(&blkif->blk_ring_lock);
	atomic_set(&blkif->refcnt, 1);
	init_waitqueue_head(&blkif->wq);
	init_completion(&blkif->drain_complete);
	atomic_set(&blkif->drain, 0);
	blkif->st_print = jiffies;
	init_waitqueue_head(&blkif->waiting_to_free);

	return blkif;
	}

	static int xen_blkif_map(struct xen_blkif *blkif, unsigned long shared_page,
	unsigned int evtchn)
	{
	int err;

	/* Already connected through? */
	if (blkif->irq)
	return 0;

	err = xenbus_map_ring_valloc(blkif->be->dev, shared_page, &blkif->blk_ring);
	if (err < 0)
	return err;

	switch (blkif->blk_protocol) {
	case BLKIF_PROTOCOL_NATIVE:
	{
	struct blkif_sring *sring;
	sring = (struct blkif_sring *)blkif->blk_ring;
	BACK_RING_INIT(&blkif->blk_rings.native, sring, PAGE_SIZE);
	break;
	}
	case BLKIF_PROTOCOL_X86_32:
	{
	struct blkif_x86_32_sring *sring_x86_32;
	sring_x86_32 = (struct blkif_x86_32_sring *)blkif->blk_ring;
	BACK_RING_INIT(&blkif->blk_rings.x86_32, sring_x86_32, PAGE_SIZE);
	break;
	}
	case BLKIF_PROTOCOL_X86_64:
	{
	struct blkif_x86_64_sring *sring_x86_64;
	sring_x86_64 = (struct blkif_x86_64_sring *)blkif->blk_ring;
	BACK_RING_INIT(&blkif->blk_rings.x86_64, sring_x86_64, PAGE_SIZE);
	break;
	}
	default:
	BUG();
	}

	err = bind_interdomain_evtchn_to_irqhandler(blkif->domid, evtchn,
	xen_blkif_be_int, 0,
	"blkif-backend", blkif);
	if (err < 0) {
	xenbus_unmap_ring_vfree(blkif->be->dev, blkif->blk_ring);
	blkif->blk_rings.common.sring = NULL;
	return err;
	}
	blkif->irq = err;

	return 0;
	}

	static void xen_blkif_disconnect(struct xen_blkif *blkif)
	{
	if (blkif->xenblkd) {
	kthread_stop(blkif->xenblkd);
	blkif->xenblkd = NULL;
	}

	atomic_dec(&blkif->refcnt);
	wait_event(blkif->waiting_to_free, atomic_read(&blkif->refcnt) == 0);
	atomic_inc(&blkif->refcnt);

	if (blkif->irq) {
	unbind_from_irqhandler(blkif->irq, blkif);
	blkif->irq = 0;
	}

	if (blkif->blk_rings.common.sring) {
	xenbus_unmap_ring_vfree(blkif->be->dev, blkif->blk_ring);
	blkif->blk_rings.common.sring = NULL;
	}
	}

	static void xen_blkif_free(struct xen_blkif *blkif)
	{
	if (!atomic_dec_and_test(&blkif->refcnt))
	BUG();
	kmem_cache_free(xen_blkif_cachep, blkif);
	}

	int __init xen_blkif_interface_init(void)
	{
	xen_blkif_cachep = kmem_cache_create("blkif_cache",
	sizeof(struct xen_blkif),
	0, 0, NULL);
	if (!xen_blkif_cachep)
	return -ENOMEM;

	return 0;
	}

	/*
	* sysfs interface for VBD I/O requests
	*/

	#define VBD_SHOW(name, format, args...) \
	static ssize_t show_##name(struct device *_dev, \
	struct device_attribute *attr, \
	char *buf) \
	{ \
	struct xenbus_device *dev = to_xenbus_device(_dev); \
	struct backend_info *be = dev_get_drvdata(&dev->dev); \
	\
	return sprintf(buf, format, ##args); \
	} \
	static DEVICE_ATTR(name, S_IRUGO, show_##name, NULL)

	VBD_SHOW(oo_req, "%d\n", be->blkif->st_oo_req);
	VBD_SHOW(rd_req, "%d\n", be->blkif->st_rd_req);
	VBD_SHOW(wr_req, "%d\n", be->blkif->st_wr_req);
	VBD_SHOW(f_req, "%d\n", be->blkif->st_f_req);
	VBD_SHOW(ds_req, "%d\n", be->blkif->st_ds_req);
	VBD_SHOW(rd_sect, "%d\n", be->blkif->st_rd_sect);
	VBD_SHOW(wr_sect, "%d\n", be->blkif->st_wr_sect);

	static struct attribute *xen_vbdstat_attrs[] = {
	&dev_attr_oo_req.attr,
	&dev_attr_rd_req.attr,
	&dev_attr_wr_req.attr,
	&dev_attr_f_req.attr,
	&dev_attr_ds_req.attr,
	&dev_attr_rd_sect.attr,
	&dev_attr_wr_sect.attr,
	NULL
	};

	static struct attribute_group xen_vbdstat_group = {
	.name = "statistics",
	.attrs = xen_vbdstat_attrs,
	};

	VBD_SHOW(physical_device, "%x:%x\n", be->major, be->minor);
	VBD_SHOW(mode, "%s\n", be->mode);

	static int xenvbd_sysfs_addif(struct xenbus_device *dev)
	{
	int error;

	error = device_create_file(&dev->dev, &dev_attr_physical_device);
	if (error)
	goto fail1;

	error = device_create_file(&dev->dev, &dev_attr_mode);
	if (error)
	goto fail2;

	error = sysfs_create_group(&dev->dev.kobj, &xen_vbdstat_group);
	if (error)
	goto fail3;

	return 0;

	fail3: sysfs_remove_group(&dev->dev.kobj, &xen_vbdstat_group);
	fail2: device_remove_file(&dev->dev, &dev_attr_mode);
	fail1: device_remove_file(&dev->dev, &dev_attr_physical_device);
	return error;
	}

	static void xenvbd_sysfs_delif(struct xenbus_device *dev)
	{
	sysfs_remove_group(&dev->dev.kobj, &xen_vbdstat_group);
	device_remove_file(&dev->dev, &dev_attr_mode);
	device_remove_file(&dev->dev, &dev_attr_physical_device);
	}


	static void xen_vbd_free(struct xen_vbd *vbd)
	{
	if (vbd->bdev)
	blkdev_put(vbd->bdev, vbd->readonly ? FMODE_READ : FMODE_WRITE);
	vbd->bdev = NULL;
	}

	static int xen_vbd_create(struct xen_blkif *blkif, blkif_vdev_t handle,
	unsigned major, unsigned minor, int readonly,
	int cdrom)
	{
	struct xen_vbd *vbd;
	struct block_device *bdev;
	struct request_queue *q;

	vbd = &blkif->vbd;
	vbd->handle = handle;
	vbd->readonly = readonly;
	vbd->type = 0;

	vbd->pdevice = MKDEV(major, minor);

	bdev = blkdev_get_by_dev(vbd->pdevice, vbd->readonly ?
	FMODE_READ : FMODE_WRITE, NULL);

	if (IS_ERR(bdev)) {
	DPRINTK("xen_vbd_create: device %08x could not be opened.\n",
	vbd->pdevice);
	return -ENOENT;
	}

	vbd->bdev = bdev;
	if (vbd->bdev->bd_disk == NULL) {
	DPRINTK("xen_vbd_create: device %08x doesn't exist.\n",
	vbd->pdevice);
	xen_vbd_free(vbd);
	return -ENOENT;
	}
	vbd->size = vbd_sz(vbd);

	if (vbd->bdev->bd_disk->flags & GENHD_FL_CD \|\| cdrom)
	vbd->type \|= VDISK_CDROM;
	if (vbd->bdev->bd_disk->flags & GENHD_FL_REMOVABLE)
	vbd->type \|= VDISK_REMOVABLE;

	q = bdev_get_queue(bdev);
	if (q && q->flush_flags)
	vbd->flush_support = true;

	if (q && blk_queue_secdiscard(q))
	vbd->discard_secure = true;

	DPRINTK("Successful creation of handle=%04x (dom=%u)\n",
	handle, blkif->domid);
	return 0;
	}
	static int xen_blkbk_remove(struct xenbus_device *dev)
	{
	struct backend_info *be = dev_get_drvdata(&dev->dev);

	DPRINTK("");

	if (be->major \|\| be->minor)
	xenvbd_sysfs_delif(dev);

	if (be->backend_watch.node) {
	unregister_xenbus_watch(&be->backend_watch);
	kfree(be->backend_watch.node);
	be->backend_watch.node = NULL;
	}

	if (be->blkif) {
	xen_blkif_disconnect(be->blkif);
	xen_vbd_free(&be->blkif->vbd);
	xen_blkif_free(be->blkif);
	be->blkif = NULL;
	}

	kfree(be);
	dev_set_drvdata(&dev->dev, NULL);
	return 0;
	}

	int xen_blkbk_flush_diskcache(struct xenbus_transaction xbt,
	struct backend_info *be, int state)
	{
	struct xenbus_device *dev = be->dev;
	int err;

	err = xenbus_printf(xbt, dev->nodename, "feature-flush-cache",
	"%d", state);
	if (err)
	dev_warn(&dev->dev, "writing feature-flush-cache (%d)", err);

	return err;
	}

	static void xen_blkbk_discard(struct xenbus_transaction xbt, struct backend_info *be)
	{
	struct xenbus_device *dev = be->dev;
	struct xen_blkif *blkif = be->blkif;
	int err;
	int state = 0;
	struct block_device *bdev = be->blkif->vbd.bdev;
	struct request_queue *q = bdev_get_queue(bdev);

	if (blk_queue_discard(q)) {
	err = xenbus_printf(xbt, dev->nodename,
	"discard-granularity", "%u",
	q->limits.discard_granularity);
	if (err) {
	dev_warn(&dev->dev, "writing discard-granularity (%d)", err);
	return;
	}
	err = xenbus_printf(xbt, dev->nodename,
	"discard-alignment", "%u",
	q->limits.discard_alignment);
	if (err) {
	dev_warn(&dev->dev, "writing discard-alignment (%d)", err);
	return;
	}
	state = 1;
	/* Optional. */
	err = xenbus_printf(xbt, dev->nodename,
	"discard-secure", "%d",
	blkif->vbd.discard_secure);
	if (err) {
	dev_warn(&dev->dev, "writing discard-secure (%d)", err);
	return;
	}
	}
	err = xenbus_printf(xbt, dev->nodename, "feature-discard",
	"%d", state);
	if (err)
	dev_warn(&dev->dev, "writing feature-discard (%d)", err);
	}
	int xen_blkbk_barrier(struct xenbus_transaction xbt,
	struct backend_info *be, int state)
	{
	struct xenbus_device *dev = be->dev;
	int err;

	err = xenbus_printf(xbt, dev->nodename, "feature-barrier",
	"%d", state);
	if (err)
	dev_warn(&dev->dev, "writing feature-barrier (%d)", err);

	return err;
	}

	/*
	* Entry point to this code when a new device is created. Allocate the basic
	* structures, and watch the store waiting for the hotplug scripts to tell us
	* the device's physical major and minor numbers. Switch to InitWait.
	*/
	static int xen_blkbk_probe(struct xenbus_device *dev,
	const struct xenbus_device_id *id)
	{
	int err;
	struct backend_info *be = kzalloc(sizeof(struct backend_info),
	GFP_KERNEL);
	if (!be) {
	xenbus_dev_fatal(dev, -ENOMEM,
	"allocating backend structure");
	return -ENOMEM;
	}
	be->dev = dev;
	dev_set_drvdata(&dev->dev, be);

	be->blkif = xen_blkif_alloc(dev->otherend_id);
	if (IS_ERR(be->blkif)) {
	err = PTR_ERR(be->blkif);
	be->blkif = NULL;
	xenbus_dev_fatal(dev, err, "creating block interface");
	goto fail;
	}

	/* setup back pointer */
	be->blkif->be = be;

	err = xenbus_watch_pathfmt(dev, &be->backend_watch, backend_changed,
	"%s/%s", dev->nodename, "physical-device");
	if (err)
	goto fail;

	err = xenbus_switch_state(dev, XenbusStateInitWait);
	if (err)
	goto fail;

	return 0;

	fail:
	DPRINTK("failed");
	xen_blkbk_remove(dev);
	return err;
	}


	/*
	* Callback received when the hotplug scripts have placed the physical-device
	* node. Read it and the mode node, and create a vbd. If the frontend is
	* ready, connect.
	*/
	static void backend_changed(struct xenbus_watch *watch,
	const char **vec, unsigned int len)
	{
	int err;
	unsigned major;
	unsigned minor;
	struct backend_info *be
	= container_of(watch, struct backend_info, backend_watch);
	struct xenbus_device *dev = be->dev;
	int cdrom = 0;
	char *device_type;

	DPRINTK("");

	err = xenbus_scanf(XBT_NIL, dev->nodename, "physical-device", "%x:%x",
	&major, &minor);
	if (XENBUS_EXIST_ERR(err)) {
	/*
	* Since this watch will fire once immediately after it is
	* registered, we expect this. Ignore it, and wait for the
	* hotplug scripts.
	*/
	return;
	}
	if (err != 2) {
	xenbus_dev_fatal(dev, err, "reading physical-device");
	return;
	}

	if ((be->major \|\| be->minor) &&
	((be->major != major) \|\| (be->minor != minor))) {
	pr_warn(DRV_PFX "changing physical device (from %x:%x to %x:%x) not supported.\n",
	be->major, be->minor, major, minor);
	return;
	}

	be->mode = xenbus_read(XBT_NIL, dev->nodename, "mode", NULL);
	if (IS_ERR(be->mode)) {
	err = PTR_ERR(be->mode);
	be->mode = NULL;
	xenbus_dev_fatal(dev, err, "reading mode");
	return;
	}

	device_type = xenbus_read(XBT_NIL, dev->otherend, "device-type", NULL);
	if (!IS_ERR(device_type)) {
	cdrom = strcmp(device_type, "cdrom") == 0;
	kfree(device_type);
	}

	if (be->major == 0 && be->minor == 0) {
	/* Front end dir is a number, which is used as the handle. */

	char *p = strrchr(dev->otherend, '/') + 1;
	long handle;
	err = strict_strtoul(p, 0, &handle);
	if (err)
	return;

	be->major = major;
	be->minor = minor;

	err = xen_vbd_create(be->blkif, handle, major, minor,
	(NULL == strchr(be->mode, 'w')), cdrom);
	if (err) {
	be->major = 0;
	be->minor = 0;
	xenbus_dev_fatal(dev, err, "creating vbd structure");
	return;
	}

	err = xenvbd_sysfs_addif(dev);
	if (err) {
	xen_vbd_free(&be->blkif->vbd);
	be->major = 0;
	be->minor = 0;
	xenbus_dev_fatal(dev, err, "creating sysfs entries");
	return;
	}

	/* We're potentially connected now */
	xen_update_blkif_status(be->blkif);
	}
	}


	/*
	* Callback received when the frontend's state changes.
	*/
	static void frontend_changed(struct xenbus_device *dev,
	enum xenbus_state frontend_state)
	{
	struct backend_info *be = dev_get_drvdata(&dev->dev);
	int err;

	DPRINTK("%s", xenbus_strstate(frontend_state));

	switch (frontend_state) {
	case XenbusStateInitialising:
	if (dev->state == XenbusStateClosed) {
	pr_info(DRV_PFX "%s: prepare for reconnect\n",
	dev->nodename);
	xenbus_switch_state(dev, XenbusStateInitWait);
	}
	break;

	case XenbusStateInitialised:
	case XenbusStateConnected:
	/*
	* Ensure we connect even when two watches fire in
	* close succession and we miss the intermediate value
	* of frontend_state.
	*/
	if (dev->state == XenbusStateConnected)
	break;

	/*
	* Enforce precondition before potential leak point.
	* xen_blkif_disconnect() is idempotent.
	*/
	xen_blkif_disconnect(be->blkif);

	err = connect_ring(be);
	if (err)
	break;
	xen_update_blkif_status(be->blkif);
	break;

	case XenbusStateClosing:
	xenbus_switch_state(dev, XenbusStateClosing);
	break;

	case XenbusStateClosed:
	xen_blkif_disconnect(be->blkif);
	xenbus_switch_state(dev, XenbusStateClosed);
	if (xenbus_dev_is_online(dev))
	break;
	/* fall through if not online */
	case XenbusStateUnknown:
	/* implies xen_blkif_disconnect() via xen_blkbk_remove() */
	device_unregister(&dev->dev);
	break;

	default:
	xenbus_dev_fatal(dev, -EINVAL, "saw state %d at frontend",
	frontend_state);
	break;
	}
	}


	/* Connection */


	/*
	* Write the physical details regarding the block device to the store, and
	* switch to Connected state.
	*/
	static void connect(struct backend_info *be)
	{
	struct xenbus_transaction xbt;
	int err;
	struct xenbus_device *dev = be->dev;

	DPRINTK("%s", dev->otherend);

	/* Supply the information about the device the frontend needs */
	again:
	err = xenbus_transaction_start(&xbt);
	if (err) {
	xenbus_dev_fatal(dev, err, "starting transaction");
	return;
	}

	/* If we can't advertise it is OK. */
	xen_blkbk_flush_diskcache(xbt, be, be->blkif->vbd.flush_support);

	xen_blkbk_discard(xbt, be);

	xen_blkbk_barrier(xbt, be, be->blkif->vbd.flush_support);

	err = xenbus_printf(xbt, dev->nodename, "sectors", "%llu",
	(unsigned long long)vbd_sz(&be->blkif->vbd));
	if (err) {
	xenbus_dev_fatal(dev, err, "writing %s/sectors",
	dev->nodename);
	goto abort;
	}

	/* FIXME: use a typename instead */
	err = xenbus_printf(xbt, dev->nodename, "info", "%u",
	be->blkif->vbd.type \|
	(be->blkif->vbd.readonly ? VDISK_READONLY : 0));
	if (err) {
	xenbus_dev_fatal(dev, err, "writing %s/info",
	dev->nodename);
	goto abort;
	}
	err = xenbus_printf(xbt, dev->nodename, "sector-size", "%lu",
	(unsigned long)
	bdev_logical_block_size(be->blkif->vbd.bdev));
	if (err) {
	xenbus_dev_fatal(dev, err, "writing %s/sector-size",
	dev->nodename);
	goto abort;
	}

	err = xenbus_transaction_end(xbt, 0);
	if (err == -EAGAIN)
	goto again;
	if (err)
	xenbus_dev_fatal(dev, err, "ending transaction");

	err = xenbus_switch_state(dev, XenbusStateConnected);
	if (err)
	xenbus_dev_fatal(dev, err, "%s: switching to Connected state",
	dev->nodename);

	return;
	abort:
	xenbus_transaction_end(xbt, 1);
	}


	static int connect_ring(struct backend_info *be)
	{
	struct xenbus_device *dev = be->dev;
	unsigned long ring_ref;
	unsigned int evtchn;
	char protocol[64] = "";
	int err;

	DPRINTK("%s", dev->otherend);

	err = xenbus_gather(XBT_NIL, dev->otherend, "ring-ref", "%lu",
	&ring_ref, "event-channel", "%u", &evtchn, NULL);
	if (err) {
	xenbus_dev_fatal(dev, err,
	"reading %s/ring-ref and event-channel",
	dev->otherend);
	return err;
	}

	be->blkif->blk_protocol = BLKIF_PROTOCOL_NATIVE;
	err = xenbus_gather(XBT_NIL, dev->otherend, "protocol",
	"%63s", protocol, NULL);
	if (err)
	strcpy(protocol, "unspecified, assuming native");
	else if (0 == strcmp(protocol, XEN_IO_PROTO_ABI_NATIVE))
	be->blkif->blk_protocol = BLKIF_PROTOCOL_NATIVE;
	else if (0 == strcmp(protocol, XEN_IO_PROTO_ABI_X86_32))
	be->blkif->blk_protocol = BLKIF_PROTOCOL_X86_32;
	else if (0 == strcmp(protocol, XEN_IO_PROTO_ABI_X86_64))
	be->blkif->blk_protocol = BLKIF_PROTOCOL_X86_64;
	else {
	xenbus_dev_fatal(dev, err, "unknown fe protocol %s", protocol);
	return -1;
	}
	pr_info(DRV_PFX "ring-ref %ld, event-channel %d, protocol %d (%s)\n",
	ring_ref, evtchn, be->blkif->blk_protocol, protocol);

	/* Map the shared frame, irq etc. */
	err = xen_blkif_map(be->blkif, ring_ref, evtchn);
	if (err) {
	xenbus_dev_fatal(dev, err, "mapping ring-ref %lu port %u",
	ring_ref, evtchn);
	return err;
	}

	return 0;
	}


	/* Driver Registration */


	static const struct xenbus_device_id xen_blkbk_ids[] = {
	{ "vbd" },
	{ "" }
	};


	static DEFINE_XENBUS_DRIVER(xen_blkbk, ,
	.probe = xen_blkbk_probe,
	.remove = xen_blkbk_remove,
	.otherend_changed = frontend_changed
	);


	int xen_blkif_xenbus_init(void)
	{
	return xenbus_register_backend(&xen_blkbk_driver);
	}