aboutsummaryrefslogtreecommitdiff
path: root/drivers/block/xen-blkback/xenbus.c
blob: f759ad4584c306acb8937c52d80c1f7b567ae986 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
/*  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_alloc(xen_blkif_cachep, GFP_KERNEL);
	if (!blkif)
		return ERR_PTR(-ENOMEM);

	memset(blkif, 0, sizeof(*blkif));
	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;
	}
}

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);

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;
}

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;

	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)
		xenbus_dev_fatal(dev, err, "writing feature-flush-cache");

	return err;
}

int xen_blkbk_discard(struct xenbus_transaction xbt, struct backend_info *be)
{
	struct xenbus_device *dev = be->dev;
	struct xen_blkif *blkif = be->blkif;
	char *type;
	int err;
	int state = 0;

	type = xenbus_read(XBT_NIL, dev->nodename, "type", NULL);
	if (!IS_ERR(type)) {
		if (strncmp(type, "file", 4) == 0) {
			state = 1;
			blkif->blk_backend_type = BLKIF_BACKEND_FILE;
		}
		if (strncmp(type, "phy", 3) == 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) {
					xenbus_dev_fatal(dev, err,
						"writing discard-granularity");
					goto kfree;
				}
				err = xenbus_printf(xbt, dev->nodename,
					"discard-alignment", "%u",
					q->limits.discard_alignment);
				if (err) {
					xenbus_dev_fatal(dev, err,
						"writing discard-alignment");
					goto kfree;
				}
				state = 1;
				blkif->blk_backend_type = BLKIF_BACKEND_PHY;
			}
		}
	} else {
		err = PTR_ERR(type);
		xenbus_dev_fatal(dev, err, "reading type");
		goto out;
	}

	err = xenbus_printf(xbt, dev->nodename, "feature-discard",
			    "%d", state);
	if (err)
		xenbus_dev_fatal(dev, err, "writing feature-discard");
kfree:
	kfree(type);
out:
	return 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)
		xenbus_dev_fatal(dev, err, "writing feature-barrier");

	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 successsion 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;
	}

	err = xen_blkbk_flush_diskcache(xbt, be, be->blkif->vbd.flush_support);
	if (err)
		goto abort;

	err = xen_blkbk_discard(xbt, be);

	/* If we can't advertise it is OK. */
	err = 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 struct xenbus_driver xen_blkbk = {
	.name = "vbd",
	.owner = THIS_MODULE,
	.ids = xen_blkbk_ids,
	.probe = xen_blkbk_probe,
	.remove = xen_blkbk_remove,
	.otherend_changed = frontend_changed
};


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