aboutsummaryrefslogtreecommitdiffstats
path: root/drivers/block/nbd.c
blob: 485345c8e6320199782aa01cdcd285b54e177482 (plain) (blame)
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
/*
 * Network block device - make block devices work over TCP
 *
 * Note that you can not swap over this thing, yet. Seems to work but
 * deadlocks sometimes - you can not swap over TCP in general.
 * 
 * Copyright 1997-2000 Pavel Machek <pavel@ucw.cz>
 * Parts copyright 2001 Steven Whitehouse <steve@chygwyn.com>
 *
 * (part of code stolen from loop.c)
 *
 * 97-3-25 compiled 0-th version, not yet tested it 
 *   (it did not work, BTW) (later that day) HEY! it works!
 *   (bit later) hmm, not that much... 2:00am next day:
 *   yes, it works, but it gives something like 50kB/sec
 * 97-4-01 complete rewrite to make it possible for many requests at 
 *   once to be processed
 * 97-4-11 Making protocol independent of endianity etc.
 * 97-9-13 Cosmetic changes
 * 98-5-13 Attempt to make 64-bit-clean on 64-bit machines
 * 99-1-11 Attempt to make 64-bit-clean on 32-bit machines <ankry@mif.pg.gda.pl>
 * 01-2-27 Fix to store proper blockcount for kernel (calculated using
 *   BLOCK_SIZE_BITS, not device blocksize) <aga@permonline.ru>
 * 01-3-11 Make nbd work with new Linux block layer code. It now supports
 *   plugging like all the other block devices. Also added in MSG_MORE to
 *   reduce number of partial TCP segments sent. <steve@chygwyn.com>
 * 01-12-6 Fix deadlock condition by making queue locks independent of
 *   the transmit lock. <steve@chygwyn.com>
 * 02-10-11 Allow hung xmit to be aborted via SIGKILL & various fixes.
 *   <Paul.Clements@SteelEye.com> <James.Bottomley@SteelEye.com>
 * 03-06-22 Make nbd work with new linux 2.5 block layer design. This fixes
 *   memory corruption from module removal and possible memory corruption
 *   from sending/receiving disk data. <ldl@aros.net>
 * 03-06-23 Cosmetic changes. <ldl@aros.net>
 * 03-06-23 Enhance diagnostics support. <ldl@aros.net>
 * 03-06-24 Remove unneeded blksize_bits field from nbd_device struct.
 *   <ldl@aros.net>
 * 03-06-24 Cleanup PARANOIA usage & code. <ldl@aros.net>
 * 04-02-19 Remove PARANOIA, plus various cleanups (Paul Clements)
 * possible FIXME: make set_sock / set_blksize / set_size / do_it one syscall
 * why not: would need access_ok and friends, would share yet another
 *          structure with userland
 */

#include <linux/major.h>

#include <linux/blkdev.h>
#include <linux/module.h>
#include <linux/init.h>
#include <linux/sched.h>
#include <linux/fs.h>
#include <linux/bio.h>
#include <linux/stat.h>
#include <linux/errno.h>
#include <linux/file.h>
#include <linux/ioctl.h>
#include <net/sock.h>

#include <linux/devfs_fs_kernel.h>

#include <asm/uaccess.h>
#include <asm/types.h>

#include <linux/nbd.h>

#define LO_MAGIC 0x68797548

#ifdef NDEBUG
#define dprintk(flags, fmt...)
#else /* NDEBUG */
#define dprintk(flags, fmt...) do { \
	if (debugflags & (flags)) printk(KERN_DEBUG fmt); \
} while (0)
#define DBG_IOCTL       0x0004
#define DBG_INIT        0x0010
#define DBG_EXIT        0x0020
#define DBG_BLKDEV      0x0100
#define DBG_RX          0x0200
#define DBG_TX          0x0400
static unsigned int debugflags;
static unsigned int nbds_max = 16;
#endif /* NDEBUG */

static struct nbd_device nbd_dev[MAX_NBD];

/*
 * Use just one lock (or at most 1 per NIC). Two arguments for this:
 * 1. Each NIC is essentially a synchronization point for all servers
 *    accessed through that NIC so there's no need to have more locks
 *    than NICs anyway.
 * 2. More locks lead to more "Dirty cache line bouncing" which will slow
 *    down each lock to the point where they're actually slower than just
 *    a single lock.
 * Thanks go to Jens Axboe and Al Viro for their LKML emails explaining this!
 */
static DEFINE_SPINLOCK(nbd_lock);

#ifndef NDEBUG
static const char *ioctl_cmd_to_ascii(int cmd)
{
	switch (cmd) {
	case NBD_SET_SOCK: return "set-sock";
	case NBD_SET_BLKSIZE: return "set-blksize";
	case NBD_SET_SIZE: return "set-size";
	case NBD_DO_IT: return "do-it";
	case NBD_CLEAR_SOCK: return "clear-sock";
	case NBD_CLEAR_QUE: return "clear-que";
	case NBD_PRINT_DEBUG: return "print-debug";
	case NBD_SET_SIZE_BLOCKS: return "set-size-blocks";
	case NBD_DISCONNECT: return "disconnect";
	case BLKROSET: return "set-read-only";
	case BLKFLSBUF: return "flush-buffer-cache";
	}
	return "unknown";
}

static const char *nbdcmd_to_ascii(int cmd)
{
	switch (cmd) {
	case  NBD_CMD_READ: return "read";
	case NBD_CMD_WRITE: return "write";
	case  NBD_CMD_DISC: return "disconnect";
	}
	return "invalid";
}
#endif /* NDEBUG */

static void nbd_end_request(struct request *req)
{
	int uptodate = (req->errors == 0) ? 1 : 0;
	request_queue_t *q = req->q;
	unsigned long flags;

	dprintk(DBG_BLKDEV, "%s: request %p: %s\n", req->rq_disk->disk_name,
			req, uptodate? "done": "failed");

	spin_lock_irqsave(q->queue_lock, flags);
	if (!end_that_request_first(req, uptodate, req->nr_sectors)) {
		end_that_request_last(req, uptodate);
	}
	spin_unlock_irqrestore(q->queue_lock, flags);
}

/*
 *  Send or receive packet.
 */
static int sock_xmit(struct socket *sock, int send, void *buf, int size,
		int msg_flags)
{
	int result;
	struct msghdr msg;
	struct kvec iov;
	unsigned long flags;
	sigset_t oldset;

	/* Allow interception of SIGKILL only
	 * Don't allow other signals to interrupt the transmission */
	spin_lock_irqsave(&current->sighand->siglock, flags);
	oldset = current->blocked;
	sigfillset(&current->blocked);
	sigdelsetmask(&current->blocked, sigmask(SIGKILL));
	recalc_sigpending();
	spin_unlock_irqrestore(&current->sighand->siglock, flags);

	do {
		sock->sk->sk_allocation = GFP_NOIO;
		iov.iov_base = buf;
		iov.iov_len = size;
		msg.msg_name = NULL;
		msg.msg_namelen = 0;
		msg.msg_control = NULL;
		msg.msg_controllen = 0;
		msg.msg_namelen = 0;
		msg.msg_flags = msg_flags | MSG_NOSIGNAL;

		if (send)
			result = kernel_sendmsg(sock, &msg, &iov, 1, size);
		else
			result = kernel_recvmsg(sock, &msg, &iov, 1, size, 0);

		if (signal_pending(current)) {
			siginfo_t info;
			spin_lock_irqsave(&current->sighand->siglock, flags);
			printk(KERN_WARNING "nbd (pid %d: %s) got signal %d\n",
				current->pid, current->comm, 
				dequeue_signal(current, &current->blocked, &info));
			spin_unlock_irqrestore(&current->sighand->siglock, flags);
			result = -EINTR;
			break;
		}

		if (result <= 0) {
			if (result == 0)
				result = -EPIPE; /* short read */
			break;
		}
		size -= result;
		buf += result;
	} while (size > 0);

	spin_lock_irqsave(&current->sighand->siglock, flags);
	current->blocked = oldset;
	recalc_sigpending();
	spin_unlock_irqrestore(&current->sighand->siglock, flags);

	return result;
}

static inline int sock_send_bvec(struct socket *sock, struct bio_vec *bvec,
		int flags)
{
	int result;
	void *kaddr = kmap(bvec->bv_page);
	result = sock_xmit(sock, 1, kaddr + bvec->bv_offset, bvec->bv_len,
			flags);
	kunmap(bvec->bv_page);
	return result;
}

static int nbd_send_req(struct nbd_device *lo, struct request *req)
{
	int result, i, flags;
	struct nbd_request request;
	unsigned long size = req->nr_sectors << 9;
	struct socket *sock = lo->sock;

	request.magic = htonl(NBD_REQUEST_MAGIC);
	request.type = htonl(nbd_cmd(req));
	request.from = cpu_to_be64((u64) req->sector << 9);
	request.len = htonl(size);
	memcpy(request.handle, &req, sizeof(req));

	down(&lo->tx_lock);

	if (!sock || !lo->sock) {
		printk(KERN_ERR "%s: Attempted send on closed socket\n",
				lo->disk->disk_name);
		goto error_out;
	}

	dprintk(DBG_TX, "%s: request %p: sending control (%s@%llu,%luB)\n",
			lo->disk->disk_name, req,
			nbdcmd_to_ascii(nbd_cmd(req)),
			(unsigned long long)req->sector << 9,
			req->nr_sectors << 9);
	result = sock_xmit(sock, 1, &request, sizeof(request),
			(nbd_cmd(req) == NBD_CMD_WRITE)? MSG_MORE: 0);
	if (result <= 0) {
		printk(KERN_ERR "%s: Send control failed (result %d)\n",
				lo->disk->disk_name, result);
		goto error_out;
	}

	if (nbd_cmd(req) == NBD_CMD_WRITE) {
		struct bio *bio;
		/*
		 * we are really probing at internals to determine
		 * whether to set MSG_MORE or not...
		 */
		rq_for_each_bio(bio, req) {
			struct bio_vec *bvec;
			bio_for_each_segment(bvec, bio, i) {
				flags = 0;
				if ((i < (bio->bi_vcnt - 1)) || bio->bi_next)
					flags = MSG_MORE;
				dprintk(DBG_TX, "%s: request %p: sending %d bytes data\n",
						lo->disk->disk_name, req,
						bvec->bv_len);
				result = sock_send_bvec(sock, bvec, flags);
				if (result <= 0) {
					printk(KERN_ERR "%s: Send data failed (result %d)\n",
							lo->disk->disk_name,
							result);
					goto error_out;
				}
			}
		}
	}
	up(&lo->tx_lock);
	return 0;

error_out:
	up(&lo->tx_lock);
	return 1;
}

static struct request *nbd_find_request(struct nbd_device *lo, char *handle)
{
	struct request *req;
	struct list_head *tmp;
	struct request *xreq;

	memcpy(&xreq, handle, sizeof(xreq));

	spin_lock(&lo->queue_lock);
	list_for_each(tmp, &lo->queue_head) {
		req = list_entry(tmp, struct request, queuelist);
		if (req != xreq)
			continue;
		list_del_init(&req->queuelist);
		spin_unlock(&lo->queue_lock);
		return req;
	}
	spin_unlock(&lo->queue_lock);
	return NULL;
}

static inline int sock_recv_bvec(struct socket *sock, struct bio_vec *bvec)
{
	int result;
	void *kaddr = kmap(bvec->bv_page);
	result = sock_xmit(sock, 0, kaddr + bvec->bv_offset, bvec->bv_len,
			MSG_WAITALL);
	kunmap(bvec->bv_page);
	return result;
}

/* NULL returned = something went wrong, inform userspace */
static struct request *nbd_read_stat(struct nbd_device *lo)
{
	int result;
	struct nbd_reply reply;
	struct request *req;
	struct socket *sock = lo->sock;

	reply.magic = 0;
	result = sock_xmit(sock, 0, &reply, sizeof(reply), MSG_WAITALL);
	if (result <= 0) {
		printk(KERN_ERR "%s: Receive control failed (result %d)\n",
				lo->disk->disk_name, result);
		goto harderror;
	}
	req = nbd_find_request(lo, reply.handle);
	if (req == NULL) {
		printk(KERN_ERR "%s: Unexpected reply (%p)\n",
				lo->disk->disk_name, reply.handle);
		result = -EBADR;
		goto harderror;
	}

	if (ntohl(reply.magic) != NBD_REPLY_MAGIC) {
		printk(KERN_ERR "%s: Wrong magic (0x%lx)\n",
				lo->disk->disk_name,
				(unsigned long)ntohl(reply.magic));
		result = -EPROTO;
		goto harderror;
	}
	if (ntohl(reply.error)) {
		printk(KERN_ERR "%s: Other side returned error (%d)\n",
				lo->disk->disk_name, ntohl(reply.error));
		req->errors++;
		return req;
	}

	dprintk(DBG_RX, "%s: request %p: got reply\n",
			lo->disk->disk_name, req);
	if (nbd_cmd(req) == NBD_CMD_READ) {
		int i;
		struct bio *bio;
		rq_for_each_bio(bio, req) {
			struct bio_vec *bvec;
			bio_for_each_segment(bvec, bio, i) {
				result = sock_recv_bvec(sock, bvec);
				if (result <= 0) {
					printk(KERN_ERR "%s: Receive data failed (result %d)\n",
							lo->disk->disk_name,
							result);
					goto harderror;
				}
				dprintk(DBG_RX, "%s: request %p: got %d bytes data\n",
					lo->disk->disk_name, req, bvec->bv_len);
			}
		}
	}
	return req;
harderror:
	lo->harderror = result;
	return NULL;
}

static void nbd_do_it(struct nbd_device *lo)
{
	struct request *req;

	BUG_ON(lo->magic != LO_MAGIC);

	while ((req = nbd_read_stat(lo)) != NULL)
		nbd_end_request(req);
	return;
}

static void nbd_clear_que(struct nbd_device *lo)
{
	struct request *req;

	BUG_ON(lo->magic != LO_MAGIC);

	do {
		req = NULL;
		spin_lock(&lo->queue_lock);
		if (!list_empty(&lo->queue_head)) {
			req = list_entry(lo->queue_head.next, struct request, queuelist);
			list_del_init(&req->queuelist);
		}
		spin_unlock(&lo->queue_lock);
		if (req) {
			req->errors++;
			nbd_end_request(req);
		}
	} while (req);
}

/*
 * We always wait for result of write, for now. It would be nice to make it optional
 * in future
 * if ((req->cmd == WRITE) && (lo->flags & NBD_WRITE_NOCHK)) 
 *   { printk( "Warning: Ignoring result!\n"); nbd_end_request( req ); }
 */

static void do_nbd_request(request_queue_t * q)
{
	struct request *req;
	
	while ((req = elv_next_request(q)) != NULL) {
		struct nbd_device *lo;

		blkdev_dequeue_request(req);
		dprintk(DBG_BLKDEV, "%s: request %p: dequeued (flags=%lx)\n",
				req->rq_disk->disk_name, req, req->flags);

		if (!(req->flags & REQ_CMD))
			goto error_out;

		lo = req->rq_disk->private_data;

		BUG_ON(lo->magic != LO_MAGIC);

		if (!lo->file) {
			printk(KERN_ERR "%s: Request when not-ready\n",
					lo->disk->disk_name);
			goto error_out;
		}
		nbd_cmd(req) = NBD_CMD_READ;
		if (rq_data_dir(req) == WRITE) {
			nbd_cmd(req) = NBD_CMD_WRITE;
			if (lo->flags & NBD_READ_ONLY) {
				printk(KERN_ERR "%s: Write on read-only\n",
						lo->disk->disk_name);
				goto error_out;
			}
		}

		req->errors = 0;
		spin_unlock_irq(q->queue_lock);

		spin_lock(&lo->queue_lock);

		if (!lo->file) {
			spin_unlock(&lo->queue_lock);
			printk(KERN_ERR "%s: failed between accept and semaphore, file lost\n",
					lo->disk->disk_name);
			req->errors++;
			nbd_end_request(req);
			spin_lock_irq(q->queue_lock);
			continue;
		}

		list_add(&req->queuelist, &lo->queue_head);
		spin_unlock(&lo->queue_lock);

		if (nbd_send_req(lo, req) != 0) {
			printk(KERN_ERR "%s: Request send failed\n",
					lo->disk->disk_name);
			if (nbd_find_request(lo, (char *)&req) != NULL) {
				/* we still own req */
				req->errors++;
				nbd_end_request(req);
			} else /* we're racing with nbd_clear_que */
				printk(KERN_DEBUG "nbd: can't find req\n");
		}

		spin_lock_irq(q->queue_lock);
		continue;

error_out:
		req->errors++;
		spin_unlock(q->queue_lock);
		nbd_end_request(req);
		spin_lock(q->queue_lock);
	}
	return;
}

static int nbd_ioctl(struct inode *inode, struct file *file,
		     unsigned int cmd, unsigned long arg)
{
	struct nbd_device *lo = inode->i_bdev->bd_disk->private_data;
	int error;
	struct request sreq ;

	if (!capable(CAP_SYS_ADMIN))
		return -EPERM;

	BUG_ON(lo->magic != LO_MAGIC);

	/* Anyone capable of this syscall can do *real bad* things */
	dprintk(DBG_IOCTL, "%s: nbd_ioctl cmd=%s(0x%x) arg=%lu\n",
			lo->disk->disk_name, ioctl_cmd_to_ascii(cmd), cmd, arg);

	switch (cmd) {
	case NBD_DISCONNECT:
	        printk(KERN_INFO "%s: NBD_DISCONNECT\n", lo->disk->disk_name);
		sreq.flags = REQ_SPECIAL;
		nbd_cmd(&sreq) = NBD_CMD_DISC;
		/*
		 * Set these to sane values in case server implementation
		 * fails to check the request type first and also to keep
		 * debugging output cleaner.
		 */
		sreq.sector = 0;
		sreq.nr_sectors = 0;
                if (!lo->sock)
			return -EINVAL;
                nbd_send_req(lo, &sreq);
                return 0;
 
	case NBD_CLEAR_SOCK:
		error = 0;
		down(&lo->tx_lock);
		lo->sock = NULL;
		up(&lo->tx_lock);
		spin_lock(&lo->queue_lock);
		file = lo->file;
		lo->file = NULL;
		spin_unlock(&lo->queue_lock);
		nbd_clear_que(lo);
		spin_lock(&lo->queue_lock);
		if (!list_empty(&lo->queue_head)) {
			printk(KERN_ERR "nbd: disconnect: some requests are in progress -> please try again.\n");
			error = -EBUSY;
		}
		spin_unlock(&lo->queue_lock);
		if (file)
			fput(file);
		return error;
	case NBD_SET_SOCK:
		if (lo->file)
			return -EBUSY;
		error = -EINVAL;
		file = fget(arg);
		if (file) {
			inode = file->f_dentry->d_inode;
			if (S_ISSOCK(inode->i_mode)) {
				lo->file = file;
				lo->sock = SOCKET_I(inode);
				error = 0;
			} else {
				fput(file);
			}
		}
		return error;
	case NBD_SET_BLKSIZE:
		lo->blksize = arg;
		lo->bytesize &= ~(lo->blksize-1);
		inode->i_bdev->bd_inode->i_size = lo->bytesize;
		set_blocksize(inode->i_bdev, lo->blksize);
		set_capacity(lo->disk, lo->bytesize >> 9);
		return 0;
	case NBD_SET_SIZE:
		lo->bytesize = arg & ~(lo->blksize-1);
		inode->i_bdev->bd_inode->i_size = lo->bytesize;
		set_blocksize(inode->i_bdev, lo->blksize);
		set_capacity(lo->disk, lo->bytesize >> 9);
		return 0;
	case NBD_SET_SIZE_BLOCKS:
		lo->bytesize = ((u64) arg) * lo->blksize;
		inode->i_bdev->bd_inode->i_size = lo->bytesize;
		set_blocksize(inode->i_bdev, lo->blksize);
		set_capacity(lo->disk, lo->bytesize >> 9);
		return 0;
	case NBD_DO_IT:
		if (!lo->file)
			return -EINVAL;
		nbd_do_it(lo);
		/* on return tidy up in case we have a signal */
		/* Forcibly shutdown the socket causing all listeners
		 * to error
		 *
		 * FIXME: This code is duplicated from sys_shutdown, but
		 * there should be a more generic interface rather than
		 * calling socket ops directly here */
		down(&lo->tx_lock);
		if (lo->sock) {
			printk(KERN_WARNING "%s: shutting down socket\n",
				lo->disk->disk_name);
			lo->sock->ops->shutdown(lo->sock,
				SEND_SHUTDOWN|RCV_SHUTDOWN);
			lo->sock = NULL;
		}
		up(&lo->tx_lock);
		spin_lock(&lo->queue_lock);
		file = lo->file;
		lo->file = NULL;
		spin_unlock(&lo->queue_lock);
		nbd_clear_que(lo);
		printk(KERN_WARNING "%s: queue cleared\n", lo->disk->disk_name);
		if (file)
			fput(file);
		return lo->harderror;
	case NBD_CLEAR_QUE:
		down(&lo->tx_lock);
		if (lo->sock) {
			up(&lo->tx_lock);
			return 0; /* probably should be error, but that would
				   * break "nbd-client -d", so just return 0 */
		}
		up(&lo->tx_lock);
		nbd_clear_que(lo);
		return 0;
	case NBD_PRINT_DEBUG:
		printk(KERN_INFO "%s: next = %p, prev = %p, head = %p\n",
			inode->i_bdev->bd_disk->disk_name,
			lo->queue_head.next, lo->queue_head.prev,
			&lo->queue_head);
		return 0;
	}
	return -EINVAL;
}

static struct block_device_operations nbd_fops =
{
	.owner =	THIS_MODULE,
	.ioctl =	nbd_ioctl,
};

/*
 * And here should be modules and kernel interface 
 *  (Just smiley confuses emacs :-)
 */

static int __init nbd_init(void)
{
	int err = -ENOMEM;
	int i;

	if (sizeof(struct nbd_request) != 28) {
		printk(KERN_CRIT "nbd: sizeof nbd_request needs to be 28 in order to work!\n" );
		return -EIO;
	}

	if (nbds_max > MAX_NBD) {
		printk(KERN_CRIT "nbd: cannot allocate more than %u nbds; %u requested.\n", MAX_NBD,
				nbds_max);
		return -EINVAL;
	}

	for (i = 0; i < nbds_max; i++) {
		struct gendisk *disk = alloc_disk(1);
		if (!disk)
			goto out;
		nbd_dev[i].disk = disk;
		/*
		 * The new linux 2.5 block layer implementation requires
		 * every gendisk to have its very own request_queue struct.
		 * These structs are big so we dynamically allocate them.
		 */
		disk->queue = blk_init_queue(do_nbd_request, &nbd_lock);
		if (!disk->queue) {
			put_disk(disk);
			goto out;
		}
	}

	if (register_blkdev(NBD_MAJOR, "nbd")) {
		err = -EIO;
		goto out;
	}

	printk(KERN_INFO "nbd: registered device at major %d\n", NBD_MAJOR);
	dprintk(DBG_INIT, "nbd: debugflags=0x%x\n", debugflags);

	devfs_mk_dir("nbd");
	for (i = 0; i < nbds_max; i++) {
		struct gendisk *disk = nbd_dev[i].disk;
		nbd_dev[i].file = NULL;
		nbd_dev[i].magic = LO_MAGIC;
		nbd_dev[i].flags = 0;
		spin_lock_init(&nbd_dev[i].queue_lock);
		INIT_LIST_HEAD(&nbd_dev[i].queue_head);
		init_MUTEX(&nbd_dev[i].tx_lock);
		nbd_dev[i].blksize = 1024;
		nbd_dev[i].bytesize = 0x7ffffc00ULL << 10; /* 2TB */
		disk->major = NBD_MAJOR;
		disk->first_minor = i;
		disk->fops = &nbd_fops;
		disk->private_data = &nbd_dev[i];
		disk->flags |= GENHD_FL_SUPPRESS_PARTITION_INFO;
		sprintf(disk->disk_name, "nbd%d", i);
		sprintf(disk->devfs_name, "nbd/%d", i);
		set_capacity(disk, 0x7ffffc00ULL << 1); /* 2 TB */
		add_disk(disk);
	}

	return 0;
out:
	while (i--) {
		blk_cleanup_queue(nbd_dev[i].disk->queue);
		put_disk(nbd_dev[i].disk);
	}
	return err;
}

static void __exit nbd_cleanup(void)
{
	int i;
	for (i = 0; i < nbds_max; i++) {
		struct gendisk *disk = nbd_dev[i].disk;
		nbd_dev[i].magic = 0;
		if (disk) {
			del_gendisk(disk);
			blk_cleanup_queue(disk->queue);
			put_disk(disk);
		}
	}
	devfs_remove("nbd");
	unregister_blkdev(NBD_MAJOR, "nbd");
	printk(KERN_INFO "nbd: unregistered device at major %d\n", NBD_MAJOR);
}

module_init(nbd_init);
module_exit(nbd_cleanup);

MODULE_DESCRIPTION("Network Block Device");
MODULE_LICENSE("GPL");

module_param(nbds_max, int, 0444);
MODULE_PARM_DESC(nbds_max, "How many network block devices to initialize.");
#ifndef NDEBUG
module_param(debugflags, int, 0644);
MODULE_PARM_DESC(debugflags, "flags for controlling debug output");
#endif