aboutsummaryrefslogtreecommitdiff
path: root/drivers/usb/mon/mon_text.c
blob: ebb04ac4857b2019d234cedb37631a877a63dbc0 (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
/*
 * The USB Monitor, inspired by Dave Harding's USBMon.
 *
 * This is a text format reader.
 */

#include <linux/kernel.h>
#include <linux/list.h>
#include <linux/usb.h>
#include <linux/time.h>
#include <linux/mutex.h>
#include <linux/debugfs.h>
#include <asm/uaccess.h>

#include "usb_mon.h"

/*
 * No, we do not want arbitrarily long data strings.
 * Use the binary interface if you want to capture bulk data!
 */
#define DATA_MAX  32

/*
 * Defined by USB 2.0 clause 9.3, table 9.2.
 */
#define SETUP_MAX  8

/*
 * This limit exists to prevent OOMs when the user process stops reading.
 * If usbmon were available to unprivileged processes, it might be open
 * to a local DoS. But we have to keep to root in order to prevent
 * password sniffing from HID devices.
 */
#define EVENT_MAX  (4*PAGE_SIZE / sizeof(struct mon_event_text))

/*
 * Potentially unlimited number; we limit it for similar allocations.
 * The usbfs limits this to 128, but we're not quite as generous.
 */
#define ISODESC_MAX   5

#define PRINTF_DFL  250   /* with 5 ISOs segs */

struct mon_iso_desc {
	int status;
	unsigned int offset;
	unsigned int length;	/* Unsigned here, signed in URB. Historic. */
};

struct mon_event_text {
	struct list_head e_link;
	int type;		/* submit, complete, etc. */
	unsigned long id;	/* From pointer, most of the time */
	unsigned int tstamp;
	int busnum;
	char devnum;
	char epnum;
	char is_in;
	char xfertype;
	int length;		/* Depends on type: xfer length or act length */
	int status;
	int interval;
	int start_frame;
	int error_count;
	char setup_flag;
	char data_flag;
	int numdesc;		/* Full number */
	struct mon_iso_desc isodesc[ISODESC_MAX];
	unsigned char setup[SETUP_MAX];
	unsigned char data[DATA_MAX];
};

#define SLAB_NAME_SZ  30
struct mon_reader_text {
	struct kmem_cache *e_slab;
	int nevents;
	struct list_head e_list;
	struct mon_reader r;	/* In C, parent class can be placed anywhere */

	wait_queue_head_t wait;
	int printf_size;
	char *printf_buf;
	struct mutex printf_lock;

	char slab_name[SLAB_NAME_SZ];
};

static struct dentry *mon_dir;		/* Usually /sys/kernel/debug/usbmon */

static void mon_text_ctor(void *, struct kmem_cache *, unsigned long);

struct mon_text_ptr {
	int cnt, limit;
	char *pbuf;
};

static struct mon_event_text *
    mon_text_read_wait(struct mon_reader_text *rp, struct file *file);
static void mon_text_read_head_t(struct mon_reader_text *rp,
	struct mon_text_ptr *p, const struct mon_event_text *ep);
static void mon_text_read_head_u(struct mon_reader_text *rp,
	struct mon_text_ptr *p, const struct mon_event_text *ep);
static void mon_text_read_statset(struct mon_reader_text *rp,
	struct mon_text_ptr *p, const struct mon_event_text *ep);
static void mon_text_read_intstat(struct mon_reader_text *rp,
	struct mon_text_ptr *p, const struct mon_event_text *ep);
static void mon_text_read_isostat(struct mon_reader_text *rp,
	struct mon_text_ptr *p, const struct mon_event_text *ep);
static void mon_text_read_isodesc(struct mon_reader_text *rp,
	struct mon_text_ptr *p, const struct mon_event_text *ep);
static void mon_text_read_data(struct mon_reader_text *rp,
    struct mon_text_ptr *p, const struct mon_event_text *ep);

/*
 * mon_text_submit
 * mon_text_complete
 *
 * May be called from an interrupt.
 *
 * This is called with the whole mon_bus locked, so no additional lock.
 */

static inline char mon_text_get_setup(struct mon_event_text *ep,
    struct urb *urb, char ev_type, struct mon_bus *mbus)
{

	if (ep->xfertype != USB_ENDPOINT_XFER_CONTROL || ev_type != 'S')
		return '-';

	if (urb->setup_packet == NULL)
		return 'Z';	/* '0' would be not as pretty. */

	memcpy(ep->setup, urb->setup_packet, SETUP_MAX);
	return 0;
}

static inline char mon_text_get_data(struct mon_event_text *ep, struct urb *urb,
    int len, char ev_type, struct mon_bus *mbus)
{
	if (len <= 0)
		return 'L';
	if (len >= DATA_MAX)
		len = DATA_MAX;

	if (ep->is_in) {
		if (ev_type != 'C')
			return '<';
	} else {
		if (ev_type != 'S')
			return '>';
	}

	/*
	 * The check to see if it's safe to poke at data has an enormous
	 * number of corner cases, but it seems that the following is
	 * more or less safe.
	 *
	 * We do not even try to look at transfer_buffer, because it can
	 * contain non-NULL garbage in case the upper level promised to
	 * set DMA for the HCD.
	 */
	if (urb->dev->bus->uses_dma &&
	    (urb->transfer_flags & URB_NO_TRANSFER_DMA_MAP)) {
		return mon_dmapeek(ep->data, urb->transfer_dma, len);
	}

	if (urb->transfer_buffer == NULL)
		return 'Z';	/* '0' would be not as pretty. */

	memcpy(ep->data, urb->transfer_buffer, len);
	return 0;
}

static inline unsigned int mon_get_timestamp(void)
{
	struct timeval tval;
	unsigned int stamp;

	do_gettimeofday(&tval);
	stamp = tval.tv_sec & 0xFFFF;	/* 2^32 = 4294967296. Limit to 4096s. */
	stamp = stamp * 1000000 + tval.tv_usec;
	return stamp;
}

static void mon_text_event(struct mon_reader_text *rp, struct urb *urb,
    char ev_type, int status)
{
	struct mon_event_text *ep;
	unsigned int stamp;
	struct usb_iso_packet_descriptor *fp;
	struct mon_iso_desc *dp;
	int i, ndesc;

	stamp = mon_get_timestamp();

	if (rp->nevents >= EVENT_MAX ||
	    (ep = kmem_cache_alloc(rp->e_slab, GFP_ATOMIC)) == NULL) {
		rp->r.m_bus->cnt_text_lost++;
		return;
	}

	ep->type = ev_type;
	ep->id = (unsigned long) urb;
	ep->busnum = urb->dev->bus->busnum;
	ep->devnum = urb->dev->devnum;
	ep->epnum = usb_endpoint_num(&urb->ep->desc);
	ep->xfertype = usb_endpoint_type(&urb->ep->desc);
	ep->is_in = usb_urb_dir_in(urb);
	ep->tstamp = stamp;
	ep->length = (ev_type == 'S') ?
	    urb->transfer_buffer_length : urb->actual_length;
	/* Collecting status makes debugging sense for submits, too */
	ep->status = status;

	if (ep->xfertype == USB_ENDPOINT_XFER_INT) {
		ep->interval = urb->interval;
	} else if (ep->xfertype == USB_ENDPOINT_XFER_ISOC) {
		ep->interval = urb->interval;
		ep->start_frame = urb->start_frame;
		ep->error_count = urb->error_count;
	}
	ep->numdesc = urb->number_of_packets;
	if (ep->xfertype == USB_ENDPOINT_XFER_ISOC &&
			urb->number_of_packets > 0) {
		if ((ndesc = urb->number_of_packets) > ISODESC_MAX)
			ndesc = ISODESC_MAX;
		fp = urb->iso_frame_desc;
		dp = ep->isodesc;
		for (i = 0; i < ndesc; i++) {
			dp->status = fp->status;
			dp->offset = fp->offset;
			dp->length = (ev_type == 'S') ?
			    fp->length : fp->actual_length;
			fp++;
			dp++;
		}
	}

	ep->setup_flag = mon_text_get_setup(ep, urb, ev_type, rp->r.m_bus);
	ep->data_flag = mon_text_get_data(ep, urb, ep->length, ev_type,
			rp->r.m_bus);

	rp->nevents++;
	list_add_tail(&ep->e_link, &rp->e_list);
	wake_up(&rp->wait);
}

static void mon_text_submit(void *data, struct urb *urb)
{
	struct mon_reader_text *rp = data;
	mon_text_event(rp, urb, 'S', -EINPROGRESS);
}

static void mon_text_complete(void *data, struct urb *urb, int status)
{
	struct mon_reader_text *rp = data;
	mon_text_event(rp, urb, 'C', status);
}

static void mon_text_error(void *data, struct urb *urb, int error)
{
	struct mon_reader_text *rp = data;
	struct mon_event_text *ep;

	if (rp->nevents >= EVENT_MAX ||
	    (ep = kmem_cache_alloc(rp->e_slab, GFP_ATOMIC)) == NULL) {
		rp->r.m_bus->cnt_text_lost++;
		return;
	}

	ep->type = 'E';
	ep->id = (unsigned long) urb;
	ep->busnum = 0;
	ep->devnum = urb->dev->devnum;
	ep->epnum = usb_endpoint_num(&urb->ep->desc);
	ep->xfertype = usb_endpoint_type(&urb->ep->desc);
	ep->is_in = usb_urb_dir_in(urb);
	ep->tstamp = 0;
	ep->length = 0;
	ep->status = error;

	ep->setup_flag = '-';
	ep->data_flag = 'E';

	rp->nevents++;
	list_add_tail(&ep->e_link, &rp->e_list);
	wake_up(&rp->wait);
}

/*
 * Fetch next event from the circular buffer.
 */
static struct mon_event_text *mon_text_fetch(struct mon_reader_text *rp,
    struct mon_bus *mbus)
{
	struct list_head *p;
	unsigned long flags;

	spin_lock_irqsave(&mbus->lock, flags);
	if (list_empty(&rp->e_list)) {
		spin_unlock_irqrestore(&mbus->lock, flags);
		return NULL;
	}
	p = rp->e_list.next;
	list_del(p);
	--rp->nevents;
	spin_unlock_irqrestore(&mbus->lock, flags);
	return list_entry(p, struct mon_event_text, e_link);
}

/*
 */
static int mon_text_open(struct inode *inode, struct file *file)
{
	struct mon_bus *mbus;
	struct mon_reader_text *rp;
	int rc;

	mutex_lock(&mon_lock);
	mbus = inode->i_private;

	rp = kzalloc(sizeof(struct mon_reader_text), GFP_KERNEL);
	if (rp == NULL) {
		rc = -ENOMEM;
		goto err_alloc;
	}
	INIT_LIST_HEAD(&rp->e_list);
	init_waitqueue_head(&rp->wait);
	mutex_init(&rp->printf_lock);

	rp->printf_size = PRINTF_DFL;
	rp->printf_buf = kmalloc(rp->printf_size, GFP_KERNEL);
	if (rp->printf_buf == NULL) {
		rc = -ENOMEM;
		goto err_alloc_pr;
	}

	rp->r.m_bus = mbus;
	rp->r.r_data = rp;
	rp->r.rnf_submit = mon_text_submit;
	rp->r.rnf_error = mon_text_error;
	rp->r.rnf_complete = mon_text_complete;

	snprintf(rp->slab_name, SLAB_NAME_SZ, "mon_text_%p", rp);
	rp->e_slab = kmem_cache_create(rp->slab_name,
	    sizeof(struct mon_event_text), sizeof(long), 0,
	    mon_text_ctor);
	if (rp->e_slab == NULL) {
		rc = -ENOMEM;
		goto err_slab;
	}

	mon_reader_add(mbus, &rp->r);

	file->private_data = rp;
	mutex_unlock(&mon_lock);
	return 0;

// err_busy:
//	kmem_cache_destroy(rp->e_slab);
err_slab:
	kfree(rp->printf_buf);
err_alloc_pr:
	kfree(rp);
err_alloc:
	mutex_unlock(&mon_lock);
	return rc;
}

/*
 * For simplicity, we read one record in one system call and throw out
 * what does not fit. This means that the following does not work:
 *   dd if=/dbg/usbmon/0t bs=10
 * Also, we do not allow seeks and do not bother advancing the offset.
 */
static ssize_t mon_text_read_t(struct file *file, char __user *buf,
				size_t nbytes, loff_t *ppos)
{
	struct mon_reader_text *rp = file->private_data;
	struct mon_event_text *ep;
	struct mon_text_ptr ptr;

	if (IS_ERR(ep = mon_text_read_wait(rp, file)))
		return PTR_ERR(ep);
	mutex_lock(&rp->printf_lock);
	ptr.cnt = 0;
	ptr.pbuf = rp->printf_buf;
	ptr.limit = rp->printf_size;

	mon_text_read_head_t(rp, &ptr, ep);
	mon_text_read_statset(rp, &ptr, ep);
	ptr.cnt += snprintf(ptr.pbuf + ptr.cnt, ptr.limit - ptr.cnt,
	    " %d", ep->length);
	mon_text_read_data(rp, &ptr, ep);

	if (copy_to_user(buf, rp->printf_buf, ptr.cnt))
		ptr.cnt = -EFAULT;
	mutex_unlock(&rp->printf_lock);
	kmem_cache_free(rp->e_slab, ep);
	return ptr.cnt;
}

static ssize_t mon_text_read_u(struct file *file, char __user *buf,
				size_t nbytes, loff_t *ppos)
{
	struct mon_reader_text *rp = file->private_data;
	struct mon_event_text *ep;
	struct mon_text_ptr ptr;

	if (IS_ERR(ep = mon_text_read_wait(rp, file)))
		return PTR_ERR(ep);
	mutex_lock(&rp->printf_lock);
	ptr.cnt = 0;
	ptr.pbuf = rp->printf_buf;
	ptr.limit = rp->printf_size;

	mon_text_read_head_u(rp, &ptr, ep);
	if (ep->type == 'E') {
		mon_text_read_statset(rp, &ptr, ep);
	} else if (ep->xfertype == USB_ENDPOINT_XFER_ISOC) {
		mon_text_read_isostat(rp, &ptr, ep);
		mon_text_read_isodesc(rp, &ptr, ep);
	} else if (ep->xfertype == USB_ENDPOINT_XFER_INT) {
		mon_text_read_intstat(rp, &ptr, ep);
	} else {
		mon_text_read_statset(rp, &ptr, ep);
	}
	ptr.cnt += snprintf(ptr.pbuf + ptr.cnt, ptr.limit - ptr.cnt,
	    " %d", ep->length);
	mon_text_read_data(rp, &ptr, ep);

	if (copy_to_user(buf, rp->printf_buf, ptr.cnt))
		ptr.cnt = -EFAULT;
	mutex_unlock(&rp->printf_lock);
	kmem_cache_free(rp->e_slab, ep);
	return ptr.cnt;
}

static struct mon_event_text *mon_text_read_wait(struct mon_reader_text *rp,
    struct file *file)
{
	struct mon_bus *mbus = rp->r.m_bus;
	DECLARE_WAITQUEUE(waita, current);
	struct mon_event_text *ep;

	add_wait_queue(&rp->wait, &waita);
	set_current_state(TASK_INTERRUPTIBLE);
	while ((ep = mon_text_fetch(rp, mbus)) == NULL) {
		if (file->f_flags & O_NONBLOCK) {
			set_current_state(TASK_RUNNING);
			remove_wait_queue(&rp->wait, &waita);
			return ERR_PTR(-EWOULDBLOCK);
		}
		/*
		 * We do not count nwaiters, because ->release is supposed
		 * to be called when all openers are gone only.
		 */
		schedule();
		if (signal_pending(current)) {
			remove_wait_queue(&rp->wait, &waita);
			return ERR_PTR(-EINTR);
		}
		set_current_state(TASK_INTERRUPTIBLE);
	}
	set_current_state(TASK_RUNNING);
	remove_wait_queue(&rp->wait, &waita);
	return ep;
}

static void mon_text_read_head_t(struct mon_reader_text *rp,
	struct mon_text_ptr *p, const struct mon_event_text *ep)
{
	char udir, utype;

	udir = (ep->is_in ? 'i' : 'o');
	switch (ep->xfertype) {
	case USB_ENDPOINT_XFER_ISOC:	utype = 'Z'; break;
	case USB_ENDPOINT_XFER_INT:	utype = 'I'; break;
	case USB_ENDPOINT_XFER_CONTROL:	utype = 'C'; break;
	default: /* PIPE_BULK */  utype = 'B';
	}
	p->cnt += snprintf(p->pbuf + p->cnt, p->limit - p->cnt,
	    "%lx %u %c %c%c:%03u:%02u",
	    ep->id, ep->tstamp, ep->type,
	    utype, udir, ep->devnum, ep->epnum);
}

static void mon_text_read_head_u(struct mon_reader_text *rp,
	struct mon_text_ptr *p, const struct mon_event_text *ep)
{
	char udir, utype;

	udir = (ep->is_in ? 'i' : 'o');
	switch (ep->xfertype) {
	case USB_ENDPOINT_XFER_ISOC:	utype = 'Z'; break;
	case USB_ENDPOINT_XFER_INT:	utype = 'I'; break;
	case USB_ENDPOINT_XFER_CONTROL:	utype = 'C'; break;
	default: /* PIPE_BULK */  utype = 'B';
	}
	p->cnt += snprintf(p->pbuf + p->cnt, p->limit - p->cnt,
	    "%lx %u %c %c%c:%d:%03u:%u",
	    ep->id, ep->tstamp, ep->type,
	    utype, udir, ep->busnum, ep->devnum, ep->epnum);
}

static void mon_text_read_statset(struct mon_reader_text *rp,
	struct mon_text_ptr *p, const struct mon_event_text *ep)
{

	if (ep->setup_flag == 0) {   /* Setup packet is present and captured */
		p->cnt += snprintf(p->pbuf + p->cnt, p->limit - p->cnt,
		    " s %02x %02x %04x %04x %04x",
		    ep->setup[0],
		    ep->setup[1],
		    (ep->setup[3] << 8) | ep->setup[2],
		    (ep->setup[5] << 8) | ep->setup[4],
		    (ep->setup[7] << 8) | ep->setup[6]);
	} else if (ep->setup_flag != '-') { /* Unable to capture setup packet */
		p->cnt += snprintf(p->pbuf + p->cnt, p->limit - p->cnt,
		    " %c __ __ ____ ____ ____", ep->setup_flag);
	} else {                     /* No setup for this kind of URB */
		p->cnt += snprintf(p->pbuf + p->cnt, p->limit - p->cnt,
		    " %d", ep->status);
	}
}

static void mon_text_read_intstat(struct mon_reader_text *rp,
	struct mon_text_ptr *p, const struct mon_event_text *ep)
{
	p->cnt += snprintf(p->pbuf + p->cnt, p->limit - p->cnt,
	    " %d:%d", ep->status, ep->interval);
}

static void mon_text_read_isostat(struct mon_reader_text *rp,
	struct mon_text_ptr *p, const struct mon_event_text *ep)
{
	if (ep->type == 'S') {
		p->cnt += snprintf(p->pbuf + p->cnt, p->limit - p->cnt,
		    " %d:%d:%d", ep->status, ep->interval, ep->start_frame);
	} else {
		p->cnt += snprintf(p->pbuf + p->cnt, p->limit - p->cnt,
		    " %d:%d:%d:%d",
		    ep->status, ep->interval, ep->start_frame, ep->error_count);
	}
}

static void mon_text_read_isodesc(struct mon_reader_text *rp,
	struct mon_text_ptr *p, const struct mon_event_text *ep)
{
	int ndesc;	/* Display this many */
	int i;
	const struct mon_iso_desc *dp;

	p->cnt += snprintf(p->pbuf + p->cnt, p->limit - p->cnt,
	    " %d", ep->numdesc);
	ndesc = ep->numdesc;
	if (ndesc > ISODESC_MAX)
		ndesc = ISODESC_MAX;
	if (ndesc < 0)
		ndesc = 0;
	dp = ep->isodesc;
	for (i = 0; i < ndesc; i++) {
		p->cnt += snprintf(p->pbuf + p->cnt, p->limit - p->cnt,
		    " %d:%u:%u", dp->status, dp->offset, dp->length);
		dp++;
	}
}

static void mon_text_read_data(struct mon_reader_text *rp,
    struct mon_text_ptr *p, const struct mon_event_text *ep)
{
	int data_len, i;

	if ((data_len = ep->length) > 0) {
		if (ep->data_flag == 0) {
			p->cnt += snprintf(p->pbuf + p->cnt, p->limit - p->cnt,
			    " =");
			if (data_len >= DATA_MAX)
				data_len = DATA_MAX;
			for (i = 0; i < data_len; i++) {
				if (i % 4 == 0) {
					p->cnt += snprintf(p->pbuf + p->cnt,
					    p->limit - p->cnt,
					    " ");
				}
				p->cnt += snprintf(p->pbuf + p->cnt,
				    p->limit - p->cnt,
				    "%02x", ep->data[i]);
			}
			p->cnt += snprintf(p->pbuf + p->cnt, p->limit - p->cnt,
			    "\n");
		} else {
			p->cnt += snprintf(p->pbuf + p->cnt, p->limit - p->cnt,
			    " %c\n", ep->data_flag);
		}
	} else {
		p->cnt += snprintf(p->pbuf + p->cnt, p->limit - p->cnt, "\n");
	}
}

static int mon_text_release(struct inode *inode, struct file *file)
{
	struct mon_reader_text *rp = file->private_data;
	struct mon_bus *mbus;
	/* unsigned long flags; */
	struct list_head *p;
	struct mon_event_text *ep;

	mutex_lock(&mon_lock);
	mbus = inode->i_private;

	if (mbus->nreaders <= 0) {
		printk(KERN_ERR TAG ": consistency error on close\n");
		mutex_unlock(&mon_lock);
		return 0;
	}
	mon_reader_del(mbus, &rp->r);

	/*
	 * In theory, e_list is protected by mbus->lock. However,
	 * after mon_reader_del has finished, the following is the case:
	 *  - we are not on reader list anymore, so new events won't be added;
	 *  - whole mbus may be dropped if it was orphaned.
	 * So, we better not touch mbus.
	 */
	/* spin_lock_irqsave(&mbus->lock, flags); */
	while (!list_empty(&rp->e_list)) {
		p = rp->e_list.next;
		ep = list_entry(p, struct mon_event_text, e_link);
		list_del(p);
		--rp->nevents;
		kmem_cache_free(rp->e_slab, ep);
	}
	/* spin_unlock_irqrestore(&mbus->lock, flags); */

	kmem_cache_destroy(rp->e_slab);
	kfree(rp->printf_buf);
	kfree(rp);

	mutex_unlock(&mon_lock);
	return 0;
}

static const struct file_operations mon_fops_text_t = {
	.owner =	THIS_MODULE,
	.open =		mon_text_open,
	.llseek =	no_llseek,
	.read =		mon_text_read_t,
	.release =	mon_text_release,
};

static const struct file_operations mon_fops_text_u = {
	.owner =	THIS_MODULE,
	.open =		mon_text_open,
	.llseek =	no_llseek,
	.read =		mon_text_read_u,
	.release =	mon_text_release,
};

int mon_text_add(struct mon_bus *mbus, const struct usb_bus *ubus)
{
	struct dentry *d;
	enum { NAMESZ = 10 };
	char name[NAMESZ];
	int busnum = ubus? ubus->busnum: 0;
	int rc;

	if (ubus != NULL) {
		rc = snprintf(name, NAMESZ, "%dt", busnum);
		if (rc <= 0 || rc >= NAMESZ)
			goto err_print_t;
		d = debugfs_create_file(name, 0600, mon_dir, mbus,
							     &mon_fops_text_t);
		if (d == NULL)
			goto err_create_t;
		mbus->dent_t = d;
	}

	rc = snprintf(name, NAMESZ, "%du", busnum);
	if (rc <= 0 || rc >= NAMESZ)
		goto err_print_u;
	d = debugfs_create_file(name, 0600, mon_dir, mbus, &mon_fops_text_u);
	if (d == NULL)
		goto err_create_u;
	mbus->dent_u = d;

	rc = snprintf(name, NAMESZ, "%ds", busnum);
	if (rc <= 0 || rc >= NAMESZ)
		goto err_print_s;
	d = debugfs_create_file(name, 0600, mon_dir, mbus, &mon_fops_stat);
	if (d == NULL)
		goto err_create_s;
	mbus->dent_s = d;

	return 1;

err_create_s:
err_print_s:
	debugfs_remove(mbus->dent_u);
	mbus->dent_u = NULL;
err_create_u:
err_print_u:
	if (ubus != NULL) {
		debugfs_remove(mbus->dent_t);
		mbus->dent_t = NULL;
	}
err_create_t:
err_print_t:
	return 0;
}

void mon_text_del(struct mon_bus *mbus)
{
	debugfs_remove(mbus->dent_u);
	if (mbus->dent_t != NULL)
		debugfs_remove(mbus->dent_t);
	debugfs_remove(mbus->dent_s);
}

/*
 * Slab interface: constructor.
 */
static void mon_text_ctor(void *mem, struct kmem_cache *slab, unsigned long sflags)
{
	/*
	 * Nothing to initialize. No, really!
	 * So, we fill it with garbage to emulate a reused object.
	 */
	memset(mem, 0xe5, sizeof(struct mon_event_text));
}

int __init mon_text_init(void)
{
	struct dentry *mondir;

	mondir = debugfs_create_dir("usbmon", NULL);
	if (IS_ERR(mondir)) {
		printk(KERN_NOTICE TAG ": debugfs is not available\n");
		return -ENODEV;
	}
	if (mondir == NULL) {
		printk(KERN_NOTICE TAG ": unable to create usbmon directory\n");
		return -ENODEV;
	}
	mon_dir = mondir;
	return 0;
}

void mon_text_exit(void)
{
	debugfs_remove(mon_dir);
}