summaryrefslogtreecommitdiff
path: root/blktrace.c
blob: 8a246613d43338d2f715dca0031dafbf164bcbef (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
/*
 * blktrace support code for fio
 */
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>

#include "flist.h"
#include "fio.h"
#include "blktrace.h"
#include "blktrace_api.h"
#include "oslib/linux-dev-lookup.h"

#define TRACE_FIFO_SIZE	8192

/*
 * fifo refill frontend, to avoid reading data in trace sized bites
 */
static int refill_fifo(struct thread_data *td, struct fifo *fifo, int fd)
{
	char buf[TRACE_FIFO_SIZE];
	unsigned int total;
	int ret;

	total = sizeof(buf);
	if (total > fifo_room(fifo))
		total = fifo_room(fifo);

	ret = read(fd, buf, total);
	if (ret < 0) {
		td_verror(td, errno, "read blktrace file");
		return -1;
	}

	if (ret > 0)
		ret = fifo_put(fifo, buf, ret);

	dprint(FD_BLKTRACE, "refill: filled %d bytes\n", ret);
	return ret;
}

/*
 * Retrieve 'len' bytes from the fifo, refilling if necessary.
 */
static int trace_fifo_get(struct thread_data *td, struct fifo *fifo, int fd,
			  void *buf, unsigned int len)
{
	if (fifo_len(fifo) < len) {
		int ret = refill_fifo(td, fifo, fd);

		if (ret < 0)
			return ret;
	}

	return fifo_get(fifo, buf, len);
}

/*
 * Just discard the pdu by seeking past it.
 */
static int discard_pdu(struct thread_data *td, struct fifo *fifo, int fd,
		       struct blk_io_trace *t)
{
	if (t->pdu_len == 0)
		return 0;

	dprint(FD_BLKTRACE, "discard pdu len %u\n", t->pdu_len);
	return trace_fifo_get(td, fifo, fd, NULL, t->pdu_len);
}

/*
 * Check if this is a blktrace binary data file. We read a single trace
 * into memory and check for the magic signature.
 */
bool is_blktrace(const char *filename, int *need_swap)
{
	struct blk_io_trace t;
	int fd, ret;

	fd = open(filename, O_RDONLY);
	if (fd < 0)
		return false;

	ret = read(fd, &t, sizeof(t));
	close(fd);

	if (ret < 0) {
		perror("read blktrace");
		return false;
	} else if (ret != sizeof(t)) {
		log_err("fio: short read on blktrace file\n");
		return false;
	}

	if ((t.magic & 0xffffff00) == BLK_IO_TRACE_MAGIC) {
		*need_swap = 0;
		return true;
	}

	/*
	 * Maybe it needs to be endian swapped...
	 */
	t.magic = fio_swap32(t.magic);
	if ((t.magic & 0xffffff00) == BLK_IO_TRACE_MAGIC) {
		*need_swap = 1;
		return true;
	}

	return false;
}

#define FMINORBITS	20
#define FMINORMASK	((1U << FMINORBITS) - 1)
#define FMAJOR(dev)	((unsigned int) ((dev) >> FMINORBITS))
#define FMINOR(dev)	((unsigned int) ((dev) & FMINORMASK))

static void trace_add_open_close_event(struct thread_data *td, int fileno, enum file_log_act action)
{
	struct io_piece *ipo;

	ipo = calloc(1, sizeof(*ipo));
	init_ipo(ipo);

	ipo->ddir = DDIR_INVAL;
	ipo->fileno = fileno;
	ipo->file_action = action;
	flist_add_tail(&ipo->list, &td->io_log_list);
}

static int trace_add_file(struct thread_data *td, __u32 device)
{
	static unsigned int last_maj, last_min, last_fileno;
	unsigned int maj = FMAJOR(device);
	unsigned int min = FMINOR(device);
	struct fio_file *f;
	char dev[256];
	unsigned int i;

	if (last_maj == maj && last_min == min)
		return last_fileno;

	last_maj = maj;
	last_min = min;

	/*
	 * check for this file in our list
	 */
	for_each_file(td, f, i)
		if (f->major == maj && f->minor == min) {
			last_fileno = f->fileno;
			return last_fileno;
		}

	strcpy(dev, "/dev");
	if (blktrace_lookup_device(td->o.replay_redirect, dev, maj, min)) {
		int fileno;

		if (td->o.replay_redirect)
			dprint(FD_BLKTRACE, "device lookup: %d/%d\n overridden"
					" with: %s\n", maj, min,
					td->o.replay_redirect);
		else
			dprint(FD_BLKTRACE, "device lookup: %d/%d\n", maj, min);

		dprint(FD_BLKTRACE, "add devices %s\n", dev);
		fileno = add_file_exclusive(td, dev);
		td->o.open_files++;
		td->files[fileno]->major = maj;
		td->files[fileno]->minor = min;
		trace_add_open_close_event(td, fileno, FIO_LOG_OPEN_FILE);
		last_fileno = fileno;
	}

	return last_fileno;
}

static void t_bytes_align(struct thread_options *o, struct blk_io_trace *t)
{
	if (!o->replay_align)
		return;

	t->bytes = (t->bytes + o->replay_align - 1) & ~(o->replay_align - 1);
}

/*
 * Store blk_io_trace data in an ipo for later retrieval.
 */
static void store_ipo(struct thread_data *td, unsigned long long offset,
		      unsigned int bytes, int rw, unsigned long long ttime,
		      int fileno)
{
	struct io_piece *ipo;

	ipo = calloc(1, sizeof(*ipo));
	init_ipo(ipo);

	ipo->offset = offset * 512;
	if (td->o.replay_scale)
		ipo->offset = ipo->offset / td->o.replay_scale;
	ipo_bytes_align(td->o.replay_align, ipo);
	ipo->len = bytes;
	ipo->delay = ttime / 1000;
	if (rw)
		ipo->ddir = DDIR_WRITE;
	else
		ipo->ddir = DDIR_READ;
	ipo->fileno = fileno;

	dprint(FD_BLKTRACE, "store ddir=%d, off=%llu, len=%lu, delay=%lu\n",
							ipo->ddir, ipo->offset,
							ipo->len, ipo->delay);
	queue_io_piece(td, ipo);
}

static void handle_trace_notify(struct blk_io_trace *t)
{
	switch (t->action) {
	case BLK_TN_PROCESS:
		dprint(FD_BLKTRACE, "got process notify: %x, %d\n",
				t->action, t->pid);
		break;
	case BLK_TN_TIMESTAMP:
		dprint(FD_BLKTRACE, "got timestamp notify: %x, %d\n",
				t->action, t->pid);
		break;
	case BLK_TN_MESSAGE:
		break;
	default:
		dprint(FD_BLKTRACE, "unknown trace act %x\n", t->action);
		break;
	}
}

static void handle_trace_discard(struct thread_data *td,
				 struct blk_io_trace *t,
				 unsigned long long ttime,
				 unsigned long *ios, unsigned int *bs)
{
	struct io_piece *ipo;
	int fileno;

	if (td->o.replay_skip & (1u << DDIR_TRIM))
		return;

	ipo = calloc(1, sizeof(*ipo));
	init_ipo(ipo);
	fileno = trace_add_file(td, t->device);

	ios[DDIR_TRIM]++;
	if (t->bytes > bs[DDIR_TRIM])
		bs[DDIR_TRIM] = t->bytes;

	td->o.size += t->bytes;

	INIT_FLIST_HEAD(&ipo->list);

	ipo->offset = t->sector * 512;
	if (td->o.replay_scale)
		ipo->offset = ipo->offset / td->o.replay_scale;
	ipo_bytes_align(td->o.replay_align, ipo);
	ipo->len = t->bytes;
	ipo->delay = ttime / 1000;
	ipo->ddir = DDIR_TRIM;
	ipo->fileno = fileno;

	dprint(FD_BLKTRACE, "store discard, off=%llu, len=%lu, delay=%lu\n",
							ipo->offset, ipo->len,
							ipo->delay);
	queue_io_piece(td, ipo);
}

static void dump_trace(struct blk_io_trace *t)
{
	log_err("blktrace: ignoring zero byte trace: action=%x\n", t->action);
}

static void handle_trace_fs(struct thread_data *td, struct blk_io_trace *t,
			    unsigned long long ttime, unsigned long *ios,
			    unsigned int *bs)
{
	int rw;
	int fileno;

	fileno = trace_add_file(td, t->device);

	rw = (t->action & BLK_TC_ACT(BLK_TC_WRITE)) != 0;

	if (rw) {
		if (td->o.replay_skip & (1u << DDIR_WRITE))
			return;
	} else {
		if (td->o.replay_skip & (1u << DDIR_READ))
			return;
	}

	if (!t->bytes) {
		if (!fio_did_warn(FIO_WARN_BTRACE_ZERO))
			dump_trace(t);
		return;
	}

	if (t->bytes > bs[rw])
		bs[rw] = t->bytes;

	ios[rw]++;
	td->o.size += t->bytes;
	store_ipo(td, t->sector, t->bytes, rw, ttime, fileno);
}

static void handle_trace_flush(struct thread_data *td, struct blk_io_trace *t,
			       unsigned long long ttime, unsigned long *ios)
{
	struct io_piece *ipo;
	int fileno;

	if (td->o.replay_skip & (1u << DDIR_SYNC))
		return;

	ipo = calloc(1, sizeof(*ipo));
	init_ipo(ipo);
	fileno = trace_add_file(td, t->device);

	ipo->delay = ttime / 1000;
	ipo->ddir = DDIR_SYNC;
	ipo->fileno = fileno;

	ios[DDIR_SYNC]++;
	dprint(FD_BLKTRACE, "store flush delay=%lu\n", ipo->delay);
	queue_io_piece(td, ipo);
}

/*
 * We only care for queue traces, most of the others are side effects
 * due to internal workings of the block layer.
 */
static void handle_trace(struct thread_data *td, struct blk_io_trace *t,
			 unsigned long *ios, unsigned int *bs)
{
	static unsigned long long last_ttime;
	unsigned long long delay = 0;

	if ((t->action & 0xffff) != __BLK_TA_QUEUE)
		return;

	if (!(t->action & BLK_TC_ACT(BLK_TC_NOTIFY))) {
		if (!last_ttime || td->o.no_stall)
			delay = 0;
		else if (td->o.replay_time_scale == 100)
			delay = t->time - last_ttime;
		else {
			double tmp = t->time - last_ttime;
			double scale;

			scale = (double) 100.0 / (double) td->o.replay_time_scale;
			tmp *= scale;
			delay = tmp;
		}
		last_ttime = t->time;
	}

	t_bytes_align(&td->o, t);

	if (t->action & BLK_TC_ACT(BLK_TC_NOTIFY))
		handle_trace_notify(t);
	else if (t->action & BLK_TC_ACT(BLK_TC_DISCARD))
		handle_trace_discard(td, t, delay, ios, bs);
	else if (t->action & BLK_TC_ACT(BLK_TC_FLUSH))
		handle_trace_flush(td, t, delay, ios);
	else
		handle_trace_fs(td, t, delay, ios, bs);
}

static void byteswap_trace(struct blk_io_trace *t)
{
	t->magic = fio_swap32(t->magic);
	t->sequence = fio_swap32(t->sequence);
	t->time = fio_swap64(t->time);
	t->sector = fio_swap64(t->sector);
	t->bytes = fio_swap32(t->bytes);
	t->action = fio_swap32(t->action);
	t->pid = fio_swap32(t->pid);
	t->device = fio_swap32(t->device);
	t->cpu = fio_swap32(t->cpu);
	t->error = fio_swap16(t->error);
	t->pdu_len = fio_swap16(t->pdu_len);
}

static bool t_is_write(struct blk_io_trace *t)
{
	return (t->action & BLK_TC_ACT(BLK_TC_WRITE | BLK_TC_DISCARD)) != 0;
}

static enum fio_ddir t_get_ddir(struct blk_io_trace *t)
{
	if (t->action & BLK_TC_ACT(BLK_TC_READ))
		return DDIR_READ;
	else if (t->action & BLK_TC_ACT(BLK_TC_WRITE))
		return DDIR_WRITE;
	else if (t->action & BLK_TC_ACT(BLK_TC_DISCARD))
		return DDIR_TRIM;

	return DDIR_INVAL;
}

static void depth_inc(struct blk_io_trace *t, int *depth)
{
	enum fio_ddir ddir;

	ddir = t_get_ddir(t);
	if (ddir != DDIR_INVAL)
		depth[ddir]++;
}

static void depth_dec(struct blk_io_trace *t, int *depth)
{
	enum fio_ddir ddir;

	ddir = t_get_ddir(t);
	if (ddir != DDIR_INVAL)
		depth[ddir]--;
}

static void depth_end(struct blk_io_trace *t, int *this_depth, int *depth)
{
	enum fio_ddir ddir = DDIR_INVAL;

	ddir = t_get_ddir(t);
	if (ddir != DDIR_INVAL) {
		depth[ddir] = max(depth[ddir], this_depth[ddir]);
		this_depth[ddir] = 0;
	}
}

/*
 * Load a blktrace file by reading all the blk_io_trace entries, and storing
 * them as io_pieces like the fio text version would do.
 */
bool load_blktrace(struct thread_data *td, const char *filename, int need_swap)
{
	struct blk_io_trace t;
	unsigned long ios[DDIR_RWDIR_SYNC_CNT] = { };
	unsigned int rw_bs[DDIR_RWDIR_CNT] = { };
	unsigned long skipped_writes;
	struct fifo *fifo;
	int fd, i, old_state, max_depth;
	struct fio_file *f;
	int this_depth[DDIR_RWDIR_CNT] = { };
	int depth[DDIR_RWDIR_CNT] = { };

	fd = open(filename, O_RDONLY);
	if (fd < 0) {
		td_verror(td, errno, "open blktrace file");
		return false;
	}

	fifo = fifo_alloc(TRACE_FIFO_SIZE);

	old_state = td_bump_runstate(td, TD_SETTING_UP);

	td->o.size = 0;
	skipped_writes = 0;
	do {
		int ret = trace_fifo_get(td, fifo, fd, &t, sizeof(t));

		if (ret < 0)
			goto err;
		else if (!ret)
			break;
		else if (ret < (int) sizeof(t)) {
			log_err("fio: short fifo get\n");
			break;
		}

		if (need_swap)
			byteswap_trace(&t);

		if ((t.magic & 0xffffff00) != BLK_IO_TRACE_MAGIC) {
			log_err("fio: bad magic in blktrace data: %x\n",
								t.magic);
			goto err;
		}
		if ((t.magic & 0xff) != BLK_IO_TRACE_VERSION) {
			log_err("fio: bad blktrace version %d\n",
								t.magic & 0xff);
			goto err;
		}
		ret = discard_pdu(td, fifo, fd, &t);
		if (ret < 0) {
			td_verror(td, ret, "blktrace lseek");
			goto err;
		} else if (t.pdu_len != ret) {
			log_err("fio: discarded %d of %d\n", ret, t.pdu_len);
			goto err;
		}
		if ((t.action & BLK_TC_ACT(BLK_TC_NOTIFY)) == 0) {
			if ((t.action & 0xffff) == __BLK_TA_QUEUE)
				depth_inc(&t, this_depth);
			else if (((t.action & 0xffff) == __BLK_TA_BACKMERGE) ||
				((t.action & 0xffff) == __BLK_TA_FRONTMERGE))
				depth_dec(&t, this_depth);
			else if ((t.action & 0xffff) == __BLK_TA_COMPLETE)
				depth_end(&t, this_depth, depth);

			if (t_is_write(&t) && read_only) {
				skipped_writes++;
				continue;
			}
		}

		handle_trace(td, &t, ios, rw_bs);
	} while (1);

	for_each_file(td, f, i)
		trace_add_open_close_event(td, f->fileno, FIO_LOG_CLOSE_FILE);

	fifo_free(fifo);
	close(fd);

	td_restore_runstate(td, old_state);

	if (!td->files_index) {
		log_err("fio: did not find replay device(s)\n");
		return false;
	}

	/*
	 * For stacked devices, we don't always get a COMPLETE event so
	 * the depth grows to insane values. Limit it to something sane(r).
	 */
	max_depth = 0;
	for (i = 0; i < DDIR_RWDIR_CNT; i++) {
		if (depth[i] > 1024)
			depth[i] = 1024;
		else if (!depth[i] && ios[i])
			depth[i] = 1;
		max_depth = max(depth[i], max_depth);
	}

	if (skipped_writes)
		log_err("fio: %s skips replay of %lu writes due to read-only\n",
						td->o.name, skipped_writes);

	if (!ios[DDIR_READ] && !ios[DDIR_WRITE] && !ios[DDIR_TRIM] &&
	    !ios[DDIR_SYNC]) {
		log_err("fio: found no ios in blktrace data\n");
		return false;
	}

	td->o.td_ddir = 0;
	if (ios[DDIR_READ]) {
		td->o.td_ddir |= TD_DDIR_READ;
		td->o.max_bs[DDIR_READ] = rw_bs[DDIR_READ];
	}
	if (ios[DDIR_WRITE]) {
		td->o.td_ddir |= TD_DDIR_WRITE;
		td->o.max_bs[DDIR_WRITE] = rw_bs[DDIR_WRITE];
	}
	if (ios[DDIR_TRIM]) {
		td->o.td_ddir |= TD_DDIR_TRIM;
		td->o.max_bs[DDIR_TRIM] = rw_bs[DDIR_TRIM];
	}

	/*
	 * We need to do direct/raw ios to the device, to avoid getting
	 * read-ahead in our way. But only do so if the minimum block size
	 * is a multiple of 4k, otherwise we don't know if it's safe to do so.
	 */
	if (!fio_option_is_set(&td->o, odirect) && !(td_min_bs(td) & 4095))
		td->o.odirect = 1;

	/*
	 * If depth wasn't manually set, use probed depth
	 */
	if (!fio_option_is_set(&td->o, iodepth))
		td->o.iodepth = td->o.iodepth_low = max_depth;

	return true;
err:
	close(fd);
	fifo_free(fifo);
	return false;
}

static int init_merge_param_list(fio_fp64_t *vals, struct blktrace_cursor *bcs,
				 int nr_logs, int def, size_t off)
{
	int i = 0, len = 0;

	while (len < FIO_IO_U_LIST_MAX_LEN && vals[len].u.f != 0.0)
		len++;

	if (len && len != nr_logs)
		return len;

	for (i = 0; i < nr_logs; i++) {
		int *val = (int *)((char *)&bcs[i] + off);
		*val = def;
		if (len)
			*val = (int)vals[i].u.f;
	}

	return 0;

}

static int find_earliest_io(struct blktrace_cursor *bcs, int nr_logs)
{
	__u64 time = ~(__u64)0;
	int idx = 0, i;

	for (i = 0; i < nr_logs; i++) {
		if (bcs[i].t.time < time) {
			time = bcs[i].t.time;
			idx = i;
		}
	}

	return idx;
}

static void merge_finish_file(struct blktrace_cursor *bcs, int i, int *nr_logs)
{
	bcs[i].iter++;
	if (bcs[i].iter < bcs[i].nr_iter) {
		lseek(bcs[i].fd, 0, SEEK_SET);
		return;
	}

	*nr_logs -= 1;

	/* close file */
	fifo_free(bcs[i].fifo);
	close(bcs[i].fd);

	/* keep active files contiguous */
	memmove(&bcs[i], &bcs[*nr_logs], sizeof(bcs[i]));
}

static int read_trace(struct thread_data *td, struct blktrace_cursor *bc)
{
	int ret = 0;
	struct blk_io_trace *t = &bc->t;

read_skip:
	/* read an io trace */
	ret = trace_fifo_get(td, bc->fifo, bc->fd, t, sizeof(*t));
	if (ret < 0) {
		return ret;
	} else if (!ret) {
		if (!bc->length)
			bc->length = bc->t.time;
		return ret;
	} else if (ret < (int) sizeof(*t)) {
		log_err("fio: short fifo get\n");
		return -1;
	}

	if (bc->swap)
		byteswap_trace(t);

	/* skip over actions that fio does not care about */
	if ((t->action & 0xffff) != __BLK_TA_QUEUE ||
	    t_get_ddir(t) == DDIR_INVAL) {
		ret = discard_pdu(td, bc->fifo, bc->fd, t);
		if (ret < 0) {
			td_verror(td, ret, "blktrace lseek");
			return ret;
		} else if (t->pdu_len != ret) {
			log_err("fio: discarded %d of %d\n", ret,
				t->pdu_len);
			return -1;
		}
		goto read_skip;
	}

	t->time = (t->time + bc->iter * bc->length) * bc->scalar / 100;

	return ret;
}

static int write_trace(FILE *fp, struct blk_io_trace *t)
{
	/* pdu is not used so just write out only the io trace */
	t->pdu_len = 0;
	return fwrite((void *)t, sizeof(*t), 1, fp);
}

int merge_blktrace_iologs(struct thread_data *td)
{
	int nr_logs = get_max_str_idx(td->o.read_iolog_file);
	struct blktrace_cursor *bcs = malloc(sizeof(struct blktrace_cursor) *
					     nr_logs);
	struct blktrace_cursor *bc;
	FILE *merge_fp;
	char *str, *ptr, *name, *merge_buf;
	int i, ret;

	ret = init_merge_param_list(td->o.merge_blktrace_scalars, bcs, nr_logs,
				    100, offsetof(struct blktrace_cursor,
						  scalar));
	if (ret) {
		log_err("fio: merge_blktrace_scalars(%d) != nr_logs(%d)\n",
			ret, nr_logs);
		goto err_param;
	}

	ret = init_merge_param_list(td->o.merge_blktrace_iters, bcs, nr_logs,
				    1, offsetof(struct blktrace_cursor,
						nr_iter));
	if (ret) {
		log_err("fio: merge_blktrace_iters(%d) != nr_logs(%d)\n",
			ret, nr_logs);
		goto err_param;
	}

	/* setup output file */
	merge_fp = fopen(td->o.merge_blktrace_file, "w");
	merge_buf = malloc(128 * 1024);
	ret = setvbuf(merge_fp, merge_buf, _IOFBF, 128 * 1024);
	if (ret)
		goto err_out_file;

	/* setup input files */
	str = ptr = strdup(td->o.read_iolog_file);
	nr_logs = 0;
	for (i = 0; (name = get_next_str(&ptr)) != NULL; i++) {
		bcs[i].fd = open(name, O_RDONLY);
		if (bcs[i].fd < 0) {
			log_err("fio: could not open file: %s\n", name);
			ret = bcs[i].fd;
			goto err_file;
		}
		bcs[i].fifo = fifo_alloc(TRACE_FIFO_SIZE);
		nr_logs++;

		if (!is_blktrace(name, &bcs[i].swap)) {
			log_err("fio: file is not a blktrace: %s\n", name);
			goto err_file;
		}

		ret = read_trace(td, &bcs[i]);
		if (ret < 0) {
			goto err_file;
		} else if (!ret) {
			merge_finish_file(bcs, i, &nr_logs);
			i--;
		}
	}
	free(str);

	/* merge files */
	while (nr_logs) {
		i = find_earliest_io(bcs, nr_logs);
		bc = &bcs[i];
		/* skip over the pdu */
		ret = discard_pdu(td, bc->fifo, bc->fd, &bc->t);
		if (ret < 0) {
			td_verror(td, ret, "blktrace lseek");
			goto err_file;
		} else if (bc->t.pdu_len != ret) {
			log_err("fio: discarded %d of %d\n", ret,
				bc->t.pdu_len);
			goto err_file;
		}

		ret = write_trace(merge_fp, &bc->t);
		ret = read_trace(td, bc);
		if (ret < 0)
			goto err_file;
		else if (!ret)
			merge_finish_file(bcs, i, &nr_logs);
	}

	/* set iolog file to read from the newly merged file */
	td->o.read_iolog_file = td->o.merge_blktrace_file;
	ret = 0;

err_file:
	/* cleanup */
	for (i = 0; i < nr_logs; i++) {
		fifo_free(bcs[i].fifo);
		close(bcs[i].fd);
	}
err_out_file:
	fflush(merge_fp);
	fclose(merge_fp);
	free(merge_buf);
err_param:
	free(bcs);

	return ret;
}