summaryrefslogtreecommitdiffstats
path: root/drivers/md/dm-switch.c
blob: 871c18fe000dfae2ef016ad64a5d8c4e0fc04e66 (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
/*
 * Copyright (C) 2010-2012 by Dell Inc.  All rights reserved.
 * Copyright (C) 2011-2013 Red Hat, Inc.
 *
 * This file is released under the GPL.
 *
 * dm-switch is a device-mapper target that maps IO to underlying block
 * devices efficiently when there are a large number of fixed-sized
 * address regions but there is no simple pattern to allow for a compact
 * mapping representation such as dm-stripe.
 */

#include <linux/device-mapper.h>

#include <linux/module.h>
#include <linux/init.h>
#include <linux/vmalloc.h>

#define DM_MSG_PREFIX "switch"

/*
 * One region_table_slot_t holds <region_entries_per_slot> region table
 * entries each of which is <region_table_entry_bits> in size.
 */
typedef unsigned long region_table_slot_t;

/*
 * A device with the offset to its start sector.
 */
struct switch_path {
	struct dm_dev *dmdev;
	sector_t start;
};

/*
 * Context block for a dm switch device.
 */
struct switch_ctx {
	struct dm_target *ti;

	unsigned nr_paths;		/* Number of paths in path_list. */

	unsigned region_size;		/* Region size in 512-byte sectors */
	unsigned long nr_regions;	/* Number of regions making up the device */
	signed char region_size_bits;	/* log2 of region_size or -1 */

	unsigned char region_table_entry_bits;	/* Number of bits in one region table entry */
	unsigned char region_entries_per_slot;	/* Number of entries in one region table slot */
	signed char region_entries_per_slot_bits;	/* log2 of region_entries_per_slot or -1 */

	region_table_slot_t *region_table;	/* Region table */

	/*
	 * Array of dm devices to switch between.
	 */
	struct switch_path path_list[0];
};

static struct switch_ctx *alloc_switch_ctx(struct dm_target *ti, unsigned nr_paths,
					   unsigned region_size)
{
	struct switch_ctx *sctx;

	sctx = kzalloc(sizeof(struct switch_ctx) + nr_paths * sizeof(struct switch_path),
		       GFP_KERNEL);
	if (!sctx)
		return NULL;

	sctx->ti = ti;
	sctx->region_size = region_size;

	ti->private = sctx;

	return sctx;
}

static int alloc_region_table(struct dm_target *ti, unsigned nr_paths)
{
	struct switch_ctx *sctx = ti->private;
	sector_t nr_regions = ti->len;
	sector_t nr_slots;

	if (!(sctx->region_size & (sctx->region_size - 1)))
		sctx->region_size_bits = __ffs(sctx->region_size);
	else
		sctx->region_size_bits = -1;

	sctx->region_table_entry_bits = 1;
	while (sctx->region_table_entry_bits < sizeof(region_table_slot_t) * 8 &&
	       (region_table_slot_t)1 << sctx->region_table_entry_bits < nr_paths)
		sctx->region_table_entry_bits++;

	sctx->region_entries_per_slot = (sizeof(region_table_slot_t) * 8) / sctx->region_table_entry_bits;
	if (!(sctx->region_entries_per_slot & (sctx->region_entries_per_slot - 1)))
		sctx->region_entries_per_slot_bits = __ffs(sctx->region_entries_per_slot);
	else
		sctx->region_entries_per_slot_bits = -1;

	if (sector_div(nr_regions, sctx->region_size))
		nr_regions++;

	if (nr_regions >= ULONG_MAX) {
		ti->error = "Region table too large";
		return -EINVAL;
	}
	sctx->nr_regions = nr_regions;

	nr_slots = nr_regions;
	if (sector_div(nr_slots, sctx->region_entries_per_slot))
		nr_slots++;

	if (nr_slots > ULONG_MAX / sizeof(region_table_slot_t)) {
		ti->error = "Region table too large";
		return -EINVAL;
	}

	sctx->region_table = vmalloc(nr_slots * sizeof(region_table_slot_t));
	if (!sctx->region_table) {
		ti->error = "Cannot allocate region table";
		return -ENOMEM;
	}

	return 0;
}

static void switch_get_position(struct switch_ctx *sctx, unsigned long region_nr,
				unsigned long *region_index, unsigned *bit)
{
	if (sctx->region_entries_per_slot_bits >= 0) {
		*region_index = region_nr >> sctx->region_entries_per_slot_bits;
		*bit = region_nr & (sctx->region_entries_per_slot - 1);
	} else {
		*region_index = region_nr / sctx->region_entries_per_slot;
		*bit = region_nr % sctx->region_entries_per_slot;
	}

	*bit *= sctx->region_table_entry_bits;
}

static unsigned switch_region_table_read(struct switch_ctx *sctx, unsigned long region_nr)
{
	unsigned long region_index;
	unsigned bit;

	switch_get_position(sctx, region_nr, &region_index, &bit);

	return (ACCESS_ONCE(sctx->region_table[region_index]) >> bit) &
		((1 << sctx->region_table_entry_bits) - 1);
}

/*
 * Find which path to use at given offset.
 */
static unsigned switch_get_path_nr(struct switch_ctx *sctx, sector_t offset)
{
	unsigned path_nr;
	sector_t p;

	p = offset;
	if (sctx->region_size_bits >= 0)
		p >>= sctx->region_size_bits;
	else
		sector_div(p, sctx->region_size);

	path_nr = switch_region_table_read(sctx, p);

	/* This can only happen if the processor uses non-atomic stores. */
	if (unlikely(path_nr >= sctx->nr_paths))
		path_nr = 0;

	return path_nr;
}

static void switch_region_table_write(struct switch_ctx *sctx, unsigned long region_nr,
				      unsigned value)
{
	unsigned long region_index;
	unsigned bit;
	region_table_slot_t pte;

	switch_get_position(sctx, region_nr, &region_index, &bit);

	pte = sctx->region_table[region_index];
	pte &= ~((((region_table_slot_t)1 << sctx->region_table_entry_bits) - 1) << bit);
	pte |= (region_table_slot_t)value << bit;
	sctx->region_table[region_index] = pte;
}

/*
 * Fill the region table with an initial round robin pattern.
 */
static void initialise_region_table(struct switch_ctx *sctx)
{
	unsigned path_nr = 0;
	unsigned long region_nr;

	for (region_nr = 0; region_nr < sctx->nr_regions; region_nr++) {
		switch_region_table_write(sctx, region_nr, path_nr);
		if (++path_nr >= sctx->nr_paths)
			path_nr = 0;
	}
}

static int parse_path(struct dm_arg_set *as, struct dm_target *ti)
{
	struct switch_ctx *sctx = ti->private;
	unsigned long long start;
	int r;

	r = dm_get_device(ti, dm_shift_arg(as), dm_table_get_mode(ti->table),
			  &sctx->path_list[sctx->nr_paths].dmdev);
	if (r) {
		ti->error = "Device lookup failed";
		return r;
	}

	if (kstrtoull(dm_shift_arg(as), 10, &start) || start != (sector_t)start) {
		ti->error = "Invalid device starting offset";
		dm_put_device(ti, sctx->path_list[sctx->nr_paths].dmdev);
		return -EINVAL;
	}

	sctx->path_list[sctx->nr_paths].start = start;

	sctx->nr_paths++;

	return 0;
}

/*
 * Destructor: Don't free the dm_target, just the ti->private data (if any).
 */
static void switch_dtr(struct dm_target *ti)
{
	struct switch_ctx *sctx = ti->private;

	while (sctx->nr_paths--)
		dm_put_device(ti, sctx->path_list[sctx->nr_paths].dmdev);

	vfree(sctx->region_table);
	kfree(sctx);
}

/*
 * Constructor arguments:
 *   <num_paths> <region_size> <num_optional_args> [<optional_args>...]
 *   [<dev_path> <offset>]+
 *
 * Optional args are to allow for future extension: currently this
 * parameter must be 0.
 */
static int switch_ctr(struct dm_target *ti, unsigned argc, char **argv)
{
	static struct dm_arg _args[] = {
		{1, (KMALLOC_MAX_SIZE - sizeof(struct switch_ctx)) / sizeof(struct switch_path), "Invalid number of paths"},
		{1, UINT_MAX, "Invalid region size"},
		{0, 0, "Invalid number of optional args"},
	};

	struct switch_ctx *sctx;
	struct dm_arg_set as;
	unsigned nr_paths, region_size, nr_optional_args;
	int r;

	as.argc = argc;
	as.argv = argv;

	r = dm_read_arg(_args, &as, &nr_paths, &ti->error);
	if (r)
		return -EINVAL;

	r = dm_read_arg(_args + 1, &as, &region_size, &ti->error);
	if (r)
		return r;

	r = dm_read_arg_group(_args + 2, &as, &nr_optional_args, &ti->error);
	if (r)
		return r;
	/* parse optional arguments here, if we add any */

	if (as.argc != nr_paths * 2) {
		ti->error = "Incorrect number of path arguments";
		return -EINVAL;
	}

	sctx = alloc_switch_ctx(ti, nr_paths, region_size);
	if (!sctx) {
		ti->error = "Cannot allocate redirection context";
		return -ENOMEM;
	}

	r = dm_set_target_max_io_len(ti, region_size);
	if (r)
		goto error;

	while (as.argc) {
		r = parse_path(&as, ti);
		if (r)
			goto error;
	}

	r = alloc_region_table(ti, nr_paths);
	if (r)
		goto error;

	initialise_region_table(sctx);

	/* For UNMAP, sending the request down any path is sufficient */
	ti->num_discard_bios = 1;

	return 0;

error:
	switch_dtr(ti);

	return r;
}

static int switch_map(struct dm_target *ti, struct bio *bio)
{
	struct switch_ctx *sctx = ti->private;
	sector_t offset = dm_target_offset(ti, bio->bi_iter.bi_sector);
	unsigned path_nr = switch_get_path_nr(sctx, offset);

	bio->bi_bdev = sctx->path_list[path_nr].dmdev->bdev;
	bio->bi_iter.bi_sector = sctx->path_list[path_nr].start + offset;

	return DM_MAPIO_REMAPPED;
}

/*
 * We need to parse hex numbers in the message as quickly as possible.
 *
 * This table-based hex parser improves performance.
 * It improves a time to load 1000000 entries compared to the condition-based
 * parser.
 *		table-based parser	condition-based parser
 * PA-RISC	0.29s			0.31s
 * Opteron	0.0495s			0.0498s
 */
static const unsigned char hex_table[256] = {
255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255,
255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255,
255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255,
0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 255, 255, 255, 255, 255, 255,
255, 10, 11, 12, 13, 14, 15, 255, 255, 255, 255, 255, 255, 255, 255, 255,
255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255,
255, 10, 11, 12, 13, 14, 15, 255, 255, 255, 255, 255, 255, 255, 255, 255,
255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255,
255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255,
255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255,
255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255,
255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255,
255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255,
255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255,
255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255,
255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255
};

static __always_inline unsigned long parse_hex(const char **string)
{
	unsigned char d;
	unsigned long r = 0;

	while ((d = hex_table[(unsigned char)**string]) < 16) {
		r = (r << 4) | d;
		(*string)++;
	}

	return r;
}

static int process_set_region_mappings(struct switch_ctx *sctx,
				       unsigned argc, char **argv)
{
	unsigned i;
	unsigned long region_index = 0;

	for (i = 1; i < argc; i++) {
		unsigned long path_nr;
		const char *string = argv[i];

		if ((*string & 0xdf) == 'R') {
			unsigned long cycle_length, num_write;

			string++;
			if (unlikely(*string == ',')) {
				DMWARN("invalid set_region_mappings argument: '%s'", argv[i]);
				return -EINVAL;
			}
			cycle_length = parse_hex(&string);
			if (unlikely(*string != ',')) {
				DMWARN("invalid set_region_mappings argument: '%s'", argv[i]);
				return -EINVAL;
			}
			string++;
			if (unlikely(!*string)) {
				DMWARN("invalid set_region_mappings argument: '%s'", argv[i]);
				return -EINVAL;
			}
			num_write = parse_hex(&string);
			if (unlikely(*string)) {
				DMWARN("invalid set_region_mappings argument: '%s'", argv[i]);
				return -EINVAL;
			}

			if (unlikely(!cycle_length) || unlikely(cycle_length - 1 > region_index)) {
				DMWARN("invalid set_region_mappings cycle length: %lu > %lu",
				       cycle_length - 1, region_index);
				return -EINVAL;
			}
			if (unlikely(region_index + num_write < region_index) ||
			    unlikely(region_index + num_write >= sctx->nr_regions)) {
				DMWARN("invalid set_region_mappings region number: %lu + %lu >= %lu",
				       region_index, num_write, sctx->nr_regions);
				return -EINVAL;
			}

			while (num_write--) {
				region_index++;
				path_nr = switch_region_table_read(sctx, region_index - cycle_length);
				switch_region_table_write(sctx, region_index, path_nr);
			}

			continue;
		}

		if (*string == ':')
			region_index++;
		else {
			region_index = parse_hex(&string);
			if (unlikely(*string != ':')) {
				DMWARN("invalid set_region_mappings argument: '%s'", argv[i]);
				return -EINVAL;
			}
		}

		string++;
		if (unlikely(!*string)) {
			DMWARN("invalid set_region_mappings argument: '%s'", argv[i]);
			return -EINVAL;
		}

		path_nr = parse_hex(&string);
		if (unlikely(*string)) {
			DMWARN("invalid set_region_mappings argument: '%s'", argv[i]);
			return -EINVAL;
		}
		if (unlikely(region_index >= sctx->nr_regions)) {
			DMWARN("invalid set_region_mappings region number: %lu >= %lu", region_index, sctx->nr_regions);
			return -EINVAL;
		}
		if (unlikely(path_nr >= sctx->nr_paths)) {
			DMWARN("invalid set_region_mappings device: %lu >= %u", path_nr, sctx->nr_paths);
			return -EINVAL;
		}

		switch_region_table_write(sctx, region_index, path_nr);
	}

	return 0;
}

/*
 * Messages are processed one-at-a-time.
 *
 * Only set_region_mappings is supported.
 */
static int switch_message(struct dm_target *ti, unsigned argc, char **argv)
{
	static DEFINE_MUTEX(message_mutex);

	struct switch_ctx *sctx = ti->private;
	int r = -EINVAL;

	mutex_lock(&message_mutex);

	if (!strcasecmp(argv[0], "set_region_mappings"))
		r = process_set_region_mappings(sctx, argc, argv);
	else
		DMWARN("Unrecognised message received.");

	mutex_unlock(&message_mutex);

	return r;
}

static void switch_status(struct dm_target *ti, status_type_t type,
			  unsigned status_flags, char *result, unsigned maxlen)
{
	struct switch_ctx *sctx = ti->private;
	unsigned sz = 0;
	int path_nr;

	switch (type) {
	case STATUSTYPE_INFO:
		result[0] = '\0';
		break;

	case STATUSTYPE_TABLE:
		DMEMIT("%u %u 0", sctx->nr_paths, sctx->region_size);
		for (path_nr = 0; path_nr < sctx->nr_paths; path_nr++)
			DMEMIT(" %s %llu", sctx->path_list[path_nr].dmdev->name,
			       (unsigned long long)sctx->path_list[path_nr].start);
		break;
	}
}

/*
 * Switch ioctl:
 *
 * Passthrough all ioctls to the path for sector 0
 */
static int switch_prepare_ioctl(struct dm_target *ti,
		struct block_device **bdev, fmode_t *mode)
{
	struct switch_ctx *sctx = ti->private;
	unsigned path_nr;

	path_nr = switch_get_path_nr(sctx, 0);

	*bdev = sctx->path_list[path_nr].dmdev->bdev;
	*mode = sctx->path_list[path_nr].dmdev->mode;

	/*
	 * Only pass ioctls through if the device sizes match exactly.
	 */
	if (ti->len + sctx->path_list[path_nr].start !=
	    i_size_read((*bdev)->bd_inode) >> SECTOR_SHIFT)
		return 1;
	return 0;
}

static int switch_iterate_devices(struct dm_target *ti,
				  iterate_devices_callout_fn fn, void *data)
{
	struct switch_ctx *sctx = ti->private;
	int path_nr;
	int r;

	for (path_nr = 0; path_nr < sctx->nr_paths; path_nr++) {
		r = fn(ti, sctx->path_list[path_nr].dmdev,
			 sctx->path_list[path_nr].start, ti->len, data);
		if (r)
			return r;
	}

	return 0;
}

static struct target_type switch_target = {
	.name = "switch",
	.version = {1, 1, 0},
	.module = THIS_MODULE,
	.ctr = switch_ctr,
	.dtr = switch_dtr,
	.map = switch_map,
	.message = switch_message,
	.status = switch_status,
	.prepare_ioctl = switch_prepare_ioctl,
	.iterate_devices = switch_iterate_devices,
};

static int __init dm_switch_init(void)
{
	int r;

	r = dm_register_target(&switch_target);
	if (r < 0)
		DMERR("dm_register_target() failed %d", r);

	return r;
}

static void __exit dm_switch_exit(void)
{
	dm_unregister_target(&switch_target);
}

module_init(dm_switch_init);
module_exit(dm_switch_exit);

MODULE_DESCRIPTION(DM_NAME " dynamic path switching target");
MODULE_AUTHOR("Kevin D. O'Kelley <Kevin_OKelley@dell.com>");
MODULE_AUTHOR("Narendran Ganapathy <Narendran_Ganapathy@dell.com>");
MODULE_AUTHOR("Jim Ramsay <Jim_Ramsay@dell.com>");
MODULE_AUTHOR("Mikulas Patocka <mpatocka@redhat.com>");
MODULE_LICENSE("GPL");