1 /*
2 * Copyright (C) 2010-2012 by Dell Inc. All rights reserved.
3 * Copyright (C) 2011-2013 Red Hat, Inc.
4 *
5 * This file is released under the GPL.
6 *
7 * dm-switch is a device-mapper target that maps IO to underlying block
8 * devices efficiently when there are a large number of fixed-sized
9 * address regions but there is no simple pattern to allow for a compact
10 * mapping representation such as dm-stripe.
11 */
12
13 #include <linux/device-mapper.h>
14
15 #include <linux/module.h>
16 #include <linux/init.h>
17 #include <linux/vmalloc.h>
18
19 #define DM_MSG_PREFIX "switch"
20
21 /*
22 * One region_table_slot_t holds <region_entries_per_slot> region table
23 * entries each of which is <region_table_entry_bits> in size.
24 */
25 typedef unsigned long region_table_slot_t;
26
27 /*
28 * A device with the offset to its start sector.
29 */
30 struct switch_path {
31 struct dm_dev *dmdev;
32 sector_t start;
33 };
34
35 /*
36 * Context block for a dm switch device.
37 */
38 struct switch_ctx {
39 struct dm_target *ti;
40
41 unsigned nr_paths; /* Number of paths in path_list. */
42
43 unsigned region_size; /* Region size in 512-byte sectors */
44 unsigned long nr_regions; /* Number of regions making up the device */
45 signed char region_size_bits; /* log2 of region_size or -1 */
46
47 unsigned char region_table_entry_bits; /* Number of bits in one region table entry */
48 unsigned char region_entries_per_slot; /* Number of entries in one region table slot */
49 signed char region_entries_per_slot_bits; /* log2 of region_entries_per_slot or -1 */
50
51 region_table_slot_t *region_table; /* Region table */
52
53 /*
54 * Array of dm devices to switch between.
55 */
56 struct switch_path path_list[0];
57 };
58
alloc_switch_ctx(struct dm_target * ti,unsigned nr_paths,unsigned region_size)59 static struct switch_ctx *alloc_switch_ctx(struct dm_target *ti, unsigned nr_paths,
60 unsigned region_size)
61 {
62 struct switch_ctx *sctx;
63
64 sctx = kzalloc(struct_size(sctx, path_list, nr_paths), GFP_KERNEL);
65 if (!sctx)
66 return NULL;
67
68 sctx->ti = ti;
69 sctx->region_size = region_size;
70
71 ti->private = sctx;
72
73 return sctx;
74 }
75
alloc_region_table(struct dm_target * ti,unsigned nr_paths)76 static int alloc_region_table(struct dm_target *ti, unsigned nr_paths)
77 {
78 struct switch_ctx *sctx = ti->private;
79 sector_t nr_regions = ti->len;
80 sector_t nr_slots;
81
82 if (!(sctx->region_size & (sctx->region_size - 1)))
83 sctx->region_size_bits = __ffs(sctx->region_size);
84 else
85 sctx->region_size_bits = -1;
86
87 sctx->region_table_entry_bits = 1;
88 while (sctx->region_table_entry_bits < sizeof(region_table_slot_t) * 8 &&
89 (region_table_slot_t)1 << sctx->region_table_entry_bits < nr_paths)
90 sctx->region_table_entry_bits++;
91
92 sctx->region_entries_per_slot = (sizeof(region_table_slot_t) * 8) / sctx->region_table_entry_bits;
93 if (!(sctx->region_entries_per_slot & (sctx->region_entries_per_slot - 1)))
94 sctx->region_entries_per_slot_bits = __ffs(sctx->region_entries_per_slot);
95 else
96 sctx->region_entries_per_slot_bits = -1;
97
98 if (sector_div(nr_regions, sctx->region_size))
99 nr_regions++;
100
101 if (nr_regions >= ULONG_MAX) {
102 ti->error = "Region table too large";
103 return -EINVAL;
104 }
105 sctx->nr_regions = nr_regions;
106
107 nr_slots = nr_regions;
108 if (sector_div(nr_slots, sctx->region_entries_per_slot))
109 nr_slots++;
110
111 if (nr_slots > ULONG_MAX / sizeof(region_table_slot_t)) {
112 ti->error = "Region table too large";
113 return -EINVAL;
114 }
115
116 sctx->region_table = vmalloc(array_size(nr_slots,
117 sizeof(region_table_slot_t)));
118 if (!sctx->region_table) {
119 ti->error = "Cannot allocate region table";
120 return -ENOMEM;
121 }
122
123 return 0;
124 }
125
switch_get_position(struct switch_ctx * sctx,unsigned long region_nr,unsigned long * region_index,unsigned * bit)126 static void switch_get_position(struct switch_ctx *sctx, unsigned long region_nr,
127 unsigned long *region_index, unsigned *bit)
128 {
129 if (sctx->region_entries_per_slot_bits >= 0) {
130 *region_index = region_nr >> sctx->region_entries_per_slot_bits;
131 *bit = region_nr & (sctx->region_entries_per_slot - 1);
132 } else {
133 *region_index = region_nr / sctx->region_entries_per_slot;
134 *bit = region_nr % sctx->region_entries_per_slot;
135 }
136
137 *bit *= sctx->region_table_entry_bits;
138 }
139
switch_region_table_read(struct switch_ctx * sctx,unsigned long region_nr)140 static unsigned switch_region_table_read(struct switch_ctx *sctx, unsigned long region_nr)
141 {
142 unsigned long region_index;
143 unsigned bit;
144
145 switch_get_position(sctx, region_nr, ®ion_index, &bit);
146
147 return (READ_ONCE(sctx->region_table[region_index]) >> bit) &
148 ((1 << sctx->region_table_entry_bits) - 1);
149 }
150
151 /*
152 * Find which path to use at given offset.
153 */
switch_get_path_nr(struct switch_ctx * sctx,sector_t offset)154 static unsigned switch_get_path_nr(struct switch_ctx *sctx, sector_t offset)
155 {
156 unsigned path_nr;
157 sector_t p;
158
159 p = offset;
160 if (sctx->region_size_bits >= 0)
161 p >>= sctx->region_size_bits;
162 else
163 sector_div(p, sctx->region_size);
164
165 path_nr = switch_region_table_read(sctx, p);
166
167 /* This can only happen if the processor uses non-atomic stores. */
168 if (unlikely(path_nr >= sctx->nr_paths))
169 path_nr = 0;
170
171 return path_nr;
172 }
173
switch_region_table_write(struct switch_ctx * sctx,unsigned long region_nr,unsigned value)174 static void switch_region_table_write(struct switch_ctx *sctx, unsigned long region_nr,
175 unsigned value)
176 {
177 unsigned long region_index;
178 unsigned bit;
179 region_table_slot_t pte;
180
181 switch_get_position(sctx, region_nr, ®ion_index, &bit);
182
183 pte = sctx->region_table[region_index];
184 pte &= ~((((region_table_slot_t)1 << sctx->region_table_entry_bits) - 1) << bit);
185 pte |= (region_table_slot_t)value << bit;
186 sctx->region_table[region_index] = pte;
187 }
188
189 /*
190 * Fill the region table with an initial round robin pattern.
191 */
initialise_region_table(struct switch_ctx * sctx)192 static void initialise_region_table(struct switch_ctx *sctx)
193 {
194 unsigned path_nr = 0;
195 unsigned long region_nr;
196
197 for (region_nr = 0; region_nr < sctx->nr_regions; region_nr++) {
198 switch_region_table_write(sctx, region_nr, path_nr);
199 if (++path_nr >= sctx->nr_paths)
200 path_nr = 0;
201 }
202 }
203
parse_path(struct dm_arg_set * as,struct dm_target * ti)204 static int parse_path(struct dm_arg_set *as, struct dm_target *ti)
205 {
206 struct switch_ctx *sctx = ti->private;
207 unsigned long long start;
208 int r;
209
210 r = dm_get_device(ti, dm_shift_arg(as), dm_table_get_mode(ti->table),
211 &sctx->path_list[sctx->nr_paths].dmdev);
212 if (r) {
213 ti->error = "Device lookup failed";
214 return r;
215 }
216
217 if (kstrtoull(dm_shift_arg(as), 10, &start) || start != (sector_t)start) {
218 ti->error = "Invalid device starting offset";
219 dm_put_device(ti, sctx->path_list[sctx->nr_paths].dmdev);
220 return -EINVAL;
221 }
222
223 sctx->path_list[sctx->nr_paths].start = start;
224
225 sctx->nr_paths++;
226
227 return 0;
228 }
229
230 /*
231 * Destructor: Don't free the dm_target, just the ti->private data (if any).
232 */
switch_dtr(struct dm_target * ti)233 static void switch_dtr(struct dm_target *ti)
234 {
235 struct switch_ctx *sctx = ti->private;
236
237 while (sctx->nr_paths--)
238 dm_put_device(ti, sctx->path_list[sctx->nr_paths].dmdev);
239
240 vfree(sctx->region_table);
241 kfree(sctx);
242 }
243
244 /*
245 * Constructor arguments:
246 * <num_paths> <region_size> <num_optional_args> [<optional_args>...]
247 * [<dev_path> <offset>]+
248 *
249 * Optional args are to allow for future extension: currently this
250 * parameter must be 0.
251 */
switch_ctr(struct dm_target * ti,unsigned argc,char ** argv)252 static int switch_ctr(struct dm_target *ti, unsigned argc, char **argv)
253 {
254 static const struct dm_arg _args[] = {
255 {1, (KMALLOC_MAX_SIZE - sizeof(struct switch_ctx)) / sizeof(struct switch_path), "Invalid number of paths"},
256 {1, UINT_MAX, "Invalid region size"},
257 {0, 0, "Invalid number of optional args"},
258 };
259
260 struct switch_ctx *sctx;
261 struct dm_arg_set as;
262 unsigned nr_paths, region_size, nr_optional_args;
263 int r;
264
265 as.argc = argc;
266 as.argv = argv;
267
268 r = dm_read_arg(_args, &as, &nr_paths, &ti->error);
269 if (r)
270 return -EINVAL;
271
272 r = dm_read_arg(_args + 1, &as, ®ion_size, &ti->error);
273 if (r)
274 return r;
275
276 r = dm_read_arg_group(_args + 2, &as, &nr_optional_args, &ti->error);
277 if (r)
278 return r;
279 /* parse optional arguments here, if we add any */
280
281 if (as.argc != nr_paths * 2) {
282 ti->error = "Incorrect number of path arguments";
283 return -EINVAL;
284 }
285
286 sctx = alloc_switch_ctx(ti, nr_paths, region_size);
287 if (!sctx) {
288 ti->error = "Cannot allocate redirection context";
289 return -ENOMEM;
290 }
291
292 r = dm_set_target_max_io_len(ti, region_size);
293 if (r)
294 goto error;
295
296 while (as.argc) {
297 r = parse_path(&as, ti);
298 if (r)
299 goto error;
300 }
301
302 r = alloc_region_table(ti, nr_paths);
303 if (r)
304 goto error;
305
306 initialise_region_table(sctx);
307
308 /* For UNMAP, sending the request down any path is sufficient */
309 ti->num_discard_bios = 1;
310
311 return 0;
312
313 error:
314 switch_dtr(ti);
315
316 return r;
317 }
318
switch_map(struct dm_target * ti,struct bio * bio)319 static int switch_map(struct dm_target *ti, struct bio *bio)
320 {
321 struct switch_ctx *sctx = ti->private;
322 sector_t offset = dm_target_offset(ti, bio->bi_iter.bi_sector);
323 unsigned path_nr = switch_get_path_nr(sctx, offset);
324
325 bio_set_dev(bio, sctx->path_list[path_nr].dmdev->bdev);
326 bio->bi_iter.bi_sector = sctx->path_list[path_nr].start + offset;
327
328 return DM_MAPIO_REMAPPED;
329 }
330
331 /*
332 * We need to parse hex numbers in the message as quickly as possible.
333 *
334 * This table-based hex parser improves performance.
335 * It improves a time to load 1000000 entries compared to the condition-based
336 * parser.
337 * table-based parser condition-based parser
338 * PA-RISC 0.29s 0.31s
339 * Opteron 0.0495s 0.0498s
340 */
341 static const unsigned char hex_table[256] = {
342 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255,
343 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255,
344 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255,
345 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 255, 255, 255, 255, 255, 255,
346 255, 10, 11, 12, 13, 14, 15, 255, 255, 255, 255, 255, 255, 255, 255, 255,
347 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255,
348 255, 10, 11, 12, 13, 14, 15, 255, 255, 255, 255, 255, 255, 255, 255, 255,
349 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255,
350 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255,
351 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255,
352 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255,
353 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255,
354 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255,
355 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255,
356 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255,
357 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255
358 };
359
parse_hex(const char ** string)360 static __always_inline unsigned long parse_hex(const char **string)
361 {
362 unsigned char d;
363 unsigned long r = 0;
364
365 while ((d = hex_table[(unsigned char)**string]) < 16) {
366 r = (r << 4) | d;
367 (*string)++;
368 }
369
370 return r;
371 }
372
process_set_region_mappings(struct switch_ctx * sctx,unsigned argc,char ** argv)373 static int process_set_region_mappings(struct switch_ctx *sctx,
374 unsigned argc, char **argv)
375 {
376 unsigned i;
377 unsigned long region_index = 0;
378
379 for (i = 1; i < argc; i++) {
380 unsigned long path_nr;
381 const char *string = argv[i];
382
383 if ((*string & 0xdf) == 'R') {
384 unsigned long cycle_length, num_write;
385
386 string++;
387 if (unlikely(*string == ',')) {
388 DMWARN("invalid set_region_mappings argument: '%s'", argv[i]);
389 return -EINVAL;
390 }
391 cycle_length = parse_hex(&string);
392 if (unlikely(*string != ',')) {
393 DMWARN("invalid set_region_mappings argument: '%s'", argv[i]);
394 return -EINVAL;
395 }
396 string++;
397 if (unlikely(!*string)) {
398 DMWARN("invalid set_region_mappings argument: '%s'", argv[i]);
399 return -EINVAL;
400 }
401 num_write = parse_hex(&string);
402 if (unlikely(*string)) {
403 DMWARN("invalid set_region_mappings argument: '%s'", argv[i]);
404 return -EINVAL;
405 }
406
407 if (unlikely(!cycle_length) || unlikely(cycle_length - 1 > region_index)) {
408 DMWARN("invalid set_region_mappings cycle length: %lu > %lu",
409 cycle_length - 1, region_index);
410 return -EINVAL;
411 }
412 if (unlikely(region_index + num_write < region_index) ||
413 unlikely(region_index + num_write >= sctx->nr_regions)) {
414 DMWARN("invalid set_region_mappings region number: %lu + %lu >= %lu",
415 region_index, num_write, sctx->nr_regions);
416 return -EINVAL;
417 }
418
419 while (num_write--) {
420 region_index++;
421 path_nr = switch_region_table_read(sctx, region_index - cycle_length);
422 switch_region_table_write(sctx, region_index, path_nr);
423 }
424
425 continue;
426 }
427
428 if (*string == ':')
429 region_index++;
430 else {
431 region_index = parse_hex(&string);
432 if (unlikely(*string != ':')) {
433 DMWARN("invalid set_region_mappings argument: '%s'", argv[i]);
434 return -EINVAL;
435 }
436 }
437
438 string++;
439 if (unlikely(!*string)) {
440 DMWARN("invalid set_region_mappings argument: '%s'", argv[i]);
441 return -EINVAL;
442 }
443
444 path_nr = parse_hex(&string);
445 if (unlikely(*string)) {
446 DMWARN("invalid set_region_mappings argument: '%s'", argv[i]);
447 return -EINVAL;
448 }
449 if (unlikely(region_index >= sctx->nr_regions)) {
450 DMWARN("invalid set_region_mappings region number: %lu >= %lu", region_index, sctx->nr_regions);
451 return -EINVAL;
452 }
453 if (unlikely(path_nr >= sctx->nr_paths)) {
454 DMWARN("invalid set_region_mappings device: %lu >= %u", path_nr, sctx->nr_paths);
455 return -EINVAL;
456 }
457
458 switch_region_table_write(sctx, region_index, path_nr);
459 }
460
461 return 0;
462 }
463
464 /*
465 * Messages are processed one-at-a-time.
466 *
467 * Only set_region_mappings is supported.
468 */
switch_message(struct dm_target * ti,unsigned argc,char ** argv,char * result,unsigned maxlen)469 static int switch_message(struct dm_target *ti, unsigned argc, char **argv,
470 char *result, unsigned maxlen)
471 {
472 static DEFINE_MUTEX(message_mutex);
473
474 struct switch_ctx *sctx = ti->private;
475 int r = -EINVAL;
476
477 mutex_lock(&message_mutex);
478
479 if (!strcasecmp(argv[0], "set_region_mappings"))
480 r = process_set_region_mappings(sctx, argc, argv);
481 else
482 DMWARN("Unrecognised message received.");
483
484 mutex_unlock(&message_mutex);
485
486 return r;
487 }
488
switch_status(struct dm_target * ti,status_type_t type,unsigned status_flags,char * result,unsigned maxlen)489 static void switch_status(struct dm_target *ti, status_type_t type,
490 unsigned status_flags, char *result, unsigned maxlen)
491 {
492 struct switch_ctx *sctx = ti->private;
493 unsigned sz = 0;
494 int path_nr;
495
496 switch (type) {
497 case STATUSTYPE_INFO:
498 result[0] = '\0';
499 break;
500
501 case STATUSTYPE_TABLE:
502 DMEMIT("%u %u 0", sctx->nr_paths, sctx->region_size);
503 for (path_nr = 0; path_nr < sctx->nr_paths; path_nr++)
504 DMEMIT(" %s %llu", sctx->path_list[path_nr].dmdev->name,
505 (unsigned long long)sctx->path_list[path_nr].start);
506 break;
507 }
508 }
509
510 /*
511 * Switch ioctl:
512 *
513 * Passthrough all ioctls to the path for sector 0
514 */
switch_prepare_ioctl(struct dm_target * ti,struct block_device ** bdev)515 static int switch_prepare_ioctl(struct dm_target *ti, struct block_device **bdev)
516 {
517 struct switch_ctx *sctx = ti->private;
518 unsigned path_nr;
519
520 path_nr = switch_get_path_nr(sctx, 0);
521
522 *bdev = sctx->path_list[path_nr].dmdev->bdev;
523
524 /*
525 * Only pass ioctls through if the device sizes match exactly.
526 */
527 if (ti->len + sctx->path_list[path_nr].start !=
528 i_size_read((*bdev)->bd_inode) >> SECTOR_SHIFT)
529 return 1;
530 return 0;
531 }
532
switch_iterate_devices(struct dm_target * ti,iterate_devices_callout_fn fn,void * data)533 static int switch_iterate_devices(struct dm_target *ti,
534 iterate_devices_callout_fn fn, void *data)
535 {
536 struct switch_ctx *sctx = ti->private;
537 int path_nr;
538 int r;
539
540 for (path_nr = 0; path_nr < sctx->nr_paths; path_nr++) {
541 r = fn(ti, sctx->path_list[path_nr].dmdev,
542 sctx->path_list[path_nr].start, ti->len, data);
543 if (r)
544 return r;
545 }
546
547 return 0;
548 }
549
550 static struct target_type switch_target = {
551 .name = "switch",
552 .version = {1, 1, 0},
553 .module = THIS_MODULE,
554 .ctr = switch_ctr,
555 .dtr = switch_dtr,
556 .map = switch_map,
557 .message = switch_message,
558 .status = switch_status,
559 .prepare_ioctl = switch_prepare_ioctl,
560 .iterate_devices = switch_iterate_devices,
561 };
562
dm_switch_init(void)563 static int __init dm_switch_init(void)
564 {
565 int r;
566
567 r = dm_register_target(&switch_target);
568 if (r < 0)
569 DMERR("dm_register_target() failed %d", r);
570
571 return r;
572 }
573
dm_switch_exit(void)574 static void __exit dm_switch_exit(void)
575 {
576 dm_unregister_target(&switch_target);
577 }
578
579 module_init(dm_switch_init);
580 module_exit(dm_switch_exit);
581
582 MODULE_DESCRIPTION(DM_NAME " dynamic path switching target");
583 MODULE_AUTHOR("Kevin D. O'Kelley <Kevin_OKelley@dell.com>");
584 MODULE_AUTHOR("Narendran Ganapathy <Narendran_Ganapathy@dell.com>");
585 MODULE_AUTHOR("Jim Ramsay <Jim_Ramsay@dell.com>");
586 MODULE_AUTHOR("Mikulas Patocka <mpatocka@redhat.com>");
587 MODULE_LICENSE("GPL");
588