root/drivers/md/dm-switch.c

DEFINITIONS

1. alloc_switch_ctx
2. alloc_region_table
3. switch_get_position
4. switch_region_table_read
5. switch_get_path_nr
6. switch_region_table_write
7. initialise_region_table
8. parse_path
9. switch_dtr
10. switch_ctr
11. switch_map
12. parse_hex
13. process_set_region_mappings
14. switch_message
15. switch_status
16. switch_prepare_ioctl
17. switch_iterate_devices
18. dm_switch_init
19. dm_switch_exit

   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 
  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 
  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 
 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 
 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, &region_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  */
 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 
 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, &region_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  */
 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 
 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  */
 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  */
 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, &region_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 
 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 
 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 
 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  */
 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 
 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  */
 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 
 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 
 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 
 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");