drivers/md/dm-switch.c

   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(sizeof(struct switch_ctx) + nr_paths * sizeof(struct switch_path),
  65                        GFP_KERNEL);
  66         if (!sctx)
  67                 return NULL;
  68
  69         sctx->ti = ti;
  70         sctx->region_size = region_size;
  71
  72         ti->private = sctx;
  73
  74         return sctx;
  75 }
  76
  77 static int alloc_region_table(struct dm_target *ti, unsigned nr_paths)
  78 {
  79         struct switch_ctx *sctx = ti->private;
  80         sector_t nr_regions = ti->len;
  81         sector_t nr_slots;
  82
  83         if (!(sctx->region_size & (sctx->region_size - 1)))
  84                 sctx->region_size_bits = __ffs(sctx->region_size);
  85         else
  86                 sctx->region_size_bits = -1;
  87
  88         sctx->region_table_entry_bits = 1;
  89         while (sctx->region_table_entry_bits < sizeof(region_table_slot_t) * 8 &&
  90                (region_table_slot_t)1 << sctx->region_table_entry_bits < nr_paths)
  91                 sctx->region_table_entry_bits++;
  92
  93         sctx->region_entries_per_slot = (sizeof(region_table_slot_t) * 8) / sctx->region_table_entry_bits;
  94         if (!(sctx->region_entries_per_slot & (sctx->region_entries_per_slot - 1)))
  95                 sctx->region_entries_per_slot_bits = __ffs(sctx->region_entries_per_slot);
  96         else
  97                 sctx->region_entries_per_slot_bits = -1;
  98
  99         if (sector_div(nr_regions, sctx->region_size))
 100                 nr_regions++;
 101
 102         sctx->nr_regions = nr_regions;
 103         if (sctx->nr_regions != nr_regions || sctx->nr_regions >= ULONG_MAX) {
 104                 ti->error = "Region table too large";
 105                 return -EINVAL;
 106         }
 107
 108         nr_slots = nr_regions;
 109         if (sector_div(nr_slots, sctx->region_entries_per_slot))
 110                 nr_slots++;
 111
 112         if (nr_slots > ULONG_MAX / sizeof(region_table_slot_t)) {
 113                 ti->error = "Region table too large";
 114                 return -EINVAL;
 115         }
 116
 117         sctx->region_table = vmalloc(nr_slots * 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 /*
 141  * Find which path to use at given offset.
 142  */
 143 static unsigned switch_get_path_nr(struct switch_ctx *sctx, sector_t offset)
 144 {
 145         unsigned long region_index;
 146         unsigned bit, path_nr;
 147         sector_t p;
 148
 149         p = offset;
 150         if (sctx->region_size_bits >= 0)
 151                 p >>= sctx->region_size_bits;
 152         else
 153                 sector_div(p, sctx->region_size);
 154
 155         switch_get_position(sctx, p, &region_index, &bit);
 156         path_nr = (ACCESS_ONCE(sctx->region_table[region_index]) >> bit) &
 157                ((1 << sctx->region_table_entry_bits) - 1);
 158
 159         /* This can only happen if the processor uses non-atomic stores. */
 160         if (unlikely(path_nr >= sctx->nr_paths))
 161                 path_nr = 0;
 162
 163         return path_nr;
 164 }
 165
 166 static void switch_region_table_write(struct switch_ctx *sctx, unsigned long region_nr,
 167                                       unsigned value)
 168 {
 169         unsigned long region_index;
 170         unsigned bit;
 171         region_table_slot_t pte;
 172
 173         switch_get_position(sctx, region_nr, &region_index, &bit);
 174
 175         pte = sctx->region_table[region_index];
 176         pte &= ~((((region_table_slot_t)1 << sctx->region_table_entry_bits) - 1) << bit);
 177         pte |= (region_table_slot_t)value << bit;
 178         sctx->region_table[region_index] = pte;
 179 }
 180
 181 /*
 182  * Fill the region table with an initial round robin pattern.
 183  */
 184 static void initialise_region_table(struct switch_ctx *sctx)
 185 {
 186         unsigned path_nr = 0;
 187         unsigned long region_nr;
 188
 189         for (region_nr = 0; region_nr < sctx->nr_regions; region_nr++) {
 190                 switch_region_table_write(sctx, region_nr, path_nr);
 191                 if (++path_nr >= sctx->nr_paths)
 192                         path_nr = 0;
 193         }
 194 }
 195
 196 static int parse_path(struct dm_arg_set *as, struct dm_target *ti)
 197 {
 198         struct switch_ctx *sctx = ti->private;
 199         unsigned long long start;
 200         int r;
 201
 202         r = dm_get_device(ti, dm_shift_arg(as), dm_table_get_mode(ti->table),
 203                           &sctx->path_list[sctx->nr_paths].dmdev);
 204         if (r) {
 205                 ti->error = "Device lookup failed";
 206                 return r;
 207         }
 208
 209         if (kstrtoull(dm_shift_arg(as), 10, &start) || start != (sector_t)start) {
 210                 ti->error = "Invalid device starting offset";
 211                 dm_put_device(ti, sctx->path_list[sctx->nr_paths].dmdev);
 212                 return -EINVAL;
 213         }
 214
 215         sctx->path_list[sctx->nr_paths].start = start;
 216
 217         sctx->nr_paths++;
 218
 219         return 0;
 220 }
 221
 222 /*
 223  * Destructor: Don't free the dm_target, just the ti->private data (if any).
 224  */
 225 static void switch_dtr(struct dm_target *ti)
 226 {
 227         struct switch_ctx *sctx = ti->private;
 228
 229         while (sctx->nr_paths--)
 230                 dm_put_device(ti, sctx->path_list[sctx->nr_paths].dmdev);
 231
 232         vfree(sctx->region_table);
 233         kfree(sctx);
 234 }
 235
 236 /*
 237  * Constructor arguments:
 238  *   <num_paths> <region_size> <num_optional_args> [<optional_args>...]
 239  *   [<dev_path> <offset>]+
 240  *
 241  * Optional args are to allow for future extension: currently this
 242  * parameter must be 0.
 243  */
 244 static int switch_ctr(struct dm_target *ti, unsigned argc, char **argv)
 245 {
 246         static struct dm_arg _args[] = {
 247                 {1, (KMALLOC_MAX_SIZE - sizeof(struct switch_ctx)) / sizeof(struct switch_path), "Invalid number of paths"},
 248                 {1, UINT_MAX, "Invalid region size"},
 249                 {0, 0, "Invalid number of optional args"},
 250         };
 251
 252         struct switch_ctx *sctx;
 253         struct dm_arg_set as;
 254         unsigned nr_paths, region_size, nr_optional_args;
 255         int r;
 256
 257         as.argc = argc;
 258         as.argv = argv;
 259
 260         r = dm_read_arg(_args, &as, &nr_paths, &ti->error);
 261         if (r)
 262                 return -EINVAL;
 263
 264         r = dm_read_arg(_args + 1, &as, &region_size, &ti->error);
 265         if (r)
 266                 return r;
 267
 268         r = dm_read_arg_group(_args + 2, &as, &nr_optional_args, &ti->error);
 269         if (r)
 270                 return r;
 271         /* parse optional arguments here, if we add any */
 272
 273         if (as.argc != nr_paths * 2) {
 274                 ti->error = "Incorrect number of path arguments";
 275                 return -EINVAL;
 276         }
 277
 278         sctx = alloc_switch_ctx(ti, nr_paths, region_size);
 279         if (!sctx) {
 280                 ti->error = "Cannot allocate redirection context";
 281                 return -ENOMEM;
 282         }
 283
 284         r = dm_set_target_max_io_len(ti, region_size);
 285         if (r)
 286                 goto error;
 287
 288         while (as.argc) {
 289                 r = parse_path(&as, ti);
 290                 if (r)
 291                         goto error;
 292         }
 293
 294         r = alloc_region_table(ti, nr_paths);
 295         if (r)
 296                 goto error;
 297
 298         initialise_region_table(sctx);
 299
 300         /* For UNMAP, sending the request down any path is sufficient */
 301         ti->num_discard_bios = 1;
 302
 303         return 0;
 304
 305 error:
 306         switch_dtr(ti);
 307
 308         return r;
 309 }
 310
 311 static int switch_map(struct dm_target *ti, struct bio *bio)
 312 {
 313         struct switch_ctx *sctx = ti->private;
 314         sector_t offset = dm_target_offset(ti, bio->bi_iter.bi_sector);
 315         unsigned path_nr = switch_get_path_nr(sctx, offset);
 316
 317         bio->bi_bdev = sctx->path_list[path_nr].dmdev->bdev;
 318         bio->bi_iter.bi_sector = sctx->path_list[path_nr].start + offset;
 319
 320         return DM_MAPIO_REMAPPED;
 321 }
 322
 323 /*
 324  * We need to parse hex numbers in the message as quickly as possible.
 325  *
 326  * This table-based hex parser improves performance.
 327  * It improves a time to load 1000000 entries compared to the condition-based
 328  * parser.
 329  *              table-based parser      condition-based parser
 330  * PA-RISC      0.29s                   0.31s
 331  * Opteron      0.0495s                 0.0498s
 332  */
 333 static const unsigned char hex_table[256] = {
 334 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255,
 335 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255,
 336 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255,
 337 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 255, 255, 255, 255, 255, 255,
 338 255, 10, 11, 12, 13, 14, 15, 255, 255, 255, 255, 255, 255, 255, 255, 255,
 339 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255,
 340 255, 10, 11, 12, 13, 14, 15, 255, 255, 255, 255, 255, 255, 255, 255, 255,
 341 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255,
 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,
 345 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255,
 346 255, 255, 255, 255, 255, 255, 255, 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, 255, 255, 255, 255, 255, 255, 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 };
 351
 352 static __always_inline unsigned long parse_hex(const char **string)
 353 {
 354         unsigned char d;
 355         unsigned long r = 0;
 356
 357         while ((d = hex_table[(unsigned char)**string]) < 16) {
 358                 r = (r << 4) | d;
 359                 (*string)++;
 360         }
 361
 362         return r;
 363 }
 364
 365 static int process_set_region_mappings(struct switch_ctx *sctx,
 366                              unsigned argc, char **argv)
 367 {
 368         unsigned i;
 369         unsigned long region_index = 0;
 370
 371         for (i = 1; i < argc; i++) {
 372                 unsigned long path_nr;
 373                 const char *string = argv[i];
 374
 375                 if (*string == ':')
 376                         region_index++;
 377                 else {
 378                         region_index = parse_hex(&string);
 379                         if (unlikely(*string != ':')) {
 380                                 DMWARN("invalid set_region_mappings argument: '%s'", argv[i]);
 381                                 return -EINVAL;
 382                         }
 383                 }
 384
 385                 string++;
 386                 if (unlikely(!*string)) {
 387                         DMWARN("invalid set_region_mappings argument: '%s'", argv[i]);
 388                         return -EINVAL;
 389                 }
 390
 391                 path_nr = parse_hex(&string);
 392                 if (unlikely(*string)) {
 393                         DMWARN("invalid set_region_mappings argument: '%s'", argv[i]);
 394                         return -EINVAL;
 395                 }
 396                 if (unlikely(region_index >= sctx->nr_regions)) {
 397                         DMWARN("invalid set_region_mappings region number: %lu >= %lu", region_index, sctx->nr_regions);
 398                         return -EINVAL;
 399                 }
 400                 if (unlikely(path_nr >= sctx->nr_paths)) {
 401                         DMWARN("invalid set_region_mappings device: %lu >= %u", path_nr, sctx->nr_paths);
 402                         return -EINVAL;
 403                 }
 404
 405                 switch_region_table_write(sctx, region_index, path_nr);
 406         }
 407
 408         return 0;
 409 }
 410
 411 /*
 412  * Messages are processed one-at-a-time.
 413  *
 414  * Only set_region_mappings is supported.
 415  */
 416 static int switch_message(struct dm_target *ti, unsigned argc, char **argv)
 417 {
 418         static DEFINE_MUTEX(message_mutex);
 419
 420         struct switch_ctx *sctx = ti->private;
 421         int r = -EINVAL;
 422
 423         mutex_lock(&message_mutex);
 424
 425         if (!strcasecmp(argv[0], "set_region_mappings"))
 426                 r = process_set_region_mappings(sctx, argc, argv);
 427         else
 428                 DMWARN("Unrecognised message received.");
 429
 430         mutex_unlock(&message_mutex);
 431
 432         return r;
 433 }
 434
 435 static void switch_status(struct dm_target *ti, status_type_t type,
 436                           unsigned status_flags, char *result, unsigned maxlen)
 437 {
 438         struct switch_ctx *sctx = ti->private;
 439         unsigned sz = 0;
 440         int path_nr;
 441
 442         switch (type) {
 443         case STATUSTYPE_INFO:
 444                 result[0] = '\0';
 445                 break;
 446
 447         case STATUSTYPE_TABLE:
 448                 DMEMIT("%u %u 0", sctx->nr_paths, sctx->region_size);
 449                 for (path_nr = 0; path_nr < sctx->nr_paths; path_nr++)
 450                         DMEMIT(" %s %llu", sctx->path_list[path_nr].dmdev->name,
 451                                (unsigned long long)sctx->path_list[path_nr].start);
 452                 break;
 453         }
 454 }
 455
 456 /*
 457  * Switch ioctl:
 458  *
 459  * Passthrough all ioctls to the path for sector 0
 460  */
 461 static int switch_ioctl(struct dm_target *ti, unsigned cmd,
 462                         unsigned long arg)
 463 {
 464         struct switch_ctx *sctx = ti->private;
 465         struct block_device *bdev;
 466         fmode_t mode;
 467         unsigned path_nr;
 468         int r = 0;
 469
 470         path_nr = switch_get_path_nr(sctx, 0);
 471
 472         bdev = sctx->path_list[path_nr].dmdev->bdev;
 473         mode = sctx->path_list[path_nr].dmdev->mode;
 474
 475         /*
 476          * Only pass ioctls through if the device sizes match exactly.
 477          */
 478         if (ti->len + sctx->path_list[path_nr].start != i_size_read(bdev->bd_inode) >> SECTOR_SHIFT)
 479                 r = scsi_verify_blk_ioctl(NULL, cmd);
 480
 481         return r ? : __blkdev_driver_ioctl(bdev, mode, cmd, arg);
 482 }
 483
 484 static int switch_iterate_devices(struct dm_target *ti,
 485                                   iterate_devices_callout_fn fn, void *data)
 486 {
 487         struct switch_ctx *sctx = ti->private;
 488         int path_nr;
 489         int r;
 490
 491         for (path_nr = 0; path_nr < sctx->nr_paths; path_nr++) {
 492                 r = fn(ti, sctx->path_list[path_nr].dmdev,
 493                          sctx->path_list[path_nr].start, ti->len, data);
 494                 if (r)
 495                         return r;
 496         }
 497
 498         return 0;
 499 }
 500
 501 static struct target_type switch_target = {
 502         .name = "switch",
 503         .version = {1, 0, 0},
 504         .module = THIS_MODULE,
 505         .ctr = switch_ctr,
 506         .dtr = switch_dtr,
 507         .map = switch_map,
 508         .message = switch_message,
 509         .status = switch_status,
 510         .ioctl = switch_ioctl,
 511         .iterate_devices = switch_iterate_devices,
 512 };
 513
 514 static int __init dm_switch_init(void)
 515 {
 516         int r;
 517
 518         r = dm_register_target(&switch_target);
 519         if (r < 0)
 520                 DMERR("dm_register_target() failed %d", r);
 521
 522         return r;
 523 }
 524
 525 static void __exit dm_switch_exit(void)
 526 {
 527         dm_unregister_target(&switch_target);
 528 }
 529
 530 module_init(dm_switch_init);
 531 module_exit(dm_switch_exit);
 532
 533 MODULE_DESCRIPTION(DM_NAME " dynamic path switching target");
 534 MODULE_AUTHOR("Kevin D. O'Kelley <Kevin_OKelley@dell.com>");
 535 MODULE_AUTHOR("Narendran Ganapathy <Narendran_Ganapathy@dell.com>");
 536 MODULE_AUTHOR("Jim Ramsay <Jim_Ramsay@dell.com>");
 537 MODULE_AUTHOR("Mikulas Patocka <mpatocka@redhat.com>");
 538 MODULE_LICENSE("GPL");