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 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 (ACCESS_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, ®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 */ 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 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 } 318 319 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->bi_bdev = 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 == ':') 384 region_index++; 385 else { 386 region_index = parse_hex(&string); 387 if (unlikely(*string != ':')) { 388 DMWARN("invalid set_region_mappings argument: '%s'", argv[i]); 389 return -EINVAL; 390 } 391 } 392 393 string++; 394 if (unlikely(!*string)) { 395 DMWARN("invalid set_region_mappings argument: '%s'", argv[i]); 396 return -EINVAL; 397 } 398 399 path_nr = parse_hex(&string); 400 if (unlikely(*string)) { 401 DMWARN("invalid set_region_mappings argument: '%s'", argv[i]); 402 return -EINVAL; 403 } 404 if (unlikely(region_index >= sctx->nr_regions)) { 405 DMWARN("invalid set_region_mappings region number: %lu >= %lu", region_index, sctx->nr_regions); 406 return -EINVAL; 407 } 408 if (unlikely(path_nr >= sctx->nr_paths)) { 409 DMWARN("invalid set_region_mappings device: %lu >= %u", path_nr, sctx->nr_paths); 410 return -EINVAL; 411 } 412 413 switch_region_table_write(sctx, region_index, path_nr); 414 } 415 416 return 0; 417 } 418 419 /* 420 * Messages are processed one-at-a-time. 421 * 422 * Only set_region_mappings is supported. 423 */ 424 static int switch_message(struct dm_target *ti, unsigned argc, char **argv) 425 { 426 static DEFINE_MUTEX(message_mutex); 427 428 struct switch_ctx *sctx = ti->private; 429 int r = -EINVAL; 430 431 mutex_lock(&message_mutex); 432 433 if (!strcasecmp(argv[0], "set_region_mappings")) 434 r = process_set_region_mappings(sctx, argc, argv); 435 else 436 DMWARN("Unrecognised message received."); 437 438 mutex_unlock(&message_mutex); 439 440 return r; 441 } 442 443 static void switch_status(struct dm_target *ti, status_type_t type, 444 unsigned status_flags, char *result, unsigned maxlen) 445 { 446 struct switch_ctx *sctx = ti->private; 447 unsigned sz = 0; 448 int path_nr; 449 450 switch (type) { 451 case STATUSTYPE_INFO: 452 result[0] = '\0'; 453 break; 454 455 case STATUSTYPE_TABLE: 456 DMEMIT("%u %u 0", sctx->nr_paths, sctx->region_size); 457 for (path_nr = 0; path_nr < sctx->nr_paths; path_nr++) 458 DMEMIT(" %s %llu", sctx->path_list[path_nr].dmdev->name, 459 (unsigned long long)sctx->path_list[path_nr].start); 460 break; 461 } 462 } 463 464 /* 465 * Switch ioctl: 466 * 467 * Passthrough all ioctls to the path for sector 0 468 */ 469 static int switch_ioctl(struct dm_target *ti, unsigned cmd, 470 unsigned long arg) 471 { 472 struct switch_ctx *sctx = ti->private; 473 struct block_device *bdev; 474 fmode_t mode; 475 unsigned path_nr; 476 int r = 0; 477 478 path_nr = switch_get_path_nr(sctx, 0); 479 480 bdev = sctx->path_list[path_nr].dmdev->bdev; 481 mode = sctx->path_list[path_nr].dmdev->mode; 482 483 /* 484 * Only pass ioctls through if the device sizes match exactly. 485 */ 486 if (ti->len + sctx->path_list[path_nr].start != i_size_read(bdev->bd_inode) >> SECTOR_SHIFT) 487 r = scsi_verify_blk_ioctl(NULL, cmd); 488 489 return r ? : __blkdev_driver_ioctl(bdev, mode, cmd, arg); 490 } 491 492 static int switch_iterate_devices(struct dm_target *ti, 493 iterate_devices_callout_fn fn, void *data) 494 { 495 struct switch_ctx *sctx = ti->private; 496 int path_nr; 497 int r; 498 499 for (path_nr = 0; path_nr < sctx->nr_paths; path_nr++) { 500 r = fn(ti, sctx->path_list[path_nr].dmdev, 501 sctx->path_list[path_nr].start, ti->len, data); 502 if (r) 503 return r; 504 } 505 506 return 0; 507 } 508 509 static struct target_type switch_target = { 510 .name = "switch", 511 .version = {1, 0, 0}, 512 .module = THIS_MODULE, 513 .ctr = switch_ctr, 514 .dtr = switch_dtr, 515 .map = switch_map, 516 .message = switch_message, 517 .status = switch_status, 518 .ioctl = switch_ioctl, 519 .iterate_devices = switch_iterate_devices, 520 }; 521 522 static int __init dm_switch_init(void) 523 { 524 int r; 525 526 r = dm_register_target(&switch_target); 527 if (r < 0) 528 DMERR("dm_register_target() failed %d", r); 529 530 return r; 531 } 532 533 static void __exit dm_switch_exit(void) 534 { 535 dm_unregister_target(&switch_target); 536 } 537 538 module_init(dm_switch_init); 539 module_exit(dm_switch_exit); 540 541 MODULE_DESCRIPTION(DM_NAME " dynamic path switching target"); 542 MODULE_AUTHOR("Kevin D. O'Kelley <[email protected]>"); 543 MODULE_AUTHOR("Narendran Ganapathy <[email protected]>"); 544 MODULE_AUTHOR("Jim Ramsay <[email protected]>"); 545 MODULE_AUTHOR("Mikulas Patocka <[email protected]>"); 546 MODULE_LICENSE("GPL"); 547