1 // SPDX-License-Identifier: GPL-2.0-only 2 /* 3 * Ram backed block device driver. 4 * 5 * Copyright (C) 2007 Nick Piggin 6 * Copyright (C) 2007 Novell Inc. 7 * 8 * Parts derived from drivers/block/rd.c, and drivers/block/loop.c, copyright 9 * of their respective owners. 10 */ 11 12 #include <linux/init.h> 13 #include <linux/initrd.h> 14 #include <linux/module.h> 15 #include <linux/moduleparam.h> 16 #include <linux/major.h> 17 #include <linux/blkdev.h> 18 #include <linux/bio.h> 19 #include <linux/highmem.h> 20 #include <linux/mutex.h> 21 #include <linux/pagemap.h> 22 #include <linux/xarray.h> 23 #include <linux/fs.h> 24 #include <linux/slab.h> 25 #include <linux/backing-dev.h> 26 #include <linux/debugfs.h> 27 28 #include <linux/uaccess.h> 29 30 /* 31 * Each block ramdisk device has a xarray brd_pages of pages that stores 32 * the pages containing the block device's contents. 33 */ 34 struct brd_device { 35 int brd_number; 36 struct gendisk *brd_disk; 37 struct list_head brd_list; 38 39 /* 40 * Backing store of pages. This is the contents of the block device. 41 */ 42 struct xarray brd_pages; 43 u64 brd_nr_pages; 44 }; 45 46 /* 47 * Look up and return a brd's page for a given sector. 48 */ 49 static struct page *brd_lookup_page(struct brd_device *brd, sector_t sector) 50 { 51 return xa_load(&brd->brd_pages, sector >> PAGE_SECTORS_SHIFT); 52 } 53 54 /* 55 * Insert a new page for a given sector, if one does not already exist. 56 */ 57 static int brd_insert_page(struct brd_device *brd, sector_t sector, gfp_t gfp) 58 { 59 pgoff_t idx = sector >> PAGE_SECTORS_SHIFT; 60 struct page *page; 61 int ret = 0; 62 63 page = brd_lookup_page(brd, sector); 64 if (page) 65 return 0; 66 67 page = alloc_page(gfp | __GFP_ZERO | __GFP_HIGHMEM); 68 if (!page) 69 return -ENOMEM; 70 71 xa_lock(&brd->brd_pages); 72 ret = __xa_insert(&brd->brd_pages, idx, page, gfp); 73 if (!ret) 74 brd->brd_nr_pages++; 75 xa_unlock(&brd->brd_pages); 76 77 if (ret < 0) { 78 __free_page(page); 79 if (ret == -EBUSY) 80 ret = 0; 81 } 82 return ret; 83 } 84 85 /* 86 * Free all backing store pages and xarray. This must only be called when 87 * there are no other users of the device. 88 */ 89 static void brd_free_pages(struct brd_device *brd) 90 { 91 struct page *page; 92 pgoff_t idx; 93 94 xa_for_each(&brd->brd_pages, idx, page) { 95 __free_page(page); 96 cond_resched(); 97 } 98 99 xa_destroy(&brd->brd_pages); 100 } 101 102 /* 103 * copy_to_brd_setup must be called before copy_to_brd. It may sleep. 104 */ 105 static int copy_to_brd_setup(struct brd_device *brd, sector_t sector, size_t n, 106 gfp_t gfp) 107 { 108 unsigned int offset = (sector & (PAGE_SECTORS-1)) << SECTOR_SHIFT; 109 size_t copy; 110 int ret; 111 112 copy = min_t(size_t, n, PAGE_SIZE - offset); 113 ret = brd_insert_page(brd, sector, gfp); 114 if (ret) 115 return ret; 116 if (copy < n) { 117 sector += copy >> SECTOR_SHIFT; 118 ret = brd_insert_page(brd, sector, gfp); 119 } 120 return ret; 121 } 122 123 /* 124 * Copy n bytes from src to the brd starting at sector. Does not sleep. 125 */ 126 static void copy_to_brd(struct brd_device *brd, const void *src, 127 sector_t sector, size_t n) 128 { 129 struct page *page; 130 void *dst; 131 unsigned int offset = (sector & (PAGE_SECTORS-1)) << SECTOR_SHIFT; 132 size_t copy; 133 134 copy = min_t(size_t, n, PAGE_SIZE - offset); 135 page = brd_lookup_page(brd, sector); 136 BUG_ON(!page); 137 138 dst = kmap_atomic(page); 139 memcpy(dst + offset, src, copy); 140 kunmap_atomic(dst); 141 142 if (copy < n) { 143 src += copy; 144 sector += copy >> SECTOR_SHIFT; 145 copy = n - copy; 146 page = brd_lookup_page(brd, sector); 147 BUG_ON(!page); 148 149 dst = kmap_atomic(page); 150 memcpy(dst, src, copy); 151 kunmap_atomic(dst); 152 } 153 } 154 155 /* 156 * Copy n bytes to dst from the brd starting at sector. Does not sleep. 157 */ 158 static void copy_from_brd(void *dst, struct brd_device *brd, 159 sector_t sector, size_t n) 160 { 161 struct page *page; 162 void *src; 163 unsigned int offset = (sector & (PAGE_SECTORS-1)) << SECTOR_SHIFT; 164 size_t copy; 165 166 copy = min_t(size_t, n, PAGE_SIZE - offset); 167 page = brd_lookup_page(brd, sector); 168 if (page) { 169 src = kmap_atomic(page); 170 memcpy(dst, src + offset, copy); 171 kunmap_atomic(src); 172 } else 173 memset(dst, 0, copy); 174 175 if (copy < n) { 176 dst += copy; 177 sector += copy >> SECTOR_SHIFT; 178 copy = n - copy; 179 page = brd_lookup_page(brd, sector); 180 if (page) { 181 src = kmap_atomic(page); 182 memcpy(dst, src, copy); 183 kunmap_atomic(src); 184 } else 185 memset(dst, 0, copy); 186 } 187 } 188 189 /* 190 * Process a single bvec of a bio. 191 */ 192 static int brd_do_bvec(struct brd_device *brd, struct page *page, 193 unsigned int len, unsigned int off, blk_opf_t opf, 194 sector_t sector) 195 { 196 void *mem; 197 int err = 0; 198 199 if (op_is_write(opf)) { 200 /* 201 * Must use NOIO because we don't want to recurse back into the 202 * block or filesystem layers from page reclaim. 203 */ 204 gfp_t gfp = opf & REQ_NOWAIT ? GFP_NOWAIT : GFP_NOIO; 205 206 err = copy_to_brd_setup(brd, sector, len, gfp); 207 if (err) 208 goto out; 209 } 210 211 mem = kmap_atomic(page); 212 if (!op_is_write(opf)) { 213 copy_from_brd(mem + off, brd, sector, len); 214 flush_dcache_page(page); 215 } else { 216 flush_dcache_page(page); 217 copy_to_brd(brd, mem + off, sector, len); 218 } 219 kunmap_atomic(mem); 220 221 out: 222 return err; 223 } 224 225 static void brd_do_discard(struct brd_device *brd, sector_t sector, u32 size) 226 { 227 sector_t aligned_sector = (sector + PAGE_SECTORS) & ~PAGE_SECTORS; 228 struct page *page; 229 230 size -= (aligned_sector - sector) * SECTOR_SIZE; 231 xa_lock(&brd->brd_pages); 232 while (size >= PAGE_SIZE && aligned_sector < rd_size * 2) { 233 page = __xa_erase(&brd->brd_pages, aligned_sector >> PAGE_SECTORS_SHIFT); 234 if (page) 235 __free_page(page); 236 aligned_sector += PAGE_SECTORS; 237 size -= PAGE_SIZE; 238 } 239 xa_unlock(&brd->brd_pages); 240 } 241 242 static void brd_submit_bio(struct bio *bio) 243 { 244 struct brd_device *brd = bio->bi_bdev->bd_disk->private_data; 245 sector_t sector = bio->bi_iter.bi_sector; 246 struct bio_vec bvec; 247 struct bvec_iter iter; 248 249 if (unlikely(op_is_discard(bio->bi_opf))) { 250 brd_do_discard(brd, sector, bio->bi_iter.bi_size); 251 bio_endio(bio); 252 return; 253 } 254 255 bio_for_each_segment(bvec, bio, iter) { 256 unsigned int len = bvec.bv_len; 257 int err; 258 259 /* Don't support un-aligned buffer */ 260 WARN_ON_ONCE((bvec.bv_offset & (SECTOR_SIZE - 1)) || 261 (len & (SECTOR_SIZE - 1))); 262 263 err = brd_do_bvec(brd, bvec.bv_page, len, bvec.bv_offset, 264 bio->bi_opf, sector); 265 if (err) { 266 if (err == -ENOMEM && bio->bi_opf & REQ_NOWAIT) { 267 bio_wouldblock_error(bio); 268 return; 269 } 270 bio_io_error(bio); 271 return; 272 } 273 sector += len >> SECTOR_SHIFT; 274 } 275 276 bio_endio(bio); 277 } 278 279 static const struct block_device_operations brd_fops = { 280 .owner = THIS_MODULE, 281 .submit_bio = brd_submit_bio, 282 }; 283 284 /* 285 * And now the modules code and kernel interface. 286 */ 287 static int rd_nr = CONFIG_BLK_DEV_RAM_COUNT; 288 module_param(rd_nr, int, 0444); 289 MODULE_PARM_DESC(rd_nr, "Maximum number of brd devices"); 290 291 unsigned long rd_size = CONFIG_BLK_DEV_RAM_SIZE; 292 module_param(rd_size, ulong, 0444); 293 MODULE_PARM_DESC(rd_size, "Size of each RAM disk in kbytes."); 294 295 static int max_part = 1; 296 module_param(max_part, int, 0444); 297 MODULE_PARM_DESC(max_part, "Num Minors to reserve between devices"); 298 299 MODULE_DESCRIPTION("Ram backed block device driver"); 300 MODULE_LICENSE("GPL"); 301 MODULE_ALIAS_BLOCKDEV_MAJOR(RAMDISK_MAJOR); 302 MODULE_ALIAS("rd"); 303 304 #ifndef MODULE 305 /* Legacy boot options - nonmodular */ 306 static int __init ramdisk_size(char *str) 307 { 308 rd_size = simple_strtol(str, NULL, 0); 309 return 1; 310 } 311 __setup("ramdisk_size=", ramdisk_size); 312 #endif 313 314 /* 315 * The device scheme is derived from loop.c. Keep them in synch where possible 316 * (should share code eventually). 317 */ 318 static LIST_HEAD(brd_devices); 319 static struct dentry *brd_debugfs_dir; 320 321 static int brd_alloc(int i) 322 { 323 struct brd_device *brd; 324 struct gendisk *disk; 325 char buf[DISK_NAME_LEN]; 326 int err = -ENOMEM; 327 struct queue_limits lim = { 328 /* 329 * This is so fdisk will align partitions on 4k, because of 330 * direct_access API needing 4k alignment, returning a PFN 331 * (This is only a problem on very small devices <= 4M, 332 * otherwise fdisk will align on 1M. Regardless this call 333 * is harmless) 334 */ 335 .physical_block_size = PAGE_SIZE, 336 .max_hw_discard_sectors = UINT_MAX, 337 .max_discard_segments = 1, 338 .discard_granularity = PAGE_SIZE, 339 .features = BLK_FEAT_SYNCHRONOUS | 340 BLK_FEAT_NOWAIT, 341 }; 342 343 list_for_each_entry(brd, &brd_devices, brd_list) 344 if (brd->brd_number == i) 345 return -EEXIST; 346 brd = kzalloc(sizeof(*brd), GFP_KERNEL); 347 if (!brd) 348 return -ENOMEM; 349 brd->brd_number = i; 350 list_add_tail(&brd->brd_list, &brd_devices); 351 352 xa_init(&brd->brd_pages); 353 354 snprintf(buf, DISK_NAME_LEN, "ram%d", i); 355 if (!IS_ERR_OR_NULL(brd_debugfs_dir)) 356 debugfs_create_u64(buf, 0444, brd_debugfs_dir, 357 &brd->brd_nr_pages); 358 359 disk = brd->brd_disk = blk_alloc_disk(&lim, NUMA_NO_NODE); 360 if (IS_ERR(disk)) { 361 err = PTR_ERR(disk); 362 goto out_free_dev; 363 } 364 disk->major = RAMDISK_MAJOR; 365 disk->first_minor = i * max_part; 366 disk->minors = max_part; 367 disk->fops = &brd_fops; 368 disk->private_data = brd; 369 strscpy(disk->disk_name, buf, DISK_NAME_LEN); 370 set_capacity(disk, rd_size * 2); 371 372 err = add_disk(disk); 373 if (err) 374 goto out_cleanup_disk; 375 376 return 0; 377 378 out_cleanup_disk: 379 put_disk(disk); 380 out_free_dev: 381 list_del(&brd->brd_list); 382 kfree(brd); 383 return err; 384 } 385 386 static void brd_probe(dev_t dev) 387 { 388 brd_alloc(MINOR(dev) / max_part); 389 } 390 391 static void brd_cleanup(void) 392 { 393 struct brd_device *brd, *next; 394 395 debugfs_remove_recursive(brd_debugfs_dir); 396 397 list_for_each_entry_safe(brd, next, &brd_devices, brd_list) { 398 del_gendisk(brd->brd_disk); 399 put_disk(brd->brd_disk); 400 brd_free_pages(brd); 401 list_del(&brd->brd_list); 402 kfree(brd); 403 } 404 } 405 406 static inline void brd_check_and_reset_par(void) 407 { 408 if (unlikely(!max_part)) 409 max_part = 1; 410 411 /* 412 * make sure 'max_part' can be divided exactly by (1U << MINORBITS), 413 * otherwise, it is possiable to get same dev_t when adding partitions. 414 */ 415 if ((1U << MINORBITS) % max_part != 0) 416 max_part = 1UL << fls(max_part); 417 418 if (max_part > DISK_MAX_PARTS) { 419 pr_info("brd: max_part can't be larger than %d, reset max_part = %d.\n", 420 DISK_MAX_PARTS, DISK_MAX_PARTS); 421 max_part = DISK_MAX_PARTS; 422 } 423 } 424 425 static int __init brd_init(void) 426 { 427 int err, i; 428 429 brd_check_and_reset_par(); 430 431 brd_debugfs_dir = debugfs_create_dir("ramdisk_pages", NULL); 432 433 for (i = 0; i < rd_nr; i++) { 434 err = brd_alloc(i); 435 if (err) 436 goto out_free; 437 } 438 439 /* 440 * brd module now has a feature to instantiate underlying device 441 * structure on-demand, provided that there is an access dev node. 442 * 443 * (1) if rd_nr is specified, create that many upfront. else 444 * it defaults to CONFIG_BLK_DEV_RAM_COUNT 445 * (2) User can further extend brd devices by create dev node themselves 446 * and have kernel automatically instantiate actual device 447 * on-demand. Example: 448 * mknod /path/devnod_name b 1 X # 1 is the rd major 449 * fdisk -l /path/devnod_name 450 * If (X / max_part) was not already created it will be created 451 * dynamically. 452 */ 453 454 if (__register_blkdev(RAMDISK_MAJOR, "ramdisk", brd_probe)) { 455 err = -EIO; 456 goto out_free; 457 } 458 459 pr_info("brd: module loaded\n"); 460 return 0; 461 462 out_free: 463 brd_cleanup(); 464 465 pr_info("brd: module NOT loaded !!!\n"); 466 return err; 467 } 468 469 static void __exit brd_exit(void) 470 { 471 472 unregister_blkdev(RAMDISK_MAJOR, "ramdisk"); 473 brd_cleanup(); 474 475 pr_info("brd: module unloaded\n"); 476 } 477 478 module_init(brd_init); 479 module_exit(brd_exit); 480 481