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 struct page *brd_insert_page(struct brd_device *brd, sector_t sector, 58 blk_opf_t opf) 59 __releases(rcu) 60 __acquires(rcu) 61 { 62 gfp_t gfp = (opf & REQ_NOWAIT) ? GFP_NOWAIT : GFP_NOIO; 63 struct page *page, *ret; 64 65 rcu_read_unlock(); 66 page = alloc_page(gfp | __GFP_ZERO | __GFP_HIGHMEM); 67 if (!page) { 68 rcu_read_lock(); 69 return ERR_PTR(-ENOMEM); 70 } 71 72 xa_lock(&brd->brd_pages); 73 ret = __xa_cmpxchg(&brd->brd_pages, sector >> PAGE_SECTORS_SHIFT, NULL, 74 page, gfp); 75 rcu_read_lock(); 76 if (ret) { 77 xa_unlock(&brd->brd_pages); 78 __free_page(page); 79 if (xa_is_err(ret)) 80 return ERR_PTR(xa_err(ret)); 81 return ret; 82 } 83 brd->brd_nr_pages++; 84 xa_unlock(&brd->brd_pages); 85 return page; 86 } 87 88 /* 89 * Free all backing store pages and xarray. This must only be called when 90 * there are no other users of the device. 91 */ 92 static void brd_free_pages(struct brd_device *brd) 93 { 94 struct page *page; 95 pgoff_t idx; 96 97 xa_for_each(&brd->brd_pages, idx, page) { 98 __free_page(page); 99 cond_resched(); 100 } 101 102 xa_destroy(&brd->brd_pages); 103 } 104 105 /* 106 * Process a single segment. The segment is capped to not cross page boundaries 107 * in both the bio and the brd backing memory. 108 */ 109 static bool brd_rw_bvec(struct brd_device *brd, struct bio *bio) 110 { 111 struct bio_vec bv = bio_iter_iovec(bio, bio->bi_iter); 112 sector_t sector = bio->bi_iter.bi_sector; 113 u32 offset = (sector & (PAGE_SECTORS - 1)) << SECTOR_SHIFT; 114 blk_opf_t opf = bio->bi_opf; 115 struct page *page; 116 void *kaddr; 117 118 bv.bv_len = min_t(u32, bv.bv_len, PAGE_SIZE - offset); 119 120 rcu_read_lock(); 121 page = brd_lookup_page(brd, sector); 122 if (!page && op_is_write(opf)) { 123 page = brd_insert_page(brd, sector, opf); 124 if (IS_ERR(page)) 125 goto out_error; 126 } 127 128 kaddr = bvec_kmap_local(&bv); 129 if (op_is_write(opf)) { 130 memcpy_to_page(page, offset, kaddr, bv.bv_len); 131 } else { 132 if (page) 133 memcpy_from_page(kaddr, page, offset, bv.bv_len); 134 else 135 memset(kaddr, 0, bv.bv_len); 136 } 137 kunmap_local(kaddr); 138 rcu_read_unlock(); 139 140 bio_advance_iter_single(bio, &bio->bi_iter, bv.bv_len); 141 return true; 142 143 out_error: 144 rcu_read_unlock(); 145 if (PTR_ERR(page) == -ENOMEM && (opf & REQ_NOWAIT)) 146 bio_wouldblock_error(bio); 147 else 148 bio_io_error(bio); 149 return false; 150 } 151 152 static void brd_free_one_page(struct rcu_head *head) 153 { 154 struct page *page = container_of(head, struct page, rcu_head); 155 156 __free_page(page); 157 } 158 159 static void brd_do_discard(struct brd_device *brd, sector_t sector, u32 size) 160 { 161 sector_t aligned_sector = round_up(sector, PAGE_SECTORS); 162 sector_t aligned_end = round_down( 163 sector + (size >> SECTOR_SHIFT), PAGE_SECTORS); 164 struct page *page; 165 166 if (aligned_end <= aligned_sector) 167 return; 168 169 xa_lock(&brd->brd_pages); 170 while (aligned_sector < aligned_end && aligned_sector < rd_size * 2) { 171 page = __xa_erase(&brd->brd_pages, aligned_sector >> PAGE_SECTORS_SHIFT); 172 if (page) { 173 call_rcu(&page->rcu_head, brd_free_one_page); 174 brd->brd_nr_pages--; 175 } 176 aligned_sector += PAGE_SECTORS; 177 } 178 xa_unlock(&brd->brd_pages); 179 } 180 181 static void brd_submit_bio(struct bio *bio) 182 { 183 struct brd_device *brd = bio->bi_bdev->bd_disk->private_data; 184 185 if (unlikely(op_is_discard(bio->bi_opf))) { 186 brd_do_discard(brd, bio->bi_iter.bi_sector, 187 bio->bi_iter.bi_size); 188 bio_endio(bio); 189 return; 190 } 191 192 do { 193 if (!brd_rw_bvec(brd, bio)) 194 return; 195 } while (bio->bi_iter.bi_size); 196 197 bio_endio(bio); 198 } 199 200 static const struct block_device_operations brd_fops = { 201 .owner = THIS_MODULE, 202 .submit_bio = brd_submit_bio, 203 }; 204 205 /* 206 * And now the modules code and kernel interface. 207 */ 208 static int rd_nr = CONFIG_BLK_DEV_RAM_COUNT; 209 module_param(rd_nr, int, 0444); 210 MODULE_PARM_DESC(rd_nr, "Maximum number of brd devices"); 211 212 unsigned long rd_size = CONFIG_BLK_DEV_RAM_SIZE; 213 module_param(rd_size, ulong, 0444); 214 MODULE_PARM_DESC(rd_size, "Size of each RAM disk in kbytes."); 215 216 static int max_part = 1; 217 module_param(max_part, int, 0444); 218 MODULE_PARM_DESC(max_part, "Num Minors to reserve between devices"); 219 220 MODULE_DESCRIPTION("Ram backed block device driver"); 221 MODULE_LICENSE("GPL"); 222 MODULE_ALIAS_BLOCKDEV_MAJOR(RAMDISK_MAJOR); 223 MODULE_ALIAS("rd"); 224 225 #ifndef MODULE 226 /* Legacy boot options - nonmodular */ 227 static int __init ramdisk_size(char *str) 228 { 229 rd_size = simple_strtol(str, NULL, 0); 230 return 1; 231 } 232 __setup("ramdisk_size=", ramdisk_size); 233 #endif 234 235 /* 236 * The device scheme is derived from loop.c. Keep them in synch where possible 237 * (should share code eventually). 238 */ 239 static LIST_HEAD(brd_devices); 240 static DEFINE_MUTEX(brd_devices_mutex); 241 static struct dentry *brd_debugfs_dir; 242 243 static struct brd_device *brd_find_or_alloc_device(int i) 244 { 245 struct brd_device *brd; 246 247 mutex_lock(&brd_devices_mutex); 248 list_for_each_entry(brd, &brd_devices, brd_list) { 249 if (brd->brd_number == i) { 250 mutex_unlock(&brd_devices_mutex); 251 return ERR_PTR(-EEXIST); 252 } 253 } 254 255 brd = kzalloc(sizeof(*brd), GFP_KERNEL); 256 if (!brd) { 257 mutex_unlock(&brd_devices_mutex); 258 return ERR_PTR(-ENOMEM); 259 } 260 brd->brd_number = i; 261 list_add_tail(&brd->brd_list, &brd_devices); 262 mutex_unlock(&brd_devices_mutex); 263 return brd; 264 } 265 266 static void brd_free_device(struct brd_device *brd) 267 { 268 mutex_lock(&brd_devices_mutex); 269 list_del(&brd->brd_list); 270 mutex_unlock(&brd_devices_mutex); 271 kfree(brd); 272 } 273 274 static int brd_alloc(int i) 275 { 276 struct brd_device *brd; 277 struct gendisk *disk; 278 char buf[DISK_NAME_LEN]; 279 int err = -ENOMEM; 280 struct queue_limits lim = { 281 /* 282 * This is so fdisk will align partitions on 4k, because of 283 * direct_access API needing 4k alignment, returning a PFN 284 * (This is only a problem on very small devices <= 4M, 285 * otherwise fdisk will align on 1M. Regardless this call 286 * is harmless) 287 */ 288 .physical_block_size = PAGE_SIZE, 289 .max_hw_discard_sectors = UINT_MAX, 290 .max_discard_segments = 1, 291 .discard_granularity = PAGE_SIZE, 292 .features = BLK_FEAT_SYNCHRONOUS | 293 BLK_FEAT_NOWAIT, 294 }; 295 296 brd = brd_find_or_alloc_device(i); 297 if (IS_ERR(brd)) 298 return PTR_ERR(brd); 299 300 xa_init(&brd->brd_pages); 301 302 snprintf(buf, DISK_NAME_LEN, "ram%d", i); 303 if (!IS_ERR_OR_NULL(brd_debugfs_dir)) 304 debugfs_create_u64(buf, 0444, brd_debugfs_dir, 305 &brd->brd_nr_pages); 306 307 disk = brd->brd_disk = blk_alloc_disk(&lim, NUMA_NO_NODE); 308 if (IS_ERR(disk)) { 309 err = PTR_ERR(disk); 310 goto out_free_dev; 311 } 312 disk->major = RAMDISK_MAJOR; 313 disk->first_minor = i * max_part; 314 disk->minors = max_part; 315 disk->fops = &brd_fops; 316 disk->private_data = brd; 317 strscpy(disk->disk_name, buf, DISK_NAME_LEN); 318 set_capacity(disk, rd_size * 2); 319 320 err = add_disk(disk); 321 if (err) 322 goto out_cleanup_disk; 323 324 return 0; 325 326 out_cleanup_disk: 327 put_disk(disk); 328 out_free_dev: 329 brd_free_device(brd); 330 return err; 331 } 332 333 static void brd_probe(dev_t dev) 334 { 335 brd_alloc(MINOR(dev) / max_part); 336 } 337 338 static void brd_cleanup(void) 339 { 340 struct brd_device *brd, *next; 341 342 debugfs_remove_recursive(brd_debugfs_dir); 343 344 list_for_each_entry_safe(brd, next, &brd_devices, brd_list) { 345 del_gendisk(brd->brd_disk); 346 put_disk(brd->brd_disk); 347 brd_free_pages(brd); 348 brd_free_device(brd); 349 } 350 } 351 352 static inline void brd_check_and_reset_par(void) 353 { 354 if (unlikely(!max_part)) 355 max_part = 1; 356 357 /* 358 * make sure 'max_part' can be divided exactly by (1U << MINORBITS), 359 * otherwise, it is possiable to get same dev_t when adding partitions. 360 */ 361 if ((1U << MINORBITS) % max_part != 0) 362 max_part = 1UL << fls(max_part); 363 364 if (max_part > DISK_MAX_PARTS) { 365 pr_info("brd: max_part can't be larger than %d, reset max_part = %d.\n", 366 DISK_MAX_PARTS, DISK_MAX_PARTS); 367 max_part = DISK_MAX_PARTS; 368 } 369 } 370 371 static int __init brd_init(void) 372 { 373 int err, i; 374 375 /* 376 * brd module now has a feature to instantiate underlying device 377 * structure on-demand, provided that there is an access dev node. 378 * 379 * (1) if rd_nr is specified, create that many upfront. else 380 * it defaults to CONFIG_BLK_DEV_RAM_COUNT 381 * (2) User can further extend brd devices by create dev node themselves 382 * and have kernel automatically instantiate actual device 383 * on-demand. Example: 384 * mknod /path/devnod_name b 1 X # 1 is the rd major 385 * fdisk -l /path/devnod_name 386 * If (X / max_part) was not already created it will be created 387 * dynamically. 388 */ 389 390 brd_check_and_reset_par(); 391 392 brd_debugfs_dir = debugfs_create_dir("ramdisk_pages", NULL); 393 394 if (__register_blkdev(RAMDISK_MAJOR, "ramdisk", brd_probe)) { 395 err = -EIO; 396 goto out_free; 397 } 398 399 for (i = 0; i < rd_nr; i++) 400 brd_alloc(i); 401 402 pr_info("brd: module loaded\n"); 403 return 0; 404 405 out_free: 406 brd_cleanup(); 407 408 pr_info("brd: module NOT loaded !!!\n"); 409 return err; 410 } 411 412 static void __exit brd_exit(void) 413 { 414 415 unregister_blkdev(RAMDISK_MAJOR, "ramdisk"); 416 brd_cleanup(); 417 418 pr_info("brd: module unloaded\n"); 419 } 420 421 module_init(brd_init); 422 module_exit(brd_exit); 423 424