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 * Process a single segment. The segment is capped to not cross page boundaries 104 * in both the bio and the brd backing memory. 105 */ 106 static bool brd_rw_bvec(struct brd_device *brd, struct bio *bio) 107 { 108 struct bio_vec bv = bio_iter_iovec(bio, bio->bi_iter); 109 sector_t sector = bio->bi_iter.bi_sector; 110 u32 offset = (sector & (PAGE_SECTORS - 1)) << SECTOR_SHIFT; 111 blk_opf_t opf = bio->bi_opf; 112 struct page *page; 113 void *kaddr; 114 115 bv.bv_len = min_t(u32, bv.bv_len, PAGE_SIZE - offset); 116 117 if (op_is_write(opf)) { 118 int err; 119 120 /* 121 * Must use NOIO because we don't want to recurse back into the 122 * block or filesystem layers from page reclaim. 123 */ 124 err = brd_insert_page(brd, sector, 125 (opf & REQ_NOWAIT) ? GFP_NOWAIT : GFP_NOIO); 126 if (err) { 127 if (err == -ENOMEM && (opf & REQ_NOWAIT)) 128 bio_wouldblock_error(bio); 129 else 130 bio_io_error(bio); 131 return false; 132 } 133 } 134 135 page = brd_lookup_page(brd, sector); 136 137 kaddr = bvec_kmap_local(&bv); 138 if (op_is_write(opf)) { 139 BUG_ON(!page); 140 memcpy_to_page(page, offset, kaddr, bv.bv_len); 141 } else { 142 if (page) 143 memcpy_from_page(kaddr, page, offset, bv.bv_len); 144 else 145 memset(kaddr, 0, bv.bv_len); 146 } 147 kunmap_local(kaddr); 148 149 bio_advance_iter_single(bio, &bio->bi_iter, bv.bv_len); 150 return true; 151 } 152 153 static void brd_do_discard(struct brd_device *brd, sector_t sector, u32 size) 154 { 155 sector_t aligned_sector = (sector + PAGE_SECTORS) & ~PAGE_SECTORS; 156 struct page *page; 157 158 size -= (aligned_sector - sector) * SECTOR_SIZE; 159 xa_lock(&brd->brd_pages); 160 while (size >= PAGE_SIZE && aligned_sector < rd_size * 2) { 161 page = __xa_erase(&brd->brd_pages, aligned_sector >> PAGE_SECTORS_SHIFT); 162 if (page) { 163 __free_page(page); 164 brd->brd_nr_pages--; 165 } 166 aligned_sector += PAGE_SECTORS; 167 size -= PAGE_SIZE; 168 } 169 xa_unlock(&brd->brd_pages); 170 } 171 172 static void brd_submit_bio(struct bio *bio) 173 { 174 struct brd_device *brd = bio->bi_bdev->bd_disk->private_data; 175 176 if (unlikely(op_is_discard(bio->bi_opf))) { 177 brd_do_discard(brd, bio->bi_iter.bi_sector, 178 bio->bi_iter.bi_size); 179 bio_endio(bio); 180 return; 181 } 182 183 do { 184 if (!brd_rw_bvec(brd, bio)) 185 return; 186 } while (bio->bi_iter.bi_size); 187 188 bio_endio(bio); 189 } 190 191 static const struct block_device_operations brd_fops = { 192 .owner = THIS_MODULE, 193 .submit_bio = brd_submit_bio, 194 }; 195 196 /* 197 * And now the modules code and kernel interface. 198 */ 199 static int rd_nr = CONFIG_BLK_DEV_RAM_COUNT; 200 module_param(rd_nr, int, 0444); 201 MODULE_PARM_DESC(rd_nr, "Maximum number of brd devices"); 202 203 unsigned long rd_size = CONFIG_BLK_DEV_RAM_SIZE; 204 module_param(rd_size, ulong, 0444); 205 MODULE_PARM_DESC(rd_size, "Size of each RAM disk in kbytes."); 206 207 static int max_part = 1; 208 module_param(max_part, int, 0444); 209 MODULE_PARM_DESC(max_part, "Num Minors to reserve between devices"); 210 211 MODULE_DESCRIPTION("Ram backed block device driver"); 212 MODULE_LICENSE("GPL"); 213 MODULE_ALIAS_BLOCKDEV_MAJOR(RAMDISK_MAJOR); 214 MODULE_ALIAS("rd"); 215 216 #ifndef MODULE 217 /* Legacy boot options - nonmodular */ 218 static int __init ramdisk_size(char *str) 219 { 220 rd_size = simple_strtol(str, NULL, 0); 221 return 1; 222 } 223 __setup("ramdisk_size=", ramdisk_size); 224 #endif 225 226 /* 227 * The device scheme is derived from loop.c. Keep them in synch where possible 228 * (should share code eventually). 229 */ 230 static LIST_HEAD(brd_devices); 231 static DEFINE_MUTEX(brd_devices_mutex); 232 static struct dentry *brd_debugfs_dir; 233 234 static struct brd_device *brd_find_or_alloc_device(int i) 235 { 236 struct brd_device *brd; 237 238 mutex_lock(&brd_devices_mutex); 239 list_for_each_entry(brd, &brd_devices, brd_list) { 240 if (brd->brd_number == i) { 241 mutex_unlock(&brd_devices_mutex); 242 return ERR_PTR(-EEXIST); 243 } 244 } 245 246 brd = kzalloc(sizeof(*brd), GFP_KERNEL); 247 if (!brd) { 248 mutex_unlock(&brd_devices_mutex); 249 return ERR_PTR(-ENOMEM); 250 } 251 brd->brd_number = i; 252 list_add_tail(&brd->brd_list, &brd_devices); 253 mutex_unlock(&brd_devices_mutex); 254 return brd; 255 } 256 257 static void brd_free_device(struct brd_device *brd) 258 { 259 mutex_lock(&brd_devices_mutex); 260 list_del(&brd->brd_list); 261 mutex_unlock(&brd_devices_mutex); 262 kfree(brd); 263 } 264 265 static int brd_alloc(int i) 266 { 267 struct brd_device *brd; 268 struct gendisk *disk; 269 char buf[DISK_NAME_LEN]; 270 int err = -ENOMEM; 271 struct queue_limits lim = { 272 /* 273 * This is so fdisk will align partitions on 4k, because of 274 * direct_access API needing 4k alignment, returning a PFN 275 * (This is only a problem on very small devices <= 4M, 276 * otherwise fdisk will align on 1M. Regardless this call 277 * is harmless) 278 */ 279 .physical_block_size = PAGE_SIZE, 280 .max_hw_discard_sectors = UINT_MAX, 281 .max_discard_segments = 1, 282 .discard_granularity = PAGE_SIZE, 283 .features = BLK_FEAT_SYNCHRONOUS | 284 BLK_FEAT_NOWAIT, 285 }; 286 287 brd = brd_find_or_alloc_device(i); 288 if (IS_ERR(brd)) 289 return PTR_ERR(brd); 290 291 xa_init(&brd->brd_pages); 292 293 snprintf(buf, DISK_NAME_LEN, "ram%d", i); 294 if (!IS_ERR_OR_NULL(brd_debugfs_dir)) 295 debugfs_create_u64(buf, 0444, brd_debugfs_dir, 296 &brd->brd_nr_pages); 297 298 disk = brd->brd_disk = blk_alloc_disk(&lim, NUMA_NO_NODE); 299 if (IS_ERR(disk)) { 300 err = PTR_ERR(disk); 301 goto out_free_dev; 302 } 303 disk->major = RAMDISK_MAJOR; 304 disk->first_minor = i * max_part; 305 disk->minors = max_part; 306 disk->fops = &brd_fops; 307 disk->private_data = brd; 308 strscpy(disk->disk_name, buf, DISK_NAME_LEN); 309 set_capacity(disk, rd_size * 2); 310 311 err = add_disk(disk); 312 if (err) 313 goto out_cleanup_disk; 314 315 return 0; 316 317 out_cleanup_disk: 318 put_disk(disk); 319 out_free_dev: 320 brd_free_device(brd); 321 return err; 322 } 323 324 static void brd_probe(dev_t dev) 325 { 326 brd_alloc(MINOR(dev) / max_part); 327 } 328 329 static void brd_cleanup(void) 330 { 331 struct brd_device *brd, *next; 332 333 debugfs_remove_recursive(brd_debugfs_dir); 334 335 list_for_each_entry_safe(brd, next, &brd_devices, brd_list) { 336 del_gendisk(brd->brd_disk); 337 put_disk(brd->brd_disk); 338 brd_free_pages(brd); 339 brd_free_device(brd); 340 } 341 } 342 343 static inline void brd_check_and_reset_par(void) 344 { 345 if (unlikely(!max_part)) 346 max_part = 1; 347 348 /* 349 * make sure 'max_part' can be divided exactly by (1U << MINORBITS), 350 * otherwise, it is possiable to get same dev_t when adding partitions. 351 */ 352 if ((1U << MINORBITS) % max_part != 0) 353 max_part = 1UL << fls(max_part); 354 355 if (max_part > DISK_MAX_PARTS) { 356 pr_info("brd: max_part can't be larger than %d, reset max_part = %d.\n", 357 DISK_MAX_PARTS, DISK_MAX_PARTS); 358 max_part = DISK_MAX_PARTS; 359 } 360 } 361 362 static int __init brd_init(void) 363 { 364 int err, i; 365 366 /* 367 * brd module now has a feature to instantiate underlying device 368 * structure on-demand, provided that there is an access dev node. 369 * 370 * (1) if rd_nr is specified, create that many upfront. else 371 * it defaults to CONFIG_BLK_DEV_RAM_COUNT 372 * (2) User can further extend brd devices by create dev node themselves 373 * and have kernel automatically instantiate actual device 374 * on-demand. Example: 375 * mknod /path/devnod_name b 1 X # 1 is the rd major 376 * fdisk -l /path/devnod_name 377 * If (X / max_part) was not already created it will be created 378 * dynamically. 379 */ 380 381 brd_check_and_reset_par(); 382 383 brd_debugfs_dir = debugfs_create_dir("ramdisk_pages", NULL); 384 385 if (__register_blkdev(RAMDISK_MAJOR, "ramdisk", brd_probe)) { 386 err = -EIO; 387 goto out_free; 388 } 389 390 for (i = 0; i < rd_nr; i++) 391 brd_alloc(i); 392 393 pr_info("brd: module loaded\n"); 394 return 0; 395 396 out_free: 397 brd_cleanup(); 398 399 pr_info("brd: module NOT loaded !!!\n"); 400 return err; 401 } 402 403 static void __exit brd_exit(void) 404 { 405 406 unregister_blkdev(RAMDISK_MAJOR, "ramdisk"); 407 brd_cleanup(); 408 409 pr_info("brd: module unloaded\n"); 410 } 411 412 module_init(brd_init); 413 module_exit(brd_exit); 414 415