1 // SPDX-License-Identifier: GPL-2.0-only
3 * Ram backed block device driver.
5 * Copyright (C) 2007 Nick Piggin
6 * Copyright (C) 2007 Novell Inc.
8 * Parts derived from drivers/block/rd.c, and drivers/block/loop.c, copyright
9 * of their respective owners.
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/radix-tree.h>
23 #include <linux/slab.h>
24 #include <linux/backing-dev.h>
26 #include <linux/uaccess.h>
28 #define PAGE_SECTORS_SHIFT (PAGE_SHIFT - SECTOR_SHIFT)
29 #define PAGE_SECTORS (1 << PAGE_SECTORS_SHIFT)
32 * Each block ramdisk device has a radix_tree brd_pages of pages that stores
33 * the pages containing the block device's contents. A brd page's ->index is
34 * its offset in PAGE_SIZE units. This is similar to, but in no way connected
35 * with, the kernel's pagecache or buffer cache (which sit above our block
41 struct request_queue *brd_queue;
42 struct gendisk *brd_disk;
43 struct list_head brd_list;
46 * Backing store of pages and lock to protect it. This is the contents
47 * of the block device.
50 struct radix_tree_root brd_pages;
54 * Look up and return a brd's page for a given sector.
56 static struct page *brd_lookup_page(struct brd_device *brd, sector_t sector)
62 * The page lifetime is protected by the fact that we have opened the
63 * device node -- brd pages will never be deleted under us, so we
64 * don't need any further locking or refcounting.
66 * This is strictly true for the radix-tree nodes as well (ie. we
67 * don't actually need the rcu_read_lock()), however that is not a
68 * documented feature of the radix-tree API so it is better to be
69 * safe here (we don't have total exclusion from radix tree updates
70 * here, only deletes).
73 idx = sector >> PAGE_SECTORS_SHIFT; /* sector to page index */
74 page = radix_tree_lookup(&brd->brd_pages, idx);
77 BUG_ON(page && page->index != idx);
83 * Insert a new page for a given sector, if one does not already exist.
85 static int brd_insert_page(struct brd_device *brd, sector_t sector)
91 page = brd_lookup_page(brd, sector);
96 * Must use NOIO because we don't want to recurse back into the
97 * block or filesystem layers from page reclaim.
99 gfp_flags = GFP_NOIO | __GFP_ZERO | __GFP_HIGHMEM;
100 page = alloc_page(gfp_flags);
104 if (radix_tree_preload(GFP_NOIO)) {
109 spin_lock(&brd->brd_lock);
110 idx = sector >> PAGE_SECTORS_SHIFT;
112 if (radix_tree_insert(&brd->brd_pages, idx, page)) {
114 page = radix_tree_lookup(&brd->brd_pages, idx);
116 BUG_ON(page->index != idx);
118 spin_unlock(&brd->brd_lock);
120 radix_tree_preload_end();
125 * Free all backing store pages and radix tree. This must only be called when
126 * there are no other users of the device.
128 #define FREE_BATCH 16
129 static void brd_free_pages(struct brd_device *brd)
131 unsigned long pos = 0;
132 struct page *pages[FREE_BATCH];
138 nr_pages = radix_tree_gang_lookup(&brd->brd_pages,
139 (void **)pages, pos, FREE_BATCH);
141 for (i = 0; i < nr_pages; i++) {
144 BUG_ON(pages[i]->index < pos);
145 pos = pages[i]->index;
146 ret = radix_tree_delete(&brd->brd_pages, pos);
147 BUG_ON(!ret || ret != pages[i]);
148 __free_page(pages[i]);
154 * It takes 3.4 seconds to remove 80GiB ramdisk.
155 * So, we need cond_resched to avoid stalling the CPU.
160 * This assumes radix_tree_gang_lookup always returns as
161 * many pages as possible. If the radix-tree code changes,
162 * so will this have to.
164 } while (nr_pages == FREE_BATCH);
168 * copy_to_brd_setup must be called before copy_to_brd. It may sleep.
170 static int copy_to_brd_setup(struct brd_device *brd, sector_t sector, size_t n)
172 unsigned int offset = (sector & (PAGE_SECTORS-1)) << SECTOR_SHIFT;
176 copy = min_t(size_t, n, PAGE_SIZE - offset);
177 ret = brd_insert_page(brd, sector);
181 sector += copy >> SECTOR_SHIFT;
182 ret = brd_insert_page(brd, sector);
188 * Copy n bytes from src to the brd starting at sector. Does not sleep.
190 static void copy_to_brd(struct brd_device *brd, const void *src,
191 sector_t sector, size_t n)
195 unsigned int offset = (sector & (PAGE_SECTORS-1)) << SECTOR_SHIFT;
198 copy = min_t(size_t, n, PAGE_SIZE - offset);
199 page = brd_lookup_page(brd, sector);
202 dst = kmap_atomic(page);
203 memcpy(dst + offset, src, copy);
208 sector += copy >> SECTOR_SHIFT;
210 page = brd_lookup_page(brd, sector);
213 dst = kmap_atomic(page);
214 memcpy(dst, src, copy);
220 * Copy n bytes to dst from the brd starting at sector. Does not sleep.
222 static void copy_from_brd(void *dst, struct brd_device *brd,
223 sector_t sector, size_t n)
227 unsigned int offset = (sector & (PAGE_SECTORS-1)) << SECTOR_SHIFT;
230 copy = min_t(size_t, n, PAGE_SIZE - offset);
231 page = brd_lookup_page(brd, sector);
233 src = kmap_atomic(page);
234 memcpy(dst, src + offset, copy);
237 memset(dst, 0, copy);
241 sector += copy >> SECTOR_SHIFT;
243 page = brd_lookup_page(brd, sector);
245 src = kmap_atomic(page);
246 memcpy(dst, src, copy);
249 memset(dst, 0, copy);
254 * Process a single bvec of a bio.
256 static int brd_do_bvec(struct brd_device *brd, struct page *page,
257 unsigned int len, unsigned int off, unsigned int op,
263 if (op_is_write(op)) {
264 err = copy_to_brd_setup(brd, sector, len);
269 mem = kmap_atomic(page);
270 if (!op_is_write(op)) {
271 copy_from_brd(mem + off, brd, sector, len);
272 flush_dcache_page(page);
274 flush_dcache_page(page);
275 copy_to_brd(brd, mem + off, sector, len);
283 static blk_qc_t brd_submit_bio(struct bio *bio)
285 struct brd_device *brd = bio->bi_disk->private_data;
288 struct bvec_iter iter;
290 sector = bio->bi_iter.bi_sector;
291 if (bio_end_sector(bio) > get_capacity(bio->bi_disk))
294 bio_for_each_segment(bvec, bio, iter) {
295 unsigned int len = bvec.bv_len;
298 /* Don't support un-aligned buffer */
299 WARN_ON_ONCE((bvec.bv_offset & (SECTOR_SIZE - 1)) ||
300 (len & (SECTOR_SIZE - 1)));
302 err = brd_do_bvec(brd, bvec.bv_page, len, bvec.bv_offset,
303 bio_op(bio), sector);
306 sector += len >> SECTOR_SHIFT;
310 return BLK_QC_T_NONE;
313 return BLK_QC_T_NONE;
316 static int brd_rw_page(struct block_device *bdev, sector_t sector,
317 struct page *page, unsigned int op)
319 struct brd_device *brd = bdev->bd_disk->private_data;
322 if (PageTransHuge(page))
324 err = brd_do_bvec(brd, page, PAGE_SIZE, 0, op, sector);
325 page_endio(page, op_is_write(op), err);
329 static const struct block_device_operations brd_fops = {
330 .owner = THIS_MODULE,
331 .submit_bio = brd_submit_bio,
332 .rw_page = brd_rw_page,
336 * And now the modules code and kernel interface.
338 static int rd_nr = CONFIG_BLK_DEV_RAM_COUNT;
339 module_param(rd_nr, int, 0444);
340 MODULE_PARM_DESC(rd_nr, "Maximum number of brd devices");
342 unsigned long rd_size = CONFIG_BLK_DEV_RAM_SIZE;
343 module_param(rd_size, ulong, 0444);
344 MODULE_PARM_DESC(rd_size, "Size of each RAM disk in kbytes.");
346 static int max_part = 1;
347 module_param(max_part, int, 0444);
348 MODULE_PARM_DESC(max_part, "Num Minors to reserve between devices");
350 MODULE_LICENSE("GPL");
351 MODULE_ALIAS_BLOCKDEV_MAJOR(RAMDISK_MAJOR);
355 /* Legacy boot options - nonmodular */
356 static int __init ramdisk_size(char *str)
358 rd_size = simple_strtol(str, NULL, 0);
361 __setup("ramdisk_size=", ramdisk_size);
365 * The device scheme is derived from loop.c. Keep them in synch where possible
366 * (should share code eventually).
368 static LIST_HEAD(brd_devices);
369 static DEFINE_MUTEX(brd_devices_mutex);
371 static struct brd_device *brd_alloc(int i)
373 struct brd_device *brd;
374 struct gendisk *disk;
376 brd = kzalloc(sizeof(*brd), GFP_KERNEL);
380 spin_lock_init(&brd->brd_lock);
381 INIT_RADIX_TREE(&brd->brd_pages, GFP_ATOMIC);
383 brd->brd_queue = blk_alloc_queue(NUMA_NO_NODE);
387 /* This is so fdisk will align partitions on 4k, because of
388 * direct_access API needing 4k alignment, returning a PFN
389 * (This is only a problem on very small devices <= 4M,
390 * otherwise fdisk will align on 1M. Regardless this call
393 blk_queue_physical_block_size(brd->brd_queue, PAGE_SIZE);
394 disk = brd->brd_disk = alloc_disk(max_part);
397 disk->major = RAMDISK_MAJOR;
398 disk->first_minor = i * max_part;
399 disk->fops = &brd_fops;
400 disk->private_data = brd;
401 disk->flags = GENHD_FL_EXT_DEVT;
402 sprintf(disk->disk_name, "ram%d", i);
403 set_capacity(disk, rd_size * 2);
405 /* Tell the block layer that this is not a rotational device */
406 blk_queue_flag_set(QUEUE_FLAG_NONROT, brd->brd_queue);
407 blk_queue_flag_clear(QUEUE_FLAG_ADD_RANDOM, brd->brd_queue);
412 blk_cleanup_queue(brd->brd_queue);
419 static void brd_free(struct brd_device *brd)
421 put_disk(brd->brd_disk);
422 blk_cleanup_queue(brd->brd_queue);
427 static struct brd_device *brd_init_one(int i, bool *new)
429 struct brd_device *brd;
432 list_for_each_entry(brd, &brd_devices, brd_list) {
433 if (brd->brd_number == i)
439 brd->brd_disk->queue = brd->brd_queue;
440 add_disk(brd->brd_disk);
441 list_add_tail(&brd->brd_list, &brd_devices);
448 static void brd_del_one(struct brd_device *brd)
450 list_del(&brd->brd_list);
451 del_gendisk(brd->brd_disk);
455 static struct kobject *brd_probe(dev_t dev, int *part, void *data)
457 struct brd_device *brd;
458 struct kobject *kobj;
461 mutex_lock(&brd_devices_mutex);
462 brd = brd_init_one(MINOR(dev) / max_part, &new);
463 kobj = brd ? get_disk_and_module(brd->brd_disk) : NULL;
464 mutex_unlock(&brd_devices_mutex);
472 static inline void brd_check_and_reset_par(void)
474 if (unlikely(!max_part))
478 * make sure 'max_part' can be divided exactly by (1U << MINORBITS),
479 * otherwise, it is possiable to get same dev_t when adding partitions.
481 if ((1U << MINORBITS) % max_part != 0)
482 max_part = 1UL << fls(max_part);
484 if (max_part > DISK_MAX_PARTS) {
485 pr_info("brd: max_part can't be larger than %d, reset max_part = %d.\n",
486 DISK_MAX_PARTS, DISK_MAX_PARTS);
487 max_part = DISK_MAX_PARTS;
491 static int __init brd_init(void)
493 struct brd_device *brd, *next;
497 * brd module now has a feature to instantiate underlying device
498 * structure on-demand, provided that there is an access dev node.
500 * (1) if rd_nr is specified, create that many upfront. else
501 * it defaults to CONFIG_BLK_DEV_RAM_COUNT
502 * (2) User can further extend brd devices by create dev node themselves
503 * and have kernel automatically instantiate actual device
504 * on-demand. Example:
505 * mknod /path/devnod_name b 1 X # 1 is the rd major
506 * fdisk -l /path/devnod_name
507 * If (X / max_part) was not already created it will be created
511 if (register_blkdev(RAMDISK_MAJOR, "ramdisk"))
514 brd_check_and_reset_par();
516 for (i = 0; i < rd_nr; i++) {
520 list_add_tail(&brd->brd_list, &brd_devices);
523 /* point of no return */
525 list_for_each_entry(brd, &brd_devices, brd_list) {
527 * associate with queue just before adding disk for
528 * avoiding to mess up failure path
530 brd->brd_disk->queue = brd->brd_queue;
531 add_disk(brd->brd_disk);
534 blk_register_region(MKDEV(RAMDISK_MAJOR, 0), 1UL << MINORBITS,
535 THIS_MODULE, brd_probe, NULL, NULL);
537 pr_info("brd: module loaded\n");
541 list_for_each_entry_safe(brd, next, &brd_devices, brd_list) {
542 list_del(&brd->brd_list);
545 unregister_blkdev(RAMDISK_MAJOR, "ramdisk");
547 pr_info("brd: module NOT loaded !!!\n");
551 static void __exit brd_exit(void)
553 struct brd_device *brd, *next;
555 list_for_each_entry_safe(brd, next, &brd_devices, brd_list)
558 blk_unregister_region(MKDEV(RAMDISK_MAJOR, 0), 1UL << MINORBITS);
559 unregister_blkdev(RAMDISK_MAJOR, "ramdisk");
561 pr_info("brd: module unloaded\n");
564 module_init(brd_init);
565 module_exit(brd_exit);