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/pagemap.h>
22 #include <linux/radix-tree.h>
24 #include <linux/slab.h>
25 #include <linux/backing-dev.h>
26 #include <linux/debugfs.h>
28 #include <linux/uaccess.h>
30 #define PAGE_SECTORS_SHIFT (PAGE_SHIFT - SECTOR_SHIFT)
31 #define PAGE_SECTORS (1 << PAGE_SECTORS_SHIFT)
34 * Each block ramdisk device has a radix_tree brd_pages of pages that stores
35 * the pages containing the block device's contents. A brd page's ->index is
36 * its offset in PAGE_SIZE units. This is similar to, but in no way connected
37 * with, the kernel's pagecache or buffer cache (which sit above our block
43 struct request_queue *brd_queue;
44 struct gendisk *brd_disk;
45 struct list_head brd_list;
48 * Backing store of pages and lock to protect it. This is the contents
49 * of the block device.
52 struct radix_tree_root brd_pages;
57 * Look up and return a brd's page for a given sector.
59 static struct page *brd_lookup_page(struct brd_device *brd, sector_t sector)
65 * The page lifetime is protected by the fact that we have opened the
66 * device node -- brd pages will never be deleted under us, so we
67 * don't need any further locking or refcounting.
69 * This is strictly true for the radix-tree nodes as well (ie. we
70 * don't actually need the rcu_read_lock()), however that is not a
71 * documented feature of the radix-tree API so it is better to be
72 * safe here (we don't have total exclusion from radix tree updates
73 * here, only deletes).
76 idx = sector >> PAGE_SECTORS_SHIFT; /* sector to page index */
77 page = radix_tree_lookup(&brd->brd_pages, idx);
80 BUG_ON(page && page->index != idx);
86 * Look up and return a brd's page for a given sector.
87 * If one does not exist, allocate an empty page, and insert that. Then
90 static struct page *brd_insert_page(struct brd_device *brd, sector_t sector)
96 page = brd_lookup_page(brd, sector);
101 * Must use NOIO because we don't want to recurse back into the
102 * block or filesystem layers from page reclaim.
104 gfp_flags = GFP_NOIO | __GFP_ZERO | __GFP_HIGHMEM;
105 page = alloc_page(gfp_flags);
109 if (radix_tree_preload(GFP_NOIO)) {
114 spin_lock(&brd->brd_lock);
115 idx = sector >> PAGE_SECTORS_SHIFT;
117 if (radix_tree_insert(&brd->brd_pages, idx, page)) {
119 page = radix_tree_lookup(&brd->brd_pages, idx);
121 BUG_ON(page->index != idx);
125 spin_unlock(&brd->brd_lock);
127 radix_tree_preload_end();
133 * Free all backing store pages and radix tree. This must only be called when
134 * there are no other users of the device.
136 #define FREE_BATCH 16
137 static void brd_free_pages(struct brd_device *brd)
139 unsigned long pos = 0;
140 struct page *pages[FREE_BATCH];
146 nr_pages = radix_tree_gang_lookup(&brd->brd_pages,
147 (void **)pages, pos, FREE_BATCH);
149 for (i = 0; i < nr_pages; i++) {
152 BUG_ON(pages[i]->index < pos);
153 pos = pages[i]->index;
154 ret = radix_tree_delete(&brd->brd_pages, pos);
155 BUG_ON(!ret || ret != pages[i]);
156 __free_page(pages[i]);
162 * It takes 3.4 seconds to remove 80GiB ramdisk.
163 * So, we need cond_resched to avoid stalling the CPU.
168 * This assumes radix_tree_gang_lookup always returns as
169 * many pages as possible. If the radix-tree code changes,
170 * so will this have to.
172 } while (nr_pages == FREE_BATCH);
176 * copy_to_brd_setup must be called before copy_to_brd. It may sleep.
178 static int copy_to_brd_setup(struct brd_device *brd, sector_t sector, size_t n)
180 unsigned int offset = (sector & (PAGE_SECTORS-1)) << SECTOR_SHIFT;
183 copy = min_t(size_t, n, PAGE_SIZE - offset);
184 if (!brd_insert_page(brd, sector))
187 sector += copy >> SECTOR_SHIFT;
188 if (!brd_insert_page(brd, sector))
195 * Copy n bytes from src to the brd starting at sector. Does not sleep.
197 static void copy_to_brd(struct brd_device *brd, const void *src,
198 sector_t sector, size_t n)
202 unsigned int offset = (sector & (PAGE_SECTORS-1)) << SECTOR_SHIFT;
205 copy = min_t(size_t, n, PAGE_SIZE - offset);
206 page = brd_lookup_page(brd, sector);
209 dst = kmap_atomic(page);
210 memcpy(dst + offset, src, copy);
215 sector += copy >> SECTOR_SHIFT;
217 page = brd_lookup_page(brd, sector);
220 dst = kmap_atomic(page);
221 memcpy(dst, src, copy);
227 * Copy n bytes to dst from the brd starting at sector. Does not sleep.
229 static void copy_from_brd(void *dst, struct brd_device *brd,
230 sector_t sector, size_t n)
234 unsigned int offset = (sector & (PAGE_SECTORS-1)) << SECTOR_SHIFT;
237 copy = min_t(size_t, n, PAGE_SIZE - offset);
238 page = brd_lookup_page(brd, sector);
240 src = kmap_atomic(page);
241 memcpy(dst, src + offset, copy);
244 memset(dst, 0, copy);
248 sector += copy >> SECTOR_SHIFT;
250 page = brd_lookup_page(brd, sector);
252 src = kmap_atomic(page);
253 memcpy(dst, src, copy);
256 memset(dst, 0, copy);
261 * Process a single bvec of a bio.
263 static int brd_do_bvec(struct brd_device *brd, struct page *page,
264 unsigned int len, unsigned int off, unsigned int op,
270 if (op_is_write(op)) {
271 err = copy_to_brd_setup(brd, sector, len);
276 mem = kmap_atomic(page);
277 if (!op_is_write(op)) {
278 copy_from_brd(mem + off, brd, sector, len);
279 flush_dcache_page(page);
281 flush_dcache_page(page);
282 copy_to_brd(brd, mem + off, sector, len);
290 static blk_qc_t brd_submit_bio(struct bio *bio)
292 struct brd_device *brd = bio->bi_bdev->bd_disk->private_data;
293 sector_t sector = bio->bi_iter.bi_sector;
295 struct bvec_iter iter;
297 bio_for_each_segment(bvec, bio, iter) {
298 unsigned int len = bvec.bv_len;
301 /* Don't support un-aligned buffer */
302 WARN_ON_ONCE((bvec.bv_offset & (SECTOR_SIZE - 1)) ||
303 (len & (SECTOR_SIZE - 1)));
305 err = brd_do_bvec(brd, bvec.bv_page, len, bvec.bv_offset,
306 bio_op(bio), sector);
309 sector += len >> SECTOR_SHIFT;
313 return BLK_QC_T_NONE;
316 return BLK_QC_T_NONE;
319 static int brd_rw_page(struct block_device *bdev, sector_t sector,
320 struct page *page, unsigned int op)
322 struct brd_device *brd = bdev->bd_disk->private_data;
325 if (PageTransHuge(page))
327 err = brd_do_bvec(brd, page, PAGE_SIZE, 0, op, sector);
328 page_endio(page, op_is_write(op), err);
332 static const struct block_device_operations brd_fops = {
333 .owner = THIS_MODULE,
334 .submit_bio = brd_submit_bio,
335 .rw_page = brd_rw_page,
339 * And now the modules code and kernel interface.
341 static int rd_nr = CONFIG_BLK_DEV_RAM_COUNT;
342 module_param(rd_nr, int, 0444);
343 MODULE_PARM_DESC(rd_nr, "Maximum number of brd devices");
345 unsigned long rd_size = CONFIG_BLK_DEV_RAM_SIZE;
346 module_param(rd_size, ulong, 0444);
347 MODULE_PARM_DESC(rd_size, "Size of each RAM disk in kbytes.");
349 static int max_part = 1;
350 module_param(max_part, int, 0444);
351 MODULE_PARM_DESC(max_part, "Num Minors to reserve between devices");
353 MODULE_LICENSE("GPL");
354 MODULE_ALIAS_BLOCKDEV_MAJOR(RAMDISK_MAJOR);
358 /* Legacy boot options - nonmodular */
359 static int __init ramdisk_size(char *str)
361 rd_size = simple_strtol(str, NULL, 0);
364 __setup("ramdisk_size=", ramdisk_size);
368 * The device scheme is derived from loop.c. Keep them in synch where possible
369 * (should share code eventually).
371 static LIST_HEAD(brd_devices);
372 static DEFINE_MUTEX(brd_devices_mutex);
373 static struct dentry *brd_debugfs_dir;
375 static struct brd_device *brd_alloc(int i)
377 struct brd_device *brd;
378 struct gendisk *disk;
379 char buf[DISK_NAME_LEN];
381 brd = kzalloc(sizeof(*brd), GFP_KERNEL);
385 spin_lock_init(&brd->brd_lock);
386 INIT_RADIX_TREE(&brd->brd_pages, GFP_ATOMIC);
388 brd->brd_queue = blk_alloc_queue(NUMA_NO_NODE);
392 snprintf(buf, DISK_NAME_LEN, "ram%d", i);
393 if (!IS_ERR_OR_NULL(brd_debugfs_dir))
394 debugfs_create_u64(buf, 0444, brd_debugfs_dir,
397 /* This is so fdisk will align partitions on 4k, because of
398 * direct_access API needing 4k alignment, returning a PFN
399 * (This is only a problem on very small devices <= 4M,
400 * otherwise fdisk will align on 1M. Regardless this call
403 blk_queue_physical_block_size(brd->brd_queue, PAGE_SIZE);
404 disk = brd->brd_disk = alloc_disk(max_part);
407 disk->major = RAMDISK_MAJOR;
408 disk->first_minor = i * max_part;
409 disk->fops = &brd_fops;
410 disk->private_data = brd;
411 disk->flags = GENHD_FL_EXT_DEVT;
412 strlcpy(disk->disk_name, buf, DISK_NAME_LEN);
413 set_capacity(disk, rd_size * 2);
415 /* Tell the block layer that this is not a rotational device */
416 blk_queue_flag_set(QUEUE_FLAG_NONROT, brd->brd_queue);
417 blk_queue_flag_clear(QUEUE_FLAG_ADD_RANDOM, brd->brd_queue);
422 blk_cleanup_queue(brd->brd_queue);
429 static void brd_free(struct brd_device *brd)
431 put_disk(brd->brd_disk);
432 blk_cleanup_queue(brd->brd_queue);
437 static void brd_probe(dev_t dev)
439 struct brd_device *brd;
440 int i = MINOR(dev) / max_part;
442 mutex_lock(&brd_devices_mutex);
443 list_for_each_entry(brd, &brd_devices, brd_list) {
444 if (brd->brd_number == i)
450 brd->brd_disk->queue = brd->brd_queue;
451 add_disk(brd->brd_disk);
452 list_add_tail(&brd->brd_list, &brd_devices);
456 mutex_unlock(&brd_devices_mutex);
459 static void brd_del_one(struct brd_device *brd)
461 list_del(&brd->brd_list);
462 del_gendisk(brd->brd_disk);
466 static inline void brd_check_and_reset_par(void)
468 if (unlikely(!max_part))
472 * make sure 'max_part' can be divided exactly by (1U << MINORBITS),
473 * otherwise, it is possiable to get same dev_t when adding partitions.
475 if ((1U << MINORBITS) % max_part != 0)
476 max_part = 1UL << fls(max_part);
478 if (max_part > DISK_MAX_PARTS) {
479 pr_info("brd: max_part can't be larger than %d, reset max_part = %d.\n",
480 DISK_MAX_PARTS, DISK_MAX_PARTS);
481 max_part = DISK_MAX_PARTS;
485 static int __init brd_init(void)
487 struct brd_device *brd, *next;
491 * brd module now has a feature to instantiate underlying device
492 * structure on-demand, provided that there is an access dev node.
494 * (1) if rd_nr is specified, create that many upfront. else
495 * it defaults to CONFIG_BLK_DEV_RAM_COUNT
496 * (2) User can further extend brd devices by create dev node themselves
497 * and have kernel automatically instantiate actual device
498 * on-demand. Example:
499 * mknod /path/devnod_name b 1 X # 1 is the rd major
500 * fdisk -l /path/devnod_name
501 * If (X / max_part) was not already created it will be created
505 if (__register_blkdev(RAMDISK_MAJOR, "ramdisk", brd_probe))
508 brd_check_and_reset_par();
510 brd_debugfs_dir = debugfs_create_dir("ramdisk_pages", NULL);
512 mutex_lock(&brd_devices_mutex);
513 for (i = 0; i < rd_nr; i++) {
517 list_add_tail(&brd->brd_list, &brd_devices);
520 /* point of no return */
522 list_for_each_entry(brd, &brd_devices, brd_list) {
524 * associate with queue just before adding disk for
525 * avoiding to mess up failure path
527 brd->brd_disk->queue = brd->brd_queue;
528 add_disk(brd->brd_disk);
530 mutex_unlock(&brd_devices_mutex);
532 pr_info("brd: module loaded\n");
536 debugfs_remove_recursive(brd_debugfs_dir);
538 list_for_each_entry_safe(brd, next, &brd_devices, brd_list) {
539 list_del(&brd->brd_list);
542 mutex_unlock(&brd_devices_mutex);
543 unregister_blkdev(RAMDISK_MAJOR, "ramdisk");
545 pr_info("brd: module NOT loaded !!!\n");
549 static void __exit brd_exit(void)
551 struct brd_device *brd, *next;
553 debugfs_remove_recursive(brd_debugfs_dir);
555 list_for_each_entry_safe(brd, next, &brd_devices, brd_list)
558 unregister_blkdev(RAMDISK_MAJOR, "ramdisk");
560 pr_info("brd: module unloaded\n");
563 module_init(brd_init);
564 module_exit(brd_exit);