2 * Ram backed block device driver.
4 * Copyright (C) 2007 Nick Piggin
5 * Copyright (C) 2007 Novell Inc.
7 * Parts derived from drivers/block/rd.c, and drivers/block/loop.c, copyright
8 * of their respective owners.
11 #include <linux/init.h>
12 #include <linux/module.h>
13 #include <linux/moduleparam.h>
14 #include <linux/major.h>
15 #include <linux/blkdev.h>
16 #include <linux/bio.h>
17 #include <linux/highmem.h>
18 #include <linux/mutex.h>
19 #include <linux/radix-tree.h>
21 #include <linux/slab.h>
22 #ifdef CONFIG_BLK_DEV_RAM_DAX
23 #include <linux/pfn_t.h>
24 #include <linux/dax.h>
25 #include <linux/uio.h>
28 #include <linux/uaccess.h>
30 #define SECTOR_SHIFT 9
31 #define PAGE_SECTORS_SHIFT (PAGE_SHIFT - SECTOR_SHIFT)
32 #define PAGE_SECTORS (1 << PAGE_SECTORS_SHIFT)
35 * Each block ramdisk device has a radix_tree brd_pages of pages that stores
36 * the pages containing the block device's contents. A brd page's ->index is
37 * its offset in PAGE_SIZE units. This is similar to, but in no way connected
38 * with, the kernel's pagecache or buffer cache (which sit above our block
44 struct request_queue *brd_queue;
45 struct gendisk *brd_disk;
46 #ifdef CONFIG_BLK_DEV_RAM_DAX
47 struct dax_device *dax_dev;
49 struct list_head brd_list;
52 * Backing store of pages and lock to protect it. This is the contents
53 * of the block device.
56 struct radix_tree_root brd_pages;
60 * Look up and return a brd's page for a given sector.
62 static DEFINE_MUTEX(brd_mutex);
63 static struct page *brd_lookup_page(struct brd_device *brd, sector_t sector)
69 * The page lifetime is protected by the fact that we have opened the
70 * device node -- brd pages will never be deleted under us, so we
71 * don't need any further locking or refcounting.
73 * This is strictly true for the radix-tree nodes as well (ie. we
74 * don't actually need the rcu_read_lock()), however that is not a
75 * documented feature of the radix-tree API so it is better to be
76 * safe here (we don't have total exclusion from radix tree updates
77 * here, only deletes).
80 idx = sector >> PAGE_SECTORS_SHIFT; /* sector to page index */
81 page = radix_tree_lookup(&brd->brd_pages, idx);
84 BUG_ON(page && page->index != idx);
90 * Look up and return a brd's page for a given sector.
91 * If one does not exist, allocate an empty page, and insert that. Then
94 static struct page *brd_insert_page(struct brd_device *brd, sector_t sector)
100 page = brd_lookup_page(brd, sector);
105 * Must use NOIO because we don't want to recurse back into the
106 * block or filesystem layers from page reclaim.
108 * Cannot support DAX and highmem, because our ->direct_access
109 * routine for DAX must return memory that is always addressable.
110 * If DAX was reworked to use pfns and kmap throughout, this
111 * restriction might be able to be lifted.
113 gfp_flags = GFP_NOIO | __GFP_ZERO;
114 #ifndef CONFIG_BLK_DEV_RAM_DAX
115 gfp_flags |= __GFP_HIGHMEM;
117 page = alloc_page(gfp_flags);
121 if (radix_tree_preload(GFP_NOIO)) {
126 spin_lock(&brd->brd_lock);
127 idx = sector >> PAGE_SECTORS_SHIFT;
129 if (radix_tree_insert(&brd->brd_pages, idx, page)) {
131 page = radix_tree_lookup(&brd->brd_pages, idx);
133 BUG_ON(page->index != idx);
135 spin_unlock(&brd->brd_lock);
137 radix_tree_preload_end();
143 * Free all backing store pages and radix tree. This must only be called when
144 * there are no other users of the device.
146 #define FREE_BATCH 16
147 static void brd_free_pages(struct brd_device *brd)
149 unsigned long pos = 0;
150 struct page *pages[FREE_BATCH];
156 nr_pages = radix_tree_gang_lookup(&brd->brd_pages,
157 (void **)pages, pos, FREE_BATCH);
159 for (i = 0; i < nr_pages; i++) {
162 BUG_ON(pages[i]->index < pos);
163 pos = pages[i]->index;
164 ret = radix_tree_delete(&brd->brd_pages, pos);
165 BUG_ON(!ret || ret != pages[i]);
166 __free_page(pages[i]);
172 * This assumes radix_tree_gang_lookup always returns as
173 * many pages as possible. If the radix-tree code changes,
174 * so will this have to.
176 } while (nr_pages == FREE_BATCH);
180 * copy_to_brd_setup must be called before copy_to_brd. It may sleep.
182 static int copy_to_brd_setup(struct brd_device *brd, sector_t sector, size_t n)
184 unsigned int offset = (sector & (PAGE_SECTORS-1)) << SECTOR_SHIFT;
187 copy = min_t(size_t, n, PAGE_SIZE - offset);
188 if (!brd_insert_page(brd, sector))
191 sector += copy >> SECTOR_SHIFT;
192 if (!brd_insert_page(brd, sector))
199 * Copy n bytes from src to the brd starting at sector. Does not sleep.
201 static void copy_to_brd(struct brd_device *brd, const void *src,
202 sector_t sector, size_t n)
206 unsigned int offset = (sector & (PAGE_SECTORS-1)) << SECTOR_SHIFT;
209 copy = min_t(size_t, n, PAGE_SIZE - offset);
210 page = brd_lookup_page(brd, sector);
213 dst = kmap_atomic(page);
214 memcpy(dst + offset, src, copy);
219 sector += copy >> SECTOR_SHIFT;
221 page = brd_lookup_page(brd, sector);
224 dst = kmap_atomic(page);
225 memcpy(dst, src, copy);
231 * Copy n bytes to dst from the brd starting at sector. Does not sleep.
233 static void copy_from_brd(void *dst, struct brd_device *brd,
234 sector_t sector, size_t n)
238 unsigned int offset = (sector & (PAGE_SECTORS-1)) << SECTOR_SHIFT;
241 copy = min_t(size_t, n, PAGE_SIZE - offset);
242 page = brd_lookup_page(brd, sector);
244 src = kmap_atomic(page);
245 memcpy(dst, src + offset, copy);
248 memset(dst, 0, copy);
252 sector += copy >> SECTOR_SHIFT;
254 page = brd_lookup_page(brd, sector);
256 src = kmap_atomic(page);
257 memcpy(dst, src, copy);
260 memset(dst, 0, copy);
265 * Process a single bvec of a bio.
267 static int brd_do_bvec(struct brd_device *brd, struct page *page,
268 unsigned int len, unsigned int off, bool is_write,
275 err = copy_to_brd_setup(brd, sector, len);
280 mem = kmap_atomic(page);
282 copy_from_brd(mem + off, brd, sector, len);
283 flush_dcache_page(page);
285 flush_dcache_page(page);
286 copy_to_brd(brd, mem + off, sector, len);
294 static blk_qc_t brd_make_request(struct request_queue *q, struct bio *bio)
296 struct block_device *bdev = bio->bi_bdev;
297 struct brd_device *brd = bdev->bd_disk->private_data;
300 struct bvec_iter iter;
302 sector = bio->bi_iter.bi_sector;
303 if (bio_end_sector(bio) > get_capacity(bdev->bd_disk))
306 bio_for_each_segment(bvec, bio, iter) {
307 unsigned int len = bvec.bv_len;
310 err = brd_do_bvec(brd, bvec.bv_page, len, bvec.bv_offset,
311 op_is_write(bio_op(bio)), sector);
314 sector += len >> SECTOR_SHIFT;
318 return BLK_QC_T_NONE;
321 return BLK_QC_T_NONE;
324 static int brd_rw_page(struct block_device *bdev, sector_t sector,
325 struct page *page, bool is_write)
327 struct brd_device *brd = bdev->bd_disk->private_data;
328 int err = brd_do_bvec(brd, page, PAGE_SIZE, 0, is_write, sector);
329 page_endio(page, is_write, err);
333 #ifdef CONFIG_BLK_DEV_RAM_DAX
334 static long __brd_direct_access(struct brd_device *brd, pgoff_t pgoff,
335 long nr_pages, void **kaddr, pfn_t *pfn)
341 page = brd_insert_page(brd, PFN_PHYS(pgoff) / 512);
344 *kaddr = page_address(page);
345 *pfn = page_to_pfn_t(page);
350 static long brd_dax_direct_access(struct dax_device *dax_dev,
351 pgoff_t pgoff, long nr_pages, void **kaddr, pfn_t *pfn)
353 struct brd_device *brd = dax_get_private(dax_dev);
355 return __brd_direct_access(brd, pgoff, nr_pages, kaddr, pfn);
358 static size_t brd_dax_copy_from_iter(struct dax_device *dax_dev, pgoff_t pgoff,
359 void *addr, size_t bytes, struct iov_iter *i)
361 return copy_from_iter(addr, bytes, i);
364 static const struct dax_operations brd_dax_ops = {
365 .direct_access = brd_dax_direct_access,
366 .copy_from_iter = brd_dax_copy_from_iter,
370 static const struct block_device_operations brd_fops = {
371 .owner = THIS_MODULE,
372 .rw_page = brd_rw_page,
376 * And now the modules code and kernel interface.
378 static int rd_nr = CONFIG_BLK_DEV_RAM_COUNT;
379 module_param(rd_nr, int, S_IRUGO);
380 MODULE_PARM_DESC(rd_nr, "Maximum number of brd devices");
382 unsigned long rd_size = CONFIG_BLK_DEV_RAM_SIZE;
383 module_param(rd_size, ulong, S_IRUGO);
384 MODULE_PARM_DESC(rd_size, "Size of each RAM disk in kbytes.");
386 static int max_part = 1;
387 module_param(max_part, int, S_IRUGO);
388 MODULE_PARM_DESC(max_part, "Num Minors to reserve between devices");
390 MODULE_LICENSE("GPL");
391 MODULE_ALIAS_BLOCKDEV_MAJOR(RAMDISK_MAJOR);
395 /* Legacy boot options - nonmodular */
396 static int __init ramdisk_size(char *str)
398 rd_size = simple_strtol(str, NULL, 0);
401 __setup("ramdisk_size=", ramdisk_size);
405 * The device scheme is derived from loop.c. Keep them in synch where possible
406 * (should share code eventually).
408 static LIST_HEAD(brd_devices);
409 static DEFINE_MUTEX(brd_devices_mutex);
411 static struct brd_device *brd_alloc(int i)
413 struct brd_device *brd;
414 struct gendisk *disk;
416 brd = kzalloc(sizeof(*brd), GFP_KERNEL);
420 spin_lock_init(&brd->brd_lock);
421 INIT_RADIX_TREE(&brd->brd_pages, GFP_ATOMIC);
423 brd->brd_queue = blk_alloc_queue(GFP_KERNEL);
427 blk_queue_make_request(brd->brd_queue, brd_make_request);
428 blk_queue_max_hw_sectors(brd->brd_queue, 1024);
430 /* This is so fdisk will align partitions on 4k, because of
431 * direct_access API needing 4k alignment, returning a PFN
432 * (This is only a problem on very small devices <= 4M,
433 * otherwise fdisk will align on 1M. Regardless this call
436 blk_queue_physical_block_size(brd->brd_queue, PAGE_SIZE);
437 disk = brd->brd_disk = alloc_disk(max_part);
440 disk->major = RAMDISK_MAJOR;
441 disk->first_minor = i * max_part;
442 disk->fops = &brd_fops;
443 disk->private_data = brd;
444 disk->queue = brd->brd_queue;
445 disk->flags = GENHD_FL_EXT_DEVT;
446 sprintf(disk->disk_name, "ram%d", i);
447 set_capacity(disk, rd_size * 2);
449 #ifdef CONFIG_BLK_DEV_RAM_DAX
450 queue_flag_set_unlocked(QUEUE_FLAG_DAX, brd->brd_queue);
451 brd->dax_dev = alloc_dax(brd, disk->disk_name, &brd_dax_ops);
459 #ifdef CONFIG_BLK_DEV_RAM_DAX
461 kill_dax(brd->dax_dev);
462 put_dax(brd->dax_dev);
465 blk_cleanup_queue(brd->brd_queue);
472 static void brd_free(struct brd_device *brd)
474 put_disk(brd->brd_disk);
475 blk_cleanup_queue(brd->brd_queue);
480 static struct brd_device *brd_init_one(int i, bool *new)
482 struct brd_device *brd;
485 list_for_each_entry(brd, &brd_devices, brd_list) {
486 if (brd->brd_number == i)
492 add_disk(brd->brd_disk);
493 list_add_tail(&brd->brd_list, &brd_devices);
500 static void brd_del_one(struct brd_device *brd)
502 list_del(&brd->brd_list);
503 #ifdef CONFIG_BLK_DEV_RAM_DAX
504 kill_dax(brd->dax_dev);
505 put_dax(brd->dax_dev);
507 del_gendisk(brd->brd_disk);
511 static struct kobject *brd_probe(dev_t dev, int *part, void *data)
513 struct brd_device *brd;
514 struct kobject *kobj;
517 mutex_lock(&brd_devices_mutex);
518 brd = brd_init_one(MINOR(dev) / max_part, &new);
519 kobj = brd ? get_disk(brd->brd_disk) : NULL;
520 mutex_unlock(&brd_devices_mutex);
528 static int __init brd_init(void)
530 struct brd_device *brd, *next;
534 * brd module now has a feature to instantiate underlying device
535 * structure on-demand, provided that there is an access dev node.
537 * (1) if rd_nr is specified, create that many upfront. else
538 * it defaults to CONFIG_BLK_DEV_RAM_COUNT
539 * (2) User can further extend brd devices by create dev node themselves
540 * and have kernel automatically instantiate actual device
541 * on-demand. Example:
542 * mknod /path/devnod_name b 1 X # 1 is the rd major
543 * fdisk -l /path/devnod_name
544 * If (X / max_part) was not already created it will be created
548 if (register_blkdev(RAMDISK_MAJOR, "ramdisk"))
551 if (unlikely(!max_part))
554 for (i = 0; i < rd_nr; i++) {
558 list_add_tail(&brd->brd_list, &brd_devices);
561 /* point of no return */
563 list_for_each_entry(brd, &brd_devices, brd_list)
564 add_disk(brd->brd_disk);
566 blk_register_region(MKDEV(RAMDISK_MAJOR, 0), 1UL << MINORBITS,
567 THIS_MODULE, brd_probe, NULL, NULL);
569 pr_info("brd: module loaded\n");
573 list_for_each_entry_safe(brd, next, &brd_devices, brd_list) {
574 list_del(&brd->brd_list);
577 unregister_blkdev(RAMDISK_MAJOR, "ramdisk");
579 pr_info("brd: module NOT loaded !!!\n");
583 static void __exit brd_exit(void)
585 struct brd_device *brd, *next;
587 list_for_each_entry_safe(brd, next, &brd_devices, brd_list)
590 blk_unregister_region(MKDEV(RAMDISK_MAJOR, 0), 1UL << MINORBITS);
591 unregister_blkdev(RAMDISK_MAJOR, "ramdisk");
593 pr_info("brd: module unloaded\n");
596 module_init(brd_init);
597 module_exit(brd_exit);