diff options
Diffstat (limited to '')
| -rw-r--r-- | drivers/block/brd.c | 530 |
1 files changed, 530 insertions, 0 deletions
diff --git a/drivers/block/brd.c b/drivers/block/brd.c new file mode 100644 index 000000000..a8a77a1ef --- /dev/null +++ b/drivers/block/brd.c @@ -0,0 +1,530 @@ +// SPDX-License-Identifier: GPL-2.0-only +/* + * Ram backed block device driver. + * + * Copyright (C) 2007 Nick Piggin + * Copyright (C) 2007 Novell Inc. + * + * Parts derived from drivers/block/rd.c, and drivers/block/loop.c, copyright + * of their respective owners. + */ + +#include <linux/init.h> +#include <linux/initrd.h> +#include <linux/module.h> +#include <linux/moduleparam.h> +#include <linux/major.h> +#include <linux/blkdev.h> +#include <linux/bio.h> +#include <linux/highmem.h> +#include <linux/mutex.h> +#include <linux/pagemap.h> +#include <linux/radix-tree.h> +#include <linux/fs.h> +#include <linux/slab.h> +#include <linux/backing-dev.h> +#include <linux/debugfs.h> + +#include <linux/uaccess.h> + +/* + * Each block ramdisk device has a radix_tree brd_pages of pages that stores + * the pages containing the block device's contents. A brd page's ->index is + * its offset in PAGE_SIZE units. This is similar to, but in no way connected + * with, the kernel's pagecache or buffer cache (which sit above our block + * device). + */ +struct brd_device { + int brd_number; + struct gendisk *brd_disk; + struct list_head brd_list; + + /* + * Backing store of pages and lock to protect it. This is the contents + * of the block device. + */ + spinlock_t brd_lock; + struct radix_tree_root brd_pages; + u64 brd_nr_pages; +}; + +/* + * Look up and return a brd's page for a given sector. + */ +static struct page *brd_lookup_page(struct brd_device *brd, sector_t sector) +{ + pgoff_t idx; + struct page *page; + + /* + * The page lifetime is protected by the fact that we have opened the + * device node -- brd pages will never be deleted under us, so we + * don't need any further locking or refcounting. + * + * This is strictly true for the radix-tree nodes as well (ie. we + * don't actually need the rcu_read_lock()), however that is not a + * documented feature of the radix-tree API so it is better to be + * safe here (we don't have total exclusion from radix tree updates + * here, only deletes). + */ + rcu_read_lock(); + idx = sector >> PAGE_SECTORS_SHIFT; /* sector to page index */ + page = radix_tree_lookup(&brd->brd_pages, idx); + rcu_read_unlock(); + + BUG_ON(page && page->index != idx); + + return page; +} + +/* + * Insert a new page for a given sector, if one does not already exist. + */ +static int brd_insert_page(struct brd_device *brd, sector_t sector, gfp_t gfp) +{ + pgoff_t idx; + struct page *page; + int ret = 0; + + page = brd_lookup_page(brd, sector); + if (page) + return 0; + + page = alloc_page(gfp | __GFP_ZERO | __GFP_HIGHMEM); + if (!page) + return -ENOMEM; + + if (radix_tree_maybe_preload(gfp)) { + __free_page(page); + return -ENOMEM; + } + + spin_lock(&brd->brd_lock); + idx = sector >> PAGE_SECTORS_SHIFT; + page->index = idx; + if (radix_tree_insert(&brd->brd_pages, idx, page)) { + __free_page(page); + page = radix_tree_lookup(&brd->brd_pages, idx); + if (!page) + ret = -ENOMEM; + else if (page->index != idx) + ret = -EIO; + } else { + brd->brd_nr_pages++; + } + spin_unlock(&brd->brd_lock); + + radix_tree_preload_end(); + return ret; +} + +/* + * Free all backing store pages and radix tree. This must only be called when + * there are no other users of the device. + */ +#define FREE_BATCH 16 +static void brd_free_pages(struct brd_device *brd) +{ + unsigned long pos = 0; + struct page *pages[FREE_BATCH]; + int nr_pages; + + do { + int i; + + nr_pages = radix_tree_gang_lookup(&brd->brd_pages, + (void **)pages, pos, FREE_BATCH); + + for (i = 0; i < nr_pages; i++) { + void *ret; + + BUG_ON(pages[i]->index < pos); + pos = pages[i]->index; + ret = radix_tree_delete(&brd->brd_pages, pos); + BUG_ON(!ret || ret != pages[i]); + __free_page(pages[i]); + } + + pos++; + + /* + * It takes 3.4 seconds to remove 80GiB ramdisk. + * So, we need cond_resched to avoid stalling the CPU. + */ + cond_resched(); + + /* + * This assumes radix_tree_gang_lookup always returns as + * many pages as possible. If the radix-tree code changes, + * so will this have to. + */ + } while (nr_pages == FREE_BATCH); +} + +/* + * copy_to_brd_setup must be called before copy_to_brd. It may sleep. + */ +static int copy_to_brd_setup(struct brd_device *brd, sector_t sector, size_t n, + gfp_t gfp) +{ + unsigned int offset = (sector & (PAGE_SECTORS-1)) << SECTOR_SHIFT; + size_t copy; + int ret; + + copy = min_t(size_t, n, PAGE_SIZE - offset); + ret = brd_insert_page(brd, sector, gfp); + if (ret) + return ret; + if (copy < n) { + sector += copy >> SECTOR_SHIFT; + ret = brd_insert_page(brd, sector, gfp); + } + return ret; +} + +/* + * Copy n bytes from src to the brd starting at sector. Does not sleep. + */ +static void copy_to_brd(struct brd_device *brd, const void *src, + sector_t sector, size_t n) +{ + struct page *page; + void *dst; + unsigned int offset = (sector & (PAGE_SECTORS-1)) << SECTOR_SHIFT; + size_t copy; + + copy = min_t(size_t, n, PAGE_SIZE - offset); + page = brd_lookup_page(brd, sector); + BUG_ON(!page); + + dst = kmap_atomic(page); + memcpy(dst + offset, src, copy); + kunmap_atomic(dst); + + if (copy < n) { + src += copy; + sector += copy >> SECTOR_SHIFT; + copy = n - copy; + page = brd_lookup_page(brd, sector); + BUG_ON(!page); + + dst = kmap_atomic(page); + memcpy(dst, src, copy); + kunmap_atomic(dst); + } +} + +/* + * Copy n bytes to dst from the brd starting at sector. Does not sleep. + */ +static void copy_from_brd(void *dst, struct brd_device *brd, + sector_t sector, size_t n) +{ + struct page *page; + void *src; + unsigned int offset = (sector & (PAGE_SECTORS-1)) << SECTOR_SHIFT; + size_t copy; + + copy = min_t(size_t, n, PAGE_SIZE - offset); + page = brd_lookup_page(brd, sector); + if (page) { + src = kmap_atomic(page); + memcpy(dst, src + offset, copy); + kunmap_atomic(src); + } else + memset(dst, 0, copy); + + if (copy < n) { + dst += copy; + sector += copy >> SECTOR_SHIFT; + copy = n - copy; + page = brd_lookup_page(brd, sector); + if (page) { + src = kmap_atomic(page); + memcpy(dst, src, copy); + kunmap_atomic(src); + } else + memset(dst, 0, copy); + } +} + +/* + * Process a single bvec of a bio. + */ +static int brd_do_bvec(struct brd_device *brd, struct page *page, + unsigned int len, unsigned int off, blk_opf_t opf, + sector_t sector) +{ + void *mem; + int err = 0; + + if (op_is_write(opf)) { + /* + * Must use NOIO because we don't want to recurse back into the + * block or filesystem layers from page reclaim. + */ + gfp_t gfp = opf & REQ_NOWAIT ? GFP_NOWAIT : GFP_NOIO; + + err = copy_to_brd_setup(brd, sector, len, gfp); + if (err) + goto out; + } + + mem = kmap_atomic(page); + if (!op_is_write(opf)) { + copy_from_brd(mem + off, brd, sector, len); + flush_dcache_page(page); + } else { + flush_dcache_page(page); + copy_to_brd(brd, mem + off, sector, len); + } + kunmap_atomic(mem); + +out: + return err; +} + +static void brd_submit_bio(struct bio *bio) +{ + struct brd_device *brd = bio->bi_bdev->bd_disk->private_data; + sector_t sector = bio->bi_iter.bi_sector; + struct bio_vec bvec; + struct bvec_iter iter; + + bio_for_each_segment(bvec, bio, iter) { + unsigned int len = bvec.bv_len; + int err; + + /* Don't support un-aligned buffer */ + WARN_ON_ONCE((bvec.bv_offset & (SECTOR_SIZE - 1)) || + (len & (SECTOR_SIZE - 1))); + + err = brd_do_bvec(brd, bvec.bv_page, len, bvec.bv_offset, + bio->bi_opf, sector); + if (err) { + if (err == -ENOMEM && bio->bi_opf & REQ_NOWAIT) { + bio_wouldblock_error(bio); + return; + } + bio_io_error(bio); + return; + } + sector += len >> SECTOR_SHIFT; + } + + bio_endio(bio); +} + +static int brd_rw_page(struct block_device *bdev, sector_t sector, + struct page *page, enum req_op op) +{ + struct brd_device *brd = bdev->bd_disk->private_data; + int err; + + if (PageTransHuge(page)) + return -ENOTSUPP; + err = brd_do_bvec(brd, page, PAGE_SIZE, 0, op, sector); + page_endio(page, op_is_write(op), err); + return err; +} + +static const struct block_device_operations brd_fops = { + .owner = THIS_MODULE, + .submit_bio = brd_submit_bio, + .rw_page = brd_rw_page, +}; + +/* + * And now the modules code and kernel interface. + */ +static int rd_nr = CONFIG_BLK_DEV_RAM_COUNT; +module_param(rd_nr, int, 0444); +MODULE_PARM_DESC(rd_nr, "Maximum number of brd devices"); + +unsigned long rd_size = CONFIG_BLK_DEV_RAM_SIZE; +module_param(rd_size, ulong, 0444); +MODULE_PARM_DESC(rd_size, "Size of each RAM disk in kbytes."); + +static int max_part = 1; +module_param(max_part, int, 0444); +MODULE_PARM_DESC(max_part, "Num Minors to reserve between devices"); + +MODULE_LICENSE("GPL"); +MODULE_ALIAS_BLOCKDEV_MAJOR(RAMDISK_MAJOR); +MODULE_ALIAS("rd"); + +#ifndef MODULE +/* Legacy boot options - nonmodular */ +static int __init ramdisk_size(char *str) +{ + rd_size = simple_strtol(str, NULL, 0); + return 1; +} +__setup("ramdisk_size=", ramdisk_size); +#endif + +/* + * The device scheme is derived from loop.c. Keep them in synch where possible + * (should share code eventually). + */ +static LIST_HEAD(brd_devices); +static struct dentry *brd_debugfs_dir; + +static int brd_alloc(int i) +{ + struct brd_device *brd; + struct gendisk *disk; + char buf[DISK_NAME_LEN]; + int err = -ENOMEM; + + list_for_each_entry(brd, &brd_devices, brd_list) + if (brd->brd_number == i) + return -EEXIST; + brd = kzalloc(sizeof(*brd), GFP_KERNEL); + if (!brd) + return -ENOMEM; + brd->brd_number = i; + list_add_tail(&brd->brd_list, &brd_devices); + + spin_lock_init(&brd->brd_lock); + INIT_RADIX_TREE(&brd->brd_pages, GFP_ATOMIC); + + snprintf(buf, DISK_NAME_LEN, "ram%d", i); + if (!IS_ERR_OR_NULL(brd_debugfs_dir)) + debugfs_create_u64(buf, 0444, brd_debugfs_dir, + &brd->brd_nr_pages); + + disk = brd->brd_disk = blk_alloc_disk(NUMA_NO_NODE); + if (!disk) + goto out_free_dev; + + disk->major = RAMDISK_MAJOR; + disk->first_minor = i * max_part; + disk->minors = max_part; + disk->fops = &brd_fops; + disk->private_data = brd; + strscpy(disk->disk_name, buf, DISK_NAME_LEN); + set_capacity(disk, rd_size * 2); + + /* + * This is so fdisk will align partitions on 4k, because of + * direct_access API needing 4k alignment, returning a PFN + * (This is only a problem on very small devices <= 4M, + * otherwise fdisk will align on 1M. Regardless this call + * is harmless) + */ + blk_queue_physical_block_size(disk->queue, PAGE_SIZE); + + /* Tell the block layer that this is not a rotational device */ + blk_queue_flag_set(QUEUE_FLAG_NONROT, disk->queue); + blk_queue_flag_clear(QUEUE_FLAG_ADD_RANDOM, disk->queue); + blk_queue_flag_set(QUEUE_FLAG_NOWAIT, disk->queue); + err = add_disk(disk); + if (err) + goto out_cleanup_disk; + + return 0; + +out_cleanup_disk: + put_disk(disk); +out_free_dev: + list_del(&brd->brd_list); + kfree(brd); + return err; +} + +static void brd_probe(dev_t dev) +{ + brd_alloc(MINOR(dev) / max_part); +} + +static void brd_cleanup(void) +{ + struct brd_device *brd, *next; + + debugfs_remove_recursive(brd_debugfs_dir); + + list_for_each_entry_safe(brd, next, &brd_devices, brd_list) { + del_gendisk(brd->brd_disk); + put_disk(brd->brd_disk); + brd_free_pages(brd); + list_del(&brd->brd_list); + kfree(brd); + } +} + +static inline void brd_check_and_reset_par(void) +{ + if (unlikely(!max_part)) + max_part = 1; + + /* + * make sure 'max_part' can be divided exactly by (1U << MINORBITS), + * otherwise, it is possiable to get same dev_t when adding partitions. + */ + if ((1U << MINORBITS) % max_part != 0) + max_part = 1UL << fls(max_part); + + if (max_part > DISK_MAX_PARTS) { + pr_info("brd: max_part can't be larger than %d, reset max_part = %d.\n", + DISK_MAX_PARTS, DISK_MAX_PARTS); + max_part = DISK_MAX_PARTS; + } +} + +static int __init brd_init(void) +{ + int err, i; + + brd_check_and_reset_par(); + + brd_debugfs_dir = debugfs_create_dir("ramdisk_pages", NULL); + + for (i = 0; i < rd_nr; i++) { + err = brd_alloc(i); + if (err) + goto out_free; + } + + /* + * brd module now has a feature to instantiate underlying device + * structure on-demand, provided that there is an access dev node. + * + * (1) if rd_nr is specified, create that many upfront. else + * it defaults to CONFIG_BLK_DEV_RAM_COUNT + * (2) User can further extend brd devices by create dev node themselves + * and have kernel automatically instantiate actual device + * on-demand. Example: + * mknod /path/devnod_name b 1 X # 1 is the rd major + * fdisk -l /path/devnod_name + * If (X / max_part) was not already created it will be created + * dynamically. + */ + + if (__register_blkdev(RAMDISK_MAJOR, "ramdisk", brd_probe)) { + err = -EIO; + goto out_free; + } + + pr_info("brd: module loaded\n"); + return 0; + +out_free: + brd_cleanup(); + + pr_info("brd: module NOT loaded !!!\n"); + return err; +} + +static void __exit brd_exit(void) +{ + + unregister_blkdev(RAMDISK_MAJOR, "ramdisk"); + brd_cleanup(); + + pr_info("brd: module unloaded\n"); +} + +module_init(brd_init); +module_exit(brd_exit); + |