// 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/xarray.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 xarray brd_pages of pages that stores
* the pages containing the block device's contents.
*/
struct brd_device {
int brd_number;
struct gendisk *brd_disk;
struct list_head brd_list;
/*
* Backing store of pages. This is the contents of the block device.
*/
struct xarray 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)
{
return xa_load(&brd->brd_pages, sector >> PAGE_SECTORS_SHIFT);
}
/*
* 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 = sector >> PAGE_SECTORS_SHIFT;
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;
xa_lock(&brd->brd_pages);
ret = __xa_insert(&brd->brd_pages, idx, page, gfp);
if (!ret)
brd->brd_nr_pages++;
xa_unlock(&brd->brd_pages);
if (ret < 0) {
__free_page(page);
if (ret == -EBUSY)
ret = 0;
}
return ret;
}
/*
* Free all backing store pages and xarray. This must only be called when
* there are no other users of the device.
*/
static void brd_free_pages(struct brd_device *brd)
{
struct page *page;
pgoff_t idx;
xa_for_each(&brd->brd_pages, idx, page) {
__free_page(page);
cond_resched();
}
xa_destroy(&brd->brd_pages);
}
/*
* 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_do_discard(struct brd_device *brd, sector_t sector, u32 size)
{
sector_t aligned_sector = (sector + PAGE_SECTORS) & ~PAGE_SECTORS;
struct page *page;
size -= (aligned_sector - sector) * SECTOR_SIZE;
xa_lock(&brd->brd_pages);
while (size >= PAGE_SIZE && aligned_sector < rd_size * 2) {
page = __xa_erase(&brd->brd_pages, aligned_sector >> PAGE_SECTORS_SHIFT);
if (page)
__free_page(page);
aligned_sector += PAGE_SECTORS;
size -= PAGE_SIZE;
}
xa_unlock(&brd->brd_pages);
}
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;
if (unlikely(op_is_discard(bio->bi_opf))) {
brd_do_discard(brd, sector, bio->bi_iter.bi_size);
bio_endio(bio);
return;
}
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 const struct block_device_operations brd_fops = {
.owner = THIS_MODULE,
.submit_bio = brd_submit_bio,
};
/*
* 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_DESCRIPTION("Ram backed block device driver");
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;
struct queue_limits lim = {
/*
* 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)
*/
.physical_block_size = PAGE_SIZE,
.max_hw_discard_sectors = UINT_MAX,
.max_discard_segments = 1,
.discard_granularity = PAGE_SIZE,
.features = BLK_FEAT_SYNCHRONOUS |
BLK_FEAT_NOWAIT,
};
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);
xa_init(&brd->brd_pages);
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(&lim, NUMA_NO_NODE);
if (IS_ERR(disk)) {
err = PTR_ERR(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);
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);
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