// 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 with reference grabbed for a given sector. */static struct page *brd_lookup_page(struct brd_device *brd, sector_t sector){	struct page *page;	XA_STATE(xas, &brd->brd_pages, sector >> PAGE_SECTORS_SHIFT); 	rcu_read_lock();repeat:	page = xas_load(&xas);	if (xas_retry(&xas, page)) {		xas_reset(&xas);		goto repeat;	} 	if (!page)		goto out; 	if (!get_page_unless_zero(page)) {		xas_reset(&xas);		goto repeat;	} 	if (unlikely(page != xas_reload(&xas))) {		put_page(page);		xas_reset(&xas);		goto repeat;	}out:	rcu_read_unlock(); 	return page;} /* * Insert a new page for a given sector, if one does not already exist. * The returned page will grab reference. */static struct page *brd_insert_page(struct brd_device *brd, sector_t sector,		blk_opf_t opf){	gfp_t gfp = (opf & REQ_NOWAIT) ? GFP_NOWAIT : GFP_NOIO;	struct page *page, *ret; 	page = alloc_page(gfp | __GFP_ZERO | __GFP_HIGHMEM);	if (!page)		return ERR_PTR(-ENOMEM); 	xa_lock(&brd->brd_pages);	ret = __xa_cmpxchg(&brd->brd_pages, sector >> PAGE_SECTORS_SHIFT, NULL,			page, gfp);	if (!ret) {		brd->brd_nr_pages++;		get_page(page);		xa_unlock(&brd->brd_pages);		return page;	} 	if (!xa_is_err(ret)) {		get_page(ret);		xa_unlock(&brd->brd_pages);		put_page(page);		return ret;	} 	xa_unlock(&brd->brd_pages);	put_page(page);	return ERR_PTR(xa_err(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) {		put_page(page);		cond_resched();	} 	xa_destroy(&brd->brd_pages);} /* * Process a single segment.  The segment is capped to not cross page boundaries * in both the bio and the brd backing memory. */static bool brd_rw_bvec(struct brd_device *brd, struct bio *bio){	struct bio_vec bv = bio_iter_iovec(bio, bio->bi_iter);	sector_t sector = bio->bi_iter.bi_sector;	u32 offset = (sector & (PAGE_SECTORS - 1)) << SECTOR_SHIFT;	blk_opf_t opf = bio->bi_opf;	struct page *page;	void *kaddr; 	bv.bv_len = min_t(u32, bv.bv_len, PAGE_SIZE - offset); 	page = brd_lookup_page(brd, sector);	if (!page && op_is_write(opf)) {		page = brd_insert_page(brd, sector, opf);		if (IS_ERR(page))			goto out_error;	} 	kaddr = bvec_kmap_local(&bv);	if (op_is_write(opf)) {		memcpy_to_page(page, offset, kaddr, bv.bv_len);	} else {		if (page)			memcpy_from_page(kaddr, page, offset, bv.bv_len);		else			memset(kaddr, 0, bv.bv_len);	}	kunmap_local(kaddr); 	bio_advance_iter_single(bio, &bio->bi_iter, bv.bv_len);	if (page)		put_page(page);	return true; out_error:	if (PTR_ERR(page) == -ENOMEM && (opf & REQ_NOWAIT))		bio_wouldblock_error(bio);	else		bio_io_error(bio);	return false;} static void brd_do_discard(struct brd_device *brd, sector_t sector, u32 size){	sector_t aligned_sector = round_up(sector, PAGE_SECTORS);	sector_t aligned_end = round_down(			sector + (size >> SECTOR_SHIFT), PAGE_SECTORS);	struct page *page; 	if (aligned_end <= aligned_sector)		return; 	xa_lock(&brd->brd_pages);	while (aligned_sector < aligned_end && aligned_sector < rd_size * 2) {		page = __xa_erase(&brd->brd_pages, aligned_sector >> PAGE_SECTORS_SHIFT);		if (page) {			put_page(page);			brd->brd_nr_pages--;		}		aligned_sector += PAGE_SECTORS;	}	xa_unlock(&brd->brd_pages);} static void brd_submit_bio(struct bio *bio){	struct brd_device *brd = bio->bi_bdev->bd_disk->private_data; 	if (unlikely(op_is_discard(bio->bi_opf))) {		brd_do_discard(brd, bio->bi_iter.bi_sector,				bio->bi_iter.bi_size);		bio_endio(bio);		return;	} 	do {		if (!brd_rw_bvec(brd, bio))			return;	} while (bio->bi_iter.bi_size); 	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){	return kstrtoul(str, 0, &rd_size) == 0;}__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 DEFINE_MUTEX(brd_devices_mutex);static struct dentry *brd_debugfs_dir; static struct brd_device *brd_find_or_alloc_device(int i){	struct brd_device *brd; 	mutex_lock(&brd_devices_mutex);	list_for_each_entry(brd, &brd_devices, brd_list) {		if (brd->brd_number == i) {			mutex_unlock(&brd_devices_mutex);			return ERR_PTR(-EEXIST);		}	} 	brd = kzalloc_obj(*brd);	if (!brd) {		mutex_unlock(&brd_devices_mutex);		return ERR_PTR(-ENOMEM);	}	brd->brd_number	= i;	list_add_tail(&brd->brd_list, &brd_devices);	mutex_unlock(&brd_devices_mutex);	return brd;} static void brd_free_device(struct brd_device *brd){	mutex_lock(&brd_devices_mutex);	list_del(&brd->brd_list);	mutex_unlock(&brd_devices_mutex);	kfree(brd);} 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,	}; 	brd = brd_find_or_alloc_device(i);	if (IS_ERR(brd))		return PTR_ERR(brd); 	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:	brd_free_device(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);		brd_free_device(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 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.	 */ 	brd_check_and_reset_par(); 	brd_debugfs_dir = debugfs_create_dir("ramdisk_pages", NULL); 	if (__register_blkdev(RAMDISK_MAJOR, "ramdisk", brd_probe)) {		err = -EIO;		goto out_free;	} 	for (i = 0; i < rd_nr; i++)		brd_alloc(i); 	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);