drivers/block/brd.c - linux - Git at Google

 // 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);
	// 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);