/*
   * 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/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/radix-tree.h>

  #include <linux/fs.h>

  #include <linux/slab.h>

  #ifdef CONFIG_BLK_DEV_RAM_DAX
  #include <linux/pfn_t.h>
  #endif

  #include <linux/uaccess.h>

  
  #define SECTOR_SHIFT		9
  #define PAGE_SECTORS_SHIFT	(PAGE_SHIFT - SECTOR_SHIFT)
  #define PAGE_SECTORS		(1 << PAGE_SECTORS_SHIFT)
  
  /*
   * 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 request_queue	*brd_queue;
  	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;
  };
  
  /*
   * Look up and return a brd's page for a given sector.
   */

  static DEFINE_MUTEX(brd_mutex);

  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;
  }
  
  /*
   * Look up and return a brd's page for a given sector.
   * If one does not exist, allocate an empty page, and insert that. Then
   * return it.
   */
  static struct page *brd_insert_page(struct brd_device *brd, sector_t sector)
  {
  	pgoff_t idx;
  	struct page *page;

  	gfp_t gfp_flags;

  
  	page = brd_lookup_page(brd, sector);
  	if (page)
  		return page;
  
  	/*
  	 * Must use NOIO because we don't want to recurse back into the
  	 * block or filesystem layers from page reclaim.

  	 *

  	 * Cannot support DAX and highmem, because our ->direct_access
  	 * routine for DAX must return memory that is always addressable.
  	 * If DAX was reworked to use pfns and kmap throughout, this

  	 * restriction might be able to be lifted.

  	 */

  	gfp_flags = GFP_NOIO | __GFP_ZERO;

  #ifndef CONFIG_BLK_DEV_RAM_DAX

  	gfp_flags |= __GFP_HIGHMEM;
  #endif

  	page = alloc_page(gfp_flags);

  	if (!page)
  		return NULL;
  
  	if (radix_tree_preload(GFP_NOIO)) {
  		__free_page(page);
  		return NULL;
  	}
  
  	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);
  		BUG_ON(!page);
  		BUG_ON(page->index != idx);

  	}

  	spin_unlock(&brd->brd_lock);
  
  	radix_tree_preload_end();
  
  	return page;
  }
  
  /*
   * 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++;
  
  		/*
  		 * 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)
  {
  	unsigned int offset = (sector & (PAGE_SECTORS-1)) << SECTOR_SHIFT;
  	size_t copy;
  
  	copy = min_t(size_t, n, PAGE_SIZE - offset);
  	if (!brd_insert_page(brd, sector))

  		return -ENOSPC;

  	if (copy < n) {
  		sector += copy >> SECTOR_SHIFT;
  		if (!brd_insert_page(brd, sector))

  			return -ENOSPC;

  	}
  	return 0;
  }
  
  /*
   * 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, bool is_write,

  			sector_t sector)
  {
  	void *mem;
  	int err = 0;

  	if (is_write) {

  		err = copy_to_brd_setup(brd, sector, len);
  		if (err)
  			goto out;
  	}

  	mem = kmap_atomic(page);

  	if (!is_write) {

  		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 blk_qc_t brd_make_request(struct request_queue *q, struct bio *bio)

  {
  	struct block_device *bdev = bio->bi_bdev;
  	struct brd_device *brd = bdev->bd_disk->private_data;

  	struct bio_vec bvec;

  	sector_t sector;

  	struct bvec_iter iter;

  	sector = bio->bi_iter.bi_sector;

  	if (bio_end_sector(bio) > get_capacity(bdev->bd_disk))

  		goto io_error;

  	bio_for_each_segment(bvec, bio, iter) {
  		unsigned int len = bvec.bv_len;

  		int err;

  		err = brd_do_bvec(brd, bvec.bv_page, len, bvec.bv_offset,
  					op_is_write(bio_op(bio)), sector);

  		if (err)

  			goto io_error;

  		sector += len >> SECTOR_SHIFT;
  	}

  	bio_endio(bio);

  	return BLK_QC_T_NONE;

  io_error:
  	bio_io_error(bio);

  	return BLK_QC_T_NONE;

  }

  static int brd_rw_page(struct block_device *bdev, sector_t sector,

  		       struct page *page, bool is_write)

  {
  	struct brd_device *brd = bdev->bd_disk->private_data;

  	int err = brd_do_bvec(brd, page, PAGE_SIZE, 0, is_write, sector);
  	page_endio(page, is_write, err);

  	return err;
  }

  #ifdef CONFIG_BLK_DEV_RAM_DAX

  static long brd_direct_access(struct block_device *bdev, sector_t sector,

  			void **kaddr, pfn_t *pfn, long size)

  {
  	struct brd_device *brd = bdev->bd_disk->private_data;
  	struct page *page;
  
  	if (!brd)
  		return -ENODEV;

  	page = brd_insert_page(brd, sector);
  	if (!page)

  		return -ENOSPC;

  	*kaddr = page_address(page);

  	*pfn = page_to_pfn_t(page);

  	return PAGE_SIZE;

  }

  #else
  #define brd_direct_access NULL

  #endif

  static const struct block_device_operations brd_fops = {

  	.owner =		THIS_MODULE,

  	.rw_page =		brd_rw_page,

  	.direct_access =	brd_direct_access,

  };
  
  /*
   * And now the modules code and kernel interface.
   */

  static int rd_nr = CONFIG_BLK_DEV_RAM_COUNT;

  module_param(rd_nr, int, S_IRUGO);

  MODULE_PARM_DESC(rd_nr, "Maximum number of brd devices");

  unsigned long rd_size = CONFIG_BLK_DEV_RAM_SIZE;
  module_param(rd_size, ulong, S_IRUGO);

  MODULE_PARM_DESC(rd_size, "Size of each RAM disk in kbytes.");

  
  static int max_part = 1;

  module_param(max_part, int, S_IRUGO);

  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 DEFINE_MUTEX(brd_devices_mutex);
  
  static struct brd_device *brd_alloc(int i)
  {
  	struct brd_device *brd;
  	struct gendisk *disk;
  
  	brd = kzalloc(sizeof(*brd), GFP_KERNEL);
  	if (!brd)
  		goto out;
  	brd->brd_number		= i;
  	spin_lock_init(&brd->brd_lock);
  	INIT_RADIX_TREE(&brd->brd_pages, GFP_ATOMIC);
  
  	brd->brd_queue = blk_alloc_queue(GFP_KERNEL);
  	if (!brd->brd_queue)
  		goto out_free_dev;

  	blk_queue_make_request(brd->brd_queue, brd_make_request);

  	blk_queue_max_hw_sectors(brd->brd_queue, 1024);

  	blk_queue_bounce_limit(brd->brd_queue, BLK_BOUNCE_ANY);

  	/* 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(brd->brd_queue, PAGE_SIZE);

  #ifdef CONFIG_BLK_DEV_RAM_DAX
  	queue_flag_set_unlocked(QUEUE_FLAG_DAX, brd->brd_queue);
  #endif

  	disk = brd->brd_disk = alloc_disk(max_part);

  	if (!disk)
  		goto out_free_queue;
  	disk->major		= RAMDISK_MAJOR;

  	disk->first_minor	= i * max_part;

  	disk->fops		= &brd_fops;
  	disk->private_data	= brd;
  	disk->queue		= brd->brd_queue;

  	disk->flags		= GENHD_FL_EXT_DEVT;

  	sprintf(disk->disk_name, "ram%d", i);
  	set_capacity(disk, rd_size * 2);
  
  	return brd;
  
  out_free_queue:
  	blk_cleanup_queue(brd->brd_queue);
  out_free_dev:
  	kfree(brd);
  out:
  	return NULL;
  }
  
  static void brd_free(struct brd_device *brd)
  {
  	put_disk(brd->brd_disk);
  	blk_cleanup_queue(brd->brd_queue);
  	brd_free_pages(brd);
  	kfree(brd);
  }

  static struct brd_device *brd_init_one(int i, bool *new)

  {
  	struct brd_device *brd;

  	*new = false;

  	list_for_each_entry(brd, &brd_devices, brd_list) {
  		if (brd->brd_number == i)
  			goto out;
  	}
  
  	brd = brd_alloc(i);
  	if (brd) {
  		add_disk(brd->brd_disk);
  		list_add_tail(&brd->brd_list, &brd_devices);
  	}

  	*new = true;

  out:
  	return brd;
  }
  
  static void brd_del_one(struct brd_device *brd)
  {
  	list_del(&brd->brd_list);
  	del_gendisk(brd->brd_disk);
  	brd_free(brd);
  }
  
  static struct kobject *brd_probe(dev_t dev, int *part, void *data)
  {
  	struct brd_device *brd;
  	struct kobject *kobj;

  	bool new;

  
  	mutex_lock(&brd_devices_mutex);

  	brd = brd_init_one(MINOR(dev) / max_part, &new);

  	kobj = brd ? get_disk(brd->brd_disk) : NULL;

  	mutex_unlock(&brd_devices_mutex);

  	if (new)
  		*part = 0;

  	return kobj;
  }
  
  static int __init brd_init(void)
  {

  	struct brd_device *brd, *next;

  	int 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.

  	 */

  	if (register_blkdev(RAMDISK_MAJOR, "ramdisk"))
  		return -EIO;

  	if (unlikely(!max_part))
  		max_part = 1;
  
  	for (i = 0; i < rd_nr; i++) {

  		brd = brd_alloc(i);
  		if (!brd)
  			goto out_free;
  		list_add_tail(&brd->brd_list, &brd_devices);
  	}
  
  	/* point of no return */
  
  	list_for_each_entry(brd, &brd_devices, brd_list)
  		add_disk(brd->brd_disk);

  	blk_register_region(MKDEV(RAMDISK_MAJOR, 0), 1UL << MINORBITS,

  				  THIS_MODULE, brd_probe, NULL, NULL);

  	pr_info("brd: module loaded
  ");

  	return 0;
  
  out_free:
  	list_for_each_entry_safe(brd, next, &brd_devices, brd_list) {
  		list_del(&brd->brd_list);
  		brd_free(brd);
  	}

  	unregister_blkdev(RAMDISK_MAJOR, "ramdisk");

  	pr_info("brd: module NOT loaded !!!
  ");

  	return -ENOMEM;
  }
  
  static void __exit brd_exit(void)
  {

  	struct brd_device *brd, *next;

  	list_for_each_entry_safe(brd, next, &brd_devices, brd_list)
  		brd_del_one(brd);

  	blk_unregister_region(MKDEV(RAMDISK_MAJOR, 0), 1UL << MINORBITS);

  	unregister_blkdev(RAMDISK_MAJOR, "ramdisk");

  
  	pr_info("brd: module unloaded
  ");

  }
  
  module_init(brd_init);
  module_exit(brd_exit);