/*
   * fs/dax.c - Direct Access filesystem code
   * Copyright (c) 2013-2014 Intel Corporation
   * Author: Matthew Wilcox <matthew.r.wilcox@intel.com>
   * Author: Ross Zwisler <ross.zwisler@linux.intel.com>
   *
   * This program is free software; you can redistribute it and/or modify it
   * under the terms and conditions of the GNU General Public License,
   * version 2, as published by the Free Software Foundation.
   *
   * This program is distributed in the hope it will be useful, but WITHOUT
   * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
   * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License for
   * more details.
   */
  
  #include <linux/atomic.h>
  #include <linux/blkdev.h>
  #include <linux/buffer_head.h>

  #include <linux/dax.h>

  #include <linux/fs.h>
  #include <linux/genhd.h>

  #include <linux/highmem.h>
  #include <linux/memcontrol.h>
  #include <linux/mm.h>

  #include <linux/mutex.h>

  #include <linux/pagevec.h>

  #include <linux/pmem.h>

  #include <linux/sched.h>

  #include <linux/uio.h>

  #include <linux/vmstat.h>

  #include <linux/pfn_t.h>

  #include <linux/sizes.h>

  #include <linux/iomap.h>
  #include "internal.h"

  /*
   * We use lowest available bit in exceptional entry for locking, other two
   * bits to determine entry type. In total 3 special bits.
   */
  #define RADIX_DAX_SHIFT	(RADIX_TREE_EXCEPTIONAL_SHIFT + 3)
  #define RADIX_DAX_PTE (1 << (RADIX_TREE_EXCEPTIONAL_SHIFT + 1))
  #define RADIX_DAX_PMD (1 << (RADIX_TREE_EXCEPTIONAL_SHIFT + 2))
  #define RADIX_DAX_TYPE_MASK (RADIX_DAX_PTE | RADIX_DAX_PMD)
  #define RADIX_DAX_TYPE(entry) ((unsigned long)entry & RADIX_DAX_TYPE_MASK)

  #define RADIX_DAX_SECTOR(entry) (((unsigned long)entry >> RADIX_DAX_SHIFT))
  #define RADIX_DAX_ENTRY(sector, pmd) ((void *)((unsigned long)sector << \

  		RADIX_DAX_SHIFT | (pmd ? RADIX_DAX_PMD : RADIX_DAX_PTE) | \
  		RADIX_TREE_EXCEPTIONAL_ENTRY))

  /* We choose 4096 entries - same as per-zone page wait tables */
  #define DAX_WAIT_TABLE_BITS 12
  #define DAX_WAIT_TABLE_ENTRIES (1 << DAX_WAIT_TABLE_BITS)
  
  wait_queue_head_t wait_table[DAX_WAIT_TABLE_ENTRIES];
  
  static int __init init_dax_wait_table(void)
  {
  	int i;
  
  	for (i = 0; i < DAX_WAIT_TABLE_ENTRIES; i++)
  		init_waitqueue_head(wait_table + i);
  	return 0;
  }
  fs_initcall(init_dax_wait_table);
  
  static wait_queue_head_t *dax_entry_waitqueue(struct address_space *mapping,
  					      pgoff_t index)
  {
  	unsigned long hash = hash_long((unsigned long)mapping ^ index,
  				       DAX_WAIT_TABLE_BITS);
  	return wait_table + hash;
  }

  static long dax_map_atomic(struct block_device *bdev, struct blk_dax_ctl *dax)
  {
  	struct request_queue *q = bdev->bd_queue;
  	long rc = -EIO;

  	dax->addr = ERR_PTR(-EIO);

  	if (blk_queue_enter(q, true) != 0)
  		return rc;
  
  	rc = bdev_direct_access(bdev, dax);
  	if (rc < 0) {

  		dax->addr = ERR_PTR(rc);

  		blk_queue_exit(q);
  		return rc;
  	}
  	return rc;
  }
  
  static void dax_unmap_atomic(struct block_device *bdev,
  		const struct blk_dax_ctl *dax)
  {
  	if (IS_ERR(dax->addr))
  		return;
  	blk_queue_exit(bdev->bd_queue);
  }

  struct page *read_dax_sector(struct block_device *bdev, sector_t n)
  {
  	struct page *page = alloc_pages(GFP_KERNEL, 0);
  	struct blk_dax_ctl dax = {
  		.size = PAGE_SIZE,
  		.sector = n & ~((((int) PAGE_SIZE) / 512) - 1),
  	};
  	long rc;
  
  	if (!page)
  		return ERR_PTR(-ENOMEM);
  
  	rc = dax_map_atomic(bdev, &dax);
  	if (rc < 0)
  		return ERR_PTR(rc);
  	memcpy_from_pmem(page_address(page), dax.addr, PAGE_SIZE);
  	dax_unmap_atomic(bdev, &dax);
  	return page;
  }

  static bool buffer_written(struct buffer_head *bh)
  {
  	return buffer_mapped(bh) && !buffer_unwritten(bh);
  }
  
  /*
   * When ext4 encounters a hole, it returns without modifying the buffer_head
   * which means that we can't trust b_size.  To cope with this, we set b_state
   * to 0 before calling get_block and, if any bit is set, we know we can trust
   * b_size.  Unfortunate, really, since ext4 knows precisely how long a hole is
   * and would save us time calling get_block repeatedly.
   */
  static bool buffer_size_valid(struct buffer_head *bh)
  {
  	return bh->b_state != 0;
  }

  
  static sector_t to_sector(const struct buffer_head *bh,
  		const struct inode *inode)
  {
  	sector_t sector = bh->b_blocknr << (inode->i_blkbits - 9);
  
  	return sector;
  }

  static ssize_t dax_io(struct inode *inode, struct iov_iter *iter,
  		      loff_t start, loff_t end, get_block_t get_block,
  		      struct buffer_head *bh)

  {

  	loff_t pos = start, max = start, bh_max = start;

  	bool hole = false;

  	struct block_device *bdev = NULL;
  	int rw = iov_iter_rw(iter), rc;
  	long map_len = 0;
  	struct blk_dax_ctl dax = {

  		.addr = ERR_PTR(-EIO),

  	};

  	unsigned blkbits = inode->i_blkbits;
  	sector_t file_blks = (i_size_read(inode) + (1 << blkbits) - 1)
  								>> blkbits;

  
  	if (rw == READ)

  		end = min(end, i_size_read(inode));
  
  	while (pos < end) {

  		size_t len;

  		if (pos == max) {

  			long page = pos >> PAGE_SHIFT;
  			sector_t block = page << (PAGE_SHIFT - blkbits);

  			unsigned first = pos - (block << blkbits);
  			long size;
  
  			if (pos == bh_max) {
  				bh->b_size = PAGE_ALIGN(end - pos);
  				bh->b_state = 0;

  				rc = get_block(inode, block, bh, rw == WRITE);
  				if (rc)

  					break;
  				if (!buffer_size_valid(bh))
  					bh->b_size = 1 << blkbits;
  				bh_max = pos - first + bh->b_size;

  				bdev = bh->b_bdev;

  				/*
  				 * We allow uninitialized buffers for writes
  				 * beyond EOF as those cannot race with faults
  				 */
  				WARN_ON_ONCE(
  					(buffer_new(bh) && block < file_blks) ||
  					(rw == WRITE && buffer_unwritten(bh)));

  			} else {
  				unsigned done = bh->b_size -
  						(bh_max - (pos - first));
  				bh->b_blocknr += done >> blkbits;
  				bh->b_size -= done;
  			}

  			hole = rw == READ && !buffer_written(bh);

  			if (hole) {

  				size = bh->b_size - first;
  			} else {

  				dax_unmap_atomic(bdev, &dax);
  				dax.sector = to_sector(bh, inode);
  				dax.size = bh->b_size;
  				map_len = dax_map_atomic(bdev, &dax);
  				if (map_len < 0) {
  					rc = map_len;

  					break;

  				}

  				dax.addr += first;
  				size = map_len - first;

  			}

  			/*
  			 * pos + size is one past the last offset for IO,
  			 * so pos + size can overflow loff_t at extreme offsets.
  			 * Cast to u64 to catch this and get the true minimum.
  			 */
  			max = min_t(u64, pos + size, end);

  		}

  		if (iov_iter_rw(iter) == WRITE) {

  			len = copy_from_iter_pmem(dax.addr, max - pos, iter);

  		} else if (!hole)

  			len = copy_to_iter((void __force *) dax.addr, max - pos,

  					iter);

  		else
  			len = iov_iter_zero(max - pos, iter);

  		if (!len) {

  			rc = -EFAULT;

  			break;

  		}

  
  		pos += len;

  		if (!IS_ERR(dax.addr))
  			dax.addr += len;

  	}

  	dax_unmap_atomic(bdev, &dax);

  	return (pos == start) ? rc : pos - start;

  }
  
  /**
   * dax_do_io - Perform I/O to a DAX file

   * @iocb: The control block for this I/O
   * @inode: The file which the I/O is directed at
   * @iter: The addresses to do I/O from or to

   * @get_block: The filesystem method used to translate file offsets to blocks
   * @end_io: A filesystem callback for I/O completion
   * @flags: See below
   *
   * This function uses the same locking scheme as do_blockdev_direct_IO:
   * If @flags has DIO_LOCKING set, we assume that the i_mutex is held by the
   * caller for writes.  For reads, we take and release the i_mutex ourselves.
   * If DIO_LOCKING is not set, the filesystem takes care of its own locking.
   * As with do_blockdev_direct_IO(), we increment i_dio_count while the I/O
   * is in progress.
   */

  ssize_t dax_do_io(struct kiocb *iocb, struct inode *inode,

  		  struct iov_iter *iter, get_block_t get_block,

  		  dio_iodone_t end_io, int flags)

  {
  	struct buffer_head bh;
  	ssize_t retval = -EINVAL;

  	loff_t pos = iocb->ki_pos;

  	loff_t end = pos + iov_iter_count(iter);
  
  	memset(&bh, 0, sizeof(bh));

  	bh.b_bdev = inode->i_sb->s_bdev;

  	if ((flags & DIO_LOCKING) && iov_iter_rw(iter) == READ)

  		inode_lock(inode);

  
  	/* Protects against truncate */

  	if (!(flags & DIO_SKIP_DIO_COUNT))
  		inode_dio_begin(inode);

  	retval = dax_io(inode, iter, pos, end, get_block, &bh);

  	if ((flags & DIO_LOCKING) && iov_iter_rw(iter) == READ)

  		inode_unlock(inode);

  	if (end_io) {
  		int err;
  
  		err = end_io(iocb, pos, retval, bh.b_private);
  		if (err)
  			retval = err;
  	}

  	if (!(flags & DIO_SKIP_DIO_COUNT))
  		inode_dio_end(inode);

  	return retval;
  }
  EXPORT_SYMBOL_GPL(dax_do_io);

  
  /*

   * DAX radix tree locking
   */
  struct exceptional_entry_key {
  	struct address_space *mapping;
  	unsigned long index;
  };
  
  struct wait_exceptional_entry_queue {
  	wait_queue_t wait;
  	struct exceptional_entry_key key;
  };
  
  static int wake_exceptional_entry_func(wait_queue_t *wait, unsigned int mode,
  				       int sync, void *keyp)
  {
  	struct exceptional_entry_key *key = keyp;
  	struct wait_exceptional_entry_queue *ewait =
  		container_of(wait, struct wait_exceptional_entry_queue, wait);
  
  	if (key->mapping != ewait->key.mapping ||
  	    key->index != ewait->key.index)
  		return 0;
  	return autoremove_wake_function(wait, mode, sync, NULL);
  }
  
  /*
   * Check whether the given slot is locked. The function must be called with
   * mapping->tree_lock held
   */
  static inline int slot_locked(struct address_space *mapping, void **slot)
  {
  	unsigned long entry = (unsigned long)
  		radix_tree_deref_slot_protected(slot, &mapping->tree_lock);
  	return entry & RADIX_DAX_ENTRY_LOCK;
  }
  
  /*
   * Mark the given slot is locked. The function must be called with
   * mapping->tree_lock held
   */
  static inline void *lock_slot(struct address_space *mapping, void **slot)
  {
  	unsigned long entry = (unsigned long)
  		radix_tree_deref_slot_protected(slot, &mapping->tree_lock);
  
  	entry |= RADIX_DAX_ENTRY_LOCK;
  	radix_tree_replace_slot(slot, (void *)entry);
  	return (void *)entry;
  }
  
  /*
   * Mark the given slot is unlocked. The function must be called with
   * mapping->tree_lock held
   */
  static inline void *unlock_slot(struct address_space *mapping, void **slot)
  {
  	unsigned long entry = (unsigned long)
  		radix_tree_deref_slot_protected(slot, &mapping->tree_lock);
  
  	entry &= ~(unsigned long)RADIX_DAX_ENTRY_LOCK;
  	radix_tree_replace_slot(slot, (void *)entry);
  	return (void *)entry;
  }
  
  /*
   * Lookup entry in radix tree, wait for it to become unlocked if it is
   * exceptional entry and return it. The caller must call
   * put_unlocked_mapping_entry() when he decided not to lock the entry or
   * put_locked_mapping_entry() when he locked the entry and now wants to
   * unlock it.
   *
   * The function must be called with mapping->tree_lock held.
   */
  static void *get_unlocked_mapping_entry(struct address_space *mapping,
  					pgoff_t index, void ***slotp)
  {
  	void *ret, **slot;
  	struct wait_exceptional_entry_queue ewait;
  	wait_queue_head_t *wq = dax_entry_waitqueue(mapping, index);
  
  	init_wait(&ewait.wait);
  	ewait.wait.func = wake_exceptional_entry_func;
  	ewait.key.mapping = mapping;
  	ewait.key.index = index;
  
  	for (;;) {
  		ret = __radix_tree_lookup(&mapping->page_tree, index, NULL,
  					  &slot);
  		if (!ret || !radix_tree_exceptional_entry(ret) ||
  		    !slot_locked(mapping, slot)) {
  			if (slotp)
  				*slotp = slot;
  			return ret;
  		}
  		prepare_to_wait_exclusive(wq, &ewait.wait,
  					  TASK_UNINTERRUPTIBLE);
  		spin_unlock_irq(&mapping->tree_lock);
  		schedule();
  		finish_wait(wq, &ewait.wait);
  		spin_lock_irq(&mapping->tree_lock);
  	}
  }
  
  /*
   * Find radix tree entry at given index. If it points to a page, return with
   * the page locked. If it points to the exceptional entry, return with the
   * radix tree entry locked. If the radix tree doesn't contain given index,
   * create empty exceptional entry for the index and return with it locked.
   *
   * Note: Unlike filemap_fault() we don't honor FAULT_FLAG_RETRY flags. For
   * persistent memory the benefit is doubtful. We can add that later if we can
   * show it helps.
   */
  static void *grab_mapping_entry(struct address_space *mapping, pgoff_t index)
  {
  	void *ret, **slot;
  
  restart:
  	spin_lock_irq(&mapping->tree_lock);
  	ret = get_unlocked_mapping_entry(mapping, index, &slot);
  	/* No entry for given index? Make sure radix tree is big enough. */
  	if (!ret) {
  		int err;
  
  		spin_unlock_irq(&mapping->tree_lock);
  		err = radix_tree_preload(
  				mapping_gfp_mask(mapping) & ~__GFP_HIGHMEM);
  		if (err)
  			return ERR_PTR(err);
  		ret = (void *)(RADIX_TREE_EXCEPTIONAL_ENTRY |
  			       RADIX_DAX_ENTRY_LOCK);
  		spin_lock_irq(&mapping->tree_lock);
  		err = radix_tree_insert(&mapping->page_tree, index, ret);
  		radix_tree_preload_end();
  		if (err) {
  			spin_unlock_irq(&mapping->tree_lock);
  			/* Someone already created the entry? */
  			if (err == -EEXIST)
  				goto restart;
  			return ERR_PTR(err);
  		}
  		/* Good, we have inserted empty locked entry into the tree. */
  		mapping->nrexceptional++;
  		spin_unlock_irq(&mapping->tree_lock);
  		return ret;
  	}
  	/* Normal page in radix tree? */
  	if (!radix_tree_exceptional_entry(ret)) {
  		struct page *page = ret;
  
  		get_page(page);
  		spin_unlock_irq(&mapping->tree_lock);
  		lock_page(page);
  		/* Page got truncated? Retry... */
  		if (unlikely(page->mapping != mapping)) {
  			unlock_page(page);
  			put_page(page);
  			goto restart;
  		}
  		return page;
  	}
  	ret = lock_slot(mapping, slot);
  	spin_unlock_irq(&mapping->tree_lock);
  	return ret;
  }
  
  void dax_wake_mapping_entry_waiter(struct address_space *mapping,
  				   pgoff_t index, bool wake_all)
  {
  	wait_queue_head_t *wq = dax_entry_waitqueue(mapping, index);
  
  	/*
  	 * Checking for locked entry and prepare_to_wait_exclusive() happens
  	 * under mapping->tree_lock, ditto for entry handling in our callers.
  	 * So at this point all tasks that could have seen our entry locked
  	 * must be in the waitqueue and the following check will see them.
  	 */
  	if (waitqueue_active(wq)) {
  		struct exceptional_entry_key key;
  
  		key.mapping = mapping;
  		key.index = index;
  		__wake_up(wq, TASK_NORMAL, wake_all ? 0 : 1, &key);
  	}
  }

  void dax_unlock_mapping_entry(struct address_space *mapping, pgoff_t index)

  {
  	void *ret, **slot;
  
  	spin_lock_irq(&mapping->tree_lock);
  	ret = __radix_tree_lookup(&mapping->page_tree, index, NULL, &slot);
  	if (WARN_ON_ONCE(!ret || !radix_tree_exceptional_entry(ret) ||
  			 !slot_locked(mapping, slot))) {
  		spin_unlock_irq(&mapping->tree_lock);
  		return;
  	}
  	unlock_slot(mapping, slot);
  	spin_unlock_irq(&mapping->tree_lock);
  	dax_wake_mapping_entry_waiter(mapping, index, false);
  }
  
  static void put_locked_mapping_entry(struct address_space *mapping,
  				     pgoff_t index, void *entry)
  {
  	if (!radix_tree_exceptional_entry(entry)) {
  		unlock_page(entry);
  		put_page(entry);
  	} else {

  		dax_unlock_mapping_entry(mapping, index);

  	}
  }
  
  /*
   * Called when we are done with radix tree entry we looked up via
   * get_unlocked_mapping_entry() and which we didn't lock in the end.
   */
  static void put_unlocked_mapping_entry(struct address_space *mapping,
  				       pgoff_t index, void *entry)
  {
  	if (!radix_tree_exceptional_entry(entry))
  		return;
  
  	/* We have to wake up next waiter for the radix tree entry lock */
  	dax_wake_mapping_entry_waiter(mapping, index, false);
  }
  
  /*
   * Delete exceptional DAX entry at @index from @mapping. Wait for radix tree
   * entry to get unlocked before deleting it.
   */
  int dax_delete_mapping_entry(struct address_space *mapping, pgoff_t index)
  {
  	void *entry;
  
  	spin_lock_irq(&mapping->tree_lock);
  	entry = get_unlocked_mapping_entry(mapping, index, NULL);
  	/*
  	 * This gets called from truncate / punch_hole path. As such, the caller
  	 * must hold locks protecting against concurrent modifications of the
  	 * radix tree (usually fs-private i_mmap_sem for writing). Since the
  	 * caller has seen exceptional entry for this index, we better find it
  	 * at that index as well...
  	 */
  	if (WARN_ON_ONCE(!entry || !radix_tree_exceptional_entry(entry))) {
  		spin_unlock_irq(&mapping->tree_lock);
  		return 0;
  	}
  	radix_tree_delete(&mapping->page_tree, index);
  	mapping->nrexceptional--;
  	spin_unlock_irq(&mapping->tree_lock);
  	dax_wake_mapping_entry_waiter(mapping, index, true);
  
  	return 1;
  }
  
  /*

   * The user has performed a load from a hole in the file.  Allocating
   * a new page in the file would cause excessive storage usage for
   * workloads with sparse files.  We allocate a page cache page instead.
   * We'll kick it out of the page cache if it's ever written to,
   * otherwise it will simply fall out of the page cache under memory
   * pressure without ever having been dirtied.
   */

  static int dax_load_hole(struct address_space *mapping, void *entry,
  			 struct vm_fault *vmf)

  {

  	struct page *page;

  	/* Hole page already exists? Return it...  */
  	if (!radix_tree_exceptional_entry(entry)) {
  		vmf->page = entry;
  		return VM_FAULT_LOCKED;
  	}

  	/* This will replace locked radix tree entry with a hole page */
  	page = find_or_create_page(mapping, vmf->pgoff,
  				   vmf->gfp_mask | __GFP_ZERO);
  	if (!page) {
  		put_locked_mapping_entry(mapping, vmf->pgoff, entry);
  		return VM_FAULT_OOM;
  	}

  	vmf->page = page;
  	return VM_FAULT_LOCKED;
  }

  static int copy_user_dax(struct block_device *bdev, sector_t sector, size_t size,
  		struct page *to, unsigned long vaddr)

  {

  	struct blk_dax_ctl dax = {

  		.sector = sector,
  		.size = size,

  	};

  	void *vto;

  	if (dax_map_atomic(bdev, &dax) < 0)
  		return PTR_ERR(dax.addr);

  	vto = kmap_atomic(to);

  	copy_user_page(vto, (void __force *)dax.addr, vaddr, to);

  	kunmap_atomic(vto);

  	dax_unmap_atomic(bdev, &dax);

  	return 0;
  }

  #define DAX_PMD_INDEX(page_index) (page_index & (PMD_MASK >> PAGE_SHIFT))

  static void *dax_insert_mapping_entry(struct address_space *mapping,
  				      struct vm_fault *vmf,
  				      void *entry, sector_t sector)

  {
  	struct radix_tree_root *page_tree = &mapping->page_tree;

  	int error = 0;
  	bool hole_fill = false;
  	void *new_entry;
  	pgoff_t index = vmf->pgoff;

  	if (vmf->flags & FAULT_FLAG_WRITE)

  		__mark_inode_dirty(mapping->host, I_DIRTY_PAGES);

  	/* Replacing hole page with block mapping? */
  	if (!radix_tree_exceptional_entry(entry)) {
  		hole_fill = true;
  		/*
  		 * Unmap the page now before we remove it from page cache below.
  		 * The page is locked so it cannot be faulted in again.
  		 */
  		unmap_mapping_range(mapping, vmf->pgoff << PAGE_SHIFT,
  				    PAGE_SIZE, 0);
  		error = radix_tree_preload(vmf->gfp_mask & ~__GFP_HIGHMEM);
  		if (error)
  			return ERR_PTR(error);

  	}

  	spin_lock_irq(&mapping->tree_lock);
  	new_entry = (void *)((unsigned long)RADIX_DAX_ENTRY(sector, false) |
  		       RADIX_DAX_ENTRY_LOCK);
  	if (hole_fill) {
  		__delete_from_page_cache(entry, NULL);
  		/* Drop pagecache reference */
  		put_page(entry);
  		error = radix_tree_insert(page_tree, index, new_entry);
  		if (error) {
  			new_entry = ERR_PTR(error);

  			goto unlock;
  		}

  		mapping->nrexceptional++;
  	} else {
  		void **slot;
  		void *ret;

  		ret = __radix_tree_lookup(page_tree, index, NULL, &slot);
  		WARN_ON_ONCE(ret != entry);
  		radix_tree_replace_slot(slot, new_entry);

  	}

  	if (vmf->flags & FAULT_FLAG_WRITE)

  		radix_tree_tag_set(page_tree, index, PAGECACHE_TAG_DIRTY);
   unlock:
  	spin_unlock_irq(&mapping->tree_lock);

  	if (hole_fill) {
  		radix_tree_preload_end();
  		/*
  		 * We don't need hole page anymore, it has been replaced with
  		 * locked radix tree entry now.
  		 */
  		if (mapping->a_ops->freepage)
  			mapping->a_ops->freepage(entry);
  		unlock_page(entry);
  		put_page(entry);
  	}
  	return new_entry;

  }
  
  static int dax_writeback_one(struct block_device *bdev,
  		struct address_space *mapping, pgoff_t index, void *entry)
  {
  	struct radix_tree_root *page_tree = &mapping->page_tree;
  	int type = RADIX_DAX_TYPE(entry);
  	struct radix_tree_node *node;
  	struct blk_dax_ctl dax;
  	void **slot;
  	int ret = 0;
  
  	spin_lock_irq(&mapping->tree_lock);
  	/*
  	 * Regular page slots are stabilized by the page lock even
  	 * without the tree itself locked.  These unlocked entries
  	 * need verification under the tree lock.
  	 */
  	if (!__radix_tree_lookup(page_tree, index, &node, &slot))
  		goto unlock;
  	if (*slot != entry)
  		goto unlock;
  
  	/* another fsync thread may have already written back this entry */
  	if (!radix_tree_tag_get(page_tree, index, PAGECACHE_TAG_TOWRITE))
  		goto unlock;
  
  	if (WARN_ON_ONCE(type != RADIX_DAX_PTE && type != RADIX_DAX_PMD)) {
  		ret = -EIO;
  		goto unlock;
  	}
  
  	dax.sector = RADIX_DAX_SECTOR(entry);
  	dax.size = (type == RADIX_DAX_PMD ? PMD_SIZE : PAGE_SIZE);
  	spin_unlock_irq(&mapping->tree_lock);
  
  	/*
  	 * We cannot hold tree_lock while calling dax_map_atomic() because it
  	 * eventually calls cond_resched().
  	 */
  	ret = dax_map_atomic(bdev, &dax);
  	if (ret < 0)
  		return ret;
  
  	if (WARN_ON_ONCE(ret < dax.size)) {
  		ret = -EIO;
  		goto unmap;
  	}
  
  	wb_cache_pmem(dax.addr, dax.size);
  
  	spin_lock_irq(&mapping->tree_lock);
  	radix_tree_tag_clear(page_tree, index, PAGECACHE_TAG_TOWRITE);
  	spin_unlock_irq(&mapping->tree_lock);
   unmap:
  	dax_unmap_atomic(bdev, &dax);
  	return ret;
  
   unlock:
  	spin_unlock_irq(&mapping->tree_lock);
  	return ret;
  }
  
  /*
   * Flush the mapping to the persistent domain within the byte range of [start,
   * end]. This is required by data integrity operations to ensure file data is
   * on persistent storage prior to completion of the operation.
   */

  int dax_writeback_mapping_range(struct address_space *mapping,
  		struct block_device *bdev, struct writeback_control *wbc)

  {
  	struct inode *inode = mapping->host;

  	pgoff_t start_index, end_index, pmd_index;
  	pgoff_t indices[PAGEVEC_SIZE];
  	struct pagevec pvec;
  	bool done = false;
  	int i, ret = 0;
  	void *entry;
  
  	if (WARN_ON_ONCE(inode->i_blkbits != PAGE_SHIFT))
  		return -EIO;

  	if (!mapping->nrexceptional || wbc->sync_mode != WB_SYNC_ALL)
  		return 0;

  	start_index = wbc->range_start >> PAGE_SHIFT;
  	end_index = wbc->range_end >> PAGE_SHIFT;

  	pmd_index = DAX_PMD_INDEX(start_index);
  
  	rcu_read_lock();
  	entry = radix_tree_lookup(&mapping->page_tree, pmd_index);
  	rcu_read_unlock();
  
  	/* see if the start of our range is covered by a PMD entry */
  	if (entry && RADIX_DAX_TYPE(entry) == RADIX_DAX_PMD)
  		start_index = pmd_index;
  
  	tag_pages_for_writeback(mapping, start_index, end_index);
  
  	pagevec_init(&pvec, 0);
  	while (!done) {
  		pvec.nr = find_get_entries_tag(mapping, start_index,
  				PAGECACHE_TAG_TOWRITE, PAGEVEC_SIZE,
  				pvec.pages, indices);
  
  		if (pvec.nr == 0)
  			break;
  
  		for (i = 0; i < pvec.nr; i++) {
  			if (indices[i] > end_index) {
  				done = true;
  				break;
  			}
  
  			ret = dax_writeback_one(bdev, mapping, indices[i],
  					pvec.pages[i]);
  			if (ret < 0)
  				return ret;
  		}
  	}

  	return 0;
  }
  EXPORT_SYMBOL_GPL(dax_writeback_mapping_range);

  static int dax_insert_mapping(struct address_space *mapping,

  		struct block_device *bdev, sector_t sector, size_t size,
  		void **entryp, struct vm_area_struct *vma, struct vm_fault *vmf)

  {

  	unsigned long vaddr = (unsigned long)vmf->virtual_address;

  	struct blk_dax_ctl dax = {

  		.sector = sector,
  		.size = size,

  	};

  	void *ret;
  	void *entry = *entryp;

  	if (dax_map_atomic(bdev, &dax) < 0)
  		return PTR_ERR(dax.addr);

  	dax_unmap_atomic(bdev, &dax);

  	ret = dax_insert_mapping_entry(mapping, vmf, entry, dax.sector);

  	if (IS_ERR(ret))
  		return PTR_ERR(ret);

  	*entryp = ret;

  	return vm_insert_mixed(vma, vaddr, dax.pfn);

  }

  /**

   * dax_fault - handle a page fault on a DAX file

   * @vma: The virtual memory area where the fault occurred
   * @vmf: The description of the fault
   * @get_block: The filesystem method used to translate file offsets to blocks
   *
   * When a page fault occurs, filesystems may call this helper in their

   * fault handler for DAX files. dax_fault() assumes the caller has done all

   * the necessary locking for the page fault to proceed successfully.
   */

  int dax_fault(struct vm_area_struct *vma, struct vm_fault *vmf,

  			get_block_t get_block)

  {
  	struct file *file = vma->vm_file;
  	struct address_space *mapping = file->f_mapping;
  	struct inode *inode = mapping->host;

  	void *entry;

  	struct buffer_head bh;
  	unsigned long vaddr = (unsigned long)vmf->virtual_address;
  	unsigned blkbits = inode->i_blkbits;
  	sector_t block;
  	pgoff_t size;
  	int error;
  	int major = 0;

  	/*
  	 * Check whether offset isn't beyond end of file now. Caller is supposed
  	 * to hold locks serializing us with truncate / punch hole so this is
  	 * a reliable test.
  	 */

  	size = (i_size_read(inode) + PAGE_SIZE - 1) >> PAGE_SHIFT;
  	if (vmf->pgoff >= size)
  		return VM_FAULT_SIGBUS;
  
  	memset(&bh, 0, sizeof(bh));
  	block = (sector_t)vmf->pgoff << (PAGE_SHIFT - blkbits);

  	bh.b_bdev = inode->i_sb->s_bdev;

  	bh.b_size = PAGE_SIZE;

  	entry = grab_mapping_entry(mapping, vmf->pgoff);
  	if (IS_ERR(entry)) {
  		error = PTR_ERR(entry);
  		goto out;

  	}
  
  	error = get_block(inode, block, &bh, 0);
  	if (!error && (bh.b_size < PAGE_SIZE))
  		error = -EIO;		/* fs corruption? */
  	if (error)

  		goto unlock_entry;

  
  	if (vmf->cow_page) {
  		struct page *new_page = vmf->cow_page;
  		if (buffer_written(&bh))

  			error = copy_user_dax(bh.b_bdev, to_sector(&bh, inode),
  					bh.b_size, new_page, vaddr);

  		else
  			clear_user_highpage(new_page, vaddr);
  		if (error)

  			goto unlock_entry;
  		if (!radix_tree_exceptional_entry(entry)) {
  			vmf->page = entry;

  			return VM_FAULT_LOCKED;

  		}

  		vmf->entry = entry;
  		return VM_FAULT_DAX_LOCKED;

  	}

  	if (!buffer_mapped(&bh)) {

  		if (vmf->flags & FAULT_FLAG_WRITE) {
  			error = get_block(inode, block, &bh, 1);
  			count_vm_event(PGMAJFAULT);
  			mem_cgroup_count_vm_event(vma->vm_mm, PGMAJFAULT);
  			major = VM_FAULT_MAJOR;
  			if (!error && (bh.b_size < PAGE_SIZE))
  				error = -EIO;
  			if (error)

  				goto unlock_entry;

  		} else {

  			return dax_load_hole(mapping, entry, vmf);

  		}
  	}

  	/* Filesystem should not return unwritten buffers to us! */

  	WARN_ON_ONCE(buffer_unwritten(&bh) || buffer_new(&bh));

  	error = dax_insert_mapping(mapping, bh.b_bdev, to_sector(&bh, inode),
  			bh.b_size, &entry, vma, vmf);

   unlock_entry:
  	put_locked_mapping_entry(mapping, vmf->pgoff, entry);

   out:
  	if (error == -ENOMEM)
  		return VM_FAULT_OOM | major;
  	/* -EBUSY is fine, somebody else faulted on the same PTE */
  	if ((error < 0) && (error != -EBUSY))
  		return VM_FAULT_SIGBUS | major;
  	return VM_FAULT_NOPAGE | major;

  }

  EXPORT_SYMBOL_GPL(dax_fault);

  #if defined(CONFIG_TRANSPARENT_HUGEPAGE)

  /*
   * The 'colour' (ie low bits) within a PMD of a page offset.  This comes up
   * more often than one might expect in the below function.
   */
  #define PG_PMD_COLOUR	((PMD_SIZE >> PAGE_SHIFT) - 1)

  static void __dax_dbg(struct buffer_head *bh, unsigned long address,
  		const char *reason, const char *fn)
  {
  	if (bh) {
  		char bname[BDEVNAME_SIZE];
  		bdevname(bh->b_bdev, bname);
  		pr_debug("%s: %s addr: %lx dev %s state %lx start %lld "
  			"length %zd fallback: %s
  ", fn, current->comm,
  			address, bname, bh->b_state, (u64)bh->b_blocknr,
  			bh->b_size, reason);
  	} else {
  		pr_debug("%s: %s addr: %lx fallback: %s
  ", fn,
  			current->comm, address, reason);
  	}
  }
  
  #define dax_pmd_dbg(bh, address, reason)	__dax_dbg(bh, address, reason, "dax_pmd")

  /**
   * dax_pmd_fault - handle a PMD fault on a DAX file
   * @vma: The virtual memory area where the fault occurred
   * @vmf: The description of the fault
   * @get_block: The filesystem method used to translate file offsets to blocks
   *
   * When a page fault occurs, filesystems may call this helper in their
   * pmd_fault handler for DAX files.
   */
  int dax_pmd_fault(struct vm_area_struct *vma, unsigned long address,

  		pmd_t *pmd, unsigned int flags, get_block_t get_block)

  {
  	struct file *file = vma->vm_file;
  	struct address_space *mapping = file->f_mapping;
  	struct inode *inode = mapping->host;
  	struct buffer_head bh;
  	unsigned blkbits = inode->i_blkbits;
  	unsigned long pmd_addr = address & PMD_MASK;
  	bool write = flags & FAULT_FLAG_WRITE;

  	struct block_device *bdev;

  	pgoff_t size, pgoff;

  	sector_t block;

  	int result = 0;

  	bool alloc = false;

  	/* dax pmd mappings require pfn_t_devmap() */

  	if (!IS_ENABLED(CONFIG_FS_DAX_PMD))
  		return VM_FAULT_FALLBACK;

  	/* Fall back to PTEs if we're going to COW */

  	if (write && !(vma->vm_flags & VM_SHARED)) {
  		split_huge_pmd(vma, pmd, address);

  		dax_pmd_dbg(NULL, address, "cow write");

  		return VM_FAULT_FALLBACK;

  	}

  	/* If the PMD would extend outside the VMA */

  	if (pmd_addr < vma->vm_start) {
  		dax_pmd_dbg(NULL, address, "vma start unaligned");

  		return VM_FAULT_FALLBACK;

  	}
  	if ((pmd_addr + PMD_SIZE) > vma->vm_end) {
  		dax_pmd_dbg(NULL, address, "vma end unaligned");

  		return VM_FAULT_FALLBACK;

  	}

  	pgoff = linear_page_index(vma, pmd_addr);

  	size = (i_size_read(inode) + PAGE_SIZE - 1) >> PAGE_SHIFT;
  	if (pgoff >= size)
  		return VM_FAULT_SIGBUS;
  	/* If the PMD would cover blocks out of the file */

  	if ((pgoff | PG_PMD_COLOUR) >= size) {
  		dax_pmd_dbg(NULL, address,
  				"offset + huge page size > file size");

  		return VM_FAULT_FALLBACK;

  	}

  
  	memset(&bh, 0, sizeof(bh));

  	bh.b_bdev = inode->i_sb->s_bdev;

  	block = (sector_t)pgoff << (PAGE_SHIFT - blkbits);
  
  	bh.b_size = PMD_SIZE;

  
  	if (get_block(inode, block, &bh, 0) != 0)

  		return VM_FAULT_SIGBUS;

  
  	if (!buffer_mapped(&bh) && write) {
  		if (get_block(inode, block, &bh, 1) != 0)
  			return VM_FAULT_SIGBUS;
  		alloc = true;

  		WARN_ON_ONCE(buffer_unwritten(&bh) || buffer_new(&bh));

  	}

  	bdev = bh.b_bdev;

  
  	/*
  	 * If the filesystem isn't willing to tell us the length of a hole,
  	 * just fall back to PTEs.  Calling get_block 512 times in a loop
  	 * would be silly.
  	 */

  	if (!buffer_size_valid(&bh) || bh.b_size < PMD_SIZE) {
  		dax_pmd_dbg(&bh, address, "allocated block too small");

  		return VM_FAULT_FALLBACK;
  	}
  
  	/*
  	 * If we allocated new storage, make sure no process has any
  	 * zero pages covering this hole
  	 */
  	if (alloc) {
  		loff_t lstart = pgoff << PAGE_SHIFT;
  		loff_t lend = lstart + PMD_SIZE - 1; /* inclusive */
  
  		truncate_pagecache_range(inode, lstart, lend);

  	}

  	if (!write && !buffer_mapped(&bh)) {

  		spinlock_t *ptl;

  		pmd_t entry;

  		struct page *zero_page = mm_get_huge_zero_page(vma->vm_mm);

  		if (unlikely(!zero_page)) {
  			dax_pmd_dbg(&bh, address, "no zero page");

  			goto fallback;

  		}

  		ptl = pmd_lock(vma->vm_mm, pmd);
  		if (!pmd_none(*pmd)) {
  			spin_unlock(ptl);

  			dax_pmd_dbg(&bh, address, "pmd already present");

  			goto fallback;
  		}

  		dev_dbg(part_to_dev(bdev->bd_part),
  				"%s: %s addr: %lx pfn: <zero> sect: %llx
  ",
  				__func__, current->comm, address,
  				(unsigned long long) to_sector(&bh, inode));

  		entry = mk_pmd(zero_page, vma->vm_page_prot);
  		entry = pmd_mkhuge(entry);
  		set_pmd_at(vma->vm_mm, pmd_addr, pmd, entry);

  		result = VM_FAULT_NOPAGE;

  		spin_unlock(ptl);

  	} else {

  		struct blk_dax_ctl dax = {
  			.sector = to_sector(&bh, inode),
  			.size = PMD_SIZE,
  		};
  		long length = dax_map_atomic(bdev, &dax);

  		if (length < 0) {

  			dax_pmd_dbg(&bh, address, "dax-error fallback");
  			goto fallback;

  		}

  		if (length < PMD_SIZE) {
  			dax_pmd_dbg(&bh, address, "dax-length too small");
  			dax_unmap_atomic(bdev, &dax);
  			goto fallback;
  		}
  		if (pfn_t_to_pfn(dax.pfn) & PG_PMD_COLOUR) {
  			dax_pmd_dbg(&bh, address, "pfn unaligned");

  			dax_unmap_atomic(bdev, &dax);

  			goto fallback;

  		}

  		if (!pfn_t_devmap(dax.pfn)) {

  			dax_unmap_atomic(bdev, &dax);

  			dax_pmd_dbg(&bh, address, "pfn not in memmap");

  			goto fallback;

  		}

  		dax_unmap_atomic(bdev, &dax);

  		/*
  		 * For PTE faults we insert a radix tree entry for reads, and
  		 * leave it clean.  Then on the first write we dirty the radix
  		 * tree entry via the dax_pfn_mkwrite() path.  This sequence
  		 * allows the dax_pfn_mkwrite() call to be simpler and avoid a
  		 * call into get_block() to translate the pgoff to a sector in
  		 * order to be able to create a new radix tree entry.
  		 *
  		 * The PMD path doesn't have an equivalent to
  		 * dax_pfn_mkwrite(), though, so for a read followed by a

  		 * write we traverse all the way through dax_pmd_fault()

  		 * twice.  This means we can just skip inserting a radix tree
  		 * entry completely on the initial read and just wait until
  		 * the write to insert a dirty entry.
  		 */
  		if (write) {

  			/*
  			 * We should insert radix-tree entry and dirty it here.
  			 * For now this is broken...
  			 */

  		}

  		dev_dbg(part_to_dev(bdev->bd_part),
  				"%s: %s addr: %lx pfn: %lx sect: %llx
  ",
  				__func__, current->comm, address,
  				pfn_t_to_pfn(dax.pfn),
  				(unsigned long long) dax.sector);

  		result |= vmf_insert_pfn_pmd(vma, address, pmd,

  				dax.pfn, write);

  	}
  
   out:

  	return result;
  
   fallback:
  	count_vm_event(THP_FAULT_FALLBACK);
  	result = VM_FAULT_FALLBACK;
  	goto out;
  }

  EXPORT_SYMBOL_GPL(dax_pmd_fault);

  #endif /* CONFIG_TRANSPARENT_HUGEPAGE */

  /**

   * dax_pfn_mkwrite - handle first write to DAX page
   * @vma: The virtual memory area where the fault occurred
   * @vmf: The description of the fault

   */
  int dax_pfn_mkwrite(struct vm_area_struct *vma, struct vm_fault *vmf)
  {

  	struct file *file = vma->vm_file;

  	struct address_space *mapping = file->f_mapping;
  	void *entry;
  	pgoff_t index = vmf->pgoff;

  	spin_lock_irq(&mapping->tree_lock);
  	entry = get_unlocked_mapping_entry(mapping, index, NULL);
  	if (!entry || !radix_tree_exceptional_entry(entry))
  		goto out;
  	radix_tree_tag_set(&mapping->page_tree, index, PAGECACHE_TAG_DIRTY);
  	put_unlocked_mapping_entry(mapping, index, entry);
  out:
  	spin_unlock_irq(&mapping->tree_lock);

  	return VM_FAULT_NOPAGE;
  }
  EXPORT_SYMBOL_GPL(dax_pfn_mkwrite);

  static bool dax_range_is_aligned(struct block_device *bdev,
  				 unsigned int offset, unsigned int length)
  {
  	unsigned short sector_size = bdev_logical_block_size(bdev);
  
  	if (!IS_ALIGNED(offset, sector_size))
  		return false;
  	if (!IS_ALIGNED(length, sector_size))
  		return false;
  
  	return true;
  }

  int __dax_zero_page_range(struct block_device *bdev, sector_t sector,
  		unsigned int offset, unsigned int length)
  {
  	struct blk_dax_ctl dax = {
  		.sector		= sector,
  		.size		= PAGE_SIZE,
  	};

  	if (dax_range_is_aligned(bdev, offset, length)) {
  		sector_t start_sector = dax.sector + (offset >> 9);
  
  		return blkdev_issue_zeroout(bdev, start_sector,
  				length >> 9, GFP_NOFS, true);
  	} else {
  		if (dax_map_atomic(bdev, &dax) < 0)
  			return PTR_ERR(dax.addr);
  		clear_pmem(dax.addr + offset, length);

  		dax_unmap_atomic(bdev, &dax);
  	}

  	return 0;
  }
  EXPORT_SYMBOL_GPL(__dax_zero_page_range);

  /**

   * dax_zero_page_range - zero a range within a page of a DAX file

   * @inode: The file being truncated
   * @from: The file offset that is being truncated to

   * @length: The number of bytes to zero

   * @get_block: The filesystem method used to translate file offsets to blocks
   *

   * This function can be called by a filesystem when it is zeroing part of a
   * page in a DAX file.  This is intended for hole-punch operations.  If
   * you are truncating a file, the helper function dax_truncate_page() may be
   * more convenient.

   */

  int dax_zero_page_range(struct inode *inode, loff_t from, unsigned length,
  							get_block_t get_block)

  {
  	struct buffer_head bh;

  	pgoff_t index = from >> PAGE_SHIFT;
  	unsigned offset = from & (PAGE_SIZE-1);

  	int err;
  
  	/* Block boundary? Nothing to do */
  	if (!length)
  		return 0;

  	BUG_ON((offset + length) > PAGE_SIZE);

  
  	memset(&bh, 0, sizeof(bh));

  	bh.b_bdev = inode->i_sb->s_bdev;

  	bh.b_size = PAGE_SIZE;

  	err = get_block(inode, index, &bh, 0);

  	if (err < 0 || !buffer_written(&bh))

  		return err;

  	return __dax_zero_page_range(bh.b_bdev, to_sector(&bh, inode),
  			offset, length);

  }

  EXPORT_SYMBOL_GPL(dax_zero_page_range);
  
  /**
   * dax_truncate_page - handle a partial page being truncated in a DAX file
   * @inode: The file being truncated
   * @from: The file offset that is being truncated to
   * @get_block: The filesystem method used to translate file offsets to blocks
   *
   * Similar to block_truncate_page(), this function can be called by a
   * filesystem when it is truncating a DAX file to handle the partial page.

   */
  int dax_truncate_page(struct inode *inode, loff_t from, get_block_t get_block)
  {

  	unsigned length = PAGE_ALIGN(from) - from;

  	return dax_zero_page_range(inode, from, length, get_block);
  }

  EXPORT_SYMBOL_GPL(dax_truncate_page);

  
  #ifdef CONFIG_FS_IOMAP
  static loff_t
  iomap_dax_actor(struct inode *inode, loff_t pos, loff_t length, void *data,
  		struct iomap *iomap)
  {
  	struct iov_iter *iter = data;
  	loff_t end = pos + length, done = 0;
  	ssize_t ret = 0;
  
  	if (iov_iter_rw(iter) == READ) {
  		end = min(end, i_size_read(inode));
  		if (pos >= end)
  			return 0;
  
  		if (iomap->type == IOMAP_HOLE || iomap->type == IOMAP_UNWRITTEN)
  			return iov_iter_zero(min(length, end - pos), iter);
  	}
  
  	if (WARN_ON_ONCE(iomap->type != IOMAP_MAPPED))
  		return -EIO;
  
  	while (pos < end) {
  		unsigned offset = pos & (PAGE_SIZE - 1);
  		struct blk_dax_ctl dax = { 0 };
  		ssize_t map_len;

  		if (fatal_signal_pending(current)) {
  			ret = -EINTR;
  			break;
  		}

  		dax.sector = iomap->blkno +
  			(((pos & PAGE_MASK) - iomap->offset) >> 9);
  		dax.size = (length + offset + PAGE_SIZE - 1) & PAGE_MASK;
  		map_len = dax_map_atomic(iomap->bdev, &dax);
  		if (map_len < 0) {
  			ret = map_len;
  			break;
  		}
  
  		dax.addr += offset;
  		map_len -= offset;
  		if (map_len > end - pos)
  			map_len = end - pos;
  
  		if (iov_iter_rw(iter) == WRITE)
  			map_len = copy_from_iter_pmem(dax.addr, map_len, iter);
  		else
  			map_len = copy_to_iter(dax.addr, map_len, iter);
  		dax_unmap_atomic(iomap->bdev, &dax);
  		if (map_len <= 0) {
  			ret = map_len ? map_len : -EFAULT;
  			break;
  		}
  
  		pos += map_len;
  		length -= map_len;
  		done += map_len;
  	}
  
  	return done ? done : ret;
  }
  
  /**
   * iomap_dax_rw - Perform I/O to a DAX file
   * @iocb:	The control block for this I/O
   * @iter:	The addresses to do I/O from or to
   * @ops:	iomap ops passed from the file system
   *
   * This function performs read and write operations to directly mapped
   * persistent memory.  The callers needs to take care of read/write exclusion
   * and evicting any page cache pages in the region under I/O.
   */
  ssize_t
  iomap_dax_rw(struct kiocb *iocb, struct iov_iter *iter,
  		struct iomap_ops *ops)
  {
  	struct address_space *mapping = iocb->ki_filp->f_mapping;
  	struct inode *inode = mapping->host;
  	loff_t pos = iocb->ki_pos, ret = 0, done = 0;
  	unsigned flags = 0;
  
  	if (iov_iter_rw(iter) == WRITE)
  		flags |= IOMAP_WRITE;
  
  	/*
  	 * Yes, even DAX files can have page cache attached to them:  A zeroed
  	 * page is inserted into the pagecache when we have to serve a write
  	 * fault on a hole.  It should never be dirtied and can simply be
  	 * dropped from the pagecache once we get real data for the page.
  	 *
  	 * XXX: This is racy against mmap, and there's nothing we can do about
  	 * it. We'll eventually need to shift this down even further so that
  	 * we can check if we allocated blocks over a hole first.
  	 */
  	if (mapping->nrpages) {
  		ret = invalidate_inode_pages2_range(mapping,
  				pos >> PAGE_SHIFT,
  				(pos + iov_iter_count(iter) - 1) >> PAGE_SHIFT);
  		WARN_ON_ONCE(ret);
  	}
  
  	while (iov_iter_count(iter)) {
  		ret = iomap_apply(inode, pos, iov_iter_count(iter), flags, ops,
  				iter, iomap_dax_actor);
  		if (ret <= 0)
  			break;
  		pos += ret;
  		done += ret;
  	}
  
  	iocb->ki_pos += done;
  	return done ? done : ret;
  }
  EXPORT_SYMBOL_GPL(iomap_dax_rw);

  
  /**
   * iomap_dax_fault - handle a page fault on a DAX file
   * @vma: The virtual memory area where the fault occurred
   * @vmf: The description of the fault
   * @ops: iomap ops passed from the file system
   *
   * When a page fault occurs, filesystems may call this helper in their fault
   * or mkwrite handler for DAX files. Assumes the caller has done all the
   * necessary locking for the page fault to proceed successfully.
   */
  int iomap_dax_fault(struct vm_area_struct *vma, struct vm_fault *vmf,
  			struct iomap_ops *ops)
  {
  	struct address_space *mapping = vma->vm_file->f_mapping;
  	struct inode *inode = mapping->host;
  	unsigned long vaddr = (unsigned long)vmf->virtual_address;
  	loff_t pos = (loff_t)vmf->pgoff << PAGE_SHIFT;
  	sector_t sector;
  	struct iomap iomap = { 0 };
  	unsigned flags = 0;
  	int error, major = 0;
  	void *entry;
  
  	/*
  	 * Check whether offset isn't beyond end of file now. Caller is supposed
  	 * to hold locks serializing us with truncate / punch hole so this is
  	 * a reliable test.
  	 */
  	if (pos >= i_size_read(inode))
  		return VM_FAULT_SIGBUS;
  
  	entry = grab_mapping_entry(mapping, vmf->pgoff);
  	if (IS_ERR(entry)) {
  		error = PTR_ERR(entry);
  		goto out;
  	}
  
  	if ((vmf->flags & FAULT_FLAG_WRITE) && !vmf->cow_page)
  		flags |= IOMAP_WRITE;
  
  	/*
  	 * Note that we don't bother to use iomap_apply here: DAX required
  	 * the file system block size to be equal the page size, which means
  	 * that we never have to deal with more than a single extent here.
  	 */
  	error = ops->iomap_begin(inode, pos, PAGE_SIZE, flags, &iomap);
  	if (error)
  		goto unlock_entry;
  	if (WARN_ON_ONCE(iomap.offset + iomap.length < pos + PAGE_SIZE)) {
  		error = -EIO;		/* fs corruption? */
  		goto unlock_entry;
  	}
  
  	sector = iomap.blkno + (((pos & PAGE_MASK) - iomap.offset) >> 9);
  
  	if (vmf->cow_page) {
  		switch (iomap.type) {
  		case IOMAP_HOLE:
  		case IOMAP_UNWRITTEN:
  			clear_user_highpage(vmf->cow_page, vaddr);
  			break;
  		case IOMAP_MAPPED:
  			error = copy_user_dax(iomap.bdev, sector, PAGE_SIZE,
  					vmf->cow_page, vaddr);
  			break;
  		default:
  			WARN_ON_ONCE(1);
  			error = -EIO;
  			break;
  		}
  
  		if (error)
  			goto unlock_entry;
  		if (!radix_tree_exceptional_entry(entry)) {
  			vmf->page = entry;
  			return VM_FAULT_LOCKED;
  		}
  		vmf->entry = entry;
  		return VM_FAULT_DAX_LOCKED;
  	}
  
  	switch (iomap.type) {
  	case IOMAP_MAPPED:
  		if (iomap.flags & IOMAP_F_NEW) {
  			count_vm_event(PGMAJFAULT);
  			mem_cgroup_count_vm_event(vma->vm_mm, PGMAJFAULT);
  			major = VM_FAULT_MAJOR;
  		}
  		error = dax_insert_mapping(mapping, iomap.bdev, sector,
  				PAGE_SIZE, &entry, vma, vmf);
  		break;
  	case IOMAP_UNWRITTEN:
  	case IOMAP_HOLE:
  		if (!(vmf->flags & FAULT_FLAG_WRITE))
  			return dax_load_hole(mapping, entry, vmf);
  		/*FALLTHRU*/
  	default:
  		WARN_ON_ONCE(1);
  		error = -EIO;
  		break;
  	}
  
   unlock_entry:
  	put_locked_mapping_entry(mapping, vmf->pgoff, entry);
   out:
  	if (error == -ENOMEM)
  		return VM_FAULT_OOM | major;
  	/* -EBUSY is fine, somebody else faulted on the same PTE */
  	if (error < 0 && error != -EBUSY)
  		return VM_FAULT_SIGBUS | major;
  	return VM_FAULT_NOPAGE | major;
  }
  EXPORT_SYMBOL_GPL(iomap_dax_fault);

  #endif /* CONFIG_FS_IOMAP */