/*
   * Copyright (C) 2010 Red Hat, Inc.
   * Copyright (c) 2016 Christoph Hellwig.
   *
   * 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/module.h>
  #include <linux/compiler.h>
  #include <linux/fs.h>
  #include <linux/iomap.h>
  #include <linux/uaccess.h>
  #include <linux/gfp.h>
  #include <linux/mm.h>
  #include <linux/swap.h>
  #include <linux/pagemap.h>

  #include <linux/pagevec.h>

  #include <linux/file.h>
  #include <linux/uio.h>
  #include <linux/backing-dev.h>
  #include <linux/buffer_head.h>

  #include <linux/task_io_accounting_ops.h>

  #include <linux/dax.h>

  #include <linux/sched/signal.h>

  #include <linux/swap.h>

  #include "internal.h"

  /*
   * Execute a iomap write on a segment of the mapping that spans a
   * contiguous range of pages that have identical block mapping state.
   *
   * This avoids the need to map pages individually, do individual allocations
   * for each page and most importantly avoid the need for filesystem specific
   * locking per page. Instead, all the operations are amortised over the entire
   * range of pages. It is assumed that the filesystems will lock whatever
   * resources they require in the iomap_begin call, and release them in the
   * iomap_end call.
   */

  loff_t

  iomap_apply(struct inode *inode, loff_t pos, loff_t length, unsigned flags,

  		const struct iomap_ops *ops, void *data, iomap_actor_t actor)

  {
  	struct iomap iomap = { 0 };
  	loff_t written = 0, ret;
  
  	/*
  	 * Need to map a range from start position for length bytes. This can
  	 * span multiple pages - it is only guaranteed to return a range of a
  	 * single type of pages (e.g. all into a hole, all mapped or all
  	 * unwritten). Failure at this point has nothing to undo.
  	 *
  	 * If allocation is required for this range, reserve the space now so
  	 * that the allocation is guaranteed to succeed later on. Once we copy
  	 * the data into the page cache pages, then we cannot fail otherwise we
  	 * expose transient stale data. If the reserve fails, we can safely
  	 * back out at this point as there is nothing to undo.
  	 */
  	ret = ops->iomap_begin(inode, pos, length, flags, &iomap);
  	if (ret)
  		return ret;
  	if (WARN_ON(iomap.offset > pos))
  		return -EIO;

  	if (WARN_ON(iomap.length == 0))
  		return -EIO;

  
  	/*
  	 * Cut down the length to the one actually provided by the filesystem,
  	 * as it might not be able to give us the whole size that we requested.
  	 */
  	if (iomap.offset + iomap.length < pos + length)
  		length = iomap.offset + iomap.length - pos;
  
  	/*
  	 * Now that we have guaranteed that the space allocation will succeed.
  	 * we can do the copy-in page by page without having to worry about
  	 * failures exposing transient data.
  	 */
  	written = actor(inode, pos, length, data, &iomap);
  
  	/*
  	 * Now the data has been copied, commit the range we've copied.  This
  	 * should not fail unless the filesystem has had a fatal error.
  	 */

  	if (ops->iomap_end) {
  		ret = ops->iomap_end(inode, pos, length,
  				     written > 0 ? written : 0,
  				     flags, &iomap);
  	}

  
  	return written ? written : ret;
  }

  static sector_t
  iomap_sector(struct iomap *iomap, loff_t pos)
  {
  	return (iomap->addr + pos - iomap->offset) >> SECTOR_SHIFT;
  }

  static void
  iomap_write_failed(struct inode *inode, loff_t pos, unsigned len)
  {
  	loff_t i_size = i_size_read(inode);
  
  	/*
  	 * Only truncate newly allocated pages beyoned EOF, even if the
  	 * write started inside the existing inode size.
  	 */
  	if (pos + len > i_size)
  		truncate_pagecache_range(inode, max(pos, i_size), pos + len);
  }
  
  static int
  iomap_write_begin(struct inode *inode, loff_t pos, unsigned len, unsigned flags,
  		struct page **pagep, struct iomap *iomap)
  {
  	pgoff_t index = pos >> PAGE_SHIFT;
  	struct page *page;
  	int status = 0;
  
  	BUG_ON(pos + len > iomap->offset + iomap->length);

  	if (fatal_signal_pending(current))
  		return -EINTR;

  	page = grab_cache_page_write_begin(inode->i_mapping, index, flags);
  	if (!page)
  		return -ENOMEM;
  
  	status = __block_write_begin_int(page, pos, len, NULL, iomap);
  	if (unlikely(status)) {
  		unlock_page(page);
  		put_page(page);
  		page = NULL;
  
  		iomap_write_failed(inode, pos, len);
  	}
  
  	*pagep = page;
  	return status;
  }
  
  static int
  iomap_write_end(struct inode *inode, loff_t pos, unsigned len,
  		unsigned copied, struct page *page)
  {
  	int ret;
  
  	ret = generic_write_end(NULL, inode->i_mapping, pos, len,
  			copied, page, NULL);
  	if (ret < len)
  		iomap_write_failed(inode, pos, len);
  	return ret;
  }
  
  static loff_t
  iomap_write_actor(struct inode *inode, loff_t pos, loff_t length, void *data,
  		struct iomap *iomap)
  {
  	struct iov_iter *i = data;
  	long status = 0;
  	ssize_t written = 0;
  	unsigned int flags = AOP_FLAG_NOFS;

  	do {
  		struct page *page;
  		unsigned long offset;	/* Offset into pagecache page */
  		unsigned long bytes;	/* Bytes to write to page */
  		size_t copied;		/* Bytes copied from user */
  
  		offset = (pos & (PAGE_SIZE - 1));
  		bytes = min_t(unsigned long, PAGE_SIZE - offset,
  						iov_iter_count(i));
  again:
  		if (bytes > length)
  			bytes = length;
  
  		/*
  		 * Bring in the user page that we will copy from _first_.
  		 * Otherwise there's a nasty deadlock on copying from the
  		 * same page as we're writing to, without it being marked
  		 * up-to-date.
  		 *
  		 * Not only is this an optimisation, but it is also required
  		 * to check that the address is actually valid, when atomic
  		 * usercopies are used, below.
  		 */
  		if (unlikely(iov_iter_fault_in_readable(i, bytes))) {
  			status = -EFAULT;
  			break;
  		}
  
  		status = iomap_write_begin(inode, pos, bytes, flags, &page,
  				iomap);
  		if (unlikely(status))
  			break;
  
  		if (mapping_writably_mapped(inode->i_mapping))
  			flush_dcache_page(page);

  		copied = iov_iter_copy_from_user_atomic(page, i, offset, bytes);

  
  		flush_dcache_page(page);

  
  		status = iomap_write_end(inode, pos, bytes, copied, page);
  		if (unlikely(status < 0))
  			break;
  		copied = status;
  
  		cond_resched();
  
  		iov_iter_advance(i, copied);
  		if (unlikely(copied == 0)) {
  			/*
  			 * If we were unable to copy any data at all, we must
  			 * fall back to a single segment length write.
  			 *
  			 * If we didn't fallback here, we could livelock
  			 * because not all segments in the iov can be copied at
  			 * once without a pagefault.
  			 */
  			bytes = min_t(unsigned long, PAGE_SIZE - offset,
  						iov_iter_single_seg_count(i));
  			goto again;
  		}
  		pos += copied;
  		written += copied;
  		length -= copied;
  
  		balance_dirty_pages_ratelimited(inode->i_mapping);
  	} while (iov_iter_count(i) && length);
  
  	return written ? written : status;
  }
  
  ssize_t
  iomap_file_buffered_write(struct kiocb *iocb, struct iov_iter *iter,

  		const struct iomap_ops *ops)

  {
  	struct inode *inode = iocb->ki_filp->f_mapping->host;
  	loff_t pos = iocb->ki_pos, ret = 0, written = 0;
  
  	while (iov_iter_count(iter)) {
  		ret = iomap_apply(inode, pos, iov_iter_count(iter),
  				IOMAP_WRITE, ops, iter, iomap_write_actor);
  		if (ret <= 0)
  			break;
  		pos += ret;
  		written += ret;
  	}
  
  	return written ? written : ret;
  }
  EXPORT_SYMBOL_GPL(iomap_file_buffered_write);

  static struct page *
  __iomap_read_page(struct inode *inode, loff_t offset)
  {
  	struct address_space *mapping = inode->i_mapping;
  	struct page *page;
  
  	page = read_mapping_page(mapping, offset >> PAGE_SHIFT, NULL);
  	if (IS_ERR(page))
  		return page;
  	if (!PageUptodate(page)) {
  		put_page(page);
  		return ERR_PTR(-EIO);
  	}
  	return page;
  }
  
  static loff_t
  iomap_dirty_actor(struct inode *inode, loff_t pos, loff_t length, void *data,
  		struct iomap *iomap)
  {
  	long status = 0;
  	ssize_t written = 0;
  
  	do {
  		struct page *page, *rpage;
  		unsigned long offset;	/* Offset into pagecache page */
  		unsigned long bytes;	/* Bytes to write to page */
  
  		offset = (pos & (PAGE_SIZE - 1));

  		bytes = min_t(loff_t, PAGE_SIZE - offset, length);

  
  		rpage = __iomap_read_page(inode, pos);
  		if (IS_ERR(rpage))
  			return PTR_ERR(rpage);
  
  		status = iomap_write_begin(inode, pos, bytes,

  					   AOP_FLAG_NOFS, &page, iomap);

  		put_page(rpage);
  		if (unlikely(status))
  			return status;
  
  		WARN_ON_ONCE(!PageUptodate(page));
  
  		status = iomap_write_end(inode, pos, bytes, bytes, page);
  		if (unlikely(status <= 0)) {
  			if (WARN_ON_ONCE(status == 0))
  				return -EIO;
  			return status;
  		}
  
  		cond_resched();
  
  		pos += status;
  		written += status;
  		length -= status;
  
  		balance_dirty_pages_ratelimited(inode->i_mapping);
  	} while (length);
  
  	return written;
  }
  
  int
  iomap_file_dirty(struct inode *inode, loff_t pos, loff_t len,

  		const struct iomap_ops *ops)

  {
  	loff_t ret;
  
  	while (len) {
  		ret = iomap_apply(inode, pos, len, IOMAP_WRITE, ops, NULL,
  				iomap_dirty_actor);
  		if (ret <= 0)
  			return ret;
  		pos += ret;
  		len -= ret;
  	}
  
  	return 0;
  }
  EXPORT_SYMBOL_GPL(iomap_file_dirty);

  static int iomap_zero(struct inode *inode, loff_t pos, unsigned offset,
  		unsigned bytes, struct iomap *iomap)
  {
  	struct page *page;
  	int status;

  	status = iomap_write_begin(inode, pos, bytes, AOP_FLAG_NOFS, &page,
  				   iomap);

  	if (status)
  		return status;
  
  	zero_user(page, offset, bytes);
  	mark_page_accessed(page);
  
  	return iomap_write_end(inode, pos, bytes, bytes, page);
  }

  static int iomap_dax_zero(loff_t pos, unsigned offset, unsigned bytes,
  		struct iomap *iomap)
  {

  	return __dax_zero_page_range(iomap->bdev, iomap->dax_dev,
  			iomap_sector(iomap, pos & PAGE_MASK), offset, bytes);

  }

  static loff_t
  iomap_zero_range_actor(struct inode *inode, loff_t pos, loff_t count,
  		void *data, struct iomap *iomap)
  {
  	bool *did_zero = data;
  	loff_t written = 0;
  	int status;
  
  	/* already zeroed?  we're done. */
  	if (iomap->type == IOMAP_HOLE || iomap->type == IOMAP_UNWRITTEN)
  	    	return count;
  
  	do {
  		unsigned offset, bytes;
  
  		offset = pos & (PAGE_SIZE - 1); /* Within page */

  		bytes = min_t(loff_t, PAGE_SIZE - offset, count);

  		if (IS_DAX(inode))
  			status = iomap_dax_zero(pos, offset, bytes, iomap);
  		else
  			status = iomap_zero(inode, pos, offset, bytes, iomap);

  		if (status < 0)
  			return status;
  
  		pos += bytes;
  		count -= bytes;
  		written += bytes;
  		if (did_zero)
  			*did_zero = true;
  	} while (count > 0);
  
  	return written;
  }
  
  int
  iomap_zero_range(struct inode *inode, loff_t pos, loff_t len, bool *did_zero,

  		const struct iomap_ops *ops)

  {
  	loff_t ret;
  
  	while (len > 0) {
  		ret = iomap_apply(inode, pos, len, IOMAP_ZERO,
  				ops, did_zero, iomap_zero_range_actor);
  		if (ret <= 0)
  			return ret;
  
  		pos += ret;
  		len -= ret;
  	}
  
  	return 0;
  }
  EXPORT_SYMBOL_GPL(iomap_zero_range);
  
  int
  iomap_truncate_page(struct inode *inode, loff_t pos, bool *did_zero,

  		const struct iomap_ops *ops)

  {

  	unsigned int blocksize = i_blocksize(inode);
  	unsigned int off = pos & (blocksize - 1);

  
  	/* Block boundary? Nothing to do */
  	if (!off)
  		return 0;
  	return iomap_zero_range(inode, pos, blocksize - off, did_zero, ops);
  }
  EXPORT_SYMBOL_GPL(iomap_truncate_page);
  
  static loff_t
  iomap_page_mkwrite_actor(struct inode *inode, loff_t pos, loff_t length,
  		void *data, struct iomap *iomap)
  {
  	struct page *page = data;
  	int ret;

  	ret = __block_write_begin_int(page, pos, length, NULL, iomap);

  	if (ret)
  		return ret;
  
  	block_commit_write(page, 0, length);
  	return length;
  }

  int iomap_page_mkwrite(struct vm_fault *vmf, const struct iomap_ops *ops)

  {
  	struct page *page = vmf->page;

  	struct inode *inode = file_inode(vmf->vma->vm_file);

  	unsigned long length;
  	loff_t offset, size;
  	ssize_t ret;
  
  	lock_page(page);
  	size = i_size_read(inode);
  	if ((page->mapping != inode->i_mapping) ||
  	    (page_offset(page) > size)) {
  		/* We overload EFAULT to mean page got truncated */
  		ret = -EFAULT;
  		goto out_unlock;
  	}
  
  	/* page is wholly or partially inside EOF */
  	if (((page->index + 1) << PAGE_SHIFT) > size)
  		length = size & ~PAGE_MASK;
  	else
  		length = PAGE_SIZE;
  
  	offset = page_offset(page);
  	while (length > 0) {

  		ret = iomap_apply(inode, offset, length,
  				IOMAP_WRITE | IOMAP_FAULT, ops, page,
  				iomap_page_mkwrite_actor);

  		if (unlikely(ret <= 0))
  			goto out_unlock;
  		offset += ret;
  		length -= ret;
  	}
  
  	set_page_dirty(page);
  	wait_for_stable_page(page);

  	return VM_FAULT_LOCKED;

  out_unlock:
  	unlock_page(page);

  	return block_page_mkwrite_return(ret);

  }
  EXPORT_SYMBOL_GPL(iomap_page_mkwrite);

  
  struct fiemap_ctx {
  	struct fiemap_extent_info *fi;
  	struct iomap prev;
  };
  
  static int iomap_to_fiemap(struct fiemap_extent_info *fi,
  		struct iomap *iomap, u32 flags)
  {
  	switch (iomap->type) {
  	case IOMAP_HOLE:
  		/* skip holes */
  		return 0;
  	case IOMAP_DELALLOC:
  		flags |= FIEMAP_EXTENT_DELALLOC | FIEMAP_EXTENT_UNKNOWN;
  		break;

  	case IOMAP_MAPPED:
  		break;

  	case IOMAP_UNWRITTEN:
  		flags |= FIEMAP_EXTENT_UNWRITTEN;
  		break;

  	case IOMAP_INLINE:
  		flags |= FIEMAP_EXTENT_DATA_INLINE;

  		break;
  	}

  	if (iomap->flags & IOMAP_F_MERGED)
  		flags |= FIEMAP_EXTENT_MERGED;

  	if (iomap->flags & IOMAP_F_SHARED)
  		flags |= FIEMAP_EXTENT_SHARED;

  	return fiemap_fill_next_extent(fi, iomap->offset,

  			iomap->addr != IOMAP_NULL_ADDR ? iomap->addr : 0,

  			iomap->length, flags);

  }
  
  static loff_t
  iomap_fiemap_actor(struct inode *inode, loff_t pos, loff_t length, void *data,
  		struct iomap *iomap)
  {
  	struct fiemap_ctx *ctx = data;
  	loff_t ret = length;
  
  	if (iomap->type == IOMAP_HOLE)
  		return length;
  
  	ret = iomap_to_fiemap(ctx->fi, &ctx->prev, 0);
  	ctx->prev = *iomap;
  	switch (ret) {
  	case 0:		/* success */
  		return length;
  	case 1:		/* extent array full */
  		return 0;
  	default:
  		return ret;
  	}
  }
  
  int iomap_fiemap(struct inode *inode, struct fiemap_extent_info *fi,

  		loff_t start, loff_t len, const struct iomap_ops *ops)

  {
  	struct fiemap_ctx ctx;
  	loff_t ret;
  
  	memset(&ctx, 0, sizeof(ctx));
  	ctx.fi = fi;
  	ctx.prev.type = IOMAP_HOLE;
  
  	ret = fiemap_check_flags(fi, FIEMAP_FLAG_SYNC);
  	if (ret)
  		return ret;

  	if (fi->fi_flags & FIEMAP_FLAG_SYNC) {
  		ret = filemap_write_and_wait(inode->i_mapping);
  		if (ret)
  			return ret;
  	}

  
  	while (len > 0) {

  		ret = iomap_apply(inode, start, len, IOMAP_REPORT, ops, &ctx,

  				iomap_fiemap_actor);

  		/* inode with no (attribute) mapping will give ENOENT */
  		if (ret == -ENOENT)
  			break;

  		if (ret < 0)
  			return ret;
  		if (ret == 0)
  			break;
  
  		start += ret;
  		len -= ret;
  	}
  
  	if (ctx.prev.type != IOMAP_HOLE) {
  		ret = iomap_to_fiemap(fi, &ctx.prev, FIEMAP_EXTENT_LAST);
  		if (ret < 0)
  			return ret;
  	}
  
  	return 0;
  }
  EXPORT_SYMBOL_GPL(iomap_fiemap);

  /*
   * Seek for SEEK_DATA / SEEK_HOLE within @page, starting at @lastoff.

   * Returns true if found and updates @lastoff to the offset in file.

   */

  static bool
  page_seek_hole_data(struct inode *inode, struct page *page, loff_t *lastoff,
  		int whence)

  {

  	const struct address_space_operations *ops = inode->i_mapping->a_ops;
  	unsigned int bsize = i_blocksize(inode), off;

  	bool seek_data = whence == SEEK_DATA;

  	loff_t poff = page_offset(page);

  	if (WARN_ON_ONCE(*lastoff >= poff + PAGE_SIZE))
  		return false;

  	if (*lastoff < poff) {

  		/*

  		 * Last offset smaller than the start of the page means we found
  		 * a hole:

  		 */

  		if (whence == SEEK_HOLE)
  			return true;
  		*lastoff = poff;
  	}

  	/*
  	 * Just check the page unless we can and should check block ranges:
  	 */
  	if (bsize == PAGE_SIZE || !ops->is_partially_uptodate)
  		return PageUptodate(page) == seek_data;
  
  	lock_page(page);
  	if (unlikely(page->mapping != inode->i_mapping))
  		goto out_unlock_not_found;
  
  	for (off = 0; off < PAGE_SIZE; off += bsize) {
  		if ((*lastoff & ~PAGE_MASK) >= off + bsize)
  			continue;
  		if (ops->is_partially_uptodate(page, off, bsize) == seek_data) {
  			unlock_page(page);
  			return true;
  		}
  		*lastoff = poff + off + bsize;
  	}
  
  out_unlock_not_found:
  	unlock_page(page);
  	return false;

  }
  
  /*
   * Seek for SEEK_DATA / SEEK_HOLE in the page cache.
   *
   * Within unwritten extents, the page cache determines which parts are holes

   * and which are data: uptodate buffer heads count as data; everything else
   * counts as a hole.

   *
   * Returns the resulting offset on successs, and -ENOENT otherwise.
   */
  static loff_t
  page_cache_seek_hole_data(struct inode *inode, loff_t offset, loff_t length,
  		int whence)
  {
  	pgoff_t index = offset >> PAGE_SHIFT;
  	pgoff_t end = DIV_ROUND_UP(offset + length, PAGE_SIZE);
  	loff_t lastoff = offset;
  	struct pagevec pvec;
  
  	if (length <= 0)
  		return -ENOENT;
  
  	pagevec_init(&pvec);
  
  	do {
  		unsigned nr_pages, i;
  
  		nr_pages = pagevec_lookup_range(&pvec, inode->i_mapping, &index,
  						end - 1);
  		if (nr_pages == 0)
  			break;
  
  		for (i = 0; i < nr_pages; i++) {
  			struct page *page = pvec.pages[i];

  			if (page_seek_hole_data(inode, page, &lastoff, whence))

  				goto check_range;

  			lastoff = page_offset(page) + PAGE_SIZE;
  		}
  		pagevec_release(&pvec);
  	} while (index < end);
  
  	/* When no page at lastoff and we are not done, we found a hole. */
  	if (whence != SEEK_HOLE)
  		goto not_found;
  
  check_range:
  	if (lastoff < offset + length)
  		goto out;
  not_found:
  	lastoff = -ENOENT;
  out:
  	pagevec_release(&pvec);
  	return lastoff;
  }

  static loff_t
  iomap_seek_hole_actor(struct inode *inode, loff_t offset, loff_t length,
  		      void *data, struct iomap *iomap)
  {
  	switch (iomap->type) {
  	case IOMAP_UNWRITTEN:
  		offset = page_cache_seek_hole_data(inode, offset, length,
  						   SEEK_HOLE);
  		if (offset < 0)
  			return length;
  		/* fall through */
  	case IOMAP_HOLE:
  		*(loff_t *)data = offset;
  		return 0;
  	default:
  		return length;
  	}
  }
  
  loff_t
  iomap_seek_hole(struct inode *inode, loff_t offset, const struct iomap_ops *ops)
  {
  	loff_t size = i_size_read(inode);
  	loff_t length = size - offset;
  	loff_t ret;

  	/* Nothing to be found before or beyond the end of the file. */
  	if (offset < 0 || offset >= size)

  		return -ENXIO;
  
  	while (length > 0) {
  		ret = iomap_apply(inode, offset, length, IOMAP_REPORT, ops,
  				  &offset, iomap_seek_hole_actor);
  		if (ret < 0)
  			return ret;
  		if (ret == 0)
  			break;
  
  		offset += ret;
  		length -= ret;
  	}
  
  	return offset;
  }
  EXPORT_SYMBOL_GPL(iomap_seek_hole);
  
  static loff_t
  iomap_seek_data_actor(struct inode *inode, loff_t offset, loff_t length,
  		      void *data, struct iomap *iomap)
  {
  	switch (iomap->type) {
  	case IOMAP_HOLE:
  		return length;
  	case IOMAP_UNWRITTEN:
  		offset = page_cache_seek_hole_data(inode, offset, length,
  						   SEEK_DATA);
  		if (offset < 0)
  			return length;
  		/*FALLTHRU*/
  	default:
  		*(loff_t *)data = offset;
  		return 0;
  	}
  }
  
  loff_t
  iomap_seek_data(struct inode *inode, loff_t offset, const struct iomap_ops *ops)
  {
  	loff_t size = i_size_read(inode);
  	loff_t length = size - offset;
  	loff_t ret;

  	/* Nothing to be found before or beyond the end of the file. */
  	if (offset < 0 || offset >= size)

  		return -ENXIO;
  
  	while (length > 0) {
  		ret = iomap_apply(inode, offset, length, IOMAP_REPORT, ops,
  				  &offset, iomap_seek_data_actor);
  		if (ret < 0)
  			return ret;
  		if (ret == 0)
  			break;
  
  		offset += ret;
  		length -= ret;
  	}
  
  	if (length <= 0)
  		return -ENXIO;
  	return offset;
  }
  EXPORT_SYMBOL_GPL(iomap_seek_data);

  /*
   * Private flags for iomap_dio, must not overlap with the public ones in
   * iomap.h:
   */

  #define IOMAP_DIO_WRITE_FUA	(1 << 28)

  #define IOMAP_DIO_NEED_SYNC	(1 << 29)

  #define IOMAP_DIO_WRITE		(1 << 30)
  #define IOMAP_DIO_DIRTY		(1 << 31)
  
  struct iomap_dio {
  	struct kiocb		*iocb;
  	iomap_dio_end_io_t	*end_io;
  	loff_t			i_size;
  	loff_t			size;
  	atomic_t		ref;
  	unsigned		flags;
  	int			error;
  
  	union {
  		/* used during submission and for synchronous completion: */
  		struct {
  			struct iov_iter		*iter;
  			struct task_struct	*waiter;
  			struct request_queue	*last_queue;
  			blk_qc_t		cookie;
  		} submit;
  
  		/* used for aio completion: */
  		struct {
  			struct work_struct	work;
  		} aio;
  	};
  };
  
  static ssize_t iomap_dio_complete(struct iomap_dio *dio)
  {
  	struct kiocb *iocb = dio->iocb;

  	struct inode *inode = file_inode(iocb->ki_filp);

  	loff_t offset = iocb->ki_pos;

  	ssize_t ret;
  
  	if (dio->end_io) {
  		ret = dio->end_io(iocb,
  				dio->error ? dio->error : dio->size,
  				dio->flags);
  	} else {
  		ret = dio->error;
  	}
  
  	if (likely(!ret)) {
  		ret = dio->size;
  		/* check for short read */

  		if (offset + ret > dio->i_size &&

  		    !(dio->flags & IOMAP_DIO_WRITE))

  			ret = dio->i_size - offset;

  		iocb->ki_pos += ret;
  	}

  	/*
  	 * Try again to invalidate clean pages which might have been cached by
  	 * non-direct readahead, or faulted in by get_user_pages() if the source
  	 * of the write was an mmap'ed region of the file we're writing.  Either
  	 * one is a pretty crazy thing to do, so we don't support it 100%.  If
  	 * this invalidation fails, tough, the write still worked...
  	 *
  	 * And this page cache invalidation has to be after dio->end_io(), as
  	 * some filesystems convert unwritten extents to real allocations in
  	 * end_io() when necessary, otherwise a racing buffer read would cache
  	 * zeros from unwritten extents.
  	 */
  	if (!dio->error &&
  	    (dio->flags & IOMAP_DIO_WRITE) && inode->i_mapping->nrpages) {
  		int err;
  		err = invalidate_inode_pages2_range(inode->i_mapping,
  				offset >> PAGE_SHIFT,
  				(offset + dio->size - 1) >> PAGE_SHIFT);

  		if (err)
  			dio_warn_stale_pagecache(iocb->ki_filp);

  	}

  	/*
  	 * If this is a DSYNC write, make sure we push it to stable storage now
  	 * that we've written data.
  	 */
  	if (ret > 0 && (dio->flags & IOMAP_DIO_NEED_SYNC))
  		ret = generic_write_sync(iocb, ret);

  	inode_dio_end(file_inode(iocb->ki_filp));
  	kfree(dio);
  
  	return ret;
  }
  
  static void iomap_dio_complete_work(struct work_struct *work)
  {
  	struct iomap_dio *dio = container_of(work, struct iomap_dio, aio.work);
  	struct kiocb *iocb = dio->iocb;

  	iocb->ki_complete(iocb, iomap_dio_complete(dio), 0);

  }
  
  /*
   * Set an error in the dio if none is set yet.  We have to use cmpxchg
   * as the submission context and the completion context(s) can race to
   * update the error.
   */
  static inline void iomap_dio_set_error(struct iomap_dio *dio, int ret)
  {
  	cmpxchg(&dio->error, 0, ret);
  }
  
  static void iomap_dio_bio_end_io(struct bio *bio)
  {
  	struct iomap_dio *dio = bio->bi_private;
  	bool should_dirty = (dio->flags & IOMAP_DIO_DIRTY);

  	if (bio->bi_status)
  		iomap_dio_set_error(dio, blk_status_to_errno(bio->bi_status));

  
  	if (atomic_dec_and_test(&dio->ref)) {
  		if (is_sync_kiocb(dio->iocb)) {
  			struct task_struct *waiter = dio->submit.waiter;
  
  			WRITE_ONCE(dio->submit.waiter, NULL);
  			wake_up_process(waiter);
  		} else if (dio->flags & IOMAP_DIO_WRITE) {
  			struct inode *inode = file_inode(dio->iocb->ki_filp);
  
  			INIT_WORK(&dio->aio.work, iomap_dio_complete_work);
  			queue_work(inode->i_sb->s_dio_done_wq, &dio->aio.work);
  		} else {
  			iomap_dio_complete_work(&dio->aio.work);
  		}
  	}
  
  	if (should_dirty) {
  		bio_check_pages_dirty(bio);
  	} else {
  		struct bio_vec *bvec;
  		int i;
  
  		bio_for_each_segment_all(bvec, bio, i)
  			put_page(bvec->bv_page);
  		bio_put(bio);
  	}
  }
  
  static blk_qc_t
  iomap_dio_zero(struct iomap_dio *dio, struct iomap *iomap, loff_t pos,
  		unsigned len)
  {
  	struct page *page = ZERO_PAGE(0);
  	struct bio *bio;
  
  	bio = bio_alloc(GFP_KERNEL, 1);

  	bio_set_dev(bio, iomap->bdev);

  	bio->bi_iter.bi_sector = iomap_sector(iomap, pos);

  	bio->bi_private = dio;
  	bio->bi_end_io = iomap_dio_bio_end_io;
  
  	get_page(page);

  	__bio_add_page(bio, page, len, 0);

  	bio_set_op_attrs(bio, REQ_OP_WRITE, REQ_SYNC | REQ_IDLE);

  
  	atomic_inc(&dio->ref);
  	return submit_bio(bio);
  }
  
  static loff_t
  iomap_dio_actor(struct inode *inode, loff_t pos, loff_t length,
  		void *data, struct iomap *iomap)
  {
  	struct iomap_dio *dio = data;

  	unsigned int blkbits = blksize_bits(bdev_logical_block_size(iomap->bdev));
  	unsigned int fs_block_size = i_blocksize(inode), pad;
  	unsigned int align = iov_iter_alignment(dio->submit.iter);

  	struct iov_iter iter;
  	struct bio *bio;
  	bool need_zeroout = false;

  	bool use_fua = false;

  	int nr_pages, ret;

  	size_t copied = 0;

  
  	if ((pos | length | align) & ((1 << blkbits) - 1))
  		return -EINVAL;
  
  	switch (iomap->type) {
  	case IOMAP_HOLE:
  		if (WARN_ON_ONCE(dio->flags & IOMAP_DIO_WRITE))
  			return -EIO;
  		/*FALLTHRU*/
  	case IOMAP_UNWRITTEN:
  		if (!(dio->flags & IOMAP_DIO_WRITE)) {

  			length = iov_iter_zero(length, dio->submit.iter);

  			dio->size += length;
  			return length;
  		}
  		dio->flags |= IOMAP_DIO_UNWRITTEN;
  		need_zeroout = true;
  		break;
  	case IOMAP_MAPPED:
  		if (iomap->flags & IOMAP_F_SHARED)
  			dio->flags |= IOMAP_DIO_COW;

  		if (iomap->flags & IOMAP_F_NEW) {

  			need_zeroout = true;

  		} else {
  			/*
  			 * Use a FUA write if we need datasync semantics, this
  			 * is a pure data IO that doesn't require any metadata
  			 * updates and the underlying device supports FUA. This
  			 * allows us to avoid cache flushes on IO completion.
  			 */
  			if (!(iomap->flags & (IOMAP_F_SHARED|IOMAP_F_DIRTY)) &&
  			    (dio->flags & IOMAP_DIO_WRITE_FUA) &&
  			    blk_queue_fua(bdev_get_queue(iomap->bdev)))
  				use_fua = true;
  		}

  		break;
  	default:
  		WARN_ON_ONCE(1);
  		return -EIO;
  	}
  
  	/*
  	 * Operate on a partial iter trimmed to the extent we were called for.
  	 * We'll update the iter in the dio once we're done with this extent.
  	 */
  	iter = *dio->submit.iter;
  	iov_iter_truncate(&iter, length);
  
  	nr_pages = iov_iter_npages(&iter, BIO_MAX_PAGES);
  	if (nr_pages <= 0)
  		return nr_pages;
  
  	if (need_zeroout) {
  		/* zero out from the start of the block to the write offset */
  		pad = pos & (fs_block_size - 1);
  		if (pad)
  			iomap_dio_zero(dio, iomap, pos - pad, pad);
  	}
  
  	do {

  		size_t n;
  		if (dio->error) {
  			iov_iter_revert(dio->submit.iter, copied);

  			return 0;

  		}

  
  		bio = bio_alloc(GFP_KERNEL, nr_pages);

  		bio_set_dev(bio, iomap->bdev);

  		bio->bi_iter.bi_sector = iomap_sector(iomap, pos);

  		bio->bi_write_hint = dio->iocb->ki_hint;

  		bio->bi_ioprio = dio->iocb->ki_ioprio;

  		bio->bi_private = dio;
  		bio->bi_end_io = iomap_dio_bio_end_io;
  
  		ret = bio_iov_iter_get_pages(bio, &iter);
  		if (unlikely(ret)) {
  			bio_put(bio);

  			return copied ? copied : ret;

  		}

  		n = bio->bi_iter.bi_size;

  		if (dio->flags & IOMAP_DIO_WRITE) {

  			bio->bi_opf = REQ_OP_WRITE | REQ_SYNC | REQ_IDLE;
  			if (use_fua)
  				bio->bi_opf |= REQ_FUA;
  			else
  				dio->flags &= ~IOMAP_DIO_WRITE_FUA;

  			task_io_account_write(n);

  		} else {

  			bio->bi_opf = REQ_OP_READ;

  			if (dio->flags & IOMAP_DIO_DIRTY)
  				bio_set_pages_dirty(bio);
  		}

  		iov_iter_advance(dio->submit.iter, n);
  
  		dio->size += n;
  		pos += n;
  		copied += n;

  
  		nr_pages = iov_iter_npages(&iter, BIO_MAX_PAGES);
  
  		atomic_inc(&dio->ref);
  
  		dio->submit.last_queue = bdev_get_queue(iomap->bdev);
  		dio->submit.cookie = submit_bio(bio);
  	} while (nr_pages);
  
  	if (need_zeroout) {
  		/* zero out from the end of the write to the end of the block */
  		pad = pos & (fs_block_size - 1);
  		if (pad)
  			iomap_dio_zero(dio, iomap, pos, fs_block_size - pad);
  	}

  	return copied;

  }

  /*
   * iomap_dio_rw() always completes O_[D]SYNC writes regardless of whether the IO

   * is being issued as AIO or not.  This allows us to optimise pure data writes
   * to use REQ_FUA rather than requiring generic_write_sync() to issue a
   * REQ_FLUSH post write. This is slightly tricky because a single request here
   * can be mapped into multiple disjoint IOs and only a subset of the IOs issued
   * may be pure data writes. In that case, we still need to do a full data sync
   * completion.

   */

  ssize_t

  iomap_dio_rw(struct kiocb *iocb, struct iov_iter *iter,
  		const struct iomap_ops *ops, iomap_dio_end_io_t end_io)

  {
  	struct address_space *mapping = iocb->ki_filp->f_mapping;
  	struct inode *inode = file_inode(iocb->ki_filp);
  	size_t count = iov_iter_count(iter);

  	loff_t pos = iocb->ki_pos, start = pos;
  	loff_t end = iocb->ki_pos + count - 1, ret = 0;

  	unsigned int flags = IOMAP_DIRECT;
  	struct blk_plug plug;
  	struct iomap_dio *dio;
  
  	lockdep_assert_held(&inode->i_rwsem);
  
  	if (!count)
  		return 0;
  
  	dio = kmalloc(sizeof(*dio), GFP_KERNEL);
  	if (!dio)
  		return -ENOMEM;
  
  	dio->iocb = iocb;
  	atomic_set(&dio->ref, 1);
  	dio->size = 0;
  	dio->i_size = i_size_read(inode);
  	dio->end_io = end_io;
  	dio->error = 0;
  	dio->flags = 0;
  
  	dio->submit.iter = iter;
  	if (is_sync_kiocb(iocb)) {
  		dio->submit.waiter = current;
  		dio->submit.cookie = BLK_QC_T_NONE;
  		dio->submit.last_queue = NULL;
  	}
  
  	if (iov_iter_rw(iter) == READ) {
  		if (pos >= dio->i_size)
  			goto out_free_dio;
  
  		if (iter->type == ITER_IOVEC)
  			dio->flags |= IOMAP_DIO_DIRTY;
  	} else {

  		flags |= IOMAP_WRITE;

  		dio->flags |= IOMAP_DIO_WRITE;

  
  		/* for data sync or sync, we need sync completion processing */

  		if (iocb->ki_flags & IOCB_DSYNC)
  			dio->flags |= IOMAP_DIO_NEED_SYNC;

  
  		/*
  		 * For datasync only writes, we optimistically try using FUA for
  		 * this IO.  Any non-FUA write that occurs will clear this flag,
  		 * hence we know before completion whether a cache flush is
  		 * necessary.
  		 */
  		if ((iocb->ki_flags & (IOCB_DSYNC | IOCB_SYNC)) == IOCB_DSYNC)
  			dio->flags |= IOMAP_DIO_WRITE_FUA;

  	}

  	if (iocb->ki_flags & IOCB_NOWAIT) {
  		if (filemap_range_has_page(mapping, start, end)) {
  			ret = -EAGAIN;
  			goto out_free_dio;
  		}
  		flags |= IOMAP_NOWAIT;
  	}

  	ret = filemap_write_and_wait_range(mapping, start, end);
  	if (ret)
  		goto out_free_dio;

  	/*
  	 * Try to invalidate cache pages for the range we're direct
  	 * writing.  If this invalidation fails, tough, the write will
  	 * still work, but racing two incompatible write paths is a
  	 * pretty crazy thing to do, so we don't support it 100%.
  	 */

  	ret = invalidate_inode_pages2_range(mapping,
  			start >> PAGE_SHIFT, end >> PAGE_SHIFT);

  	if (ret)
  		dio_warn_stale_pagecache(iocb->ki_filp);

  	ret = 0;

  	if (iov_iter_rw(iter) == WRITE && !is_sync_kiocb(iocb) &&
  	    !inode->i_sb->s_dio_done_wq) {
  		ret = sb_init_dio_done_wq(inode->i_sb);
  		if (ret < 0)
  			goto out_free_dio;
  	}

  	inode_dio_begin(inode);
  
  	blk_start_plug(&plug);
  	do {
  		ret = iomap_apply(inode, pos, count, flags, ops, dio,
  				iomap_dio_actor);
  		if (ret <= 0) {
  			/* magic error code to fall back to buffered I/O */
  			if (ret == -ENOTBLK)
  				ret = 0;
  			break;
  		}
  		pos += ret;

  
  		if (iov_iter_rw(iter) == READ && pos >= dio->i_size)
  			break;

  	} while ((count = iov_iter_count(iter)) > 0);
  	blk_finish_plug(&plug);
  
  	if (ret < 0)
  		iomap_dio_set_error(dio, ret);

  	/*
  	 * If all the writes we issued were FUA, we don't need to flush the
  	 * cache on IO completion. Clear the sync flag for this case.
  	 */
  	if (dio->flags & IOMAP_DIO_WRITE_FUA)
  		dio->flags &= ~IOMAP_DIO_NEED_SYNC;

  	if (!atomic_dec_and_test(&dio->ref)) {
  		if (!is_sync_kiocb(iocb))
  			return -EIOCBQUEUED;
  
  		for (;;) {
  			set_current_state(TASK_UNINTERRUPTIBLE);
  			if (!READ_ONCE(dio->submit.waiter))
  				break;
  
  			if (!(iocb->ki_flags & IOCB_HIPRI) ||
  			    !dio->submit.last_queue ||

  			    !blk_poll(dio->submit.last_queue,

  					 dio->submit.cookie))

  				io_schedule();
  		}
  		__set_current_state(TASK_RUNNING);
  	}

  	ret = iomap_dio_complete(dio);

  	return ret;

  
  out_free_dio:
  	kfree(dio);
  	return ret;
  }
  EXPORT_SYMBOL_GPL(iomap_dio_rw);

  
  /* Swapfile activation */
  
  #ifdef CONFIG_SWAP
  struct iomap_swapfile_info {
  	struct iomap iomap;		/* accumulated iomap */
  	struct swap_info_struct *sis;
  	uint64_t lowest_ppage;		/* lowest physical addr seen (pages) */
  	uint64_t highest_ppage;		/* highest physical addr seen (pages) */
  	unsigned long nr_pages;		/* number of pages collected */
  	int nr_extents;			/* extent count */
  };
  
  /*
   * Collect physical extents for this swap file.  Physical extents reported to
   * the swap code must be trimmed to align to a page boundary.  The logical
   * offset within the file is irrelevant since the swapfile code maps logical
   * page numbers of the swap device to the physical page-aligned extents.
   */
  static int iomap_swapfile_add_extent(struct iomap_swapfile_info *isi)
  {
  	struct iomap *iomap = &isi->iomap;
  	unsigned long nr_pages;
  	uint64_t first_ppage;
  	uint64_t first_ppage_reported;
  	uint64_t next_ppage;
  	int error;
  
  	/*
  	 * Round the start up and the end down so that the physical
  	 * extent aligns to a page boundary.
  	 */
  	first_ppage = ALIGN(iomap->addr, PAGE_SIZE) >> PAGE_SHIFT;
  	next_ppage = ALIGN_DOWN(iomap->addr + iomap->length, PAGE_SIZE) >>
  			PAGE_SHIFT;
  
  	/* Skip too-short physical extents. */
  	if (first_ppage >= next_ppage)
  		return 0;
  	nr_pages = next_ppage - first_ppage;
  
  	/*
  	 * Calculate how much swap space we're adding; the first page contains
  	 * the swap header and doesn't count.  The mm still wants that first
  	 * page fed to add_swap_extent, however.
  	 */
  	first_ppage_reported = first_ppage;
  	if (iomap->offset == 0)
  		first_ppage_reported++;
  	if (isi->lowest_ppage > first_ppage_reported)
  		isi->lowest_ppage = first_ppage_reported;
  	if (isi->highest_ppage < (next_ppage - 1))
  		isi->highest_ppage = next_ppage - 1;
  
  	/* Add extent, set up for the next call. */
  	error = add_swap_extent(isi->sis, isi->nr_pages, nr_pages, first_ppage);
  	if (error < 0)
  		return error;
  	isi->nr_extents += error;
  	isi->nr_pages += nr_pages;
  	return 0;
  }
  
  /*
   * Accumulate iomaps for this swap file.  We have to accumulate iomaps because
   * swap only cares about contiguous page-aligned physical extents and makes no
   * distinction between written and unwritten extents.
   */
  static loff_t iomap_swapfile_activate_actor(struct inode *inode, loff_t pos,
  		loff_t count, void *data, struct iomap *iomap)
  {
  	struct iomap_swapfile_info *isi = data;
  	int error;

  	switch (iomap->type) {
  	case IOMAP_MAPPED:
  	case IOMAP_UNWRITTEN:
  		/* Only real or unwritten extents. */
  		break;
  	case IOMAP_INLINE:
  		/* No inline data. */

  		pr_err("swapon: file is inline
  ");
  		return -EINVAL;

  	default:

  		pr_err("swapon: file has unallocated extents
  ");
  		return -EINVAL;
  	}

  	/* No uncommitted metadata or shared blocks. */
  	if (iomap->flags & IOMAP_F_DIRTY) {
  		pr_err("swapon: file is not committed
  ");
  		return -EINVAL;
  	}
  	if (iomap->flags & IOMAP_F_SHARED) {
  		pr_err("swapon: file has shared extents
  ");
  		return -EINVAL;
  	}

  	/* Only one bdev per swap file. */
  	if (iomap->bdev != isi->sis->bdev) {
  		pr_err("swapon: file is on multiple devices
  ");
  		return -EINVAL;
  	}

  
  	if (isi->iomap.length == 0) {
  		/* No accumulated extent, so just store it. */
  		memcpy(&isi->iomap, iomap, sizeof(isi->iomap));
  	} else if (isi->iomap.addr + isi->iomap.length == iomap->addr) {
  		/* Append this to the accumulated extent. */
  		isi->iomap.length += iomap->length;
  	} else {
  		/* Otherwise, add the retained iomap and store this one. */
  		error = iomap_swapfile_add_extent(isi);
  		if (error)
  			return error;
  		memcpy(&isi->iomap, iomap, sizeof(isi->iomap));
  	}

  	return count;

  }
  
  /*
   * Iterate a swap file's iomaps to construct physical extents that can be
   * passed to the swapfile subsystem.
   */
  int iomap_swapfile_activate(struct swap_info_struct *sis,
  		struct file *swap_file, sector_t *pagespan,
  		const struct iomap_ops *ops)
  {
  	struct iomap_swapfile_info isi = {
  		.sis = sis,
  		.lowest_ppage = (sector_t)-1ULL,
  	};
  	struct address_space *mapping = swap_file->f_mapping;
  	struct inode *inode = mapping->host;
  	loff_t pos = 0;
  	loff_t len = ALIGN_DOWN(i_size_read(inode), PAGE_SIZE);
  	loff_t ret;
  
  	ret = filemap_write_and_wait(inode->i_mapping);
  	if (ret)
  		return ret;
  
  	while (len > 0) {
  		ret = iomap_apply(inode, pos, len, IOMAP_REPORT,
  				ops, &isi, iomap_swapfile_activate_actor);
  		if (ret <= 0)
  			return ret;
  
  		pos += ret;
  		len -= ret;
  	}
  
  	if (isi.iomap.length) {
  		ret = iomap_swapfile_add_extent(&isi);
  		if (ret)
  			return ret;
  	}
  
  	*pagespan = 1 + isi.highest_ppage - isi.lowest_ppage;
  	sis->max = isi.nr_pages;
  	sis->pages = isi.nr_pages - 1;
  	sis->highest_bit = isi.nr_pages - 1;
  	return isi.nr_extents;
  }
  EXPORT_SYMBOL_GPL(iomap_swapfile_activate);
  #endif /* CONFIG_SWAP */

  
  static loff_t
  iomap_bmap_actor(struct inode *inode, loff_t pos, loff_t length,
  		void *data, struct iomap *iomap)
  {
  	sector_t *bno = data, addr;
  
  	if (iomap->type == IOMAP_MAPPED) {
  		addr = (pos - iomap->offset + iomap->addr) >> inode->i_blkbits;
  		if (addr > INT_MAX)
  			WARN(1, "would truncate bmap result
  ");
  		else
  			*bno = addr;
  	}
  	return 0;
  }
  
  /* legacy ->bmap interface.  0 is the error return (!) */
  sector_t
  iomap_bmap(struct address_space *mapping, sector_t bno,
  		const struct iomap_ops *ops)
  {
  	struct inode *inode = mapping->host;
  	loff_t pos = bno >> inode->i_blkbits;
  	unsigned blocksize = i_blocksize(inode);
  
  	if (filemap_write_and_wait(mapping))
  		return 0;
  
  	bno = 0;
  	iomap_apply(inode, pos, blocksize, 0, ops, &bno, iomap_bmap_actor);
  	return bno;
  }
  EXPORT_SYMBOL_GPL(iomap_bmap);