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

  #include <linux/dax.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,
  		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;
  
  	/*
  	 * 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 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;
  
  	/*
  	 * Copies from kernel address space cannot fail (NFSD is a big user).
  	 */
  	if (!iter_is_iovec(i))
  		flags |= AOP_FLAG_UNINTERRUPTIBLE;
  
  	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,
  		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(unsigned long, 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 | AOP_FLAG_UNINTERRUPTIBLE,
  				&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,
  		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_UNINTERRUPTIBLE | 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)
  {
  	sector_t sector = iomap->blkno +
  		(((pos & ~(PAGE_SIZE - 1)) - iomap->offset) >> 9);
  
  	return __dax_zero_page_range(iomap->bdev, sector, 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(unsigned, 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,
  		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,
  		struct iomap_ops *ops)
  {
  	unsigned blocksize = (1 << inode->i_blkbits);
  	unsigned 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_area_struct *vma, struct vm_fault *vmf,
  		struct iomap_ops *ops)
  {
  	struct page *page = vmf->page;
  	struct inode *inode = file_inode(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,
  				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 0;
  out_unlock:
  	unlock_page(page);
  	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_UNWRITTEN:
  		flags |= FIEMAP_EXTENT_UNWRITTEN;
  		break;
  	case IOMAP_MAPPED:
  		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->blkno != IOMAP_NULL_BLOCK ? iomap->blkno << 9: 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, 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);