/*

   * Copyright (c) 2000-2005 Silicon Graphics, Inc.
   * All Rights Reserved.

   *

   * This program is free software; you can redistribute it and/or
   * modify it under the terms of the GNU General Public License as

   * published by the Free Software Foundation.
   *

   * This program is distributed in the hope that it would 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.

   *

   * You should have received a copy of the GNU General Public License
   * along with this program; if not, write the Free Software Foundation,
   * Inc.,  51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA

   */

  #include "xfs.h"

  #include "xfs_shared.h"

  #include "xfs_format.h"
  #include "xfs_log_format.h"
  #include "xfs_trans_resv.h"

  #include "xfs_mount.h"

  #include "xfs_inode.h"

  #include "xfs_trans.h"

  #include "xfs_inode_item.h"

  #include "xfs_alloc.h"

  #include "xfs_error.h"

  #include "xfs_iomap.h"

  #include "xfs_trace.h"

  #include "xfs_bmap.h"

  #include "xfs_bmap_util.h"

  #include "xfs_bmap_btree.h"

  #include "xfs_reflink.h"

  #include <linux/gfp.h>

  #include <linux/mpage.h>

  #include <linux/pagevec.h>

  #include <linux/writeback.h>

  /* flags for direct write completions */
  #define XFS_DIO_FLAG_UNWRITTEN	(1 << 0)
  #define XFS_DIO_FLAG_APPEND	(1 << 1)

  #define XFS_DIO_FLAG_COW	(1 << 2)

  /*
   * structure owned by writepages passed to individual writepage calls
   */
  struct xfs_writepage_ctx {
  	struct xfs_bmbt_irec    imap;
  	bool			imap_valid;
  	unsigned int		io_type;

  	struct xfs_ioend	*ioend;
  	sector_t		last_block;
  };

  void

  xfs_count_page_state(
  	struct page		*page,
  	int			*delalloc,

  	int			*unwritten)
  {
  	struct buffer_head	*bh, *head;

  	*delalloc = *unwritten = 0;

  
  	bh = head = page_buffers(page);
  	do {

  		if (buffer_unwritten(bh))

  			(*unwritten) = 1;
  		else if (buffer_delay(bh))
  			(*delalloc) = 1;
  	} while ((bh = bh->b_this_page) != head);
  }

  struct block_device *

  xfs_find_bdev_for_inode(

  	struct inode		*inode)

  {

  	struct xfs_inode	*ip = XFS_I(inode);

  	struct xfs_mount	*mp = ip->i_mount;

  	if (XFS_IS_REALTIME_INODE(ip))

  		return mp->m_rtdev_targp->bt_bdev;
  	else
  		return mp->m_ddev_targp->bt_bdev;
  }

  /*

   * We're now finished for good with this page.  Update the page state via the
   * associated buffer_heads, paying attention to the start and end offsets that
   * we need to process on the page.

   *
   * Landmine Warning: bh->b_end_io() will call end_page_writeback() on the last
   * buffer in the IO. Once it does this, it is unsafe to access the bufferhead or
   * the page at all, as we may be racing with memory reclaim and it can free both
   * the bufferhead chain and the page as it will see the page as clean and
   * unused.

   */
  static void
  xfs_finish_page_writeback(
  	struct inode		*inode,
  	struct bio_vec		*bvec,
  	int			error)
  {

  	unsigned int		end = bvec->bv_offset + bvec->bv_len - 1;

  	struct buffer_head	*head, *bh, *next;

  	unsigned int		off = 0;

  	unsigned int		bsize;

  
  	ASSERT(bvec->bv_offset < PAGE_SIZE);

  	ASSERT((bvec->bv_offset & ((1 << inode->i_blkbits) - 1)) == 0);

  	ASSERT(end < PAGE_SIZE);

  	ASSERT((bvec->bv_len & ((1 << inode->i_blkbits) - 1)) == 0);

  
  	bh = head = page_buffers(bvec->bv_page);

  	bsize = bh->b_size;

  	do {

  		next = bh->b_this_page;

  		if (off < bvec->bv_offset)
  			goto next_bh;
  		if (off > end)
  			break;
  		bh->b_end_io(bh, !error);
  next_bh:

  		off += bsize;
  	} while ((bh = next) != head);

  }
  
  /*
   * We're now finished for good with this ioend structure.  Update the page
   * state, release holds on bios, and finally free up memory.  Do not use the
   * ioend after this.

   */

  STATIC void
  xfs_destroy_ioend(

  	struct xfs_ioend	*ioend,
  	int			error)

  {

  	struct inode		*inode = ioend->io_inode;

  	struct bio		*last = ioend->io_bio;

  	struct bio		*bio, *next;

  	for (bio = &ioend->io_inline_bio; bio; bio = next) {

  		struct bio_vec	*bvec;
  		int		i;

  		/*
  		 * For the last bio, bi_private points to the ioend, so we
  		 * need to explicitly end the iteration here.
  		 */
  		if (bio == last)
  			next = NULL;
  		else
  			next = bio->bi_private;

  		/* walk each page on bio, ending page IO on them */
  		bio_for_each_segment_all(bvec, bio, i)
  			xfs_finish_page_writeback(inode, bvec, error);
  
  		bio_put(bio);

  	}

  }
  
  /*

   * Fast and loose check if this write could update the on-disk inode size.
   */
  static inline bool xfs_ioend_is_append(struct xfs_ioend *ioend)
  {
  	return ioend->io_offset + ioend->io_size >
  		XFS_I(ioend->io_inode)->i_d.di_size;
  }

  STATIC int
  xfs_setfilesize_trans_alloc(
  	struct xfs_ioend	*ioend)
  {
  	struct xfs_mount	*mp = XFS_I(ioend->io_inode)->i_mount;
  	struct xfs_trans	*tp;
  	int			error;

  	error = xfs_trans_alloc(mp, &M_RES(mp)->tr_fsyncts, 0, 0, 0, &tp);
  	if (error)

  		return error;

  
  	ioend->io_append_trans = tp;
  
  	/*

  	 * We may pass freeze protection with a transaction.  So tell lockdep

  	 * we released it.
  	 */

  	__sb_writers_release(ioend->io_inode->i_sb, SB_FREEZE_FS);

  	/*

  	 * We hand off the transaction to the completion thread now, so
  	 * clear the flag here.
  	 */
  	current_restore_flags_nested(&tp->t_pflags, PF_FSTRANS);
  	return 0;
  }

  /*

   * Update on-disk file size now that data has been written to disk.

   */

  STATIC int

  __xfs_setfilesize(

  	struct xfs_inode	*ip,
  	struct xfs_trans	*tp,
  	xfs_off_t		offset,
  	size_t			size)

  {

  	xfs_fsize_t		isize;

  	xfs_ilock(ip, XFS_ILOCK_EXCL);

  	isize = xfs_new_eof(ip, offset + size);

  	if (!isize) {
  		xfs_iunlock(ip, XFS_ILOCK_EXCL);

  		xfs_trans_cancel(tp);

  		return 0;

  	}

  	trace_xfs_setfilesize(ip, offset, size);

  
  	ip->i_d.di_size = isize;
  	xfs_trans_ijoin(tp, ip, XFS_ILOCK_EXCL);
  	xfs_trans_log_inode(tp, ip, XFS_ILOG_CORE);

  	return xfs_trans_commit(tp);

  }

  int
  xfs_setfilesize(
  	struct xfs_inode	*ip,
  	xfs_off_t		offset,
  	size_t			size)
  {
  	struct xfs_mount	*mp = ip->i_mount;
  	struct xfs_trans	*tp;
  	int			error;
  
  	error = xfs_trans_alloc(mp, &M_RES(mp)->tr_fsyncts, 0, 0, 0, &tp);
  	if (error)
  		return error;
  
  	return __xfs_setfilesize(ip, tp, offset, size);
  }

  STATIC int
  xfs_setfilesize_ioend(

  	struct xfs_ioend	*ioend,
  	int			error)

  {
  	struct xfs_inode	*ip = XFS_I(ioend->io_inode);
  	struct xfs_trans	*tp = ioend->io_append_trans;
  
  	/*
  	 * The transaction may have been allocated in the I/O submission thread,
  	 * thus we need to mark ourselves as being in a transaction manually.
  	 * Similarly for freeze protection.
  	 */
  	current_set_flags_nested(&tp->t_pflags, PF_FSTRANS);

  	__sb_writers_acquired(VFS_I(ip)->i_sb, SB_FREEZE_FS);

  	/* we abort the update if there was an IO error */

  	if (error) {

  		xfs_trans_cancel(tp);

  		return error;

  	}

  	return __xfs_setfilesize(ip, tp, ioend->io_offset, ioend->io_size);

  }

  /*

   * IO write completion.

   */
  STATIC void

  xfs_end_io(

  	struct work_struct *work)

  {

  	struct xfs_ioend	*ioend =
  		container_of(work, struct xfs_ioend, io_work);
  	struct xfs_inode	*ip = XFS_I(ioend->io_inode);
  	int			error = ioend->io_bio->bi_error;

  	/*
  	 * Set an error if the mount has shut down and proceed with end I/O
  	 * processing so it can perform whatever cleanups are necessary.
  	 */
  	if (XFS_FORCED_SHUTDOWN(ip->i_mount))

  		error = -EIO;

  	/*

  	 * For a CoW extent, we need to move the mapping from the CoW fork
  	 * to the data fork.  If instead an error happened, just dump the
  	 * new blocks.
  	 */
  	if (ioend->io_type == XFS_IO_COW) {
  		if (error)
  			goto done;
  		if (ioend->io_bio->bi_error) {
  			error = xfs_reflink_cancel_cow_range(ip,
  					ioend->io_offset, ioend->io_size);
  			goto done;
  		}
  		error = xfs_reflink_end_cow(ip, ioend->io_offset,
  				ioend->io_size);
  		if (error)
  			goto done;
  	}
  
  	/*

  	 * For unwritten extents we need to issue transactions to convert a
  	 * range to normal written extens after the data I/O has finished.

  	 * Detecting and handling completion IO errors is done individually
  	 * for each case as different cleanup operations need to be performed
  	 * on error.

  	 */

  	if (ioend->io_type == XFS_IO_UNWRITTEN) {

  		if (error)

  			goto done;

  		error = xfs_iomap_write_unwritten(ip, ioend->io_offset,
  						  ioend->io_size);

  	} else if (ioend->io_append_trans) {

  		error = xfs_setfilesize_ioend(ioend, error);

  	} else {

  		ASSERT(!xfs_ioend_is_append(ioend) ||
  		       ioend->io_type == XFS_IO_COW);

  	}

  done:

  	xfs_destroy_ioend(ioend, error);

  }

  STATIC void
  xfs_end_bio(
  	struct bio		*bio)

  {

  	struct xfs_ioend	*ioend = bio->bi_private;
  	struct xfs_mount	*mp = XFS_I(ioend->io_inode)->i_mount;

  	if (ioend->io_type == XFS_IO_UNWRITTEN || ioend->io_type == XFS_IO_COW)

  		queue_work(mp->m_unwritten_workqueue, &ioend->io_work);
  	else if (ioend->io_append_trans)
  		queue_work(mp->m_data_workqueue, &ioend->io_work);
  	else
  		xfs_destroy_ioend(ioend, bio->bi_error);

  }

  STATIC int
  xfs_map_blocks(
  	struct inode		*inode,
  	loff_t			offset,

  	struct xfs_bmbt_irec	*imap,

  	int			type)

  {

  	struct xfs_inode	*ip = XFS_I(inode);
  	struct xfs_mount	*mp = ip->i_mount;

  	ssize_t			count = 1 << inode->i_blkbits;

  	xfs_fileoff_t		offset_fsb, end_fsb;
  	int			error = 0;

  	int			bmapi_flags = XFS_BMAPI_ENTIRE;
  	int			nimaps = 1;
  
  	if (XFS_FORCED_SHUTDOWN(mp))

  		return -EIO;

  	ASSERT(type != XFS_IO_COW);

  	if (type == XFS_IO_UNWRITTEN)

  		bmapi_flags |= XFS_BMAPI_IGSTATE;

  	xfs_ilock(ip, XFS_ILOCK_SHARED);

  	ASSERT(ip->i_d.di_format != XFS_DINODE_FMT_BTREE ||
  	       (ip->i_df.if_flags & XFS_IFEXTENTS));

  	ASSERT(offset <= mp->m_super->s_maxbytes);

  	if (offset + count > mp->m_super->s_maxbytes)
  		count = mp->m_super->s_maxbytes - offset;

  	end_fsb = XFS_B_TO_FSB(mp, (xfs_ufsize_t)offset + count);
  	offset_fsb = XFS_B_TO_FSBT(mp, offset);

  	error = xfs_bmapi_read(ip, offset_fsb, end_fsb - offset_fsb,
  				imap, &nimaps, bmapi_flags);

  	/*
  	 * Truncate an overwrite extent if there's a pending CoW
  	 * reservation before the end of this extent.  This forces us
  	 * to come back to writepage to take care of the CoW.
  	 */
  	if (nimaps && type == XFS_IO_OVERWRITE)
  		xfs_reflink_trim_irec_to_next_cow(ip, offset_fsb, imap);

  	xfs_iunlock(ip, XFS_ILOCK_SHARED);

  	if (error)

  		return error;

  	if (type == XFS_IO_DELALLOC &&

  	    (!nimaps || isnullstartblock(imap->br_startblock))) {

  		error = xfs_iomap_write_allocate(ip, XFS_DATA_FORK, offset,
  				imap);

  		if (!error)

  			trace_xfs_map_blocks_alloc(ip, offset, count, type, imap);

  		return error;

  	}

  #ifdef DEBUG

  	if (type == XFS_IO_UNWRITTEN) {

  		ASSERT(nimaps);
  		ASSERT(imap->br_startblock != HOLESTARTBLOCK);
  		ASSERT(imap->br_startblock != DELAYSTARTBLOCK);
  	}
  #endif
  	if (nimaps)
  		trace_xfs_map_blocks_found(ip, offset, count, type, imap);
  	return 0;

  }

  STATIC bool

  xfs_imap_valid(

  	struct inode		*inode,

  	struct xfs_bmbt_irec	*imap,

  	xfs_off_t		offset)

  {

  	offset >>= inode->i_blkbits;

  	return offset >= imap->br_startoff &&
  		offset < imap->br_startoff + imap->br_blockcount;

  }

  STATIC void
  xfs_start_buffer_writeback(
  	struct buffer_head	*bh)
  {
  	ASSERT(buffer_mapped(bh));
  	ASSERT(buffer_locked(bh));
  	ASSERT(!buffer_delay(bh));
  	ASSERT(!buffer_unwritten(bh));
  
  	mark_buffer_async_write(bh);
  	set_buffer_uptodate(bh);
  	clear_buffer_dirty(bh);
  }
  
  STATIC void
  xfs_start_page_writeback(
  	struct page		*page,

  	int			clear_dirty)

  {
  	ASSERT(PageLocked(page));
  	ASSERT(!PageWriteback(page));

  
  	/*
  	 * if the page was not fully cleaned, we need to ensure that the higher
  	 * layers come back to it correctly. That means we need to keep the page
  	 * dirty, and for WB_SYNC_ALL writeback we need to ensure the
  	 * PAGECACHE_TAG_TOWRITE index mark is not removed so another attempt to
  	 * write this page in this writeback sweep will be made.
  	 */
  	if (clear_dirty) {

  		clear_page_dirty_for_io(page);

  		set_page_writeback(page);
  	} else
  		set_page_writeback_keepwrite(page);

  	unlock_page(page);

  }

  static inline int xfs_bio_add_buffer(struct bio *bio, struct buffer_head *bh)

  {
  	return bio_add_page(bio, bh->b_page, bh->b_size, bh_offset(bh));
  }
  
  /*

   * Submit the bio for an ioend. We are passed an ioend with a bio attached to
   * it, and we submit that bio. The ioend may be used for multiple bio
   * submissions, so we only want to allocate an append transaction for the ioend
   * once. In the case of multiple bio submission, each bio will take an IO
   * reference to the ioend to ensure that the ioend completion is only done once
   * all bios have been submitted and the ioend is really done.

   *
   * If @fail is non-zero, it means that we have a situation where some part of
   * the submission process has failed after we have marked paged for writeback

   * and unlocked them. In this situation, we need to fail the bio and ioend
   * rather than submit it to IO. This typically only happens on a filesystem
   * shutdown.

   */

  STATIC int

  xfs_submit_ioend(

  	struct writeback_control *wbc,

  	struct xfs_ioend	*ioend,

  	int			status)

  {

  	/* Reserve log space if we might write beyond the on-disk inode size. */
  	if (!status &&

  	    ioend->io_type != XFS_IO_UNWRITTEN &&

  	    xfs_ioend_is_append(ioend) &&
  	    !ioend->io_append_trans)

  		status = xfs_setfilesize_trans_alloc(ioend);

  	ioend->io_bio->bi_private = ioend;
  	ioend->io_bio->bi_end_io = xfs_end_bio;

  	bio_set_op_attrs(ioend->io_bio, REQ_OP_WRITE,
  			 (wbc->sync_mode == WB_SYNC_ALL) ? WRITE_SYNC : 0);

  	/*
  	 * If we are failing the IO now, just mark the ioend with an
  	 * error and finish it. This will run IO completion immediately
  	 * as there is only one reference to the ioend at this point in
  	 * time.
  	 */
  	if (status) {

  		ioend->io_bio->bi_error = status;
  		bio_endio(ioend->io_bio);

  		return status;
  	}

  	submit_bio(ioend->io_bio);

  	return 0;

  }

  static void
  xfs_init_bio_from_bh(
  	struct bio		*bio,
  	struct buffer_head	*bh)
  {
  	bio->bi_iter.bi_sector = bh->b_blocknr * (bh->b_size >> 9);
  	bio->bi_bdev = bh->b_bdev;
  }

  static struct xfs_ioend *
  xfs_alloc_ioend(
  	struct inode		*inode,
  	unsigned int		type,
  	xfs_off_t		offset,
  	struct buffer_head	*bh)
  {
  	struct xfs_ioend	*ioend;
  	struct bio		*bio;

  	bio = bio_alloc_bioset(GFP_NOFS, BIO_MAX_PAGES, xfs_ioend_bioset);
  	xfs_init_bio_from_bh(bio, bh);
  
  	ioend = container_of(bio, struct xfs_ioend, io_inline_bio);
  	INIT_LIST_HEAD(&ioend->io_list);
  	ioend->io_type = type;
  	ioend->io_inode = inode;
  	ioend->io_size = 0;
  	ioend->io_offset = offset;
  	INIT_WORK(&ioend->io_work, xfs_end_io);
  	ioend->io_append_trans = NULL;
  	ioend->io_bio = bio;
  	return ioend;
  }
  
  /*
   * Allocate a new bio, and chain the old bio to the new one.
   *
   * Note that we have to do perform the chaining in this unintuitive order
   * so that the bi_private linkage is set up in the right direction for the
   * traversal in xfs_destroy_ioend().
   */
  static void
  xfs_chain_bio(
  	struct xfs_ioend	*ioend,
  	struct writeback_control *wbc,
  	struct buffer_head	*bh)
  {
  	struct bio *new;
  
  	new = bio_alloc(GFP_NOFS, BIO_MAX_PAGES);
  	xfs_init_bio_from_bh(new, bh);
  
  	bio_chain(ioend->io_bio, new);
  	bio_get(ioend->io_bio);		/* for xfs_destroy_ioend */

  	bio_set_op_attrs(ioend->io_bio, REQ_OP_WRITE,
  			  (wbc->sync_mode == WB_SYNC_ALL) ? WRITE_SYNC : 0);

  	submit_bio(ioend->io_bio);

  	ioend->io_bio = new;

  }
  
  /*
   * Test to see if we've been building up a completion structure for
   * earlier buffers -- if so, we try to append to this ioend if we
   * can, otherwise we finish off any current ioend and start another.

   * Return the ioend we finished off so that the caller can submit it
   * once it has finished processing the dirty page.

   */
  STATIC void
  xfs_add_to_ioend(
  	struct inode		*inode,
  	struct buffer_head	*bh,

  	xfs_off_t		offset,

  	struct xfs_writepage_ctx *wpc,

  	struct writeback_control *wbc,

  	struct list_head	*iolist)

  {

  	if (!wpc->ioend || wpc->io_type != wpc->ioend->io_type ||

  	    bh->b_blocknr != wpc->last_block + 1 ||
  	    offset != wpc->ioend->io_offset + wpc->ioend->io_size) {

  		if (wpc->ioend)
  			list_add(&wpc->ioend->io_list, iolist);

  		wpc->ioend = xfs_alloc_ioend(inode, wpc->io_type, offset, bh);

  	}

  	/*
  	 * If the buffer doesn't fit into the bio we need to allocate a new
  	 * one.  This shouldn't happen more than once for a given buffer.
  	 */
  	while (xfs_bio_add_buffer(wpc->ioend->io_bio, bh) != bh->b_size)
  		xfs_chain_bio(wpc->ioend, wbc, bh);

  	wpc->ioend->io_size += bh->b_size;
  	wpc->last_block = bh->b_blocknr;

  	xfs_start_buffer_writeback(bh);

  }

  STATIC void

  xfs_map_buffer(

  	struct inode		*inode,

  	struct buffer_head	*bh,

  	struct xfs_bmbt_irec	*imap,

  	xfs_off_t		offset)

  {
  	sector_t		bn;

  	struct xfs_mount	*m = XFS_I(inode)->i_mount;

  	xfs_off_t		iomap_offset = XFS_FSB_TO_B(m, imap->br_startoff);
  	xfs_daddr_t		iomap_bn = xfs_fsb_to_db(XFS_I(inode), imap->br_startblock);

  	ASSERT(imap->br_startblock != HOLESTARTBLOCK);
  	ASSERT(imap->br_startblock != DELAYSTARTBLOCK);

  	bn = (iomap_bn >> (inode->i_blkbits - BBSHIFT)) +

  	      ((offset - iomap_offset) >> inode->i_blkbits);

  	ASSERT(bn || XFS_IS_REALTIME_INODE(XFS_I(inode)));

  
  	bh->b_blocknr = bn;
  	set_buffer_mapped(bh);
  }
  
  STATIC void

  xfs_map_at_offset(

  	struct inode		*inode,

  	struct buffer_head	*bh,

  	struct xfs_bmbt_irec	*imap,

  	xfs_off_t		offset)

  {

  	ASSERT(imap->br_startblock != HOLESTARTBLOCK);
  	ASSERT(imap->br_startblock != DELAYSTARTBLOCK);

  	xfs_map_buffer(inode, bh, imap, offset);

  	set_buffer_mapped(bh);
  	clear_buffer_delay(bh);

  	clear_buffer_unwritten(bh);

  }
  
  /*

   * Test if a given page contains at least one buffer of a given @type.
   * If @check_all_buffers is true, then we walk all the buffers in the page to
   * try to find one of the type passed in. If it is not set, then the caller only
   * needs to check the first buffer on the page for a match.

   */

  STATIC bool

  xfs_check_page_type(

  	struct page		*page,

  	unsigned int		type,
  	bool			check_all_buffers)

  {

  	struct buffer_head	*bh;
  	struct buffer_head	*head;

  	if (PageWriteback(page))
  		return false;
  	if (!page->mapping)
  		return false;
  	if (!page_has_buffers(page))
  		return false;

  	bh = head = page_buffers(page);
  	do {
  		if (buffer_unwritten(bh)) {
  			if (type == XFS_IO_UNWRITTEN)
  				return true;
  		} else if (buffer_delay(bh)) {

  			if (type == XFS_IO_DELALLOC)

  				return true;
  		} else if (buffer_dirty(bh) && buffer_mapped(bh)) {

  			if (type == XFS_IO_OVERWRITE)

  				return true;
  		}

  		/* If we are only checking the first buffer, we are done now. */
  		if (!check_all_buffers)
  			break;
  	} while ((bh = bh->b_this_page) != head);

  	return false;

  }

  STATIC void
  xfs_vm_invalidatepage(
  	struct page		*page,

  	unsigned int		offset,
  	unsigned int		length)

  {

  	trace_xfs_invalidatepage(page->mapping->host, page, offset,
  				 length);
  	block_invalidatepage(page, offset, length);

  }
  
  /*
   * If the page has delalloc buffers on it, we need to punch them out before we
   * invalidate the page. If we don't, we leave a stale delalloc mapping on the
   * inode that can trip a BUG() in xfs_get_blocks() later on if a direct IO read
   * is done on that same region - the delalloc extent is returned when none is
   * supposed to be there.
   *
   * We prevent this by truncating away the delalloc regions on the page before
   * invalidating it. Because they are delalloc, we can do this without needing a
   * transaction. Indeed - if we get ENOSPC errors, we have to be able to do this
   * truncation without a transaction as there is no space left for block
   * reservation (typically why we see a ENOSPC in writeback).
   *
   * This is not a performance critical path, so for now just do the punching a
   * buffer head at a time.
   */
  STATIC void
  xfs_aops_discard_page(
  	struct page		*page)
  {
  	struct inode		*inode = page->mapping->host;
  	struct xfs_inode	*ip = XFS_I(inode);
  	struct buffer_head	*bh, *head;
  	loff_t			offset = page_offset(page);

  	if (!xfs_check_page_type(page, XFS_IO_DELALLOC, true))

  		goto out_invalidate;

  	if (XFS_FORCED_SHUTDOWN(ip->i_mount))
  		goto out_invalidate;

  	xfs_alert(ip->i_mount,

  		"page discard on page %p, inode 0x%llx, offset %llu.",
  			page, ip->i_ino, offset);
  
  	xfs_ilock(ip, XFS_ILOCK_EXCL);
  	bh = head = page_buffers(page);
  	do {

  		int		error;

  		xfs_fileoff_t	start_fsb;

  
  		if (!buffer_delay(bh))
  			goto next_buffer;

  		start_fsb = XFS_B_TO_FSBT(ip->i_mount, offset);
  		error = xfs_bmap_punch_delalloc_range(ip, start_fsb, 1);

  		if (error) {
  			/* something screwed, just bail */

  			if (!XFS_FORCED_SHUTDOWN(ip->i_mount)) {

  				xfs_alert(ip->i_mount,

  			"page discard unable to remove delalloc mapping.");

  			}

  			break;
  		}
  next_buffer:

  		offset += 1 << inode->i_blkbits;

  
  	} while ((bh = bh->b_this_page) != head);
  
  	xfs_iunlock(ip, XFS_ILOCK_EXCL);
  out_invalidate:

  	xfs_vm_invalidatepage(page, 0, PAGE_SIZE);

  	return;
  }

  static int
  xfs_map_cow(
  	struct xfs_writepage_ctx *wpc,
  	struct inode		*inode,
  	loff_t			offset,
  	unsigned int		*new_type)
  {
  	struct xfs_inode	*ip = XFS_I(inode);
  	struct xfs_bmbt_irec	imap;
  	bool			is_cow = false, need_alloc = false;
  	int			error;
  
  	/*
  	 * If we already have a valid COW mapping keep using it.
  	 */
  	if (wpc->io_type == XFS_IO_COW) {
  		wpc->imap_valid = xfs_imap_valid(inode, &wpc->imap, offset);
  		if (wpc->imap_valid) {
  			*new_type = XFS_IO_COW;
  			return 0;
  		}
  	}
  
  	/*
  	 * Else we need to check if there is a COW mapping at this offset.
  	 */
  	xfs_ilock(ip, XFS_ILOCK_SHARED);
  	is_cow = xfs_reflink_find_cow_mapping(ip, offset, &imap, &need_alloc);
  	xfs_iunlock(ip, XFS_ILOCK_SHARED);
  
  	if (!is_cow)
  		return 0;
  
  	/*
  	 * And if the COW mapping has a delayed extent here we need to
  	 * allocate real space for it now.
  	 */
  	if (need_alloc) {
  		error = xfs_iomap_write_allocate(ip, XFS_COW_FORK, offset,
  				&imap);
  		if (error)
  			return error;
  	}
  
  	wpc->io_type = *new_type = XFS_IO_COW;
  	wpc->imap_valid = true;
  	wpc->imap = imap;
  	return 0;
  }

  /*

   * We implement an immediate ioend submission policy here to avoid needing to
   * chain multiple ioends and hence nest mempool allocations which can violate
   * forward progress guarantees we need to provide. The current ioend we are
   * adding buffers to is cached on the writepage context, and if the new buffer
   * does not append to the cached ioend it will create a new ioend and cache that
   * instead.
   *
   * If a new ioend is created and cached, the old ioend is returned and queued
   * locally for submission once the entire page is processed or an error has been
   * detected.  While ioends are submitted immediately after they are completed,
   * batching optimisations are provided by higher level block plugging.
   *
   * At the end of a writeback pass, there will be a cached ioend remaining on the
   * writepage context that the caller will need to submit.
   */

  static int
  xfs_writepage_map(
  	struct xfs_writepage_ctx *wpc,

  	struct writeback_control *wbc,

  	struct inode		*inode,
  	struct page		*page,
  	loff_t			offset,
  	__uint64_t              end_offset)
  {

  	LIST_HEAD(submit_list);
  	struct xfs_ioend	*ioend, *next;

  	struct buffer_head	*bh, *head;
  	ssize_t			len = 1 << inode->i_blkbits;
  	int			error = 0;

  	int			count = 0;

  	int			uptodate = 1;

  	unsigned int		new_type;

  
  	bh = head = page_buffers(page);
  	offset = page_offset(page);

  	do {
  		if (offset >= end_offset)
  			break;
  		if (!buffer_uptodate(bh))
  			uptodate = 0;
  
  		/*
  		 * set_page_dirty dirties all buffers in a page, independent
  		 * of their state.  The dirty state however is entirely
  		 * meaningless for holes (!mapped && uptodate), so skip
  		 * buffers covering holes here.
  		 */
  		if (!buffer_mapped(bh) && buffer_uptodate(bh)) {
  			wpc->imap_valid = false;
  			continue;
  		}

  		if (buffer_unwritten(bh))
  			new_type = XFS_IO_UNWRITTEN;
  		else if (buffer_delay(bh))
  			new_type = XFS_IO_DELALLOC;
  		else if (buffer_uptodate(bh))
  			new_type = XFS_IO_OVERWRITE;
  		else {

  			if (PageUptodate(page))
  				ASSERT(buffer_mapped(bh));
  			/*
  			 * This buffer is not uptodate and will not be
  			 * written to disk.  Ensure that we will put any
  			 * subsequent writeable buffers into a new
  			 * ioend.
  			 */
  			wpc->imap_valid = false;
  			continue;
  		}

  		if (xfs_is_reflink_inode(XFS_I(inode))) {
  			error = xfs_map_cow(wpc, inode, offset, &new_type);
  			if (error)
  				goto out;
  		}
  
  		if (wpc->io_type != new_type) {
  			wpc->io_type = new_type;
  			wpc->imap_valid = false;
  		}

  		if (wpc->imap_valid)
  			wpc->imap_valid = xfs_imap_valid(inode, &wpc->imap,
  							 offset);
  		if (!wpc->imap_valid) {
  			error = xfs_map_blocks(inode, offset, &wpc->imap,
  					     wpc->io_type);
  			if (error)

  				goto out;

  			wpc->imap_valid = xfs_imap_valid(inode, &wpc->imap,
  							 offset);
  		}
  		if (wpc->imap_valid) {
  			lock_buffer(bh);
  			if (wpc->io_type != XFS_IO_OVERWRITE)
  				xfs_map_at_offset(inode, bh, &wpc->imap, offset);

  			xfs_add_to_ioend(inode, bh, offset, wpc, wbc, &submit_list);

  			count++;
  		}

  	} while (offset += len, ((bh = bh->b_this_page) != head));
  
  	if (uptodate && bh == head)
  		SetPageUptodate(page);

  	ASSERT(wpc->ioend || list_empty(&submit_list));

  out:

  	/*

  	 * On error, we have to fail the ioend here because we have locked
  	 * buffers in the ioend. If we don't do this, we'll deadlock
  	 * invalidating the page as that tries to lock the buffers on the page.
  	 * Also, because we may have set pages under writeback, we have to make
  	 * sure we run IO completion to mark the error state of the IO
  	 * appropriately, so we can't cancel the ioend directly here. That means
  	 * we have to mark this page as under writeback if we included any
  	 * buffers from it in the ioend chain so that completion treats it
  	 * correctly.

  	 *

  	 * If we didn't include the page in the ioend, the on error we can
  	 * simply discard and unlock it as there are no other users of the page
  	 * or it's buffers right now. The caller will still need to trigger
  	 * submission of outstanding ioends on the writepage context so they are
  	 * treated correctly on error.

  	 */

  	if (count) {
  		xfs_start_page_writeback(page, !error);
  
  		/*
  		 * Preserve the original error if there was one, otherwise catch
  		 * submission errors here and propagate into subsequent ioend
  		 * submissions.
  		 */
  		list_for_each_entry_safe(ioend, next, &submit_list, io_list) {
  			int error2;
  
  			list_del_init(&ioend->io_list);
  			error2 = xfs_submit_ioend(wbc, ioend, error);
  			if (error2 && !error)
  				error = error2;
  		}
  	} else if (error) {

  		xfs_aops_discard_page(page);
  		ClearPageUptodate(page);
  		unlock_page(page);

  	} else {
  		/*
  		 * We can end up here with no error and nothing to write if we
  		 * race with a partial page truncate on a sub-page block sized
  		 * filesystem. In that case we need to mark the page clean.
  		 */
  		xfs_start_page_writeback(page, 1);
  		end_page_writeback(page);

  	}

  	mapping_set_error(page->mapping, error);
  	return error;
  }

  /*

   * Write out a dirty page.
   *
   * For delalloc space on the page we need to allocate space and flush it.
   * For unwritten space on the page we need to start the conversion to
   * regular allocated space.

   * For any other dirty buffer heads on the page we should flush them.

   */

  STATIC int

  xfs_do_writepage(

  	struct page		*page,

  	struct writeback_control *wbc,
  	void			*data)

  {

  	struct xfs_writepage_ctx *wpc = data;

  	struct inode		*inode = page->mapping->host;

  	loff_t			offset;

  	__uint64_t              end_offset;

  	pgoff_t                 end_index;

  	trace_xfs_writepage(inode, page, 0, 0);

  	ASSERT(page_has_buffers(page));

  	/*
  	 * Refuse to write the page out if we are called from reclaim context.
  	 *

  	 * This avoids stack overflows when called from deeply used stacks in
  	 * random callers for direct reclaim or memcg reclaim.  We explicitly
  	 * allow reclaim from kswapd as the stack usage there is relatively low.

  	 *

  	 * This should never happen except in the case of a VM regression so
  	 * warn about it.

  	 */

  	if (WARN_ON_ONCE((current->flags & (PF_MEMALLOC|PF_KSWAPD)) ==
  			PF_MEMALLOC))

  		goto redirty;

  	/*

  	 * Given that we do not allow direct reclaim to call us, we should
  	 * never be called while in a filesystem transaction.

  	 */

  	if (WARN_ON_ONCE(current->flags & PF_FSTRANS))

  		goto redirty;

  	/*

  	 * Is this page beyond the end of the file?
  	 *

  	 * The page index is less than the end_index, adjust the end_offset
  	 * to the highest offset that this page should represent.
  	 * -----------------------------------------------------
  	 * |			file mapping	       | <EOF> |
  	 * -----------------------------------------------------
  	 * | Page ... | Page N-2 | Page N-1 |  Page N  |       |
  	 * ^--------------------------------^----------|--------
  	 * |     desired writeback range    |      see else    |
  	 * ---------------------------------^------------------|
  	 */

  	offset = i_size_read(inode);

  	end_index = offset >> PAGE_SHIFT;

  	if (page->index < end_index)

  		end_offset = (xfs_off_t)(page->index + 1) << PAGE_SHIFT;

  	else {
  		/*
  		 * Check whether the page to write out is beyond or straddles
  		 * i_size or not.
  		 * -------------------------------------------------------
  		 * |		file mapping		        | <EOF>  |
  		 * -------------------------------------------------------
  		 * | Page ... | Page N-2 | Page N-1 |  Page N   | Beyond |
  		 * ^--------------------------------^-----------|---------
  		 * |				    |      Straddles     |
  		 * ---------------------------------^-----------|--------|
  		 */

  		unsigned offset_into_page = offset & (PAGE_SIZE - 1);

  
  		/*

  		 * Skip the page if it is fully outside i_size, e.g. due to a
  		 * truncate operation that is in progress. We must redirty the
  		 * page so that reclaim stops reclaiming it. Otherwise
  		 * xfs_vm_releasepage() is called on it and gets confused.

  		 *
  		 * Note that the end_index is unsigned long, it would overflow
  		 * if the given offset is greater than 16TB on 32-bit system
  		 * and if we do check the page is fully outside i_size or not
  		 * via "if (page->index >= end_index + 1)" as "end_index + 1"
  		 * will be evaluated to 0.  Hence this page will be redirtied
  		 * and be written out repeatedly which would result in an
  		 * infinite loop, the user program that perform this operation
  		 * will hang.  Instead, we can verify this situation by checking
  		 * if the page to write is totally beyond the i_size or if it's
  		 * offset is just equal to the EOF.

  		 */

  		if (page->index > end_index ||
  		    (page->index == end_index && offset_into_page == 0))

  			goto redirty;

  
  		/*
  		 * The page straddles i_size.  It must be zeroed out on each
  		 * and every writepage invocation because it may be mmapped.
  		 * "A file is mapped in multiples of the page size.  For a file

  		 * that is not a multiple of the page size, the remaining

  		 * memory is zeroed when mapped, and writes to that region are
  		 * not written out to the file."
  		 */

  		zero_user_segment(page, offset_into_page, PAGE_SIZE);

  
  		/* Adjust the end_offset to the end of file */
  		end_offset = offset;

  	}

  	return xfs_writepage_map(wpc, wbc, inode, page, offset, end_offset);

  redirty:

  	redirty_page_for_writepage(wbc, page);
  	unlock_page(page);
  	return 0;

  }

  STATIC int

  xfs_vm_writepage(
  	struct page		*page,
  	struct writeback_control *wbc)
  {
  	struct xfs_writepage_ctx wpc = {
  		.io_type = XFS_IO_INVALID,
  	};
  	int			ret;
  
  	ret = xfs_do_writepage(page, wbc, &wpc);

  	if (wpc.ioend)
  		ret = xfs_submit_ioend(wbc, wpc.ioend, ret);
  	return ret;

  }
  
  STATIC int

  xfs_vm_writepages(
  	struct address_space	*mapping,
  	struct writeback_control *wbc)
  {

  	struct xfs_writepage_ctx wpc = {
  		.io_type = XFS_IO_INVALID,
  	};
  	int			ret;

  	xfs_iflags_clear(XFS_I(mapping->host), XFS_ITRUNCATED);

  	if (dax_mapping(mapping))
  		return dax_writeback_mapping_range(mapping,
  				xfs_find_bdev_for_inode(mapping->host), wbc);

  	ret = write_cache_pages(mapping, wbc, xfs_do_writepage, &wpc);

  	if (wpc.ioend)
  		ret = xfs_submit_ioend(wbc, wpc.ioend, ret);
  	return ret;

  }

  /*
   * Called to move a page into cleanable state - and from there

   * to be released. The page should already be clean. We always

   * have buffer heads in this call.
   *

   * Returns 1 if the page is ok to release, 0 otherwise.

   */
  STATIC int

  xfs_vm_releasepage(

  	struct page		*page,
  	gfp_t			gfp_mask)
  {

  	int			delalloc, unwritten;

  	trace_xfs_releasepage(page->mapping->host, page, 0, 0);

  	/*
  	 * mm accommodates an old ext3 case where clean pages might not have had
  	 * the dirty bit cleared. Thus, it can send actual dirty pages to
  	 * ->releasepage() via shrink_active_list(). Conversely,
  	 * block_invalidatepage() can send pages that are still marked dirty
  	 * but otherwise have invalidated buffers.
  	 *

  	 * We want to release the latter to avoid unnecessary buildup of the
  	 * LRU, skip the former and warn if we've left any lingering
  	 * delalloc/unwritten buffers on clean pages. Skip pages with delalloc
  	 * or unwritten buffers and warn if the page is not dirty. Otherwise
  	 * try to release the buffers.

  	 */

  	xfs_count_page_state(page, &delalloc, &unwritten);

  	if (delalloc) {
  		WARN_ON_ONCE(!PageDirty(page));

  		return 0;

  	}
  	if (unwritten) {
  		WARN_ON_ONCE(!PageDirty(page));

  		return 0;

  	}

  	return try_to_free_buffers(page);
  }

  /*

   * When we map a DIO buffer, we may need to pass flags to
   * xfs_end_io_direct_write to tell it what kind of write IO we are doing.

   *
   * Note that for DIO, an IO to the highest supported file block offset (i.e.
   * 2^63 - 1FSB bytes) will result in the offset + count overflowing a signed 64
   * bit variable. Hence if we see this overflow, we have to assume that the IO is
   * extending the file size. We won't know for sure until IO completion is run
   * and the actual max write offset is communicated to the IO completion
   * routine.

   */
  static void
  xfs_map_direct(
  	struct inode		*inode,
  	struct buffer_head	*bh_result,
  	struct xfs_bmbt_irec	*imap,

  	xfs_off_t		offset,
  	bool			is_cow)

  {

  	uintptr_t		*flags = (uintptr_t *)&bh_result->b_private;

  	xfs_off_t		size = bh_result->b_size;

  	trace_xfs_get_blocks_map_direct(XFS_I(inode), offset, size,

  		ISUNWRITTEN(imap) ? XFS_IO_UNWRITTEN : is_cow ? XFS_IO_COW :
  		XFS_IO_OVERWRITE, imap);

  	if (ISUNWRITTEN(imap)) {
  		*flags |= XFS_DIO_FLAG_UNWRITTEN;
  		set_buffer_defer_completion(bh_result);

  	} else if (is_cow) {
  		*flags |= XFS_DIO_FLAG_COW;
  		set_buffer_defer_completion(bh_result);
  	}
  	if (offset + size > i_size_read(inode) || offset + size < 0) {

  		*flags |= XFS_DIO_FLAG_APPEND;

  		set_buffer_defer_completion(bh_result);

  	}
  }

  /*
   * If this is O_DIRECT or the mpage code calling tell them how large the mapping
   * is, so that we can avoid repeated get_blocks calls.
   *
   * If the mapping spans EOF, then we have to break the mapping up as the mapping
   * for blocks beyond EOF must be marked new so that sub block regions can be
   * correctly zeroed. We can't do this for mappings within EOF unless the mapping
   * was just allocated or is unwritten, otherwise the callers would overwrite
   * existing data with zeros. Hence we have to split the mapping into a range up
   * to and including EOF, and a second mapping for beyond EOF.
   */
  static void
  xfs_map_trim_size(
  	struct inode		*inode,
  	sector_t		iblock,
  	struct buffer_head	*bh_result,
  	struct xfs_bmbt_irec	*imap,
  	xfs_off_t		offset,
  	ssize_t			size)
  {
  	xfs_off_t		mapping_size;
  
  	mapping_size = imap->br_startoff + imap->br_blockcount - iblock;
  	mapping_size <<= inode->i_blkbits;
  
  	ASSERT(mapping_size > 0);
  	if (mapping_size > size)
  		mapping_size = size;
  	if (offset < i_size_read(inode) &&
  	    offset + mapping_size >= i_size_read(inode)) {
  		/* limit mapping to block that spans EOF */
  		mapping_size = roundup_64(i_size_read(inode) - offset,
  					  1 << inode->i_blkbits);
  	}
  	if (mapping_size > LONG_MAX)
  		mapping_size = LONG_MAX;
  
  	bh_result->b_size = mapping_size;
  }

  /* Bounce unaligned directio writes to the page cache. */
  static int
  xfs_bounce_unaligned_dio_write(
  	struct xfs_inode	*ip,
  	xfs_fileoff_t		offset_fsb,
  	struct xfs_bmbt_irec	*imap)
  {
  	struct xfs_bmbt_irec	irec;
  	xfs_fileoff_t		delta;
  	bool			shared;
  	bool			x;
  	int			error;
  
  	irec = *imap;
  	if (offset_fsb > irec.br_startoff) {
  		delta = offset_fsb - irec.br_startoff;
  		irec.br_blockcount -= delta;
  		irec.br_startblock += delta;
  		irec.br_startoff = offset_fsb;
  	}
  	error = xfs_reflink_trim_around_shared(ip, &irec, &shared, &x);
  	if (error)
  		return error;
  
  	/*
  	 * We're here because we're trying to do a directio write to a
  	 * region that isn't aligned to a filesystem block.  If any part
  	 * of the extent is shared, fall back to buffered mode to handle
  	 * the RMW.  This is done by returning -EREMCHG ("remote addr
  	 * changed"), which is caught further up the call stack.
  	 */
  	if (shared) {
  		trace_xfs_reflink_bounce_dio_write(ip, imap);
  		return -EREMCHG;
  	}
  	return 0;
  }

  STATIC int

  __xfs_get_blocks(

  	struct inode		*inode,
  	sector_t		iblock,

  	struct buffer_head	*bh_result,
  	int			create,

  	bool			direct,
  	bool			dax_fault)

  {

  	struct xfs_inode	*ip = XFS_I(inode);
  	struct xfs_mount	*mp = ip->i_mount;
  	xfs_fileoff_t		offset_fsb, end_fsb;
  	int			error = 0;
  	int			lockmode = 0;

  	struct xfs_bmbt_irec	imap;

  	int			nimaps = 1;

  	xfs_off_t		offset;
  	ssize_t			size;

  	int			new = 0;

  	bool			is_cow = false;
  	bool			need_alloc = false;

  	BUG_ON(create && !direct);

  	if (XFS_FORCED_SHUTDOWN(mp))

  		return -EIO;

  	offset = (xfs_off_t)iblock << inode->i_blkbits;

  	ASSERT(bh_result->b_size >= (1 << inode->i_blkbits));
  	size = bh_result->b_size;

  	if (!create && offset >= i_size_read(inode))

  		return 0;

  	/*
  	 * Direct I/O is usually done on preallocated files, so try getting

  	 * a block mapping without an exclusive lock first.

  	 */

  	lockmode = xfs_ilock_data_map_shared(ip);

  	ASSERT(offset <= mp->m_super->s_maxbytes);
  	if (offset + size > mp->m_super->s_maxbytes)
  		size = mp->m_super->s_maxbytes - offset;

  	end_fsb = XFS_B_TO_FSB(mp, (xfs_ufsize_t)offset + size);
  	offset_fsb = XFS_B_TO_FSBT(mp, offset);

  	if (create && direct && xfs_is_reflink_inode(ip))
  		is_cow = xfs_reflink_find_cow_mapping(ip, offset, &imap,
  					&need_alloc);
  	if (!is_cow) {
  		error = xfs_bmapi_read(ip, offset_fsb, end_fsb - offset_fsb,
  					&imap, &nimaps, XFS_BMAPI_ENTIRE);
  		/*
  		 * Truncate an overwrite extent if there's a pending CoW
  		 * reservation before the end of this extent.  This
  		 * forces us to come back to get_blocks to take care of
  		 * the CoW.
  		 */
  		if (create && direct && nimaps &&
  		    imap.br_startblock != HOLESTARTBLOCK &&
  		    imap.br_startblock != DELAYSTARTBLOCK &&
  		    !ISUNWRITTEN(&imap))
  			xfs_reflink_trim_irec_to_next_cow(ip, offset_fsb,
  					&imap);
  	}
  	ASSERT(!need_alloc);

  	if (error)

  		goto out_unlock;

  	/*
  	 * The only time we can ever safely find delalloc blocks on direct I/O
  	 * is a dio write to post-eof speculative preallocation. All other
  	 * scenarios are indicative of a problem or misuse (such as mixing
  	 * direct and mapped I/O).
  	 *
  	 * The file may be unmapped by the time we get here so we cannot
  	 * reliably fail the I/O based on mapping. Instead, fail the I/O if this
  	 * is a read or a write within eof. Otherwise, carry on but warn as a
  	 * precuation if the file happens to be mapped.
  	 */
  	if (direct && imap.br_startblock == DELAYSTARTBLOCK) {
  		if (!create || offset < i_size_read(VFS_I(ip))) {
  			WARN_ON_ONCE(1);
  			error = -EIO;
  			goto out_unlock;
  		}
  		WARN_ON_ONCE(mapping_mapped(VFS_I(ip)->i_mapping));
  	}

  	/* for DAX, we convert unwritten extents directly */

  	if (create &&
  	    (!nimaps ||
  	     (imap.br_startblock == HOLESTARTBLOCK ||

  	      imap.br_startblock == DELAYSTARTBLOCK) ||
  	     (IS_DAX(inode) && ISUNWRITTEN(&imap)))) {

  		/*
  		 * xfs_iomap_write_direct() expects the shared lock. It
  		 * is unlocked on return.
  		 */
  		if (lockmode == XFS_ILOCK_EXCL)
  			xfs_ilock_demote(ip, lockmode);

  		error = xfs_iomap_write_direct(ip, offset, size,
  					       &imap, nimaps);
  		if (error)
  			return error;
  		new = 1;

  		trace_xfs_get_blocks_alloc(ip, offset, size,
  				ISUNWRITTEN(&imap) ? XFS_IO_UNWRITTEN
  						   : XFS_IO_DELALLOC, &imap);

  	} else if (nimaps) {

  		trace_xfs_get_blocks_found(ip, offset, size,
  				ISUNWRITTEN(&imap) ? XFS_IO_UNWRITTEN
  						   : XFS_IO_OVERWRITE, &imap);

  		xfs_iunlock(ip, lockmode);

  	} else {
  		trace_xfs_get_blocks_notfound(ip, offset, size);
  		goto out_unlock;
  	}

  	if (IS_DAX(inode) && create) {
  		ASSERT(!ISUNWRITTEN(&imap));
  		/* zeroing is not needed at a higher layer */
  		new = 0;
  	}

  	/* trim mapping down to size requested */

  	xfs_map_trim_size(inode, iblock, bh_result, &imap, offset, size);

  	/*
  	 * For unwritten extents do not report a disk address in the buffered
  	 * read case (treat as if we're reading into a hole).
  	 */

  	if (imap.br_startblock != HOLESTARTBLOCK &&

  	    imap.br_startblock != DELAYSTARTBLOCK &&
  	    (create || !ISUNWRITTEN(&imap))) {

  		if (create && direct && !is_cow) {
  			error = xfs_bounce_unaligned_dio_write(ip, offset_fsb,
  					&imap);
  			if (error)
  				return error;
  		}

  		xfs_map_buffer(inode, bh_result, &imap, offset);
  		if (ISUNWRITTEN(&imap))

  			set_buffer_unwritten(bh_result);

  		/* direct IO needs special help */

  		if (create) {

  			if (dax_fault)
  				ASSERT(!ISUNWRITTEN(&imap));
  			else

  				xfs_map_direct(inode, bh_result, &imap, offset,
  						is_cow);

  		}

  	}

  	/*
  	 * If this is a realtime file, data may be on a different device.
  	 * to that pointed to from the buffer_head b_bdev currently.
  	 */

  	bh_result->b_bdev = xfs_find_bdev_for_inode(inode);

  	/*

  	 * If we previously allocated a block out beyond eof and we are now
  	 * coming back to use it then we will need to flag it as new even if it
  	 * has a disk address.
  	 *
  	 * With sub-block writes into unwritten extents we also need to mark
  	 * the buffer as new so that the unwritten parts of the buffer gets
  	 * correctly zeroed.

  	 */
  	if (create &&
  	    ((!buffer_mapped(bh_result) && !buffer_uptodate(bh_result)) ||

  	     (offset >= i_size_read(inode)) ||

  	     (new || ISUNWRITTEN(&imap))))

  		set_buffer_new(bh_result);

  	return 0;

  
  out_unlock:
  	xfs_iunlock(ip, lockmode);

  	return error;

  }
  
  int

  xfs_get_blocks(

  	struct inode		*inode,
  	sector_t		iblock,
  	struct buffer_head	*bh_result,
  	int			create)
  {

  	return __xfs_get_blocks(inode, iblock, bh_result, create, false, false);

  }

  int

  xfs_get_blocks_direct(

  	struct inode		*inode,
  	sector_t		iblock,

  	struct buffer_head	*bh_result,
  	int			create)
  {

  	return __xfs_get_blocks(inode, iblock, bh_result, create, true, false);
  }
  
  int
  xfs_get_blocks_dax_fault(
  	struct inode		*inode,
  	sector_t		iblock,
  	struct buffer_head	*bh_result,
  	int			create)
  {
  	return __xfs_get_blocks(inode, iblock, bh_result, create, true, true);

  }

  /*
   * Complete a direct I/O write request.
   *
   * xfs_map_direct passes us some flags in the private data to tell us what to
   * do.  If no flags are set, then the write IO is an overwrite wholly within
   * the existing allocated file size and so there is nothing for us to do.
   *
   * Note that in this case the completion can be called in interrupt context,
   * whereas if we have flags set we will always be called in task context
   * (i.e. from a workqueue).
   */

  int

  xfs_end_io_direct_write(
  	struct kiocb		*iocb,

  	loff_t			offset,

  	ssize_t			size,
  	void			*private)

  {

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

  	uintptr_t		flags = (uintptr_t)private;
  	int			error = 0;

  	trace_xfs_end_io_direct_write(ip, offset, size);

  	if (XFS_FORCED_SHUTDOWN(ip->i_mount))

  		return -EIO;

  	if (size <= 0)
  		return size;

  
  	/*

  	 * The flags tell us whether we are doing unwritten extent conversions

  	 * or an append transaction that updates the on-disk file size. These
  	 * cases are the only cases where we should *potentially* be needing

  	 * to update the VFS inode size.

  	 */
  	if (flags == 0) {
  		ASSERT(offset + size <= i_size_read(inode));
  		return 0;
  	}
  
  	/*

  	 * We need to update the in-core inode size here so that we don't end up

  	 * with the on-disk inode size being outside the in-core inode size. We
  	 * have no other method of updating EOF for AIO, so always do it here
  	 * if necessary.

  	 *
  	 * We need to lock the test/set EOF update as we can be racing with
  	 * other IO completions here to update the EOF. Failing to serialise
  	 * here can result in EOF moving backwards and Bad Things Happen when
  	 * that occurs.

  	 */

  	spin_lock(&ip->i_flags_lock);

  	if (offset + size > i_size_read(inode))
  		i_size_write(inode, offset + size);

  	spin_unlock(&ip->i_flags_lock);

  	if (flags & XFS_DIO_FLAG_COW)
  		error = xfs_reflink_end_cow(ip, offset, size);

  	if (flags & XFS_DIO_FLAG_UNWRITTEN) {
  		trace_xfs_end_io_direct_write_unwritten(ip, offset, size);

  		error = xfs_iomap_write_unwritten(ip, offset, size);

  	}

  	if (flags & XFS_DIO_FLAG_APPEND) {

  		trace_xfs_end_io_direct_write_append(ip, offset, size);

  		error = xfs_setfilesize(ip, offset, size);

  	}

  	return error;

  }

  STATIC ssize_t
  xfs_vm_direct_IO(

  	struct kiocb		*iocb,

  	struct iov_iter		*iter)

  {

  	/*

  	 * We just need the method present so that open/fcntl allow direct I/O.

  	 */

  	return -EINVAL;

  }

  
  STATIC sector_t

  xfs_vm_bmap(

  	struct address_space	*mapping,
  	sector_t		block)
  {
  	struct inode		*inode = (struct inode *)mapping->host;

  	struct xfs_inode	*ip = XFS_I(inode);

  	trace_xfs_vm_bmap(XFS_I(inode));

  	xfs_ilock(ip, XFS_IOLOCK_SHARED);

  
  	/*
  	 * The swap code (ab-)uses ->bmap to get a block mapping and then
  	 * bypasseѕ the file system for actual I/O.  We really can't allow
  	 * that on reflinks inodes, so we have to skip out here.  And yes,
  	 * 0 is the magic code for a bmap error..
  	 */
  	if (xfs_is_reflink_inode(ip)) {
  		xfs_iunlock(ip, XFS_IOLOCK_SHARED);
  		return 0;
  	}

  	filemap_write_and_wait(mapping);

  	xfs_iunlock(ip, XFS_IOLOCK_SHARED);

  	return generic_block_bmap(mapping, block, xfs_get_blocks);

  }
  
  STATIC int

  xfs_vm_readpage(

  	struct file		*unused,
  	struct page		*page)
  {

  	trace_xfs_vm_readpage(page->mapping->host, 1);

  	return mpage_readpage(page, xfs_get_blocks);

  }
  
  STATIC int

  xfs_vm_readpages(

  	struct file		*unused,
  	struct address_space	*mapping,
  	struct list_head	*pages,
  	unsigned		nr_pages)
  {

  	trace_xfs_vm_readpages(mapping->host, nr_pages);

  	return mpage_readpages(mapping, pages, nr_pages, xfs_get_blocks);

  }

  /*
   * This is basically a copy of __set_page_dirty_buffers() with one
   * small tweak: buffers beyond EOF do not get marked dirty. If we mark them
   * dirty, we'll never be able to clean them because we don't write buffers
   * beyond EOF, and that means we can't invalidate pages that span EOF
   * that have been marked dirty. Further, the dirty state can leak into
   * the file interior if the file is extended, resulting in all sorts of
   * bad things happening as the state does not match the underlying data.
   *
   * XXX: this really indicates that bufferheads in XFS need to die. Warts like
   * this only exist because of bufferheads and how the generic code manages them.
   */
  STATIC int
  xfs_vm_set_page_dirty(
  	struct page		*page)
  {
  	struct address_space	*mapping = page->mapping;
  	struct inode		*inode = mapping->host;
  	loff_t			end_offset;
  	loff_t			offset;
  	int			newly_dirty;
  
  	if (unlikely(!mapping))
  		return !TestSetPageDirty(page);
  
  	end_offset = i_size_read(inode);
  	offset = page_offset(page);
  
  	spin_lock(&mapping->private_lock);
  	if (page_has_buffers(page)) {
  		struct buffer_head *head = page_buffers(page);
  		struct buffer_head *bh = head;
  
  		do {
  			if (offset < end_offset)
  				set_buffer_dirty(bh);
  			bh = bh->b_this_page;
  			offset += 1 << inode->i_blkbits;
  		} while (bh != head);
  	}

  	/*

  	 * Lock out page->mem_cgroup migration to keep PageDirty
  	 * synchronized with per-memcg dirty page counters.

  	 */

  	lock_page_memcg(page);

  	newly_dirty = !TestSetPageDirty(page);
  	spin_unlock(&mapping->private_lock);
  
  	if (newly_dirty) {
  		/* sigh - __set_page_dirty() is static, so copy it here, too */
  		unsigned long flags;
  
  		spin_lock_irqsave(&mapping->tree_lock, flags);
  		if (page->mapping) {	/* Race with truncate? */
  			WARN_ON_ONCE(!PageUptodate(page));

  			account_page_dirtied(page, mapping);

  			radix_tree_tag_set(&mapping->page_tree,
  					page_index(page), PAGECACHE_TAG_DIRTY);
  		}
  		spin_unlock_irqrestore(&mapping->tree_lock, flags);

  	}

  	unlock_page_memcg(page);

  	if (newly_dirty)
  		__mark_inode_dirty(mapping->host, I_DIRTY_PAGES);

  	return newly_dirty;
  }

  const struct address_space_operations xfs_address_space_operations = {

  	.readpage		= xfs_vm_readpage,
  	.readpages		= xfs_vm_readpages,
  	.writepage		= xfs_vm_writepage,

  	.writepages		= xfs_vm_writepages,