Adding upstream version 6.1.76.upstream/6.1.76

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 1761 insertions, 0 deletions

diff --git a/fs/ntfs/aops.c b/fs/ntfs/aops.c
new file mode 100644
index 000000000..9364d35b4
--- /dev/null
+++ b/fs/ntfs/aops.c
@@ -0,0 +1,1761 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/**
+ * aops.c - NTFS kernel address space operations and page cache handling.
+ *
+ * Copyright (c) 2001-2014 Anton Altaparmakov and Tuxera Inc.
+ * Copyright (c) 2002 Richard Russon
+ */
+
+#include <linux/errno.h>
+#include <linux/fs.h>
+#include <linux/gfp.h>
+#include <linux/mm.h>
+#include <linux/pagemap.h>
+#include <linux/swap.h>
+#include <linux/buffer_head.h>
+#include <linux/writeback.h>
+#include <linux/bit_spinlock.h>
+#include <linux/bio.h>
+
+#include "aops.h"
+#include "attrib.h"
+#include "debug.h"
+#include "inode.h"
+#include "mft.h"
+#include "runlist.h"
+#include "types.h"
+#include "ntfs.h"
+
+/**
+ * ntfs_end_buffer_async_read - async io completion for reading attributes
+ * @bh:		buffer head on which io is completed
+ * @uptodate:	whether @bh is now uptodate or not
+ *
+ * Asynchronous I/O completion handler for reading pages belonging to the
+ * attribute address space of an inode.  The inodes can either be files or
+ * directories or they can be fake inodes describing some attribute.
+ *
+ * If NInoMstProtected(), perform the post read mst fixups when all IO on the
+ * page has been completed and mark the page uptodate or set the error bit on
+ * the page.  To determine the size of the records that need fixing up, we
+ * cheat a little bit by setting the index_block_size in ntfs_inode to the ntfs
+ * record size, and index_block_size_bits, to the log(base 2) of the ntfs
+ * record size.
+ */
+static void ntfs_end_buffer_async_read(struct buffer_head *bh, int uptodate)
+{
+	unsigned long flags;
+	struct buffer_head *first, *tmp;
+	struct page *page;
+	struct inode *vi;
+	ntfs_inode *ni;
+	int page_uptodate = 1;
+
+	page = bh->b_page;
+	vi = page->mapping->host;
+	ni = NTFS_I(vi);
+
+	if (likely(uptodate)) {
+		loff_t i_size;
+		s64 file_ofs, init_size;
+
+		set_buffer_uptodate(bh);
+
+		file_ofs = ((s64)page->index << PAGE_SHIFT) +
+				bh_offset(bh);
+		read_lock_irqsave(&ni->size_lock, flags);
+		init_size = ni->initialized_size;
+		i_size = i_size_read(vi);
+		read_unlock_irqrestore(&ni->size_lock, flags);
+		if (unlikely(init_size > i_size)) {
+			/* Race with shrinking truncate. */
+			init_size = i_size;
+		}
+		/* Check for the current buffer head overflowing. */
+		if (unlikely(file_ofs + bh->b_size > init_size)) {
+			int ofs;
+			void *kaddr;
+
+			ofs = 0;
+			if (file_ofs < init_size)
+				ofs = init_size - file_ofs;
+			kaddr = kmap_atomic(page);
+			memset(kaddr + bh_offset(bh) + ofs, 0,
+					bh->b_size - ofs);
+			flush_dcache_page(page);
+			kunmap_atomic(kaddr);
+		}
+	} else {
+		clear_buffer_uptodate(bh);
+		SetPageError(page);
+		ntfs_error(ni->vol->sb, "Buffer I/O error, logical block "
+				"0x%llx.", (unsigned long long)bh->b_blocknr);
+	}
+	first = page_buffers(page);
+	spin_lock_irqsave(&first->b_uptodate_lock, flags);
+	clear_buffer_async_read(bh);
+	unlock_buffer(bh);
+	tmp = bh;
+	do {
+		if (!buffer_uptodate(tmp))
+			page_uptodate = 0;
+		if (buffer_async_read(tmp)) {
+			if (likely(buffer_locked(tmp)))
+				goto still_busy;
+			/* Async buffers must be locked. */
+			BUG();
+		}
+		tmp = tmp->b_this_page;
+	} while (tmp != bh);
+	spin_unlock_irqrestore(&first->b_uptodate_lock, flags);
+	/*
+	 * If none of the buffers had errors then we can set the page uptodate,
+	 * but we first have to perform the post read mst fixups, if the
+	 * attribute is mst protected, i.e. if NInoMstProteced(ni) is true.
+	 * Note we ignore fixup errors as those are detected when
+	 * map_mft_record() is called which gives us per record granularity
+	 * rather than per page granularity.
+	 */
+	if (!NInoMstProtected(ni)) {
+		if (likely(page_uptodate && !PageError(page)))
+			SetPageUptodate(page);
+	} else {
+		u8 *kaddr;
+		unsigned int i, recs;
+		u32 rec_size;
+
+		rec_size = ni->itype.index.block_size;
+		recs = PAGE_SIZE / rec_size;
+		/* Should have been verified before we got here... */
+		BUG_ON(!recs);
+		kaddr = kmap_atomic(page);
+		for (i = 0; i < recs; i++)
+			post_read_mst_fixup((NTFS_RECORD*)(kaddr +
+					i * rec_size), rec_size);
+		kunmap_atomic(kaddr);
+		flush_dcache_page(page);
+		if (likely(page_uptodate && !PageError(page)))
+			SetPageUptodate(page);
+	}
+	unlock_page(page);
+	return;
+still_busy:
+	spin_unlock_irqrestore(&first->b_uptodate_lock, flags);
+	return;
+}
+
+/**
+ * ntfs_read_block - fill a @page of an address space with data
+ * @page:	page cache page to fill with data
+ *
+ * Fill the page @page of the address space belonging to the @page->host inode.
+ * We read each buffer asynchronously and when all buffers are read in, our io
+ * completion handler ntfs_end_buffer_read_async(), if required, automatically
+ * applies the mst fixups to the page before finally marking it uptodate and
+ * unlocking it.
+ *
+ * We only enforce allocated_size limit because i_size is checked for in
+ * generic_file_read().
+ *
+ * Return 0 on success and -errno on error.
+ *
+ * Contains an adapted version of fs/buffer.c::block_read_full_folio().
+ */
+static int ntfs_read_block(struct page *page)
+{
+	loff_t i_size;
+	VCN vcn;
+	LCN lcn;
+	s64 init_size;
+	struct inode *vi;
+	ntfs_inode *ni;
+	ntfs_volume *vol;
+	runlist_element *rl;
+	struct buffer_head *bh, *head, *arr[MAX_BUF_PER_PAGE];
+	sector_t iblock, lblock, zblock;
+	unsigned long flags;
+	unsigned int blocksize, vcn_ofs;
+	int i, nr;
+	unsigned char blocksize_bits;
+
+	vi = page->mapping->host;
+	ni = NTFS_I(vi);
+	vol = ni->vol;
+
+	/* $MFT/$DATA must have its complete runlist in memory at all times. */
+	BUG_ON(!ni->runlist.rl && !ni->mft_no && !NInoAttr(ni));
+
+	blocksize = vol->sb->s_blocksize;
+	blocksize_bits = vol->sb->s_blocksize_bits;
+
+	if (!page_has_buffers(page)) {
+		create_empty_buffers(page, blocksize, 0);
+		if (unlikely(!page_has_buffers(page))) {
+			unlock_page(page);
+			return -ENOMEM;
+		}
+	}
+	bh = head = page_buffers(page);
+	BUG_ON(!bh);
+
+	/*
+	 * We may be racing with truncate.  To avoid some of the problems we
+	 * now take a snapshot of the various sizes and use those for the whole
+	 * of the function.  In case of an extending truncate it just means we
+	 * may leave some buffers unmapped which are now allocated.  This is
+	 * not a problem since these buffers will just get mapped when a write
+	 * occurs.  In case of a shrinking truncate, we will detect this later
+	 * on due to the runlist being incomplete and if the page is being
+	 * fully truncated, truncate will throw it away as soon as we unlock
+	 * it so no need to worry what we do with it.
+	 */
+	iblock = (s64)page->index << (PAGE_SHIFT - blocksize_bits);
+	read_lock_irqsave(&ni->size_lock, flags);
+	lblock = (ni->allocated_size + blocksize - 1) >> blocksize_bits;
+	init_size = ni->initialized_size;
+	i_size = i_size_read(vi);
+	read_unlock_irqrestore(&ni->size_lock, flags);
+	if (unlikely(init_size > i_size)) {
+		/* Race with shrinking truncate. */
+		init_size = i_size;
+	}
+	zblock = (init_size + blocksize - 1) >> blocksize_bits;
+
+	/* Loop through all the buffers in the page. */
+	rl = NULL;
+	nr = i = 0;
+	do {
+		int err = 0;
+
+		if (unlikely(buffer_uptodate(bh)))
+			continue;
+		if (unlikely(buffer_mapped(bh))) {
+			arr[nr++] = bh;
+			continue;
+		}
+		bh->b_bdev = vol->sb->s_bdev;
+		/* Is the block within the allowed limits? */
+		if (iblock < lblock) {
+			bool is_retry = false;
+
+			/* Convert iblock into corresponding vcn and offset. */
+			vcn = (VCN)iblock << blocksize_bits >>
+					vol->cluster_size_bits;
+			vcn_ofs = ((VCN)iblock << blocksize_bits) &
+					vol->cluster_size_mask;
+			if (!rl) {
+lock_retry_remap:
+				down_read(&ni->runlist.lock);
+				rl = ni->runlist.rl;
+			}
+			if (likely(rl != NULL)) {
+				/* Seek to element containing target vcn. */
+				while (rl->length && rl[1].vcn <= vcn)
+					rl++;
+				lcn = ntfs_rl_vcn_to_lcn(rl, vcn);
+			} else
+				lcn = LCN_RL_NOT_MAPPED;
+			/* Successful remap. */
+			if (lcn >= 0) {
+				/* Setup buffer head to correct block. */
+				bh->b_blocknr = ((lcn << vol->cluster_size_bits)
+						+ vcn_ofs) >> blocksize_bits;
+				set_buffer_mapped(bh);
+				/* Only read initialized data blocks. */
+				if (iblock < zblock) {
+					arr[nr++] = bh;
+					continue;
+				}
+				/* Fully non-initialized data block, zero it. */
+				goto handle_zblock;
+			}
+			/* It is a hole, need to zero it. */
+			if (lcn == LCN_HOLE)
+				goto handle_hole;
+			/* If first try and runlist unmapped, map and retry. */
+			if (!is_retry && lcn == LCN_RL_NOT_MAPPED) {
+				is_retry = true;
+				/*
+				 * Attempt to map runlist, dropping lock for
+				 * the duration.
+				 */
+				up_read(&ni->runlist.lock);
+				err = ntfs_map_runlist(ni, vcn);
+				if (likely(!err))
+					goto lock_retry_remap;
+				rl = NULL;
+			} else if (!rl)
+				up_read(&ni->runlist.lock);
+			/*
+			 * If buffer is outside the runlist, treat it as a
+			 * hole.  This can happen due to concurrent truncate
+			 * for example.
+			 */
+			if (err == -ENOENT || lcn == LCN_ENOENT) {
+				err = 0;
+				goto handle_hole;
+			}
+			/* Hard error, zero out region. */
+			if (!err)
+				err = -EIO;
+			bh->b_blocknr = -1;
+			SetPageError(page);
+			ntfs_error(vol->sb, "Failed to read from inode 0x%lx, "
+					"attribute type 0x%x, vcn 0x%llx, "
+					"offset 0x%x because its location on "
+					"disk could not be determined%s "
+					"(error code %i).", ni->mft_no,
+					ni->type, (unsigned long long)vcn,
+					vcn_ofs, is_retry ? " even after "
+					"retrying" : "", err);
+		}
+		/*
+		 * Either iblock was outside lblock limits or
+		 * ntfs_rl_vcn_to_lcn() returned error.  Just zero that portion
+		 * of the page and set the buffer uptodate.
+		 */
+handle_hole:
+		bh->b_blocknr = -1UL;
+		clear_buffer_mapped(bh);
+handle_zblock:
+		zero_user(page, i * blocksize, blocksize);
+		if (likely(!err))
+			set_buffer_uptodate(bh);
+	} while (i++, iblock++, (bh = bh->b_this_page) != head);
+
+	/* Release the lock if we took it. */
+	if (rl)
+		up_read(&ni->runlist.lock);
+
+	/* Check we have at least one buffer ready for i/o. */
+	if (nr) {
+		struct buffer_head *tbh;
+
+		/* Lock the buffers. */
+		for (i = 0; i < nr; i++) {
+			tbh = arr[i];
+			lock_buffer(tbh);
+			tbh->b_end_io = ntfs_end_buffer_async_read;
+			set_buffer_async_read(tbh);
+		}
+		/* Finally, start i/o on the buffers. */
+		for (i = 0; i < nr; i++) {
+			tbh = arr[i];
+			if (likely(!buffer_uptodate(tbh)))
+				submit_bh(REQ_OP_READ, tbh);
+			else
+				ntfs_end_buffer_async_read(tbh, 1);
+		}
+		return 0;
+	}
+	/* No i/o was scheduled on any of the buffers. */
+	if (likely(!PageError(page)))
+		SetPageUptodate(page);
+	else /* Signal synchronous i/o error. */
+		nr = -EIO;
+	unlock_page(page);
+	return nr;
+}
+
+/**
+ * ntfs_read_folio - fill a @folio of a @file with data from the device
+ * @file:	open file to which the folio @folio belongs or NULL
+ * @folio:	page cache folio to fill with data
+ *
+ * For non-resident attributes, ntfs_read_folio() fills the @folio of the open
+ * file @file by calling the ntfs version of the generic block_read_full_folio()
+ * function, ntfs_read_block(), which in turn creates and reads in the buffers
+ * associated with the folio asynchronously.
+ *
+ * For resident attributes, OTOH, ntfs_read_folio() fills @folio by copying the
+ * data from the mft record (which at this stage is most likely in memory) and
+ * fills the remainder with zeroes. Thus, in this case, I/O is synchronous, as
+ * even if the mft record is not cached at this point in time, we need to wait
+ * for it to be read in before we can do the copy.
+ *
+ * Return 0 on success and -errno on error.
+ */
+static int ntfs_read_folio(struct file *file, struct folio *folio)
+{
+	struct page *page = &folio->page;
+	loff_t i_size;
+	struct inode *vi;
+	ntfs_inode *ni, *base_ni;
+	u8 *addr;
+	ntfs_attr_search_ctx *ctx;
+	MFT_RECORD *mrec;
+	unsigned long flags;
+	u32 attr_len;
+	int err = 0;
+
+retry_readpage:
+	BUG_ON(!PageLocked(page));
+	vi = page->mapping->host;
+	i_size = i_size_read(vi);
+	/* Is the page fully outside i_size? (truncate in progress) */
+	if (unlikely(page->index >= (i_size + PAGE_SIZE - 1) >>
+			PAGE_SHIFT)) {
+		zero_user(page, 0, PAGE_SIZE);
+		ntfs_debug("Read outside i_size - truncated?");
+		goto done;
+	}
+	/*
+	 * This can potentially happen because we clear PageUptodate() during
+	 * ntfs_writepage() of MstProtected() attributes.
+	 */
+	if (PageUptodate(page)) {
+		unlock_page(page);
+		return 0;
+	}
+	ni = NTFS_I(vi);
+	/*
+	 * Only $DATA attributes can be encrypted and only unnamed $DATA
+	 * attributes can be compressed.  Index root can have the flags set but
+	 * this means to create compressed/encrypted files, not that the
+	 * attribute is compressed/encrypted.  Note we need to check for
+	 * AT_INDEX_ALLOCATION since this is the type of both directory and
+	 * index inodes.
+	 */
+	if (ni->type != AT_INDEX_ALLOCATION) {
+		/* If attribute is encrypted, deny access, just like NT4. */
+		if (NInoEncrypted(ni)) {
+			BUG_ON(ni->type != AT_DATA);
+			err = -EACCES;
+			goto err_out;
+		}
+		/* Compressed data streams are handled in compress.c. */
+		if (NInoNonResident(ni) && NInoCompressed(ni)) {
+			BUG_ON(ni->type != AT_DATA);
+			BUG_ON(ni->name_len);
+			return ntfs_read_compressed_block(page);
+		}
+	}
+	/* NInoNonResident() == NInoIndexAllocPresent() */
+	if (NInoNonResident(ni)) {
+		/* Normal, non-resident data stream. */
+		return ntfs_read_block(page);
+	}
+	/*
+	 * Attribute is resident, implying it is not compressed or encrypted.
+	 * This also means the attribute is smaller than an mft record and
+	 * hence smaller than a page, so can simply zero out any pages with
+	 * index above 0.  Note the attribute can actually be marked compressed
+	 * but if it is resident the actual data is not compressed so we are
+	 * ok to ignore the compressed flag here.
+	 */
+	if (unlikely(page->index > 0)) {
+		zero_user(page, 0, PAGE_SIZE);
+		goto done;
+	}
+	if (!NInoAttr(ni))
+		base_ni = ni;
+	else
+		base_ni = ni->ext.base_ntfs_ino;
+	/* Map, pin, and lock the mft record. */
+	mrec = map_mft_record(base_ni);
+	if (IS_ERR(mrec)) {
+		err = PTR_ERR(mrec);
+		goto err_out;
+	}
+	/*
+	 * If a parallel write made the attribute non-resident, drop the mft
+	 * record and retry the read_folio.
+	 */
+	if (unlikely(NInoNonResident(ni))) {
+		unmap_mft_record(base_ni);
+		goto retry_readpage;
+	}
+	ctx = ntfs_attr_get_search_ctx(base_ni, mrec);
+	if (unlikely(!ctx)) {
+		err = -ENOMEM;
+		goto unm_err_out;
+	}
+	err = ntfs_attr_lookup(ni->type, ni->name, ni->name_len,
+			CASE_SENSITIVE, 0, NULL, 0, ctx);
+	if (unlikely(err))
+		goto put_unm_err_out;
+	attr_len = le32_to_cpu(ctx->attr->data.resident.value_length);
+	read_lock_irqsave(&ni->size_lock, flags);
+	if (unlikely(attr_len > ni->initialized_size))
+		attr_len = ni->initialized_size;
+	i_size = i_size_read(vi);
+	read_unlock_irqrestore(&ni->size_lock, flags);
+	if (unlikely(attr_len > i_size)) {
+		/* Race with shrinking truncate. */
+		attr_len = i_size;
+	}
+	addr = kmap_atomic(page);
+	/* Copy the data to the page. */
+	memcpy(addr, (u8*)ctx->attr +
+			le16_to_cpu(ctx->attr->data.resident.value_offset),
+			attr_len);
+	/* Zero the remainder of the page. */
+	memset(addr + attr_len, 0, PAGE_SIZE - attr_len);
+	flush_dcache_page(page);
+	kunmap_atomic(addr);
+put_unm_err_out:
+	ntfs_attr_put_search_ctx(ctx);
+unm_err_out:
+	unmap_mft_record(base_ni);
+done:
+	SetPageUptodate(page);
+err_out:
+	unlock_page(page);
+	return err;
+}
+
+#ifdef NTFS_RW
+
+/**
+ * ntfs_write_block - write a @page to the backing store
+ * @page:	page cache page to write out
+ * @wbc:	writeback control structure
+ *
+ * This function is for writing pages belonging to non-resident, non-mst
+ * protected attributes to their backing store.
+ *
+ * For a page with buffers, map and write the dirty buffers asynchronously
+ * under page writeback. For a page without buffers, create buffers for the
+ * page, then proceed as above.
+ *
+ * If a page doesn't have buffers the page dirty state is definitive. If a page
+ * does have buffers, the page dirty state is just a hint, and the buffer dirty
+ * state is definitive. (A hint which has rules: dirty buffers against a clean
+ * page is illegal. Other combinations are legal and need to be handled. In
+ * particular a dirty page containing clean buffers for example.)
+ *
+ * Return 0 on success and -errno on error.
+ *
+ * Based on ntfs_read_block() and __block_write_full_page().
+ */
+static int ntfs_write_block(struct page *page, struct writeback_control *wbc)
+{
+	VCN vcn;
+	LCN lcn;
+	s64 initialized_size;
+	loff_t i_size;
+	sector_t block, dblock, iblock;
+	struct inode *vi;
+	ntfs_inode *ni;
+	ntfs_volume *vol;
+	runlist_element *rl;
+	struct buffer_head *bh, *head;
+	unsigned long flags;
+	unsigned int blocksize, vcn_ofs;
+	int err;
+	bool need_end_writeback;
+	unsigned char blocksize_bits;
+
+	vi = page->mapping->host;
+	ni = NTFS_I(vi);
+	vol = ni->vol;
+
+	ntfs_debug("Entering for inode 0x%lx, attribute type 0x%x, page index "
+			"0x%lx.", ni->mft_no, ni->type, page->index);
+
+	BUG_ON(!NInoNonResident(ni));
+	BUG_ON(NInoMstProtected(ni));
+	blocksize = vol->sb->s_blocksize;
+	blocksize_bits = vol->sb->s_blocksize_bits;
+	if (!page_has_buffers(page)) {
+		BUG_ON(!PageUptodate(page));
+		create_empty_buffers(page, blocksize,
+				(1 << BH_Uptodate) | (1 << BH_Dirty));
+		if (unlikely(!page_has_buffers(page))) {
+			ntfs_warning(vol->sb, "Error allocating page "
+					"buffers.  Redirtying page so we try "
+					"again later.");
+			/*
+			 * Put the page back on mapping->dirty_pages, but leave
+			 * its buffers' dirty state as-is.
+			 */
+			redirty_page_for_writepage(wbc, page);
+			unlock_page(page);
+			return 0;
+		}
+	}
+	bh = head = page_buffers(page);
+	BUG_ON(!bh);
+
+	/* NOTE: Different naming scheme to ntfs_read_block()! */
+
+	/* The first block in the page. */
+	block = (s64)page->index << (PAGE_SHIFT - blocksize_bits);
+
+	read_lock_irqsave(&ni->size_lock, flags);
+	i_size = i_size_read(vi);
+	initialized_size = ni->initialized_size;
+	read_unlock_irqrestore(&ni->size_lock, flags);
+
+	/* The first out of bounds block for the data size. */
+	dblock = (i_size + blocksize - 1) >> blocksize_bits;
+
+	/* The last (fully or partially) initialized block. */
+	iblock = initialized_size >> blocksize_bits;
+
+	/*
+	 * Be very careful.  We have no exclusion from block_dirty_folio
+	 * here, and the (potentially unmapped) buffers may become dirty at
+	 * any time.  If a buffer becomes dirty here after we've inspected it
+	 * then we just miss that fact, and the page stays dirty.
+	 *
+	 * Buffers outside i_size may be dirtied by block_dirty_folio;
+	 * handle that here by just cleaning them.
+	 */
+
+	/*
+	 * Loop through all the buffers in the page, mapping all the dirty
+	 * buffers to disk addresses and handling any aliases from the
+	 * underlying block device's mapping.
+	 */
+	rl = NULL;
+	err = 0;
+	do {
+		bool is_retry = false;
+
+		if (unlikely(block >= dblock)) {
+			/*
+			 * Mapped buffers outside i_size will occur, because
+			 * this page can be outside i_size when there is a
+			 * truncate in progress. The contents of such buffers
+			 * were zeroed by ntfs_writepage().
+			 *
+			 * FIXME: What about the small race window where
+			 * ntfs_writepage() has not done any clearing because
+			 * the page was within i_size but before we get here,
+			 * vmtruncate() modifies i_size?
+			 */
+			clear_buffer_dirty(bh);
+			set_buffer_uptodate(bh);
+			continue;
+		}
+
+		/* Clean buffers are not written out, so no need to map them. */
+		if (!buffer_dirty(bh))
+			continue;
+
+		/* Make sure we have enough initialized size. */
+		if (unlikely((block >= iblock) &&
+				(initialized_size < i_size))) {
+			/*
+			 * If this page is fully outside initialized
+			 * size, zero out all pages between the current
+			 * initialized size and the current page. Just
+			 * use ntfs_read_folio() to do the zeroing
+			 * transparently.
+			 */
+			if (block > iblock) {
+				// TODO:
+				// For each page do:
+				// - read_cache_page()
+				// Again for each page do:
+				// - wait_on_page_locked()
+				// - Check (PageUptodate(page) &&
+				//			!PageError(page))
+				// Update initialized size in the attribute and
+				// in the inode.
+				// Again, for each page do:
+				//	block_dirty_folio();
+				// put_page()
+				// We don't need to wait on the writes.
+				// Update iblock.
+			}
+			/*
+			 * The current page straddles initialized size. Zero
+			 * all non-uptodate buffers and set them uptodate (and
+			 * dirty?). Note, there aren't any non-uptodate buffers
+			 * if the page is uptodate.
+			 * FIXME: For an uptodate page, the buffers may need to
+			 * be written out because they were not initialized on
+			 * disk before.
+			 */
+			if (!PageUptodate(page)) {
+				// TODO:
+				// Zero any non-uptodate buffers up to i_size.
+				// Set them uptodate and dirty.
+			}
+			// TODO:
+			// Update initialized size in the attribute and in the
+			// inode (up to i_size).
+			// Update iblock.
+			// FIXME: This is inefficient. Try to batch the two
+			// size changes to happen in one go.
+			ntfs_error(vol->sb, "Writing beyond initialized size "
+					"is not supported yet. Sorry.");
+			err = -EOPNOTSUPP;
+			break;
+			// Do NOT set_buffer_new() BUT DO clear buffer range
+			// outside write request range.
+			// set_buffer_uptodate() on complete buffers as well as
+			// set_buffer_dirty().
+		}
+
+		/* No need to map buffers that are already mapped. */
+		if (buffer_mapped(bh))
+			continue;
+
+		/* Unmapped, dirty buffer. Need to map it. */
+		bh->b_bdev = vol->sb->s_bdev;
+
+		/* Convert block into corresponding vcn and offset. */
+		vcn = (VCN)block << blocksize_bits;
+		vcn_ofs = vcn & vol->cluster_size_mask;
+		vcn >>= vol->cluster_size_bits;
+		if (!rl) {
+lock_retry_remap:
+			down_read(&ni->runlist.lock);
+			rl = ni->runlist.rl;
+		}
+		if (likely(rl != NULL)) {
+			/* Seek to element containing target vcn. */
+			while (rl->length && rl[1].vcn <= vcn)
+				rl++;
+			lcn = ntfs_rl_vcn_to_lcn(rl, vcn);
+		} else
+			lcn = LCN_RL_NOT_MAPPED;
+		/* Successful remap. */
+		if (lcn >= 0) {
+			/* Setup buffer head to point to correct block. */
+			bh->b_blocknr = ((lcn << vol->cluster_size_bits) +
+					vcn_ofs) >> blocksize_bits;
+			set_buffer_mapped(bh);
+			continue;
+		}
+		/* It is a hole, need to instantiate it. */
+		if (lcn == LCN_HOLE) {
+			u8 *kaddr;
+			unsigned long *bpos, *bend;
+
+			/* Check if the buffer is zero. */
+			kaddr = kmap_atomic(page);
+			bpos = (unsigned long *)(kaddr + bh_offset(bh));
+			bend = (unsigned long *)((u8*)bpos + blocksize);
+			do {
+				if (unlikely(*bpos))
+					break;
+			} while (likely(++bpos < bend));
+			kunmap_atomic(kaddr);
+			if (bpos == bend) {
+				/*
+				 * Buffer is zero and sparse, no need to write
+				 * it.
+				 */
+				bh->b_blocknr = -1;
+				clear_buffer_dirty(bh);
+				continue;
+			}
+			// TODO: Instantiate the hole.
+			// clear_buffer_new(bh);
+			// clean_bdev_bh_alias(bh);
+			ntfs_error(vol->sb, "Writing into sparse regions is "
+					"not supported yet. Sorry.");
+			err = -EOPNOTSUPP;
+			break;
+		}
+		/* If first try and runlist unmapped, map and retry. */
+		if (!is_retry && lcn == LCN_RL_NOT_MAPPED) {
+			is_retry = true;
+			/*
+			 * Attempt to map runlist, dropping lock for
+			 * the duration.
+			 */
+			up_read(&ni->runlist.lock);
+			err = ntfs_map_runlist(ni, vcn);
+			if (likely(!err))
+				goto lock_retry_remap;
+			rl = NULL;
+		} else if (!rl)
+			up_read(&ni->runlist.lock);
+		/*
+		 * If buffer is outside the runlist, truncate has cut it out
+		 * of the runlist.  Just clean and clear the buffer and set it
+		 * uptodate so it can get discarded by the VM.
+		 */
+		if (err == -ENOENT || lcn == LCN_ENOENT) {
+			bh->b_blocknr = -1;
+			clear_buffer_dirty(bh);
+			zero_user(page, bh_offset(bh), blocksize);
+			set_buffer_uptodate(bh);
+			err = 0;
+			continue;
+		}
+		/* Failed to map the buffer, even after retrying. */
+		if (!err)
+			err = -EIO;
+		bh->b_blocknr = -1;
+		ntfs_error(vol->sb, "Failed to write to inode 0x%lx, "
+				"attribute type 0x%x, vcn 0x%llx, offset 0x%x "
+				"because its location on disk could not be "
+				"determined%s (error code %i).", ni->mft_no,
+				ni->type, (unsigned long long)vcn,
+				vcn_ofs, is_retry ? " even after "
+				"retrying" : "", err);
+		break;
+	} while (block++, (bh = bh->b_this_page) != head);
+
+	/* Release the lock if we took it. */
+	if (rl)
+		up_read(&ni->runlist.lock);
+
+	/* For the error case, need to reset bh to the beginning. */
+	bh = head;
+
+	/* Just an optimization, so ->read_folio() is not called later. */
+	if (unlikely(!PageUptodate(page))) {
+		int uptodate = 1;
+		do {
+			if (!buffer_uptodate(bh)) {
+				uptodate = 0;
+				bh = head;
+				break;
+			}
+		} while ((bh = bh->b_this_page) != head);
+		if (uptodate)
+			SetPageUptodate(page);
+	}
+
+	/* Setup all mapped, dirty buffers for async write i/o. */
+	do {
+		if (buffer_mapped(bh) && buffer_dirty(bh)) {
+			lock_buffer(bh);
+			if (test_clear_buffer_dirty(bh)) {
+				BUG_ON(!buffer_uptodate(bh));
+				mark_buffer_async_write(bh);
+			} else
+				unlock_buffer(bh);
+		} else if (unlikely(err)) {
+			/*
+			 * For the error case. The buffer may have been set
+			 * dirty during attachment to a dirty page.
+			 */
+			if (err != -ENOMEM)
+				clear_buffer_dirty(bh);
+		}
+	} while ((bh = bh->b_this_page) != head);
+
+	if (unlikely(err)) {
+		// TODO: Remove the -EOPNOTSUPP check later on...
+		if (unlikely(err == -EOPNOTSUPP))
+			err = 0;
+		else if (err == -ENOMEM) {
+			ntfs_warning(vol->sb, "Error allocating memory. "
+					"Redirtying page so we try again "
+					"later.");
+			/*
+			 * Put the page back on mapping->dirty_pages, but
+			 * leave its buffer's dirty state as-is.
+			 */
+			redirty_page_for_writepage(wbc, page);
+			err = 0;
+		} else
+			SetPageError(page);
+	}
+
+	BUG_ON(PageWriteback(page));
+	set_page_writeback(page);	/* Keeps try_to_free_buffers() away. */
+
+	/* Submit the prepared buffers for i/o. */
+	need_end_writeback = true;
+	do {
+		struct buffer_head *next = bh->b_this_page;
+		if (buffer_async_write(bh)) {
+			submit_bh(REQ_OP_WRITE, bh);
+			need_end_writeback = false;
+		}
+		bh = next;
+	} while (bh != head);
+	unlock_page(page);
+
+	/* If no i/o was started, need to end_page_writeback(). */
+	if (unlikely(need_end_writeback))
+		end_page_writeback(page);
+
+	ntfs_debug("Done.");
+	return err;
+}
+
+/**
+ * ntfs_write_mst_block - write a @page to the backing store
+ * @page:	page cache page to write out
+ * @wbc:	writeback control structure
+ *
+ * This function is for writing pages belonging to non-resident, mst protected
+ * attributes to their backing store.  The only supported attributes are index
+ * allocation and $MFT/$DATA.  Both directory inodes and index inodes are
+ * supported for the index allocation case.
+ *
+ * The page must remain locked for the duration of the write because we apply
+ * the mst fixups, write, and then undo the fixups, so if we were to unlock the
+ * page before undoing the fixups, any other user of the page will see the
+ * page contents as corrupt.
+ *
+ * We clear the page uptodate flag for the duration of the function to ensure
+ * exclusion for the $MFT/$DATA case against someone mapping an mft record we
+ * are about to apply the mst fixups to.
+ *
+ * Return 0 on success and -errno on error.
+ *
+ * Based on ntfs_write_block(), ntfs_mft_writepage(), and
+ * write_mft_record_nolock().
+ */
+static int ntfs_write_mst_block(struct page *page,
+		struct writeback_control *wbc)
+{
+	sector_t block, dblock, rec_block;
+	struct inode *vi = page->mapping->host;
+	ntfs_inode *ni = NTFS_I(vi);
+	ntfs_volume *vol = ni->vol;
+	u8 *kaddr;
+	unsigned int rec_size = ni->itype.index.block_size;
+	ntfs_inode *locked_nis[PAGE_SIZE / NTFS_BLOCK_SIZE];
+	struct buffer_head *bh, *head, *tbh, *rec_start_bh;
+	struct buffer_head *bhs[MAX_BUF_PER_PAGE];
+	runlist_element *rl;
+	int i, nr_locked_nis, nr_recs, nr_bhs, max_bhs, bhs_per_rec, err, err2;
+	unsigned bh_size, rec_size_bits;
+	bool sync, is_mft, page_is_dirty, rec_is_dirty;
+	unsigned char bh_size_bits;
+
+	if (WARN_ON(rec_size < NTFS_BLOCK_SIZE))
+		return -EINVAL;
+
+	ntfs_debug("Entering for inode 0x%lx, attribute type 0x%x, page index "
+			"0x%lx.", vi->i_ino, ni->type, page->index);
+	BUG_ON(!NInoNonResident(ni));
+	BUG_ON(!NInoMstProtected(ni));
+	is_mft = (S_ISREG(vi->i_mode) && !vi->i_ino);
+	/*
+	 * NOTE: ntfs_write_mst_block() would be called for $MFTMirr if a page
+	 * in its page cache were to be marked dirty.  However this should
+	 * never happen with the current driver and considering we do not
+	 * handle this case here we do want to BUG(), at least for now.
+	 */
+	BUG_ON(!(is_mft || S_ISDIR(vi->i_mode) ||
+			(NInoAttr(ni) && ni->type == AT_INDEX_ALLOCATION)));
+	bh_size = vol->sb->s_blocksize;
+	bh_size_bits = vol->sb->s_blocksize_bits;
+	max_bhs = PAGE_SIZE / bh_size;
+	BUG_ON(!max_bhs);
+	BUG_ON(max_bhs > MAX_BUF_PER_PAGE);
+
+	/* Were we called for sync purposes? */
+	sync = (wbc->sync_mode == WB_SYNC_ALL);
+
+	/* Make sure we have mapped buffers. */
+	bh = head = page_buffers(page);
+	BUG_ON(!bh);
+
+	rec_size_bits = ni->itype.index.block_size_bits;
+	BUG_ON(!(PAGE_SIZE >> rec_size_bits));
+	bhs_per_rec = rec_size >> bh_size_bits;
+	BUG_ON(!bhs_per_rec);
+
+	/* The first block in the page. */
+	rec_block = block = (sector_t)page->index <<
+			(PAGE_SHIFT - bh_size_bits);
+
+	/* The first out of bounds block for the data size. */
+	dblock = (i_size_read(vi) + bh_size - 1) >> bh_size_bits;
+
+	rl = NULL;
+	err = err2 = nr_bhs = nr_recs = nr_locked_nis = 0;
+	page_is_dirty = rec_is_dirty = false;
+	rec_start_bh = NULL;
+	do {
+		bool is_retry = false;
+
+		if (likely(block < rec_block)) {
+			if (unlikely(block >= dblock)) {
+				clear_buffer_dirty(bh);
+				set_buffer_uptodate(bh);
+				continue;
+			}
+			/*
+			 * This block is not the first one in the record.  We
+			 * ignore the buffer's dirty state because we could
+			 * have raced with a parallel mark_ntfs_record_dirty().
+			 */
+			if (!rec_is_dirty)
+				continue;
+			if (unlikely(err2)) {
+				if (err2 != -ENOMEM)
+					clear_buffer_dirty(bh);
+				continue;
+			}
+		} else /* if (block == rec_block) */ {
+			BUG_ON(block > rec_block);
+			/* This block is the first one in the record. */
+			rec_block += bhs_per_rec;
+			err2 = 0;
+			if (unlikely(block >= dblock)) {
+				clear_buffer_dirty(bh);
+				continue;
+			}
+			if (!buffer_dirty(bh)) {
+				/* Clean records are not written out. */
+				rec_is_dirty = false;
+				continue;
+			}
+			rec_is_dirty = true;
+			rec_start_bh = bh;
+		}
+		/* Need to map the buffer if it is not mapped already. */
+		if (unlikely(!buffer_mapped(bh))) {
+			VCN vcn;
+			LCN lcn;
+			unsigned int vcn_ofs;
+
+			bh->b_bdev = vol->sb->s_bdev;
+			/* Obtain the vcn and offset of the current block. */
+			vcn = (VCN)block << bh_size_bits;
+			vcn_ofs = vcn & vol->cluster_size_mask;
+			vcn >>= vol->cluster_size_bits;
+			if (!rl) {
+lock_retry_remap:
+				down_read(&ni->runlist.lock);
+				rl = ni->runlist.rl;
+			}
+			if (likely(rl != NULL)) {
+				/* Seek to element containing target vcn. */
+				while (rl->length && rl[1].vcn <= vcn)
+					rl++;
+				lcn = ntfs_rl_vcn_to_lcn(rl, vcn);
+			} else
+				lcn = LCN_RL_NOT_MAPPED;
+			/* Successful remap. */
+			if (likely(lcn >= 0)) {
+				/* Setup buffer head to correct block. */
+				bh->b_blocknr = ((lcn <<
+						vol->cluster_size_bits) +
+						vcn_ofs) >> bh_size_bits;
+				set_buffer_mapped(bh);
+			} else {
+				/*
+				 * Remap failed.  Retry to map the runlist once
+				 * unless we are working on $MFT which always
+				 * has the whole of its runlist in memory.
+				 */
+				if (!is_mft && !is_retry &&
+						lcn == LCN_RL_NOT_MAPPED) {
+					is_retry = true;
+					/*
+					 * Attempt to map runlist, dropping
+					 * lock for the duration.
+					 */
+					up_read(&ni->runlist.lock);
+					err2 = ntfs_map_runlist(ni, vcn);
+					if (likely(!err2))
+						goto lock_retry_remap;
+					if (err2 == -ENOMEM)
+						page_is_dirty = true;
+					lcn = err2;
+				} else {
+					err2 = -EIO;
+					if (!rl)
+						up_read(&ni->runlist.lock);
+				}
+				/* Hard error.  Abort writing this record. */
+				if (!err || err == -ENOMEM)
+					err = err2;
+				bh->b_blocknr = -1;
+				ntfs_error(vol->sb, "Cannot write ntfs record "
+						"0x%llx (inode 0x%lx, "
+						"attribute type 0x%x) because "
+						"its location on disk could "
+						"not be determined (error "
+						"code %lli).",
+						(long long)block <<
+						bh_size_bits >>
+						vol->mft_record_size_bits,
+						ni->mft_no, ni->type,
+						(long long)lcn);
+				/*
+				 * If this is not the first buffer, remove the
+				 * buffers in this record from the list of
+				 * buffers to write and clear their dirty bit
+				 * if not error -ENOMEM.
+				 */
+				if (rec_start_bh != bh) {
+					while (bhs[--nr_bhs] != rec_start_bh)
+						;
+					if (err2 != -ENOMEM) {
+						do {
+							clear_buffer_dirty(
+								rec_start_bh);
+						} while ((rec_start_bh =
+								rec_start_bh->
+								b_this_page) !=
+								bh);
+					}
+				}
+				continue;
+			}
+		}
+		BUG_ON(!buffer_uptodate(bh));
+		BUG_ON(nr_bhs >= max_bhs);
+		bhs[nr_bhs++] = bh;
+	} while (block++, (bh = bh->b_this_page) != head);
+	if (unlikely(rl))
+		up_read(&ni->runlist.lock);
+	/* If there were no dirty buffers, we are done. */
+	if (!nr_bhs)
+		goto done;
+	/* Map the page so we can access its contents. */
+	kaddr = kmap(page);
+	/* Clear the page uptodate flag whilst the mst fixups are applied. */
+	BUG_ON(!PageUptodate(page));
+	ClearPageUptodate(page);
+	for (i = 0; i < nr_bhs; i++) {
+		unsigned int ofs;
+
+		/* Skip buffers which are not at the beginning of records. */
+		if (i % bhs_per_rec)
+			continue;
+		tbh = bhs[i];
+		ofs = bh_offset(tbh);
+		if (is_mft) {
+			ntfs_inode *tni;
+			unsigned long mft_no;
+
+			/* Get the mft record number. */
+			mft_no = (((s64)page->index << PAGE_SHIFT) + ofs)
+					>> rec_size_bits;
+			/* Check whether to write this mft record. */
+			tni = NULL;
+			if (!ntfs_may_write_mft_record(vol, mft_no,
+					(MFT_RECORD*)(kaddr + ofs), &tni)) {
+				/*
+				 * The record should not be written.  This
+				 * means we need to redirty the page before
+				 * returning.
+				 */
+				page_is_dirty = true;
+				/*
+				 * Remove the buffers in this mft record from
+				 * the list of buffers to write.
+				 */
+				do {
+					bhs[i] = NULL;
+				} while (++i % bhs_per_rec);
+				continue;
+			}
+			/*
+			 * The record should be written.  If a locked ntfs
+			 * inode was returned, add it to the array of locked
+			 * ntfs inodes.
+			 */
+			if (tni)
+				locked_nis[nr_locked_nis++] = tni;
+		}
+		/* Apply the mst protection fixups. */
+		err2 = pre_write_mst_fixup((NTFS_RECORD*)(kaddr + ofs),
+				rec_size);
+		if (unlikely(err2)) {
+			if (!err || err == -ENOMEM)
+				err = -EIO;
+			ntfs_error(vol->sb, "Failed to apply mst fixups "
+					"(inode 0x%lx, attribute type 0x%x, "
+					"page index 0x%lx, page offset 0x%x)!"
+					"  Unmount and run chkdsk.", vi->i_ino,
+					ni->type, page->index, ofs);
+			/*
+			 * Mark all the buffers in this record clean as we do
+			 * not want to write corrupt data to disk.
+			 */
+			do {
+				clear_buffer_dirty(bhs[i]);
+				bhs[i] = NULL;
+			} while (++i % bhs_per_rec);
+			continue;
+		}
+		nr_recs++;
+	}
+	/* If no records are to be written out, we are done. */
+	if (!nr_recs)
+		goto unm_done;
+	flush_dcache_page(page);
+	/* Lock buffers and start synchronous write i/o on them. */
+	for (i = 0; i < nr_bhs; i++) {
+		tbh = bhs[i];
+		if (!tbh)
+			continue;
+		if (!trylock_buffer(tbh))
+			BUG();
+		/* The buffer dirty state is now irrelevant, just clean it. */
+		clear_buffer_dirty(tbh);
+		BUG_ON(!buffer_uptodate(tbh));
+		BUG_ON(!buffer_mapped(tbh));
+		get_bh(tbh);
+		tbh->b_end_io = end_buffer_write_sync;
+		submit_bh(REQ_OP_WRITE, tbh);
+	}
+	/* Synchronize the mft mirror now if not @sync. */
+	if (is_mft && !sync)
+		goto do_mirror;
+do_wait:
+	/* Wait on i/o completion of buffers. */
+	for (i = 0; i < nr_bhs; i++) {
+		tbh = bhs[i];
+		if (!tbh)
+			continue;
+		wait_on_buffer(tbh);
+		if (unlikely(!buffer_uptodate(tbh))) {
+			ntfs_error(vol->sb, "I/O error while writing ntfs "
+					"record buffer (inode 0x%lx, "
+					"attribute type 0x%x, page index "
+					"0x%lx, page offset 0x%lx)!  Unmount "
+					"and run chkdsk.", vi->i_ino, ni->type,
+					page->index, bh_offset(tbh));
+			if (!err || err == -ENOMEM)
+				err = -EIO;
+			/*
+			 * Set the buffer uptodate so the page and buffer
+			 * states do not become out of sync.
+			 */
+			set_buffer_uptodate(tbh);
+		}
+	}
+	/* If @sync, now synchronize the mft mirror. */
+	if (is_mft && sync) {
+do_mirror:
+		for (i = 0; i < nr_bhs; i++) {
+			unsigned long mft_no;
+			unsigned int ofs;
+
+			/*
+			 * Skip buffers which are not at the beginning of
+			 * records.
+			 */
+			if (i % bhs_per_rec)
+				continue;
+			tbh = bhs[i];
+			/* Skip removed buffers (and hence records). */
+			if (!tbh)
+				continue;
+			ofs = bh_offset(tbh);
+			/* Get the mft record number. */
+			mft_no = (((s64)page->index << PAGE_SHIFT) + ofs)
+					>> rec_size_bits;
+			if (mft_no < vol->mftmirr_size)
+				ntfs_sync_mft_mirror(vol, mft_no,
+						(MFT_RECORD*)(kaddr + ofs),
+						sync);
+		}
+		if (!sync)
+			goto do_wait;
+	}
+	/* Remove the mst protection fixups again. */
+	for (i = 0; i < nr_bhs; i++) {
+		if (!(i % bhs_per_rec)) {
+			tbh = bhs[i];
+			if (!tbh)
+				continue;
+			post_write_mst_fixup((NTFS_RECORD*)(kaddr +
+					bh_offset(tbh)));
+		}
+	}
+	flush_dcache_page(page);
+unm_done:
+	/* Unlock any locked inodes. */
+	while (nr_locked_nis-- > 0) {
+		ntfs_inode *tni, *base_tni;
+		
+		tni = locked_nis[nr_locked_nis];
+		/* Get the base inode. */
+		mutex_lock(&tni->extent_lock);
+		if (tni->nr_extents >= 0)
+			base_tni = tni;
+		else {
+			base_tni = tni->ext.base_ntfs_ino;
+			BUG_ON(!base_tni);
+		}
+		mutex_unlock(&tni->extent_lock);
+		ntfs_debug("Unlocking %s inode 0x%lx.",
+				tni == base_tni ? "base" : "extent",
+				tni->mft_no);
+		mutex_unlock(&tni->mrec_lock);
+		atomic_dec(&tni->count);
+		iput(VFS_I(base_tni));
+	}
+	SetPageUptodate(page);
+	kunmap(page);
+done:
+	if (unlikely(err && err != -ENOMEM)) {
+		/*
+		 * Set page error if there is only one ntfs record in the page.
+		 * Otherwise we would loose per-record granularity.
+		 */
+		if (ni->itype.index.block_size == PAGE_SIZE)
+			SetPageError(page);
+		NVolSetErrors(vol);
+	}
+	if (page_is_dirty) {
+		ntfs_debug("Page still contains one or more dirty ntfs "
+				"records.  Redirtying the page starting at "
+				"record 0x%lx.", page->index <<
+				(PAGE_SHIFT - rec_size_bits));
+		redirty_page_for_writepage(wbc, page);
+		unlock_page(page);
+	} else {
+		/*
+		 * Keep the VM happy.  This must be done otherwise the
+		 * radix-tree tag PAGECACHE_TAG_DIRTY remains set even though
+		 * the page is clean.
+		 */
+		BUG_ON(PageWriteback(page));
+		set_page_writeback(page);
+		unlock_page(page);
+		end_page_writeback(page);
+	}
+	if (likely(!err))
+		ntfs_debug("Done.");
+	return err;
+}
+
+/**
+ * ntfs_writepage - write a @page to the backing store
+ * @page:	page cache page to write out
+ * @wbc:	writeback control structure
+ *
+ * This is called from the VM when it wants to have a dirty ntfs page cache
+ * page cleaned.  The VM has already locked the page and marked it clean.
+ *
+ * For non-resident attributes, ntfs_writepage() writes the @page by calling
+ * the ntfs version of the generic block_write_full_page() function,
+ * ntfs_write_block(), which in turn if necessary creates and writes the
+ * buffers associated with the page asynchronously.
+ *
+ * For resident attributes, OTOH, ntfs_writepage() writes the @page by copying
+ * the data to the mft record (which at this stage is most likely in memory).
+ * The mft record is then marked dirty and written out asynchronously via the
+ * vfs inode dirty code path for the inode the mft record belongs to or via the
+ * vm page dirty code path for the page the mft record is in.
+ *
+ * Based on ntfs_read_folio() and fs/buffer.c::block_write_full_page().
+ *
+ * Return 0 on success and -errno on error.
+ */
+static int ntfs_writepage(struct page *page, struct writeback_control *wbc)
+{
+	loff_t i_size;
+	struct inode *vi = page->mapping->host;
+	ntfs_inode *base_ni = NULL, *ni = NTFS_I(vi);
+	char *addr;
+	ntfs_attr_search_ctx *ctx = NULL;
+	MFT_RECORD *m = NULL;
+	u32 attr_len;
+	int err;
+
+retry_writepage:
+	BUG_ON(!PageLocked(page));
+	i_size = i_size_read(vi);
+	/* Is the page fully outside i_size? (truncate in progress) */
+	if (unlikely(page->index >= (i_size + PAGE_SIZE - 1) >>
+			PAGE_SHIFT)) {
+		struct folio *folio = page_folio(page);
+		/*
+		 * The page may have dirty, unmapped buffers.  Make them
+		 * freeable here, so the page does not leak.
+		 */
+		block_invalidate_folio(folio, 0, folio_size(folio));
+		folio_unlock(folio);
+		ntfs_debug("Write outside i_size - truncated?");
+		return 0;
+	}
+	/*
+	 * Only $DATA attributes can be encrypted and only unnamed $DATA
+	 * attributes can be compressed.  Index root can have the flags set but
+	 * this means to create compressed/encrypted files, not that the
+	 * attribute is compressed/encrypted.  Note we need to check for
+	 * AT_INDEX_ALLOCATION since this is the type of both directory and
+	 * index inodes.
+	 */
+	if (ni->type != AT_INDEX_ALLOCATION) {
+		/* If file is encrypted, deny access, just like NT4. */
+		if (NInoEncrypted(ni)) {
+			unlock_page(page);
+			BUG_ON(ni->type != AT_DATA);
+			ntfs_debug("Denying write access to encrypted file.");
+			return -EACCES;
+		}
+		/* Compressed data streams are handled in compress.c. */
+		if (NInoNonResident(ni) && NInoCompressed(ni)) {
+			BUG_ON(ni->type != AT_DATA);
+			BUG_ON(ni->name_len);
+			// TODO: Implement and replace this with
+			// return ntfs_write_compressed_block(page);
+			unlock_page(page);
+			ntfs_error(vi->i_sb, "Writing to compressed files is "
+					"not supported yet.  Sorry.");
+			return -EOPNOTSUPP;
+		}
+		// TODO: Implement and remove this check.
+		if (NInoNonResident(ni) && NInoSparse(ni)) {
+			unlock_page(page);
+			ntfs_error(vi->i_sb, "Writing to sparse files is not "
+					"supported yet.  Sorry.");
+			return -EOPNOTSUPP;
+		}
+	}
+	/* NInoNonResident() == NInoIndexAllocPresent() */
+	if (NInoNonResident(ni)) {
+		/* We have to zero every time due to mmap-at-end-of-file. */
+		if (page->index >= (i_size >> PAGE_SHIFT)) {
+			/* The page straddles i_size. */
+			unsigned int ofs = i_size & ~PAGE_MASK;
+			zero_user_segment(page, ofs, PAGE_SIZE);
+		}
+		/* Handle mst protected attributes. */
+		if (NInoMstProtected(ni))
+			return ntfs_write_mst_block(page, wbc);
+		/* Normal, non-resident data stream. */
+		return ntfs_write_block(page, wbc);
+	}
+	/*
+	 * Attribute is resident, implying it is not compressed, encrypted, or
+	 * mst protected.  This also means the attribute is smaller than an mft
+	 * record and hence smaller than a page, so can simply return error on
+	 * any pages with index above 0.  Note the attribute can actually be
+	 * marked compressed but if it is resident the actual data is not
+	 * compressed so we are ok to ignore the compressed flag here.
+	 */
+	BUG_ON(page_has_buffers(page));
+	BUG_ON(!PageUptodate(page));
+	if (unlikely(page->index > 0)) {
+		ntfs_error(vi->i_sb, "BUG()! page->index (0x%lx) > 0.  "
+				"Aborting write.", page->index);
+		BUG_ON(PageWriteback(page));
+		set_page_writeback(page);
+		unlock_page(page);
+		end_page_writeback(page);
+		return -EIO;
+	}
+	if (!NInoAttr(ni))
+		base_ni = ni;
+	else
+		base_ni = ni->ext.base_ntfs_ino;
+	/* Map, pin, and lock the mft record. */
+	m = map_mft_record(base_ni);
+	if (IS_ERR(m)) {
+		err = PTR_ERR(m);
+		m = NULL;
+		ctx = NULL;
+		goto err_out;
+	}
+	/*
+	 * If a parallel write made the attribute non-resident, drop the mft
+	 * record and retry the writepage.
+	 */
+	if (unlikely(NInoNonResident(ni))) {
+		unmap_mft_record(base_ni);
+		goto retry_writepage;
+	}
+	ctx = ntfs_attr_get_search_ctx(base_ni, m);
+	if (unlikely(!ctx)) {
+		err = -ENOMEM;
+		goto err_out;
+	}
+	err = ntfs_attr_lookup(ni->type, ni->name, ni->name_len,
+			CASE_SENSITIVE, 0, NULL, 0, ctx);
+	if (unlikely(err))
+		goto err_out;
+	/*
+	 * Keep the VM happy.  This must be done otherwise the radix-tree tag
+	 * PAGECACHE_TAG_DIRTY remains set even though the page is clean.
+	 */
+	BUG_ON(PageWriteback(page));
+	set_page_writeback(page);
+	unlock_page(page);
+	attr_len = le32_to_cpu(ctx->attr->data.resident.value_length);
+	i_size = i_size_read(vi);
+	if (unlikely(attr_len > i_size)) {
+		/* Race with shrinking truncate or a failed truncate. */
+		attr_len = i_size;
+		/*
+		 * If the truncate failed, fix it up now.  If a concurrent
+		 * truncate, we do its job, so it does not have to do anything.
+		 */
+		err = ntfs_resident_attr_value_resize(ctx->mrec, ctx->attr,
+				attr_len);
+		/* Shrinking cannot fail. */
+		BUG_ON(err);
+	}
+	addr = kmap_atomic(page);
+	/* Copy the data from the page to the mft record. */
+	memcpy((u8*)ctx->attr +
+			le16_to_cpu(ctx->attr->data.resident.value_offset),
+			addr, attr_len);
+	/* Zero out of bounds area in the page cache page. */
+	memset(addr + attr_len, 0, PAGE_SIZE - attr_len);
+	kunmap_atomic(addr);
+	flush_dcache_page(page);
+	flush_dcache_mft_record_page(ctx->ntfs_ino);
+	/* We are done with the page. */
+	end_page_writeback(page);
+	/* Finally, mark the mft record dirty, so it gets written back. */
+	mark_mft_record_dirty(ctx->ntfs_ino);
+	ntfs_attr_put_search_ctx(ctx);
+	unmap_mft_record(base_ni);
+	return 0;
+err_out:
+	if (err == -ENOMEM) {
+		ntfs_warning(vi->i_sb, "Error allocating memory. Redirtying "
+				"page so we try again later.");
+		/*
+		 * Put the page back on mapping->dirty_pages, but leave its
+		 * buffers' dirty state as-is.
+		 */
+		redirty_page_for_writepage(wbc, page);
+		err = 0;
+	} else {
+		ntfs_error(vi->i_sb, "Resident attribute write failed with "
+				"error %i.", err);
+		SetPageError(page);
+		NVolSetErrors(ni->vol);
+	}
+	unlock_page(page);
+	if (ctx)
+		ntfs_attr_put_search_ctx(ctx);
+	if (m)
+		unmap_mft_record(base_ni);
+	return err;
+}
+
+#endif	/* NTFS_RW */
+
+/**
+ * ntfs_bmap - map logical file block to physical device block
+ * @mapping:	address space mapping to which the block to be mapped belongs
+ * @block:	logical block to map to its physical device block
+ *
+ * For regular, non-resident files (i.e. not compressed and not encrypted), map
+ * the logical @block belonging to the file described by the address space
+ * mapping @mapping to its physical device block.
+ *
+ * The size of the block is equal to the @s_blocksize field of the super block
+ * of the mounted file system which is guaranteed to be smaller than or equal
+ * to the cluster size thus the block is guaranteed to fit entirely inside the
+ * cluster which means we do not need to care how many contiguous bytes are
+ * available after the beginning of the block.
+ *
+ * Return the physical device block if the mapping succeeded or 0 if the block
+ * is sparse or there was an error.
+ *
+ * Note: This is a problem if someone tries to run bmap() on $Boot system file
+ * as that really is in block zero but there is nothing we can do.  bmap() is
+ * just broken in that respect (just like it cannot distinguish sparse from
+ * not available or error).
+ */
+static sector_t ntfs_bmap(struct address_space *mapping, sector_t block)
+{
+	s64 ofs, size;
+	loff_t i_size;
+	LCN lcn;
+	unsigned long blocksize, flags;
+	ntfs_inode *ni = NTFS_I(mapping->host);
+	ntfs_volume *vol = ni->vol;
+	unsigned delta;
+	unsigned char blocksize_bits, cluster_size_shift;
+
+	ntfs_debug("Entering for mft_no 0x%lx, logical block 0x%llx.",
+			ni->mft_no, (unsigned long long)block);
+	if (ni->type != AT_DATA || !NInoNonResident(ni) || NInoEncrypted(ni)) {
+		ntfs_error(vol->sb, "BMAP does not make sense for %s "
+				"attributes, returning 0.",
+				(ni->type != AT_DATA) ? "non-data" :
+				(!NInoNonResident(ni) ? "resident" :
+				"encrypted"));
+		return 0;
+	}
+	/* None of these can happen. */
+	BUG_ON(NInoCompressed(ni));
+	BUG_ON(NInoMstProtected(ni));
+	blocksize = vol->sb->s_blocksize;
+	blocksize_bits = vol->sb->s_blocksize_bits;
+	ofs = (s64)block << blocksize_bits;
+	read_lock_irqsave(&ni->size_lock, flags);
+	size = ni->initialized_size;
+	i_size = i_size_read(VFS_I(ni));
+	read_unlock_irqrestore(&ni->size_lock, flags);
+	/*
+	 * If the offset is outside the initialized size or the block straddles
+	 * the initialized size then pretend it is a hole unless the
+	 * initialized size equals the file size.
+	 */
+	if (unlikely(ofs >= size || (ofs + blocksize > size && size < i_size)))
+		goto hole;
+	cluster_size_shift = vol->cluster_size_bits;
+	down_read(&ni->runlist.lock);
+	lcn = ntfs_attr_vcn_to_lcn_nolock(ni, ofs >> cluster_size_shift, false);
+	up_read(&ni->runlist.lock);
+	if (unlikely(lcn < LCN_HOLE)) {
+		/*
+		 * Step down to an integer to avoid gcc doing a long long
+		 * comparision in the switch when we know @lcn is between
+		 * LCN_HOLE and LCN_EIO (i.e. -1 to -5).
+		 *
+		 * Otherwise older gcc (at least on some architectures) will
+		 * try to use __cmpdi2() which is of course not available in
+		 * the kernel.
+		 */
+		switch ((int)lcn) {
+		case LCN_ENOENT:
+			/*
+			 * If the offset is out of bounds then pretend it is a
+			 * hole.
+			 */
+			goto hole;
+		case LCN_ENOMEM:
+			ntfs_error(vol->sb, "Not enough memory to complete "
+					"mapping for inode 0x%lx.  "
+					"Returning 0.", ni->mft_no);
+			break;
+		default:
+			ntfs_error(vol->sb, "Failed to complete mapping for "
+					"inode 0x%lx.  Run chkdsk.  "
+					"Returning 0.", ni->mft_no);
+			break;
+		}
+		return 0;
+	}
+	if (lcn < 0) {
+		/* It is a hole. */
+hole:
+		ntfs_debug("Done (returning hole).");
+		return 0;
+	}
+	/*
+	 * The block is really allocated and fullfils all our criteria.
+	 * Convert the cluster to units of block size and return the result.
+	 */
+	delta = ofs & vol->cluster_size_mask;
+	if (unlikely(sizeof(block) < sizeof(lcn))) {
+		block = lcn = ((lcn << cluster_size_shift) + delta) >>
+				blocksize_bits;
+		/* If the block number was truncated return 0. */
+		if (unlikely(block != lcn)) {
+			ntfs_error(vol->sb, "Physical block 0x%llx is too "
+					"large to be returned, returning 0.",
+					(long long)lcn);
+			return 0;
+		}
+	} else
+		block = ((lcn << cluster_size_shift) + delta) >>
+				blocksize_bits;
+	ntfs_debug("Done (returning block 0x%llx).", (unsigned long long)lcn);
+	return block;
+}
+
+/**
+ * ntfs_normal_aops - address space operations for normal inodes and attributes
+ *
+ * Note these are not used for compressed or mst protected inodes and
+ * attributes.
+ */
+const struct address_space_operations ntfs_normal_aops = {
+	.read_folio	= ntfs_read_folio,
+#ifdef NTFS_RW
+	.writepage	= ntfs_writepage,
+	.dirty_folio	= block_dirty_folio,
+#endif /* NTFS_RW */
+	.bmap		= ntfs_bmap,
+	.migrate_folio	= buffer_migrate_folio,
+	.is_partially_uptodate = block_is_partially_uptodate,
+	.error_remove_page = generic_error_remove_page,
+};
+
+/**
+ * ntfs_compressed_aops - address space operations for compressed inodes
+ */
+const struct address_space_operations ntfs_compressed_aops = {
+	.read_folio	= ntfs_read_folio,
+#ifdef NTFS_RW
+	.writepage	= ntfs_writepage,
+	.dirty_folio	= block_dirty_folio,
+#endif /* NTFS_RW */
+	.migrate_folio	= buffer_migrate_folio,
+	.is_partially_uptodate = block_is_partially_uptodate,
+	.error_remove_page = generic_error_remove_page,
+};
+
+/**
+ * ntfs_mst_aops - general address space operations for mst protecteed inodes
+ *		   and attributes
+ */
+const struct address_space_operations ntfs_mst_aops = {
+	.read_folio	= ntfs_read_folio,	/* Fill page with data. */
+#ifdef NTFS_RW
+	.writepage	= ntfs_writepage,	/* Write dirty page to disk. */
+	.dirty_folio	= filemap_dirty_folio,
+#endif /* NTFS_RW */
+	.migrate_folio	= buffer_migrate_folio,
+	.is_partially_uptodate	= block_is_partially_uptodate,
+	.error_remove_page = generic_error_remove_page,
+};
+
+#ifdef NTFS_RW
+
+/**
+ * mark_ntfs_record_dirty - mark an ntfs record dirty
+ * @page:	page containing the ntfs record to mark dirty
+ * @ofs:	byte offset within @page at which the ntfs record begins
+ *
+ * Set the buffers and the page in which the ntfs record is located dirty.
+ *
+ * The latter also marks the vfs inode the ntfs record belongs to dirty
+ * (I_DIRTY_PAGES only).
+ *
+ * If the page does not have buffers, we create them and set them uptodate.
+ * The page may not be locked which is why we need to handle the buffers under
+ * the mapping->private_lock.  Once the buffers are marked dirty we no longer
+ * need the lock since try_to_free_buffers() does not free dirty buffers.
+ */
+void mark_ntfs_record_dirty(struct page *page, const unsigned int ofs) {
+	struct address_space *mapping = page->mapping;
+	ntfs_inode *ni = NTFS_I(mapping->host);
+	struct buffer_head *bh, *head, *buffers_to_free = NULL;
+	unsigned int end, bh_size, bh_ofs;
+
+	BUG_ON(!PageUptodate(page));
+	end = ofs + ni->itype.index.block_size;
+	bh_size = VFS_I(ni)->i_sb->s_blocksize;
+	spin_lock(&mapping->private_lock);
+	if (unlikely(!page_has_buffers(page))) {
+		spin_unlock(&mapping->private_lock);
+		bh = head = alloc_page_buffers(page, bh_size, true);
+		spin_lock(&mapping->private_lock);
+		if (likely(!page_has_buffers(page))) {
+			struct buffer_head *tail;
+
+			do {
+				set_buffer_uptodate(bh);
+				tail = bh;
+				bh = bh->b_this_page;
+			} while (bh);
+			tail->b_this_page = head;
+			attach_page_private(page, head);
+		} else
+			buffers_to_free = bh;
+	}
+	bh = head = page_buffers(page);
+	BUG_ON(!bh);
+	do {
+		bh_ofs = bh_offset(bh);
+		if (bh_ofs + bh_size <= ofs)
+			continue;
+		if (unlikely(bh_ofs >= end))
+			break;
+		set_buffer_dirty(bh);
+	} while ((bh = bh->b_this_page) != head);
+	spin_unlock(&mapping->private_lock);
+	filemap_dirty_folio(mapping, page_folio(page));
+	if (unlikely(buffers_to_free)) {
+		do {
+			bh = buffers_to_free->b_this_page;
+			free_buffer_head(buffers_to_free);
+			buffers_to_free = bh;
+		} while (buffers_to_free);
+	}
+}
+
+#endif /* NTFS_RW */