// SPDX-License-Identifier: GPL-2.0-or-later
/*
 * file.c - NTFS kernel file operations.  Part of the Linux-NTFS project.
 *
 * Copyright (c) 2001-2015 Anton Altaparmakov and Tuxera Inc.
 */

#include <linux/backing-dev.h>
#include <linux/buffer_head.h>
#include <linux/gfp.h>
#include <linux/pagemap.h>
#include <linux/pagevec.h>
#include <linux/sched/signal.h>
#include <linux/swap.h>
#include <linux/uio.h>
#include <linux/writeback.h>

#include <asm/page.h>
#include <linux/uaccess.h>

#include "attrib.h"
#include "bitmap.h"
#include "inode.h"
#include "debug.h"
#include "lcnalloc.h"
#include "malloc.h"
#include "mft.h"
#include "ntfs.h"

/**
 * ntfs_file_open - called when an inode is about to be opened
 * @vi:         inode to be opened
 * @filp:       file structure describing the inode
 *
 * Limit file size to the page cache limit on architectures where unsigned long
 * is 32-bits. This is the most we can do for now without overflowing the page
 * cache page index. Doing it this way means we don't run into problems because
 * of existing too large files. It would be better to allow the user to read
 * the beginning of the file but I doubt very much anyone is going to hit this
 * check on a 32-bit architecture, so there is no point in adding the extra
 * complexity required to support this.
 *
 * On 64-bit architectures, the check is hopefully optimized away by the
 * compiler.
 *
 * After the check passes, just call generic_file_open() to do its work.
 */
static int ntfs_file_open(struct inode *vi, struct file *filp)
{
        if (sizeof(unsigned long) < 8) {
                if (i_size_read(vi) > MAX_LFS_FILESIZE)
                        return -EOVERFLOW;
        }
        return generic_file_open(vi, filp);
}

#ifdef NTFS_RW

/**
 * ntfs_attr_extend_initialized - extend the initialized size of an attribute
 * @ni:                 ntfs inode of the attribute to extend
 * @new_init_size:      requested new initialized size in bytes
 *
 * Extend the initialized size of an attribute described by the ntfs inode @ni
 * to @new_init_size bytes.  This involves zeroing any non-sparse space between
 * the old initialized size and @new_init_size both in the page cache and on
 * disk (if relevant complete pages are already uptodate in the page cache then
 * these are simply marked dirty).
 *
 * As a side-effect, the file size (vfs inode->i_size) may be incremented as,
 * in the resident attribute case, it is tied to the initialized size and, in
 * the non-resident attribute case, it may not fall below the initialized size.
 *
 * Note that if the attribute is resident, we do not need to touch the page
 * cache at all.  This is because if the page cache page is not uptodate we
 * bring it uptodate later, when doing the write to the mft record since we
 * then already have the page mapped.  And if the page is uptodate, the
 * non-initialized region will already have been zeroed when the page was
 * brought uptodate and the region may in fact already have been overwritten
 * with new data via mmap() based writes, so we cannot just zero it.  And since
 * POSIX specifies that the behaviour of resizing a file whilst it is mmap()ped
 * is unspecified, we choose not to do zeroing and thus we do not need to touch
 * the page at all.  For a more detailed explanation see ntfs_truncate() in
 * fs/ntfs/inode.c.
 *
 * Return 0 on success and -errno on error.  In the case that an error is
 * encountered it is possible that the initialized size will already have been
 * incremented some way towards @new_init_size but it is guaranteed that if
 * this is the case, the necessary zeroing will also have happened and that all
 * metadata is self-consistent.
 *
 * Locking: i_mutex on the vfs inode corrseponsind to the ntfs inode @ni must be
 *          held by the caller.
 */
static int ntfs_attr_extend_initialized(ntfs_inode *ni, const s64 new_init_size)
{
        s64 old_init_size;
        loff_t old_i_size;
        pgoff_t index, end_index;
        unsigned long flags;
        struct inode *vi = VFS_I(ni);
        ntfs_inode *base_ni;
        MFT_RECORD *m = NULL;
        ATTR_RECORD *a;
        ntfs_attr_search_ctx *ctx = NULL;
        struct address_space *mapping;
        struct page *page = NULL;
        u8 *kattr;
        int err;
        u32 attr_len;

        read_lock_irqsave(&ni->size_lock, flags);
        old_init_size = ni->initialized_size;
        old_i_size = i_size_read(vi);
        BUG_ON(new_init_size > ni->allocated_size);
        read_unlock_irqrestore(&ni->size_lock, flags);
        ntfs_debug("Entering for i_ino 0x%lx, attribute type 0x%x, "
                        "old_initialized_size 0x%llx, "
                        "new_initialized_size 0x%llx, i_size 0x%llx.",
                        vi->i_ino, (unsigned)le32_to_cpu(ni->type),
                        (unsigned long long)old_init_size,
                        (unsigned long long)new_init_size, old_i_size);
        if (!NInoAttr(ni))
                base_ni = ni;
        else
                base_ni = ni->ext.base_ntfs_ino;
        /* Use goto to reduce indentation and we need the label below anyway. */
        if (NInoNonResident(ni))
                goto do_non_resident_extend;
        BUG_ON(old_init_size != old_i_size);
        m = map_mft_record(base_ni);
        if (IS_ERR(m)) {
                err = PTR_ERR(m);
                m = NULL;
                goto err_out;
        }
        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)) {
                if (err == -ENOENT)
                        err = -EIO;
                goto err_out;
        }
        m = ctx->mrec;
        a = ctx->attr;
        BUG_ON(a->non_resident);
        /* The total length of the attribute value. */
        attr_len = le32_to_cpu(a->data.resident.value_length);
        BUG_ON(old_i_size != (loff_t)attr_len);
        /*
         * Do the zeroing in the mft record and update the attribute size in
         * the mft record.
         */
        kattr = (u8*)a + le16_to_cpu(a->data.resident.value_offset);
        memset(kattr + attr_len, 0, new_init_size - attr_len);
        a->data.resident.value_length = cpu_to_le32((u32)new_init_size);
        /* Finally, update the sizes in the vfs and ntfs inodes. */
        write_lock_irqsave(&ni->size_lock, flags);
        i_size_write(vi, new_init_size);
        ni->initialized_size = new_init_size;
        write_unlock_irqrestore(&ni->size_lock, flags);
        goto done;
do_non_resident_extend:
        /*
         * If the new initialized size @new_init_size exceeds the current file
         * size (vfs inode->i_size), we need to extend the file size to the
         * new initialized size.
         */
        if (new_init_size > old_i_size) {
                m = map_mft_record(base_ni);
                if (IS_ERR(m)) {
                        err = PTR_ERR(m);
                        m = NULL;
                        goto err_out;
                }
                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)) {
                        if (err == -ENOENT)
                                err = -EIO;
                        goto err_out;
                }
                m = ctx->mrec;
                a = ctx->attr;
                BUG_ON(!a->non_resident);
                BUG_ON(old_i_size != (loff_t)
                                sle64_to_cpu(a->data.non_resident.data_size));
                a->data.non_resident.data_size = cpu_to_sle64(new_init_size);
                flush_dcache_mft_record_page(ctx->ntfs_ino);
                mark_mft_record_dirty(ctx->ntfs_ino);
                /* Update the file size in the vfs inode. */
                i_size_write(vi, new_init_size);
                ntfs_attr_put_search_ctx(ctx);
                ctx = NULL;
                unmap_mft_record(base_ni);
                m = NULL;
        }
        mapping = vi->i_mapping;
        index = old_init_size >> PAGE_SHIFT;
        end_index = (new_init_size + PAGE_SIZE - 1) >> PAGE_SHIFT;
        do {
                /*
                 * Read the page.  If the page is not present, this will zero
                 * the uninitialized regions for us.
                 */
                page = read_mapping_page(mapping, index, NULL);
                if (IS_ERR(page)) {
                        err = PTR_ERR(page);
                        goto init_err_out;
                }
                if (unlikely(PageError(page))) {
                        put_page(page);
                        err = -EIO;
                        goto init_err_out;
                }
                /*
                 * Update the initialized size in the ntfs inode.  This is
                 * enough to make ntfs_writepage() work.
                 */
                write_lock_irqsave(&ni->size_lock, flags);
                ni->initialized_size = (s64)(index + 1) << PAGE_SHIFT;
                if (ni->initialized_size > new_init_size)
                        ni->initialized_size = new_init_size;
                write_unlock_irqrestore(&ni->size_lock, flags);
                /* Set the page dirty so it gets written out. */
                set_page_dirty(page);
                put_page(page);
                /*
                 * Play nice with the vm and the rest of the system.  This is
                 * very much needed as we can potentially be modifying the
                 * initialised size from a very small value to a really huge
                 * value, e.g.
                 *      f = open(somefile, O_TRUNC);
                 *      truncate(f, 10GiB);
                 *      seek(f, 10GiB);
                 *      write(f, 1);
                 * And this would mean we would be marking dirty hundreds of
                 * thousands of pages or as in the above example more than
                 * two and a half million pages!
                 *
                 * TODO: For sparse pages could optimize this workload by using
                 * the FsMisc / MiscFs page bit as a "PageIsSparse" bit.  This
                 * would be set in readpage for sparse pages and here we would
                 * not need to mark dirty any pages which have this bit set.
                 * The only caveat is that we have to clear the bit everywhere
                 * where we allocate any clusters that lie in the page or that
                 * contain the page.
                 *
                 * TODO: An even greater optimization would be for us to only
                 * call readpage() on pages which are not in sparse regions as
                 * determined from the runlist.  This would greatly reduce the
                 * number of pages we read and make dirty in the case of sparse
                 * files.
                 */
                balance_dirty_pages_ratelimited(mapping);
                cond_resched();
        } while (++index < end_index);
        read_lock_irqsave(&ni->size_lock, flags);
        BUG_ON(ni->initialized_size != new_init_size);
        read_unlock_irqrestore(&ni->size_lock, flags);
        /* Now bring in sync the initialized_size in the mft record. */
        m = map_mft_record(base_ni);
        if (IS_ERR(m)) {
                err = PTR_ERR(m);
                m = NULL;
                goto init_err_out;
        }
        ctx = ntfs_attr_get_search_ctx(base_ni, m);
        if (unlikely(!ctx)) {
                err = -ENOMEM;
                goto init_err_out;
        }
        err = ntfs_attr_lookup(ni->type, ni->name, ni->name_len,
                        CASE_SENSITIVE, 0, NULL, 0, ctx);
        if (unlikely(err)) {
                if (err == -ENOENT)
                        err = -EIO;
                goto init_err_out;
        }
        m = ctx->mrec;
        a = ctx->attr;
        BUG_ON(!a->non_resident);
        a->data.non_resident.initialized_size = cpu_to_sle64(new_init_size);
done:
        flush_dcache_mft_record_page(ctx->ntfs_ino);
        mark_mft_record_dirty(ctx->ntfs_ino);
        if (ctx)
                ntfs_attr_put_search_ctx(ctx);
        if (m)
                unmap_mft_record(base_ni);
        ntfs_debug("Done, initialized_size 0x%llx, i_size 0x%llx.",
                        (unsigned long long)new_init_size, i_size_read(vi));
        return 0;
init_err_out:
        write_lock_irqsave(&ni->size_lock, flags);
        ni->initialized_size = old_init_size;
        write_unlock_irqrestore(&ni->size_lock, flags);
err_out:
        if (ctx)
                ntfs_attr_put_search_ctx(ctx);
        if (m)
                unmap_mft_record(base_ni);
        ntfs_debug("Failed.  Returning error code %i.", err);
        return err;
}

static ssize_t ntfs_prepare_file_for_write(struct kiocb *iocb,
                struct iov_iter *from)
{
        loff_t pos;
        s64 end, ll;
        ssize_t err;
        unsigned long flags;
        struct file *file = iocb->ki_filp;
        struct inode *vi = file_inode(file);
        ntfs_inode *base_ni, *ni = NTFS_I(vi);
        ntfs_volume *vol = ni->vol;

        ntfs_debug("Entering for i_ino 0x%lx, attribute type 0x%x, pos "
                        "0x%llx, count 0x%zx.", vi->i_ino,
                        (unsigned)le32_to_cpu(ni->type),
                        (unsigned long long)iocb->ki_pos,
                        iov_iter_count(from));
        err = generic_write_checks(iocb, from);
        if (unlikely(err <= 0))
                goto out;
        /*
         * All checks have passed.  Before we start doing any writing we want
         * to abort any totally illegal writes.
         */
        BUG_ON(NInoMstProtected(ni));
        BUG_ON(ni->type != AT_DATA);
        /* If file is encrypted, deny access, just like NT4. */
        if (NInoEncrypted(ni)) {
                /* Only $DATA attributes can be encrypted. */
                /*
                 * Reminder for later: Encrypted files are _always_
                 * non-resident so that the content can always be encrypted.
                 */
                ntfs_debug("Denying write access to encrypted file.");
                err = -EACCES;
                goto out;
        }
        if (NInoCompressed(ni)) {
                /* Only unnamed $DATA attribute can be compressed. */
                BUG_ON(ni->name_len);
                /*
                 * Reminder for later: If resident, the data is not actually
                 * compressed.  Only on the switch to non-resident does
                 * compression kick in.  This is in contrast to encrypted files
                 * (see above).
                 */
                ntfs_error(vi->i_sb, "Writing to compressed files is not "
                                "implemented yet.  Sorry.");
                err = -EOPNOTSUPP;
                goto out;
        }
        base_ni = ni;
        if (NInoAttr(ni))
                base_ni = ni->ext.base_ntfs_ino;
        err = file_remove_privs(file);
        if (unlikely(err))
                goto out;
        /*
         * Our ->update_time method always succeeds thus file_update_time()
         * cannot fail either so there is no need to check the return code.
         */
        file_update_time(file);
        pos = iocb->ki_pos;
        /* The first byte after the last cluster being written to. */
        end = (pos + iov_iter_count(from) + vol->cluster_size_mask) &
                        ~(u64)vol->cluster_size_mask;
        /*
         * If the write goes beyond the allocated size, extend the allocation
         * to cover the whole of the write, rounded up to the nearest cluster.
         */
        read_lock_irqsave(&ni->size_lock, flags);
        ll = ni->allocated_size;
        read_unlock_irqrestore(&ni->size_lock, flags);
        if (end > ll) {
                /*
                 * Extend the allocation without changing the data size.
                 *
                 * Note we ensure the allocation is big enough to at least
                 * write some data but we do not require the allocation to be
                 * complete, i.e. it may be partial.
                 */
                ll = ntfs_attr_extend_allocation(ni, end, -1, pos);
                if (likely(ll >= 0)) {
                        BUG_ON(pos >= ll);
                        /* If the extension was partial truncate the write. */
                        if (end > ll) {
                                ntfs_debug("Truncating write to inode 0x%lx, "
                                                "attribute type 0x%x, because "
                                                "the allocation was only "
                                                "partially extended.",
                                                vi->i_ino, (unsigned)
                                                le32_to_cpu(ni->type));
                                iov_iter_truncate(from, ll - pos);
                        }
                } else {
                        err = ll;
                        read_lock_irqsave(&ni->size_lock, flags);
                        ll = ni->allocated_size;
                        read_unlock_irqrestore(&ni->size_lock, flags);
                        /* Perform a partial write if possible or fail. */
                        if (pos < ll) {
                                ntfs_debug("Truncating write to inode 0x%lx "
                                                "attribute type 0x%x, because "
                                                "extending the allocation "
                                                "failed (error %d).",
                                                vi->i_ino, (unsigned)
                                                le32_to_cpu(ni->type),
                                                (int)-err);
                                iov_iter_truncate(from, ll - pos);
                        } else {
                                if (err != -ENOSPC)
                                        ntfs_error(vi->i_sb, "Cannot perform "
                                                        "write to inode "
                                                        "0x%lx, attribute "
                                                        "type 0x%x, because "
                                                        "extending the "
                                                        "allocation failed "
                                                        "(error %ld).",
                                                        vi->i_ino, (unsigned)
                                                        le32_to_cpu(ni->type),
                                                        (long)-err);
                                else
                                        ntfs_debug("Cannot perform write to "
                                                        "inode 0x%lx, "
                                                        "attribute type 0x%x, "
                                                        "because there is not "
                                                        "space left.",
                                                        vi->i_ino, (unsigned)
                                                        le32_to_cpu(ni->type));
                                goto out;
                        }
                }
        }
        /*
         * If the write starts beyond the initialized size, extend it up to the
         * beginning of the write and initialize all non-sparse space between
         * the old initialized size and the new one.  This automatically also
         * increments the vfs inode->i_size to keep it above or equal to the
         * initialized_size.
         */
        read_lock_irqsave(&ni->size_lock, flags);
        ll = ni->initialized_size;
        read_unlock_irqrestore(&ni->size_lock, flags);
        if (pos > ll) {
                /*
                 * Wait for ongoing direct i/o to complete before proceeding.
                 * New direct i/o cannot start as we hold i_mutex.
                 */
                inode_dio_wait(vi);
                err = ntfs_attr_extend_initialized(ni, pos);
                if (unlikely(err < 0))
                        ntfs_error(vi->i_sb, "Cannot perform write to inode "
                                        "0x%lx, attribute type 0x%x, because "
                                        "extending the initialized size "
                                        "failed (error %d).", vi->i_ino,
                                        (unsigned)le32_to_cpu(ni->type),
                                        (int)-err);
        }
out:
        return err;
}

/**
 * __ntfs_grab_cache_pages - obtain a number of locked pages
 * @mapping:    address space mapping from which to obtain page cache pages
 * @index:      starting index in @mapping at which to begin obtaining pages
 * @nr_pages:   number of page cache pages to obtain
 * @pages:      array of pages in which to return the obtained page cache pages
 * @cached_page: allocated but as yet unused page
 *
 * Obtain @nr_pages locked page cache pages from the mapping @mapping and
 * starting at index @index.
 *
 * If a page is newly created, add it to lru list
 *
 * Note, the page locks are obtained in ascending page index order.
 */
static inline int __ntfs_grab_cache_pages(struct address_space *mapping,
                pgoff_t index, const unsigned nr_pages, struct page **pages,
                struct page **cached_page)
{
        int err, nr;

        BUG_ON(!nr_pages);
        err = nr = 0;
        do {
                pages[nr] = find_get_page_flags(mapping, index, FGP_LOCK |
                                FGP_ACCESSED);
                if (!pages[nr]) {
                        if (!*cached_page) {
                                *cached_page = page_cache_alloc(mapping);
                                if (unlikely(!*cached_page)) {
                                        err = -ENOMEM;
                                        goto err_out;
                                }
                        }
                        err = add_to_page_cache_lru(*cached_page, mapping,
                                   index,
                                   mapping_gfp_constraint(mapping, GFP_KERNEL));
                        if (unlikely(err)) {
                                if (err == -EEXIST)
                                        continue;
                                goto err_out;
                        }
                        pages[nr] = *cached_page;
                        *cached_page = NULL;
                }
                index++;
                nr++;
        } while (nr < nr_pages);
out:
        return err;
err_out:
        while (nr > 0) {
                unlock_page(pages[--nr]);
                put_page(pages[nr]);
        }
        goto out;
}

static inline int ntfs_submit_bh_for_read(struct buffer_head *bh)
{
        lock_buffer(bh);
        get_bh(bh);
        bh->b_end_io = end_buffer_read_sync;
        return submit_bh(REQ_OP_READ, 0, bh);
}

/**
 * ntfs_prepare_pages_for_non_resident_write - prepare pages for receiving data
 * @pages:      array of destination pages
 * @nr_pages:   number of pages in @pages
 * @pos:        byte position in file at which the write begins
 * @bytes:      number of bytes to be written
 *
 * This is called for non-resident attributes from ntfs_file_buffered_write()
 * with i_mutex held on the inode (@pages[0]->mapping->host).  There are
 * @nr_pages pages in @pages which are locked but not kmap()ped.  The source
 * data has not yet been copied into the @pages.
 * 
 * Need to fill any holes with actual clusters, allocate buffers if necessary,
 * ensure all the buffers are mapped, and bring uptodate any buffers that are
 * only partially being written to.
 *
 * If @nr_pages is greater than one, we are guaranteed that the cluster size is
 * greater than PAGE_SIZE, that all pages in @pages are entirely inside
 * the same cluster and that they are the entirety of that cluster, and that
 * the cluster is sparse, i.e. we need to allocate a cluster to fill the hole.
 *
 * i_size is not to be modified yet.
 *
 * Return 0 on success or -errno on error.
 */
static int ntfs_prepare_pages_for_non_resident_write(struct page **pages,
                unsigned nr_pages, s64 pos, size_t bytes)
{
        VCN vcn, highest_vcn = 0, cpos, cend, bh_cpos, bh_cend;
        LCN lcn;
        s64 bh_pos, vcn_len, end, initialized_size;
        sector_t lcn_block;
        struct page *page;
        struct inode *vi;
        ntfs_inode *ni, *base_ni = NULL;
        ntfs_volume *vol;
        runlist_element *rl, *rl2;
        struct buffer_head *bh, *head, *wait[2], **wait_bh = wait;
        ntfs_attr_search_ctx *ctx = NULL;
        MFT_RECORD *m = NULL;
        ATTR_RECORD *a = NULL;
        unsigned long flags;
        u32 attr_rec_len = 0;
        unsigned blocksize, u;
        int err, mp_size;
        bool rl_write_locked, was_hole, is_retry;
        unsigned char blocksize_bits;
        struct {
                u8 runlist_merged:1;
                u8 mft_attr_mapped:1;
                u8 mp_rebuilt:1;
                u8 attr_switched:1;
        } status = { 0, 0, 0, 0 };

        BUG_ON(!nr_pages);
        BUG_ON(!pages);
        BUG_ON(!*pages);
        vi = pages[0]->mapping->host;
        ni = NTFS_I(vi);
        vol = ni->vol;
        ntfs_debug("Entering for inode 0x%lx, attribute type 0x%x, start page "
                        "index 0x%lx, nr_pages 0x%x, pos 0x%llx, bytes 0x%zx.",
                        vi->i_ino, ni->type, pages[0]->index, nr_pages,
                        (long long)pos, bytes);
        blocksize = vol->sb->s_blocksize;
        blocksize_bits = vol->sb->s_blocksize_bits;
        u = 0;
        do {
                page = pages[u];
                BUG_ON(!page);
                /*
                 * create_empty_buffers() will create uptodate/dirty buffers if
                 * the page is uptodate/dirty.
                 */
                if (!page_has_buffers(page)) {
                        create_empty_buffers(page, blocksize, 0);
                        if (unlikely(!page_has_buffers(page)))
                                return -ENOMEM;
                }
        } while (++u < nr_pages);
        rl_write_locked = false;
        rl = NULL;
        err = 0;
        vcn = lcn = -1;
        vcn_len = 0;
        lcn_block = -1;
        was_hole = false;
        cpos = pos >> vol->cluster_size_bits;
        end = pos + bytes;
        cend = (end + vol->cluster_size - 1) >> vol->cluster_size_bits;
        /*
         * Loop over each page and for each page over each buffer.  Use goto to
         * reduce indentation.
         */
        u = 0;
do_next_page:
        page = pages[u];
        bh_pos = (s64)page->index << PAGE_SHIFT;
        bh = head = page_buffers(page);
        do {
                VCN cdelta;
                s64 bh_end;
                unsigned bh_cofs;

                /* Clear buffer_new on all buffers to reinitialise state. */
                if (buffer_new(bh))
                        clear_buffer_new(bh);
                bh_end = bh_pos + blocksize;
                bh_cpos = bh_pos >> vol->cluster_size_bits;
                bh_cofs = bh_pos & vol->cluster_size_mask;
                if (buffer_mapped(bh)) {
                        /*
                         * The buffer is already mapped.  If it is uptodate,
                         * ignore it.
                         */
                        if (buffer_uptodate(bh))
                                continue;
                        /*
                         * The buffer is not uptodate.  If the page is uptodate
                         * set the buffer uptodate and otherwise ignore it.
                         */
                        if (PageUptodate(page)) {
                                set_buffer_uptodate(bh);
                                continue;
                        }
                        /*
                         * Neither the page nor the buffer are uptodate.  If
                         * the buffer is only partially being written to, we
                         * need to read it in before the write, i.e. now.
                         */
                        if ((bh_pos < pos && bh_end > pos) ||
                                        (bh_pos < end && bh_end > end)) {
                                /*
                                 * If the buffer is fully or partially within
                                 * the initialized size, do an actual read.
                                 * Otherwise, simply zero the buffer.
                                 */
                                read_lock_irqsave(&ni->size_lock, flags);
                                initialized_size = ni->initialized_size;
                                read_unlock_irqrestore(&ni->size_lock, flags);
                                if (bh_pos < initialized_size) {
                                        ntfs_submit_bh_for_read(bh);
                                        *wait_bh++ = bh;
                                } else {
                                        zero_user(page, bh_offset(bh),
                                                        blocksize);
                                        set_buffer_uptodate(bh);
                                }
                        }
                        continue;
                }
                /* Unmapped buffer.  Need to map it. */
                bh->b_bdev = vol->sb->s_bdev;
                /*
                 * If the current buffer is in the same clusters as the map
                 * cache, there is no need to check the runlist again.  The
                 * map cache is made up of @vcn, which is the first cached file
                 * cluster, @vcn_len which is the number of cached file
                 * clusters, @lcn is the device cluster corresponding to @vcn,
                 * and @lcn_block is the block number corresponding to @lcn.
                 */
                cdelta = bh_cpos - vcn;
                if (likely(!cdelta || (cdelta > 0 && cdelta < vcn_len))) {
map_buffer_cached:
                        BUG_ON(lcn < 0);
                        bh->b_blocknr = lcn_block +
                                        (cdelta << (vol->cluster_size_bits -
                                        blocksize_bits)) +
                                        (bh_cofs >> blocksize_bits);
                        set_buffer_mapped(bh);
                        /*
                         * If the page is uptodate so is the buffer.  If the
                         * buffer is fully outside the write, we ignore it if
                         * it was already allocated and we mark it dirty so it
                         * gets written out if we allocated it.  On the other
                         * hand, if we allocated the buffer but we are not
                         * marking it dirty we set buffer_new so we can do
                         * error recovery.
                         */
                        if (PageUptodate(page)) {
                                if (!buffer_uptodate(bh))
                                        set_buffer_uptodate(bh);
                                if (unlikely(was_hole)) {
                                        /* We allocated the buffer. */
                                        clean_bdev_bh_alias(bh);
                                        if (bh_end <= pos || bh_pos >= end)
                                                mark_buffer_dirty(bh);
                                        else
                                                set_buffer_new(bh);
                                }
                                continue;
                        }
                        /* Page is _not_ uptodate. */
                        if (likely(!was_hole)) {
                                /*
                                 * Buffer was already allocated.  If it is not
                                 * uptodate and is only partially being written
                                 * to, we need to read it in before the write,
                                 * i.e. now.
                                 */
                                if (!buffer_uptodate(bh) && bh_pos < end &&
                                                bh_end > pos &&
                                                (bh_pos < pos ||
                                                bh_end > end)) {
                                        /*
                                         * If the buffer is fully or partially
                                         * within the initialized size, do an
                                         * actual read.  Otherwise, simply zero
                                         * the buffer.
                                         */
                                        read_lock_irqsave(&ni->size_lock,
                                                        flags);
                                        initialized_size = ni->initialized_size;
                                        read_unlock_irqrestore(&ni->size_lock,
                                                        flags);
                                        if (bh_pos < initialized_size) {
                                                ntfs_submit_bh_for_read(bh);
                                                *wait_bh++ = bh;
                                        } else {
                                                zero_user(page, bh_offset(bh),
                                                                blocksize);
                                                set_buffer_uptodate(bh);
                                        }
                                }
                                continue;
                        }
                        /* We allocated the buffer. */
                        clean_bdev_bh_alias(bh);
                        /*
                         * If the buffer is fully outside the write, zero it,
                         * set it uptodate, and mark it dirty so it gets
                         * written out.  If it is partially being written to,
                         * zero region surrounding the write but leave it to
                         * commit write to do anything else.  Finally, if the
                         * buffer is fully being overwritten, do nothing.
                         */
                        if (bh_end <= pos || bh_pos >= end) {
                                if (!buffer_uptodate(bh)) {
                                        zero_user(page, bh_offset(bh),
                                                        blocksize);
                                        set_buffer_uptodate(bh);
                                }
                                mark_buffer_dirty(bh);
                                continue;
                        }
                        set_buffer_new(bh);
                        if (!buffer_uptodate(bh) &&
                                        (bh_pos < pos || bh_end > end)) {
                                u8 *kaddr;
                                unsigned pofs;
                                        
                                kaddr = kmap_atomic(page);
                                if (bh_pos < pos) {
                                        pofs = bh_pos & ~PAGE_MASK;
                                        memset(kaddr + pofs, 0, pos - bh_pos);
                                }
                                if (bh_end > end) {
                                        pofs = end & ~PAGE_MASK;
                                        memset(kaddr + pofs, 0, bh_end - end);
                                }
                                kunmap_atomic(kaddr);
                                flush_dcache_page(page);
                        }
                        continue;
                }
                /*
                 * Slow path: this is the first buffer in the cluster.  If it
                 * is outside allocated size and is not uptodate, zero it and
                 * set it uptodate.
                 */
                read_lock_irqsave(&ni->size_lock, flags);
                initialized_size = ni->allocated_size;
                read_unlock_irqrestore(&ni->size_lock, flags);
                if (bh_pos > initialized_size) {
                        if (PageUptodate(page)) {
                                if (!buffer_uptodate(bh))
                                        set_buffer_uptodate(bh);
                        } else if (!buffer_uptodate(bh)) {
                                zero_user(page, bh_offset(bh), blocksize);
                                set_buffer_uptodate(bh);
                        }
                        continue;
                }
                is_retry = false;
                if (!rl) {
                        down_read(&ni->runlist.lock);
retry_remap:
                        rl = ni->runlist.rl;
                }
                if (likely(rl != NULL)) {
                        /* Seek to element containing target cluster. */
                        while (rl->length && rl[1].vcn <= bh_cpos)
                                rl++;
                        lcn = ntfs_rl_vcn_to_lcn(rl, bh_cpos);
                        if (likely(lcn >= 0)) {
                                /*
                                 * Successful remap, setup the map cache and
                                 * use that to deal with the buffer.
                                 */
                                was_hole = false;
                                vcn = bh_cpos;
                                vcn_len = rl[1].vcn - vcn;
                                lcn_block = lcn << (vol->cluster_size_bits -
                                                blocksize_bits);
                                cdelta = 0;
                                /*
                                 * If the number of remaining clusters touched
                                 * by the write is smaller or equal to the
                                 * number of cached clusters, unlock the
                                 * runlist as the map cache will be used from
                                 * now on.
                                 */
                                if (likely(vcn + vcn_len >= cend)) {
                                        if (rl_write_locked) {
                                                up_write(&ni->runlist.lock);
                                                rl_write_locked = false;
                                        } else
                                                up_read(&ni->runlist.lock);
                                        rl = NULL;
                                }
                                goto map_buffer_cached;
                        }
                } else
                        lcn = LCN_RL_NOT_MAPPED;
                /*
                 * If it is not a hole and not out of bounds, the runlist is
                 * probably unmapped so try to map it now.
                 */
                if (unlikely(lcn != LCN_HOLE && lcn != LCN_ENOENT)) {
                        if (likely(!is_retry && lcn == LCN_RL_NOT_MAPPED)) {
                                /* Attempt to map runlist. */
                                if (!rl_write_locked) {
                                        /*
                                         * We need the runlist locked for
                                         * writing, so if it is locked for
                                         * reading relock it now and retry in
                                         * case it changed whilst we dropped
                                         * the lock.
                                         */
                                        up_read(&ni->runlist.lock);
                                        down_write(&ni->runlist.lock);
                                        rl_write_locked = true;
                                        goto retry_remap;
                                }
                                err = ntfs_map_runlist_nolock(ni, bh_cpos,
                                                NULL);
                                if (likely(!err)) {
                                        is_retry = true;
                                        goto retry_remap;
                                }
                                /*
                                 * If @vcn is out of bounds, pretend @lcn is
                                 * LCN_ENOENT.  As long as the buffer is out
                                 * of bounds this will work fine.
                                 */
                                if (err == -ENOENT) {
                                        lcn = LCN_ENOENT;
                                        err = 0;
                                        goto rl_not_mapped_enoent;
                                }
                        } else
                                err = -EIO;
                        /* Failed to map the buffer, even after retrying. */
                        bh->b_blocknr = -1;
                        ntfs_error(vol->sb, "Failed to write to inode 0x%lx, "
                                        "attribute type 0x%x, vcn 0x%llx, "
                                        "vcn offset 0x%x, because its "
                                        "location on disk could not be "
                                        "determined%s (error code %i).",
                                        ni->mft_no, ni->type,
                                        (unsigned long long)bh_cpos,
                                        (unsigned)bh_pos &
                                        vol->cluster_size_mask,
                                        is_retry ? " even after retrying" : "",
                                        err);
                        break;
                }
rl_not_mapped_enoent:
                /*
                 * The buffer is in a hole or out of bounds.  We need to fill
                 * the hole, unless the buffer is in a cluster which is not
                 * touched by the write, in which case we just leave the buffer
                 * unmapped.  This can only happen when the cluster size is
                 * less than the page cache size.
                 */
                if (unlikely(vol->cluster_size < PAGE_SIZE)) {
                        bh_cend = (bh_end + vol->cluster_size - 1) >>
                                        vol->cluster_size_bits;
                        if ((bh_cend <= cpos || bh_cpos >= cend)) {
                                bh->b_blocknr = -1;
                                /*
                                 * If the buffer is uptodate we skip it.  If it
                                 * is not but the page is uptodate, we can set
                                 * the buffer uptodate.  If the page is not
                                 * uptodate, we can clear the buffer and set it
                                 * uptodate.  Whether this is worthwhile is
                                 * debatable and this could be removed.
                                 */
                                if (PageUptodate(page)) {
                                        if (!buffer_uptodate(bh))
                                                set_buffer_uptodate(bh);
                                } else if (!buffer_uptodate(bh)) {
                                        zero_user(page, bh_offset(bh),
                                                blocksize);
                                        set_buffer_uptodate(bh);
                                }
                                continue;
                        }
                }
                /*
                 * Out of bounds buffer is invalid if it was not really out of
                 * bounds.
                 */
                BUG_ON(lcn != LCN_HOLE);
                /*
                 * We need the runlist locked for writing, so if it is locked
                 * for reading relock it now and retry in case it changed
                 * whilst we dropped the lock.
                 */
                BUG_ON(!rl);
                if (!rl_write_locked) {
                        up_read(&ni->runlist.lock);
                        down_write(&ni->runlist.lock);
                        rl_write_locked = true;
                        goto retry_remap;
                }
                /* Find the previous last allocated cluster. */
                BUG_ON(rl->lcn != LCN_HOLE);
                lcn = -1;
                rl2 = rl;
                while (--rl2 >= ni->runlist.rl) {
                        if (rl2->lcn >= 0) {
                                lcn = rl2->lcn + rl2->length;
                                break;
                        }
                }
                rl2 = ntfs_cluster_alloc(vol, bh_cpos, 1, lcn, DATA_ZONE,
                                false);
                if (IS_ERR(rl2)) {
                        err = PTR_ERR(rl2);
                        ntfs_debug("Failed to allocate cluster, error code %i.",
                                        err);
                        break;
                }
                lcn = rl2->lcn;
                rl = ntfs_runlists_merge(ni->runlist.rl, rl2);
                if (IS_ERR(rl)) {
                        err = PTR_ERR(rl);
                        if (err != -ENOMEM)
                                err = -EIO;
                        if (ntfs_cluster_free_from_rl(vol, rl2)) {
                                ntfs_error(vol->sb, "Failed to release "
                                                "allocated cluster in error "
                                                "code path.  Run chkdsk to "
                                                "recover the lost cluster.");
                                NVolSetErrors(vol);

                        }
                        ntfs_free(rl2);
                        break;
                }
                ni->runlist.rl = rl;
                status.runlist_merged = 1;
                ntfs_debug("Allocated cluster, lcn 0x%llx.",
                                (unsigned long long)lcn);
                /* Map and lock the mft record and get the attribute record. */
                if (!NInoAttr(ni))
                        base_ni = ni;
                else
                        base_ni = ni->ext.base_ntfs_ino;
                m = map_mft_record(base_ni);
                if (IS_ERR(m)) {
                        err = PTR_ERR(m);
                        break;
                }
                ctx = ntfs_attr_get_search_ctx(base_ni, m);
                if (unlikely(!ctx)) {
                        err = -ENOMEM;
                        unmap_mft_record(base_ni);
                        break;
                }
                status.mft_attr_mapped = 1;
                err = ntfs_attr_lookup(ni->type, ni->name, ni->name_len,
                                CASE_SENSITIVE, bh_cpos, NULL, 0, ctx);
                if (unlikely(err)) {
                        if (err == -ENOENT)
                                err = -EIO;
                        break;
                }
                m = ctx->mrec;
                a = ctx->attr;
                /*
                 * Find the runlist element with which the attribute extent
                 * starts.  Note, we cannot use the _attr_ version because we
                 * have mapped the mft record.  That is ok because we know the
                 * runlist fragment must be mapped already to have ever gotten
                 * here, so we can just use the _rl_ version.
                 */
                vcn = sle64_to_cpu(a->data.non_resident.lowest_vcn);
                rl2 = ntfs_rl_find_vcn_nolock(rl, vcn);
                BUG_ON(!rl2);
                BUG_ON(!rl2->length);
                BUG_ON(rl2->lcn < LCN_HOLE);
                highest_vcn = sle64_to_cpu(a->data.non_resident.highest_vcn);
                /*
                 * If @highest_vcn is zero, calculate the real highest_vcn
                 * (which can really be zero).
                 */
                if (!highest_vcn)
                        highest_vcn = (sle64_to_cpu(
                                        a->data.non_resident.allocated_size) >>
                                        vol->cluster_size_bits) - 1;
                /*
                 * Determine the size of the mapping pairs array for the new
                 * extent, i.e. the old extent with the hole filled.
                 */
                mp_size = ntfs_get_size_for_mapping_pairs(vol, rl2, vcn,
                                highest_vcn);
                if (unlikely(mp_size <= 0)) {
                        if (!(err = mp_size))
                                err = -EIO;
                        ntfs_debug("Failed to get size for mapping pairs "
                                        "array, error code %i.", err);
                        break;
                }
                /*
                 * Resize the attribute record to fit the new mapping pairs
                 * array.
                 */
                attr_rec_len = le32_to_cpu(a->length);
                err = ntfs_attr_record_resize(m, a, mp_size + le16_to_cpu(
                                a->data.non_resident.mapping_pairs_offset));
                if (unlikely(err)) {
                        BUG_ON(err != -ENOSPC);
                        // TODO: Deal with this by using the current attribute
                        // and fill it with as much of the mapping pairs
                        // array as possible.  Then loop over each attribute
                        // extent rewriting the mapping pairs arrays as we go
                        // along and if when we reach the end we have not
                        // enough space, try to resize the last attribute
                        // extent and if even that fails, add a new attribute
                        // extent.
                        // We could also try to resize at each step in the hope
                        // that we will not need to rewrite every single extent.
                        // Note, we may need to decompress some extents to fill
                        // the runlist as we are walking the extents...
                        ntfs_error(vol->sb, "Not enough space in the mft "
                                        "record for the extended attribute "
                                        "record.  This case is not "
                                        "implemented yet.");
                        err = -EOPNOTSUPP;
                        break ;
                }
                status.mp_rebuilt = 1;
                /*
                 * Generate the mapping pairs array directly into the attribute
                 * record.
                 */
                err = ntfs_mapping_pairs_build(vol, (u8*)a + le16_to_cpu(
                                a->data.non_resident.mapping_pairs_offset),
                                mp_size, rl2, vcn, highest_vcn, NULL);
                if (unlikely(err)) {
                        ntfs_error(vol->sb, "Cannot fill hole in inode 0x%lx, "
                                        "attribute type 0x%x, because building "
                                        "the mapping pairs failed with error "
                                        "code %i.", vi->i_ino,
                                        (unsigned)le32_to_cpu(ni->type), err);
                        err = -EIO;
                        break;
                }
                /* Update the highest_vcn but only if it was not set. */
                if (unlikely(!a->data.non_resident.highest_vcn))
                        a->data.non_resident.highest_vcn =
                                        cpu_to_sle64(highest_vcn);
                /*
                 * If the attribute is sparse/compressed, update the compressed
                 * size in the ntfs_inode structure and the attribute record.
                 */
                if (likely(NInoSparse(ni) || NInoCompressed(ni))) {
                        /*
                         * If we are not in the first attribute extent, switch
                         * to it, but first ensure the changes will make it to
                         * disk later.
                         */
                        if (a->data.non_resident.lowest_vcn) {
                                flush_dcache_mft_record_page(ctx->ntfs_ino);
                                mark_mft_record_dirty(ctx->ntfs_ino);
                                ntfs_attr_reinit_search_ctx(ctx);
                                err = ntfs_attr_lookup(ni->type, ni->name,
                                                ni->name_len, CASE_SENSITIVE,
                                                0, NULL, 0, ctx);
                                if (unlikely(err)) {
                                        status.attr_switched = 1;
                                        break;
                                }
                                /* @m is not used any more so do not set it. */
                                a = ctx->attr;
                        }
                        write_lock_irqsave(&ni->size_lock, flags);
                        ni->itype.compressed.size += vol->cluster_size;
                        a->data.non_resident.compressed_size =
                                        cpu_to_sle64(ni->itype.compressed.size);
                        write_unlock_irqrestore(&ni->size_lock, flags);
                }
                /* Ensure the changes make it to disk. */
                flush_dcache_mft_record_page(ctx->ntfs_ino);
                mark_mft_record_dirty(ctx->ntfs_ino);
                ntfs_attr_put_search_ctx(ctx);
                unmap_mft_record(base_ni);
                /* Successfully filled the hole. */
                status.runlist_merged = 0;
                status.mft_attr_mapped = 0;
                status.mp_rebuilt = 0;
                /* Setup the map cache and use that to deal with the buffer. */
                was_hole = true;
                vcn = bh_cpos;
                vcn_len = 1;
                lcn_block = lcn << (vol->cluster_size_bits - blocksize_bits);
                cdelta = 0;
                /*
                 * If the number of remaining clusters in the @pages is smaller
                 * or equal to the number of cached clusters, unlock the
                 * runlist as the map cache will be used from now on.
                 */
                if (likely(vcn + vcn_len >= cend)) {
                        up_write(&ni->runlist.lock);
                        rl_write_locked = false;
                        rl = NULL;
                }
                goto map_buffer_cached;
        } while (bh_pos += blocksize, (bh = bh->b_this_page) != head);
        /* If there are no errors, do the next page. */
        if (likely(!err && ++u < nr_pages))
                goto do_next_page;
        /* If there are no errors, release the runlist lock if we took it. */
        if (likely(!err)) {
                if (unlikely(rl_write_locked)) {
                        up_write(&ni->runlist.lock);
                        rl_write_locked = false;
                } else if (unlikely(rl))
                        up_read(&ni->runlist.lock);
                rl = NULL;
        }
        /* If we issued read requests, let them complete. */
        read_lock_irqsave(&ni->size_lock, flags);
        initialized_size = ni->initialized_size;
        read_unlock_irqrestore(&ni->size_lock, flags);
        while (wait_bh > wait) {
                bh = *--wait_bh;
                wait_on_buffer(bh);
                if (likely(buffer_uptodate(bh))) {
                        page = bh->b_page;
                        bh_pos = ((s64)page->index << PAGE_SHIFT) +
                                        bh_offset(bh);
                        /*
                         * If the buffer overflows the initialized size, need
                         * to zero the overflowing region.
                         */
                        if (unlikely(bh_pos + blocksize > initialized_size)) {
                                int ofs = 0;

                                if (likely(bh_pos < initialized_size))
                                        ofs = initialized_size - bh_pos;
                                zero_user_segment(page, bh_offset(bh) + ofs,
                                                blocksize);
                        }
                } else /* if (unlikely(!buffer_uptodate(bh))) */
                        err = -EIO;
        }
        if (likely(!err)) {
                /* Clear buffer_new on all buffers. */
                u = 0;
                do {
                        bh = head = page_buffers(pages[u]);
                        do {
                                if (buffer_new(bh))
                                        clear_buffer_new(bh);
                        } while ((bh = bh->b_this_page) != head);
                } while (++u < nr_pages);
                ntfs_debug("Done.");
                return err;
        }
        if (status.attr_switched) {
                /* Get back to the attribute extent we modified. */
                ntfs_attr_reinit_search_ctx(ctx);
                if (ntfs_attr_lookup(ni->type, ni->name, ni->name_len,
                                CASE_SENSITIVE, bh_cpos, NULL, 0, ctx)) {
                        ntfs_error(vol->sb, "Failed to find required "
                                        "attribute extent of attribute in "
                                        "error code path.  Run chkdsk to "
                                        "recover.");
                        write_lock_irqsave(&ni->size_lock, flags);
                        ni->itype.compressed.size += vol->cluster_size;
                        write_unlock_irqrestore(&ni->size_lock, flags);
                        flush_dcache_mft_record_page(ctx->ntfs_ino);
                        mark_mft_record_dirty(ctx->ntfs_ino);
                        /*
                         * The only thing that is now wrong is the compressed
                         * size of the base attribute extent which chkdsk
                         * should be able to fix.
                         */
                        NVolSetErrors(vol);
                } else {
                        m = ctx->mrec;
                        a = ctx->attr;
                        status.attr_switched = 0;
                }
        }
        /*
         * If the runlist has been modified, need to restore it by punching a
         * hole into it and we then need to deallocate the on-disk cluster as
         * well.  Note, we only modify the runlist if we are able to generate a
         * new mapping pairs array, i.e. only when the mapped attribute extent
         * is not switched.
         */
        if (status.runlist_merged && !status.attr_switched) {
                BUG_ON(!rl_write_locked);
                /* Make the file cluster we allocated sparse in the runlist. */
                if (ntfs_rl_punch_nolock(vol, &ni->runlist, bh_cpos, 1)) {
                        ntfs_error(vol->sb, "Failed to punch hole into "
                                        "attribute runlist in error code "
                                        "path.  Run chkdsk to recover the "
                                        "lost cluster.");
                        NVolSetErrors(vol);
                } else /* if (success) */ {
                        status.runlist_merged = 0;
                        /*
                         * Deallocate the on-disk cluster we allocated but only
                         * if we succeeded in punching its vcn out of the
                         * runlist.
                         */
                        down_write(&vol->lcnbmp_lock);
                        if (ntfs_bitmap_clear_bit(vol->lcnbmp_ino, lcn)) {
                                ntfs_error(vol->sb, "Failed to release "
                                                "allocated cluster in error "
                                                "code path.  Run chkdsk to "
                                                "recover the lost cluster.");
                                NVolSetErrors(vol);
                        }
                        up_write(&vol->lcnbmp_lock);
                }
        }
        /*
         * Resize the attribute record to its old size and rebuild the mapping
         * pairs array.  Note, we only can do this if the runlist has been
         * restored to its old state which also implies that the mapped
         * attribute extent is not switched.
         */
        if (status.mp_rebuilt && !status.runlist_merged) {
                if (ntfs_attr_record_resize(m, a, attr_rec_len)) {
                        ntfs_error(vol->sb, "Failed to restore attribute "
                                        "record in error code path.  Run "
                                        "chkdsk to recover.");
                        NVolSetErrors(vol);
                } else /* if (success) */ {
                        if (ntfs_mapping_pairs_build(vol, (u8*)a +
                                        le16_to_cpu(a->data.non_resident.
                                        mapping_pairs_offset), attr_rec_len -
                                        le16_to_cpu(a->data.non_resident.
                                        mapping_pairs_offset), ni->runlist.rl,
                                        vcn, highest_vcn, NULL)) {
                                ntfs_error(vol->sb, "Failed to restore "
                                                "mapping pairs array in error "
                                                "code path.  Run chkdsk to "
                                                "recover.");
                                NVolSetErrors(vol);
                        }
                        flush_dcache_mft_record_page(ctx->ntfs_ino);
                        mark_mft_record_dirty(ctx->ntfs_ino);
                }
        }
        /* Release the mft record and the attribute. */
        if (status.mft_attr_mapped) {
                ntfs_attr_put_search_ctx(ctx);
                unmap_mft_record(base_ni);
        }
        /* Release the runlist lock. */
        if (rl_write_locked)
                up_write(&ni->runlist.lock);
        else if (rl)
                up_read(&ni->runlist.lock);
        /*
         * Zero out any newly allocated blocks to avoid exposing stale data.
         * If BH_New is set, we know that the block was newly allocated above
         * and that it has not been fully zeroed and marked dirty yet.
         */
        nr_pages = u;
        u = 0;
        end = bh_cpos << vol->cluster_size_bits;
        do {
                page = pages[u];
                bh = head = page_buffers(page);
                do {
                        if (u == nr_pages &&
                                        ((s64)page->index << PAGE_SHIFT) +
                                        bh_offset(bh) >= end)
                                break;
                        if (!buffer_new(bh))
                                continue;
                        clear_buffer_new(bh);
                        if (!buffer_uptodate(bh)) {
                                if (PageUptodate(page))
                                        set_buffer_uptodate(bh);
                                else {
                                        zero_user(page, bh_offset(bh),
                                                        blocksize);
                                        set_buffer_uptodate(bh);
                                }
                        }
                        mark_buffer_dirty(bh);
                } while ((bh = bh->b_this_page) != head);
        } while (++u <= nr_pages);
        ntfs_error(vol->sb, "Failed.  Returning error code %i.", err);
        return err;
}

static inline void ntfs_flush_dcache_pages(struct page **pages,
                unsigned nr_pages)
{
        BUG_ON(!nr_pages);
        /*
         * Warning: Do not do the decrement at the same time as the call to
         * flush_dcache_page() because it is a NULL macro on i386 and hence the
         * decrement never happens so the loop never terminates.
         */
        do {
                --nr_pages;
                flush_dcache_page(pages[nr_pages]);
        } while (nr_pages > 0);
}

/**
 * ntfs_commit_pages_after_non_resident_write - commit the received data
 * @pages:      array of destination pages
 * @nr_pages:   number of pages in @pages
 * @pos:        byte position in file at which the write begins
 * @bytes:      number of bytes to be written
 *
 * See description of ntfs_commit_pages_after_write(), below.
 */
static inline int ntfs_commit_pages_after_non_resident_write(
                struct page **pages, const unsigned nr_pages,
                s64 pos, size_t bytes)
{
        s64 end, initialized_size;
        struct inode *vi;
        ntfs_inode *ni, *base_ni;
        struct buffer_head *bh, *head;
        ntfs_attr_search_ctx *ctx;
        MFT_RECORD *m;
        ATTR_RECORD *a;
        unsigned long flags;
        unsigned blocksize, u;
        int err;

        vi = pages[0]->mapping->host;
        ni = NTFS_I(vi);
        blocksize = vi->i_sb->s_blocksize;
        end = pos + bytes;
        u = 0;
        do {
                s64 bh_pos;
                struct page *page;
                bool partial;

                page = pages[u];
                bh_pos = (s64)page->index << PAGE_SHIFT;
                bh = head = page_buffers(page);
                partial = false;
                do {
                        s64 bh_end;

                        bh_end = bh_pos + blocksize;
                        if (bh_end <= pos || bh_pos >= end) {
                                if (!buffer_uptodate(bh))
                                        partial = true;
                        } else {
                                set_buffer_uptodate(bh);
                                mark_buffer_dirty(bh);
                        }
                } while (bh_pos += blocksize, (bh = bh->b_this_page) != head);
                /*
                 * If all buffers are now uptodate but the page is not, set the
                 * page uptodate.
                 */
                if (!partial && !PageUptodate(page))
                        SetPageUptodate(page);
        } while (++u < nr_pages);
        /*
         * Finally, if we do not need to update initialized_size or i_size we
         * are finished.
         */
        read_lock_irqsave(&ni->size_lock, flags);
        initialized_size = ni->initialized_size;
        read_unlock_irqrestore(&ni->size_lock, flags);
        if (end <= initialized_size) {
                ntfs_debug("Done.");
                return 0;
        }
        /*
         * Update initialized_size/i_size as appropriate, both in the inode and
         * the mft record.
         */
        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;
        }
        BUG_ON(!NInoNonResident(ni));
        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)) {
                if (err == -ENOENT)
                        err = -EIO;
                goto err_out;
        }
        a = ctx->attr;
        BUG_ON(!a->non_resident);
        write_lock_irqsave(&ni->size_lock, flags);
        BUG_ON(end > ni->allocated_size);
        ni->initialized_size = end;
        a->data.non_resident.initialized_size = cpu_to_sle64(end);
        if (end > i_size_read(vi)) {
                i_size_write(vi, end);
                a->data.non_resident.data_size =
                                a->data.non_resident.initialized_size;
        }
        write_unlock_irqrestore(&ni->size_lock, flags);
        /* Mark the mft record dirty, so it gets written back. */
        flush_dcache_mft_record_page(ctx->ntfs_ino);
        mark_mft_record_dirty(ctx->ntfs_ino);
        ntfs_attr_put_search_ctx(ctx);
        unmap_mft_record(base_ni);
        ntfs_debug("Done.");
        return 0;
err_out:
        if (ctx)
                ntfs_attr_put_search_ctx(ctx);
        if (m)
                unmap_mft_record(base_ni);
        ntfs_error(vi->i_sb, "Failed to update initialized_size/i_size (error "
                        "code %i).", err);
        if (err != -ENOMEM)
                NVolSetErrors(ni->vol);
        return err;
}

/**
 * ntfs_commit_pages_after_write - commit the received data
 * @pages:      array of destination pages
 * @nr_pages:   number of pages in @pages
 * @pos:        byte position in file at which the write begins
 * @bytes:      number of bytes to be written
 *
 * This is called from ntfs_file_buffered_write() with i_mutex held on the inode
 * (@pages[0]->mapping->host).  There are @nr_pages pages in @pages which are
 * locked but not kmap()ped.  The source data has already been copied into the
 * @page.  ntfs_prepare_pages_for_non_resident_write() has been called before
 * the data was copied (for non-resident attributes only) and it returned
 * success.
 *
 * Need to set uptodate and mark dirty all buffers within the boundary of the
 * write.  If all buffers in a page are uptodate we set the page uptodate, too.
 *
 * Setting the buffers dirty ensures that they get written out later when
 * ntfs_writepage() is invoked by the VM.
 *
 * Finally, we need to update i_size and initialized_size as appropriate both
 * in the inode and the mft record.
 *
 * This is modelled after fs/buffer.c::generic_commit_write(), which marks
 * buffers uptodate and dirty, sets the page uptodate if all buffers in the
 * page are uptodate, and updates i_size if the end of io is beyond i_size.  In
 * that case, it also marks the inode dirty.
 *
 * If things have gone as outlined in
 * ntfs_prepare_pages_for_non_resident_write(), we do not need to do any page
 * content modifications here for non-resident attributes.  For resident
 * attributes we need to do the uptodate bringing here which we combine with
 * the copying into the mft record which means we save one atomic kmap.
 *
 * Return 0 on success or -errno on error.
 */
static int ntfs_commit_pages_after_write(struct page **pages,
                const unsigned nr_pages, s64 pos, size_t bytes)
{
        s64 end, initialized_size;
        loff_t i_size;
        struct inode *vi;
        ntfs_inode *ni, *base_ni;
        struct page *page;
        ntfs_attr_search_ctx *ctx;
        MFT_RECORD *m;
        ATTR_RECORD *a;
        char *kattr, *kaddr;
        unsigned long flags;
        u32 attr_len;
        int err;

        BUG_ON(!nr_pages);
        BUG_ON(!pages);
        page = pages[0];
        BUG_ON(!page);
        vi = page->mapping->host;
        ni = NTFS_I(vi);
        ntfs_debug("Entering for inode 0x%lx, attribute type 0x%x, start page "
                        "index 0x%lx, nr_pages 0x%x, pos 0x%llx, bytes 0x%zx.",
                        vi->i_ino, ni->type, page->index, nr_pages,
                        (long long)pos, bytes);
        if (NInoNonResident(ni))
                return ntfs_commit_pages_after_non_resident_write(pages,
                                nr_pages, pos, bytes);
        BUG_ON(nr_pages > 1);
        /*
         * Attribute is resident, implying it is not compressed, encrypted, or
         * sparse.
         */
        if (!NInoAttr(ni))
                base_ni = ni;
        else
                base_ni = ni->ext.base_ntfs_ino;
        BUG_ON(NInoNonResident(ni));
        /* 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;
        }
        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)) {
                if (err == -ENOENT)
                        err = -EIO;
                goto err_out;
        }
        a = ctx->attr;
        BUG_ON(a->non_resident);
        /* The total length of the attribute value. */
        attr_len = le32_to_cpu(a->data.resident.value_length);
        i_size = i_size_read(vi);
        BUG_ON(attr_len != i_size);
        BUG_ON(pos > attr_len);
        end = pos + bytes;
        BUG_ON(end > le32_to_cpu(a->length) -
                        le16_to_cpu(a->data.resident.value_offset));
        kattr = (u8*)a + le16_to_cpu(a->data.resident.value_offset);
        kaddr = kmap_atomic(page);
        /* Copy the received data from the page to the mft record. */
        memcpy(kattr + pos, kaddr + pos, bytes);
        /* Update the attribute length if necessary. */
        if (end > attr_len) {
                attr_len = end;
                a->data.resident.value_length = cpu_to_le32(attr_len);
        }
        /*
         * If the page is not uptodate, bring the out of bounds area(s)
         * uptodate by copying data from the mft record to the page.
         */
        if (!PageUptodate(page)) {
                if (pos > 0)
                        memcpy(kaddr, kattr, pos);
                if (end < attr_len)
                        memcpy(kaddr + end, kattr + end, attr_len - end);
                /* Zero the region outside the end of the attribute value. */
                memset(kaddr + attr_len, 0, PAGE_SIZE - attr_len);
                flush_dcache_page(page);
                SetPageUptodate(page);
        }
        kunmap_atomic(kaddr);
        /* Update initialized_size/i_size if necessary. */
        read_lock_irqsave(&ni->size_lock, flags);
        initialized_size = ni->initialized_size;
        BUG_ON(end > ni->allocated_size);
        read_unlock_irqrestore(&ni->size_lock, flags);
        BUG_ON(initialized_size != i_size);
        if (end > initialized_size) {
                write_lock_irqsave(&ni->size_lock, flags);
                ni->initialized_size = end;
                i_size_write(vi, end);
                write_unlock_irqrestore(&ni->size_lock, flags);
        }
        /* Mark the mft record dirty, so it gets written back. */
        flush_dcache_mft_record_page(ctx->ntfs_ino);
        mark_mft_record_dirty(ctx->ntfs_ino);
        ntfs_attr_put_search_ctx(ctx);
        unmap_mft_record(base_ni);
        ntfs_debug("Done.");
        return 0;
err_out:
        if (err == -ENOMEM) {
                ntfs_warning(vi->i_sb, "Error allocating memory required to "
                                "commit the write.");
                if (PageUptodate(page)) {
                        ntfs_warning(vi->i_sb, "Page is uptodate, setting "
                                        "dirty so the write will be retried "
                                        "later on by the VM.");
                        /*
                         * Put the page on mapping->dirty_pages, but leave its
                         * buffers' dirty state as-is.
                         */
                        __set_page_dirty_nobuffers(page);
                        err = 0;
                } else
                        ntfs_error(vi->i_sb, "Page is not uptodate.  Written "
                                        "data has been lost.");
        } else {
                ntfs_error(vi->i_sb, "Resident attribute commit write failed "
                                "with error %i.", err);
                NVolSetErrors(ni->vol);
        }
        if (ctx)
                ntfs_attr_put_search_ctx(ctx);
        if (m)
                unmap_mft_record(base_ni);
        return err;
}

/*
 * Copy as much as we can into the pages and return the number of bytes which
 * were successfully copied.  If a fault is encountered then clear the pages
 * out to (ofs + bytes) and return the number of bytes which were copied.
 */
static size_t ntfs_copy_from_user_iter(struct page **pages, unsigned nr_pages,
                unsigned ofs, struct iov_iter *i, size_t bytes)
{
        struct page **last_page = pages + nr_pages;
        size_t total = 0;
        struct iov_iter data = *i;
        unsigned len, copied;

        do {
                len = PAGE_SIZE - ofs;
                if (len > bytes)
                        len = bytes;
                copied = iov_iter_copy_from_user_atomic(*pages, &data, ofs,
                                len);
                total += copied;
                bytes -= copied;
                if (!bytes)
                        break;
                iov_iter_advance(&data, copied);
                if (copied < len)
                        goto err;
                ofs = 0;
        } while (++pages < last_page);
out:
        return total;
err:
        /* Zero the rest of the target like __copy_from_user(). */
        len = PAGE_SIZE - copied;
        do {
                if (len > bytes)
                        len = bytes;
                zero_user(*pages, copied, len);
                bytes -= len;
                copied = 0;
                len = PAGE_SIZE;
        } while (++pages < last_page);
        goto out;
}

/**
 * ntfs_perform_write - perform buffered write to a file
 * @file:       file to write to
 * @i:          iov_iter with data to write
 * @pos:        byte offset in file at which to begin writing to
 */
static ssize_t ntfs_perform_write(struct file *file, struct iov_iter *i,
                loff_t pos)
{
        struct address_space *mapping = file->f_mapping;
        struct inode *vi = mapping->host;
        ntfs_inode *ni = NTFS_I(vi);
        ntfs_volume *vol = ni->vol;
        struct page *pages[NTFS_MAX_PAGES_PER_CLUSTER];
        struct page *cached_page = NULL;
        VCN last_vcn;
        LCN lcn;
        size_t bytes;
        ssize_t status, written = 0;
        unsigned nr_pages;

        ntfs_debug("Entering for i_ino 0x%lx, attribute type 0x%x, pos "
                        "0x%llx, count 0x%lx.", vi->i_ino,
                        (unsigned)le32_to_cpu(ni->type),
                        (unsigned long long)pos,
                        (unsigned long)iov_iter_count(i));
        /*
         * If a previous ntfs_truncate() failed, repeat it and abort if it
         * fails again.
         */
        if (unlikely(NInoTruncateFailed(ni))) {
                int err;

                inode_dio_wait(vi);
                err = ntfs_truncate(vi);
                if (err || NInoTruncateFailed(ni)) {
                        if (!err)
                                err = -EIO;
                        ntfs_error(vol->sb, "Cannot perform write to inode "
                                        "0x%lx, attribute type 0x%x, because "
                                        "ntfs_truncate() failed (error code "
                                        "%i).", vi->i_ino,
                                        (unsigned)le32_to_cpu(ni->type), err);
                        return err;
                }
        }
        /*
         * Determine the number of pages per cluster for non-resident
         * attributes.
         */
        nr_pages = 1;
        if (vol->cluster_size > PAGE_SIZE && NInoNonResident(ni))
                nr_pages = vol->cluster_size >> PAGE_SHIFT;
        last_vcn = -1;
        do {
                VCN vcn;
                pgoff_t idx, start_idx;
                unsigned ofs, do_pages, u;
                size_t copied;

                start_idx = idx = pos >> PAGE_SHIFT;
                ofs = pos & ~PAGE_MASK;
                bytes = PAGE_SIZE - ofs;
                do_pages = 1;
                if (nr_pages > 1) {
                        vcn = pos >> vol->cluster_size_bits;
                        if (vcn != last_vcn) {
                                last_vcn = vcn;
                                /*
                                 * Get the lcn of the vcn the write is in.  If
                                 * it is a hole, need to lock down all pages in
                                 * the cluster.
                                 */
                                down_read(&ni->runlist.lock);
                                lcn = ntfs_attr_vcn_to_lcn_nolock(ni, pos >>
                                                vol->cluster_size_bits, false);
                                up_read(&ni->runlist.lock);
                                if (unlikely(lcn < LCN_HOLE)) {
                                        if (lcn == LCN_ENOMEM)
                                                status = -ENOMEM;
                                        else {
                                                status = -EIO;
                                                ntfs_error(vol->sb, "Cannot "
                                                        "perform write to "
                                                        "inode 0x%lx, "
                                                        "attribute type 0x%x, "
                                                        "because the attribute "
                                                        "is corrupt.",
                                                        vi->i_ino, (unsigned)
                                                        le32_to_cpu(ni->type));
                                        }
                                        break;
                                }
                                if (lcn == LCN_HOLE) {
                                        start_idx = (pos & ~(s64)
                                                        vol->cluster_size_mask)
                                                        >> PAGE_SHIFT;
                                        bytes = vol->cluster_size - (pos &
                                                        vol->cluster_size_mask);
                                        do_pages = nr_pages;
                                }
                        }
                }
                if (bytes > iov_iter_count(i))
                        bytes = iov_iter_count(i);
again:
                /*
                 * Bring in the user page(s) that we will copy from _first_.
                 * Otherwise there is a nasty deadlock on copying from the same
                 * page(s) as we are writing to, without it/them being marked
                 * up-to-date.  Note, at present there is nothing to stop the
                 * pages being swapped out between us bringing them into memory
                 * and doing the actual copying.
                 */
                if (unlikely(iov_iter_fault_in_readable(i, bytes))) {
                        status = -EFAULT;
                        break;
                }
                /* Get and lock @do_pages starting at index @start_idx. */
                status = __ntfs_grab_cache_pages(mapping, start_idx, do_pages,
                                pages, &cached_page);
                if (unlikely(status))
                        break;
                /*
                 * For non-resident attributes, we need to fill any holes with
                 * actual clusters and ensure all bufferes are mapped.  We also
                 * need to bring uptodate any buffers that are only partially
                 * being written to.
                 */
                if (NInoNonResident(ni)) {
                        status = ntfs_prepare_pages_for_non_resident_write(
                                        pages, do_pages, pos, bytes);
                        if (unlikely(status)) {
                                do {
                                        unlock_page(pages[--do_pages]);
                                        put_page(pages[do_pages]);
                                } while (do_pages);
                                break;
                        }
                }
                u = (pos >> PAGE_SHIFT) - pages[0]->index;
                copied = ntfs_copy_from_user_iter(pages + u, do_pages - u, ofs,
                                        i, bytes);
                ntfs_flush_dcache_pages(pages + u, do_pages - u);
                status = 0;
                if (likely(copied == bytes)) {
                        status = ntfs_commit_pages_after_write(pages, do_pages,
                                        pos, bytes);
                        if (!status)
                                status = bytes;
                }
                do {
                        unlock_page(pages[--do_pages]);
                        put_page(pages[do_pages]);
                } while (do_pages);
                if (unlikely(status < 0))
                        break;
                copied = status;
                cond_resched();
                if (unlikely(!copied)) {
                        size_t sc;

                        /*
                         * We failed to copy anything.  Fall back to single
                         * segment length write.
                         *
                         * This is needed to avoid possible livelock in the
                         * case that all segments in the iov cannot be copied
                         * at once without a pagefault.
                         */
                        sc = iov_iter_single_seg_count(i);
                        if (bytes > sc)
                                bytes = sc;
                        goto again;
                }
                iov_iter_advance(i, copied);
                pos += copied;
                written += copied;
                balance_dirty_pages_ratelimited(mapping);
                if (fatal_signal_pending(current)) {
                        status = -EINTR;
                        break;
                }
        } while (iov_iter_count(i));
        if (cached_page)
                put_page(cached_page);
        ntfs_debug("Done.  Returning %s (written 0x%lx, status %li).",
                        written ? "written" : "status", (unsigned long)written,
                        (long)status);
        return written ? written : status;
}

/**
 * ntfs_file_write_iter - simple wrapper for ntfs_file_write_iter_nolock()
 * @iocb:       IO state structure
 * @from:       iov_iter with data to write
 *
 * Basically the same as generic_file_write_iter() except that it ends up
 * up calling ntfs_perform_write() instead of generic_perform_write() and that
 * O_DIRECT is not implemented.
 */
static ssize_t ntfs_file_write_iter(struct kiocb *iocb, struct iov_iter *from)
{
        struct file *file = iocb->ki_filp;
        struct inode *vi = file_inode(file);
        ssize_t written = 0;
        ssize_t err;

        inode_lock(vi);
        /* We can write back this queue in page reclaim. */
        current->backing_dev_info = inode_to_bdi(vi);
        err = ntfs_prepare_file_for_write(iocb, from);
        if (iov_iter_count(from) && !err)
                written = ntfs_perform_write(file, from, iocb->ki_pos);
        current->backing_dev_info = NULL;
        inode_unlock(vi);
        iocb->ki_pos += written;
        if (likely(written > 0))
                written = generic_write_sync(iocb, written);
        return written ? written : err;
}

/**
 * ntfs_file_fsync - sync a file to disk
 * @filp:       file to be synced
 * @datasync:   if non-zero only flush user data and not metadata
 *
 * Data integrity sync of a file to disk.  Used for fsync, fdatasync, and msync
 * system calls.  This function is inspired by fs/buffer.c::file_fsync().
 *
 * If @datasync is false, write the mft record and all associated extent mft
 * records as well as the $DATA attribute and then sync the block device.
 *
 * If @datasync is true and the attribute is non-resident, we skip the writing
 * of the mft record and all associated extent mft records (this might still
 * happen due to the write_inode_now() call).
 *
 * Also, if @datasync is true, we do not wait on the inode to be written out
 * but we always wait on the page cache pages to be written out.
 *
 * Locking: Caller must hold i_mutex on the inode.
 *
 * TODO: We should probably also write all attribute/index inodes associated
 * with this inode but since we have no simple way of getting to them we ignore
 * this problem for now.
 */
static int ntfs_file_fsync(struct file *filp, loff_t start, loff_t end,
                           int datasync)
{
        struct inode *vi = filp->f_mapping->host;
        int err, ret = 0;

        ntfs_debug("Entering for inode 0x%lx.", vi->i_ino);

        err = file_write_and_wait_range(filp, start, end);
        if (err)
                return err;
        inode_lock(vi);

        BUG_ON(S_ISDIR(vi->i_mode));
        if (!datasync || !NInoNonResident(NTFS_I(vi)))
                ret = __ntfs_write_inode(vi, 1);
        write_inode_now(vi, !datasync);
        /*
         * NOTE: If we were to use mapping->private_list (see ext2 and
         * fs/buffer.c) for dirty blocks then we could optimize the below to be
         * sync_mapping_buffers(vi->i_mapping).
         */
        err = sync_blockdev(vi->i_sb->s_bdev);
        if (unlikely(err && !ret))
                ret = err;
        if (likely(!ret))
                ntfs_debug("Done.");
        else
                ntfs_warning(vi->i_sb, "Failed to f%ssync inode 0x%lx.  Error "
                                "%u.", datasync ? "data" : "", vi->i_ino, -ret);
        inode_unlock(vi);

        return ret;
}

#endif /* NTFS_RW */

const struct file_operations ntfs_file_ops = {
        .llseek         = generic_file_llseek,
        .read_iter      = generic_file_read_iter,
#ifdef NTFS_RW
        .write_iter     = ntfs_file_write_iter,
        .fsync          = ntfs_file_fsync,
#endif /* NTFS_RW */
        .mmap           = generic_file_mmap,
        .open           = ntfs_file_open,
        .splice_read    = generic_file_splice_read,
};

const struct inode_operations ntfs_file_inode_ops = {
#ifdef NTFS_RW
        .setattr        = ntfs_setattr,
#endif /* NTFS_RW */
};

const struct file_operations ntfs_empty_file_ops = {};

const struct inode_operations ntfs_empty_inode_ops = {};