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file.c

/*
 * file.c - NTFS kernel file operations.  Part of the Linux-NTFS project.
 *
 * Copyright (c) 2001-2006 Anton Altaparmakov
 *
 * This program/include file is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License as published
 * by the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 *
 * This program/include file is distributed in the hope that it will be
 * useful, but WITHOUT ANY WARRANTY; without even the implied warranty
 * of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program (in the main directory of the Linux-NTFS
 * distribution in the file COPYING); if not, write to the Free Software
 * Foundation,Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
 */

#include <linux/buffer_head.h>
#include <linux/pagemap.h>
#include <linux/pagevec.h>
#include <linux/sched.h>
#include <linux/swap.h>
#include <linux/uio.h>
#include <linux/writeback.h>

#include <asm/page.h>
#include <asm/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 -EFBIG;
      }
      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
 * @cached_page:  store any allocated but unused page here
 * @lru_pvec:           lru-buffering pagevec of the caller
 *
 * 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.
 *
 * @cached_page and @lru_pvec are just optimizations for dealing with multiple
 * pages.
 *
 * 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,
            struct page **cached_page, struct pagevec *lru_pvec)
{
      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_CACHE_SHIFT;
      end_index = (new_init_size + PAGE_CACHE_SIZE - 1) >> PAGE_CACHE_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;
            }
            wait_on_page_locked(page);
            if (unlikely(!PageUptodate(page) || PageError(page))) {
                  page_cache_release(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_CACHE_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);
            page_cache_release(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;
}

/**
 * ntfs_fault_in_pages_readable -
 *
 * Fault a number of userspace pages into pagetables.
 *
 * Unlike include/linux/pagemap.h::fault_in_pages_readable(), this one copes
 * with more than two userspace pages as well as handling the single page case
 * elegantly.
 *
 * If you find this difficult to understand, then think of the while loop being
 * the following code, except that we do without the integer variable ret:
 *
 *    do {
 *          ret = __get_user(c, uaddr);
 *          uaddr += PAGE_SIZE;
 *    } while (!ret && uaddr < end);
 *
 * Note, the final __get_user() may well run out-of-bounds of the user buffer,
 * but _not_ out-of-bounds of the page the user buffer belongs to, and since
 * this is only a read and not a write, and since it is still in the same page,
 * it should not matter and this makes the code much simpler.
 */
static inline void ntfs_fault_in_pages_readable(const char __user *uaddr,
            int bytes)
{
      const char __user *end;
      volatile char c;

      /* Set @end to the first byte outside the last page we care about. */
      end = (const char __user*)PAGE_ALIGN((ptrdiff_t __user)uaddr + bytes);

      while (!__get_user(c, uaddr) && (uaddr += PAGE_SIZE, uaddr < end))
            ;
}

/**
 * ntfs_fault_in_pages_readable_iovec -
 *
 * Same as ntfs_fault_in_pages_readable() but operates on an array of iovecs.
 */
static inline void ntfs_fault_in_pages_readable_iovec(const struct iovec *iov,
            size_t iov_ofs, int bytes)
{
      do {
            const char __user *buf;
            unsigned len;

            buf = iov->iov_base + iov_ofs;
            len = iov->iov_len - iov_ofs;
            if (len > bytes)
                  len = bytes;
            ntfs_fault_in_pages_readable(buf, len);
            bytes -= len;
            iov++;
            iov_ofs = 0;
      } while (bytes);
}

/**
 * __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
 * @lru_pvec:     lru-buffering pagevec of caller
 *
 * Obtain @nr_pages locked page cache pages from the mapping @maping and
 * starting at index @index.
 *
 * If a page is newly created, increment its refcount and add it to the
 * caller's lru-buffering pagevec @lru_pvec.
 *
 * This is the same as mm/filemap.c::__grab_cache_page(), except that @nr_pages
 * are obtained at once instead of just one page and that 0 is returned on
 * success and -errno on error.
 *
 * 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, struct pagevec *lru_pvec)
{
      int err, nr;

      BUG_ON(!nr_pages);
      err = nr = 0;
      do {
            pages[nr] = find_lock_page(mapping, index);
            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(*cached_page, mapping, index,
                              GFP_KERNEL);
                  if (unlikely(err)) {
                        if (err == -EEXIST)
                              continue;
                        goto err_out;
                  }
                  pages[nr] = *cached_page;
                  page_cache_get(*cached_page);
                  if (unlikely(!pagevec_add(lru_pvec, *cached_page)))
                        __pagevec_lru_add(lru_pvec);
                  *cached_page = NULL;
            }
            index++;
            nr++;
      } while (nr < nr_pages);
out:
      return err;
err_out:
      while (nr > 0) {
            unlock_page(pages[--nr]);
            page_cache_release(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(READ, 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_CACHE_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 {
            struct page *page = pages[u];
            /*
             * 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_CACHE_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 {
                              u8 *kaddr = kmap_atomic(page, KM_USER0);
                              memset(kaddr + bh_offset(bh), 0,
                                          blocksize);
                              kunmap_atomic(kaddr, KM_USER0);
                              flush_dcache_page(page);
                              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. */
                              unmap_underlying_metadata(bh->b_bdev,
                                          bh->b_blocknr);
                              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 {
                                    u8 *kaddr = kmap_atomic(page,
                                                KM_USER0);
                                    memset(kaddr + bh_offset(bh),
                                                0, blocksize);
                                    kunmap_atomic(kaddr, KM_USER0);
                                    flush_dcache_page(page);
                                    set_buffer_uptodate(bh);
                              }
                        }
                        continue;
                  }
                  /* We allocated the buffer. */
                  unmap_underlying_metadata(bh->b_bdev, bh->b_blocknr);
                  /*
                   * 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)) {
                              u8 *kaddr = kmap_atomic(page, KM_USER0);
                              memset(kaddr + bh_offset(bh), 0,
                                          blocksize);
                              kunmap_atomic(kaddr, KM_USER0);
                              flush_dcache_page(page);
                              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, KM_USER0);
                        if (bh_pos < pos) {
                              pofs = bh_pos & ~PAGE_CACHE_MASK;
                              memset(kaddr + pofs, 0, pos - bh_pos);
                        }
                        if (bh_end > end) {
                              pofs = end & ~PAGE_CACHE_MASK;
                              memset(kaddr + pofs, 0, bh_end - end);
                        }
                        kunmap_atomic(kaddr, KM_USER0);
                        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)) {
                        u8 *kaddr = kmap_atomic(page, KM_USER0);
                        memset(kaddr + bh_offset(bh), 0, blocksize);
                        kunmap_atomic(kaddr, KM_USER0);
                        flush_dcache_page(page);
                        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_CACHE_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)) {
                              u8 *kaddr = kmap_atomic(page, KM_USER0);
                              memset(kaddr + bh_offset(bh), 0,
                                          blocksize);
                              kunmap_atomic(kaddr, KM_USER0);
                              flush_dcache_page(page);
                              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_CACHE_SHIFT) +
                              bh_offset(bh);
                  /*
                   * If the buffer overflows the initialized size, need
                   * to zero the overflowing region.
                   */
                  if (unlikely(bh_pos + blocksize > initialized_size)) {
                        u8 *kaddr;
                        int ofs = 0;

                        if (likely(bh_pos < initialized_size))
                              ofs = initialized_size - bh_pos;
                        kaddr = kmap_atomic(page, KM_USER0);
                        memset(kaddr + bh_offset(bh) + ofs, 0,
                                    blocksize - ofs);
                        kunmap_atomic(kaddr, KM_USER0);
                        flush_dcache_page(page);
                  }
            } 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_CACHE_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 {
                              u8 *kaddr = kmap_atomic(page, KM_USER0);
                              memset(kaddr + bh_offset(bh), 0,
                                          blocksize);
                              kunmap_atomic(kaddr, KM_USER0);
                              flush_dcache_page(page);
                              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;
}

/*
 * Copy as much as we can into the pages and return the number of bytes which
 * were sucessfully copied.  If a fault is encountered then clear the pages
 * out to (ofs + bytes) and return the number of bytes which were copied.
 */
static inline size_t ntfs_copy_from_user(struct page **pages,
            unsigned nr_pages, unsigned ofs, const char __user *buf,
            size_t bytes)
{
      struct page **last_page = pages + nr_pages;
      char *kaddr;
      size_t total = 0;
      unsigned len;
      int left;

      do {
            len = PAGE_CACHE_SIZE - ofs;
            if (len > bytes)
                  len = bytes;
            kaddr = kmap_atomic(*pages, KM_USER0);
            left = __copy_from_user_inatomic(kaddr + ofs, buf, len);
            kunmap_atomic(kaddr, KM_USER0);
            if (unlikely(left)) {
                  /* Do it the slow way. */
                  kaddr = kmap(*pages);
                  left = __copy_from_user(kaddr + ofs, buf, len);
                  kunmap(*pages);
                  if (unlikely(left))
                        goto err_out;
            }
            total += len;
            bytes -= len;
            if (!bytes)
                  break;
            buf += len;
            ofs = 0;
      } while (++pages < last_page);
out:
      return total;
err_out:
      total += len - left;
      /* Zero the rest of the target like __copy_from_user(). */
      while (++pages < last_page) {
            bytes -= len;
            if (!bytes)
                  break;
            len = PAGE_CACHE_SIZE;
            if (len > bytes)
                  len = bytes;
            kaddr = kmap_atomic(*pages, KM_USER0);
            memset(kaddr, 0, len);
            kunmap_atomic(kaddr, KM_USER0);
      }
      goto out;
}

static size_t __ntfs_copy_from_user_iovec_inatomic(char *vaddr,
            const struct iovec *iov, size_t iov_ofs, size_t bytes)
{
      size_t total = 0;

      while (1) {
            const char __user *buf = iov->iov_base + iov_ofs;
            unsigned len;
            size_t left;

            len = iov->iov_len - iov_ofs;
            if (len > bytes)
                  len = bytes;
            left = __copy_from_user_inatomic(vaddr, buf, len);
            total += len;
            bytes -= len;
            vaddr += len;
            if (unlikely(left)) {
                  total -= left;
                  break;
            }
            if (!bytes)
                  break;
            iov++;
            iov_ofs = 0;
      }
      return total;
}

static inline void ntfs_set_next_iovec(const struct iovec **iovp,
            size_t *iov_ofsp, size_t bytes)
{
      const struct iovec *iov = *iovp;
      size_t iov_ofs = *iov_ofsp;

      while (bytes) {
            unsigned len;

            len = iov->iov_len - iov_ofs;
            if (len > bytes)
                  len = bytes;
            bytes -= len;
            iov_ofs += len;
            if (iov->iov_len == iov_ofs) {
                  iov++;
                  iov_ofs = 0;
            }
      }
      *iovp = iov;
      *iov_ofsp = iov_ofs;
}

/*
 * This has the same side-effects and return value as ntfs_copy_from_user().
 * The difference is that on a fault we need to memset the remainder of the
 * pages (out to offset + bytes), to emulate ntfs_copy_from_user()'s
 * single-segment behaviour.
 *
 * We call the same helper (__ntfs_copy_from_user_iovec_inatomic()) both
 * when atomic and when not atomic.  This is ok because
 * __ntfs_copy_from_user_iovec_inatomic() calls __copy_from_user_inatomic()
 * and it is ok to call this when non-atomic.
 * Infact, the only difference between __copy_from_user_inatomic() and
 * __copy_from_user() is that the latter calls might_sleep() and the former
 * should not zero the tail of the buffer on error.  And on many
 * architectures __copy_from_user_inatomic() is just defined to
 * __copy_from_user() so it makes no difference at all on those architectures.
 */
static inline size_t ntfs_copy_from_user_iovec(struct page **pages,
            unsigned nr_pages, unsigned ofs, const struct iovec **iov,
            size_t *iov_ofs, size_t bytes)
{
      struct page **last_page = pages + nr_pages;
      char *kaddr;
      size_t copied, len, total = 0;

      do {
            len = PAGE_CACHE_SIZE - ofs;
            if (len > bytes)
                  len = bytes;
            kaddr = kmap_atomic(*pages, KM_USER0);
            copied = __ntfs_copy_from_user_iovec_inatomic(kaddr + ofs,
                        *iov, *iov_ofs, len);
            kunmap_atomic(kaddr, KM_USER0);
            if (unlikely(copied != len)) {
                  /* Do it the slow way. */
                  kaddr = kmap(*pages);
                  copied = __ntfs_copy_from_user_iovec_inatomic(kaddr + ofs,
                              *iov, *iov_ofs, len);
                  /*
                   * Zero the rest of the target like __copy_from_user().
                   */
                  memset(kaddr + ofs + copied, 0, len - copied);
                  kunmap(*pages);
                  if (unlikely(copied != len))
                        goto err_out;
            }
            total += len;
            bytes -= len;
            if (!bytes)
                  break;
            ntfs_set_next_iovec(iov, iov_ofs, len);
            ofs = 0;
      } while (++pages < last_page);
out:
      return total;
err_out:
      total += copied;
      /* Zero the rest of the target like __copy_from_user(). */
      while (++pages < last_page) {
            bytes -= len;
            if (!bytes)
                  break;
            len = PAGE_CACHE_SIZE;
            if (len > bytes)
                  len = bytes;
            kaddr = kmap_atomic(*pages, KM_USER0);
            memset(kaddr, 0, len);
            kunmap_atomic(kaddr, KM_USER0);
      }
      goto out;
}

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_CACHE_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, KM_USER0);
      /* 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_CACHE_SIZE - attr_len);
            flush_dcache_page(page);
            SetPageUptodate(page);
      }
      kunmap_atomic(kaddr, KM_USER0);
      /* 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) {
            unsigned long flags;

            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;
}

/**
 * ntfs_file_buffered_write -
 *
 * Locking: The vfs is holding ->i_mutex on the inode.
 */
static ssize_t ntfs_file_buffered_write(struct kiocb *iocb,
            const struct iovec *iov, unsigned long nr_segs,
            loff_t pos, loff_t *ppos, size_t count)
{
      struct file *file = iocb->ki_filp;
      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;
      char __user *buf = NULL;
      s64 end, ll;
      VCN last_vcn;
      LCN lcn;
      unsigned long flags;
      size_t bytes, iov_ofs = 0;    /* Offset in the current iovec. */
      ssize_t status, written;
      unsigned nr_pages;
      int err;
      struct pagevec lru_pvec;

      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)count);
      if (unlikely(!count))
            return 0;
      BUG_ON(NInoMstProtected(ni));
      /*
       * If the attribute is not an index root and it is encrypted or
       * compressed, we cannot write to it yet.  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)) {
                  /*
                   * 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.");
                  return -EACCES;
            }
            if (NInoCompressed(ni)) {
                  /* Only unnamed $DATA attribute can be compressed. */
                  BUG_ON(ni->type != AT_DATA);
                  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.");
                  return -EOPNOTSUPP;
            }
      }
      /*
       * If a previous ntfs_truncate() failed, repeat it and abort if it
       * fails again.
       */
      if (unlikely(NInoTruncateFailed(ni))) {
            down_write(&vi->i_alloc_sem);
            err = ntfs_truncate(vi);
            up_write(&vi->i_alloc_sem);
            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;
            }
      }
      /* The first byte after the write. */
      end = pos + count;
      /*
       * 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. */
            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));
                        end = ll;
                        count = 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 code %i).",
                                    vi->i_ino, (unsigned)
                                    le32_to_cpu(ni->type), err);
                        end = ll;
                        count = ll - pos;
                  } else {
                        ntfs_error(vol->sb, "Cannot perform write to "
                                    "inode 0x%lx, attribute type "
                                    "0x%x, because extending the "
                                    "allocation failed (error "
                                    "code %i).", vi->i_ino,
                                    (unsigned)
                                    le32_to_cpu(ni->type), err);
                        return err;
                  }
            }
      }
      pagevec_init(&lru_pvec, 0);
      written = 0;
      /*
       * 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) {
            err = ntfs_attr_extend_initialized(ni, pos, &cached_page,
                        &lru_pvec);
            if (err < 0) {
                  ntfs_error(vol->sb, "Cannot perform write to inode "
                              "0x%lx, attribute type 0x%x, because "
                              "extending the initialized size "
                              "failed (error code %i).", vi->i_ino,
                              (unsigned)le32_to_cpu(ni->type), err);
                  status = err;
                  goto err_out;
            }
      }
      /*
       * Determine the number of pages per cluster for non-resident
       * attributes.
       */
      nr_pages = 1;
      if (vol->cluster_size > PAGE_CACHE_SIZE && NInoNonResident(ni))
            nr_pages = vol->cluster_size >> PAGE_CACHE_SHIFT;
      /* Finally, perform the actual write. */
      last_vcn = -1;
      if (likely(nr_segs == 1))
            buf = iov->iov_base;
      do {
            VCN vcn;
            pgoff_t idx, start_idx;
            unsigned ofs, do_pages, u;
            size_t copied;

            start_idx = idx = pos >> PAGE_CACHE_SHIFT;
            ofs = pos & ~PAGE_CACHE_MASK;
            bytes = PAGE_CACHE_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)) {
                              status = -EIO;
                              if (lcn == LCN_ENOMEM)
                                    status = -ENOMEM;
                              else
                                    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_CACHE_SHIFT;
                              bytes = vol->cluster_size - (pos &
                                          vol->cluster_size_mask);
                              do_pages = nr_pages;
                        }
                  }
            }
            if (bytes > count)
                  bytes = count;
            /*
             * 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 (likely(nr_segs == 1))
                  ntfs_fault_in_pages_readable(buf, bytes);
            else
                  ntfs_fault_in_pages_readable_iovec(iov, iov_ofs, bytes);
            /* Get and lock @do_pages starting at index @start_idx. */
            status = __ntfs_grab_cache_pages(mapping, start_idx, do_pages,
                        pages, &cached_page, &lru_pvec);
            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)) {
                        loff_t i_size;

                        do {
                              unlock_page(pages[--do_pages]);
                              page_cache_release(pages[do_pages]);
                        } while (do_pages);
                        /*
                         * The write preparation may have instantiated
                         * allocated space outside i_size.  Trim this
                         * off again.  We can ignore any errors in this
                         * case as we will just be waisting a bit of
                         * allocated space, which is not a disaster.
                         */
                        i_size = i_size_read(vi);
                        if (pos + bytes > i_size)
                              vmtruncate(vi, i_size);
                        break;
                  }
            }
            u = (pos >> PAGE_CACHE_SHIFT) - pages[0]->index;
            if (likely(nr_segs == 1)) {
                  copied = ntfs_copy_from_user(pages + u, do_pages - u,
                              ofs, buf, bytes);
                  buf += copied;
            } else
                  copied = ntfs_copy_from_user_iovec(pages + u,
                              do_pages - u, ofs, &iov, &iov_ofs,
                              bytes);
            ntfs_flush_dcache_pages(pages + u, do_pages - u);
            status = ntfs_commit_pages_after_write(pages, do_pages, pos,
                        bytes);
            if (likely(!status)) {
                  written += copied;
                  count -= copied;
                  pos += copied;
                  if (unlikely(copied != bytes))
                        status = -EFAULT;
            }
            do {
                  unlock_page(pages[--do_pages]);
                  mark_page_accessed(pages[do_pages]);
                  page_cache_release(pages[do_pages]);
            } while (do_pages);
            if (unlikely(status))
                  break;
            balance_dirty_pages_ratelimited(mapping);
            cond_resched();
      } while (count);
err_out:
      *ppos = pos;
      if (cached_page)
            page_cache_release(cached_page);
      /* For now, when the user asks for O_SYNC, we actually give O_DSYNC. */
      if (likely(!status)) {
            if (unlikely((file->f_flags & O_SYNC) || IS_SYNC(vi))) {
                  if (!mapping->a_ops->writepage || !is_sync_kiocb(iocb))
                        status = generic_osync_inode(vi, mapping,
                                    OSYNC_METADATA|OSYNC_DATA);
            }
      }
      pagevec_lru_add(&lru_pvec);
      ntfs_debug("Done.  Returning %s (written 0x%lx, status %li).",
                  written ? "written" : "status", (unsigned long)written,
                  (long)status);
      return written ? written : status;
}

/**
 * ntfs_file_aio_write_nolock -
 */
static ssize_t ntfs_file_aio_write_nolock(struct kiocb *iocb,
            const struct iovec *iov, unsigned long nr_segs, loff_t *ppos)
{
      struct file *file = iocb->ki_filp;
      struct address_space *mapping = file->f_mapping;
      struct inode *inode = mapping->host;
      loff_t pos;
      unsigned long seg;
      size_t count;           /* after file limit checks */
      ssize_t written, err;

      count = 0;
      for (seg = 0; seg < nr_segs; seg++) {
            const struct iovec *iv = &iov[seg];
            /*
             * If any segment has a negative length, or the cumulative
             * length ever wraps negative then return -EINVAL.
             */
            count += iv->iov_len;
            if (unlikely((ssize_t)(count|iv->iov_len) < 0))
                  return -EINVAL;
            if (access_ok(VERIFY_READ, iv->iov_base, iv->iov_len))
                  continue;
            if (!seg)
                  return -EFAULT;
            nr_segs = seg;
            count -= iv->iov_len;   /* This segment is no good */
            break;
      }
      pos = *ppos;
      vfs_check_frozen(inode->i_sb, SB_FREEZE_WRITE);
      /* We can write back this queue in page reclaim. */
      current->backing_dev_info = mapping->backing_dev_info;
      written = 0;
      err = generic_write_checks(file, &pos, &count, S_ISBLK(inode->i_mode));
      if (err)
            goto out;
      if (!count)
            goto out;
      err = remove_suid(file->f_dentry);
      if (err)
            goto out;
      file_update_time(file);
      written = ntfs_file_buffered_write(iocb, iov, nr_segs, pos, ppos,
                  count);
out:
      current->backing_dev_info = NULL;
      return written ? written : err;
}

/**
 * ntfs_file_aio_write -
 */
static ssize_t ntfs_file_aio_write(struct kiocb *iocb, const char __user *buf,
            size_t count, loff_t pos)
{
      struct file *file = iocb->ki_filp;
      struct address_space *mapping = file->f_mapping;
      struct inode *inode = mapping->host;
      ssize_t ret;
      struct iovec local_iov = { .iov_base = (void __user *)buf,
                           .iov_len = count };

      BUG_ON(iocb->ki_pos != pos);

      mutex_lock(&inode->i_mutex);
      ret = ntfs_file_aio_write_nolock(iocb, &local_iov, 1, &iocb->ki_pos);
      mutex_unlock(&inode->i_mutex);
      if (ret > 0 && ((file->f_flags & O_SYNC) || IS_SYNC(inode))) {
            int err = sync_page_range(inode, mapping, pos, ret);
            if (err < 0)
                  ret = err;
      }
      return ret;
}

/**
 * ntfs_file_writev -
 *
 * Basically the same as generic_file_writev() except that it ends up calling
 * ntfs_file_aio_write_nolock() instead of __generic_file_aio_write_nolock().
 */
static ssize_t ntfs_file_writev(struct file *file, const struct iovec *iov,
            unsigned long nr_segs, loff_t *ppos)
{
      struct address_space *mapping = file->f_mapping;
      struct inode *inode = mapping->host;
      struct kiocb kiocb;
      ssize_t ret;

      mutex_lock(&inode->i_mutex);
      init_sync_kiocb(&kiocb, file);
      ret = ntfs_file_aio_write_nolock(&kiocb, iov, nr_segs, ppos);
      if (ret == -EIOCBQUEUED)
            ret = wait_on_sync_kiocb(&kiocb);
      mutex_unlock(&inode->i_mutex);
      if (ret > 0 && ((file->f_flags & O_SYNC) || IS_SYNC(inode))) {
            int err = sync_page_range(inode, mapping, *ppos - ret, ret);
            if (err < 0)
                  ret = err;
      }
      return ret;
}

/**
 * ntfs_file_write - simple wrapper for ntfs_file_writev()
 */
static ssize_t ntfs_file_write(struct file *file, const char __user *buf,
            size_t count, loff_t *ppos)
{
      struct iovec local_iov = { .iov_base = (void __user *)buf,
                           .iov_len = count };

      return ntfs_file_writev(file, &local_iov, 1, ppos);
}

/**
 * ntfs_file_fsync - sync a file to disk
 * @filp:   file to be synced
 * @dentry: dentry describing the file to sync
 * @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.
 *
 * Note: In the past @filp could be NULL so we ignore it as we don't need it
 * anyway.
 *
 * 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, struct dentry *dentry,
            int datasync)
{
      struct inode *vi = dentry->d_inode;
      int err, ret = 0;

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

#endif /* NTFS_RW */

const struct file_operations ntfs_file_ops = {
      .llseek           = generic_file_llseek,   /* Seek inside file. */
      .read       = generic_file_read,     /* Read from file. */
      .aio_read   = generic_file_aio_read, /* Async read from file. */
      .readv            = generic_file_readv,    /* Read from file. */
#ifdef NTFS_RW
      .write            = ntfs_file_write,       /* Write to file. */
      .aio_write  = ntfs_file_aio_write,   /* Async write to file. */
      .writev           = ntfs_file_writev,      /* Write to file. */
      /*.release  = ,*/              /* Last file is closed.  See
                                        fs/ext2/file.c::
                                        ext2_release_file() for
                                        how to use this to discard
                                        preallocated space for
                                        write opened files. */
      .fsync            = ntfs_file_fsync,       /* Sync a file to disk. */
      /*.aio_fsync      = ,*/              /* Sync all outstanding async
                                        i/o operations on a
                                        kiocb. */
#endif /* NTFS_RW */
      /*.ioctl    = ,*/              /* Perform function on the
                                        mounted filesystem. */
      .mmap       = generic_file_mmap,     /* Mmap file. */
      .open       = ntfs_file_open,  /* Open file. */
      .sendfile   = generic_file_sendfile, /* Zero-copy data send with
                                        the data source being on
                                        the ntfs partition.  We do
                                        not need to care about the
                                        data destination. */
      /*.sendpage = ,*/              /* Zero-copy data send with
                                        the data destination being
                                        on the ntfs partition.  We
                                        do not need to care about
                                        the data source. */
};

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

const struct file_operations ntfs_empty_file_ops = {};

struct inode_operations ntfs_empty_inode_ops = {};

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