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	Version: linux-6.0.1 spark-3.0.0 hadoop-3.2.0-src hadoop-3.3.0-src spark-2.4.7 linux-4.15.13 hadoop-2.7.4-src Revert   Change

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

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