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runlist.c

/**
 * runlist.c - NTFS runlist handling code.  Part of the Linux-NTFS project.
 *
 * Copyright (c) 2001-2007 Anton Altaparmakov
 * Copyright (c) 2002-2005 Richard Russon
 *
 * 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 "debug.h"
#include "dir.h"
#include "endian.h"
#include "malloc.h"
#include "ntfs.h"

/**
 * ntfs_rl_mm - runlist memmove
 *
 * It is up to the caller to serialize access to the runlist @base.
 */
static inline void ntfs_rl_mm(runlist_element *base, int dst, int src,
            int size)
{
      if (likely((dst != src) && (size > 0)))
            memmove(base + dst, base + src, size * sizeof(*base));
}

/**
 * ntfs_rl_mc - runlist memory copy
 *
 * It is up to the caller to serialize access to the runlists @dstbase and
 * @srcbase.
 */
static inline void ntfs_rl_mc(runlist_element *dstbase, int dst,
            runlist_element *srcbase, int src, int size)
{
      if (likely(size > 0))
            memcpy(dstbase + dst, srcbase + src, size * sizeof(*dstbase));
}

/**
 * ntfs_rl_realloc - Reallocate memory for runlists
 * @rl:           original runlist
 * @old_size:     number of runlist elements in the original runlist @rl
 * @new_size:     number of runlist elements we need space for
 *
 * As the runlists grow, more memory will be required.  To prevent the
 * kernel having to allocate and reallocate large numbers of small bits of
 * memory, this function returns an entire page of memory.
 *
 * It is up to the caller to serialize access to the runlist @rl.
 *
 * N.B.  If the new allocation doesn't require a different number of pages in
 *       memory, the function will return the original pointer.
 *
 * On success, return a pointer to the newly allocated, or recycled, memory.
 * On error, return -errno. The following error codes are defined:
 *    -ENOMEM     - Not enough memory to allocate runlist array.
 *    -EINVAL     - Invalid parameters were passed in.
 */
static inline runlist_element *ntfs_rl_realloc(runlist_element *rl,
            int old_size, int new_size)
{
      runlist_element *new_rl;

      old_size = PAGE_ALIGN(old_size * sizeof(*rl));
      new_size = PAGE_ALIGN(new_size * sizeof(*rl));
      if (old_size == new_size)
            return rl;

      new_rl = ntfs_malloc_nofs(new_size);
      if (unlikely(!new_rl))
            return ERR_PTR(-ENOMEM);

      if (likely(rl != NULL)) {
            if (unlikely(old_size > new_size))
                  old_size = new_size;
            memcpy(new_rl, rl, old_size);
            ntfs_free(rl);
      }
      return new_rl;
}

/**
 * ntfs_rl_realloc_nofail - Reallocate memory for runlists
 * @rl:           original runlist
 * @old_size:     number of runlist elements in the original runlist @rl
 * @new_size:     number of runlist elements we need space for
 *
 * As the runlists grow, more memory will be required.  To prevent the
 * kernel having to allocate and reallocate large numbers of small bits of
 * memory, this function returns an entire page of memory.
 *
 * This function guarantees that the allocation will succeed.  It will sleep
 * for as long as it takes to complete the allocation.
 *
 * It is up to the caller to serialize access to the runlist @rl.
 *
 * N.B.  If the new allocation doesn't require a different number of pages in
 *       memory, the function will return the original pointer.
 *
 * On success, return a pointer to the newly allocated, or recycled, memory.
 * On error, return -errno. The following error codes are defined:
 *    -ENOMEM     - Not enough memory to allocate runlist array.
 *    -EINVAL     - Invalid parameters were passed in.
 */
static inline runlist_element *ntfs_rl_realloc_nofail(runlist_element *rl,
            int old_size, int new_size)
{
      runlist_element *new_rl;

      old_size = PAGE_ALIGN(old_size * sizeof(*rl));
      new_size = PAGE_ALIGN(new_size * sizeof(*rl));
      if (old_size == new_size)
            return rl;

      new_rl = ntfs_malloc_nofs_nofail(new_size);
      BUG_ON(!new_rl);

      if (likely(rl != NULL)) {
            if (unlikely(old_size > new_size))
                  old_size = new_size;
            memcpy(new_rl, rl, old_size);
            ntfs_free(rl);
      }
      return new_rl;
}

/**
 * ntfs_are_rl_mergeable - test if two runlists can be joined together
 * @dst:    original runlist
 * @src:    new runlist to test for mergeability with @dst
 *
 * Test if two runlists can be joined together. For this, their VCNs and LCNs
 * must be adjacent.
 *
 * It is up to the caller to serialize access to the runlists @dst and @src.
 *
 * Return: true   Success, the runlists can be merged.
 *       false  Failure, the runlists cannot be merged.
 */
static inline bool ntfs_are_rl_mergeable(runlist_element *dst,
            runlist_element *src)
{
      BUG_ON(!dst);
      BUG_ON(!src);

      /* We can merge unmapped regions even if they are misaligned. */
      if ((dst->lcn == LCN_RL_NOT_MAPPED) && (src->lcn == LCN_RL_NOT_MAPPED))
            return true;
      /* If the runs are misaligned, we cannot merge them. */
      if ((dst->vcn + dst->length) != src->vcn)
            return false;
      /* If both runs are non-sparse and contiguous, we can merge them. */
      if ((dst->lcn >= 0) && (src->lcn >= 0) &&
                  ((dst->lcn + dst->length) == src->lcn))
            return true;
      /* If we are merging two holes, we can merge them. */
      if ((dst->lcn == LCN_HOLE) && (src->lcn == LCN_HOLE))
            return true;
      /* Cannot merge. */
      return false;
}

/**
 * __ntfs_rl_merge - merge two runlists without testing if they can be merged
 * @dst:    original, destination runlist
 * @src:    new runlist to merge with @dst
 *
 * Merge the two runlists, writing into the destination runlist @dst. The
 * caller must make sure the runlists can be merged or this will corrupt the
 * destination runlist.
 *
 * It is up to the caller to serialize access to the runlists @dst and @src.
 */
static inline void __ntfs_rl_merge(runlist_element *dst, runlist_element *src)
{
      dst->length += src->length;
}

/**
 * ntfs_rl_append - append a runlist after a given element
 * @dst:    original runlist to be worked on
 * @dsize:  number of elements in @dst (including end marker)
 * @src:    runlist to be inserted into @dst
 * @ssize:  number of elements in @src (excluding end marker)
 * @loc:    append the new runlist @src after this element in @dst
 *
 * Append the runlist @src after element @loc in @dst.  Merge the right end of
 * the new runlist, if necessary. Adjust the size of the hole before the
 * appended runlist.
 *
 * It is up to the caller to serialize access to the runlists @dst and @src.
 *
 * On success, return a pointer to the new, combined, runlist. Note, both
 * runlists @dst and @src are deallocated before returning so you cannot use
 * the pointers for anything any more. (Strictly speaking the returned runlist
 * may be the same as @dst but this is irrelevant.)
 *
 * On error, return -errno. Both runlists are left unmodified. The following
 * error codes are defined:
 *    -ENOMEM     - Not enough memory to allocate runlist array.
 *    -EINVAL     - Invalid parameters were passed in.
 */
static inline runlist_element *ntfs_rl_append(runlist_element *dst,
            int dsize, runlist_element *src, int ssize, int loc)
{
      bool right = false;     /* Right end of @src needs merging. */
      int marker;       /* End of the inserted runs. */

      BUG_ON(!dst);
      BUG_ON(!src);

      /* First, check if the right hand end needs merging. */
      if ((loc + 1) < dsize)
            right = ntfs_are_rl_mergeable(src + ssize - 1, dst + loc + 1);

      /* Space required: @dst size + @src size, less one if we merged. */
      dst = ntfs_rl_realloc(dst, dsize, dsize + ssize - right);
      if (IS_ERR(dst))
            return dst;
      /*
       * We are guaranteed to succeed from here so can start modifying the
       * original runlists.
       */

      /* First, merge the right hand end, if necessary. */
      if (right)
            __ntfs_rl_merge(src + ssize - 1, dst + loc + 1);

      /* First run after the @src runs that have been inserted. */
      marker = loc + ssize + 1;

      /* Move the tail of @dst out of the way, then copy in @src. */
      ntfs_rl_mm(dst, marker, loc + 1 + right, dsize - (loc + 1 + right));
      ntfs_rl_mc(dst, loc + 1, src, 0, ssize);

      /* Adjust the size of the preceding hole. */
      dst[loc].length = dst[loc + 1].vcn - dst[loc].vcn;

      /* We may have changed the length of the file, so fix the end marker */
      if (dst[marker].lcn == LCN_ENOENT)
            dst[marker].vcn = dst[marker - 1].vcn + dst[marker - 1].length;

      return dst;
}

/**
 * ntfs_rl_insert - insert a runlist into another
 * @dst:    original runlist to be worked on
 * @dsize:  number of elements in @dst (including end marker)
 * @src:    new runlist to be inserted
 * @ssize:  number of elements in @src (excluding end marker)
 * @loc:    insert the new runlist @src before this element in @dst
 *
 * Insert the runlist @src before element @loc in the runlist @dst. Merge the
 * left end of the new runlist, if necessary. Adjust the size of the hole
 * after the inserted runlist.
 *
 * It is up to the caller to serialize access to the runlists @dst and @src.
 *
 * On success, return a pointer to the new, combined, runlist. Note, both
 * runlists @dst and @src are deallocated before returning so you cannot use
 * the pointers for anything any more. (Strictly speaking the returned runlist
 * may be the same as @dst but this is irrelevant.)
 *
 * On error, return -errno. Both runlists are left unmodified. The following
 * error codes are defined:
 *    -ENOMEM     - Not enough memory to allocate runlist array.
 *    -EINVAL     - Invalid parameters were passed in.
 */
static inline runlist_element *ntfs_rl_insert(runlist_element *dst,
            int dsize, runlist_element *src, int ssize, int loc)
{
      bool left = false;      /* Left end of @src needs merging. */
      bool disc = false;      /* Discontinuity between @dst and @src. */
      int marker;       /* End of the inserted runs. */

      BUG_ON(!dst);
      BUG_ON(!src);

      /*
       * disc => Discontinuity between the end of @dst and the start of @src.
       *       This means we might need to insert a "not mapped" run.
       */
      if (loc == 0)
            disc = (src[0].vcn > 0);
      else {
            s64 merged_length;

            left = ntfs_are_rl_mergeable(dst + loc - 1, src);

            merged_length = dst[loc - 1].length;
            if (left)
                  merged_length += src->length;

            disc = (src[0].vcn > dst[loc - 1].vcn + merged_length);
      }
      /*
       * Space required: @dst size + @src size, less one if we merged, plus
       * one if there was a discontinuity.
       */
      dst = ntfs_rl_realloc(dst, dsize, dsize + ssize - left + disc);
      if (IS_ERR(dst))
            return dst;
      /*
       * We are guaranteed to succeed from here so can start modifying the
       * original runlist.
       */
      if (left)
            __ntfs_rl_merge(dst + loc - 1, src);
      /*
       * First run after the @src runs that have been inserted.
       * Nominally,  @marker equals @loc + @ssize, i.e. location + number of
       * runs in @src.  However, if @left, then the first run in @src has
       * been merged with one in @dst.  And if @disc, then @dst and @src do
       * not meet and we need an extra run to fill the gap.
       */
      marker = loc + ssize - left + disc;

      /* Move the tail of @dst out of the way, then copy in @src. */
      ntfs_rl_mm(dst, marker, loc, dsize - loc);
      ntfs_rl_mc(dst, loc + disc, src, left, ssize - left);

      /* Adjust the VCN of the first run after the insertion... */
      dst[marker].vcn = dst[marker - 1].vcn + dst[marker - 1].length;
      /* ... and the length. */
      if (dst[marker].lcn == LCN_HOLE || dst[marker].lcn == LCN_RL_NOT_MAPPED)
            dst[marker].length = dst[marker + 1].vcn - dst[marker].vcn;

      /* Writing beyond the end of the file and there is a discontinuity. */
      if (disc) {
            if (loc > 0) {
                  dst[loc].vcn = dst[loc - 1].vcn + dst[loc - 1].length;
                  dst[loc].length = dst[loc + 1].vcn - dst[loc].vcn;
            } else {
                  dst[loc].vcn = 0;
                  dst[loc].length = dst[loc + 1].vcn;
            }
            dst[loc].lcn = LCN_RL_NOT_MAPPED;
      }
      return dst;
}

/**
 * ntfs_rl_replace - overwrite a runlist element with another runlist
 * @dst:    original runlist to be worked on
 * @dsize:  number of elements in @dst (including end marker)
 * @src:    new runlist to be inserted
 * @ssize:  number of elements in @src (excluding end marker)
 * @loc:    index in runlist @dst to overwrite with @src
 *
 * Replace the runlist element @dst at @loc with @src. Merge the left and
 * right ends of the inserted runlist, if necessary.
 *
 * It is up to the caller to serialize access to the runlists @dst and @src.
 *
 * On success, return a pointer to the new, combined, runlist. Note, both
 * runlists @dst and @src are deallocated before returning so you cannot use
 * the pointers for anything any more. (Strictly speaking the returned runlist
 * may be the same as @dst but this is irrelevant.)
 *
 * On error, return -errno. Both runlists are left unmodified. The following
 * error codes are defined:
 *    -ENOMEM     - Not enough memory to allocate runlist array.
 *    -EINVAL     - Invalid parameters were passed in.
 */
static inline runlist_element *ntfs_rl_replace(runlist_element *dst,
            int dsize, runlist_element *src, int ssize, int loc)
{
      signed delta;
      bool left = false;      /* Left end of @src needs merging. */
      bool right = false;     /* Right end of @src needs merging. */
      int tail;         /* Start of tail of @dst. */
      int marker;       /* End of the inserted runs. */

      BUG_ON(!dst);
      BUG_ON(!src);

      /* First, see if the left and right ends need merging. */
      if ((loc + 1) < dsize)
            right = ntfs_are_rl_mergeable(src + ssize - 1, dst + loc + 1);
      if (loc > 0)
            left = ntfs_are_rl_mergeable(dst + loc - 1, src);
      /*
       * Allocate some space.  We will need less if the left, right, or both
       * ends get merged.  The -1 accounts for the run being replaced.
       */
      delta = ssize - 1 - left - right;
      if (delta > 0) {
            dst = ntfs_rl_realloc(dst, dsize, dsize + delta);
            if (IS_ERR(dst))
                  return dst;
      }
      /*
       * We are guaranteed to succeed from here so can start modifying the
       * original runlists.
       */

      /* First, merge the left and right ends, if necessary. */
      if (right)
            __ntfs_rl_merge(src + ssize - 1, dst + loc + 1);
      if (left)
            __ntfs_rl_merge(dst + loc - 1, src);
      /*
       * Offset of the tail of @dst.  This needs to be moved out of the way
       * to make space for the runs to be copied from @src, i.e. the first
       * run of the tail of @dst.
       * Nominally, @tail equals @loc + 1, i.e. location, skipping the
       * replaced run.  However, if @right, then one of @dst's runs is
       * already merged into @src.
       */
      tail = loc + right + 1;
      /*
       * First run after the @src runs that have been inserted, i.e. where
       * the tail of @dst needs to be moved to.
       * Nominally, @marker equals @loc + @ssize, i.e. location + number of
       * runs in @src.  However, if @left, then the first run in @src has
       * been merged with one in @dst.
       */
      marker = loc + ssize - left;

      /* Move the tail of @dst out of the way, then copy in @src. */
      ntfs_rl_mm(dst, marker, tail, dsize - tail);
      ntfs_rl_mc(dst, loc, src, left, ssize - left);

      /* We may have changed the length of the file, so fix the end marker. */
      if (dsize - tail > 0 && dst[marker].lcn == LCN_ENOENT)
            dst[marker].vcn = dst[marker - 1].vcn + dst[marker - 1].length;
      return dst;
}

/**
 * ntfs_rl_split - insert a runlist into the centre of a hole
 * @dst:    original runlist to be worked on
 * @dsize:  number of elements in @dst (including end marker)
 * @src:    new runlist to be inserted
 * @ssize:  number of elements in @src (excluding end marker)
 * @loc:    index in runlist @dst at which to split and insert @src
 *
 * Split the runlist @dst at @loc into two and insert @new in between the two
 * fragments. No merging of runlists is necessary. Adjust the size of the
 * holes either side.
 *
 * It is up to the caller to serialize access to the runlists @dst and @src.
 *
 * On success, return a pointer to the new, combined, runlist. Note, both
 * runlists @dst and @src are deallocated before returning so you cannot use
 * the pointers for anything any more. (Strictly speaking the returned runlist
 * may be the same as @dst but this is irrelevant.)
 *
 * On error, return -errno. Both runlists are left unmodified. The following
 * error codes are defined:
 *    -ENOMEM     - Not enough memory to allocate runlist array.
 *    -EINVAL     - Invalid parameters were passed in.
 */
static inline runlist_element *ntfs_rl_split(runlist_element *dst, int dsize,
            runlist_element *src, int ssize, int loc)
{
      BUG_ON(!dst);
      BUG_ON(!src);

      /* Space required: @dst size + @src size + one new hole. */
      dst = ntfs_rl_realloc(dst, dsize, dsize + ssize + 1);
      if (IS_ERR(dst))
            return dst;
      /*
       * We are guaranteed to succeed from here so can start modifying the
       * original runlists.
       */

      /* Move the tail of @dst out of the way, then copy in @src. */
      ntfs_rl_mm(dst, loc + 1 + ssize, loc, dsize - loc);
      ntfs_rl_mc(dst, loc + 1, src, 0, ssize);

      /* Adjust the size of the holes either size of @src. */
      dst[loc].length         = dst[loc+1].vcn       - dst[loc].vcn;
      dst[loc+ssize+1].vcn    = dst[loc+ssize].vcn   + dst[loc+ssize].length;
      dst[loc+ssize+1].length = dst[loc+ssize+2].vcn - dst[loc+ssize+1].vcn;

      return dst;
}

/**
 * ntfs_runlists_merge - merge two runlists into one
 * @drl:    original runlist to be worked on
 * @srl:    new runlist to be merged into @drl
 *
 * First we sanity check the two runlists @srl and @drl to make sure that they
 * are sensible and can be merged. The runlist @srl must be either after the
 * runlist @drl or completely within a hole (or unmapped region) in @drl.
 *
 * It is up to the caller to serialize access to the runlists @drl and @srl.
 *
 * Merging of runlists is necessary in two cases:
 *   1. When attribute lists are used and a further extent is being mapped.
 *   2. When new clusters are allocated to fill a hole or extend a file.
 *
 * There are four possible ways @srl can be merged. It can:
 *    - be inserted at the beginning of a hole,
 *    - split the hole in two and be inserted between the two fragments,
 *    - be appended at the end of a hole, or it can
 *    - replace the whole hole.
 * It can also be appended to the end of the runlist, which is just a variant
 * of the insert case.
 *
 * On success, return a pointer to the new, combined, runlist. Note, both
 * runlists @drl and @srl are deallocated before returning so you cannot use
 * the pointers for anything any more. (Strictly speaking the returned runlist
 * may be the same as @dst but this is irrelevant.)
 *
 * On error, return -errno. Both runlists are left unmodified. The following
 * error codes are defined:
 *    -ENOMEM     - Not enough memory to allocate runlist array.
 *    -EINVAL     - Invalid parameters were passed in.
 *    -ERANGE     - The runlists overlap and cannot be merged.
 */
runlist_element *ntfs_runlists_merge(runlist_element *drl,
            runlist_element *srl)
{
      int di, si;       /* Current index into @[ds]rl. */
      int sstart;       /* First index with lcn > LCN_RL_NOT_MAPPED. */
      int dins;         /* Index into @drl at which to insert @srl. */
      int dend, send;         /* Last index into @[ds]rl. */
      int dfinal, sfinal;     /* The last index into @[ds]rl with
                           lcn >= LCN_HOLE. */
      int marker = 0;
      VCN marker_vcn = 0;

#ifdef DEBUG
      ntfs_debug("dst:");
      ntfs_debug_dump_runlist(drl);
      ntfs_debug("src:");
      ntfs_debug_dump_runlist(srl);
#endif

      /* Check for silly calling... */
      if (unlikely(!srl))
            return drl;
      if (IS_ERR(srl) || IS_ERR(drl))
            return ERR_PTR(-EINVAL);

      /* Check for the case where the first mapping is being done now. */
      if (unlikely(!drl)) {
            drl = srl;
            /* Complete the source runlist if necessary. */
            if (unlikely(drl[0].vcn)) {
                  /* Scan to the end of the source runlist. */
                  for (dend = 0; likely(drl[dend].length); dend++)
                        ;
                  dend++;
                  drl = ntfs_rl_realloc(drl, dend, dend + 1);
                  if (IS_ERR(drl))
                        return drl;
                  /* Insert start element at the front of the runlist. */
                  ntfs_rl_mm(drl, 1, 0, dend);
                  drl[0].vcn = 0;
                  drl[0].lcn = LCN_RL_NOT_MAPPED;
                  drl[0].length = drl[1].vcn;
            }
            goto finished;
      }

      si = di = 0;

      /* Skip any unmapped start element(s) in the source runlist. */
      while (srl[si].length && srl[si].lcn < LCN_HOLE)
            si++;

      /* Can't have an entirely unmapped source runlist. */
      BUG_ON(!srl[si].length);

      /* Record the starting points. */
      sstart = si;

      /*
       * Skip forward in @drl until we reach the position where @srl needs to
       * be inserted. If we reach the end of @drl, @srl just needs to be
       * appended to @drl.
       */
      for (; drl[di].length; di++) {
            if (drl[di].vcn + drl[di].length > srl[sstart].vcn)
                  break;
      }
      dins = di;

      /* Sanity check for illegal overlaps. */
      if ((drl[di].vcn == srl[si].vcn) && (drl[di].lcn >= 0) &&
                  (srl[si].lcn >= 0)) {
            ntfs_error(NULL, "Run lists overlap. Cannot merge!");
            return ERR_PTR(-ERANGE);
      }

      /* Scan to the end of both runlists in order to know their sizes. */
      for (send = si; srl[send].length; send++)
            ;
      for (dend = di; drl[dend].length; dend++)
            ;

      if (srl[send].lcn == LCN_ENOENT)
            marker_vcn = srl[marker = send].vcn;

      /* Scan to the last element with lcn >= LCN_HOLE. */
      for (sfinal = send; sfinal >= 0 && srl[sfinal].lcn < LCN_HOLE; sfinal--)
            ;
      for (dfinal = dend; dfinal >= 0 && drl[dfinal].lcn < LCN_HOLE; dfinal--)
            ;

      {
      bool start;
      bool finish;
      int ds = dend + 1;            /* Number of elements in drl & srl */
      int ss = sfinal - sstart + 1;

      start  = ((drl[dins].lcn <  LCN_RL_NOT_MAPPED) ||    /* End of file   */
              (drl[dins].vcn == srl[sstart].vcn));         /* Start of hole */
      finish = ((drl[dins].lcn >= LCN_RL_NOT_MAPPED) &&    /* End of file   */
             ((drl[dins].vcn + drl[dins].length) <=      /* End of hole   */
              (srl[send - 1].vcn + srl[send - 1].length)));

      /* Or we will lose an end marker. */
      if (finish && !drl[dins].length)
            ss++;
      if (marker && (drl[dins].vcn + drl[dins].length > srl[send - 1].vcn))
            finish = false;
#if 0
      ntfs_debug("dfinal = %i, dend = %i", dfinal, dend);
      ntfs_debug("sstart = %i, sfinal = %i, send = %i", sstart, sfinal, send);
      ntfs_debug("start = %i, finish = %i", start, finish);
      ntfs_debug("ds = %i, ss = %i, dins = %i", ds, ss, dins);
#endif
      if (start) {
            if (finish)
                  drl = ntfs_rl_replace(drl, ds, srl + sstart, ss, dins);
            else
                  drl = ntfs_rl_insert(drl, ds, srl + sstart, ss, dins);
      } else {
            if (finish)
                  drl = ntfs_rl_append(drl, ds, srl + sstart, ss, dins);
            else
                  drl = ntfs_rl_split(drl, ds, srl + sstart, ss, dins);
      }
      if (IS_ERR(drl)) {
            ntfs_error(NULL, "Merge failed.");
            return drl;
      }
      ntfs_free(srl);
      if (marker) {
            ntfs_debug("Triggering marker code.");
            for (ds = dend; drl[ds].length; ds++)
                  ;
            /* We only need to care if @srl ended after @drl. */
            if (drl[ds].vcn <= marker_vcn) {
                  int slots = 0;

                  if (drl[ds].vcn == marker_vcn) {
                        ntfs_debug("Old marker = 0x%llx, replacing "
                                    "with LCN_ENOENT.",
                                    (unsigned long long)
                                    drl[ds].lcn);
                        drl[ds].lcn = LCN_ENOENT;
                        goto finished;
                  }
                  /*
                   * We need to create an unmapped runlist element in
                   * @drl or extend an existing one before adding the
                   * ENOENT terminator.
                   */
                  if (drl[ds].lcn == LCN_ENOENT) {
                        ds--;
                        slots = 1;
                  }
                  if (drl[ds].lcn != LCN_RL_NOT_MAPPED) {
                        /* Add an unmapped runlist element. */
                        if (!slots) {
                              drl = ntfs_rl_realloc_nofail(drl, ds,
                                          ds + 2);
                              slots = 2;
                        }
                        ds++;
                        /* Need to set vcn if it isn't set already. */
                        if (slots != 1)
                              drl[ds].vcn = drl[ds - 1].vcn +
                                          drl[ds - 1].length;
                        drl[ds].lcn = LCN_RL_NOT_MAPPED;
                        /* We now used up a slot. */
                        slots--;
                  }
                  drl[ds].length = marker_vcn - drl[ds].vcn;
                  /* Finally add the ENOENT terminator. */
                  ds++;
                  if (!slots)
                        drl = ntfs_rl_realloc_nofail(drl, ds, ds + 1);
                  drl[ds].vcn = marker_vcn;
                  drl[ds].lcn = LCN_ENOENT;
                  drl[ds].length = (s64)0;
            }
      }
      }

finished:
      /* The merge was completed successfully. */
      ntfs_debug("Merged runlist:");
      ntfs_debug_dump_runlist(drl);
      return drl;
}

/**
 * ntfs_mapping_pairs_decompress - convert mapping pairs array to runlist
 * @vol:    ntfs volume on which the attribute resides
 * @attr:   attribute record whose mapping pairs array to decompress
 * @old_rl: optional runlist in which to insert @attr's runlist
 *
 * It is up to the caller to serialize access to the runlist @old_rl.
 *
 * Decompress the attribute @attr's mapping pairs array into a runlist. On
 * success, return the decompressed runlist.
 *
 * If @old_rl is not NULL, decompressed runlist is inserted into the
 * appropriate place in @old_rl and the resultant, combined runlist is
 * returned. The original @old_rl is deallocated.
 *
 * On error, return -errno. @old_rl is left unmodified in that case.
 *
 * The following error codes are defined:
 *    -ENOMEM     - Not enough memory to allocate runlist array.
 *    -EIO  - Corrupt runlist.
 *    -EINVAL     - Invalid parameters were passed in.
 *    -ERANGE     - The two runlists overlap.
 *
 * FIXME: For now we take the conceptionally simplest approach of creating the
 * new runlist disregarding the already existing one and then splicing the
 * two into one, if that is possible (we check for overlap and discard the new
 * runlist if overlap present before returning ERR_PTR(-ERANGE)).
 */
runlist_element *ntfs_mapping_pairs_decompress(const ntfs_volume *vol,
            const ATTR_RECORD *attr, runlist_element *old_rl)
{
      VCN vcn;          /* Current vcn. */
      LCN lcn;          /* Current lcn. */
      s64 deltaxcn;           /* Change in [vl]cn. */
      runlist_element *rl;    /* The output runlist. */
      u8 *buf;          /* Current position in mapping pairs array. */
      u8 *attr_end;           /* End of attribute. */
      int rlsize;       /* Size of runlist buffer. */
      u16 rlpos;        /* Current runlist position in units of
                           runlist_elements. */
      u8 b;             /* Current byte offset in buf. */

#ifdef DEBUG
      /* Make sure attr exists and is non-resident. */
      if (!attr || !attr->non_resident || sle64_to_cpu(
                  attr->data.non_resident.lowest_vcn) < (VCN)0) {
            ntfs_error(vol->sb, "Invalid arguments.");
            return ERR_PTR(-EINVAL);
      }
#endif
      /* Start at vcn = lowest_vcn and lcn 0. */
      vcn = sle64_to_cpu(attr->data.non_resident.lowest_vcn);
      lcn = 0;
      /* Get start of the mapping pairs array. */
      buf = (u8*)attr + le16_to_cpu(
                  attr->data.non_resident.mapping_pairs_offset);
      attr_end = (u8*)attr + le32_to_cpu(attr->length);
      if (unlikely(buf < (u8*)attr || buf > attr_end)) {
            ntfs_error(vol->sb, "Corrupt attribute.");
            return ERR_PTR(-EIO);
      }
      /* If the mapping pairs array is valid but empty, nothing to do. */
      if (!vcn && !*buf)
            return old_rl;
      /* Current position in runlist array. */
      rlpos = 0;
      /* Allocate first page and set current runlist size to one page. */
      rl = ntfs_malloc_nofs(rlsize = PAGE_SIZE);
      if (unlikely(!rl))
            return ERR_PTR(-ENOMEM);
      /* Insert unmapped starting element if necessary. */
      if (vcn) {
            rl->vcn = 0;
            rl->lcn = LCN_RL_NOT_MAPPED;
            rl->length = vcn;
            rlpos++;
      }
      while (buf < attr_end && *buf) {
            /*
             * Allocate more memory if needed, including space for the
             * not-mapped and terminator elements. ntfs_malloc_nofs()
             * operates on whole pages only.
             */
            if (((rlpos + 3) * sizeof(*old_rl)) > rlsize) {
                  runlist_element *rl2;

                  rl2 = ntfs_malloc_nofs(rlsize + (int)PAGE_SIZE);
                  if (unlikely(!rl2)) {
                        ntfs_free(rl);
                        return ERR_PTR(-ENOMEM);
                  }
                  memcpy(rl2, rl, rlsize);
                  ntfs_free(rl);
                  rl = rl2;
                  rlsize += PAGE_SIZE;
            }
            /* Enter the current vcn into the current runlist element. */
            rl[rlpos].vcn = vcn;
            /*
             * Get the change in vcn, i.e. the run length in clusters.
             * Doing it this way ensures that we signextend negative values.
             * A negative run length doesn't make any sense, but hey, I
             * didn't make up the NTFS specs and Windows NT4 treats the run
             * length as a signed value so that's how it is...
             */
            b = *buf & 0xf;
            if (b) {
                  if (unlikely(buf + b > attr_end))
                        goto io_error;
                  for (deltaxcn = (s8)buf[b--]; b; b--)
                        deltaxcn = (deltaxcn << 8) + buf[b];
            } else { /* The length entry is compulsory. */
                  ntfs_error(vol->sb, "Missing length entry in mapping "
                              "pairs array.");
                  deltaxcn = (s64)-1;
            }
            /*
             * Assume a negative length to indicate data corruption and
             * hence clean-up and return NULL.
             */
            if (unlikely(deltaxcn < 0)) {
                  ntfs_error(vol->sb, "Invalid length in mapping pairs "
                              "array.");
                  goto err_out;
            }
            /*
             * Enter the current run length into the current runlist
             * element.
             */
            rl[rlpos].length = deltaxcn;
            /* Increment the current vcn by the current run length. */
            vcn += deltaxcn;
            /*
             * There might be no lcn change at all, as is the case for
             * sparse clusters on NTFS 3.0+, in which case we set the lcn
             * to LCN_HOLE.
             */
            if (!(*buf & 0xf0))
                  rl[rlpos].lcn = LCN_HOLE;
            else {
                  /* Get the lcn change which really can be negative. */
                  u8 b2 = *buf & 0xf;
                  b = b2 + ((*buf >> 4) & 0xf);
                  if (buf + b > attr_end)
                        goto io_error;
                  for (deltaxcn = (s8)buf[b--]; b > b2; b--)
                        deltaxcn = (deltaxcn << 8) + buf[b];
                  /* Change the current lcn to its new value. */
                  lcn += deltaxcn;
#ifdef DEBUG
                  /*
                   * On NTFS 1.2-, apparently can have lcn == -1 to
                   * indicate a hole. But we haven't verified ourselves
                   * whether it is really the lcn or the deltaxcn that is
                   * -1. So if either is found give us a message so we
                   * can investigate it further!
                   */
                  if (vol->major_ver < 3) {
                        if (unlikely(deltaxcn == (LCN)-1))
                              ntfs_error(vol->sb, "lcn delta == -1");
                        if (unlikely(lcn == (LCN)-1))
                              ntfs_error(vol->sb, "lcn == -1");
                  }
#endif
                  /* Check lcn is not below -1. */
                  if (unlikely(lcn < (LCN)-1)) {
                        ntfs_error(vol->sb, "Invalid LCN < -1 in "
                                    "mapping pairs array.");
                        goto err_out;
                  }
                  /* Enter the current lcn into the runlist element. */
                  rl[rlpos].lcn = lcn;
            }
            /* Get to the next runlist element. */
            rlpos++;
            /* Increment the buffer position to the next mapping pair. */
            buf += (*buf & 0xf) + ((*buf >> 4) & 0xf) + 1;
      }
      if (unlikely(buf >= attr_end))
            goto io_error;
      /*
       * If there is a highest_vcn specified, it must be equal to the final
       * vcn in the runlist - 1, or something has gone badly wrong.
       */
      deltaxcn = sle64_to_cpu(attr->data.non_resident.highest_vcn);
      if (unlikely(deltaxcn && vcn - 1 != deltaxcn)) {
mpa_err:
            ntfs_error(vol->sb, "Corrupt mapping pairs array in "
                        "non-resident attribute.");
            goto err_out;
      }
      /* Setup not mapped runlist element if this is the base extent. */
      if (!attr->data.non_resident.lowest_vcn) {
            VCN max_cluster;

            max_cluster = ((sle64_to_cpu(
                        attr->data.non_resident.allocated_size) +
                        vol->cluster_size - 1) >>
                        vol->cluster_size_bits) - 1;
            /*
             * A highest_vcn of zero means this is a single extent
             * attribute so simply terminate the runlist with LCN_ENOENT).
             */
            if (deltaxcn) {
                  /*
                   * If there is a difference between the highest_vcn and
                   * the highest cluster, the runlist is either corrupt
                   * or, more likely, there are more extents following
                   * this one.
                   */
                  if (deltaxcn < max_cluster) {
                        ntfs_debug("More extents to follow; deltaxcn "
                                    "= 0x%llx, max_cluster = "
                                    "0x%llx",
                                    (unsigned long long)deltaxcn,
                                    (unsigned long long)
                                    max_cluster);
                        rl[rlpos].vcn = vcn;
                        vcn += rl[rlpos].length = max_cluster -
                                    deltaxcn;
                        rl[rlpos].lcn = LCN_RL_NOT_MAPPED;
                        rlpos++;
                  } else if (unlikely(deltaxcn > max_cluster)) {
                        ntfs_error(vol->sb, "Corrupt attribute.  "
                                    "deltaxcn = 0x%llx, "
                                    "max_cluster = 0x%llx",
                                    (unsigned long long)deltaxcn,
                                    (unsigned long long)
                                    max_cluster);
                        goto mpa_err;
                  }
            }
            rl[rlpos].lcn = LCN_ENOENT;
      } else /* Not the base extent. There may be more extents to follow. */
            rl[rlpos].lcn = LCN_RL_NOT_MAPPED;

      /* Setup terminating runlist element. */
      rl[rlpos].vcn = vcn;
      rl[rlpos].length = (s64)0;
      /* If no existing runlist was specified, we are done. */
      if (!old_rl) {
            ntfs_debug("Mapping pairs array successfully decompressed:");
            ntfs_debug_dump_runlist(rl);
            return rl;
      }
      /* Now combine the new and old runlists checking for overlaps. */
      old_rl = ntfs_runlists_merge(old_rl, rl);
      if (likely(!IS_ERR(old_rl)))
            return old_rl;
      ntfs_free(rl);
      ntfs_error(vol->sb, "Failed to merge runlists.");
      return old_rl;
io_error:
      ntfs_error(vol->sb, "Corrupt attribute.");
err_out:
      ntfs_free(rl);
      return ERR_PTR(-EIO);
}

/**
 * ntfs_rl_vcn_to_lcn - convert a vcn into a lcn given a runlist
 * @rl:           runlist to use for conversion
 * @vcn:    vcn to convert
 *
 * Convert the virtual cluster number @vcn of an attribute into a logical
 * cluster number (lcn) of a device using the runlist @rl to map vcns to their
 * corresponding lcns.
 *
 * It is up to the caller to serialize access to the runlist @rl.
 *
 * Since lcns must be >= 0, we use negative return codes with special meaning:
 *
 * Return code          Meaning / Description
 * ==================================================
 *  LCN_HOLE            Hole / not allocated on disk.
 *  LCN_RL_NOT_MAPPED   This is part of the runlist which has not been
 *                inserted into the runlist yet.
 *  LCN_ENOENT          There is no such vcn in the attribute.
 *
 * Locking: - The caller must have locked the runlist (for reading or writing).
 *        - This function does not touch the lock, nor does it modify the
 *          runlist.
 */
LCN ntfs_rl_vcn_to_lcn(const runlist_element *rl, const VCN vcn)
{
      int i;

      BUG_ON(vcn < 0);
      /*
       * If rl is NULL, assume that we have found an unmapped runlist. The
       * caller can then attempt to map it and fail appropriately if
       * necessary.
       */
      if (unlikely(!rl))
            return LCN_RL_NOT_MAPPED;

      /* Catch out of lower bounds vcn. */
      if (unlikely(vcn < rl[0].vcn))
            return LCN_ENOENT;

      for (i = 0; likely(rl[i].length); i++) {
            if (unlikely(vcn < rl[i+1].vcn)) {
                  if (likely(rl[i].lcn >= (LCN)0))
                        return rl[i].lcn + (vcn - rl[i].vcn);
                  return rl[i].lcn;
            }
      }
      /*
       * The terminator element is setup to the correct value, i.e. one of
       * LCN_HOLE, LCN_RL_NOT_MAPPED, or LCN_ENOENT.
       */
      if (likely(rl[i].lcn < (LCN)0))
            return rl[i].lcn;
      /* Just in case... We could replace this with BUG() some day. */
      return LCN_ENOENT;
}

#ifdef NTFS_RW

/**
 * ntfs_rl_find_vcn_nolock - find a vcn in a runlist
 * @rl:           runlist to search
 * @vcn:    vcn to find
 *
 * Find the virtual cluster number @vcn in the runlist @rl and return the
 * address of the runlist element containing the @vcn on success.
 *
 * Return NULL if @rl is NULL or @vcn is in an unmapped part/out of bounds of
 * the runlist.
 *
 * Locking: The runlist must be locked on entry.
 */
runlist_element *ntfs_rl_find_vcn_nolock(runlist_element *rl, const VCN vcn)
{
      BUG_ON(vcn < 0);
      if (unlikely(!rl || vcn < rl[0].vcn))
            return NULL;
      while (likely(rl->length)) {
            if (unlikely(vcn < rl[1].vcn)) {
                  if (likely(rl->lcn >= LCN_HOLE))
                        return rl;
                  return NULL;
            }
            rl++;
      }
      if (likely(rl->lcn == LCN_ENOENT))
            return rl;
      return NULL;
}

/**
 * ntfs_get_nr_significant_bytes - get number of bytes needed to store a number
 * @n:            number for which to get the number of bytes for
 *
 * Return the number of bytes required to store @n unambiguously as
 * a signed number.
 *
 * This is used in the context of the mapping pairs array to determine how
 * many bytes will be needed in the array to store a given logical cluster
 * number (lcn) or a specific run length.
 *
 * Return the number of bytes written.  This function cannot fail.
 */
static inline int ntfs_get_nr_significant_bytes(const s64 n)
{
      s64 l = n;
      int i;
      s8 j;

      i = 0;
      do {
            l >>= 8;
            i++;
      } while (l != 0 && l != -1);
      j = (n >> 8 * (i - 1)) & 0xff;
      /* If the sign bit is wrong, we need an extra byte. */
      if ((n < 0 && j >= 0) || (n > 0 && j < 0))
            i++;
      return i;
}

/**
 * ntfs_get_size_for_mapping_pairs - get bytes needed for mapping pairs array
 * @vol:    ntfs volume (needed for the ntfs version)
 * @rl:           locked runlist to determine the size of the mapping pairs of
 * @first_vcn:    first vcn which to include in the mapping pairs array
 * @last_vcn:     last vcn which to include in the mapping pairs array
 *
 * Walk the locked runlist @rl and calculate the size in bytes of the mapping
 * pairs array corresponding to the runlist @rl, starting at vcn @first_vcn and
 * finishing with vcn @last_vcn.
 *
 * A @last_vcn of -1 means end of runlist and in that case the size of the
 * mapping pairs array corresponding to the runlist starting at vcn @first_vcn
 * and finishing at the end of the runlist is determined.
 *
 * This for example allows us to allocate a buffer of the right size when
 * building the mapping pairs array.
 *
 * If @rl is NULL, just return 1 (for the single terminator byte).
 *
 * Return the calculated size in bytes on success.  On error, return -errno.
 * The following error codes are defined:
 *    -EINVAL     - Run list contains unmapped elements.  Make sure to only pass
 *            fully mapped runlists to this function.
 *    -EIO  - The runlist is corrupt.
 *
 * Locking: @rl must be locked on entry (either for reading or writing), it
 *        remains locked throughout, and is left locked upon return.
 */
int ntfs_get_size_for_mapping_pairs(const ntfs_volume *vol,
            const runlist_element *rl, const VCN first_vcn,
            const VCN last_vcn)
{
      LCN prev_lcn;
      int rls;
      bool the_end = false;

      BUG_ON(first_vcn < 0);
      BUG_ON(last_vcn < -1);
      BUG_ON(last_vcn >= 0 && first_vcn > last_vcn);
      if (!rl) {
            BUG_ON(first_vcn);
            BUG_ON(last_vcn > 0);
            return 1;
      }
      /* Skip to runlist element containing @first_vcn. */
      while (rl->length && first_vcn >= rl[1].vcn)
            rl++;
      if (unlikely((!rl->length && first_vcn > rl->vcn) ||
                  first_vcn < rl->vcn))
            return -EINVAL;
      prev_lcn = 0;
      /* Always need the termining zero byte. */
      rls = 1;
      /* Do the first partial run if present. */
      if (first_vcn > rl->vcn) {
            s64 delta, length = rl->length;

            /* We know rl->length != 0 already. */
            if (unlikely(length < 0 || rl->lcn < LCN_HOLE))
                  goto err_out;
            /*
             * If @stop_vcn is given and finishes inside this run, cap the
             * run length.
             */
            if (unlikely(last_vcn >= 0 && rl[1].vcn > last_vcn)) {
                  s64 s1 = last_vcn + 1;
                  if (unlikely(rl[1].vcn > s1))
                        length = s1 - rl->vcn;
                  the_end = true;
            }
            delta = first_vcn - rl->vcn;
            /* Header byte + length. */
            rls += 1 + ntfs_get_nr_significant_bytes(length - delta);
            /*
             * If the logical cluster number (lcn) denotes a hole and we
             * are on NTFS 3.0+, we don't store it at all, i.e. we need
             * zero space.  On earlier NTFS versions we just store the lcn.
             * Note: this assumes that on NTFS 1.2-, holes are stored with
             * an lcn of -1 and not a delta_lcn of -1 (unless both are -1).
             */
            if (likely(rl->lcn >= 0 || vol->major_ver < 3)) {
                  prev_lcn = rl->lcn;
                  if (likely(rl->lcn >= 0))
                        prev_lcn += delta;
                  /* Change in lcn. */
                  rls += ntfs_get_nr_significant_bytes(prev_lcn);
            }
            /* Go to next runlist element. */
            rl++;
      }
      /* Do the full runs. */
      for (; rl->length && !the_end; rl++) {
            s64 length = rl->length;

            if (unlikely(length < 0 || rl->lcn < LCN_HOLE))
                  goto err_out;
            /*
             * If @stop_vcn is given and finishes inside this run, cap the
             * run length.
             */
            if (unlikely(last_vcn >= 0 && rl[1].vcn > last_vcn)) {
                  s64 s1 = last_vcn + 1;
                  if (unlikely(rl[1].vcn > s1))
                        length = s1 - rl->vcn;
                  the_end = true;
            }
            /* Header byte + length. */
            rls += 1 + ntfs_get_nr_significant_bytes(length);
            /*
             * If the logical cluster number (lcn) denotes a hole and we
             * are on NTFS 3.0+, we don't store it at all, i.e. we need
             * zero space.  On earlier NTFS versions we just store the lcn.
             * Note: this assumes that on NTFS 1.2-, holes are stored with
             * an lcn of -1 and not a delta_lcn of -1 (unless both are -1).
             */
            if (likely(rl->lcn >= 0 || vol->major_ver < 3)) {
                  /* Change in lcn. */
                  rls += ntfs_get_nr_significant_bytes(rl->lcn -
                              prev_lcn);
                  prev_lcn = rl->lcn;
            }
      }
      return rls;
err_out:
      if (rl->lcn == LCN_RL_NOT_MAPPED)
            rls = -EINVAL;
      else
            rls = -EIO;
      return rls;
}

/**
 * ntfs_write_significant_bytes - write the significant bytes of a number
 * @dst:    destination buffer to write to
 * @dst_max:      pointer to last byte of destination buffer for bounds checking
 * @n:            number whose significant bytes to write
 *
 * Store in @dst, the minimum bytes of the number @n which are required to
 * identify @n unambiguously as a signed number, taking care not to exceed
 * @dest_max, the maximum position within @dst to which we are allowed to
 * write.
 *
 * This is used when building the mapping pairs array of a runlist to compress
 * a given logical cluster number (lcn) or a specific run length to the minumum
 * size possible.
 *
 * Return the number of bytes written on success.  On error, i.e. the
 * destination buffer @dst is too small, return -ENOSPC.
 */
static inline int ntfs_write_significant_bytes(s8 *dst, const s8 *dst_max,
            const s64 n)
{
      s64 l = n;
      int i;
      s8 j;

      i = 0;
      do {
            if (unlikely(dst > dst_max))
                  goto err_out;
            *dst++ = l & 0xffll;
            l >>= 8;
            i++;
      } while (l != 0 && l != -1);
      j = (n >> 8 * (i - 1)) & 0xff;
      /* If the sign bit is wrong, we need an extra byte. */
      if (n < 0 && j >= 0) {
            if (unlikely(dst > dst_max))
                  goto err_out;
            i++;
            *dst = (s8)-1;
      } else if (n > 0 && j < 0) {
            if (unlikely(dst > dst_max))
                  goto err_out;
            i++;
            *dst = (s8)0;
      }
      return i;
err_out:
      return -ENOSPC;
}

/**
 * ntfs_mapping_pairs_build - build the mapping pairs array from a runlist
 * @vol:    ntfs volume (needed for the ntfs version)
 * @dst:    destination buffer to which to write the mapping pairs array
 * @dst_len:      size of destination buffer @dst in bytes
 * @rl:           locked runlist for which to build the mapping pairs array
 * @first_vcn:    first vcn which to include in the mapping pairs array
 * @last_vcn:     last vcn which to include in the mapping pairs array
 * @stop_vcn:     first vcn outside destination buffer on success or -ENOSPC
 *
 * Create the mapping pairs array from the locked runlist @rl, starting at vcn
 * @first_vcn and finishing with vcn @last_vcn and save the array in @dst.
 * @dst_len is the size of @dst in bytes and it should be at least equal to the
 * value obtained by calling ntfs_get_size_for_mapping_pairs().
 *
 * A @last_vcn of -1 means end of runlist and in that case the mapping pairs
 * array corresponding to the runlist starting at vcn @first_vcn and finishing
 * at the end of the runlist is created.
 *
 * If @rl is NULL, just write a single terminator byte to @dst.
 *
 * On success or -ENOSPC error, if @stop_vcn is not NULL, *@stop_vcn is set to
 * the first vcn outside the destination buffer.  Note that on error, @dst has
 * been filled with all the mapping pairs that will fit, thus it can be treated
 * as partial success, in that a new attribute extent needs to be created or
 * the next extent has to be used and the mapping pairs build has to be
 * continued with @first_vcn set to *@stop_vcn.
 *
 * Return 0 on success and -errno on error.  The following error codes are
 * defined:
 *    -EINVAL     - Run list contains unmapped elements.  Make sure to only pass
 *            fully mapped runlists to this function.
 *    -EIO  - The runlist is corrupt.
 *    -ENOSPC     - The destination buffer is too small.
 *
 * Locking: @rl must be locked on entry (either for reading or writing), it
 *        remains locked throughout, and is left locked upon return.
 */
int ntfs_mapping_pairs_build(const ntfs_volume *vol, s8 *dst,
            const int dst_len, const runlist_element *rl,
            const VCN first_vcn, const VCN last_vcn, VCN *const stop_vcn)
{
      LCN prev_lcn;
      s8 *dst_max, *dst_next;
      int err = -ENOSPC;
      bool the_end = false;
      s8 len_len, lcn_len;

      BUG_ON(first_vcn < 0);
      BUG_ON(last_vcn < -1);
      BUG_ON(last_vcn >= 0 && first_vcn > last_vcn);
      BUG_ON(dst_len < 1);
      if (!rl) {
            BUG_ON(first_vcn);
            BUG_ON(last_vcn > 0);
            if (stop_vcn)
                  *stop_vcn = 0;
            /* Terminator byte. */
            *dst = 0;
            return 0;
      }
      /* Skip to runlist element containing @first_vcn. */
      while (rl->length && first_vcn >= rl[1].vcn)
            rl++;
      if (unlikely((!rl->length && first_vcn > rl->vcn) ||
                  first_vcn < rl->vcn))
            return -EINVAL;
      /*
       * @dst_max is used for bounds checking in
       * ntfs_write_significant_bytes().
       */
      dst_max = dst + dst_len - 1;
      prev_lcn = 0;
      /* Do the first partial run if present. */
      if (first_vcn > rl->vcn) {
            s64 delta, length = rl->length;

            /* We know rl->length != 0 already. */
            if (unlikely(length < 0 || rl->lcn < LCN_HOLE))
                  goto err_out;
            /*
             * If @stop_vcn is given and finishes inside this run, cap the
             * run length.
             */
            if (unlikely(last_vcn >= 0 && rl[1].vcn > last_vcn)) {
                  s64 s1 = last_vcn + 1;
                  if (unlikely(rl[1].vcn > s1))
                        length = s1 - rl->vcn;
                  the_end = true;
            }
            delta = first_vcn - rl->vcn;
            /* Write length. */
            len_len = ntfs_write_significant_bytes(dst + 1, dst_max,
                        length - delta);
            if (unlikely(len_len < 0))
                  goto size_err;
            /*
             * If the logical cluster number (lcn) denotes a hole and we
             * are on NTFS 3.0+, we don't store it at all, i.e. we need
             * zero space.  On earlier NTFS versions we just write the lcn
             * change.  FIXME: Do we need to write the lcn change or just
             * the lcn in that case?  Not sure as I have never seen this
             * case on NT4. - We assume that we just need to write the lcn
             * change until someone tells us otherwise... (AIA)
             */
            if (likely(rl->lcn >= 0 || vol->major_ver < 3)) {
                  prev_lcn = rl->lcn;
                  if (likely(rl->lcn >= 0))
                        prev_lcn += delta;
                  /* Write change in lcn. */
                  lcn_len = ntfs_write_significant_bytes(dst + 1 +
                              len_len, dst_max, prev_lcn);
                  if (unlikely(lcn_len < 0))
                        goto size_err;
            } else
                  lcn_len = 0;
            dst_next = dst + len_len + lcn_len + 1;
            if (unlikely(dst_next > dst_max))
                  goto size_err;
            /* Update header byte. */
            *dst = lcn_len << 4 | len_len;
            /* Position at next mapping pairs array element. */
            dst = dst_next;
            /* Go to next runlist element. */
            rl++;
      }
      /* Do the full runs. */
      for (; rl->length && !the_end; rl++) {
            s64 length = rl->length;

            if (unlikely(length < 0 || rl->lcn < LCN_HOLE))
                  goto err_out;
            /*
             * If @stop_vcn is given and finishes inside this run, cap the
             * run length.
             */
            if (unlikely(last_vcn >= 0 && rl[1].vcn > last_vcn)) {
                  s64 s1 = last_vcn + 1;
                  if (unlikely(rl[1].vcn > s1))
                        length = s1 - rl->vcn;
                  the_end = true;
            }
            /* Write length. */
            len_len = ntfs_write_significant_bytes(dst + 1, dst_max,
                        length);
            if (unlikely(len_len < 0))
                  goto size_err;
            /*
             * If the logical cluster number (lcn) denotes a hole and we
             * are on NTFS 3.0+, we don't store it at all, i.e. we need
             * zero space.  On earlier NTFS versions we just write the lcn
             * change.  FIXME: Do we need to write the lcn change or just
             * the lcn in that case?  Not sure as I have never seen this
             * case on NT4. - We assume that we just need to write the lcn
             * change until someone tells us otherwise... (AIA)
             */
            if (likely(rl->lcn >= 0 || vol->major_ver < 3)) {
                  /* Write change in lcn. */
                  lcn_len = ntfs_write_significant_bytes(dst + 1 +
                              len_len, dst_max, rl->lcn - prev_lcn);
                  if (unlikely(lcn_len < 0))
                        goto size_err;
                  prev_lcn = rl->lcn;
            } else
                  lcn_len = 0;
            dst_next = dst + len_len + lcn_len + 1;
            if (unlikely(dst_next > dst_max))
                  goto size_err;
            /* Update header byte. */
            *dst = lcn_len << 4 | len_len;
            /* Position at next mapping pairs array element. */
            dst = dst_next;
      }
      /* Success. */
      err = 0;
size_err:
      /* Set stop vcn. */
      if (stop_vcn)
            *stop_vcn = rl->vcn;
      /* Add terminator byte. */
      *dst = 0;
      return err;
err_out:
      if (rl->lcn == LCN_RL_NOT_MAPPED)
            err = -EINVAL;
      else
            err = -EIO;
      return err;
}

/**
 * ntfs_rl_truncate_nolock - truncate a runlist starting at a specified vcn
 * @vol:    ntfs volume (needed for error output)
 * @runlist:      runlist to truncate
 * @new_length:   the new length of the runlist in VCNs
 *
 * Truncate the runlist described by @runlist as well as the memory buffer
 * holding the runlist elements to a length of @new_length VCNs.
 *
 * If @new_length lies within the runlist, the runlist elements with VCNs of
 * @new_length and above are discarded.  As a special case if @new_length is
 * zero, the runlist is discarded and set to NULL.
 *
 * If @new_length lies beyond the runlist, a sparse runlist element is added to
 * the end of the runlist @runlist or if the last runlist element is a sparse
 * one already, this is extended.
 *
 * Note, no checking is done for unmapped runlist elements.  It is assumed that
 * the caller has mapped any elements that need to be mapped already.
 *
 * Return 0 on success and -errno on error.
 *
 * Locking: The caller must hold @runlist->lock for writing.
 */
int ntfs_rl_truncate_nolock(const ntfs_volume *vol, runlist *const runlist,
            const s64 new_length)
{
      runlist_element *rl;
      int old_size;

      ntfs_debug("Entering for new_length 0x%llx.", (long long)new_length);
      BUG_ON(!runlist);
      BUG_ON(new_length < 0);
      rl = runlist->rl;
      if (!new_length) {
            ntfs_debug("Freeing runlist.");
            runlist->rl = NULL;
            if (rl)
                  ntfs_free(rl);
            return 0;
      }
      if (unlikely(!rl)) {
            /*
             * Create a runlist consisting of a sparse runlist element of
             * length @new_length followed by a terminator runlist element.
             */
            rl = ntfs_malloc_nofs(PAGE_SIZE);
            if (unlikely(!rl)) {
                  ntfs_error(vol->sb, "Not enough memory to allocate "
                              "runlist element buffer.");
                  return -ENOMEM;
            }
            runlist->rl = rl;
            rl[1].length = rl->vcn = 0;
            rl->lcn = LCN_HOLE;
            rl[1].vcn = rl->length = new_length;
            rl[1].lcn = LCN_ENOENT;
            return 0;
      }
      BUG_ON(new_length < rl->vcn);
      /* Find @new_length in the runlist. */
      while (likely(rl->length && new_length >= rl[1].vcn))
            rl++;
      /*
       * If not at the end of the runlist we need to shrink it.
       * If at the end of the runlist we need to expand it.
       */
      if (rl->length) {
            runlist_element *trl;
            bool is_end;

            ntfs_debug("Shrinking runlist.");
            /* Determine the runlist size. */
            trl = rl + 1;
            while (likely(trl->length))
                  trl++;
            old_size = trl - runlist->rl + 1;
            /* Truncate the run. */
            rl->length = new_length - rl->vcn;
            /*
             * If a run was partially truncated, make the following runlist
             * element a terminator.
             */
            is_end = false;
            if (rl->length) {
                  rl++;
                  if (!rl->length)
                        is_end = true;
                  rl->vcn = new_length;
                  rl->length = 0;
            }
            rl->lcn = LCN_ENOENT;
            /* Reallocate memory if necessary. */
            if (!is_end) {
                  int new_size = rl - runlist->rl + 1;
                  rl = ntfs_rl_realloc(runlist->rl, old_size, new_size);
                  if (IS_ERR(rl))
                        ntfs_warning(vol->sb, "Failed to shrink "
                                    "runlist buffer.  This just "
                                    "wastes a bit of memory "
                                    "temporarily so we ignore it "
                                    "and return success.");
                  else
                        runlist->rl = rl;
            }
      } else if (likely(/* !rl->length && */ new_length > rl->vcn)) {
            ntfs_debug("Expanding runlist.");
            /*
             * If there is a previous runlist element and it is a sparse
             * one, extend it.  Otherwise need to add a new, sparse runlist
             * element.
             */
            if ((rl > runlist->rl) && ((rl - 1)->lcn == LCN_HOLE))
                  (rl - 1)->length = new_length - (rl - 1)->vcn;
            else {
                  /* Determine the runlist size. */
                  old_size = rl - runlist->rl + 1;
                  /* Reallocate memory if necessary. */
                  rl = ntfs_rl_realloc(runlist->rl, old_size,
                              old_size + 1);
                  if (IS_ERR(rl)) {
                        ntfs_error(vol->sb, "Failed to expand runlist "
                                    "buffer, aborting.");
                        return PTR_ERR(rl);
                  }
                  runlist->rl = rl;
                  /*
                   * Set @rl to the same runlist element in the new
                   * runlist as before in the old runlist.
                   */
                  rl += old_size - 1;
                  /* Add a new, sparse runlist element. */
                  rl->lcn = LCN_HOLE;
                  rl->length = new_length - rl->vcn;
                  /* Add a new terminator runlist element. */
                  rl++;
                  rl->length = 0;
            }
            rl->vcn = new_length;
            rl->lcn = LCN_ENOENT;
      } else /* if (unlikely(!rl->length && new_length == rl->vcn)) */ {
            /* Runlist already has same size as requested. */
            rl->lcn = LCN_ENOENT;
      }
      ntfs_debug("Done.");
      return 0;
}

/**
 * ntfs_rl_punch_nolock - punch a hole into a runlist
 * @vol:    ntfs volume (needed for error output)
 * @runlist:      runlist to punch a hole into
 * @start:  starting VCN of the hole to be created
 * @length: size of the hole to be created in units of clusters
 *
 * Punch a hole into the runlist @runlist starting at VCN @start and of size
 * @length clusters.
 *
 * Return 0 on success and -errno on error, in which case @runlist has not been
 * modified.
 *
 * If @start and/or @start + @length are outside the runlist return error code
 * -ENOENT.
 *
 * If the runlist contains unmapped or error elements between @start and @start
 * + @length return error code -EINVAL.
 *
 * Locking: The caller must hold @runlist->lock for writing.
 */
int ntfs_rl_punch_nolock(const ntfs_volume *vol, runlist *const runlist,
            const VCN start, const s64 length)
{
      const VCN end = start + length;
      s64 delta;
      runlist_element *rl, *rl_end, *rl_real_end, *trl;
      int old_size;
      bool lcn_fixup = false;

      ntfs_debug("Entering for start 0x%llx, length 0x%llx.",
                  (long long)start, (long long)length);
      BUG_ON(!runlist);
      BUG_ON(start < 0);
      BUG_ON(length < 0);
      BUG_ON(end < 0);
      rl = runlist->rl;
      if (unlikely(!rl)) {
            if (likely(!start && !length))
                  return 0;
            return -ENOENT;
      }
      /* Find @start in the runlist. */
      while (likely(rl->length && start >= rl[1].vcn))
            rl++;
      rl_end = rl;
      /* Find @end in the runlist. */
      while (likely(rl_end->length && end >= rl_end[1].vcn)) {
            /* Verify there are no unmapped or error elements. */
            if (unlikely(rl_end->lcn < LCN_HOLE))
                  return -EINVAL;
            rl_end++;
      }
      /* Check the last element. */
      if (unlikely(rl_end->length && rl_end->lcn < LCN_HOLE))
            return -EINVAL;
      /* This covers @start being out of bounds, too. */
      if (!rl_end->length && end > rl_end->vcn)
            return -ENOENT;
      if (!length)
            return 0;
      if (!rl->length)
            return -ENOENT;
      rl_real_end = rl_end;
      /* Determine the runlist size. */
      while (likely(rl_real_end->length))
            rl_real_end++;
      old_size = rl_real_end - runlist->rl + 1;
      /* If @start is in a hole simply extend the hole. */
      if (rl->lcn == LCN_HOLE) {
            /*
             * If both @start and @end are in the same sparse run, we are
             * done.
             */
            if (end <= rl[1].vcn) {
                  ntfs_debug("Done (requested hole is already sparse).");
                  return 0;
            }
extend_hole:
            /* Extend the hole. */
            rl->length = end - rl->vcn;
            /* If @end is in a hole, merge it with the current one. */
            if (rl_end->lcn == LCN_HOLE) {
                  rl_end++;
                  rl->length = rl_end->vcn - rl->vcn;
            }
            /* We have done the hole.  Now deal with the remaining tail. */
            rl++;
            /* Cut out all runlist elements up to @end. */
            if (rl < rl_end)
                  memmove(rl, rl_end, (rl_real_end - rl_end + 1) *
                              sizeof(*rl));
            /* Adjust the beginning of the tail if necessary. */
            if (end > rl->vcn) {
                  delta = end - rl->vcn;
                  rl->vcn = end;
                  rl->length -= delta;
                  /* Only adjust the lcn if it is real. */
                  if (rl->lcn >= 0)
                        rl->lcn += delta;
            }
shrink_allocation:
            /* Reallocate memory if the allocation changed. */
            if (rl < rl_end) {
                  rl = ntfs_rl_realloc(runlist->rl, old_size,
                              old_size - (rl_end - rl));
                  if (IS_ERR(rl))
                        ntfs_warning(vol->sb, "Failed to shrink "
                                    "runlist buffer.  This just "
                                    "wastes a bit of memory "
                                    "temporarily so we ignore it "
                                    "and return success.");
                  else
                        runlist->rl = rl;
            }
            ntfs_debug("Done (extend hole).");
            return 0;
      }
      /*
       * If @start is at the beginning of a run things are easier as there is
       * no need to split the first run.
       */
      if (start == rl->vcn) {
            /*
             * @start is at the beginning of a run.
             *
             * If the previous run is sparse, extend its hole.
             *
             * If @end is not in the same run, switch the run to be sparse
             * and extend the newly created hole.
             *
             * Thus both of these cases reduce the problem to the above
             * case of "@start is in a hole".
             */
            if (rl > runlist->rl && (rl - 1)->lcn == LCN_HOLE) {
                  rl--;
                  goto extend_hole;
            }
            if (end >= rl[1].vcn) {
                  rl->lcn = LCN_HOLE;
                  goto extend_hole;
            }
            /*
             * The final case is when @end is in the same run as @start.
             * For this need to split the run into two.  One run for the
             * sparse region between the beginning of the old run, i.e.
             * @start, and @end and one for the remaining non-sparse
             * region, i.e. between @end and the end of the old run.
             */
            trl = ntfs_rl_realloc(runlist->rl, old_size, old_size + 1);
            if (IS_ERR(trl))
                  goto enomem_out;
            old_size++;
            if (runlist->rl != trl) {
                  rl = trl + (rl - runlist->rl);
                  rl_end = trl + (rl_end - runlist->rl);
                  rl_real_end = trl + (rl_real_end - runlist->rl);
                  runlist->rl = trl;
            }
split_end:
            /* Shift all the runs up by one. */
            memmove(rl + 1, rl, (rl_real_end - rl + 1) * sizeof(*rl));
            /* Finally, setup the two split runs. */
            rl->lcn = LCN_HOLE;
            rl->length = length;
            rl++;
            rl->vcn += length;
            /* Only adjust the lcn if it is real. */
            if (rl->lcn >= 0 || lcn_fixup)
                  rl->lcn += length;
            rl->length -= length;
            ntfs_debug("Done (split one).");
            return 0;
      }
      /*
       * @start is neither in a hole nor at the beginning of a run.
       *
       * If @end is in a hole, things are easier as simply truncating the run
       * @start is in to end at @start - 1, deleting all runs after that up
       * to @end, and finally extending the beginning of the run @end is in
       * to be @start is all that is needed.
       */
      if (rl_end->lcn == LCN_HOLE) {
            /* Truncate the run containing @start. */
            rl->length = start - rl->vcn;
            rl++;
            /* Cut out all runlist elements up to @end. */
            if (rl < rl_end)
                  memmove(rl, rl_end, (rl_real_end - rl_end + 1) *
                              sizeof(*rl));
            /* Extend the beginning of the run @end is in to be @start. */
            rl->vcn = start;
            rl->length = rl[1].vcn - start;
            goto shrink_allocation;
      }
      /* 
       * If @end is not in a hole there are still two cases to distinguish.
       * Either @end is or is not in the same run as @start.
       *
       * The second case is easier as it can be reduced to an already solved
       * problem by truncating the run @start is in to end at @start - 1.
       * Then, if @end is in the next run need to split the run into a sparse
       * run followed by a non-sparse run (already covered above) and if @end
       * is not in the next run switching it to be sparse, again reduces the
       * problem to the already covered case of "@start is in a hole".
       */
      if (end >= rl[1].vcn) {
            /*
             * If @end is not in the next run, reduce the problem to the
             * case of "@start is in a hole".
             */
            if (rl[1].length && end >= rl[2].vcn) {
                  /* Truncate the run containing @start. */
                  rl->length = start - rl->vcn;
                  rl++;
                  rl->vcn = start;
                  rl->lcn = LCN_HOLE;
                  goto extend_hole;
            }
            trl = ntfs_rl_realloc(runlist->rl, old_size, old_size + 1);
            if (IS_ERR(trl))
                  goto enomem_out;
            old_size++;
            if (runlist->rl != trl) {
                  rl = trl + (rl - runlist->rl);
                  rl_end = trl + (rl_end - runlist->rl);
                  rl_real_end = trl + (rl_real_end - runlist->rl);
                  runlist->rl = trl;
            }
            /* Truncate the run containing @start. */
            rl->length = start - rl->vcn;
            rl++;
            /*
             * @end is in the next run, reduce the problem to the case
             * where "@start is at the beginning of a run and @end is in
             * the same run as @start".
             */
            delta = rl->vcn - start;
            rl->vcn = start;
            if (rl->lcn >= 0) {
                  rl->lcn -= delta;
                  /* Need this in case the lcn just became negative. */
                  lcn_fixup = true;
            }
            rl->length += delta;
            goto split_end;
      }
      /*
       * The first case from above, i.e. @end is in the same run as @start.
       * We need to split the run into three.  One run for the non-sparse
       * region between the beginning of the old run and @start, one for the
       * sparse region between @start and @end, and one for the remaining
       * non-sparse region, i.e. between @end and the end of the old run.
       */
      trl = ntfs_rl_realloc(runlist->rl, old_size, old_size + 2);
      if (IS_ERR(trl))
            goto enomem_out;
      old_size += 2;
      if (runlist->rl != trl) {
            rl = trl + (rl - runlist->rl);
            rl_end = trl + (rl_end - runlist->rl);
            rl_real_end = trl + (rl_real_end - runlist->rl);
            runlist->rl = trl;
      }
      /* Shift all the runs up by two. */
      memmove(rl + 2, rl, (rl_real_end - rl + 1) * sizeof(*rl));
      /* Finally, setup the three split runs. */
      rl->length = start - rl->vcn;
      rl++;
      rl->vcn = start;
      rl->lcn = LCN_HOLE;
      rl->length = length;
      rl++;
      delta = end - rl->vcn;
      rl->vcn = end;
      rl->lcn += delta;
      rl->length -= delta;
      ntfs_debug("Done (split both).");
      return 0;
enomem_out:
      ntfs_error(vol->sb, "Not enough memory to extend runlist buffer.");
      return -ENOMEM;
}

#endif /* NTFS_RW */

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