text: /**
   * 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 minimum
   * 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 */
  