Linux-2.6.12-rc2v2.6.12-rc2

Initial git repository build. I'm not bothering with the full history,
even though we have it. We can create a separate "historical" git
archive of that later if we want to, and in the meantime it's about
3.2GB when imported into git - space that would just make the early
git days unnecessarily complicated, when we don't have a lot of good
infrastructure for it.

Let it rip!

1 files changed, 1438 insertions, 0 deletions

diff --git a/fs/ntfs/runlist.c b/fs/ntfs/runlist.c
new file mode 100644
index 0000000..8438fb1
--- /dev/null
+++ b/fs/ntfs/runlist.c
@@ -0,0 +1,1438 @@
+/**
+ * runlist.c - NTFS runlist handling code.  Part of the Linux-NTFS project.
+ *
+ * Copyright (c) 2001-2004 Anton Altaparmakov
+ * Copyright (c) 2002 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 and 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_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);
+
+	if ((dst->lcn < 0) || (src->lcn < 0))     /* Are we merging holes? */
+		return FALSE;
+	if ((dst->lcn + dst->length) != src->lcn) /* Are the runs contiguous? */
+		return FALSE;
+	if ((dst->vcn + dst->length) != src->vcn) /* Are the runs misaligned? */
+		return FALSE;
+
+	return TRUE;
+}
+
+/**
+ * __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;
+	int magic;
+
+	BUG_ON(!dst);
+	BUG_ON(!src);
+
+	/* First, check if the right hand end needs merging. */
+	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);
+
+	magic = loc + ssize;
+
+	/* Move the tail of @dst out of the way, then copy in @src. */
+	ntfs_rl_mm(dst, magic + 1, 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[magic + 1].lcn == LCN_ENOENT)
+		dst[magic + 1].vcn = dst[magic].vcn + dst[magic].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;
+	BOOL disc = FALSE;	/* Discontinuity */
+	BOOL hole = FALSE;	/* Following a hole */
+	int magic;
+
+	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 hole.
+	 * hole => @dst ends with a hole or an unmapped region which we can
+	 *	   extend to match the discontinuity. */
+	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);
+		if (disc)
+			hole = (dst[loc - 1].lcn == LCN_HOLE);
+	}
+
+	/* Space required: @dst size + @src size, less one if we merged, plus
+	 * one if there was a discontinuity, less one for a trailing hole. */
+	dst = ntfs_rl_realloc(dst, dsize, dsize + ssize - left + disc - hole);
+	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);
+
+	magic = loc + ssize - left + disc - hole;
+
+	/* Move the tail of @dst out of the way, then copy in @src. */
+	ntfs_rl_mm(dst, magic, loc, dsize - loc);
+	ntfs_rl_mc(dst, loc + disc - hole, src, left, ssize - left);
+
+	/* Adjust the VCN of the last run ... */
+	if (dst[magic].lcn <= LCN_HOLE)
+		dst[magic].vcn = dst[magic - 1].vcn + dst[magic - 1].length;
+	/* ... and the length. */
+	if (dst[magic].lcn == LCN_HOLE || dst[magic].lcn == LCN_RL_NOT_MAPPED)
+		dst[magic].length = dst[magic + 1].vcn - dst[magic].vcn;
+
+	/* Writing beyond the end of the file and there's a discontinuity. */
+	if (disc) {
+		if (hole)
+			dst[loc - 1].length = dst[loc].vcn - dst[loc - 1].vcn;
+		else {
+			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;
+		}
+
+		magic += hole;
+
+		if (dst[magic].lcn == LCN_ENOENT)
+			dst[magic].vcn = dst[magic - 1].vcn +
+					dst[magic - 1].length;
+	}
+	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)
+{
+	BOOL left = FALSE;
+	BOOL right;
+	int magic;
+
+	BUG_ON(!dst);
+	BUG_ON(!src);
+
+	/* First, merge the left and right ends, if necessary. */
+	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'll need less if the left, right, or both
+	 * ends were merged. */
+	dst = ntfs_rl_realloc(dst, dsize, dsize + ssize - left - right);
+	if (IS_ERR(dst))
+		return dst;
+	/*
+	 * We are guaranteed to succeed from here so can start modifying the
+	 * original runlists.
+	 */
+	if (right)
+		__ntfs_rl_merge(src + ssize - 1, dst + loc + 1);
+	if (left)
+		__ntfs_rl_merge(dst + loc - 1, src);
+
+	/* FIXME: What does this mean? (AIA) */
+	magic = loc + ssize - left;
+
+	/* Move the tail of @dst out of the way, then copy in @src. */
+	ntfs_rl_mm(dst, magic, loc + right + 1, dsize - loc - right - 1);
+	ntfs_rl_mc(dst, loc, src, left, ssize - left);
+
+	/* We may have changed the length of the file, so fix the end marker */
+	if (dst[magic].lcn == LCN_ENOENT)
+		dst[magic].vcn = dst[magic - 1].vcn + dst[magic - 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++)
+				;
+			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'll lose an end marker */
+	if (start && finish && (drl[dins].length == 0))
+		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) {
+					/* FIXME/TODO: We need to have the
+					 * extra memory already! (AIA) */
+					drl = ntfs_rl_realloc(drl, ds, ds + 2);
+					if (!drl)
+						goto critical_error;
+					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) {
+				/* FIXME/TODO: We need to have the extra
+				 * memory already! (AIA) */
+				drl = ntfs_rl_realloc(drl, ds, ds + 1);
+				if (!drl)
+					goto critical_error;
+			}
+			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;
+
+critical_error:
+	/* Critical error! We cannot afford to fail here. */
+	ntfs_error(NULL, "Critical error! Not enough memory.");
+	panic("NTFS: Cannot continue.");
+}
+
+/**
+ * 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);
+	}
+	/* 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;
+		/*
+		 * 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 values with special meaning:
+ *
+ * Return value			Meaning / Description
+ * ==================================================
+ *  -1 = LCN_HOLE		Hole / not allocated on disk.
+ *  -2 = LCN_RL_NOT_MAPPED	This is part of the runlist which has not been
+ *				inserted into the runlist yet.
+ *  -3 = 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.
+ */
+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;
+}
+
+/**
+ * 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
+ * @start_vcn:	vcn at which to start 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 @start_vcn.
+ * 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 start_vcn)
+{
+	LCN prev_lcn;
+	int rls;
+
+	BUG_ON(start_vcn < 0);
+	if (!rl) {
+		BUG_ON(start_vcn);
+		return 1;
+	}
+	/* Skip to runlist element containing @start_vcn. */
+	while (rl->length && start_vcn >= rl[1].vcn)
+		rl++;
+	if ((!rl->length && start_vcn > rl->vcn) || start_vcn < rl->vcn)
+		return -EINVAL;
+	prev_lcn = 0;
+	/* Always need the termining zero byte. */
+	rls = 1;
+	/* Do the first partial run if present. */
+	if (start_vcn > rl->vcn) {
+		s64 delta;
+
+		/* We know rl->length != 0 already. */
+		if (rl->length < 0 || rl->lcn < LCN_HOLE)
+			goto err_out;
+		delta = start_vcn - rl->vcn;
+		/* Header byte + length. */
+		rls += 1 + ntfs_get_nr_significant_bytes(rl->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 (rl->lcn >= 0 || vol->major_ver < 3) {
+			prev_lcn = rl->lcn;
+			if (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; rl++) {
+		if (rl->length < 0 || rl->lcn < LCN_HOLE)
+			goto err_out;
+		/* Header byte + length. */
+		rls += 1 + ntfs_get_nr_significant_bytes(rl->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 (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 (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 (dst > dst_max)
+			goto err_out;
+		i++;
+		*dst = (s8)-1;
+	} else if (n > 0 && j < 0) {
+		if (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
+ * @start_vcn:	vcn at which to start 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
+ * @start_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().
+ *
+ * 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 @start_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 start_vcn, VCN *const stop_vcn)
+{
+	LCN prev_lcn;
+	s8 *dst_max, *dst_next;
+	int err = -ENOSPC;
+	s8 len_len, lcn_len;
+
+	BUG_ON(start_vcn < 0);
+	BUG_ON(dst_len < 1);
+	if (!rl) {
+		BUG_ON(start_vcn);
+		if (stop_vcn)
+			*stop_vcn = 0;
+		/* Terminator byte. */
+		*dst = 0;
+		return 0;
+	}
+	/* Skip to runlist element containing @start_vcn. */
+	while (rl->length && start_vcn >= rl[1].vcn)
+		rl++;
+	if ((!rl->length && start_vcn > rl->vcn) || start_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 (start_vcn > rl->vcn) {
+		s64 delta;
+
+		/* We know rl->length != 0 already. */
+		if (rl->length < 0 || rl->lcn < LCN_HOLE)
+			goto err_out;
+		delta = start_vcn - rl->vcn;
+		/* Write length. */
+		len_len = ntfs_write_significant_bytes(dst + 1, dst_max,
+				rl->length - delta);
+		if (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 (rl->lcn >= 0 || vol->major_ver < 3) {
+			prev_lcn = rl->lcn;
+			if (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 (lcn_len < 0)
+				goto size_err;
+		} else
+			lcn_len = 0;
+		dst_next = dst + len_len + lcn_len + 1;
+		if (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; rl++) {
+		if (rl->length < 0 || rl->lcn < LCN_HOLE)
+			goto err_out;
+		/* Write length. */
+		len_len = ntfs_write_significant_bytes(dst + 1, dst_max,
+				rl->length);
+		if (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 (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 (lcn_len < 0)
+				goto size_err;
+			prev_lcn = rl->lcn;
+		} else
+			lcn_len = 0;
+		dst_next = dst + len_len + lcn_len + 1;
+		if (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
+ * @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.
+ *
+ * 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.
+ *
+ * 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 (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;
+}