Linux-2.6.12-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 000000000000..8438fb1da219
--- /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;
+}