NTFS: Fix various bugs in the runlist merging code. (Based on libntfs

      changes by Richard Russon.)

Signed-off-by: Anton Altaparmakov <aia21@cantab.net>

diff --git a/fs/ntfs/ChangeLog b/fs/ntfs/ChangeLog
index 49eafbd..c7e9237 100644 (file)
--- a/fs/ntfs/ChangeLog
+++ b/fs/ntfs/ChangeLog
@@ -92,6 +92,8 @@ ToDo/Notes:
          an octal number to conform to how chmod(1) works, too.  Thanks to
          Giuseppe Bilotta and Horst von Brand for pointing out the errors of
          my ways.
+       - Fix various bugs in the runlist merging code.  (Based on libntfs
+         changes by Richard Russon.)
 
 2.1.23 - Implement extension of resident files and make writing safe as well as
         many bug fixes, cleanups, and enhancements...

diff --git a/fs/ntfs/runlist.c b/fs/ntfs/runlist.c
index f5b2ac9..e2665d0 100644 (file)
--- a/fs/ntfs/runlist.c
+++ b/fs/ntfs/runlist.c
@@ -2,7 +2,7 @@
  * runlist.c - NTFS runlist handling code.  Part of the Linux-NTFS project.
  *
  * Copyright (c) 2001-2005 Anton Altaparmakov
- * Copyright (c) 2002 Richard Russon
+ * Copyright (c) 2002-2005 Richard Russon
  *
  * This program/include file is free software; you can redistribute it and/or
  * modify it under the terms of the GNU General Public License as published
@@ -214,8 +214,8 @@ static inline void __ntfs_rl_merge(runlist_element *dst, runlist_element *src)
 static inline runlist_element *ntfs_rl_append(runlist_element *dst,
                int dsize, runlist_element *src, int ssize, int loc)
 {
-       BOOL right;
-       int magic;
+       BOOL right;     /* Right end of @src needs merging. */
+       int marker;     /* End of the inserted runs. */
 
        BUG_ON(!dst);
        BUG_ON(!src);
@@ -236,18 +236,19 @@ static inline runlist_element *ntfs_rl_append(runlist_element *dst,
        if (right)
                __ntfs_rl_merge(src + ssize - 1, dst + loc + 1);
 
-       magic = loc + ssize;
+       /* First run after the @src runs that have been inserted. */
+       marker = loc + ssize + 1;
 
        /* Move the tail of @dst out of the way, then copy in @src. */
-       ntfs_rl_mm(dst, magic + 1, loc + 1 + right, dsize - loc - 1 - right);
+       ntfs_rl_mm(dst, marker, loc + 1 + right, dsize - (loc + 1 + right));
        ntfs_rl_mc(dst, loc + 1, src, 0, ssize);
 
        /* Adjust the size of the preceding hole. */
        dst[loc].length = dst[loc + 1].vcn - dst[loc].vcn;
 
        /* We may have changed the length of the file, so fix the end marker */
-       if (dst[magic + 1].lcn == LCN_ENOENT)
-               dst[magic + 1].vcn = dst[magic].vcn + dst[magic].length;
+       if (dst[marker].lcn == LCN_ENOENT)
+               dst[marker].vcn = dst[marker - 1].vcn + dst[marker - 1].length;
 
        return dst;
 }
@@ -279,18 +280,17 @@ static inline runlist_element *ntfs_rl_append(runlist_element *dst,
 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;
+       BOOL left = FALSE;      /* Left end of @src needs merging. */
+       BOOL disc = FALSE;      /* Discontinuity between @dst and @src. */
+       int marker;             /* End of the inserted runs. */
 
        BUG_ON(!dst);
        BUG_ON(!src);
 
-       /* disc => Discontinuity between the end of @dst and the start of @src.
-        *         This means we might need to insert a hole.
-        * hole => @dst ends with a hole or an unmapped region which we can
-        *         extend to match the discontinuity. */
+       /*
+        * disc => Discontinuity between the end of @dst and the start of @src.
+        *         This means we might need to insert a "not mapped" run.
+        */
        if (loc == 0)
                disc = (src[0].vcn > 0);
        else {
@@ -303,58 +303,49 @@ static inline runlist_element *ntfs_rl_insert(runlist_element *dst,
                        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);
+       /*
+        * Space required: @dst size + @src size, less one if we merged, plus
+        * one if there was a discontinuity.
+        */
+       dst = ntfs_rl_realloc(dst, dsize, dsize + ssize - left + disc);
        if (IS_ERR(dst))
                return dst;
        /*
         * We are guaranteed to succeed from here so can start modifying the
         * original runlist.
         */
-
        if (left)
                __ntfs_rl_merge(dst + loc - 1, src);
-
-       magic = loc + ssize - left + disc - hole;
+       /*
+        * First run after the @src runs that have been inserted.
+        * Nominally,  @marker equals @loc + @ssize, i.e. location + number of
+        * runs in @src.  However, if @left, then the first run in @src has
+        * been merged with one in @dst.  And if @disc, then @dst and @src do
+        * not meet and we need an extra run to fill the gap.
+        */
+       marker = loc + ssize - left + disc;
 
        /* Move the tail of @dst out of the way, then copy in @src. */
-       ntfs_rl_mm(dst, magic, loc, dsize - loc);
-       ntfs_rl_mc(dst, loc + disc - hole, src, left, ssize - left);
+       ntfs_rl_mm(dst, marker, loc, dsize - loc);
+       ntfs_rl_mc(dst, loc + disc, 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;
+       /* Adjust the VCN of the first run after the insertion... */
+       dst[marker].vcn = dst[marker - 1].vcn + dst[marker - 1].length;
        /* ... and the length. */
-       if (dst[magic].lcn == LCN_HOLE || dst[magic].lcn == LCN_RL_NOT_MAPPED)
-               dst[magic].length = dst[magic + 1].vcn - dst[magic].vcn;
+       if (dst[marker].lcn == LCN_HOLE || dst[marker].lcn == LCN_RL_NOT_MAPPED)
+               dst[marker].length = dst[marker + 1].vcn - dst[marker].vcn;
 
-       /* Writing beyond the end of the file and there's a discontinuity. */
+       /* Writing beyond the end of the file and there is 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;
+               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;
                }
-
-               magic += hole;
-
-               if (dst[magic].lcn == LCN_ENOENT)
-                       dst[magic].vcn = dst[magic - 1].vcn +
-                                       dst[magic - 1].length;
+               dst[loc].lcn = LCN_RL_NOT_MAPPED;
        }
        return dst;
 }
@@ -385,9 +376,10 @@ static inline runlist_element *ntfs_rl_insert(runlist_element *dst,
 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;
+       BOOL left = FALSE;      /* Left end of @src needs merging. */
+       BOOL right;             /* Right end of @src needs merging. */
+       int tail;               /* Start of tail of @dst. */
+       int marker;             /* End of the inserted runs. */
 
        BUG_ON(!dst);
        BUG_ON(!src);
@@ -396,9 +388,10 @@ static inline runlist_element *ntfs_rl_replace(runlist_element *dst,
        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. */
+       /*
+        * Allocate some space.  We will 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;
@@ -410,17 +403,28 @@ static inline runlist_element *ntfs_rl_replace(runlist_element *dst,
                __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;
+       /*
+        * First run of @dst that needs to be moved out of the way to make
+        * space for the runs to be copied from @src, i.e. the first run of the
+        * tail of @dst.
+        */
+       tail = loc + right + 1;
+       /*
+        * First run after the @src runs that have been inserted, i.e. where
+        * the tail of @dst needs to be moved to.
+        * Nominally, marker equals @loc + @ssize, i.e. location + number of
+        * runs in @src).  However, if @left, then the first run in @src has
+        * been merged with one in @dst.
+        */
+       marker = loc + ssize - left;
 
        /* Move the tail of @dst out of the way, then copy in @src. */
-       ntfs_rl_mm(dst, magic, loc + right + 1, dsize - loc - right - 1);
+       ntfs_rl_mm(dst, marker, tail, dsize - tail);
        ntfs_rl_mc(dst, loc, src, left, ssize - left);
 
-       /* We may have changed the length of the file, so fix the end marker */
-       if (dst[magic].lcn == LCN_ENOENT)
-               dst[magic].vcn = dst[magic - 1].vcn + dst[magic - 1].length;
+       /* We may have changed the length of the file, so fix the end marker. */
+       if (dsize - tail > 0 && dst[marker].lcn == LCN_ENOENT)
+               dst[marker].vcn = dst[marker - 1].vcn + dst[marker - 1].length;
        return dst;
 }