Fix a bug in Dets concerning repair of almost full tables

A Dets table with sufficiently large buckets could not always be repaired.
(Reported by Gordon Guthrie.)

The format of Dets files has been modified. When downgrading tables
created with the new system will be repaired. Otherwise the
modification should not be noticeable.

5 files changed, 189 insertions, 98 deletions

diff --git a/lib/stdlib/src/dets.erl b/lib/stdlib/src/dets.erl
index 7ed9c4b695..c0f9ce34b0 100644
--- a/lib/stdlib/src/dets.erl
+++ b/lib/stdlib/src/dets.erl
@@ -1754,17 +1754,6 @@ system_code_change(State, _Module, _OldVsn, _Extra) ->
 %%% Internal functions
 %%%----------------------------------------------------------------------
 
-constants(FH, FileName) ->
-    Version = FH#fileheader.version,
-    if 
-        Version =< 8 ->
-            dets_v8:constants();
-        Version =:= 9 ->
-            dets_v9:constants();
-        true ->
-            throw({error, {not_a_dets_file, FileName}})
-    end.
-
 %% -> {ok, Fd, fileheader()} | throw(Error)
 read_file_header(FileName, Access, RamFile) ->
     BF = if
@@ -1842,7 +1831,11 @@ do_bchunk_init(Head, Tab) ->
 		    {H2, {error, old_version}};
 		Parms ->
                     L = dets_utils:all_allocated(H2),
-                    C0 = #dets_cont{no_objs = default, bin = <<>>, alloc = L},
+                    Bin = if
+                              L =:= <<>> -> eof;
+                              true -> <<>>
+                          end,
+                    C0 = #dets_cont{no_objs = default, bin = Bin, alloc = L},
 		    BinParms = term_to_binary(Parms),
 		    {H2, {C0#dets_cont{tab = Tab, proc = self(),what = bchunk},
                           [BinParms]}}
@@ -2478,9 +2471,7 @@ fopen2(Fname, Tab) ->
             Do = case Mod:check_file_header(FH, Fd) of
                      {ok, Head1, ExtraInfo} ->
                          Head2 = Head1#head{filename = Fname},
-                         try Mod:init_freelist(Head2, ExtraInfo) of
-                             Ftab ->
-                                 {ok, Head1#head{freelists = Ftab}}
+                         try {ok, Mod:init_freelist(Head2, ExtraInfo)}
                          catch
                              throw:_ ->
                                  {repair, " has bad free lists, repairing ..."}
@@ -2574,9 +2565,7 @@ fopen_existing_file(Tab, OpenArgs) ->
     Do = case Wh of
              {Tag, Hd, Extra} when Tag =:= final; Tag =:= compact ->
                  Hd1 = Hd#head{filename = Fname},
-                 try Mod:init_freelist(Hd1, Extra) of
-                     Ftab ->
-                         {Tag, Hd#head{freelists = Ftab}}
+                 try {Tag, Mod:init_freelist(Hd1, Extra)}
                  catch
                      throw:_ ->
                          {repair, " has bad free lists, repairing ..."}
@@ -3164,8 +3153,12 @@ init_scan(Head, NoObjs) ->
     check_safe_fixtable(Head),
     FreeLists = dets_utils:get_freelists(Head),
     Base = Head#head.base,
-    {From, To} = dets_utils:find_next_allocated(FreeLists, Base, Base),
-    #dets_cont{no_objs = NoObjs, bin = <<>>, alloc = {From, To, <<>>}}.
+    case dets_utils:find_next_allocated(FreeLists, Base, Base) of
+        {From, To} ->
+            #dets_cont{no_objs = NoObjs, bin = <<>>, alloc = {From,To,<<>>}};
+        none ->
+            #dets_cont{no_objs = NoObjs, bin = eof, alloc = <<>>}
+    end.
 
 check_safe_fixtable(Head) ->
     case (Head#head.fixed =:= false) andalso 
@@ -3266,18 +3259,18 @@ view(FileName) ->
     case catch read_file_header(FileName, read, false) of
         {ok, Fd, FH} ->
 	    Mod = FH#fileheader.mod,
-            try
-                case Mod:check_file_header(FH, Fd) of
-                    {ok, H0, ExtraInfo} ->
-                        Ftab = Mod:init_freelist(H0, ExtraInfo),
-                        {_Bump, Base} = constants(FH, FileName),
-                        H = H0#head{freelists=Ftab, base = Base},
-                        v_free_list(H),
-                        Mod:v_segments(H),
-                        ok;
-                    X ->
-                        X
-                end
+            try Mod:check_file_header(FH, Fd) of
+                {ok, H0, ExtraInfo} ->
+                    Mod = FH#fileheader.mod,
+                    case Mod:check_file_header(FH, Fd) of
+                        {ok, H0, ExtraInfo} ->
+                            H = Mod:init_freelist(H0, ExtraInfo),
+                            v_free_list(H),
+                            Mod:v_segments(H),
+                            ok;
+                        X ->
+                            X
+                    end
             after file:close(Fd)
             end;
 	X -> 
diff --git a/lib/stdlib/src/dets.hrl b/lib/stdlib/src/dets.hrl
index fbffc9d008..a3f99357a2 100644
--- a/lib/stdlib/src/dets.hrl
+++ b/lib/stdlib/src/dets.hrl
@@ -1,7 +1,7 @@
 %% 
 %% %CopyrightBegin%
 %% 
-%% Copyright Ericsson AB 2001-2010. All Rights Reserved.
+%% Copyright Ericsson AB 2001-2011. All Rights Reserved.
 %% 
 %% The contents of this file are subject to the Erlang Public License,
 %% Version 1.1, (the "License"); you may not use this file except in
@@ -92,6 +92,7 @@
 %% Info extracted from the file header.
 -record(fileheader, {
 	  freelist,
+          fl_base,
 	  cookie,
 	  closed_properly,
 	  type,
diff --git a/lib/stdlib/src/dets_v8.erl b/lib/stdlib/src/dets_v8.erl
index cdd38d5604..3e962a1c8b 100644
--- a/lib/stdlib/src/dets_v8.erl
+++ b/lib/stdlib/src/dets_v8.erl
@@ -21,7 +21,7 @@
 %% Dets files, implementation part. This module handles versions up to
 %% and including 8(c). To be called from dets.erl only.
 
--export([constants/0, mark_dirty/1, read_file_header/2,
+-export([mark_dirty/1, read_file_header/2,
          check_file_header/2, do_perform_save/1, initiate_file/11,
          init_freelist/2, fsck_input/4,
          bulk_input/3, output_objs/4, write_cache/1, may_grow/3,
@@ -196,10 +196,6 @@
 %%-define(DEBUGF(X,Y), io:format(X, Y)).
 -define(DEBUGF(X,Y), void).
 
-%% {Bump}
-constants() ->
-    {?BUMP, ?BASE}.
-
 %% -> ok | throw({NewHead,Error})
 mark_dirty(Head) ->
     Dirty = [{?CLOSED_PROPERLY_POS, <<?NOT_PROPERLY_CLOSED:32>>}],
@@ -308,8 +304,9 @@ init_freelist(Head, {convert_freelist,_Version}) ->
     Pos = Head#head.freelists_p,
     case catch prterm(Head, Pos, ?OHDSZ) of
 	{0, _Sz, Term}  ->
-	    FreeList = lists:reverse(Term),
-	    dets_utils:init_slots_from_old_file(FreeList, Ftab);
+	    FreeList1 = lists:reverse(Term),
+            FreeList = dets_utils:init_slots_from_old_file(FreeList1, Ftab),
+            Head#head{freelists = FreeList, base = ?BASE};
 	_ ->
 	    throw({error, {bad_freelists, Head#head.filename}})
     end;
@@ -318,7 +315,7 @@ init_freelist(Head, _) ->
     Pos = Head#head.freelists_p,
     case catch prterm(Head, Pos, ?OHDSZ) of
 	{0, _Sz, Term}  ->
-	    Term;
+            Head#head{freelists = Term, base = ?BASE};
 	_ ->
 	    throw({error, {bad_freelists, Head#head.filename}})
     end.
@@ -331,6 +328,7 @@ read_file_header(Fd, FileName) ->
     {ok, EOF} = dets_utils:position_close(Fd, FileName, eof),
     {ok, <<FileSize:32>>} = dets_utils:pread_close(Fd, FileName, EOF-4, 4),
     FH = #fileheader{freelist = Freelist,
+                     fl_base = ?BASE,
 		     cookie = Cookie,
 		     closed_properly = CP,
 		     type = dets_utils:code_to_type(Type2),
@@ -413,7 +411,7 @@ check_file_header(FH, Fd) ->
 	      version = ?FILE_FORMAT_VERSION,
 	      mod = ?MODULE,
 	      bump = ?BUMP,
-	      base = ?BASE},
+	      base = FH#fileheader.fl_base},
 	    {ok, H, ExtraInfo};
 	Error ->
 	    Error
diff --git a/lib/stdlib/src/dets_v9.erl b/lib/stdlib/src/dets_v9.erl
index 132af01f79..f577b4410f 100644
--- a/lib/stdlib/src/dets_v9.erl
+++ b/lib/stdlib/src/dets_v9.erl
@@ -1,7 +1,7 @@
 %%
 %% %CopyrightBegin%
 %% 
-%% Copyright Ericsson AB 2001-2010. All Rights Reserved.
+%% Copyright Ericsson AB 2001-2011. All Rights Reserved.
 %% 
 %% The contents of this file are subject to the Erlang Public License,
 %% Version 1.1, (the "License"); you may not use this file except in
@@ -21,7 +21,7 @@
 %% Dets files, implementation part. This module handles version 9.
 %% To be called from dets.erl only.
 
--export([constants/0, mark_dirty/1, read_file_header/2,
+-export([mark_dirty/1, read_file_header/2,
          check_file_header/2, do_perform_save/1, initiate_file/11,
          prep_table_copy/9, init_freelist/2, fsck_input/4,
          bulk_input/3, output_objs/4, bchunk_init/2,
@@ -70,6 +70,17 @@
 %%    16     MD5-sum for the 44 plus 112 bytes before the MD5-sum.
 %%           (FreelistsPointer, Cookie and ClosedProperly are not digested.)
 %%    128    Reserved for future versions. Initially zeros.
+%%           Version 9(d), introduced in R15A, has instead:
+%%    112    28 counters for the buddy system sizes (as for 9(b)).
+%%    16     MD5-sum for the 44 plus 112 bytes before the MD5-sum.
+%%           (FreelistsPointer, Cookie and ClosedProperly are not digested.)
+%%    4      Base of the buddy system.
+%%           0 (zero) if the base is equal to ?BASE. Compatible with R14B.
+%%           File size at the end of the file is RealFileSize - Base.
+%%           The reason for modifying file size is that when a file created
+%%           by R15 is read by R14 a repair takes place immediately, which
+%%           is acceptable when downgrading.
+%%    124    Reserved for future versions. Initially zeros.
 %%  ---
 %%  ------------------ end of file header
 %%    4*256  SegmentArray Pointers.
@@ -86,7 +97,7 @@
 %%  -----------------------------
 %%    ???    Free lists
 %%  -----------------------------
-%%    4      File size, in bytes. 
+%%    4      File size, in bytes. See 9(d) obove.
 
 %%  Before we can find an object we must find the slot where the
 %%  object resides. Each slot is a (possibly empty) list (or chain) of
@@ -177,14 +188,14 @@
 %%% File header
 %%%
 
--define(RESERVED, 128).        % Reserved for future use.
+-define(RESERVED, 124).        % Reserved for future use.
 
 -define(COLL_CNTRS, (28*4)).     % Counters for the buddy system.
 -define(MD5SZ, 16).
+-define(FL_BASE, 4).
 
--define(HEADSZ, 
-        56+?COLL_CNTRS+?MD5SZ). % The size of the file header, in bytes,
-                                % not including the reserved part.
+-define(HEADSZ, 56+?COLL_CNTRS  % The size of the file header, in bytes,
+            +?MD5SZ+?FL_BASE).  % not including the reserved part.
 -define(HEADEND, (?HEADSZ+?RESERVED)). 
                                % End of header and reserved area.
 -define(SEGSZ, 512).           % Size of a segment, in words. SZOBJP*SEGSZP.
@@ -270,10 +281,6 @@
 %%-define(DEBUGF(X,Y), io:format(X, Y)).
 -define(DEBUGF(X,Y), void).
 
-%% {Bump}
-constants() ->
-    {?BUMP, ?BASE}.
-
 %% -> ok | throw({NewHead,Error})
 mark_dirty(Head) ->
     Dirty = [{?CLOSED_PROPERLY_POS, <<?NOT_PROPERLY_CLOSED:32>>}],
@@ -356,7 +363,7 @@ init_file(Fd, Tab, Fname, Type, Kp, MinSlots, MaxSlots, Ram, CacheSz,
       cache = dets_utils:new_cache(CacheSz),
       version = ?FILE_FORMAT_VERSION,
       bump = ?BUMP,
-      base = ?BASE,
+      base = ?BASE, % to be overwritten
       mod = ?MODULE
      },
 
@@ -378,13 +385,20 @@ init_file(Fd, Tab, Fname, Type, Kp, MinSlots, MaxSlots, Ram, CacheSz,
     {Head1, Ws1} = init_parts(Head0, 0, no_parts(Next), Zero, []),
     NoSegs = no_segs(Next),
 
-    {Head, WsI, WsP} = init_segments(Head1, 0, NoSegs, Zero, [], []),
+    {Head2, WsI, WsP} = init_segments(Head1, 0, NoSegs, Zero, [], []),
     Ws2 = if
 	      DoInitSegments -> WsP ++ WsI;
 	      true -> WsP
 	 end,
     dets_utils:pwrite(Fd, Fname, [W0 | lists:append(Ws1) ++ Ws2]),
-    true = hash_invars(Head),
+    true = hash_invars(Head2),
+    %% The allocations that have been made so far (parts, segments)
+    %% are permanent; the table will never shrink. Therefore the base
+    %% of the Buddy system can be set to the first free object.
+    %% This is used in allocate_all(), see below.
+    {_, Where, _} = dets_utils:alloc(Head2, ?BUMP),
+    NewFtab = dets_utils:init_alloc(Where),
+    Head = Head2#head{freelists = NewFtab, base = Where},
     {ok, Head}.
 
 %% Returns a power of two not less than 256.
@@ -451,8 +465,9 @@ read_file_header(Fd, FileName) ->
       Version:32,    M:32,       Next:32,       Kp:32,
       NoObjects:32,  NoKeys:32,  MinNoSlots:32, MaxNoSlots:32,
       HashMethod:32, N:32, NoCollsB:?COLL_CNTRS/binary, 
-      MD5:?MD5SZ/binary>> = Bin,
-    <<_:12/binary,MD5DigestedPart:(?HEADSZ-?MD5SZ-12)/binary,_/binary>> = Bin,
+      MD5:?MD5SZ/binary, FlBase:32>> = Bin,
+    <<_:12/binary,MD5DigestedPart:(?HEADSZ-?MD5SZ-?FL_BASE-12)/binary,
+      _/binary>> = Bin,
     {ok, EOF} = dets_utils:position_close(Fd, FileName, eof),
     {ok, <<FileSize:32>>} = dets_utils:pread_close(Fd, FileName, EOF-4, 4),
     {CL, <<>>} = lists:foldl(fun(LSz, {Acc,<<NN:32,R/binary>>}) -> 
@@ -468,8 +483,12 @@ read_file_header(Fd, FileName) ->
 	    true ->
 		lists:reverse(CL)
 	end,
-			     
+    Base = case FlBase of
+               0 -> ?BASE;
+               _ -> FlBase
+           end,
     FH = #fileheader{freelist = FreeList,
+                     fl_base = Base,
 		     cookie = Cookie,
 		     closed_properly = CP,
 		     type = dets_utils:code_to_type(Type2),
@@ -486,7 +505,7 @@ read_file_header(Fd, FileName) ->
                      read_md5 = MD5,
                      has_md5 = <<0:?MD5SZ/unit:8>> =/= MD5,
                      md5 = erlang:md5(MD5DigestedPart),
-		     trailer = FileSize,
+		     trailer = FileSize + FlBase,
 		     eof = EOF,
 		     n = N,
 		     mod = ?MODULE},
@@ -544,7 +563,7 @@ check_file_header(FH, Fd) ->
 	      version = ?FILE_FORMAT_VERSION,
 	      mod = ?MODULE,
 	      bump = ?BUMP,
-	      base = ?BASE},
+	      base = FH#fileheader.fl_base},
 	    {ok, H, ExtraInfo};
 	Error ->
 	    Error
@@ -1185,41 +1204,25 @@ write_loop(Head, BytesToWrite, Bin) ->
     write_loop(Head, BytesToWrite, SmallBin).
 
 %% By allocating bigger objects before smaller ones, holes in the
-%% buddy system memory map are avoided. Unfortunately, the segments
-%% are always allocated first, so if there are objects bigger than a
-%% segment, there is a hole to handle. (Haven't considered placing the
-%% segments among other objects of the same size.)
+%% buddy system memory map are avoided.
 allocate_all_objects(Head, SizeT) ->
     DTL = lists:reverse(lists:keysort(1, ets:tab2list(SizeT))),
     MaxSz = element(1, hd(DTL)),
-    SegSize = ?ACTUAL_SEG_SIZE,
-    {Head1, HSz, HN, HA} = alloc_hole(MaxSz, Head, SegSize),
-    {Head2, NL} = allocate_all(Head1, DTL, []),
+    {Head1, NL} = allocate_all(Head, DTL, []),
     %% Find the position that will be the end of the file by allocating
     %% a minimal object.
-    {_Head, EndOfFile, _} = dets_utils:alloc(Head2, ?BUMP),
-    Head3 = free_hole(Head2, HSz, HN, HA),
-    NewHead = Head3#head{maxobjsize = max_objsize(Head3#head.no_collections)},
+    {_Head, EndOfFile, _} = dets_utils:alloc(Head1, ?BUMP),
+    NewHead = Head1#head{maxobjsize = max_objsize(Head1#head.no_collections)},
     {NewHead, NL, MaxSz, EndOfFile}.
 
-alloc_hole(LSize, Head, SegSz) when ?POW(LSize-1) > SegSz ->
-    Size = ?POW(LSize-1),
-    {_, SegAddr, _} = dets_utils:alloc(Head, adjsz(SegSz)),
-    {_, Addr, _} = dets_utils:alloc(Head, adjsz(Size)),
-    N = (Addr - SegAddr) div SegSz,
-    Head1 = dets_utils:alloc_many(Head, SegSz, N, SegAddr),
-    {Head1, SegSz, N, SegAddr};
-alloc_hole(_MaxSz, Head, _SegSz) ->
-    {Head, 0, 0, 0}.
-
-free_hole(Head, _Size, 0, _Addr) ->
-    Head;
-free_hole(Head, Size, N, Addr) ->
-    {Head1, _} = dets_utils:free(Head, Addr, adjsz(Size)),
-    free_hole(Head1, Size, N-1, Addr+Size).
-
 %% One (temporary) file for each buddy size, write all objects of that
 %% size to the file.
+%%
+%% Before R15 a "hole" was needed before the first bucket if the size
+%% of the biggest bucket was greater than the size of a segment. The
+%% hole proved to be a problem with almost full tables with huge
+%% buckets. Since R15 the hole is no longer needed due to the fact
+%% that the base of the Buddy system is flexible.
 allocate_all(Head, [{?FSCK_SEGMENT,_,Data,_}], L) ->
     %% And one file for the segments...
     %% Note that space for the array parts and the segments has
@@ -1593,23 +1596,28 @@ do_perform_save(H) ->
     H1 = H#head{freelists_p = FreeListsPointer},
     {FLW, FLSize} = free_lists_to_file(H1),
     FileSize = FreeListsPointer + FLSize + 4,
-    ok = dets_utils:write(H1, [FLW | <<FileSize:32>>]),
+    AdjustedFileSize = case H#head.base of
+                           ?BASE -> FileSize;
+                           Base -> FileSize - Base
+                       end,
+    ok = dets_utils:write(H1, [FLW | <<AdjustedFileSize:32>>]),
     FileHeader = file_header(H1, FreeListsPointer, ?CLOSED_PROPERLY),
     case dets_utils:debug_mode() of
         true -> 
-            TmpHead = H1#head{freelists = init_freelist(H1, true), 
-                              fixed = false},
+            TmpHead0 = init_freelist(H1#head{fixed = false}, true),
+            TmpHead = TmpHead0#head{base = H1#head.base},
             case 
                 catch dets_utils:all_allocated_as_list(TmpHead)
                       =:= dets_utils:all_allocated_as_list(H1)
-                of
+            of
                 true -> 
                     dets_utils:pwrite(H1, [{0, FileHeader}]);
                 _ -> 
+                    throw(
                     dets_utils:corrupt_reason(H1, {failed_to_save_free_lists,
                                                    FreeListsPointer,
                                                    TmpHead#head.freelists,
-                                                   H1#head.freelists})
+                                                   H1#head.freelists}))
             end;
         false ->
             dets_utils:pwrite(H1, [{0, FileHeader}])
@@ -1648,7 +1656,11 @@ file_header(Head, FreeListsPointer, ClosedProperly, NoColls) ->
               true -> erlang:md5(DigH);
               false -> <<0:?MD5SZ/unit:8>>
           end,
-    [H1, DigH, MD5 | <<0:?RESERVED/unit:8>>].
+    Base = case Head#head.base of
+               ?BASE -> <<0:32>>;
+               FlBase -> <<FlBase:32>>
+           end,
+    [H1, DigH, MD5, Base | <<0:?RESERVED/unit:8>>].
 
 %% Going through some trouble to avoid creating one single binary for
 %% the free lists. If the free lists are huge, binary_to_term and
@@ -1695,8 +1707,8 @@ free_lists_from_file(H, Pos) ->
     case catch bin_to_tree([], H, start, FL, -1, []) of
 	{'EXIT', _} ->
 	    throw({error, {bad_freelists, H#head.filename}});
-	Reply ->
-	    Reply
+        Ftab ->
+            H#head{freelists = Ftab, base = ?BASE}
     end.
 
 bin_to_tree(Bin, H, LastPos, Ftab, A0, L) ->
diff --git a/lib/stdlib/test/dets_SUITE.erl b/lib/stdlib/test/dets_SUITE.erl
index b68d83b12d..63767aeda6 100644
--- a/lib/stdlib/test/dets_SUITE.erl
+++ b/lib/stdlib/test/dets_SUITE.erl
@@ -34,6 +34,8 @@
 -define(datadir(Conf), ?config(data_dir, Conf)).
 -endif.
 
+-compile(r13). % OTP-9607
+
 -export([all/0, suite/0,groups/0,init_per_suite/1, end_per_suite/1, 
 	 init_per_group/2,end_per_group/2, 
 	 not_run/1, newly_started/1, basic_v8/1, basic_v9/1,
@@ -53,7 +55,7 @@
          simultaneous_open/1, insert_new/1, repair_continuation/1,
          otp_5487/1, otp_6206/1, otp_6359/1, otp_4738/1, otp_7146/1,
          otp_8070/1, otp_8856/1, otp_8898/1, otp_8899/1, otp_8903/1,
-         otp_8923/1, otp_9282/1]).
+         otp_8923/1, otp_9282/1, otp_9607/1]).
 
 -export([dets_dirty_loop/0]).
 
@@ -112,7 +114,7 @@ all() ->
 	     many_clients, otp_4906, otp_5402, simultaneous_open,
 	     insert_new, repair_continuation, otp_5487, otp_6206,
 	     otp_6359, otp_4738, otp_7146, otp_8070, otp_8856, otp_8898,
-	     otp_8899, otp_8903, otp_8923, otp_9282]
+	     otp_8899, otp_8903, otp_8923, otp_9282, otp_9607]
     end.
 
 groups() -> 
@@ -554,7 +556,11 @@ dets_dirty_loop() ->
 	{From, [write, Name, Value]} ->
 	    Ret = dets:insert(Name, Value),
 	    From ! {self(), Ret},
-	    dets_dirty_loop()
+	    dets_dirty_loop();
+        {From, [close, Name]} ->
+            Ret = dets:close(Name),
+            From ! {self(), Ret},
+            dets_dirty_loop()
     end.
 
 
@@ -3882,10 +3888,91 @@ some_calls(Tab, Config) ->
     ?line ok = dets:close(T),
     file:delete(File).
 
+otp_9607(doc) ->
+    ["OTP-9607. Test downgrading the slightly changed format."];
+otp_9607(suite) ->
+    [];
+otp_9607(Config) when is_list(Config) ->
+    %% Note: the bug is about almost full tables. The fix of that
+    %% problem is *not* tested here.
+    Version = r13b,
+    case ?t:is_release_available(atom_to_list(Version)) of
+        true ->
+            T = otp_9607,
+            File = filename(T, Config),
+            Key = a,
+            Value = 1,
+            Args = [{file,File}],
+            ?line {ok, T} = dets:open_file(T, Args),
+            ?line ok = dets:insert(T, {Key, Value}),
+            ?line ok = dets:close(T),
+
+            ?line Call = fun(P, A) ->
+                                 P ! {self(), A},
+                                 receive
+                                     {P, Ans} ->
+                                         Ans
+                                 after 5000 ->
+                                         exit(other_process_dead)
+                                 end
+                         end,
+            %% Create a file on the modified format, read the file
+            %% with an emulator that doesn't know about the modified
+            %% format.
+            ?line {ok, Node} = start_node_rel(Version, Version, slave),
+            ?line Pid = rpc:call(Node, erlang, spawn,
+                                 [?MODULE, dets_dirty_loop, []]),
+            ?line {error,{needs_repair, File}} =
+                Call(Pid, [open, T, Args++[{repair,false}]]),
+            io:format("Expect repair:~n"),
+            ?line {ok, T} = Call(Pid, [open, T, Args]),
+            ?line [{Key,Value}] = Call(Pid, [read, T, Key]),
+            ?line ok = Call(Pid, [close, T]),
+            file:delete(File),
+
+            %% Create a file on the unmodified format. Modify the file
+            %% using an emulator that must not turn the file into the
+            %% modified format. Read the file and make sure it is not
+            %% repaired.
+            ?line {ok, T} = Call(Pid, [open, T, Args]),
+            ?line ok = Call(Pid, [write, T, {Key,Value}]),
+            ?line [{Key,Value}] = Call(Pid, [read, T, Key]),
+            ?line ok = Call(Pid, [close, T]),
+
+            Key2 = b,
+            Value2 = 2,
+
+            ?line {ok, T} = dets:open_file(T, Args),
+            ?line [{Key,Value}] = dets:lookup(T, Key),
+            ?line ok = dets:insert(T, {Key2,Value2}),
+            ?line ok = dets:close(T),
+
+            ?line {ok, T} = Call(Pid, [open, T, Args++[{repair,false}]]),
+            ?line [{Key2,Value2}] = Call(Pid, [read, T, Key2]),
+            ?line ok = Call(Pid, [close, T]),
+
+            ?t:stop_node(Node),
+            file:delete(File),
+            ok;
+        false ->
+	    {skipped, "No support for old node"}
+    end.
+
+
+
 %%
 %% Parts common to several test cases
 %% 
 
+start_node_rel(Name, Rel, How) ->
+    Release = [{release, atom_to_list(Rel)}],
+    ?line Pa = filename:dirname(code:which(?MODULE)),
+    ?line test_server:start_node(Name, How,
+                                 [{args,
+                                   " -kernel net_setuptime 100 "
+                                   " -pa " ++ Pa},
+                                  {erl, Release}]).
+
 crash(File, Where) ->
     crash(File, Where, 10).