mnesia_schema.erl

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                    verbose("Create Directory ~p~n", [Dir]),
                    ok;
                {error, Reason} ->
                    verbose("Cannot create mnesia dir ~p~n", [Reason]),
                    {error, {"Cannot create Mnesia dir", Dir, Reason}}
            end
    end;
opt_create_dir(false, _) ->
    {error, {has_no_disc, node()}}.
    
check_can_write(Dir) ->
    case file:read_file_info(Dir) of
        {ok, FI} when FI#file_info.type == directory,
		      FI#file_info.access == read_write ->
            ok;
        {ok, _} ->
            {error, "Not allowed to write in Mnesia dir", Dir};
        _ ->
            {error, "Non existent Mnesia dir", Dir}
    end.

lock_schema() ->
    mnesia_lib:lock_table(schema).

unlock_schema() ->
    mnesia_lib:unlock_table(schema).

read_schema(Keep) ->
    read_schema(Keep, false).

%% The schema may be read for several reasons.
%% If Mnesia is not already started the read intention
%% we normally do not want the ets table named schema
%% be left around.
%% If Keep == true, the ets table schema is kept
%% If Keep == false, the ets table schema is removed
%%
%% Returns {ok, Source, SchemaCstruct} or {error, Reason}
%% Source may be: default | ram | disc | fallback

read_schema(Keep, IgnoreFallback) ->
    lock_schema(),
    Res = 
        case mnesia:system_info(is_running) of
            yes ->
                {ok, ram, get_create_list(schema)};
            _IsRunning ->
                    case mnesia_monitor:use_dir() of
                        true ->
                            read_disc_schema(Keep, IgnoreFallback);
                        false when Keep == true ->
                            Args = [{keypos, 2}, public, named_table, set],
                            mnesia_monitor:mktab(schema, Args),
                            CreateList = get_initial_schema(ram_copies, []),
                            ?ets_insert(schema,{schema, schema, CreateList}),
                            {ok, default, CreateList};
                        false when Keep == false ->
			    CreateList = get_initial_schema(ram_copies, []),
                            {ok, default, CreateList}
                    end
        end,
    unlock_schema(),
    Res.

read_disc_schema(Keep, IgnoreFallback) ->
    Running = mnesia:system_info(is_running),
    case mnesia_bup:fallback_exists() of
        true when IgnoreFallback == false, Running /= yes ->
             mnesia_bup:fallback_to_schema();
        _ ->  
            %% If we're running, we read the schema file even
            %% if fallback exists
            Dat = mnesia_lib:tab2dat(schema),
            case mnesia_lib:exists(Dat) of
                true ->
                    do_read_disc_schema(Dat, Keep);
                false ->
		    Dmp = mnesia_lib:tab2dmp(schema),
		    case mnesia_lib:exists(Dmp) of
			true ->
			    %% May only happen when toggling of
			    %% schema storage type has been
			    %% interrupted
			    do_read_disc_schema(Dmp, Keep);
			false ->
			    {error, "No schema file exists"}
		    end
            end
    end.

do_read_disc_schema(Fname, Keep) ->
    T = 
        case Keep of
            false ->
                Args = [{keypos, 2}, public, set],
                ?ets_new_table(schema, Args);
            true ->
                Args = [{keypos, 2}, public, named_table, set],
                mnesia_monitor:mktab(schema, Args)
        end,
    Repair = mnesia_monitor:get_env(auto_repair),
    Res =  % BUGBUG Fixa till dcl!
        case mnesia_lib:dets_to_ets(schema, T, Fname, set, Repair, no) of
            loaded -> {ok, disc, ?ets_lookup_element(T, schema, 3)};
            Other -> {error, {"Cannot read schema", Fname, Other}}
        end,
    case Keep of
        true -> ignore;
        false -> ?ets_delete_table(T)
    end,
    Res.

get_initial_schema(SchemaStorage, Nodes) ->
    Cs = #cstruct{name = schema,
		  record_name = schema,
		  attributes = [table, cstruct]},    
    Cs2 =
	case SchemaStorage of
        ram_copies -> Cs#cstruct{ram_copies = Nodes};
        disc_copies -> Cs#cstruct{disc_copies = Nodes}
    end,
    cs2list(Cs2).

read_cstructs_from_disc() ->
    %% Assumptions: 
    %% - local schema lock in global
    %% - use_dir is true
    %% - Mnesia is not running
    %% - Ignore fallback

    Fname = mnesia_lib:tab2dat(schema),
    case mnesia_lib:exists(Fname) of
	true ->
	    Args = [{file, Fname},
		    {keypos, 2},
		    {repair, mnesia_monitor:get_env(auto_repair)},
		    {type, set}],
	    case dets:open_file(make_ref(), Args) of
		{ok, Tab} ->
		    Fun = fun({_, _, List}) ->
				  {continue, list2cs(List)}
			  end,
		    Cstructs = dets:traverse(Tab, Fun),
		    dets:close(Tab),
		    {ok, Cstructs};  
		{error, Reason} ->
		    {error, Reason}
	    end;
	false ->
	    {error, "No schema file exists"}
    end.
    
%% We run a very special type of transactions when we
%% we want to manipulate the schema.

get_tid_ts_and_lock(Tab, Intent) ->
    TidTs = get(mnesia_activity_state),
    case TidTs of
	{_Mod, Tid, Ts} when record(Ts, tidstore)->
	    Store = Ts#tidstore.store,
	    case Intent of
		read -> mnesia_locker:rlock_table(Tid, Store, Tab);
		write -> mnesia_locker:wlock_table(Tid, Store, Tab);
		none -> ignore
	    end,
	    TidTs;
	_ ->
	    mnesia:abort(no_transaction)
    end.

schema_transaction(Fun) ->
    case get(mnesia_activity_state) of
	undefined ->
	    Args = [self(), Fun, whereis(mnesia_controller)],
	    Pid = spawn_link(?MODULE, schema_coordinator, Args),
	    receive
		{transaction_done, Res, Pid} -> Res;
		{'EXIT', Pid, R} -> {aborted, {transaction_crashed, R}}
	    end;
	_ ->
            {aborted, nested_transaction}
    end.

%% This process may dump the transaction log, and should
%% therefore not be run in an application process
%% 
schema_coordinator(Client, _Fun, undefined) ->
    Res = {aborted, {node_not_running, node()}},
    Client ! {transaction_done, Res, self()},
    unlink(Client);
    
schema_coordinator(Client, Fun, Controller) when pid(Controller) ->
    %% Do not trap exit in order to automatically die
    %% when the controller dies

    link(Controller),
    unlink(Client),
    
    %% Fulfull the transaction even if the client dies     
    Res = mnesia:transaction(Fun),
    Client ! {transaction_done, Res, self()},
    unlink(Controller),         % Avoids spurious exit message
    unlink(whereis(mnesia_tm)), % Avoids spurious exit message
    exit(normal).

%% The make* rotines return a list of ops, this function
%% inserts em all in the Store and maintains the local order
%% of ops.

insert_schema_ops({_Mod, _Tid, Ts}, SchemaIOps) ->
    do_insert_schema_ops(Ts#tidstore.store, SchemaIOps).
    
do_insert_schema_ops(Store, [Head | Tail]) ->
    ?ets_insert(Store, Head),
    do_insert_schema_ops(Store, Tail);
do_insert_schema_ops(_Store, []) ->
    ok.

cs2list(Cs) when record(Cs, cstruct) ->
    Tags = record_info(fields, cstruct),
    rec2list(Tags, 2, Cs);
cs2list(CreateList) when list(CreateList) ->
    CreateList.

rec2list([Tag | Tags], Pos, Rec) ->
    Val = element(Pos, Rec),
    [{Tag, Val} | rec2list(Tags, Pos + 1, Rec)];
rec2list([], _Pos, _Rec) ->
    [].

list2cs(List) when list(List) ->
    Name = pick(unknown, name, List, must),
    Type = pick(Name, type, List, set),
    Rc0 = pick(Name, ram_copies, List, []),
    Dc = pick(Name, disc_copies, List, []),
    Doc = pick(Name, disc_only_copies, List, []),
    Rc = case {Rc0, Dc, Doc} of
             {[], [], []} -> [node()];
             _ -> Rc0
         end,
    LC = pick(Name, local_content, List, false),
    RecName = pick(Name, record_name, List, Name),
    Attrs = pick(Name, attributes, List, [key, val]),
    Snmp = pick(Name, snmp, List, []),
    LoadOrder = pick(Name, load_order, List, 0),
    AccessMode = pick(Name, access_mode, List, read_write),
    UserProps = pick(Name, user_properties, List, []),
    verify({alt, [nil, list]}, mnesia_lib:etype(UserProps),
	   {bad_type, Name, {user_properties, UserProps}}),
    Cookie = pick(Name, cookie, List, ?unique_cookie),
    Version = pick(Name, version, List, {{2, 0}, []}),
    Ix = pick(Name, index, List, []),
    verify({alt, [nil, list]}, mnesia_lib:etype(Ix),
	   {bad_type, Name, {index, [Ix]}}),
    Ix2 = [attr_to_pos(I, Attrs) || I <- Ix],

    Frag = pick(Name, frag_properties, List, []),
    verify({alt, [nil, list]}, mnesia_lib:etype(Frag),
	   {badarg, Name, {frag_properties, Frag}}), 
        
    Keys = check_keys(Name, List, record_info(fields, cstruct)),
    check_duplicates(Name, Keys),
    #cstruct{name = Name,
             ram_copies = Rc,
             disc_copies = Dc,
             disc_only_copies = Doc,
             type = Type,
             index = Ix2,
             snmp = Snmp,
             load_order = LoadOrder,
             access_mode = AccessMode,
             local_content = LC,
	     record_name = RecName,
             attributes = Attrs,
             user_properties = lists:sort(UserProps),
	     frag_properties = lists:sort(Frag),
             cookie = Cookie,
             version = Version};
list2cs(Other) ->
    mnesia:abort({badarg, Other}).

pick(Tab, Key, List, Default) ->
    case lists:keysearch(Key, 1, List) of
        false  when Default == must ->
            mnesia:abort({badarg, Tab, "Missing key", Key, List});
        false ->
            Default;
        {value, {Key, Value}} ->
            Value;
	{value, BadArg} ->
	    mnesia:abort({bad_type, Tab, BadArg})
    end.

%% Convert attribute name to integer if neccessary
attr_tab_to_pos(_Tab, Pos) when integer(Pos) ->
    Pos;
attr_tab_to_pos(Tab, Attr) ->
    attr_to_pos(Attr, val({Tab, attributes})).
    
%% Convert attribute name to integer if neccessary
attr_to_pos(Pos, _Attrs) when integer(Pos) ->
    Pos;
attr_to_pos(Attr, Attrs) when atom(Attr) ->
    attr_to_pos(Attr, Attrs, 2);
attr_to_pos(Attr, _) ->
    mnesia:abort({bad_type, Attr}).

attr_to_pos(Attr, [Attr | _Attrs], Pos) ->
    Pos;
attr_to_pos(Attr, [_ | Attrs], Pos) ->
    attr_to_pos(Attr, Attrs, Pos + 1);
attr_to_pos(Attr, _, _) ->
    mnesia:abort({bad_type, Attr}).
    
check_keys(Tab, [{Key, _Val} | Tail], Items) ->
    case lists:member(Key, Items) of
        true ->  [Key | check_keys(Tab, Tail, Items)];
        false -> mnesia:abort({badarg, Tab, Key})
    end;
check_keys(_, [], _) ->
    [];
check_keys(Tab, Arg, _) ->
    mnesia:abort({badarg, Tab, Arg}).

check_duplicates(Tab, Keys) ->
    case has_duplicates(Keys) of
        false -> ok;
        true -> mnesia:abort({badarg, Tab, "Duplicate keys", Keys})
    end.

has_duplicates([H | T]) ->
    case lists:member(H, T) of
        true -> true;
        false -> has_duplicates(T)
    end;
has_duplicates([]) ->
    false.

%% This is the only place where we check the validity of data
verify_cstruct(Cs) when record(Cs, cstruct) ->
    verify_nodes(Cs),

    Tab = Cs#cstruct.name,
    verify(atom, mnesia_lib:etype(Tab), {bad_type, Tab}),
    Type = Cs#cstruct.type,
    verify(true, lists:member(Type, [set, bag, ordered_set]),
	   {bad_type, Tab, {type, Type}}),

    %% Currently ordered_set is not supported for disk_only_copies.
    if 
 	Type == ordered_set, Cs#cstruct.disc_only_copies /= [] ->
	    mnesia:abort({bad_type, Tab, {not_supported, Type, disc_only_copies}});
	true ->
	    ok
    end,

    RecName = Cs#cstruct.record_name,
    verify(atom, mnesia_lib:etype(RecName),
	   {bad_type, Tab, {record_name, RecName}}),

    Attrs = Cs#cstruct.attributes,
    verify(list, mnesia_lib:etype(Attrs),
	   {bad_type, Tab, {attributes, Attrs}}),

    Arity = length(Attrs) + 1,
    verify(true, Arity > 2, {bad_type, Tab, {attributes, Attrs}}),
    
    lists:foldl(fun(Attr,_Other) when Attr == snmp ->
                        mnesia:abort({bad_type, Tab, {attributes, [Attr]}});
                   (Attr,Other) -> 
                        verify(atom, mnesia_lib:etype(Attr),
                               {bad_type, Tab, {attributes, [Attr]}}),
                        verify(false, lists:member(Attr, Other),
                               {combine_error, Tab, {attributes, [Attr | Other]}}),
                        [Attr | Other]
                end,
                [],
                Attrs),

    Index = Cs#cstruct.index,
    verify({alt, [nil, list]}, mnesia_lib:etype(Index),
	   {bad_type, Tab, {index, Index}}),
    
    IxFun =
        fun(Pos) ->
                verify(true, fun() ->
                                     if
					 integer(Pos),
                                         Pos > 2,
                                         Pos =< Arity ->
                                             true;
                                         true -> false
                                     end
                             end,
                       {bad_type, Tab, {index, [Pos]}})
        end,
    lists:foreach(IxFun, Index),
    
    LC = Cs#cstruct.local_content,
    verify({alt, [true, false]}, LC,
	   {bad_type, Tab, {local_content, LC}}),
    Access = Cs#cstruct.access_mode,
    verify({alt, [read_write, read_only]}, Access,