Permanent storage implementation

1 files changed, 95 insertions, 0 deletions

diff --git a/src/perm.erl b/src/perm.erl
new file mode 100644
index 0000000..2ce5b46
--- /dev/null
+++ b/src/perm.erl
@@ -0,0 +1,95 @@
+%%
+%% Copyright (c) 2014 Kungliga Tekniska Högskolan
+%% (KTH Royal Institute of Technology, Stockholm, Sweden).
+%%
+
+-module(perm).
+-export([ensurefile/3]).
+
+fsync(Name) ->
+    fsyncport:fsync(Name).
+
+readfile_and_verify(Name, Content) ->
+    case file:read_file(Name) of
+        {ok, ContentsReadBinary} ->
+            ContentsRead = binary_to_list(ContentsReadBinary),
+            if Content == ContentsRead ->
+                    ok;
+               true ->
+                    {error, "File contents differ"}
+            end;
+        {error, Error} ->
+            {error, Error}
+    end.
+
+writefile(Name, NurseryName, Content) ->
+    case file:open(NurseryName, [write, exclusive]) of
+        {ok, File} ->
+            %io:format("Write file: ~p~n", [Name]),
+            ok = file:write(File, Content),
+            file:close(File),
+	    Result = file:rename(NurseryName, Name),
+	    Result;
+        {error, eexist} ->
+	    %% Should not happen, file name should be unique
+            {error, eexist};
+        {error, Error} ->
+            {error, Error}
+    end.
+
+make_dir(Name) ->
+    case file:make_dir(Name) of
+	ok ->
+	    ok;
+	{error, eexist} ->
+	    ok;
+	{error, Error} ->
+	    {error, Error}
+    end.
+
+make_dirs([]) ->
+    ok;
+make_dirs([Name | Rest]) ->
+    case make_dir(Name) of
+	ok ->
+	    make_dirs(Rest);
+	{error, Error} ->
+	    {error, Error}
+    end.
+
+path_for_key(Rootdir, Key) ->
+    Name = hex:bin_to_hexstr(Key),
+    [C1, C2, C3, C4, C5, C6 | _] = Name,
+    Firstlevel = Rootdir ++ [C1, C2],
+    Secondlevel = Firstlevel ++ "/" ++ [C3, C4],
+    Thirdlevel = Secondlevel ++ "/" ++ [C5, C6],
+    Fullpath = Thirdlevel ++ "/" ++ Name,
+    {[Firstlevel, Secondlevel, Thirdlevel], Fullpath}.
+
+tempfilename(Base) ->
+    {MegaSecs, Secs, MicroSecs} = now(),
+    Filename = io_lib:format("~s-~s-~p.~p", [Base, os:getpid(),
+			     MegaSecs * 1000000 + Secs, MicroSecs]),
+    Filename.
+
+ensurefile(Rootdir, Key, Content) ->
+    {Dirs, Path} = path_for_key(Rootdir, Key),
+    case readfile_and_verify(Path, Content) of
+	ok ->
+	    lists:foreach(fun (Dir) -> fsync(Dir) end, [Path, Rootdir | Dirs]);
+	{error, enoent} ->
+            case make_dirs([Rootdir, Rootdir ++ "nursery/"] ++ Dirs) of
+		ok ->
+		    NurseryName = Rootdir ++ "nursery/" ++
+                        tempfilename(hex:bin_to_hexstr(Key)),
+		    _Result = writefile(Path, NurseryName, Content),
+		    lists:foreach(fun (Dir) ->
+                                          fsync(Dir)
+                                  end,
+                                  [Path, Rootdir | Dirs]); %% XXX check results
+		{error, Error} ->
+		    io:format("Error creating directory: ~w~n", [Error])
+	    end;
+	{error, Error} ->
+	    exit({perm, fileerror, "Error reading file", Error})
+    end.