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diff --git a/src/System/Torrent/Storage.hs b/src/System/Torrent/Storage.hs
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+-- |
+--   Copyright   :  (c) Sam T. 2013
+--   License     :  MIT
+--   Maintainer  :  pxqr.sta@gmail.com
+--   Stability   :  experimental
+--   Portability :  non-portable
+--
+--   This module implements mapping from single continious block space
+--   to file storage. Storage can be used in two modes:
+--
+--     * As in memory storage - in this case we don't touch filesystem.
+--
+--     * As ordinary mmaped file storage - when we need to store
+--       data in the filesystem.
+--
+--
+{-# LANGUAGE DoAndIfThenElse #-}
+{-# LANGUAGE NamedFieldPuns  #-}
+{-# LANGUAGE RecordWildCards #-}
+module Cobit.Storage
+       ( Storage
+
+         -- * Construction
+       , mapStorage, unmapStorage, withStorage
+
+         -- * Modification
+       , getBlk, putBlk
+       ) where
+
+import Control.Applicative
+import Control.Exception
+import Control.Monad
+import Data.ByteString as B
+import qualified Data.ByteString.Lazy as Lazy
+import Data.List as L
+import System.FilePath
+import System.Directory
+
+import Data.Torrent
+import Network.BitTorrent
+import System.IO.MMap.Fixed
+
+
+data Storage = Storage {
+    session :: SwarmSession
+
+    -- | Used to map linear block addresses to disjoint mallocated/mmaped adresses.
+  , stPayload :: Fixed
+
+    -- | Used to find out block offsets.
+  , stPieceSize :: Int
+
+    -- | Used to verify pieces and set finally mark piece as verified.
+  , stHashes :: ByteString
+  }
+
+-- TODO doc args
+mapStorage :: Int -> Maybe FilePath -> FilePath -> ContentInfo -> IO Storage
+mapStorage blkSize statusPath contentPath ci = do
+  let content_paths = contentLayout contentPath ci
+  mapM_ mkDir (L.map fst content_paths)
+  Storage <$> coalesceFiles content_paths
+          <*> getAllocator statusPath (pieceCount ci) (blockCount blkSize ci)
+          <*> pure (ciPieceLength ci)
+          <*> pure (ciPieces ci)
+  where
+    getAllocator (Just path) = error "getAllocator"
+    getAllocator Nothing     = error "getAllocator"
+
+    mkDir path = do
+      let dirPath = fst (splitFileName path)
+      exist <- doesDirectoryExist dirPath
+      unless exist $ do
+        createDirectoryIfMissing True dirPath
+
+unmapStorage :: Storage -> IO ()
+unmapStorage st = error "unmapStorage"
+
+
+withStorage :: Int -> Maybe FilePath -> FilePath -> ContentInfo
+            -> (Storage -> IO a)
+            -> IO a
+withStorage blkSize statusPath contentPath t =
+  bracket (mapStorage blkSize statusPath contentPath t) unmapStorage
+
+isAvailable :: BlockIx -> Storage -> IO Bool
+isAvailable ix Storage {..} = error "isAvailable"
+
+
+putBlk :: Block -> Storage -> IO ()
+putBlk blk @ Block {..}  st @ Storage {..} = do
+  available <- isAvailable (blockIx blk) st
+  unless available $
+    writeBytes (blkInterval stPieceSize blk) (Lazy.fromChunks [blkData]) stPayload
+
+-- TODO
+getBlk :: BlockIx -> Storage -> IO (Maybe Block)
+getBlk ix @ BlockIx {..}  st @ Storage {..} = do
+    available <- isAvailable ix st
+    if available
+      then Just <$> do
+        bs <- readBytes (ixInterval stPieceSize ix) stPayload
+        return $ Block ixPiece ixOffset (Lazy.toStrict bs)
+      else return Nothing
+
+ixInterval :: Int -> BlockIx -> FixedInterval
+ixInterval pieceSize BlockIx {..} =
+  interval (ixPiece * pieceSize + ixOffset) ixLength
+
+blkInterval :: Int -> Block -> FixedInterval
+blkInterval pieceSize Block {..} =
+  interval (blkPiece * pieceSize + blkOffset) (B.length blkData)
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