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{-# LANGUAGE ForeignFunctionInterface #-}
module Mmap where
import Control.Exception
import Data.ByteString (ByteString)
import qualified Data.ByteString.Unsafe as BS
import Foreign
import Foreign.C.Types
import System.Posix.IO
import System.Posix.Types
foreign import ccall "ircbrowse_mmap"
c_mmap :: CInt -> Ptr CSize -> IO (Ptr Word8)
-- fd out length
foreign import ccall "ircbrowse_munmap"
c_munmap :: Ptr Word8 -> CSize -> IO ()
-- addr length
mapFile :: FilePath -> IO ByteString
mapFile path = mask_ $ do
-- open can fail without repercussions
Fd fd <- openFd path ReadOnly defaultFileFlags
-- do the mmap; if it fails, close the file, ignoring exceptions there
(addr, filelen) <-
catchNoPropagate @SomeException
(alloca $ \lengthp -> do
addr <- c_mmap fd lengthp
lengthval <- peek lengthp
return (addr, lengthval))
(\e -> do
catch @SomeException (closeFd (Fd fd))
(\_ -> return ())
rethrowIO e)
-- mmap succeeded, close the file
catchNoPropagate @SomeException (closeFd (Fd fd))
(\e -> do
-- putStrLn ("[munmap " ++ show addr ++ " as close(2) handler]")
c_munmap addr filelen
rethrowIO e)
-- close succeeded, we're safe now since bytestring construction will not
-- fail (and no exceptions are coming from outside as we're masked)
if addr == nullPtr
then fail "mapFile: could not mmap"
else BS.unsafePackCStringFinalizer addr (fromIntegral @CSize @Int filelen)
(do -- putStrLn ("[munmap " ++ show addr ++ "]")
c_munmap addr filelen)
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