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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
import AtomicPrint
foreign import ccall "tirclogv_mmap"
c_mmap :: CInt -> Ptr CSize -> IO (Ptr Word8)
-- fd out length
foreign import ccall "tirclogv_munmap"
c_munmap :: Ptr Word8 -> CSize -> IO ()
-- addr length
-- | Returns Nothing if the open(2) fails.
mapFile :: FilePath -> IO (Maybe ByteString)
mapFile path = mask_ $ do
-- if open fails, we simply return Nothing, and nothing has happened yet so that's fine
try @IOException (openFd path ReadOnly defaultFileFlags) >>= \case
Left _ -> return Nothing
Right (Fd fd) -> do
-- do the mmap; if it fails, close the file, ignoring exceptions there
(addr, filelen) <-
onException
(alloca $ \lengthp -> do
addr <- c_mmap fd lengthp
lengthval <- peek lengthp
return (addr, lengthval))
(catch @SomeException (closeFd (Fd fd))
(\_ -> return ()))
-- mmap succeeded, close the file; if closing fails, something is badly wrong, so unmap, and if that throws an exception propagate that
onException
(closeFd (Fd fd))
(do atomicPrintNoWaitS ("[munmap " ++ show addr ++ " as close(2) exception handler]")
c_munmap addr filelen)
-- 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 do bs <- BS.unsafePackCStringFinalizer addr (fromIntegral @CSize @Int filelen)
(do atomicPrintNoWaitS ("[munmap " ++ show addr ++ "]")
c_munmap addr filelen)
atomicPrintNoWaitS ("[mmap " ++ show addr ++ "]")
return (Just bs)
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