System/Posix/Internals.hs

    {-# LANGUAGE Trustworthy #-}
    {-# LANGUAGE CPP, NoImplicitPrelude, CApiFFI #-}
    {-# OPTIONS_HADDOCK hide #-}

    -----------------------------------------------------------------------------
    -- |
    -- Module      :  System.Posix.Internals
    -- Copyright   :  (c) The University of Glasgow, 1992-2002
    -- License     :  see libraries/base/LICENSE
    --
    -- Maintainer  :  cvs-ghc@haskell.org
    -- Stability   :  internal
    -- Portability :  non-portable (requires POSIX)
    --
    -- POSIX support layer for the standard libraries.
    -- This library is built on *every* platform, including Win32.
    --
    -- Non-posix compliant in order to support the following features:
    --      * S_ISSOCK (no sockets in POSIX)
    --
    -----------------------------------------------------------------------------

    module System.Posix.Internals where

    #include "HsBaseConfig.h"

    import System.Posix.Types

    import Foreign
    import Foreign.C

    -- import Data.Bits
    import Data.Maybe

    #if !defined(HTYPE_TCFLAG_T)
    import System.IO.Error
    #endif

    import GHC.Base
    import GHC.Num
    import GHC.Real
    import GHC.IO
    import GHC.IO.IOMode
    import GHC.IO.Exception
    import GHC.IO.Device
    #ifndef mingw32_HOST_OS
    import {-# SOURCE #-} GHC.IO.Encoding (getFileSystemEncoding)
    import qualified GHC.Foreign as GHC
    #endif

    -- ---------------------------------------------------------------------------
    -- Debugging the base package

    puts :: String -> IO ()
    puts s = withCAStringLen (s ++ "\n") $ \(p, len) -> do
                -- In reality should be withCString, but assume ASCII to avoid loop
                -- if this is called by GHC.Foreign
               _ <- c_write 1 (castPtr p) (fromIntegral len)
               return ()

    -- ---------------------------------------------------------------------------
    -- Types

    data {-# CTYPE "struct flock" #-} CFLock
    data {-# CTYPE "struct group" #-} CGroup
    data {-# CTYPE "struct lconv" #-} CLconv
    data {-# CTYPE "struct passwd" #-} CPasswd
    data {-# CTYPE "struct sigaction" #-} CSigaction
    data {-# CTYPE "sigset_t" #-} CSigset
    data {-# CTYPE "struct stat" #-}  CStat
    data {-# CTYPE "struct termios" #-} CTermios
    data {-# CTYPE "struct tm" #-} CTm
    data {-# CTYPE "struct tms" #-} CTms
    data {-# CTYPE "struct utimbuf" #-} CUtimbuf
    data {-# CTYPE "struct utsname" #-} CUtsname

    type FD = CInt

    -- ---------------------------------------------------------------------------
    -- stat()-related stuff

    fdFileSize :: FD -> IO Integer
    fdFileSize fd =
      allocaBytes sizeof_stat $ \ p_stat -> do
        throwErrnoIfMinus1Retry_ "fileSize" $
            c_fstat fd p_stat
        c_mode <- st_mode p_stat :: IO CMode
        if not (s_isreg c_mode)
            then return (-1)
            else do
          c_size <- st_size p_stat
          return (fromIntegral c_size)

    fileType :: FilePath -> IO IODeviceType
    fileType file =
      allocaBytes sizeof_stat $ \ p_stat -> do
      withFilePath file $ \p_file -> do
        throwErrnoIfMinus1Retry_ "fileType" $
          c_stat p_file p_stat
        statGetType p_stat

    -- NOTE: On Win32 platforms, this will only work with file descriptors
    -- referring to file handles. i.e., it'll fail for socket FDs.
    fdStat :: FD -> IO (IODeviceType, CDev, CIno)
    fdStat fd =
      allocaBytes sizeof_stat $ \ p_stat -> do
        throwErrnoIfMinus1Retry_ "fdType" $
            c_fstat fd p_stat
        ty <- statGetType p_stat
        dev <- st_dev p_stat
        ino <- st_ino p_stat
        return (ty,dev,ino)

    fdType :: FD -> IO IODeviceType
    fdType fd = do (ty,_,_) <- fdStat fd; return ty

    statGetType :: Ptr CStat -> IO IODeviceType
    statGetType p_stat = do
      c_mode <- st_mode p_stat :: IO CMode
      case () of
          _ | s_isdir c_mode        -> return Directory
            | s_isfifo c_mode || s_issock c_mode || s_ischr  c_mode
                                    -> return Stream
            | s_isreg c_mode        -> return RegularFile
             -- Q: map char devices to RawDevice too?
            | s_isblk c_mode        -> return RawDevice
            | otherwise             -> ioError ioe_unknownfiletype

    ioe_unknownfiletype :: IOException
    ioe_unknownfiletype = IOError Nothing UnsupportedOperation "fdType"
                            "unknown file type"
                            Nothing
                            Nothing

    fdGetMode :: FD -> IO IOMode
    #if defined(mingw32_HOST_OS)
    fdGetMode _ = do
        -- We don't have a way of finding out which flags are set on FDs
        -- on Windows, so make a handle that thinks that anything goes.
        let flags = o_RDWR
    #else
    fdGetMode fd = do
        flags <- throwErrnoIfMinus1Retry "fdGetMode"
                    (c_fcntl_read fd const_f_getfl)
    #endif
        let
           wH  = (flags .&. o_WRONLY) /= 0
           aH  = (flags .&. o_APPEND) /= 0
           rwH = (flags .&. o_RDWR) /= 0

           mode
             | wH && aH  = AppendMode
             | wH        = WriteMode
             | rwH       = ReadWriteMode
             | otherwise = ReadMode

        return mode

    #ifdef mingw32_HOST_OS
    withFilePath :: FilePath -> (CWString -> IO a) -> IO a
    withFilePath = withCWString

    newFilePath :: FilePath -> IO CWString
    newFilePath = newCWString

    peekFilePath :: CWString -> IO FilePath
    peekFilePath = peekCWString
    #else

    withFilePath :: FilePath -> (CString -> IO a) -> IO a
    newFilePath :: FilePath -> IO CString
    peekFilePath :: CString -> IO FilePath
    peekFilePathLen :: CStringLen -> IO FilePath

    withFilePath fp f = getFileSystemEncoding >>= \enc -> GHC.withCString enc fp f
    newFilePath fp = getFileSystemEncoding >>= \enc -> GHC.newCString enc fp
    peekFilePath fp = getFileSystemEncoding >>= \enc -> GHC.peekCString enc fp
    peekFilePathLen fp = getFileSystemEncoding >>= \enc -> GHC.peekCStringLen enc fp

    #endif

    -- ---------------------------------------------------------------------------
    -- Terminal-related stuff

    #if defined(HTYPE_TCFLAG_T)

    setEcho :: FD -> Bool -> IO ()
    setEcho fd on = do
      tcSetAttr fd $ \ p_tios -> do
        lflag <- c_lflag p_tios :: IO CTcflag
        let new_lflag
             | on        = lflag .|. fromIntegral const_echo
             | otherwise = lflag .&. complement (fromIntegral const_echo)
        poke_c_lflag p_tios (new_lflag :: CTcflag)

    getEcho :: FD -> IO Bool
    getEcho fd = do
      tcSetAttr fd $ \ p_tios -> do
        lflag <- c_lflag p_tios :: IO CTcflag
        return ((lflag .&. fromIntegral const_echo) /= 0)

    setCooked :: FD -> Bool -> IO ()
    setCooked fd cooked =
      tcSetAttr fd $ \ p_tios -> do

        -- turn on/off ICANON
        lflag <- c_lflag p_tios :: IO CTcflag
        let new_lflag | cooked    = lflag .|. (fromIntegral const_icanon)
                      | otherwise = lflag .&. complement (fromIntegral const_icanon)
        poke_c_lflag p_tios (new_lflag :: CTcflag)

        -- set VMIN & VTIME to 1/0 respectively
        when (not cooked) $ do
                c_cc <- ptr_c_cc p_tios
                let vmin  = (c_cc `plusPtr` (fromIntegral const_vmin))  :: Ptr Word8
                    vtime = (c_cc `plusPtr` (fromIntegral const_vtime)) :: Ptr Word8
                poke vmin  1
                poke vtime 0

    tcSetAttr :: FD -> (Ptr CTermios -> IO a) -> IO a
    tcSetAttr fd fun = do
         allocaBytes sizeof_termios  $ \p_tios -> do
            throwErrnoIfMinus1Retry_ "tcSetAttr"
               (c_tcgetattr fd p_tios)

            -- Save a copy of termios, if this is a standard file descriptor.
            -- These terminal settings are restored in hs_exit().
            when (fd <= 2) $ do
              p <- get_saved_termios fd
              when (p == nullPtr) $ do
                 saved_tios <- mallocBytes sizeof_termios
                 copyBytes saved_tios p_tios sizeof_termios
                 set_saved_termios fd saved_tios

            -- tcsetattr() when invoked by a background process causes the process
            -- to be sent SIGTTOU regardless of whether the process has TOSTOP set
            -- in its terminal flags (try it...).  This function provides a
            -- wrapper which temporarily blocks SIGTTOU around the call, making it
            -- transparent.
            allocaBytes sizeof_sigset_t $ \ p_sigset -> do
              allocaBytes sizeof_sigset_t $ \ p_old_sigset -> do
                 throwErrnoIfMinus1_ "sigemptyset" $
                     c_sigemptyset p_sigset
                 throwErrnoIfMinus1_ "sigaddset" $
                     c_sigaddset   p_sigset const_sigttou
                 throwErrnoIfMinus1_ "sigprocmask" $
                     c_sigprocmask const_sig_block p_sigset p_old_sigset
                 r <- fun p_tios  -- do the business
                 throwErrnoIfMinus1Retry_ "tcSetAttr" $
                     c_tcsetattr fd const_tcsanow p_tios
                 throwErrnoIfMinus1_ "sigprocmask" $
                     c_sigprocmask const_sig_setmask p_old_sigset nullPtr
                 return r

    foreign import ccall unsafe "HsBase.h __hscore_get_saved_termios"
       get_saved_termios :: CInt -> IO (Ptr CTermios)

    foreign import ccall unsafe "HsBase.h __hscore_set_saved_termios"
       set_saved_termios :: CInt -> (Ptr CTermios) -> IO ()

    #else

    -- 'raw' mode for Win32 means turn off 'line input' (=> buffering and
    -- character translation for the console.) The Win32 API for doing
    -- this is GetConsoleMode(), which also requires echoing to be disabled
    -- when turning off 'line input' processing. Notice that turning off
    -- 'line input' implies enter/return is reported as '\r' (and it won't
    -- report that character until another character is input..odd.) This
    -- latter feature doesn't sit too well with IO actions like IO.hGetLine..
    -- consider yourself warned.
    setCooked :: FD -> Bool -> IO ()
    setCooked fd cooked = do
      x <- set_console_buffering fd (if cooked then 1 else 0)
      if (x /= 0)
       then ioError (ioe_unk_error "setCooked" "failed to set buffering")
       else return ()

    ioe_unk_error :: String -> String -> IOException
    ioe_unk_error loc msg
     = ioeSetErrorString (mkIOError OtherError loc Nothing Nothing) msg

    -- Note: echoing goes hand in hand with enabling 'line input' / raw-ness
    -- for Win32 consoles, hence setEcho ends up being the inverse of setCooked.
    setEcho :: FD -> Bool -> IO ()
    setEcho fd on = do
      x <- set_console_echo fd (if on then 1 else 0)
      if (x /= 0)
       then ioError (ioe_unk_error "setEcho" "failed to set echoing")
       else return ()

    getEcho :: FD -> IO Bool
    getEcho fd = do
      r <- get_console_echo fd
      if (r == (-1))
       then ioError (ioe_unk_error "getEcho" "failed to get echoing")
       else return (r == 1)

    foreign import ccall unsafe "consUtils.h set_console_buffering__"
       set_console_buffering :: CInt -> CInt -> IO CInt

    foreign import ccall unsafe "consUtils.h set_console_echo__"
       set_console_echo :: CInt -> CInt -> IO CInt

    foreign import ccall unsafe "consUtils.h get_console_echo__"
       get_console_echo :: CInt -> IO CInt

    foreign import ccall unsafe "consUtils.h is_console__"
       is_console :: CInt -> IO CInt

    #endif

    -- ---------------------------------------------------------------------------
    -- Turning on non-blocking for a file descriptor

    setNonBlockingFD :: FD -> Bool -> IO ()
    #if !defined(mingw32_HOST_OS)
    setNonBlockingFD fd set = do
      flags <- throwErrnoIfMinus1Retry "setNonBlockingFD"
                     (c_fcntl_read fd const_f_getfl)
      let flags' | set       = flags .|. o_NONBLOCK
                 | otherwise = flags .&. complement o_NONBLOCK
      when (flags /= flags') $ do
        -- An error when setting O_NONBLOCK isn't fatal: on some systems
        -- there are certain file handles on which this will fail (eg. /dev/null
        -- on FreeBSD) so we throw away the return code from fcntl_write.
        _ <- c_fcntl_write fd const_f_setfl (fromIntegral flags')
        return ()
    #else

    -- bogus defns for win32
    setNonBlockingFD _ _ = return ()

    #endif

    -- -----------------------------------------------------------------------------
    -- Set close-on-exec for a file descriptor

    #if !defined(mingw32_HOST_OS)
    setCloseOnExec :: FD -> IO ()
    setCloseOnExec fd = do
      throwErrnoIfMinus1_ "setCloseOnExec" $
        c_fcntl_write fd const_f_setfd const_fd_cloexec
    #endif

    -- -----------------------------------------------------------------------------
    -- foreign imports

    #if !defined(mingw32_HOST_OS)
    type CFilePath = CString
    #else
    type CFilePath = CWString
    #endif

    foreign import ccall unsafe "HsBase.h __hscore_open"
       c_open :: CFilePath -> CInt -> CMode -> IO CInt

    foreign import ccall safe "HsBase.h __hscore_open"
       c_safe_open :: CFilePath -> CInt -> CMode -> IO CInt

    foreign import ccall unsafe "HsBase.h __hscore_fstat"
       c_fstat :: CInt -> Ptr CStat -> IO CInt

    foreign import ccall unsafe "HsBase.h __hscore_lstat"
       lstat :: CFilePath -> Ptr CStat -> IO CInt

    {- Note: Win32 POSIX functions
    Functions that are not part of the POSIX standards were
    at some point deprecated by Microsoft. This deprecation
    was performed by renaming the functions according to the
    C++ ABI Section 17.6.4.3.2b. This was done to free up the
    namespace of normal Windows programs since Windows isn't
    POSIX compliant anyway.

    These were working before since the RTS was re-exporting
    these symbols under the undeprecated names. This is no longer
    being done. See #11223

    See https://msdn.microsoft.com/en-us/library/ms235384.aspx
    for more.

    However since we can't hope to get people to support Windows
    packages we should support the deprecated names. See #12497
    -}
    foreign import capi unsafe "unistd.h lseek"
       c_lseek :: CInt -> COff -> CInt -> IO COff

    foreign import ccall unsafe "HsBase.h access"
       c_access :: CString -> CInt -> IO CInt

    foreign import ccall unsafe "HsBase.h chmod"
       c_chmod :: CString -> CMode -> IO CInt

    foreign import ccall unsafe "HsBase.h close"
       c_close :: CInt -> IO CInt

    foreign import ccall unsafe "HsBase.h creat"
       c_creat :: CString -> CMode -> IO CInt

    foreign import ccall unsafe "HsBase.h dup"
       c_dup :: CInt -> IO CInt

    foreign import ccall unsafe "HsBase.h dup2"
       c_dup2 :: CInt -> CInt -> IO CInt

    foreign import ccall unsafe "HsBase.h isatty"
       c_isatty :: CInt -> IO CInt

    #if defined(mingw32_HOST_OS)
    -- See Note: Windows types
    foreign import capi unsafe "HsBase.h _read"
       c_read :: CInt -> Ptr Word8 -> CUInt -> IO CInt

    -- See Note: Windows types
    foreign import capi safe "HsBase.h _read"
       c_safe_read :: CInt -> Ptr Word8 -> CUInt -> IO CInt

    foreign import ccall unsafe "HsBase.h _umask"
       c_umask :: CMode -> IO CMode

    -- See Note: Windows types
    foreign import capi unsafe "HsBase.h _write"
       c_write :: CInt -> Ptr Word8 -> CUInt -> IO CInt

    -- See Note: Windows types
    foreign import capi safe "HsBase.h _write"
       c_safe_write :: CInt -> Ptr Word8 -> CUInt -> IO CInt

    foreign import ccall unsafe "HsBase.h _pipe"
       c_pipe :: Ptr CInt -> IO CInt
    #else
    -- We use CAPI as on some OSs (eg. Linux) this is wrapped by a macro
    -- which redirects to the 64-bit-off_t versions when large file
    -- support is enabled.

    -- See Note: Windows types
    foreign import capi unsafe "HsBase.h read"
       c_read :: CInt -> Ptr Word8 -> CSize -> IO CSsize

    -- See Note: Windows types
    foreign import capi safe "HsBase.h read"
       c_safe_read :: CInt -> Ptr Word8 -> CSize -> IO CSsize

    foreign import ccall unsafe "HsBase.h umask"
       c_umask :: CMode -> IO CMode

    -- See Note: Windows types
    foreign import capi unsafe "HsBase.h write"
       c_write :: CInt -> Ptr Word8 -> CSize -> IO CSsize

    -- See Note: Windows types
    foreign import capi safe "HsBase.h write"
       c_safe_write :: CInt -> Ptr Word8 -> CSize -> IO CSsize

    foreign import ccall unsafe "HsBase.h pipe"
       c_pipe :: Ptr CInt -> IO CInt
    #endif

    foreign import ccall unsafe "HsBase.h unlink"
       c_unlink :: CString -> IO CInt

    foreign import capi unsafe "HsBase.h utime"
       c_utime :: CString -> Ptr CUtimbuf -> IO CInt

    foreign import ccall unsafe "HsBase.h getpid"
       c_getpid :: IO CPid

    foreign import ccall unsafe "HsBase.h __hscore_stat"
       c_stat :: CFilePath -> Ptr CStat -> IO CInt

    foreign import ccall unsafe "HsBase.h __hscore_ftruncate"
       c_ftruncate :: CInt -> COff -> IO CInt

    #if !defined(mingw32_HOST_OS)
    foreign import capi unsafe "HsBase.h fcntl"
       c_fcntl_read  :: CInt -> CInt -> IO CInt

    foreign import capi unsafe "HsBase.h fcntl"
       c_fcntl_write :: CInt -> CInt -> CLong -> IO CInt

    foreign import capi unsafe "HsBase.h fcntl"
       c_fcntl_lock  :: CInt -> CInt -> Ptr CFLock -> IO CInt

    foreign import ccall unsafe "HsBase.h fork"
       c_fork :: IO CPid

    foreign import ccall unsafe "HsBase.h link"
       c_link :: CString -> CString -> IO CInt

    -- capi is required at least on Android
    foreign import capi unsafe "HsBase.h mkfifo"
       c_mkfifo :: CString -> CMode -> IO CInt

    foreign import capi unsafe "signal.h sigemptyset"
       c_sigemptyset :: Ptr CSigset -> IO CInt

    foreign import capi unsafe "signal.h sigaddset"
       c_sigaddset :: Ptr CSigset -> CInt -> IO CInt

    foreign import capi unsafe "signal.h sigprocmask"
       c_sigprocmask :: CInt -> Ptr CSigset -> Ptr CSigset -> IO CInt

    -- capi is required at least on Android
    foreign import capi unsafe "HsBase.h tcgetattr"
       c_tcgetattr :: CInt -> Ptr CTermios -> IO CInt

    -- capi is required at least on Android
    foreign import capi unsafe "HsBase.h tcsetattr"
       c_tcsetattr :: CInt -> CInt -> Ptr CTermios -> IO CInt

    foreign import ccall unsafe "HsBase.h waitpid"
       c_waitpid :: CPid -> Ptr CInt -> CInt -> IO CPid
    #endif

    -- POSIX flags only:
    foreign import ccall unsafe "HsBase.h __hscore_o_rdonly" o_RDONLY :: CInt
    foreign import ccall unsafe "HsBase.h __hscore_o_wronly" o_WRONLY :: CInt
    foreign import ccall unsafe "HsBase.h __hscore_o_rdwr"   o_RDWR   :: CInt
    foreign import ccall unsafe "HsBase.h __hscore_o_append" o_APPEND :: CInt
    foreign import ccall unsafe "HsBase.h __hscore_o_creat"  o_CREAT  :: CInt
    foreign import ccall unsafe "HsBase.h __hscore_o_excl"   o_EXCL   :: CInt
    foreign import ccall unsafe "HsBase.h __hscore_o_trunc"  o_TRUNC  :: CInt

    -- non-POSIX flags.
    foreign import ccall unsafe "HsBase.h __hscore_o_noctty"   o_NOCTTY   :: CInt
    foreign import ccall unsafe "HsBase.h __hscore_o_nonblock" o_NONBLOCK :: CInt
    foreign import ccall unsafe "HsBase.h __hscore_o_binary"   o_BINARY   :: CInt

    foreign import capi unsafe "sys/stat.h S_ISREG"  c_s_isreg  :: CMode -> CInt
    foreign import capi unsafe "sys/stat.h S_ISCHR"  c_s_ischr  :: CMode -> CInt
    foreign import capi unsafe "sys/stat.h S_ISBLK"  c_s_isblk  :: CMode -> CInt
    foreign import capi unsafe "sys/stat.h S_ISDIR"  c_s_isdir  :: CMode -> CInt
    foreign import capi unsafe "sys/stat.h S_ISFIFO" c_s_isfifo :: CMode -> CInt

    s_isreg  :: CMode -> Bool
    s_isreg cm = c_s_isreg cm /= 0
    s_ischr  :: CMode -> Bool
    s_ischr cm = c_s_ischr cm /= 0
    s_isblk  :: CMode -> Bool
    s_isblk cm = c_s_isblk cm /= 0
    s_isdir  :: CMode -> Bool
    s_isdir cm = c_s_isdir cm /= 0
    s_isfifo :: CMode -> Bool
    s_isfifo cm = c_s_isfifo cm /= 0

    foreign import ccall unsafe "HsBase.h __hscore_sizeof_stat" sizeof_stat :: Int
    foreign import ccall unsafe "HsBase.h __hscore_st_mtime" st_mtime :: Ptr CStat -> IO CTime
    #ifdef mingw32_HOST_OS
    foreign import ccall unsafe "HsBase.h __hscore_st_size" st_size :: Ptr CStat -> IO Int64
    #else
    foreign import ccall unsafe "HsBase.h __hscore_st_size" st_size :: Ptr CStat -> IO COff
    #endif
    foreign import ccall unsafe "HsBase.h __hscore_st_mode" st_mode :: Ptr CStat -> IO CMode
    foreign import ccall unsafe "HsBase.h __hscore_st_dev" st_dev :: Ptr CStat -> IO CDev
    foreign import ccall unsafe "HsBase.h __hscore_st_ino" st_ino :: Ptr CStat -> IO CIno

    foreign import ccall unsafe "HsBase.h __hscore_echo"         const_echo :: CInt
    foreign import ccall unsafe "HsBase.h __hscore_tcsanow"      const_tcsanow :: CInt
    foreign import ccall unsafe "HsBase.h __hscore_icanon"       const_icanon :: CInt
    foreign import ccall unsafe "HsBase.h __hscore_vmin"         const_vmin   :: CInt
    foreign import ccall unsafe "HsBase.h __hscore_vtime"        const_vtime  :: CInt
    foreign import ccall unsafe "HsBase.h __hscore_sigttou"      const_sigttou :: CInt
    foreign import ccall unsafe "HsBase.h __hscore_sig_block"    const_sig_block :: CInt
    foreign import ccall unsafe "HsBase.h __hscore_sig_setmask"  const_sig_setmask :: CInt
    foreign import ccall unsafe "HsBase.h __hscore_f_getfl"      const_f_getfl :: CInt
    foreign import ccall unsafe "HsBase.h __hscore_f_setfl"      const_f_setfl :: CInt
    foreign import ccall unsafe "HsBase.h __hscore_f_setfd"      const_f_setfd :: CInt
    foreign import ccall unsafe "HsBase.h __hscore_fd_cloexec"   const_fd_cloexec :: CLong

    #if defined(HTYPE_TCFLAG_T)
    foreign import ccall unsafe "HsBase.h __hscore_sizeof_termios"  sizeof_termios :: Int
    foreign import ccall unsafe "HsBase.h __hscore_sizeof_sigset_t" sizeof_sigset_t :: Int

    foreign import ccall unsafe "HsBase.h __hscore_lflag" c_lflag :: Ptr CTermios -> IO CTcflag
    foreign import ccall unsafe "HsBase.h __hscore_poke_lflag" poke_c_lflag :: Ptr CTermios -> CTcflag -> IO ()
    foreign import ccall unsafe "HsBase.h __hscore_ptr_c_cc" ptr_c_cc  :: Ptr CTermios -> IO (Ptr Word8)
    #endif

    s_issock :: CMode -> Bool
    #if !defined(mingw32_HOST_OS)
    s_issock cmode = c_s_issock cmode /= 0
    foreign import capi unsafe "sys/stat.h S_ISSOCK" c_s_issock :: CMode -> CInt
    #else
    s_issock _ = False
    #endif

    foreign import ccall unsafe "__hscore_bufsiz"  dEFAULT_BUFFER_SIZE :: Int
    foreign import capi  unsafe "stdio.h value SEEK_CUR" sEEK_CUR :: CInt
    foreign import capi  unsafe "stdio.h value SEEK_SET" sEEK_SET :: CInt
    foreign import capi  unsafe "stdio.h value SEEK_END" sEEK_END :: CInt

    {-
    Note: Windows types

    Windows' _read and _write have types that differ from POSIX. They take an
    unsigned int for lengh and return a signed int where POSIX uses size_t and
    ssize_t. Those are different on x86_64 and equivalent on x86. We import them
    with the types in Microsoft's documentation which means that c_read,
    c_safe_read, c_write and c_safe_write have different Haskell types depending on
    the OS.
    -}