IOCtl.hs

{-# LANGUAGE ForeignFunctionInterface #-}
{- |
Module      : Graphics.V4L2.IOCtl
Maintainer  : claude@mathr.co.uk
Stability   : no
Portability : no

Heavily based on the 'ioctl' package (c) Maciej Piechotka.

-}
module Graphics.V4L2.IOCtl
  ( ioctl
  , ioctl_
  , ioctl'
  , zero
  ) where

import Foreign (Ptr, Storable, alloca, castPtr, peek, sizeOf, with)
import Foreign.C (CInt(..), CSize(..), throwErrnoIfMinus1_)
import System.Posix.IOCtl (IOControl(ioctlReq))
import System.IO.Unsafe (unsafePerformIO)

import Bindings.LibV4L2 (c'v4l2_ioctl)

import Graphics.V4L2.Device (Device)

c_ioctl' :: IOControl req d => Device -> req -> Ptr d -> IO ()
c_ioctl' f req p =
    throwErrnoIfMinus1_ "ioctl" $
        c'v4l2_ioctl (fromIntegral f) (fromIntegral $ ioctlReq req) (castPtr p)

-- | Calls a ioctl reading the structure after the call
ioctl :: IOControl req d
      => Device -- ^ The file descriptor 
      -> req -- ^ The request
      -> d -- ^ The data
      -> IO d -- ^ The data after the call
ioctl f req d = with d $ \p -> c_ioctl' f req p >> peek p

-- | Call a ioctl ignoring the result
ioctl_ :: IOControl req d
       => Device -- ^ The file descriptor
       -> req -- ^ The request
       -> d -- ^ The data
       -> IO ()
ioctl_ f req d = with d $ \p -> c_ioctl' f req p

-- | Call a ioctl with uninitialized data
ioctl' :: IOControl req d
       => Device -- ^ The file descriptor
       -> req -- ^ The request
       -> IO d -- ^ The data
ioctl' f req = alloca $ \p -> c_ioctl' f req p >> peek p

{- |  A value obtained by peeking cleared memory. -}
zero :: Storable a => IO a
zero = alloca $ \p -> c'memset p 0 (fromIntegral $ sizeOf (undefined `asTypeOf` unsafePerformIO (peek p))) >> peek p

foreign import ccall "string.h memset" c'memset :: Ptr a -> CInt -> CSize -> IO (Ptr a)