使用GNU / Linux系统调用`splice`在Haskell中进行零拷贝Socket到Socket数据传输

时间:2012-04-09 22:26:25

标签: linux sockets haskell network-programming splice

更新:Nemo先生的回答有助于解决问题!下面的代码包含修复程序!请参阅下面的nb Falsenb True来电。

还有一个名为splice 的新Haskell软件包(它具有最具名的套接字数据传输循环的特定于操作系统和可移植的实现)

我有以下(Haskell)代码:

#ifdef LINUX_SPLICE
#include <fcntl.h>
{-# LANGUAGE CPP #-}
{-# LANGUAGE ForeignFunctionInterface #-}
#endif

module Network.Socket.Splice (
    Length
  , zeroCopy
  , splice
#ifdef LINUX_SPLICE
  , c_splice
#endif
  ) where

import Data.Word
import Foreign.Ptr

import Network.Socket
import Control.Monad
import Control.Exception
import System.Posix.Types
import System.Posix.IO

#ifdef LINUX_SPLICE
import Data.Int
import Data.Bits
import Unsafe.Coerce
import Foreign.C.Types
import Foreign.C.Error
import System.Posix.Internals
#else
import System.IO
import Foreign.Marshal.Alloc
#endif


zeroCopy :: Bool
zeroCopy =
#ifdef LINUX_SPLICE
  True
#else
  False
#endif


type Length =
#ifdef LINUX_SPLICE
  (#type size_t)
#else
  Int
#endif


-- | The 'splice' function pipes data from
--   one socket to another in a loop.
--   On Linux this happens in kernel space with
--   zero copying between kernel and user spaces.
--   On other operating systems, a portable
--   implementation utilizes a user space buffer
--   allocated with 'mallocBytes'; 'hGetBufSome'
--   and 'hPut' are then used to avoid repeated 
--   tiny allocations as would happen with 'recv'
--   'sendAll' calls from the 'bytestring' package.
splice :: Length -> Socket -> Socket -> IO ()
splice l (MkSocket x _ _ _ _) (MkSocket y _ _ _ _) = do

  let e  = error "splice ended"

#ifdef LINUX_SPLICE

  (r,w) <- createPipe
  print ('+',r,w)
  let s  = Fd x -- source
  let t  = Fd y -- target
  let c  = throwErrnoIfMinus1 "Network.Socket.Splice.splice"
  let u  = unsafeCoerce :: (#type ssize_t) -> (#type size_t)
  let fs = sPLICE_F_MOVE .|. sPLICE_F_MORE
  let nb v = do setNonBlockingFD x v
                setNonBlockingFD y v
  nb False
  finally
    (forever $ do 
       b <- c $ c_splice s nullPtr w nullPtr    l  fs
       if b > 0
         then   c_splice r nullPtr t nullPtr (u b) fs)
         else   e
    (do closeFd r
        closeFd w
        nb True
        print ('-',r,w))

#else

  -- ..    

#endif


#ifdef LINUX_SPLICE
-- SPLICE

-- fcntl.h
-- ssize_t splice(
--   int          fd_in,
--   loff_t*      off_in,
--   int          fd_out,
--   loff_t*      off_out,
--   size_t       len,
--   unsigned int flags
-- );

foreign import ccall "splice"
  c_splice
  :: Fd
  -> Ptr (#type loff_t)
  -> Fd
  -> Ptr (#type loff_t)
  -> (#type size_t)
  -> Word
  -> IO (#type ssize_t)

sPLICE_F_MOVE :: Word
sPLICE_F_MOVE = (#const "SPLICE_F_MOVE")

sPLICE_F_MORE :: Word
sPLICE_F_MORE = (#const "SPLICE_F_MORE")
#endif

注意: 现在上面的代码正常工作!由于Nemo,以下代码不再有效!

我使用两个打开且已连接的套接字(已使用套接字API splicesend调用已经用于传输最少数量的握手数据)来调用上面定义的recv处理并与hGetLinehPut)一起使用,我一直得到:

Network.Socket.Splice.splice: resource exhausted (Resource temporarily unavailable)

在第一个c_splice呼叫网站上:c_splice返回-1并将一些errno设置为读取EAGAIN的值(可能为resource exhausted | resource temporarily unavailable)当抬起头来。

我测试了使用不同splice值调用Length10248192

2 个答案:

答案 0 :(得分:12)

我不知道Haskell,但“资源暂时不可用”是EAGAIN

默认情况下它看起来像Haskell sets its sockets to non-blocking mode。因此,如果您在没有数据时尝试从一个读取数据,或者在缓冲区已满时尝试写入一个数据,那么您将失败并使用EAGAIN

弄清楚如何将套接字更改为阻止模式,我打赌你会解决你的问题。

[更新]

或者,在尝试读取或写入套接字之前,请调用selectpoll。但是你仍然需要处理EAGAIN,因为有一些罕见的极端情况,其中Linux select将指示套接字已准备就绪,而实际上并非如此。

答案 1 :(得分:0)

sendfile()系统调用对你有用吗?如果是这样,您可以使用sendfile package