[Haskell-cafe] advanced cabal configuration

[Lana Black]

On 21:06 Tue 19 May     , Kazu Yamamoto wrote:
> Hi,
> 
> I'm a maintainer of simple-sendfile and need to implement the
> following is to rescue 32bit Linux:
> 
> - If the COff size is 8, the following FFI is used:
> 
> 	foreign import ccall unsafe "sendfile64"
> 	    c_sendfile :: Fd -> Fd -> Ptr COff -> CSize -> IO (#type ssize_t)
> 
> - Otherwise, the following FFI is used:
> 
> 	foreign import ccall unsafe "sendfile"
> 	    c_sendfile :: Fd -> Fd -> Ptr COff -> CSize -> IO (#type ssize_t)
> 
> How can I implement this?
> 
> I guess that Setup.hs should evaluate (sizeOf (1 :: COff)) and define
> a C macro, say LARGE_OFFSET and write the following code.
> 
>         #ifdef LARGE_OFFSET
> 	foreign import ccall unsafe "sendfile64"
>         #else
> 	foreign import ccall unsafe "sendfile"
>         #endif
> 
> I have no experience to use Build-Type: other than Simple in cabal
> files.  Would someone explain how to implement it concretely or
> suggest examples which implement similar things?
> 
> For more informaion, please read:
> 	https://github.com/yesodweb/wai/issues/372
> 
> Thanks.
> 
> --Kazu
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I believe you could use __USE_FILE_OFFSET64 macro imported from
sys/types.h. I'm not sure if it's present on other than linux/glibc
systems though.