%% Copyright (c) 2011-2015, Michael Santos <michael.santos@gmail.com>
%% All rights reserved.
%%
%% Redistribution and use in source and binary forms, with or without
%% modification, are permitted provided that the following conditions
%% are met:
%%
%% Redistributions of source code must retain the above copyright
%% notice, this list of conditions and the following disclaimer.
%%
%% Redistributions in binary form must reproduce the above copyright
%% notice, this list of conditions and the following disclaimer in the
%% documentation and/or other materials provided with the distribution.
%%
%% Neither the name of the author nor the names of its contributors
%% may be used to endorse or promote products derived from this software
%% without specific prior written permission.
%%
%% THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
%% "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
%% LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
%% FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
%% COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
%% INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
%% BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
%% LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
%% CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
%% LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
%% ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
%% POSSIBILITY OF SUCH DAMAGE.
-module(procket_ioctl).

-export([
        in/0, out/0, void/0,
        in/1, out/1, void/1,
        ioc/4,
        io/2, ior/3,
        iow/3, iowr/3
    ]).


%%
%% Calculate the values of the ioctl request macros at runtime.
%%

%% On BSD systems, the top 3 bits indicate the direction of the request:
%%
%%     8 : ioctl parameter will be copied from user space into the kernel
%%     4 : ioctl parameter will be copied into the user supplied buffer from
%%         the kernel
%%     2 : no parameters are used
%%
%% The remaining 13 bits are used to indicate the size of the parameter.
%%
%% On Linux systems, only the top 2 bits are used. Setting both bits to 0
%% indicates a void parameter. The meaning of the bits is reversed:
%%
%%     8 : ioctl parameter will be copied into the user supplied buffer from
%%         the kernel
%%     4 : ioctl parameter will be copied from user space into the kernel
%%
%% The remaining 14 bits is used to hold the length of the parameter.
%%
%% BSD: <<IN:1, OUT:1, VOID:1, Length:13, Group:8, Command:8>>
%%
%% _IOC_OUT = 0x40000000
%% _IOC_IN  = 0x80000000
%%
%% #define _IOR(g,n,t) _IOC(IOC_OUT, (g), (n), sizeof(t))
%% #define _IOW(g,n,t) _IOC(IOC_IN, (g), (n), sizeof(t))
%%
%% Linux: <<OUT:1, IN:1, Length:14, Group:8, Command:8>>
%%
%% _IOC_OUT = 0x80000000
%% _IOC_IN  = 0x40000000
%%
%% #define _IOR(g,n,t) _IOC(_IOC_READ,(g),(n),(t))
%% #define _IOW(g,n,t) _IOC(_IOC_WRITE,(g),(n),(t))
%%

%% BSD: _IOC_IN
%% Linux: _IOC_WRITE << _IOC_DIRSHIFT (16)
in() -> in(os()).
in(bsd) -> 16#80000000;
in(linux) -> 16#40000000.

%% BSD: _IOC_OUT
%% Linux: _IOC_READ << _IOC_DIRSHIFT (16)
out() -> out(os()).
out(bsd) -> 16#40000000;
out(linux) -> 16#80000000.

%% BSD: _IOC_VOID
%% Linux: _IOC_NONE
void() -> void(os()).
void(bsd) -> 16#20000000;
void(linux) -> 0.

-define(IOCPARM_MASK, 16#1fff).

ioc(Inout,Group,Num,Len) ->
    Size = case os() of
        bsd -> Len band ?IOCPARM_MASK;
        linux -> Len
    end,
    Inout bor (Size bsl 16) bor (Group bsl 8) bor Num.

io(Type,NR) ->
    ioc(void(), Type, NR, 0).

ior(Type,NR,Size) ->
    ioc(out(), Type, NR, Size).

iow(Type,NR,Size) ->
    ioc(in(), Type, NR, Size).

iowr(Type,NR,Size) ->
    ioc(in() bor out(), Type, NR, Size).


os() ->
    case os:type() of
        {unix, linux} -> linux;
        {unix,BSD} when BSD == darwin;
            BSD == openbsd;
            BSD == netbsd;
            BSD == freebsd -> bsd
    end.