procket

%%% @copyright 2011-2023 Michael Santos <michael.santos@gmail.com>
%%% All rights reserved.
%%%
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%%%
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%%% this list of conditions and the following disclaimer.
%%%
%%% 2. Redistributions in binary form must reproduce the above copyright
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%%% this software without specific prior written permission.
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-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.