[erlang-questions] Passing parameters to a port driver

[Sebastian Bello]

Hi Per,

thanks for your response.
Ideally I would like to perform something like

Port = open_port({spawn, "./mylib parm1 parm2"}, [])

at the Erlang side, and be able to parse /parmN /from the C side:

static ErlDrvData driver_start(ErlDrvPort port, char *buff) {
   
    // parse parameters from *buff
}

That's all; is that possible with a linked-in driver?
Thanks,
    Sebastian-


Per Hedeland escribió:
> Sebastian Bello <sebastian.bello@REDACTED> wrote:
>   
>> There is no argc/argv in a linked in driver as far as I know.
>>     
>
> Hm, it was a while ago, but according to your quote I wrote:
>
>   
>>> (An external port program would (at least on *nix) get
>>> the Command in the argc/argv arguments to main()...)
>>>       
>
> I'm sorry, but I'm quite unable to parse that as a claim that a driver
> would get argc/argv, so I have no idea why you feel the need to state
> that it doesn't. But you're quite correct of course.
>
>   
>> On the 
>> driver side you have
>>    static ErlDrvData driver_start(ErlDrvPort port, char *buff)
>>     
>
> Exactly, and as I recall your question was what was in the "buff", which
> I explained.
>
>   
>> and buff just points to the driver name;
>>     
>
> It points to (a C-style copy of) whatever string you passed to
> open_port/2. As far as open_port is concerned, the driver name ends at
> the first space (which is quite analogous to / consistent with how the
> string is parsed in the case of an external port program, though I
> hesitate to mention it...).
>
>   
>> if you load the driver with 
>> parameters you just get an "open_error".
>>     
>
> Please share the code that gives that result. Of course open_port
> doesn't "load the driver", but I assume it's open_port you're talking
> about - anyway that's what *I* am talking about. I'm successfully using
> the technique I described in commercial product code - in fact it's used
> in the OTP code too, e.g. in the dbg module.
>
>   
>> Any other ideas?
>>     
>
> None needed.
>
> --Per
>
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