Re: WSDD Service Module

["Ludovic Courtès" <ludo@gnu.org>]

Hi,

(+Cc: guix-devel.)

Simon Streit <simon@netpanic.org> skribis:

> Ludovic Courtès <ludo@gnu.org> writes:
>> My understanding is that you intend the ‘interface’ field to be either
>> #f or a string, is that right?
>
> I think it rather be a list of strings,

Then I recommend calling it ‘interfaces’ (plural).

>> When you write:
>>
>>   (interface)
>>
>> that means: “call the procedure bound to ‘interface’, passing it zero
>> arguments”.  However, if ‘interface’ is a string, you cannot call it, so
>> you get a wrong-type-to-apply error.
>>
>> Likewise, ‘for-each’ expects its second argument to be a list.  But
>> here, ‘interface’ is supposedly a string, not a list, so if you do:
>>
>>   (for-each (lambda …) interface)
>>
>> you’ll get a wrong-type-argument error.
>
> So I changed it, that interface is usually an empty list now, and with
> for-each I'd like to have it expanded.  Good thing is, I've gotten at
> least a step further, but only after hard coding the list as an argument
> in the for-each expression.  So it should work?  It still doesn't.  And
> I still don't understand how it is somehow not passed as a list
> properly.  
>
> One thing I noticed, after hard coding the argument, the procedure is
> not properly expanded in the constructor.  How come?  This is the output
> in the service file:
>
> (make-forkexec-constructor
>  (list "/gnu/store/6jpn21wnnyz59ii634hfbk34yy48nxrq-wsdd-0.6.4/bin/wsdd" "--hoplimit" "1" for-each
>        (lambda
>            (arg)
>          (format #t "--interface ~s "
>                  (arg)))
>        (interface)
>        "--workgroup" "WORKGROUP")
>  #:user "wsdd" #:group "wsdd" #:log-file "/var/log/wsdd.log")

This reads “(interface)”, meaning that (1) ‘interface’ must be a
procedure, since you’re calling it, and (2) ‘interface’ must be bound
(the variable must be defined there).

However, ‘interface’ is unbound here.  You probably meant to write,
within your gexp:

  #~(make-forkexec-constructor
      … #$@(map (lambda …) interfaces)
      …)

which would expand to:

  (make-forkexec-constructor
    … "--interface=eth0" "--interface=eth1"
    …)

The #$@ bit (‘ungexp-splicing’) means that the (map …) bit executes
beforehand and that its results is staged in that generated shepherd
file.

HTH,
Ludo’.