[dccp] Re: wildcard service code?

[Eddie Kohler <kohler at CS.UCLA.EDU>]

Hi,

As we discussed previously, my preferred implementation would have  
been to stick the Service Code in the sockaddr.  Then there wouldn't  
be an extra step to frustrate users.  You vetoed that, I forget why,  
but I wasn't convinced by your arguments.

The lack of a Service Code wildcard is intentional.  As we discussed,  
we will not add a wildcard service code, since this would open a huge  
hole in the service code mechanism.  It would be better to remove  
Service Codes entirely, which we will not do.

We would prefer that every application writer apply for, and use, an  
application-specific Service Code as soon as possible; so the current  
default, which encourages that behavior, is fine.  Although I would  
discourage this, the document does not prevent the Linux  
implementation from starting up with Service Code 0; we say that  
Service Code 0 MUST NOT be *allocated*, not that it must not be used.

Eddie


On Nov 22, 2005, at 11:05 AM, Yoshifumi Nishida wrote:

> Eddie,
>
> Sorry, This might be too late to bring this up, but I have one
> comment on service code. If I could have a little chance,
> I would like to put this on the table and see what other people think.
>
> In section 8.1.2 of the draft-ietf-dccp-spec-12.txt, it says:
>
>   Service Code 0 represents the absence of a meaningful Service
>   Code, and MUST NOT be allocated.
>
> To comply with this, the linux implementation sets service code to -1
> as the initial value and a program will get EPROTO if it doesn't
> set a proper service code with setsockopt().
>
> (see: http://linux-net.osdl.org/index.php/DCCP#FAQ)
>
> It seems to me that this might cause a little confusion to some  
> application
> programmers.
>
> But, if we could have service code 0 as a wildcard service code which
> indicates that the application doesn't care about the service code  
> and accepts
> any value of service code, we don't have to set a service code if  
> we don't
> need to use it.
> Or, if we could use service code 0 as the absence of a meaningful  
> service and
> use it as the initial value, we can get similar effect.
>
> I think we had better avoid mandatory use of setsockopt if it's  
> possible and
> a wildcard service code may be uselful in some situations.
>
> Thanks,
> --
> Yoshifumi Nishida
> nishida at csl.sony.co.jp
> Sony Computer Science Laboratories, Inc.