Re: Detecting IP_TOS (and IPPROTO_IP vs. SOL_IP)

[Philip Prindeville]

On 3/26/10 12:51 PM, Ralf Wildenhues wrote:
> Hello Philip,
>
> * Philip A. Prindeville wrote on Mon, Mar 22, 2010 at 08:42:51AM CET:
>    
> > Calling the sequence:
> >
> > setsockopt(fd, XXXX, IP_TOS,&foo, sizeof(foo));
> >
> > can be tricky.  Linux uses SOL_IP for XXXX, whereas Solaris and BSD use
> > IPPROTO_IP for this instead.
> >
> > Not sure what MacOS or HP-UX do.
> >
> > Do the newer versions of autoconf have canned code for detecting what to
> > use?
> >      
> No.
>
> My version of Linux defines both SOL_IP and IPPROTO_IP to the same
> value.  Since changing it would seem to break the API, I *think*
> if looking at Linux alone you should be able to just go with IPPROTO_IP.
> Untested, you get to keep the pieces if it breaks.
>    

Except, of course, that most people widely agree that using the protocol 
number as a synonym for the layer number was a poor design choice, and 
one that was eventually corrected (via the introduction of SOL_IP).

Thus I would argue the opposite: that always using SOL_IP is the correct 
approach, i.e.

#ifndef SOL_IP
#define SOL_IP IPPROTO_IP
#endif
...

    r = setsockopt(s, SOL_IP,&qos, sizeof(qos));


In summary, the API was already broken, and propagating that usage model is 
probably not a good thing.



> > And if not, can someone please add it?
> >
> > I just grepped the 2.65 tarball but didn't find anything in there.
> >      
> Generally, for such issues it might be a good idea to just use gnulib if
> you can; but I just looked and it doesn't address this particular issue
> yet.
>
> Cheers,
> Ralf
>    

Yeah, a lot of runtimes don't use gnulib, like APR...

-Philip