Re: Issues found by inetutils-ifconfig.
Quoting Mats Erik Andersson (2015-07-17 13:04:59)
> Thursday den 16 July 2015 klockan 13:01 skrev Justus Winter detta:
> >
> > > * The hardware type of an adaper is encoded in the member
> > > `ifr_hwaddr.sa_family' of `struct ifreq'. An ethernet
> > > adapter will correctly state ARPHRD_ETHER (= 1), while
> > > the loopback adapter `lo' will be in error with a value 4.
> > > The correct value is ARPHRD_LOOPBACK (= 772), which is
> > > in use by GNU/Linux. See the header <net/if_arp.h>.
> > > The value 4 is ARPHRD_PRONET, the PROnet token ring!
> >
> > That is surprising indeed. A superficial look revealed that it should
> > indeed be set to ARPHRD_LOOPBACK:
> >
> > % grep ARPHRD_LOOPBACK
> > pfinet/linux-src/include/linux/if_arp.h:#define ARPHRD_LOOPBACK 772 /* Loopback device */
> > [...]
> > pfinet/loopback.c: dev->type = ARPHRD_LOOPBACK;
>
> A possibly relevant observation: The obtained value 4 is
> identical to ARPHRD_LOOPBACK & 0x00ff. Is 'dev->type'
> of length 16 bits, i.e., a short integer like 'sa_family'?
Hmm, it is an `unsigned short' indeed, but that should be sufficient
to hold the value 772. But it is plausible that the value is silently
truncated to 8 bit somewhere.
Justus
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