On Thu, Mar 05, 2009 at 10:03:25AM +0300, Eugene Berdnikov wrote:
> Linux? It works for me:
>
> s0 = socket(PF_INET,SOCK_DGRAM,0);
> if (s0<0)
> perror ("socket");
>
> ret = ioctl(s0, SIOCSIFFLAGS, &ifr);
> if (ret < 0)
> perror("set flags");
>
> I think that if SIOCGIFFLAGS succeeds on some fd, then SIOCSIFFLAGS
> should also succeed or return an error. So this is a kernel bug.
Some digging shows that ioctl's to fd, such as SIOCGIFFLAGS, return
things different from visible network device state. Probably you
can only do those ioctl's that are listed in linux/if_tun.h, and
the mistery is why kernel doesn't return EINVAL if ioctl is called
with wrong function number.
I looked through kernel tun.c code -- it seems correct to me.
However, the bug may be somewhere else.
So, you should create socket, fill interface name field in ifr,
get flags via ioctl with this socket, and work with derived data.
That's what ifconfig does.
--
Eugene Berdnikov
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