How do I get the link state (whether cable is plugged in or not) of an ethernet interface? Is it enough to query the IFF_RUNNING flag in if_flags field of ifreq structure, via a SIOCGIFFLAGS ioctl, or is something more required.

(BTW, I already tried the ioctl method, with no luck. Below is the code I used.)

int retVal;
struct ifreq ifr;
retVal = ioctl(sockData->sockInt, SIOCGIFFLAGS, &ifr);
if (retVal < 0)
{
debug_printf(DEBUG_NORMAL, "Interface %s not found!\n", ctx->intName);
return FALSE;
}

if (((ifr.ifr_flags & IFF_UP) == IFF_UP) && ((ifr.ifr_flags & IFF_RUNNING) == IFF_RUNNING))
{
return TRUE;
} else {
SET_FLAG(ctx->flags, WAS_DOWN);
return FALSE;
}

Any ideas, guys?

I'd be looking at the source of ethtool and see how they do it ;}

Thanks Tinkster. Tried it but no dice. Its using the netif_carrier_ok function, which I think cannot be used in userspace. Further on the netif_carrier_ok function tests the flag (or macro) __LINK_STATE_NOCARRIER, from a set of flags contained in net_device structure, which, again, cannot be used from userspace (I think ). Do correct me if I'm wrong.

Any other ideas, dude? Thanks in advance

Save as intStat.sh (and make executable, chmod 775
Usage: intStat.sh eth?

Example: intStat.sh eth0

Output:
eth0: UP

Perhaps i need to make myself clearer. I have to do this via a C program ONLY, no scripts allowed.

Another thing. I am doing this as part of running xsupplicant (open source Linux version). I notice that the the IFF_RUNNING flag is updated properly each time before I run xsupplicant. However, after I simply run xsupplicant once, the flag is no longer updated. Wierd.

Any ideas guys?

do you have found working code sample?

klsc: Please look at the date of the last post to prevent resurrecting a thread that is almost two years old.