Re: ioctl() SOS -- Please help

[Corinna Vinschen <corinna@vinschen.de>]

"Ashish C. Nagre" wrote:
> I have made a strange observation, when the following call is made:
> 
>         ioctl(fd, SIOCGIFFLAGS, (char *)&ifr)
> 
> The value returned in the member ifr.ifr_ifru.ifru_flags is different
> when I just run the executable compared to when I run it in the
> debugger.
>         ifr.ifr_ifru.ifru_flags = 34 (executable)
>         ifr.ifr_ifru.ifru_flags = 99 (in gdb)
> [...]
>  Why are the flags returned with different values ?

The flags are computed through the address of the interface.
Is it possible, that you are testing it on a RAS device, e.g
a modem line? When a modem line isn't connected, it returns
the IP address 0.0.0.0, when it's connected, it returns a legal
address.
In case of address 0.0.0.0, the cygwin DLL knows, that the interface
isn't connected and so returns the flags
	IFF_NOTRAILERS | IFF_BROADCAST
The hex value of the above flags is 0x34.

If the address is a legal IP address, the cygwin DLL knows that the
interface is connected and so returns
	IFF_NOTRAILERS | IFF_BROADCAST | IFF_UP | IFF_RUNNING
The hex code is 0x99.

You see, both values are possible and you should check it out, if
you have tested it under different conditions.

Regards,
Corinna

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