Check if interface supports Device Polling

Eduardo Meyer dudu.meyer at
Wed Oct 22 08:30:59 PDT 2008

On Wed, Oct 22, 2008 at 1:24 PM, Jeremy Chadwick <koitsu at> wrote:
> On Wed, Oct 22, 2008 at 08:12:28AM -0700, Jeremy Chadwick wrote:
>> > # ifconfig -v rl0 caps
>> > Capabilities: 48
>> The above patch is completely unnecessary.  The -m flag in ifconfig
>> will do what you want.
>> However, the existing ifconfig code does not print POLLING as a
>> capability, which is where the bug truly lies.
>> I'll provide a patch that extends the capability list properly, and will
>> allow you to determine a full capability list.
> I'm both correct and incorrect.
> Correct: ifconfig -m will show you want.  No need for the patch.
> Incorrect: I missed the "POLLING" part of #define IFCAPBITS in
> ifconfig.c -- it is in fact listed there.
> Maybe the polling bit is only made available if you've built a kernel
> with "option DEVICE_POLLING"?  For example, I can do "ifconfig em1
> polling", which returns no error, but "ifconfig -m em1" does not show
> POLLING.  (My kernel does NOT have DEVICE_POLLING defined.)
> In your above output, capabilities is 0x48, which means POLLING is
> available, and VLAN_MTU is available.  You did not provide us output of
> "ifconfig -m rl0", but I'd be inclined to believe "POLLING" is shown
> there... I hope.  :-)
> Also, it appears ifconfig does not print TOE4 or TOE6 capability bits;
> that's probably a missing feature.
> --
> | Jeremy Chadwick                                jdc at |
> | Parodius Networking              |
> | UNIX Systems Administrator                  Mountain View, CA, USA |
> | Making life hard for others since 1977.              PGP: 4BD6C0CB |

You are right. My mistake, its there, in the "capabilities" line when
-m is issued.

Thank you Jeremy.

Eduardo Meyer
pessoal: dudu.meyer at
profissional: ddm.farmaciap at

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