I believe what Julian means is the following:
1. in the driver, I do this
ifp->if_flags |= IFF_KNOWS_LINK_STATE;
2. In route.h, I do this
if (ifp->flags & IFF_KNOWS_LINK_STATE) && (ifp->if_link_state ==
LINK_STATE_UP)
return 1;
-- Qing
On Fri, Mar 12, 2010 at 12:26 AM, Robert N. M. Watson
<rwat...@freebsd.org> wrote:
>
> On Mar 12, 2010, at 8:11 AM, Qing Li wrote:
>
>> I like Julian's suggestion because it is simple and very low risk.
>> And there isn't a need to check for interface type any more.
>> Here is why:
>>
>> 1. The interfaces that are popular and modern are already supporting
>> link_state. So for these drivers, and there are just a few, I will go set
>> its if_flags to include "can change link_state".
>>
>> 2. For the existing dated drivers, because that flag bit is never set,
>> no check is done.
>>
>> 3. In the mean time, we try to convert the drivers progressively.
>>
>> 4. If one wants to do ECMP and not having packets go into a black
>> hole when the physical link is down, that person can ping the ML
>> and ask for driver compatibility list. If we haven't converted that
>> particular driver by then, we will update the driver if it's capable
>> at that time.
>
>
> Today, we support three link state values:
>
> 170 /*
> 171 * Values for if_link_state.
> 172 */
> 173 #define LINK_STATE_UNKNOWN 0 /* link invalid/unknown */
> 174 #define LINK_STATE_DOWN 1 /* link is down */
> 175 #define LINK_STATE_UP 2 /* link is up */
>
> I'm confused about Julian's proposal because it seems to me that we already
> know when a driver hasn't set or is unable to determine the link state: it
> will (should) be set to LINK_STATE_UNKNOWN by default.
>
> So the only question we don't know the answer to, at run-time, is whether a
> driver may *ever* set the link state (i.e., it thinks it knows how to), and
> hence whether or not tools like dhclient should try to wait for that to
> happen. That is the problem that an interface capability would solve.
>
> For the purposes of ECMP, you just need to decide on your policy: map UNKNOWN
> to either UP or DOWN for your purposes.
>
> Robert
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