On Mar 12, 2010, at 8:30 AM, Qing Li wrote: > 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;
Please do *NOT* do this: (1) Do not overload if_flags with more run-time set flags without well-defined atomicity properties (2) Why isn't LINK_STATE_UNKNOWN already sufficient here? The only change I think would be useful is adding a new IFCAP flag that allows a driver to statically declare that it will someday set the link state. But I don't think that helps with ECMP, that's just for the benefit of programs like dhclient that care about future events rather than current state. Robert > > -- 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 _______________________________________________ svn-src-all@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/svn-src-all To unsubscribe, send any mail to "svn-src-all-unsubscr...@freebsd.org"
