26.02.2016 16:52, Josef Bacik пишет: > On 02/26/2016 05:22 AM, Andrei Borzenkov wrote: >> On Wed, Feb 24, 2016 at 10:11 PM, Josef Bacik <jba...@fb.com> wrote: >>> Sometimes DNS responses come in slower than we poll for them which >>> can lead us >>> to process multiple DNS packets which overflows the addresses array. >>> So instead >>> realloc the array each time to make sure we are accounting for any >>> answers we >>> currently have in the address array. We also move the caching of the >>> addresses >>> outside of the recv hook so we can be sure to cache all the responses >>> at once >>> instead of one packet at a time. Thanks, >>> >> >> This still does not address the problem that we stop waiting for >> further packets as soon as we get any response, so we still depend on >> delivery order to get correct record. >> >> What about following >> >> - send both A and AAAA query concurrently if requested >> - keep track of both requests (i.e. have data.id[2] and >> data.addresses[2]) >> - reset request ID (or otherwise mark it as "received") as soon as we >> got reply. Note that reply may contain no addresses - NXDOMAIN is >> prerfectly valid - so condition should not be "got any record of type >> A or AAAA" as it is now but rather simply "got reply to request with >> id XX". This also allows us to implement negative caching at some >> point :) > > So we check the rcode so a NXDOMAIN response will just be discarded, we > don't have to worry about this case. > >> - return both A and AAAA results separately to grub_net_dns_lookup() >> - combine them in grub_net_dns_lookup() depending on preference - i.e. >> put either A or AAAA first in final result. >> >> This seems to cover all issues so far - we do not wait too long, we >> are guaranteed to get both A and AAAA if we request them and we return >> them in proper order for further processing. >> >> Do I miss something? >> > > So my patch previous to this one changes it so DNS servers we get from > dhcp are bound to either ipv4 or ipv6, so the only way we get > PREFER_IPV* is if an admin sets it.
In this case I do not follow why you want to collect multiple answers in the first place. The only reason for me was to make sure we have both A and AAAA replies; otherwise every reply packet is supposed to contain exactly the same content. Following this logic the right thing to do is to just drop all subsequent duplicated replies. > So now the only time we'll get both > an A _and_ an AAAA record is if we have both types of interfaces on the > system, so it won't matter which answer is first as we'll be able to > send traffic to either. User can set preference using net_add_dns --prefer-ipvX | --only-ipvX. We should respect it. > I just side-stepped the issue by making it so > that (at least automatically) we aren't asking for both records unless > we are sure we have an interface to go along with both types of records. I'll reply to your other patch. _______________________________________________ Grub-devel mailing list Grub-devel@gnu.org https://lists.gnu.org/mailman/listinfo/grub-devel
