24.02.2016 01:02, Josef Bacik пишет: > On 02/15/2016 01:45 AM, Andrei Borzenkov wrote: >> On Thu, Feb 11, 2016 at 12:21 AM, Josef Bacik <jba...@fb.com> wrote: >>> If we have dns servers that we prefer to get AAAA records from we'll >>> send a >>> packet and immediately check data.naddresses to see if we got a >>> response. If we >>> didn't we'll then send a request for an A record, and _then_ we'll >>> poll the >>> card. So if the DNS server doesn't respond between us sending the >>> packet and >>> checking data.naddresses we'll send a request for the A record and >>> then poll the >>> card. Instead we need to make sure we poll after we issue each >>> request to make >>> sure we give the server enough time to respond to our initial request. >>> >>> Signed-off-by: Josef Bacik <jba...@fb.com> >>> --- >>> grub-core/net/dns.c | 2 +- >>> 1 file changed, 1 insertion(+), 1 deletion(-) >>> >>> diff --git a/grub-core/net/dns.c b/grub-core/net/dns.c >>> index 82a3307..86e609b 100644 >>> --- a/grub-core/net/dns.c >>> +++ b/grub-core/net/dns.c >>> @@ -587,12 +587,12 @@ grub_net_dns_lookup (const char *name, >>> grub_errno = GRUB_ERR_NONE; >>> err = err2; >>> } >>> + grub_net_poll_cards (200, &data.stop); >> >> One consideration is that it will increase timeouts in case of >> non-responsive servers, as now they are processed sequentially. >> >> But more importantly, this is still hit and miss - we rely on delivery >> order which is non-deterministic. We really need to ask for all and >> filter on receiving side. Two possible implementations are >> >> 1. Keep track of IPv4 and IPv6 answers separately; if non-preferred >> answer is received, continue to wait for preferred one until timeout. >> >> 2. Queries for both A and AAAA in the same packet and filter out answers. >> >> The 2 looks better. It avoids extra timeouts (at least if we assume >> that all DNS servers are equally authoritative) because as soon as we >> get any response we can stop polling. >> >> This will also indirectly fix another reported issue as we now can >> ignore any duplicate packet. >> >> Would you consider implementing it? > > Got this all implemented, started testing it and it just wasn't working, > come to find out our dns server (also bind) doesn't support more than > one question per packet.
Oh! :( Sorry, I really did not expect it, given that multi-query was in DNS RFC from the very beginning. > So instead I'm going to keep track of which > type my DNS servers support and only do those questions. Updating the > cache is kind of a pain in the ass, I'll probably make it so we just > update in place the existing cache with the new answers. Thanks, > > Josef > _______________________________________________ Grub-devel mailing list Grub-devel@gnu.org https://lists.gnu.org/mailman/listinfo/grub-devel
