Date: Mon, 26 Oct 2015 17:37:20 -0700 From: Tim Hockin <thockin@...gle.com> To: musl@...ts.openwall.com Subject: Re: Re: Would love to see reconsideration for domain and search wrt 2) my understanding is that you get at-most-one-of `search` or `domain`. On Mon, Oct 26, 2015 at 5:30 PM, Rich Felker <dalias@...c.org> wrote: > On Fri, Oct 23, 2015 at 01:31:09AM -0400, Rich Felker wrote: >> > > BTW I think there are other strong reasons to move to a model based on >> > > a local nameserver that does the unioning, not just performance. The >> > > most compelling is DNSSEC, which requires a trusted channel between >> > > the nameserver and the stub resolver in order for results to be >> > > meaningful/trusted. In the future everybody should be running a >> > > nameserver on localhost to do DNSSEC signature validation. In that >> > > scheme, resolv.conf would just contain 127.0.0.1 (or could be omitted >> > > entirely since that's the default, at least on musl). >> > >> > I can see a local nameserver doing resolution, but doing search >> > expansion seems like a stretch (and superfluous since it is local). >> >> Search would also get a lot of performance benefit from doing in the >> caching nameserver, but I agree with your assessment that it's a >> separate issue and that there's no _need_ to do it at that level to >> ensure correctness. So for now let's focus on a plan for adding >> suitable search domain support in musl. >> >> I believe search only affects DNS queries, not hosts file lookups, >> right? So it should be at the name_from_dns stage in lookup_name.c. >> The simplest implementation approach is probably to wrap name_from_dns >> with a name_from_dns_search function that reads the search domains and >> repeatedly calls name_from_dns until it gets success. > > I noticed in the process of trying to draft code to do this that there > will be a lot of code duplication with the resolv.conf parsing in > res_msend.c, and that this code has some stupid bugs (for example it > stops parsing after it gets 3 nameservers, so it might miss options > later in the file), so I think I'll take a look at factoring it into a > new function to gather all the interesting information from > resolv.conf that can be used in both places. > > A couple additional things I noticed from resolv.conf(5): > > 1. The default domain used by glibc is not the dns root but rather the > domain portion of the local hostname determined by gethostname(). > Is there any value in duplicating this? Does anyone want/need it? > > 2. It's not clear from the documentation of "search" whether its > presence overrides/suppresses the "domain" (default or set by > resolv.conf) or adds additional searches before or after it. Which > should it do? > > While glibc/legacy behavior is worth looking at, I don't think we need > to look at things from a standpoint of exactly duplicating that. > Meeting real-world modern application needs while avoiding > inconveniencing users with stupid/unwanted behavior should be the > primary goal. > > Rich
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