В Thu, 12 Dec 2013 14:09:42 +0100 Marcel Holtmann <mar...@holtmann.org> пишет:
> Hi Lennart, > > >> why do we have to spawn threads or do forks for DNS. This looks all > >> pretty expensive. In ConnMan for example we just wrote our own async > >> DNS using a mainloop. Works perfectly fine and is dirt cheap. > > > > Well, we don't fork threads/processes for each call but reuse them. > > > > What libasyncns does what your solution doesn't do is go via NSS. This > > means /etc/hosts, nss-myhostname, nss-ldap, nss-mdns and so on just > > work, while that all is lost when doing DNS natively. > > > > I am pretty sure we should not bypass NSS for this. > > actually NSS for DNS is pretty nasty stuff. I am pretty sure we should bypass > it and create a proper implementation. Is anybody actually using NIS or LDAP > for domain name resolution? > Yes, there are solutions that are using LDAP for hostname resolution quite heavily - actually are based around LDAP without any local /etc/hosts. > The problem with NSS is that it still does not fix the fundamental problem. > It is sequential and blocking. You can spawn as many threads as you want and > it will stay sequential. > > I fully agree with you that we need to consider /etc/hosts, the local > hostname and also mDNS, but I get the feeling it would be more beneficial to > just build that in. ConnMan ships a DNS proxy cache to actually be able to be > smart and parallel. We did not bother with the details like /etc/hosts so far > since our use cases always had an empty /etc/hosts with just localhost only > anyway. However that is easy to fix. > > Spawning threads or forking is expensive (even if you reuse it) comparing to > what you actually do here. You just want to resolve a host. It is especially > expensive since you can not control on what is actually used. And there are > clearly use cases where you have to ask a specific nameserver or set of > nameservers. > > Regards > > Marcel > > _______________________________________________ > systemd-devel mailing list > systemd-devel@lists.freedesktop.org > http://lists.freedesktop.org/mailman/listinfo/systemd-devel _______________________________________________ systemd-devel mailing list systemd-devel@lists.freedesktop.org http://lists.freedesktop.org/mailman/listinfo/systemd-devel
