Hacker News Reader

Comment by ahartmetz | Hacker News Reader

Look forward to ye olde uncle Lennart's old-timey sales pitch.

I'm gonna summarize the Varlink talk: DBus is, and I quote, "very very very complex" and his system with JSON for low-level IPC is, in fact, the best thing since sliced bread and has no significant flaws. It works basically just like HTTP so the web people will love it. Kernel support for more great shit pending! I'm not sure where the hardon for a new IPC system with lernel (keeping that typo) support is from, but he's been trying for 15 years now. AFAICT, the service discovery problem could be solved by a user space service without much trouble. I mean if the whole thing wasn't an exercise in bad technological taste.

View on HN

I think you are misrepresenting this;

Varlink is based on much more conventional UNIX technology than Dbus, which is decades old: You connect to a named UNIX socket through its socket file in the filesystem (man page: unix(7)).

This is an old mechanism and it is known to work well. It does not require a broker service, it works right at system startup, and it does not require a working user database for permission checks (which would be a circular dependency for systemd in some configurations). If at all, I am surprised that systemd didn't use that earlier.

The main thing that Varlink standardizes on top of that is a JSON-based serialization format for a series of request/response pairs. But that seems like a lightweight addition.

It also does not require kernel support to work, the kernel support is already there. He mentioned in the talk that he'd like to be able to "tag" UNIX sockets that speak varlink as such, with kernel support. But that is not a prerequisite to use this at all. The service discovery -- and he said that in the talk as well -- is simply done by listing socket files in the file system, and by having a convention for where they are created.

What do you connect to, when you connect to varlink, if there is no broker service?

It's kinda weird to present this as a DBus alternative when it doesn't even offer the same facilities, particularly many-to-many communication.

Though I have a pretty good idea of where a Varlink broker would turn up and which init system it would be tied to.

Very typical systemd–developer style.

Those are pathname UNIX domain sockets, so you address them through the socket file, which is conventionally stored somewhere under /run.

You can run "netstat --listening --unix" to list the UNIX domain servers on your system, to get an impression.

See https://man7.org/linux/man-pages/man7/unix.7.html

And what does the socket connect to?

I do not share your view of old timey sales pitch, at least for the talk about systemd nspawn OCI container support.

If anything, that talk was a tad low effort, with even dismissive answers — "Yes" and "No?" as full answers to audience questions, with no follow up?! Still very informative though!

The Varlink talk really was very salesy for a Fosdem presentation. Shouldn't be long until the recording becomes available, feel free to tell me I was wrong after watching it.

It's mainly re-hashed. I think I've seen the same talk twice before? At least once.

It's a very "I've made a cool thing. This is what I think is cool about it" type of talk. Which I don't think is uncommon for FOSDEM. Maybe a bit uncommon for a higher profile figure like Lennart.

> It's mainly re-hashed. I think I've seen the same talk twice before? At least once.

He held a similar talk at All Systems Go I think (I missed the talk here at FOSDEM).

> It's a very "I've made a cool thing. This is what I think is cool about it" type of talk.

Varlink isn't something he just made up, he mearly "adopted it" (started making use of it). It existed before, but I don't know anything that really made use of it before.

Who made it up, then?

The official-looking website at https://varlink.org doesn't give any information about who the authors are, as far as I can tell, but the screenshots show the username "kay". There's a git repo for libvarlink [1] where the first commits (from 2017) are by Kay Sievers, who is one of the systemd developers.

An announcement post [2] from later in 2017, by Harald Hoyer, says that the varlink protocol was created by Kay Sievers and Lars Karlitski in "our team", presumably referring to the systemd team.

So the systemd developers "adopted" their own thing from themselves?

[1] https://github.com/varlink/libvarlink

[2] https://harald.hoyer.xyz/2017/12/18/varlink/

While I guess you aren't wrong, I also wouldn't say you are entirely correct that Kay is a systemd developer. He use to work on udev, but hasn't been active in any meaningful way on it for 2 years before varlinks release[1]. For what it was made I can't really say, but Lennart hadn't start integrating Varlink until a while after its release (I think I remember it being like 2021 or so when he started making use of it, after another check it seems the start of varlink stuff in systemd was 2019[2]).

[1]: https://github.com/systemd/systemd/commits/main/?author=kays...

[2]: https://github.com/search?q=repo%3Asystemd%2Fsystemd+varlink...

Kay Sievers' Wikipedia page cites a blog post by Lennart Poettering [1] which says that systemd was designed in "close cooperation" with Kay Sievers and that Harald Hoyer was also involved, so it seems pretty clear that he's on the team that develops systemd, the team that Harald Hoyer referred to as "our team". All three of them gave a talk [2] together in 2013 about what they were developing.

If Lennart Poettering "adopted" varlink, he seems to have done so from members of his own team ("our team") who created varlink and who are also fellow co-creators of systemd.

[1] https://0pointer.de/blog/projects/systemd.html#faqs

[2] https://www.youtube.com/watch?v=_rrpjYD373A

Reply on news.ycombinator.com