Nobody expects the spanish plonk squad! [LWN.net]

Nobody expects the spanish plonk squad!

Posted Nov 28, 2014 22:47 UTC (Fri) by dlang (guest, #313)
In reply to: Nobody expects the spanish plonk squad! by anselm
Parent article: The Grumpy Editor's guide to surviving the systemd debate

well, if it's used by things outside of udev, then it's an "external API", and since LP is calling out that Gentoo is going to have to change things as a result, it sure seems like things other than udev are affected.

On the other hand, if you ignore the claims about systemd being modular and consider udev just an internal component of systemd, and users have to go all-or-nothing with systemd, then it could be an "internal API" of systemd.

But that would make the claims that systemd isn't forcing you to use everything a lie.

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Nobody expects the spanish plonk squad!

Posted Nov 28, 2014 23:05 UTC (Fri) by anselm (subscriber, #2796) [Link] (4 responses)

well, if it's used by things outside of udev, then it's an "external API", and since LP is calling out that Gentoo is going to have to change things as a result, it sure seems like things other than udev are affected

I think Lennart called out Gentoo because they forked udev (IIRC mostly because they didn't like that the udev and systemd repositories were merged). AFAIK the netlink-based interface is what the kernel uses to talk to udev, so once that is replaced by kdbus then the Gentoo version of udev will also have to start using kdbus (either by adopting the userspace kdbus binding that is part of systemd, which does not force you to take on anything else from systemd, or by implementing another kdbus binding), or else the Gentoo people will need to maintain their own version of the kernel side of things, too.

On the other hand, if you ignore the claims about systemd being modular and consider udev just an internal component of systemd, and users have to go all-or-nothing with systemd, then it could be an "internal API" of systemd.

I don't think that systemd's degree of modularity has anything to do with the problem at hand. Udev is really quite independent of systemd, and AFAIK the netlink-based communications protocol is used by udev but by nothing else in systemd. As long as this is only used by udev and the kernel, it remains an internal interface, and it is reasonable to change it if that makes technical sense. Hence my question whether anything outside of udev uses it (and Gentoo's udev fork doesn't really count).

Nobody expects the spanish plonk squad!

Posted Nov 29, 2014 0:39 UTC (Sat) by mgb (guest, #3226) [Link]

> Hence my question whether anything outside of udev uses it (and Gentoo's udev fork doesn't really count).

Will your proposed kernel changes break eudev?

Nobody expects the spanish plonk squad!

Posted Dec 10, 2014 16:32 UTC (Wed) by nix (subscriber, #2304) [Link] (2 responses)

Sorry, last I encountered it, udev was userspace, right? And there are other things that do what udev does (Gentoo's fork, eudev, perhaps mdev?). That makes this a userspace/kernel ABI in my eyes, with multiple users, making breaking it verboten. What's worse they are multiple boot-critical users!

Nobody expects the spanish plonk squad!

Posted Dec 10, 2014 20:53 UTC (Wed) by mathstuf (subscriber, #69389) [Link] (1 responses)

It's backwards. My understanding: the kernel and udev currently communicate over netlink. Newer udev will only talk over kdbus (netlink isn't going away in the kernel) and kdbus requires some userspace process to set up the bus (which systemd currently does). Gentoo can fix this by writing their own kdbus setup tool (which is what the warning was about).

Nobody expects the spanish plonk squad!

Posted Dec 11, 2014 17:04 UTC (Thu) by nix (subscriber, #2304) [Link]

Ah, so this is 'newer udev will require a bleeding-edge kernel yet again', not 'we're going to break everyone using older udev and force them to upgrade'. So I'm not as annoyed as I might be, and Al is probably more annoyed...