switch-to-configuration.pl: Interact via DBus

[ocharles]

Currently switch-to-configuration.pl uses system() calls to interact
with DBus. This can be error prone, especially when we are parsing
output that could change. In this commit, almost all calls to the
systemctl binary have been replaced with equivalent operations via DBus.

[ocharles]

This obviously needs people to help test. So far I've tried enabling and disabling services, and it has behaved as expected.

[shlevy]

+1. @edolstra are you willing to take a look at this? Otherwise I will but it may be some time before I can do it properly.

[edolstra]

Seems like a good idea to me (but haven't tested yet). The only downside would be that switch-to-configuration will fail if dbus is down. But I guess that won't be a problem anymore in the glorious kdbus future.

[shlevy]

@edolstra do you have any thoughts on what should be tested for this? It seems like something we should have.

[shlevy]

I don't have time to test this right now, but I've added the 14.04 milestone so that we make sure it gets in soon.

[shlevy]

Will test and try to get this in before 14.04, unless @edolstra objects.

[shlevy]

@ocharles This looks good to me, can you bring it up to date and we can merge?

[ocharles]

Sure thing, will try and get that done tonight or tomorrow.
On 19 Apr 2014 02:18, "Shea Levy" notifications@github.com wrote:

@ocharles https://github.com/ocharles This looks good to me, can you
bring it up to date and we can merge?

Reply to this email directly or view it on GitHubhttps://github.com//pull/1665#issuecomment-40856952
.

[edolstra]

Just updated systemd to 212, but I don't think it changes the d-bus API. (It did change the "systemctl" output...)

[ocharles]

I've merged master in - do we want to get this in for the next release, or give it time to have more testing? I think for something so essential, we may be better waiting.

[shlevy]

We'll have a week+ for testing after this is in, I'd like to get this in if you're up for it. I tested the current state already against nixpkgs of a few weeks ago

[ocharles]

Sure, I'm fine with that - just wanted to make sure others were :)

On Sun, Apr 20, 2014 at 7:39 PM, Shea Levy notifications@github.com wrote:

We'll have a week+ for testing after this is in, I'd like to get this in
if you're up for it. I tested the current state already against nixpkgs of
a few weeks ago

Reply to this email directly or view it on GitHubhttps://github.com//pull/1665#issuecomment-40901617
.

[shlevy]

@ocharles Is this ready to merge?

[ocharles]

I'm just testing it now, will merge if everything checks out OK.

[edolstra]

So has anybody tested what happens if dbus is restarted by switch-to-configuration?

[lucabrunox]

I've nixos-rebuild switch from old master to new master (3b93b7b + #2344)

updating GRUB 2 menu...
stopping the following units: .......(including dbus)................. 
org.freedesktop.DBus.Error.Disconnected: Connection is closed

Then dbus was dead. I could systemctl start dbus and it was alive. Doing switch and got the same problem as above.
Then I nixos-rebuild boot, rebooted and it worked fine. Did a nixos-rebuild switch and:

updating GRUB 2 menu...
stopping the following units: local-fs.target, network-interfaces.target, remote-fs.target
NOT restarting the following units: display-manager.service
activating the configuration...
setting up /etc...
restarting the following units: polkit.service
no introspection data available for method 'Restart' in object '/org/freedesktop/systemd1', and object is not cast to any interface at /nix/store/5v9f24b4kr0pxg5afbbskr0hk830nssl-perl-Net-DBus-1.0.0/lib/perl5/site_perl/5.16.3/x86_64-linux-thread-multi/Net/DBus/RemoteObject.pm line 405.

[shlevy]

Reverted for now, as @ocharles may not have time to look at the problems caused by the new systemd in conjunction with this. We will revisit after 14.04.

[vcunat]

Hmm, it seems impossible to reopen a merged PR.

[ocharles]

Don't worry, I'll open a new one shortly
On 22 Apr 2014 09:26, "Vladimír Čunát" notifications@github.com wrote:

Hmm, it seems impossible to reopen a merged PR.

—
Reply to this email directly or view it on GitHubhttps://github.com//pull/1665#issuecomment-41015158
.

[edolstra]

Another that occured to me is that starting units via d-bus breaks password prompts. (Systemctl spawns systemd-tty-ask-password-agent --watch to perform password prompts made by systemd-ask-password calls in units.)

[shlevy]

How does systemctl work if not via dbus?

[edolstra]

Systemctl doesn't use dbus at all if you're running as root. Also, it does more than talk to systemd - it also starts systemd-tty-ask-password-agent.

[shlevy]

Right, but what interface does it use?

[edolstra]

The /run/systemd/private Unix domain socket.