Bug 13271

Summary:	systemd-resolved: /etc/resolv.conf link broken on per-package build
Product:	buildroot	Reporter:	Michael Nosthoff <buildroot>
Component:	Other	Assignee:	unassigned
Status:	RESOLVED FIXED
Severity:	normal	CC:	buildroot, leojrfs, yann.morin.1998
Priority:	P5
Version:	2021.02
Target Milestone:	---
Hardware:	All
OS:	Linux
Host:		Target:
Build:
Attachments:	skeleton-init-systemd per-package workaround

Description Michael Nosthoff 2020-10-13 13:53:34 UTC

Issue:

systemd-resolved needs the /etc/resolv.conf entry like this:

/etc/resolv.conf -> ../run/systemd/resolve/stub-resolv.conf

When using per-package build this isn't the case anymore. It still has the default value from the skeleton:

/etc/resolv.conf -> ../tmp/resolv.conf


Analysis:

this is the code currently creating the link:

ifeq ($(BR2_PACKAGE_SYSTEMD_RESOLVED),y)
define SYSTEMD_INSTALL_RESOLVCONF_HOOK
	ln -sf ../run/systemd/resolve/resolv.conf \
		$(TARGET_DIR)/etc/resolv.conf
endef


As I learned on irc this doesn't work with per-package build as it is not allowed to alter files from another package (even the skeleton). So this is why it doesn't work.


Conclusion:

I'm not sure if this is properly fixable by the systemd package itself or if this needs a removal from the skeleton with all its consequences.

Any Ideas welcome...

Comment 1 Leo 2021-03-25 20:38:04 UTC

Created attachment 8836 [details]
skeleton-init-systemd per-package workaround

I can confirm this.

This kind of issues might happen when using `per-package`.
The reason for this is that `target-finalize` rsyncs all the target subdirectories under the package directory (example: `$O/per-package/foo/target`) in alphabetic order:

```
$(call per-package-rsync,$(sort $(PACKAGES)),target,$(TARGET_DIR))
```

So, files in the final target, might get consecutively overwritten in that process by the content of each package `per-package` `target` directory.

In this case, `udev` is one of the packages that overrides the `resolv.conf`, it comes after `systemd` in the rsync order previously mentioned.

`udev` depends on `toolchain` which in turn depends on `skeleton-init-systemd`, where `resolv.conf` is a link to `../tmp/resolv.conf`, thus, `$O/per-package/udev/target/etc/resolv.conf` gets its value by rsyncing `$O/per-package/toolchain/target/etc/resolv.conf` just before building.


Ideally, rsync would execute in dependency order instead of alphabetic order. I tried to tinker around that, but had not much success. Im not sure how to solve this problem.


In the meanwhile, I attach a patch for `skeleton-init-systemd.mk`, which solves this specific issue. Im not sure it is the best way to solve this problem, for the reasons I just mentioned.

Any thoughts?

Comment 2 Leo 2021-03-25 20:49:02 UTC

btw, this is still reproducible on 2021.02

Comment 3 Yann E. MORIN 2021-03-27 21:11:06 UTC

Michael, All,

> define SYSTEMD_INSTALL_RESOLVCONF_HOOK
> 	ln -sf ../run/systemd/resolve/resolv.conf \
> 		$(TARGET_DIR)/etc/resolv.conf
> endef
> [...]
> SYSTEMD_POST_INSTALL_TARGET_HOOKS += \
> 	SYSTEMD_INSTALL_RESOLVCONF_HOOK

Indeed, a hook doing such changes should be made to be a target-fianlize
hook rather than a post-target-install hook.

In systemd, there is already a target-finalize hook, for the nsswitch
configuration file.

Care to send a patch, please?

Regards,
Yann E. MORIN.

Comment 4 Yann E. MORIN 2021-04-13 19:16:07 UTC

Michael, All,

Thanks for the report.

This is now supposedly fixed with commit 511fbda0be that has just been pushed.

Regards,
Yann E. MORIN.