New: systemd-resolved: /etc/resolv.conf link broken on per-package build

https://bugs.busybox.net/show_bug.cgi?id=13271

Bug ID: 13271
Summary: systemd-resolved: /etc/resolv.conf link broken on
per-package build
Product: buildroot
Version: 2020.08.1
Hardware: All
OS: Linux
Status: NEW
Severity: normal
Priority: P5
Component: Other
Assignee: unassigned at buildroot.uclibc.org
Reporter: posted at heine.so
CC: buildroot at uclibc.org
Target Milestone: ---

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...

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https://bugs.busybox.net/show_bug.cgi?id=13271

Leo <[email protected]> changed:

What |Removed |Added
----------------------------------------------------------------------------
CC| |leojrfs at gmail.com

--- Comment #1 from Leo <[email protected]> ---
Created attachment 8836
--> https://bugs.busybox.net/attachment.cgi?id=8836&action=edit
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?

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Leo <[email protected]> changed:

What |Removed |Added
----------------------------------------------------------------------------

            Version|2020.08.1                   |2021.02

--- Comment #2 from Leo <[email protected]> ---
btw, this is still reproducible on 2021.02

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Yann E. MORIN <[email protected]> changed:

What |Removed |Added
----------------------------------------------------------------------------
CC| |yann.morin.1998 at free.fr

--- Comment #3 from Yann E. MORIN <[email protected]> --- Michael, All,

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.

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Yann E. MORIN <[email protected]> changed:

What |Removed |Added
----------------------------------------------------------------------------

             Status|NEW                         |RESOLVED
         Resolution|---                         |FIXED

--- Comment #4 from Yann E. MORIN <[email protected]> --- Michael, All,

Thanks for the report.

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

Regards,
Yann E. MORIN.

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