[Bug 1868892] Re: initramfs-tools/hooks/udev for network *.link really sucks

[Balint Reczey]

@sil2100 The Debian MR landed and I'm fixing it in groovy with the next
merge - currently being tested in Bileto.
https://bileto.ubuntu.com/#/ticket/3801

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https://bugs.launchpad.net/bugs/1868892

Title:
  initramfs-tools/hooks/udev for network *.link really sucks

Status in systemd package in Ubuntu:
  In Progress
Status in systemd source package in Xenial:
  In Progress
Status in systemd source package in Bionic:
  In Progress
Status in systemd source package in Eoan:
  In Progress
Status in systemd source package in Focal:
  In Progress

Bug description:
  [impact]

  If the /{etc,lib}/systemd/network directory itself is a symlink, the find
  command will not actually find any of the files in the dir it links to.

  [test case]

  $ sudo touch /etc/systemd/network/lp1868892.link
  $ sudo update-initramfs -u
  update-initramfs: Generating /boot/initrd.img-5.4.0-21-generic
  ...
  $ sudo lsinitramfs /boot/initrd.img-5.4.0-21-generic | grep lp1868892
  usr/lib/systemd/network/lp1868892.link
  $ sudo mv /etc/systemd/network /etc/systemd/network.abc
  $ sudo ln -s network.abc /etc/systemd/network
  $ sudo update-initramfs -u
  $ sudo lsinitramfs /boot/initrd.img-5.4.0-21-generic | grep lp1868892
  $ 

  [regression potential]

  this adjusts how link files are included in the initramfs, so
  regressions would likely occur when creating new initramfs, such as
  failure to create initramfs at all, or failure to properly copy link
  files into the initramfs, causing network setup failure.

  [scope]

  this is a Debian/Ubuntu specific file, and the Debian MR was just
  opened, so this is needed for Debian and all releases of Ubuntu.

  [other info]

  This bug likely has a very limited impact, as it is uncommon to
  symlink either the /lib/systemd/network or /etc/systemd/network dirs.

  [original description]

  If one creates e.g. /etc/systemd/network.cu and
  /etc/systemd/network.fc and symlinks  /etc/systemd/network to one of
  them, network setup will fail on reboot, because /usr/share/initramfs-
  tools/hooks/udev does a very poor job: it simply checks for a
  directory instead of the link files and therefore skips copying
  required files to the ram image. Another poor job is done when copying
  the files to the ram image: instead of following symlinks it copies
  them as which in turn makes them useless, because it does not copy the
  related dirs and thus the symlinks point to nothing. So keeping the
  system in an consistent state which such poor scripts is very hard,
  asking for trouble.

  Suggested fix is attached.

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