[Bug 1929560] Update Released

[Brian Murray]

The verification of the Stable Release Update for systemd has completed
successfully and the package is now being released to -updates.
Subsequently, the Ubuntu Stable Release Updates Team is being
unsubscribed and will not receive messages about this bug report.  In
the event that you encounter a regression using the package from
-updates please report a new bug using ubuntu-bug and tag the bug report
regression-update so we can easily find any regressions.

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https://bugs.launchpad.net/bugs/1929560

Title:
  link mac isn't set if already up

Status in systemd:
  Fix Released
Status in systemd package in Ubuntu:
  Fix Released
Status in systemd source package in Bionic:
  Fix Committed
Status in systemd source package in Focal:
  Fix Committed
Status in systemd source package in Groovy:
  Fix Released

Bug description:
  [impact]

  if link is already up, configured mac isn't set

  this also affects the master/nomaster configuration

  [test case]

  create .network config for the link, for example:

  [Match]
  Name=eth0

  [Link]
  MACAddress=00:16:3e:ff:ff:ff

  [Network]
  DHCP=yes

  
  make sure the link is already up, and restart systemd-networkd:

  root at test-f:/etc/systemd/network# ip l show eth0
  61: eth0 at if62: <BROADCAST,MULTICAST> mtu 1500 qdisc noqueue state DOWN mode DEFAULT group default qlen 1000
      link/ether 00:16:3e:fc:b2:00 brd ff:ff:ff:ff:ff:ff link-netnsid 0
  root at test-f:/etc/systemd/network# ip l set dev eth0 up
  root at test-f:/etc/systemd/network# ip l show eth0
  61: eth0 at if62: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue state UP mode DEFAULT group default qlen 1000
      link/ether 00:16:3e:fc:b2:00 brd ff:ff:ff:ff:ff:ff link-netnsid 0
  root at test-f:/etc/systemd/network# systemctl restart systemd-networkd
  root at test-f:/etc/systemd/network# ip l show eth0
  61: eth0 at if62: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue state UP mode DEFAULT group default qlen 1000
      link/ether 00:16:3e:fc:b2:00 brd ff:ff:ff:ff:ff:ff link-netnsid 0
  root at test-f:/etc/systemd/network# ip l set dev eth0 down
  root at test-f:/etc/systemd/network# ip l show eth0
  61: eth0 at if62: <BROADCAST,MULTICAST> mtu 1500 qdisc noqueue state DOWN mode DEFAULT group default qlen 1000
      link/ether 00:16:3e:fc:b2:00 brd ff:ff:ff:ff:ff:ff link-netnsid 0
  root at test-f:/etc/systemd/network# systemctl restart systemd-networkd
  root at test-f:/etc/systemd/network# ip l show eth0
  61: eth0 at if62: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue state UP mode DEFAULT group default qlen 1000
      link/ether 00:16:3e:ff:ff:ff brd ff:ff:ff:ff:ff:ff link-netnsid 0

  [regression potential]

  any regression would likely result in incorrectly set link mac and/or
  master, or failure to correctly set mac and/or master

  [scope]

  this is needed for g and earlier

  this is fixed upstream by commit
  e16e4b3bedc57919b3ecb4096e941709a5d39b8a which is included in v247 so
  this is fixed already in h and later

  [other info]

  this moves the configuration of the link mac and master out of the
  link_up() function, so this also allows repeated calls to link_up()
  without reconfiguring the link mac and master. That behavior is useful
  for the commits for bug 1664844

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