[Bug 1913763] Re: hyperv: unable to distinguish PTP devices

[Dan Streetman]

ddstreet at ddstreet-test:~$ dpkg -l systemd|grep systemd
ii  systemd        229-4ubuntu21.29 amd64        system and service manager
ddstreet at ddstreet-test:~$ ls -l /dev/ptp*
crw------- 1 root root 247, 0 Apr  1 17:29 /dev/ptp0
crw------- 1 root root 247, 1 Apr  1 17:29 /dev/ptp1
ddstreet at ddstreet-test:~$ grep . /sys/class/ptp/*/clock_name
/sys/class/ptp/ptp0/clock_name:hyperv
/sys/class/ptp/ptp1/clock_name:mlx5_p2p


ddstreet at ddstreet-test:~$ dpkg -l systemd|grep systemd
ii  systemd        229-4ubuntu21.30 amd64        system and service manager
ddstreet at ddstreet-test:~$ ls -l /dev/ptp*
crw------- 1 root root 247, 0 Apr  1 17:33 /dev/ptp0
crw------- 1 root root 247, 1 Apr  1 17:33 /dev/ptp1
lrwxrwxrwx 1 root root      4 Apr  1 17:33 /dev/ptp_hyperv -> ptp0
ddstreet at ddstreet-test:~$ grep . /sys/class/ptp/*/clock_name
/sys/class/ptp/ptp0/clock_name:hyperv
/sys/class/ptp/ptp1/clock_name:mlx5_p2p


** Tags removed: verification-needed verification-needed-xenial
** Tags added: verification-done verification-done-xenial

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https://bugs.launchpad.net/bugs/1913763

Title:
  hyperv: unable to distinguish PTP devices

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

Bug description:
  [impact]

  the /dev/ptp0 device for a hyperv instance may not be the correct,
  hyperv-provided, ptp device.

  [test case]

  on some hyperv instance types, particularly those that might contain
  passthrough network card(s) that also provide ptp, the first ptp
  device may not be the correct one to use for ptp, e.g. there may be
  multiple ones:

  $ ls /dev/ptp*
  /dev/ptp0 /dev/ptp1
  $ cat /sys/class/ptp/ptp0/clock_name
  hyperv
  $ cat /sys/class/ptp/ptp1/clock_name
  mlx5_p2p

  the order can change across boots, so a consistent way of addressing
  the hyperv-provided one is needed

  [regression potential]

  any regression would involve failure to properly create the ptp
  symlink, or other failure while udev is processing newly detected ptp
  device(s)

  [scope]

  this is needed in all releases

  this was fixed upstream with the commit
  32e868f058da8b90add00b2958c516241c532b70 which is not yet included in
  any release

  [original description]

  Hyperv provides a PTP device. On system with multiple PTP devices,
  services like Chrony don't have a way to know which one is which.

  We would like to have a udev rule to create a symlink to the hyperv
  clock. This way, services could be configured to always use this clock
  no matter if it is ptp0, ptp1, etc..

  For example:

  ```
  SUBSYSTEM=="ptp", ATTR{clock_name}=="hyperv", SYMLINK += "ptp_hyperv"
  ```

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