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[Ubuntu Foundations Team Bug Bot <1435687@xxxxxxxxxxxxxxxxxx>]

The attachment "Avoid duplicated udev match rules" seems to be a patch.
If it isn't, please remove the "patch" flag from the attachment, remove
the "patch" tag, and if you are a member of the ~ubuntu-reviewers,
unsubscribe the team.

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** Tags added: patch

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https://bugs.launchpad.net/bugs/1435687

Title:
  disable/enable WiFi on devices with read-only rootfs, the wifi network
  name will auto plus 1

Status in systemd:
  Unknown
Status in systemd package in Ubuntu:
  New

Bug description:
  On devices with read-only rootfs, e.g. mobile phones, nic device
  number (wlan<N>) may increase every time disabled and re-enabled. To
  be more precisely, this happens only on devices when disabling a NIC
  removes the corresponding driver.

  "/lib/udev/rules.d/75-persistent-net-generator.rules" checks whether
  NAME attribute has been assigned to wlan<N> device: if yes, skip all
  the followed steps, or, call to "/lib/udev/write_net_rules" to
  generate a persistent device name rule file. That persistent file
  should be created under "/etc/udev/rules.d" and named "70-persistent-
  net.rules", so it guarantees NAME attribute should be assigned if
  available before being read. However, when rootfs was previously
  mounted as read-only, a file "/run/udev/tmp-rules--70-persistent-
  net.rules" is created instead. This temporary file is supposed to be
  moved back into "/etc/udev/rules.d" by a systemd service udev-finish
  right after the system finishes start-up chaos. Again, if rootfs is
  still mounted as read-only, this move will certainly fail. One last
  important thing, /run/udev is _NOT_ included in udev rules inclusion
  paths, so any rules written here will not be taken into account when
  processing uevents.

  So, when wlan0 is probed for the first time on a device with read-only
  rootfs, udev creates "/run/udev/tmp-ruiles--70-persistent-net.rules"
  and inserts one rule for it. When wlan0 is disabled and re-enabled,
  since "/run/udev/tmp-rules--70-persistent-net.rules" is not taken into
  account, its NAME attribute will not be set, and udev recognize it as
  a new nic and tries to write another rule for it again. However, in
  this time, "wlan0" has been taken in the previously written temporary
  rules file, so "wlan1" is chosen instead, and an exactly the same
  matching rule (except for NAME= part) is appended to "/run/udev/tmp-
  rules--70-persistent-net.rules". When the device is again disabled and
  re-enabled, "wlan2" will be assigned. And so on ....

  This is a cloned bug from Debian bug 780705 (https://bugs.debian.org
  /cgi-bin/bugreport.cgi?bug=780705), which affects Ubuntu Phone.

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