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[Launchpad Bug Tracker <1435687@xxxxxxxxxxxxxxxxxx>]

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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.

** Affects: systemd
     Importance: Unknown
         Status: Fix Released

** Affects: ubuntu-settings (Ubuntu)
     Importance: Undecided
         Status: New


** Tags: patch
-- 
disable/enable WiFi on devices with read-only rootfs, the wifi network name will auto plus 1
https://bugs.launchpad.net/bugs/1435687
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