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Message #64527
[Bug 1435687] Re: disable/enable WiFi on devices with read-only rootfs, the wifi network name will auto plus 1
** Changed in: systemd
Status: Unknown => Fix Released
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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:
Fix Released
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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References