[yocto] udev-cache problems

[Maxim Osipov]

Hi all,

I've a poky/Yocto 1.8 system for an imx6 board equipped with U-Blox SARA-U2
GSM/GPRS module connected via USB. The modem is seen as
several /dev/ttyACM* devices. I use ofono 1.16 to work with the modem.
After startup ofono doesn't detect the modem - it starts
to identify the modem if I restart manually udev daemon (by calling
/etc/init.d/udev restart).
Problem with ofono modem detection during startup disappears if I disable
udev-cache in /etc/default/udev-cache:
by commenting out DEVCACHE variable.

So I've analyzed /etc/init.d/udev and udev-cache scripts.
In my opinion the udev script has problems:

* One funny thing appears during system startup.
First udev computes system configuration and compares it with cached one.
And they are identical! So udev decides that its cache is correct and sets
the flag not_first_boot which leads to call of udevadm command with a lot
of --subsystem-nomatch options (option '--subsystem-nomatch=tty' causes
problems with ofono detection of ttyACM*). But during script execution it
seems that system configuration changes (have a look at trace below - it
seems that /dev/ttyACM* appear after system configuration computation).

*) Ok. Let's restart udev manually. Now udev detects that stored udev-cache
is not correct and it creates file /dev/shm/udev-regen as a flag to
regenerate the cache. But it will be regenerated during subsequent call of
/etc/init.d/udev (it calls internally /etc/init.d/udev-cache script).
Definitely, in case of HW (cold) reboot this flag will disappear,
so as a result /etc/udev-cache.tar.gz file will not be regenerated.

Is there any fix solving properly described problems (except workarounds
like disabling udev-cache or removal of option --subsystem-nomatch=tty from
'udevadm trigger --action=add' call)?

Kind regards,
Maxim.

usb 1-1.3: new high-speed USB device number 3 using ci_hdrc
+ export TZ=/etc/localtime
+ TZ=/etc/localtime
+ '[' -d /sys/class ']'
+ '[' -r /proc/mounts ']'
+ '[' -x /lib/udev/udevd ']'
+ SYSCONF_CACHED=/etc/udev/cache.data
+ SYSCONF_TMP=/dev/shm/udev.cache
+ DEVCACHE_REGEN=/dev/shm/udev-regen
+ CMP_FILE_LIST='/proc/version /proc/cmdline /proc/devices'
+ '[' -f /proc/atags ']'
+ META_FILE_LIST='lib/udev/rules.d/* etc/udev/rules.d/*'
+ '[' -f /etc/default/udev-cache ']'
+ . /etc/default/udev-cache
++ DEVCACHE=/etc/udev-cache.tar.gz
++ PROBE_PLATFORM_BUS=yes
+ '[' -f /etc/udev/udev.conf ']'
+ . /etc/udev/udev.conf
++ udev_run=/var/run/udev
+ '[' -f /etc/default/rcS ']'
+ . /etc/default/rcS
++ TMPTIME=0
++ SULOGIN=no
++ DELAYLOGIN=no
++ UTC=yes
++ VERBOSE=no
++ EDITMOTD=no
++ ENABLE_ROOTFS_FSCK=no
++ FSCKFIX=yes
++ VOLATILE_ENABLE_CACHE=yes
++ ROOTFS_READ_ONLY=no
+ case "$1" in
+cdc_acm 1-1.3:1.0: ttyACM0: USB ACM device
export ACTION=add
+ ACTION=add
+ echo 'Starting udev'
Startincdc_acm 1-1.3:1.2: ttyACM1: USB ACM device
g udev
+ grep -q devtmpfs /proc/filesystems
+ LANG=C
+ awk '$2 == "/dev" && ($3 == "devtmpfs")cdc_acm 1-1.3:1.4: ttyACM2: USB
ACM device
{ exit 1 }' /proc/mounts
+ '[' -e /dev/pts ']'
+ mkdir -m 0755cdc_acm 1-1.3:1.6: ttyACM3: USB ACM device
/dev/pts
+ '[' -e /dev/shm ']'
+ mkdir -m 1777 /dev/shm
+ mkdcdc_acm 1-1.3:1.8: ttyACM4: USB ACM device
ir -m 1777 -p /var/volatile/tmp
+ '[' /etc/udev-cache.tar.gz '!=cdc_acm 1-1.3:1.10: ttyACM5: USB ACM device
' '' ']'
+ '[' -e /etc/udev-cache.tar.gz ']'
+ sysconf_cmd
+ ccdc_acm 1-1.3:1.12: ttyACM6: USB ACM device
at -- /proc/version /proc/cmdline /proc/devices
+ awk -F/ '{print $1 " " $NF;}'
+ stat -c '%s %Y %n' -- lib/udev/rules.d/40-usb_modeswitch.rules
lib/udev/rules.d/42-usb-hid-pm.rules
lib/udev/rules.d/50-udev-default.rules
lib/udev/rules.d/60-cdrom_id.rules lib/udev/rules.d/60-persistent-als2
lib/udev/rules.d/75-tty-description.rules
lib/udev/rules.d/78-sound-card.rules lib/udev/rules.d/80-drivers.rules
lib/udev/rules.d/85-regulatory.rules
lib/udev/rules.d/95-keyboard-force-release.rules lib/udev/rus
+ cmp /etc/udev/cache.data /dev/shm/udev.cache
+ tar xmf /etc/udev-cache.tar.gz -C / -m
+ not_first_boot=1
+ '[' no '!=' no ']'
+ '[' -e /dev/shm/udev.cache ']'
+ rm -f /dev/shm/udev.cache
+ '[' -e /dev/shm/udev-regen ']'
+ kill_udevd
+ '[' -e /proc/sys/kernel/hotplug ']'
+ echo -e '\000'
+ /lib/udev/udevd -d
+ udevadm control --env=STARTUP=1
+ '[' 1 '!=' '' ']'
+ '[' yes '!=' yes ']'
+ PLATFORM_BUS_NOMATCH=
+ udevadm trigger --action=add --subsystem-nomatch=tty
--subsystem-nomatch=mem --subsystem-nomatch=vc
--subsystem-nomatch=vtconsole --subsystem-nomatch=misc
--subsystem-nomatch=dcon --subsystem-nomatch=pci_bus x
+ exit 0
+ udevadm settle --timeout=3
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