Hi there,
I have a rather strange problem: "udevd" is is renaming my "ath0" interface to something else during "wifi up". 
root@white1:~# wifi up
ath0 no private ioctls.
ath0 no private ioctls.
ath0 no private ioctls.
ath0 no private ioctls.
ath0 no private ioctls.
ifconfig: SIOCGIFFLAGS: No such device
/sbin/uci: Parse error (invalid command) at line 45, byte 1
/sbin/uci: Parse error (invalid command) at line 45, byte 1
ifconfig: SIOCSIFADDR: No such device
Error for wireless request "Set ESSID" (8B1B) :
GET failed on device ath0 ; No such device.
Error for wireless request "Set ESSID" (8B1A) :
SET failed on device ath0 ; No such device.
/sbin/uci: Parse error (invalid command) at line 45, byte 1
/sbin/uci: Parse error (invalid command) at line 45, byte 1
ath0 no private ioctls.
Configuration file: /var/run/hostapd-ath0.conf
ioctl(SIOCGIFINDEX): No such device
madwifi driver initialization failed.
rmdir[ctrl_interface]: No such file or directory
enable_atheros(wifi0): Failed to set up hostapd for interface ath0
ifconfig: SIOCGIFFLAGS: No such device
wlanconfig: ioctl: No such device
root@white1:~#when calling dmesg afterwards, it shows me:
br-lan: port 2(ath0) entering disabled state
device ath0 left promiscuous mode
br-lan: port 2(ath0) entering disabled state
udev: starting version 142
udev: starting version 142
udev: renamed network interface ath0 to ath3Wifi does not work of course.
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However when I kill udevd before doing "wifi up", everything works. Wifi up gives me:
/sbin/uci: Parse error (invalid command) at line 45, byte 1
Configuration file: /var/run/hostapd-ath0.conf
Using interface ath0 with hwaddr 00:23:cd:ba:2e:1f and ssid 'red'and dmesg shows:
br-lan: port 2(ath0) entering disabled state
device ath0 left promiscuous mode
br-lan: port 2(ath0) entering disabled state
device ath0 entered promiscuous mode
br-lan: port 2(ath0) entering forwarding statelg, Mr.M
I'll post a solution when I have found one, cause I need udevd.