Created attachment 2710 [details]
proposed fix

runqemu script fails in a strange way if tap0 is already taken.
It starts but no root is specified so the kernel panics. It's a bit misleading since has nothing to do with root fs.

Acquiring lockfile for tap0@NONE...                                                                                                                                                           
Using preconfigured tap device 'tap0@NONE'                                                                                                                                                    
If this is not intended, touch /tmp/qemu-tap-locks/tap0@NONE.skip to make runqemu skip tap0@NONE.                                                                                             
/home/sherpya/poky/scripts/runqemu-internal: line 256: 0@NONE: value too great for base (error token is "0@NONE")    

by touching the file, the scripts creates tap1 instead and it works

as I see the script uses ip link to get tap devices on my kernel 4.1.6
it shows them as:
5: tap0@NONE: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UNKNOWN mode DEFAULT group default qlen 100
    link/ether 72:15:34:8b:75:a9 brd ff:ff:ff:ff:ff:ff
7: tap1@NONE: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP mode DEFAULT group default qlen 500
    link/ether 32:f1:bb:36:25:c6 brd ff:ff:ff:ff:ff:ff

attached patch fixes the problem using a regexp instead, it's made against fido, but since it's one liner it should not be difficult to apply to master

a side note, you don't need to pipe grep, awk already does it