iwi(4) in ibss mode

[Taylor R Campbell <campbell+netbsd%mumble.net@localhost>]

(I am not subscribed to this list, so please cc me in replies.)

I'd like to use a machine with an iwi(4) device, iwi0, as a wireless
gateway, so I want to put iwi0 into hostap or ibss mode.  iwi(4)
doesn't support hostap mode, as far as I can tell, so that leaves ibss
mode.  But whenever I bring iwi0 up in ibss mode with an ssid set, the
kernel reports `iwi0: fatal error' about one second later.

# ifconfig iwi0
iwi0: flags=8802<BROADCAST,SIMPLEX,MULTICAST> mtu 1500
        ssid ""
        powersave off
        address: ...
        media: IEEE802.11 autoselect
        status: no network
        inet6 fe80:...%iwi0 prefixlen 64 scopeid 0x3
# ifconfig iwi0 mediaopt adhoc ssid fnord up
# ifconfig iwi0
iwi0: flags=8843<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST> mtu 1500
        ssid fnord
        powersave off
        chan 1
        address: ...
        media: IEEE802.11 autoselect adhoc
        status: no network
        inet6 fe80:...%iwi0 prefixlen 64 scopeid 0x3
iwi0: fatal error
# ifconfig iwi0
iwi0: flags=8802<BROADCAST,SIMPLEX,MULTICAST> mtu 1500
        ssid fnord
        powersave off
        chan 1
        address: ...
        media: IEEE802.11 autoselect adhoc
        status: no network
        inet6 fe80:...%iwi0 prefixlen 64 scopeid 0x3

Furthermore, if I start from the initial state (shown in the output of
the first ifconfig command), and run

# ifconfig iwi0 mediaopt adhoc up

without setting an ssid, so that I see

# ifconfig iwi0
iwi0: flags=8843<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST> mtu 1500
        ssid ""
        powersave off
        chan 1
        address: ...
        media: IEEE802.11 autoselect adhoc
        status: no network
        inet6 fe80:...%iwi0 prefixlen 64 scopeid 0x3

then soon, after a few minutes, the kernel repeatedly reports `rtk0:
watchdog timeout', and my ethernet interface (rtk0) starts dropping
all frames.

Both these failures -- `iwi0: fatal error' and `rtk0: watchdog
timeout' -- are reproducible.  Below is the excerpt of dmesg output
from boot for the rtk0 and iwi0 interfaces.

Suggestions?

# egrep '(rtk|iwi)' < /var/run/dmesg.boot
rtk0 at pci2 dev 1 function 0: Realtek 8139 10/100BaseTX (rev. 0x10)
rtk0: interrupting at irq 5
rtk0: Ethernet address ...
rlphy0 at rtk0 phy 7: Realtek internal PHY
iwi0 at pci2 dev 2 function 0: vendor 0x8086 product 0x4220 (rev. 0x05)
iwi0: interrupting at irq 5
iwi0: 802.11 address ...
iwi0: 11b rates: 1Mbps 2Mbps 5.5Mbps 11Mbps
iwi0: 11g rates: 1Mbps 2Mbps 5.5Mbps 11Mbps 6Mbps 9Mbps 12Mbps 18Mbps 24Mbps 
36Mbps 48Mbps 54Mbps