Ath9k as AP in Arch Linux

I have a Macbook with an Atheros AR5008 wireless network adapter, which is supposed to be able to act as an AP. Some time ago I used Madwifi driver for it. It includes a tool that can create multiple “virtual adapters” and I could use one as an AP to share either my wired or wireless network. However now I use the stock ath9k driver in the kernel, and I need my Macbook to share its PPP connection wirelessly with my iPhone. It is claimed that ath9k has the ability to put my adapter into master mode, but I could not just do iwconfig wlan0 mode Master to get it.

After some research, it looked like to me that ath9k did that by implementing the hostap driver, which was utilized by the hostapd program. Then I found this document, that described all that was needed to be done. I do not need DHCP, so that falls into four steps.

  1. Set up my wireless adapter, my PPP interface has IP address like 118.207.x.y, so I can safely use 192.168.1.0/24 as my wireless LAN IPs.
    # ifconfig wlan0 192.168.1.1 netmask 255.255.255.0
  2. Config hostapd by editing /etc/hostapd/hostapd.conf. Change interface and SSID. Then start hostapd daemon by
    # /etc/rc.d/hostapd start
  3. Enable IP forwarding by
    # echo 1 > /proc/sys/net/ipv4/ip_forward
    then optionally make it permanent by editing /etc/sysctl.conf and setting net.ipv4.ip_forward to 1.
  4. Actually forward IP packets with iptables,
    # iptables -t nat -A POSTROUTING -o ppp0 -j MASQUERADE
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