路由器还有不少空间，但是安装新应用是提示 /overlay 空间不够。
I want to install openssh-server on my "KAMIKAZE (bleeding edge,
r23485)".
Unfortunately, "/overlay" has not enough space.

 root at OpenWrt:/# df
  Filesystem           1K-blocks      Used Available Use% Mounted on
  /dev/root                 1536      1536         0 100% /rom
  tmpfs                     6720      1340      5380  20% /tmp
  tmpfs                      512         0       512   0% /dev
  /dev/mtdblock3            1408       368      1040  26% /overlay
  mini_fo:/overlay          1536      1536         0 100% /

 root at OpenWrt:/# cat /etc/opkg.conf 
  src/gz snapshots
    http://downloads.openwrt.org/snapshots/trunk/brcm47xx/packages dest
  root / dest ram /tmp
  lists_dir ext /var/opkg-lists
  option overlay_root /overlay

"/tmp" seems to be a goob choice:
- I would create "/tmp/overlay"
- What else to do for the "mini_fo:" device?
我的路由器没有USB接口。