Mysterious rsync/ssh/scp hang

When I was writing a wrapper script for ease of syncing files with my cell-phone, I encountered this mysterious rsync hang when connecting to the phone.

The idea is to convert the phone to rndis mode after it is connect to PC with USB, then use rsync over the usb0 network device on the PC.

The command to convert phone's mode is like following: 

adb shell su -c "
    setsid setsid sh -c '
        setprop persist.sys.usb.config rndis,adb;
        while ! netcfg|grep 'rndis0.*UP'; do
            netcfg rndis0 up; 
        done;
        ifconfig rndis0 192.168.15.244
    '"

After that, I will use rsync to the phone, 192.168.15.244, but unfortunately, it hangs.

After a few debugging, I found out that it's because I have not made sure the rndis path is up after I issue that long adb command! So basically this means when I start rsync, the usb0 device is not there.

Fixing it is easy, just make sure you don't change the phone's rndis state unnecessary, and if you must change it, then wait a few seconds before you use the usb0 network.

Code is at scp-to-phone.