Default [Q] f2fs format tool problem, help!!

I met a question when I tried to make my nexus7 format /data to f2fs. When I went to recvoery mode and type $mkfs.f2fs , it appeared error message: "mkfs.f2fs: applet not found ". Here is my steps:

1. Merge kernel patch to support f2fs in my device kernel, and it worked.
2. Modified which in android_external_f2fs-tools to give statically links to CWM. Add "LOCAL_LDLIBS := --static"
3. Add "TARGET_USERIMAGES_USE_F2FS := true" in

Did anything I should modified? Help plz

Here is my envirentment:
Android version: 4.4.2
CMW version:
ROM: CM-11
Device: Nexus 7 (2012 GSM)
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