editing geli code to write something in a file

[s m]

hello all

for some reason, i want to do some extra process when entered passphrase is
correct in geli. in order to do that, i edit geli code (g_eli.c file) and
add my code to g_eli_taste function. every thing is ok except writing some
thing in a file. i can't use any standard library here. is there any way to
do that? should i use kernel functions which works with vnode in order to
do that??? if yes, how should i do it? please give me a point.

thanks in advance
SAM