Modifying Xen source code, my own codes don't seems to execute

Modifying Xen source code, my own codes don't seems to execute

I am learning Xen, I want to add some my own codes, then make and make
install, but when I execute some commands, I can't see any changes. e.g. I
add some lines in tools/python/xen/xm/migrate.py
def main(argv):
opts = gopts
opts.reset()
args = opts.parse(argv)
if len(args) != 2:
raise OptionError('Invalid number of arguments')
"""start of my code"""
fp = open("/m.log",'w')
fp.write('start')
fp.close()
"""end of my code"""
....
As above, I create a file, and then write something, but after I make &&
make install, when I execute it, I can't find the file. I logged in root,
so I am sure I have approprite priviledge. p.s. my Xen version is 4.1.2
Thank you...