You can get the latest xv6 code from following location

git clone git://pdos.csail.mit.edu/xv6/xv6.git

Now just apply the patches using following command

patch -p1 < {patch_file_name}
for e.g.
patch -p1 < 0001-adding-a-system-call-to-get-open-fds-by-a-process.patch

And then compile your xv6 and check :) 

or you can clone the custom xv6 with all the patches :-

git clone https://github.com/pawanpraka1/my_xv6.git.