Why get_fs_names return NULL?

Why get_fs_names return NULL?

[wilbur.chan]

I am going to start a kernel using ramdisk, but  kernel panic  when
mounting the ramdisk fs.


After traped the code , I found that , when kernel invoked
get_fs_names, it got a NULL list of existing file system names.

That is to say,
prepare_namespace--->mount_root-->mount_block_root-->get_fs_names-->get_filesystem_list
 ,

return  a list of nothing...

I thought that , maybe module_init(init_ext2_fs) failed , but I don't
know why? and how to solve it ?

here is my ramdisk script:

mkdir initrd
dd if=/dev/zero of=initrd.img bs=1k count=4096
mke2fs -F -v -m0 initrd.img
mount -o loop initrd.img initrd
cp -av rootfs/* initrd
sync
umount initrd
sync
gzip -f -9 initrd.img
sync
./mkimage -T ramdisk -C gzip -n ' Ramdisk Image' -d initrd.img.gz
your.ramdisk.u-boot