a question about kernel porting

[zouqiong <zouqiong@ict.ac.cn>]

while i am porting, when the kernel are about to mount the ext3 fs,
kernel panic happens. kernel panic: VFS: Unable to mount root fs
on /dev/hda1 or unknown-block(0,0)

when i trace the kernel, function kobj_lookup returns NULL,
kobj_lookup(bdev_map, dev, part), the value of the dev is 0,

and in function kobj_lookup() , it exits because 
if (p->dev > dev || p->dev + p->range - 1 < dev)
  continue;

can some one tell me the reason?
is it i omit something in the way of my poring or is it the kernel bug? 
how to find out it?
thx

-- 
zouqiong <zouqiong@ict.ac.cn>