mini2440 nfs 挂载文件系统出错。

TCP cubic registered
NET: Registered protocol family 17
s3c2410-rtc s3c2410-rtc: hctosys: invalid date/time
Root-NFS: No NFS server available, giving up.
VFS: Unable to mount root fs via NFS, trying floppy.
VFS: Cannot open root device "<NULL>" or unknown-block(2,0)
Please append a correct "root=" boot option; here are the available partitions:
1f00             256 mtdblock0 (driver?)
1f01             128 mtdblock1one_wire_status: 4
 (driver?)
1f02            5120 mtdblock2 (driver?)
1f03          256640 mtdblock3 (driver?)
1f04          262144 mtdblock4 (driver?)
Kernel panic - not syncing: VFS: Unable to mount root fs on unknown-block(2,0)
one_wire_status: 4
Backtrace:
[<c00341cc>] (dump_backtrace+0x0/0x10c) from [<c0329f3c>] (dump_stack+0x18/0x1c)
 r7:c03dba08 r6:00008000 r5:c3923000 r4:c0481c90
[<c0329f24>] (dump_stack+0x0/0x1c) from [<c0329f8c>] (panic+0x4c/0x114)
[<c0329f40>] (panic+0x0/0x114) from [<c0008dbc>] (mount_block_root+0x174/0x228)
 r3:c38663ec r2:00000000 r1:c3823f60 r0:c03db9a0
[<c0008c48>] (mount_block_root+0x0/0x228) from [<c0008f34>] (mount_root+0xc4/0xfc)
[<c0008e70>] (mount_root+0x0/0xfc) from [<c0009094>] (prepare_namespace+0x128/0x180)
 r5:c001f2e4 r4:c0481660one_wire_status: 2[<c0008f6c>] (prepare_namespace+0x0/0x180) from [<c00084b0>] (kernel_init+0xe0/0x114)
 r5:c001f2e4 r4:c0481420
[<c00083d0>] (kernel_init+0x0/0x114) from [<c004bbbc>] (do_exit+0x0/0x620)
 r5:00000000 r4:00000000one_wire_status: 4

我想通过nfs挂载文件系统出现如上错误。（内核 和bootloader 都是原装已经烧录好的。 文件系统也是光盘里直接解压的。）
（另外奇怪的是我今天才注册帐号，去年就在这发帖了？）