用NFS可以挂上光盘给的根文件系统，却挂不了自己做的，如果下载到板子里的话，都可以。
下面是部分信息：
VFS: Unable to mount root fs via NFS, trying floppy.
VFS: Cannot open root device "nfs" or unknown-block(2,0)
Please append a correct "root=" boot option; here are the available partitions:
1f00 256 mtdblock0 (driver?)
1f01 128 mtdblock1 (driver?)
1f02 5120 mtdblock2 (driver?)
1f03 1043072 mtdblock3 (driver?)
1f04 1048576 mtdblock4 (driver?)
Kernel panic - not syncing: VFS: Unable to mount root fs on unknown-block(2,0)
Backtrace:
[<c0035270>] (dump_backtrace+0x0/0x10c) from [<c03958f0>] (dump_stack+0x18/0x1c)
r7:c39230cb r6:c0503ed0 r5:c3923000 r4:c3823f40
[<c03958d8>] (dump_stack+0x0/0x1c) from [<c0395940>] (panic+0x4c/0x134)
[<c03958f4>] (panic+0x0/0x134) from [<c0008e9c>] (mount_block_root+0x178/0x234)
r3:00000000 r2:c385a92c r1:c3823f40 r0:c0453700
[<c0008d24>] (mount_block_root+0x0/0x234) from [<c0009008>] (mount_root+0xb0/0xf
4)
[<c0008f58>] (mount_root+0x0/0xf4) from [<c0009144>] (prepare_namespace+0xf8/0x1
90)
r7:c05038a0 r6:c0021808 r5:c0021808 r4:c0021818
[<c000904c>] (prepare_namespace+0x0/0x190) from [<c00084c0>] (kernel_init+0xf0/0
x124)
r7:00000000 r6:c00200dc r5:c00205d4 r4:c00205d4
[<c00083d0>] (kernel_init+0x0/0x124) from [<c004d1a4>] (do_exit+0x0/0x62c)
r7:00000000 r6:00000000 r5:00000000 r4:00000000
