musb_hdrc musb_hdrc: new USB bus registered, assigned bus number 1
usb usb1: configuration #1 chosen from 1 choice
hub 1-0:1.0: USB hub found
hub 1-0:1.0: 1 port detected
mice: PS/2 mouse device common for all mice
davinci-mmc davinci-mmc.0: Supporting 4-bit mode
davinci-mmc davinci-mmc.0: Using DMA mode
Advanced Linux Sound Architecture Driver Version 1.0.12rc1 (Thu Jun 22 13:55:50
2006 UTC).
ASoC version 0.13.1
MUX: initialized MCBSP
AIC3X Audio Codec 0.1
asoc: aic3x  davinci-i2s mapping ok
ALSA device list:
  #0: DaVinci EVM (aic3x)
TCP bic registered
NET: Registered protocol family 1
VFS: Cannot open root device "nfs" or unknown-block(0,255)
Time: timer0_1 clocksource has been installed.
Clock event device timer0_0 configured with caps set: 08
Switched to high resolution mode on CPU 0
Please append a correct "root=" boot option
Kernel panic - not syncing: VFS: Unable to mount root fs on unknown-block(0,255)
上面是我的板子上启动显示的信息，跑到最后显示vfs mount失败。在我裁剪内核之前系统能正常启动，现在跑到这就挂掉了。是不是我的那个模块裁剪错了？
用service nfs status查看主机的vfs服务都正常运行
bootargs参数设置如下：
setenv bootargs console=ttyS0,115200n8 noinitrd rwip=192.168.1.188:192.168.1.181:192.168.1.1:255.255.255.0:::offroot=/dev/nfs nfsroot=192.168.1.181:/home/coo/dm6446/nfs_rootfs,nolock mem=64M

这该是什么问题?该怎么解决？

setenv bootargs console=ttyS0,115200n8 noinitrd rw ip=192.168.1.188:192.168.1.181:192.168.1.1:255.255.255.0:::off root=/dev/nfs nfsroot=192.168.1.181:/home/coo/dm6446/nfs_rootfs,nolock mem=64M

参数之间注意加空格。
另外你的 kernel 中的 ROOT_NFS 打开了没有?

│ CONFIG_ROOT_NFS:                                                                                                                   │  
  │                                                                                                                                    │  
  │ If you want your system to mount its root file system via NFS,                                                                     │  
  │ choose Y here.  This is common practice for managing systems                                                                       │  
  │ without local permanent storage.  For details, read                                                                                │  
  │ .                                                                                      │  
  │                                                                                                                                    │  
  │ Most people say N here.                                                                                                            │  
  │                                                                                                                                    │  
  │ Symbol: ROOT_NFS [=y]                                                                                                              │  
  │ Prompt: Root file system on NFS                                                                                                    │  
  │   Defined at fs/Kconfig:1223                                                                                                       │  
  │   Depends on: NETWORK_FILESYSTEMS && NFS_FS=y && IP_PNP                                                                            │  
  │   Location:                                                                                                                        │  
  │     -> File systems                                                                                                                │  
  │       -> Network File Systems (NETWORK_FILESYSTEMS [=y])                                                                           │  
  │         -> NFS client support (NFS_FS [=y])                                                                                        │  
  │