setenv bootargs "root=/dev/nfs nfsroot=192.168.0.100:/work/openwrt/rootfs,vers=3 ip=192.168.0.101:::255.255.255.0::eth1 nfsrootdebug"
setenv bootcmd "tftp 84000000 openwrt-ipq40xx-qcom_ap-dk01.1-c1-fit-uImage.itb && bootm 84000000"
首先开启NFS客户端
<*> NFS client support
< > NFS client support for NFS version 2
<*> NFS client support for NFS version 3
[ ] NFS client support for the NFSv3 ACL protocol extension
< > NFS client support for NFS version 4
[ ] Provide swap over NFS support
然后开启rootfs nfs，需要开启IP_PNP，才能开启ROOT_NFS
CONFIG_IP_PNP
[*] IP: kernel level autoconfiguration
CONFIG_ROOT_NFS
[*] Root file system on NFS
注意使用make kernel_menuconfig开启CONFIG_ROOT_NFS后，还不行，openwrt会把它删除，还需要在make menuconfig中开启：
Global build settings → Kernel build options
[*] Compile the kernel with rootfs on NFS
能正常启动，但是启动到netifd时，ip变了，导致nfs断掉：
[ 1.354496] IPv6: ADDRCONF(NETDEV_UP): eth1: link is not ready
[ 3.442784] ess_edma c080000.edma: eth1: GMAC Link is up with phy_speed=1000
[ 3.451735] IPv6: ADDRCONF(NETDEV_CHANGE): eth1: link becomes ready
[ 3.482195] IP-Config: Complete:
[ 3.482482] device=eth1, hwaddr=92:98:36:73:3b:10, ipaddr=192.168.0.101, mask=255.255.255.0, gw=255.255.255.255
[ 3.484736] host=192.168.0.101, domain=, nis-domain=(none)
[ 3.495546] bootserver=255.255.255.255, rootserver=192.�[ 3.508556] root_dev 255
[ 3.508782] Root-NFS: nfsroot=/work/openwrt/rootfs,vers=3
[ 3.512046] NFS: nfs mount opts='vers=2,udp,rsize=4096,wsize=4096,vers=3,nolock,addr=192.168.0.100'
[ 3.515559] NFS: parsing nfs mount option 'vers=2'
[ 3.524460] NFS: parsing nfs mount option 'udp'
[ 3.529616] NFS: parsing nfs mount option 'rsize=4096'
[ 3.534245] NFS: parsing nfs mount option 'wsize=4096'
[ 3.539603] NFS: parsing nfs mount option 'vers=3'
[ 3.544912] NFS: parsing nfs mount option 'nolock'
[ 3.549843] NFS: parsing nfs mount option 'addr=192.168.0.100'
[ 3.554817] NFS: MNTPATH: '/work/openwrt/rootfs'
[ 3.560783] NFS: sending MNT request for 192.168.0.100:/work/openwrt/rootfs
[ 3.581350] NFS: received 1 auth flavors
[ 3.581379] NFS: auth flavor[0]: 1
[ 3.584448] NFS: MNT request succeeded
[ 3.587897] NFS: attempting to use auth flavor 1
[ 3.612507] VFS: Mounted root (nfs filesystem) readonly on device 0:10.
[ 3.614096] Freeing unused kernel memory: 1024K
[ 3.714884] init: Console is alive