在开发板上使用netboot的方式启动Linux系统时无法通过NFS网络文件系统挂载根文件系统的解决过程记录

初始症状描述

网线连接情况如下：

按下面的命令设置u-boot：

01-运行下面的命令指定设备树文件的名字：

setenv fdt_file imx6ull-14x14-evk.dtb

注意：不需要设置内核镜像的名字，因为u-boot知道内核镜像的名字为zImage

02-运行下面的命令关闭自动配置 IP:
即不需要之前在博文 https://blog.youkuaiyun.com/wenhao_ir/article/details/145662136 看到的BOOTP协议(即DHCP协议)去自动获得IP，其实这里也没有DHCP服务器，你想用也不用了。

setenv ip_dyn no

03-运行下面的命令设置TFTP和NFS的服务器地址(在这里就是Ubuntu系统的地址)：

setenv serverip 192.168.5.11

04-运行下面的命令设置开发板的IP地址：

setenv ipaddr 192.168.5.9

05-运行下面的命令设置NFS网络文件系统的目录：

setenv nfsroot /home/book/mybuild/nfs_linux_rootfs

命令汇总如下：

setenv fdt_file imx6ull-14x14-evk.dtb
setenv ip_dyn no
setenv serverip 192.168.5.11
setenv ipaddr 192.168.5.9
setenv nfsroot /home/book/mybuild/nfs_linux_rootfs

然后运行下面的命令从网络启动Linux系统了：

run netboot

发现能通过TFTP把内核和设备树文件下载到内存中，但是在内核的启动过程中，卡在下面这里：

[   80.421313] IP-Config: Retrying forever (NFS root)...
[   80.527467] SMSC LAN8710/LAN8720 20b4000.ethernet-1:01: attached PHY driver [SMSC LAN8710/LAN8720] (mii_bus:phy_addr=20b4000.ethernet-1:01, irq=POLL)
[   80.647347] SMSC LAN8710/LAN8720 20b4000.ethernet-1:00: attached PHY driver [SMSC LAN8710/LAN8720] (mii_bus:phy_addr=20b4000.ethernet-1:00, irq=POLL)
[   82.647600] fec 20b4000.ethernet eth0: Link is Up - 100Mbps/Full - flow control rx/tx
[   82.667322] IPv6: ADDRCONF(NETDEV_CHANGE): eth0: link becomes ready
[   82.696965] Sending DHCP requests ......
[  125.927255] imx-sdma 20ec000.sdma: external firmware not found, using ROM firmware
[  155.796796]  timed out!
[  155.811068] IP-Config: Retrying forever (NFS root)...
[  155.917329] SMSC LAN8710/LAN8720 20b4000.ethernet-1:01: attached PHY driver [SMSC LAN8710/LAN8720] (mii_bus:phy_addr=20b4000.ethernet-1:01, irq=POLL)
[  156.037354] SMSC LAN8710/LAN8720 20b4000.ethernet-1:00: attached PHY driver [SMSC LAN8710/LAN8720] (mii_bus:phy_addr=20b4000.ethernet-1:00, irq=POLL)
[  158.007635] fec 20b4000.ethernet eth0: Link is Up - 100Mbps/Full - flow control rx/tx
[  158.026868] IPv6: ADDRCONF(NETDEV_CHANGE): eth0: link becomes ready
[  158.056900] Sending DHCP requests .....
[  213.216793] . timed out!
[  243.231282] IP-Config: Retrying forever (NFS root)...
......
......
......
[ 7384.209601] IP-Config: Retrying forever (NFS root)...
[ 7384.317180] SMSC LAN8710/LAN8720 20b4000.ethernet-1:01: attached PHY driver [SMSC LAN8710/LAN8720] (mii_bus:phy_addr=20b4000.ethernet-1:01, irq=POLL)
[ 7384.437248] SMSC LAN8710/LAN8720 20b4000.ethernet-1:00: attached PHY driver [SMSC LAN8710/LAN8720] (mii_bus:phy_addr=20b4000.ethernet-1:00, irq=POLL)
[ 7386.407606] fec 20b4000.ethernet eth0: Link is Up - 100Mbps/Full - flow control rx/tx
[ 7386.427294] IPv6: ADDRCONF(NETDEV_CHANGE): eth0: link becomes ready
[ 7386.456932] Sending DHCP requests