Qemu builds ARM vexpress development environment (Part 3) ---- NFS network root file system

In the previous article "Qemu builds ARM vexpress development environment (II) ---- Start the Linux kernel through u-boot", it has been realized to load the kernel through u-boot to start the development board and mount the root file system. This article describes how to mount the root file system through the NFS network.

Through the NFS network root file system, the development board can mount the root file system on another PC host through the NFS network after starting the kernel through u-boot. It provides great convenience for work and study in the development and debugging stage. You can directly develop and compile drivers or APPs on the Linux host, and copy the target files to the NFS service directory for use (the files are equivalent to being copied to the root file system of the development board). You can also directly modify other files in the rootfs file system on the host side, which is equivalent to directly modifying them on the development board.

This article introduces the steps to mount the network root file system using NFS. This method is not only applicable to the ARM vexpress development board environment built by Qemu, but also to all other development board entities.

Since the NFS network file system production methods of each development board are the same, you can also refer to the NFS network file system production method part in the Exynos4412 and NanopiNEO development board environment construction.

1. Environment Configuration

Linux host supports NFS service

Modify bootargs startup parameters

Set up NFS as the root file system

Set the host NFS file system address

The kernel supports NFS mounting file systems

2. Install and configure NFS service

2.1 Enabling NFS service on Linux host

Install:

# sudo apt install nfs-kernel-server

Configure NFS:

# vim /etc/exports

// Add NFS shared directory

/home/mcy/qemu/rootfs *(rw, sync, no_root_squash, no_subtree_check)

    rw Readable and writable operation

    sync Keep the contents of memory and disk synchronized

    no_root_squash The Linux host no longer sets the development board to an anonymous user, and can operate file reading and writing

    no_subtree_check Do not check the root file system subdirectory files

Restart the NFS service:

sudo /etc/init.d/rpcbind restart

sudo /etc/init.d/nfs-kernel-server restart

or:

# systemctl restart nfs-kernel-server

Check whether the NFS shared directory is created:

# sudo showmount -e

Export list for mcy-VirtualBox:

/home/mcy/qemu/rootfs *

Note:

When using the NFS network file system, the Linux host needs to close the system firewall; otherwise, the system will fail during operation.

2.2 Development board configuration supports NFS network

Modify the startup parameters in u-boot:

# vim include/configs/

CONFIG_BOOTCOMMAND

    setenv bootargs 'root=/dev/nfs rw   

    nfsroot=192.168.0.105:/home/mcy/qemu/rootfs init=/linuxrc   

    ip=192.168.0.110 console=ttyAMA0';   

Configure the kernel to support NFS mounting file systems

Improve NFS file system

Reboot command

3. Create a root file system

Compile busybox

nfs

Linux System Utilities --->

    [*] mount (30 kb)

        [*] Support mounting NFS file systems on Linux < 2.6.23

Create a rootfs directory and create files under the rootfs directory:

# mkdir etc

# cd etc

# vim inittab

::sysinit:/etc/init.d/rcS // Execute the rcS script

#::respawn:-/bin/sh

#tty2::askfirst:-/bin/sh

#::ctrlaltdel:/bin/umount -a -r

console::askfirst:-/bin/sh

::ctrlaltdel:/sbin/reboot

::shutdown:/bin/umount -a -r

# vim init.d/rcS

#!/bin/sh

PATH=/sbin:/bin:/user/sbin:/usr/bin

LD_LIBRARY_PATH=/lib

export PATH LD_LIBRARY_PATH

mount -a // Mount the root file system fstab

mkdir -p /dev/pts

mount -t devpts devpts dev/pts

mdev -s

mkdir -p /var/lock

echo "......"

# vim fstab

proc /proc proc defaults 0 0

tmpfs /tmp tmpfs default 0 0

sysfs /sys sysfs default 0 0

tmpfs /dev tmpfs default 0 0

var /dev tmpfs default 0 0

ramfs /dev ramfs default 0 0

# vim profile

PS1='xiami@vexpress:w #'

export PS1

You can also modify or set PS1 in ~/.bashrc

Startup process:

After the Linux kernel starts, mount the root file system

Start the init process, bootargs init=/linuxrc, and start the first user process

Read the inittab script in the user process,

Building other directories

Other directories can be empty directories

# cd rootfs

# mkdir proc mnt tmp sys root