FileSystem on Rishav's Digital Garden

Generating Package Patch for Buildroot

Tue, 20 May 2025 10:13:00 +0000

Generating a Patch Using `diff`

1. Extract the Original Source

Ensure you have a pristine copy of the original source for comparison. You can extract it from the tarball in the dl directory:

tar -xf dl/<package>-<version>.tar.gz -C /tmp/

This will create a directory like /tmp/<package>-<version>/.

Using buildroot’s mechanism

Clean the build directory and apply current patches of buildroot

make <pkg>-dirclean # Remove <pkg> build directory
make <pkg>-extract # Extract <pkg> sources
make <pkg>-patch # Apply patches to <pkg> (Optional)

cp -r output/build/<package> /tmp/

2. Generate the Patch

Use the diff command to create a unified diff between the original and modified sources:

Boot to recovery filesystem

Thu, 15 May 2025 14:59:00 +0000

Process

Mount recovery partition into temporary location

mkdir -p /mnt/recovery
mount /dev/mmcblk0p6 /mnt/recovery

Prepare old_root directory

mkdir -p /mnt/recovery/mnt/old_root

Switch root using pivot_root

cd /mnt/recovery
pivot_root . mnt/old_root

Now:

New root is /mnt/recovery (i.e., /)
The previous root (e.g., initramfs or mainfs) is now mounted at /mnt/old_root

Note: The chroot must be available under the old root and under the new root(recovery)

Remount /proc, /sys, /dev, etc

mount -t proc proc /proc
mount -t sysfs sysfs /sys
mount -o bind /mnt/old_root/dev /dev
mount -o bind /mnt/old_root/tmp /tmp
mount -o bind /mnt/old_root/run /run

Start a shell inside of new root

exec /bin/sh

Mount root filesystem from NFS

Setup nfs-service on host machine (refer this)
Mount NFS filesystem into the board

mount -t nfs -o nolock 192.168.1.27:/home/rishav/Public /mnt/nfsroot

Mount ext image as a loopback device

mkdir -p /mnt/local
cp /mnt/nfs/rootfs.ext4 /tmp/rootfs.ext4
mount -o loop /tmp/rootfs.ext4 /mnt/local

References

Manual page of pivot_root
Also see difference between pivot_root and chroot

Kernel Space vs User Space

Tue, 04 Feb 2025 17:23:00 +0000

Overview

Kernel Space: This is where the Linux kernel executes and provides low-level access to hardware, system memory management, process scheduling, and device drivers. Kernel space has privileged access to system resources and is protected from direct user interference. For example, when a user requests data from a hardware sensor, the kernel driver handles communication with the hardware, processes the request, and returns the data to user space through system calls.
User Space: This is where applications and system utilities run. User-space processes operate with restricted privileges and interact with the kernel via system calls, libraries, and IPC mechanisms. For example, a user-space daemon may monitor the watchdog status by writing to /dev/watchdog, or a mobile app may read light intensity from /sys/bus/i2c/devices/1-0039/lux.

Communication Methods between Kernel and User Space

There are several ways to facilitate communication between user space and kernel space in an embedded Linux environment:

Making File System

Mon, 11 Nov 2024 19:14:00 +0000

Overview

Get the final files into a directory eg. target and treat it as root(/) directory of target board/system.
Generate users eg. root, admin, ssh, etc
Generate device lists
Clean few files
Generate ext image using mkfs

Taking reference from buildroot common.mk and ext2.mk

scripts/makedevs -d output/build/buildroot-fs/full_devices_table.txt output/build/buildroot-fs/ext2/target

mkfs.ext4 -d output/build/buildroot-fs/ext2/target -r 1 -N 0 -m 5 -L rootfs -O ^64bit output/images/rootfs.ext2 2G

# Fakeroot execution complete

/opt/rk3588_nvrx/host/sbin/resize2fs -M output/images/rootfs.ext2
/opt/rk3588_nvrx/host/sbin/e2fsck -fy /output/images/rootfs.ext2
/opt/rk3588_nvrx/host/sbin/resize2fs -M /output/images/rootfs.ext2

Fakeroot Script

#!/bin/sh
set -ex
chown -h -R 0:0 $(TARGET)
$(HOST_DIR)/bin/makedevs -d full_devices_table.txt $(TARGET)
$(HOST_DIR)/sbin/mkfs.ext4 -d $(TARGET) -r 1 -N 0 -m 5 -L "rootfs" -O ^64bit rootfs.ext2 "2G"

Post EXT4

$(HOST_DIR)/sbin/resize2fs -M rootfs.ext2
$(HOST_DIR)/sbin/e2fsck -fy rootfs.ext2
$(HOST_DIR)/sbin/tune2fs -m 5 rootfs.ext2
$(HOST_DIR)/sbin/resize2fs -M rootfs.ext2

Testing on Host

sudo mount -o loop path/to/rootfs.ext4 /tmp/fs_path

Makedevs

Creates a batch of special files as specified in a device table.

FileSystem on Rishav's Digital Garden

Generating Package Patch for Buildroot

Generating a Patch Using diff

1. Extract the Original Source

Using buildroot’s mechanism

2. Generate the Patch

Boot to recovery filesystem

Process

Mount root filesystem from NFS

References

Kernel Space vs User Space

Overview

Communication Methods between Kernel and User Space

Making File System

Overview

Fakeroot Script

Post EXT4

Testing on Host

Makedevs

Generating a Patch Using `diff`