1. Linux Kernel Internals

Importance:

Understanding kernel internals is crucial for BSP and driver development as it helps in debugging, optimizing performance, and modifying the kernel to meet hardware-specific requirements.

Topics:

  • Kernel Architecture: [Monolithic vs Microkernel]({< ref “/posts/monolithic-vs-microkernel/” >}}), [Kernel Space vs User Space|Kernel and User Space interactions]({< ref “/posts/kernel-space-vs-user-space|kernel-and-user-space-interactions/” >}}).
  • Process Management: Understanding task_struct, process states, scheduling algorithms.
  • Interrupt Handling: SoftIRQs, tasklets, bottom halves, handling IRQs efficiently.
  • Memory Management: Paging, kmalloc/vmalloc, slab allocator, ARM MMU and memory regions.
  • [../../0-Inbox/syscalls|Syscalls]({< ref “/posts/../../0-inbox/syscalls|syscalls/” >}}): How system calls work, writing custom syscalls.
  • [Kernel Synchronization in Linux|Kernel Synchronization]({< ref “/posts/kernel-synchronization-in-linux|kernel-synchronization/” >}}): Spinlocks, mutexes, semaphores, barriers, RCU.
  • Workqueues and Timers: Deferred execution, using timers for scheduling tasks.

2. Linux Device Drivers

Importance:

Device drivers are the bridge between hardware and the OS. Understanding drivers is crucial for embedded systems and BSP development.

Topics:

  • Character Drivers: open(), read(), write(), ioctl() implementations.
  • Block Drivers: Block layer, request queues, I/O scheduling.
  • Platform Drivers: Registering platform devices, working with platform_driver.
  • Peripheral Drivers ([I2C]({< ref “/posts/i2c/” >}}), [SPI]({< ref “/posts/spi/” >}}), [UART]({< ref “/posts/uart/” >}}), GPIO): Writing and debugging [Character Device Management in Kernel Drivers|drivers]({< ref “/posts/character-device-management-in-kernel-drivers|drivers/” >}}).
  • Power Management: Implementing runtime PM, suspend/resume operations.
  • Interrupt Handling: Requesting IRQs, shared interrupts, threaded IRQs.
  • DMA Handling: Understanding DMA API, memory mappings.

3. Board Support Package (BSP) Development

Importance:

BSP development is fundamental in embedded systems as it enables the OS to run on custom hardware.

Topics:

  • Boot Process & Bootloaders: U-Boot configuration, boot sequence.
  • Device Tree (DTS/DTSI): Writing device tree files, overlays.
  • Kernel Configuration & Compilation: Using menuconfig, defconfig, Kconfig.
  • Root Filesystem & Init System: Understanding BusyBox, systemd integration.
  • Flash Storage Handling: MTD subsystem, eMMC, NAND, SPI-NOR.
  • Clock & Power Management: Configuring common clock framework, PMIC integration.

4. Filesystems & Storage

Importance:

A deep understanding of filesystems is necessary for debugging and optimizing embedded storage solutions.

Topics:

  • VFS (Virtual Filesystem Switch): inode, dentry, superblock structures.
  • Filesystems (EXT4, XFS, UBIFS, JFFS2): Understanding journaling, flash filesystems.
  • Block Layer & IO Scheduling: Elevator schedulers (BFQ, CFQ, noop).
  • Storage Performance Tuning: Tools like fio, iostat, blktrace.

5. Debugging & Performance Tuning

Importance:

Kernel debugging skills are essential for troubleshooting and performance optimization.

Topics:

  • Debugging Tools: gdb, kgdb, kdb, ftrace, perf.
  • Kernel Panics & OOPS Analysis: Using dmesg, analyzing stack traces.
  • Live Patching & Crash Analysis: kexec, crash utility.
  • Profiling & Tracing: perf, eBPF, bpftrace, SystemTap.
  • Race Condition & Deadlock Debugging: Using lockdep, detecting spinlock issues.

6. Security in the Kernel

Importance:

Security mechanisms are crucial for preventing vulnerabilities in embedded systems.

Topics:

  • LSM (Linux Security Modules): SELinux, AppArmor.
  • Secure Boot & Verified Boot: UEFI Secure Boot, dm-verity, ARM TrustZone, OPTee.
  • Memory Protections: KASLR, W^X policy.
  • Syscall Filtering & Sandboxing: Seccomp, cgroups, namespaces.

7. Real-Time Linux & Performance Optimization

Importance:

For time-sensitive embedded applications, real-time (RT) Linux provides deterministic behaviour(refer [3-Resource/Platform/RTOS (FreeRTOS) vs Linux Kernel|RTOS]({< ref “/posts/3-resource/platform/rtos-(freertos)-vs-linux-kernel|rtos/” >}})).

Topics:

  • PREEMPT-RT Patches: Real-time scheduling policies.
  • CPU Isolation & Affinity: Configuring isolcpus, taskset.
  • Kernel Latency Measurement: Using cyclictest, rt-tests.
  • Scheduler Policies: SCHED_FIFO, SCHED_RR, SCHED_DEADLINE.

8. Virtualization & Containers

Importance:

Virtualization and containers are widely used in modern BSPs for resource isolation.

Topics:

  • KVM/QEMU for Kernel Development: Running the kernel in QEMU, Virtio, ARM-specific virtualization (EL2, EL3 modes).
  • cgroups & Namespaces: Managing resource isolation.
  • Device Passthrough & VFIO: PCI passthrough, IOMMU.
  • Container Security: Using SELinux/AppArmor for container isolation.

9. Networking & Protocol Stack

Importance:

Networking knowledge is necessary for developing network drivers and optimizing performance.

Topics:

  • TCP/IP Stack in Linux: Netfilter, skb_buff, struct socket.
  • Packet Filtering & Traffic Shaping: iptables, tc.
  • Networking Drivers: Writing NIC drivers, debugging performance issues.
  • Wi-Fi & Bluetooth Stack: cfg80211, rfkill.

10. Build Systems & Toolchains

Importance:

Understanding build systems is crucial for compiling and customizing embedded systems.

Topics:

  • Cross-Compilation & Toolchains: Using Buildroot toolchain.
  • Build Systems: Yocto Project, OpenEmbedded.
  • Kernel Build System: Makefile, Kbuild, kconfig.
  • Static & Dynamic Linking: Differences between shared and static libraries.

Conclusion

  • Strong debugging skills.
  • Deep understanding of kernel internals and device drivers.
  • Experience in BSP and board bring-up.
  • Ability to optimize performance and ensure security.
  • Hands-on experience with build systems and toolchains.