Nice article on using printk for debugging. It explains the usage, log level, rate limiting and one time messaging, changing the size of printk buffer, debugging early boot problems etc.
Refer Debugging by printing
Category: Linux
A nice article on kubernetes.
Source: What Is Kubernetes? An Introduction to the Container Orchestration Platform
Nice article on how to enable and use the sysrq key.
Source: Linux Magic System Request Key Hacks — The Linux Kernel documentation
Udev in linux subsystem helps to write scripts to do a specific action when a new device is added or an existing device is removed from the system.
The following article helps you to write your own basic script by identifying a device and adding the specific udev rules. Refer An introduction to Udev: The Linux subsystem for managing device events for more details.
What is a Toolchain?
Its a set of tools linked together by specific stages which can be used to run on a specific machine.
It contains tools for compiling, debugging , binary file manipulation and analysis.
There are pre-built toolchain available in internet. We can build our own using automated tool chain build tools or from scratch.
What are the types of Toolchain available?
Tool chains are run on 3 machine types
Build – The machine where the tool chain is first built.
Host – The machine where the tool chain is used to generate the target binary.
Target – The machine where the target binary is run.
Based on the above below are the Toolchain types
Native – The build, host and target are the same architecture. E.G:- The GCC compiler coming with RedHat x86 version
Cross Compiled – The build and host are same architecture, but the target is different. E.G:- Using x86 GCC creating a cross compiled GCC which generates binary to run on an ARM processor.
Cross Native – The host and target are of the same architecture. E.G;- Using x86 GCC create a cross native arm GCC, which can be used in an ARM Linux OS to generate binary which runs on ARM processor.
Canadian Build – The architecture for all the build, host and target differs. E.G:- Using X86 GCC create an ARM GCC which generates binary to run on a PPC machine. In this case build and target can be same architecture.
What are the Toolchain components?
The main components are
Binutils – as,ld,readelf etc
Compiler – gcc,g++ etc
C library – glibc, uclibc etc
Debugger – gdb
Kernel – headers
What are the stages in building a Toolchain?
1. Download sources for the components
2. Set the environment variables for the Toolchain build. e.g:- setting the build, host, target architecture and intermediate installation directories.
3. Build first the binutils
4. Build the bootstrap gcc with options –with-gnu-as –with-gnu-ld to instruct the compiler to use binutils assembler and linker than native assembler and linker.
5. Build glibc
6. Build gcc again with newly build glibc with options –with-gnu-as –with-gnu-ld to instruct the compiler to use binutils assembler and linker than native
7. Build gcc again with newly build glibc with options –with-gnu-as –with-gnu-ld to instruct the compiler to use binutils assembler and linker than native. This is to compare the binaries and make sure you are getting the same output and no compiler bug.
8. Use the Toolchain to build your application.
9. Run your application on the target machine.
What are the options for building a Toolchain?
Option 1: Build your own
Option 2: Prebuilt Toolchain. e.g:- CodeSourcery, Linoro(ARM) etc
Option 3: Automated Toolchain build systems. e.g:- Buildroot, Open ADK, crosstool-NG
Note:- The option 2 and 3 helps in quick development as the dependencies between the Toolchain components will be taken care by the maintainers of the Toolchain build systems.
The following tutorial introduces you both to Vim’s built-in Cscope support, and to a set of maps that make searching more convenient.
The maximum transmission unit (MTU) of a network interface is the size of the largest block of data that can be transmitted as a single unit. Anything larger than the MTU must be broken into smaller units prior to transmission. The following link has a short passage on modifying the MTU.
Change the MTU of a network interface
If you want to change the MTU in the linux kernel source code the macro can be found in
the location
linux/include/uapi/linux/if_ether.h
The macro name is ETH_DATA_LEN and if you are increasing it you need to increase the frame length also. The macro for from length is ETH_FRAME_LEN. I did experiment to modify MTU to 1508. So I modified the ETH_DATA_LEN to 1508 and frame length to 1522.
After the same through ifconfig I was able to set the mtu to 1508.
e.g:- ifconfig eth0 mtu 1508
Setting anything beyond ETH_DATA_LEN the ifconfig will return “SIOCSIFMTU: Invalid argument”. Also changing to any values beyond 1500 ensure your network devices support.