Calling C Functions from OCaml OCaml provides robust FFI (Foreign Function Interface) capabilities for calling C code. This is essential when you need to use existing C libraries or write performance-critical sections in C. Using the Unix Module The simplest approach for Unix/Linux system calls is the built-in Unix module, which wraps common POSIX functions…
Consistency Models in Distributed Systems Consistency models define the guarantees that a distributed system makes about the order and visibility of data modifications across nodes. Understanding these models is essential when designing systems, choosing databases, or debugging data anomalies in production. Strong Consistency Models Strict Consistency is the ideal but rarely achievable model. It guarantees…
Transactional Memory Learning Materials Transactional memory (TM) is a synchronization mechanism that simplifies concurrent programming by allowing multiple threads to execute code atomically without explicit lock management. If you’re getting into this area, here are the best resources and practical approaches to build solid understanding. Foundational Reading The classic reference is still Transactional Memory by…
Installing PHP with Apache on Fedora This guide covers setting up PHP with Apache’s httpd on Fedora systems. The setup provides standard PHP support suitable for most development and production environments. Install Apache httpd Start by installing the Apache web server package: sudo dnf install httpd On Fedora 22 and later, dnf is the default…
Apply sysctl.conf Changes Without Rebooting When you modify /etc/sysctl.conf, the changes take effect on the next reboot. To apply them immediately without rebooting, use the sysctl -p command: sudo sysctl -p This reads the configuration file and applies all settings to the running kernel. Reloading Specific Configuration Files By default, sysctl -p reads from /etc/sysctl.conf….
Creating a Swap Partition on Linux Swap space is essential for system stability, allowing the kernel to move less-frequently-used memory pages to disk when physical RAM is exhausted. Here’s how to set up a dedicated swap partition. Step 1: Create the Partition Use fdisk, gdisk (for GPT disks), or parted to create a new partition….
Using hex() for basic conversion The hex() function converts an integer to a hexadecimal string with a 0x prefix: i = 255 print(hex(i)) # Output: 0xff This works for negative numbers too: print(hex(-42)) # Output: -0x2a String formatting for control For more control over the output, use f-strings or the format() method with format specifiers:…
Disabling All Swaps on Linux To disable all active swap spaces on Linux, run: swapoff -a The -a flag targets all currently enabled swap devices and files. This forces the kernel and applications to rely entirely on physical RAM. When You’d Do This Disabling swap is useful for: Performance testing: Eliminating swap I/O variance to…
x86-64 calling convention in GCC The x86-64 architecture on Linux follows the System V AMD64 ABI calling convention. Understanding this is essential when writing assembly, optimizing code, debugging, or interfacing with C libraries. Register usage for arguments Integer and pointer arguments use these registers in order: RDI — first argument RSI — second argument RDX…
Configure CMake with Debug Build Type To enable debugging, configure your CMake build with CMAKE_BUILD_TYPE set to Debug. This tells CMake to invoke the compiler with the -g flag, generating debug symbols that tools like gdb and lldb need. From your project’s root directory: cmake -DCMAKE_BUILD_TYPE=Debug -B build cd build make The -B build flag…
Getting File Size in C There are several ways to determine a file’s size in C, each with different trade-offs. Choose based on whether you have a file descriptor, stream, or just the filename. Using stat() with a Filename If you know the filename, stat() is the most straightforward approach: #include <sys/stat.h> #include <stdio.h> int…
Installing LaTeX on Linux LaTeX is a document preparation system widely used for scientific and technical documents. Most modern workflows use pdflatex or xelatex to compile directly to PDF, avoiding the outdated DVI → PostScript → PDF pipeline. Debian/Ubuntu sudo apt-get update sudo apt-get install texlive-latex-base texlive-latex-extra texlive-fonts-recommended For a complete installation with all packages:…
Windows 7 64-bit fails to install on VirtualBox with status code 0xc0000225 The error “Windows failed to start” with status code 0xc0000225 during Windows 7 64-bit installation on VirtualBox typically indicates a hardware abstraction layer (HAL) compatibility issue. This happens because the VM’s default configuration doesn’t properly expose interrupt controller details to the guest OS….
Passing kernel parameters to Xen DomUs Kernel parameters often need to be passed to Xen DomUs during boot or for troubleshooting. Common scenarios include booting into single-user mode for recovery, enabling kernel debugging, or adjusting memory/CPU settings at runtime. Using the extra parameter The simplest method is passing kernel parameters via the extra= option when…
Code Size vs Alignment: Why Modern CPUs Prefer Correctness Over Density The conventional wisdom that smaller code is always better has been thoroughly invalidated on modern processors. A statement from kernel development circles captured this well: for performance-critical paths like interrupt handlers, large-but-correctly-aligned-and-optimized code consistently outperforms byte-packed alternatives. Consider this comparison: mov eax, [foo] add…
Using MAP_NORESERVE for Oversized Memory Mappings When you mmap() a range larger than your system’s total physical memory plus swap, the kernel normally reserves swap space to back the mapping. If that reservation would exceed available swap, mmap() fails with ENOMEM. The MAP_NORESERVE flag lets you bypass this reservation requirement. Understanding the Default Behavior By…
NFSv4 Port Forwarding and External Network Access NFSv4 significantly simplifies network exposure compared to NFSv3. Where NFSv3 requires managing multiple dynamic ports (mountd, statd, lockd), NFSv4 uses only port 111 (rpcbind) and port 2049 (NFS). This makes firewall configuration and port forwarding straightforward. For production environments, consider implementing Kerberos authentication (krb5, krb5i, or krb5p) instead…
.NET Core 2.1: What Actually Shipped This post covers .NET Core 2.1, which released in May 2018. Some of the predicted features below didn’t materialize as described; we’ll clarify what actually landed versus what was speculated. What is .NET Core? .NET Core is Microsoft’s open-source, cross-platform runtime for building applications in C#, F#, and Visual…
The encoding of x86 and x86-64 instructions is well documented in Intel or AMD’s manuals. However, they are not quite easy for beginners to start with to learn encoding of the x86-64 instructions. In this post, I will give a list of useful manuals for understanding and studying the x86-64 instruction encoding, a brief introduction…
Introduction As we know, network subsystems are important in computer systems since they are I/O systems and need to be optimized with many algorithms and skills. This article will introduce how QEMU/KVM [2] network part works. In order to put everything simple and easy to understand, we will begin with several examples and then understand…