Linux kernel – Oleg Kutkov personal blog

Analysis and reverse-engineering of the original Starlink router

Oleg Kutkov — Sat, 25 Dec 2021 01:05:00 +0000

While waiting for my Dishy, I decided to find and buy the Starlink router separately. Sure, it might be just a WiFi router, but it was very curious what’s inside. Spoiler: there are some interesting implementation details. Lucky enough, I found the router on eBay. It’s the first generation of the router. Currently, it’s impossible to buy (separately) the second…

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Writing a PCI device driver for Linux

Oleg Kutkov — Wed, 06 Jan 2021 23:05:57 +0000

In this article, I want to discuss some basics of the Linux PCI/PCIe drivers development. I think this issue is not properly covered, and some existing information is might be outdated. I will show basic concepts and important structures, and this is might be a good beginner guide for newbie driver developers. The PCI bus is the most popular way…

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Linux block device driver

Oleg Kutkov — Mon, 10 Feb 2020 00:28:46 +0000

My article about character devices is quite popular, so I decided to write something about another big class of devices in Linux – block devices. This type of device is used to access various storage hardware types – hard disks, SSD, etc. Here I want to describe blk-mq based devices in modern (>= 5.0) Linux kernels and a previous type…

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C++ in Linux kernel

Oleg Kutkov — Sat, 09 Nov 2019 22:52:36 +0000

Linux kernel is written in C (and in Assembly in platform-specific portions) language. C language is the only language allowed to write kernel modules. And there is no problem in most cases. But sometimes, some stranger things may be required. Let’s see how to use C++ for the Linux kernel modules. Of course, it’s not a common situation. But imagine…

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Printing sk_buff data

Oleg Kutkov — Wed, 16 Oct 2019 22:41:31 +0000

Sometimes when working with network packets inside the Linux kernel, it might be very useful to print packet contents to see what is actually going on. Here I’m describing how to print packet from sk_buff structure and analyze this data with Wireshark. In this short note, I will not describe capturing the packets inside the kernel but only show how…

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Modifying Linux network routes using netlink

Oleg Kutkov — Wed, 28 Aug 2019 23:14:11 +0000

Last time we talked about getting a Linux routing table with a simple Netlink code. Now it’s time to do more interesting stuff. Let’s add and delete some routes using the power of the Netlink! At the end of this article, we will create a command-line utility with syntax similar to ip route command, which can add and delete custom…

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Getting Linux routing table using netlink

Oleg Kutkov — Sun, 24 Mar 2019 01:42:51 +0000

In the previous article, we discussed the monitoring of the network interfaces using Netlink. Now it’s time to do something more complex and interesting. Let’s discover how to get and print the system routing table like “ip route” command. The routing table is a runtime in-memory data structure that stores the routes (and in some cases, metrics associated with those…

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Monitoring Linux networking state using netlink

Oleg Kutkov — Tue, 13 Feb 2018 23:38:20 +0000

Once in my work, I needed to monitor all changes in the Linux networking subsystem: adding or deleting IP addresses, routes, etc. Maybe the best way to do this is to use socket-based Netlink technology. Using Netlink, we can “subscribe” to some network-related notifications from the kernel. It’s also possible to send commands to the network stack and change the…

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