I got an interesting issue while debugging a BPF program. The BPF program
couldn’t be loaded because of an “invalid memory access” error. Though the
access was completely within the valid memory boundary, the verifier was still
not happy about it.
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My First Kernel Patch
Summary
Recently, I submitted my first kernel
patch.
I will note down the basic workflow of submitting code to kernel in this post.
This folder contains more
detailed instructions on how to become a kernel developer. My note will only
contain minimal steps for a noob like me.
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Set up OfflineIMAP + Mutt on Mac
Summary Recently, I submitted my first kernel patch. One of the lessons I learned is that kernel mail server doesn’t accept HTML content in emails. To make sure my email contains absolutely no HTML, I set up a text-based email client (Mutt + OfflineIMAP) on my laptop. This post is...
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Use Map-in-Map in BPF programs via Libbpf
Introduction
Among all BPF map types, two special ones, BPF_MAP_TYPE_ARRAY_OF_MAPS and
BPF_MAP_TYPE_HASH_OF_MAPS, are more complex than others. As the names imply,
they are “map-in-map”, meaning that the value of each entry is also a map.
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Always Use always_inline In BPF Programs
TL;DR Recently, I solved a tricky bug in a BPF program. Because inline instead of always_inline was used to declare a function, when the function body grew big, the compiler decided to not inline it. Then the BPF program was not able to be loaded due to some verification error....
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How Is Ping Deduplexed?
Preface
A few days back, one of my friends asked an interesting question - How is ping
deduplexed by Linux kernel network stack? In other words, when a Linux machine
receives the ping reply, how does it know which socket to send to?
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Linux Bridge Port Flags
Overview
Linux bridge can set flags on a port. The defined flags (until Linux 4.0) are:
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The Spinning Tree Protocol
How it guarantees a loop-free topology
Overview We talked about what is a bridge (switch) and how it works here and here. However, we only saw the topology in which one bridge is used to merge LANs. In real life, redundancy is always necessary in order to provide high availability. For example, instead of using only...
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Rate Limiting Part 2
Guava Implementation
Overview
In previous pos, we learned some rate limiting
algorithms. In this article, we will see how rate limiting is implemented in
Google Guava library.
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Rate Limiting Part 1
Algorithms
Overview In general, rate limiting is used to control the consumption rate of a resource. For example, up to 10 requests can be served by the server per minute. Or up to 1MB data can be sent to the network per second. Rate limiting is necessary for protecting a system...
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