Kernel - Pagecache - Core
· ☕ 3 分钟

address_space 数据结构

Page cahce 的核心数据结构是 addrees_space。一般来说，每个 inode （Kernel 用来存放文件元信息的内存中的数据结构，可以视为一个文件的描述信息）中包含一个 addrees_space 。

2月4日 - IT当年今日
· ☕ 3 分钟

2月4日 - IT当年今日

1943年2月4日 Ken Thompson 出生

Ken

简介

Unix 来源于一个程序员想玩游戏

肯尼斯·汤普森（Kenneth Thompson）与丹尼斯·里奇（Dennis Ritchie）一起在AT＆T贝尔实验室开发了UNIX。 UNIX操作系统结合了Multics提供的许多分时和文件管理功能，并由此得名。 （Multics是1960年代中期的一个项目，代表了创建多用户，多任务操作系统的第一项努力。）UNIX操作系统迅速赢得了广泛的关注，尤其是在工程师和科学家中。

2020年的回顾;2021年的一些想法
· ☕ 4 分钟
· ☕ 4 分钟

https://tenzir.com/blog/production-debugging-bpftrace-uprobes/
https://shaharmike.com/cpp/vtable-part1/

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#include <iostream>

class Parent {
 public:
  virtual void Foo() {}
  virtual void FooNotOverridden() {}
};

class Derived : public Parent {
 public:
  void Foo() override {}
};

int main() {
  Parent p1, p2;
  Derived d1, d2;

  std::cout << "done" << std::endl;
}

$ # compile our code with debug symbols and start debugging using gdb
$ clang++ -std=c++14 -stdlib=libc++ -g main.cpp && gdb ./a.out
...
(gdb) # ask gdb to automatically demangle C++ symbols
(gdb) set print asm-demangle on
(gdb) set print demangle on
(gdb) # set breakpoint at main
(gdb) b main
Breakpoint 1 at 0x4009ac: file main.cpp, line 15.
(gdb) run
Starting program: /home/shmike/cpp/a.out

Breakpoint 1, main () at main.cpp:15
15	  Parent p1, p2;
(gdb) # skip to next line
(gdb) n
16	  Derived d1, d2;
(gdb) # skip to next line
(gdb) n
18	  std::cout << "done" << std::endl;
(gdb) # print p1, p2, d1, d2 - we'll talk about what the output means soon
(gdb) p p1
$1 = {_vptr$Parent = 0x400bb8 <vtable for Parent+16>}
(gdb) p p2
$2 = {_vptr$Parent = 0x400bb8 <vtable for Parent+16>}
(gdb) p d1
$3 = {<Parent> = {_vptr$Parent = 0x400b50 <vtable for Derived+16>}, <No data fields>}
(gdb) p d2
$4 = {<Parent> = {_vptr$Parent = 0x400b50 <vtable for Derived+16>}, <No data fields>}

Here’s what we learned from the above:

· ☕ 3 分钟

Terminology

  • Cluster: a logical service with a set of endpoints that Envoy forwards requests to.

  • Downstream: an entity connecting to Envoy. This may be a local application (in a sidecar model) or a network node. In non-sidecar models, this is a remote client.

  • Endpoints: network nodes that implement a logical service. They are grouped into clusters. Endpoints in a cluster are upstream of an Envoy proxy.

  • Filter: a module in the connection or request processing pipeline providing some aspect of request handling. An analogy from Unix is the composition of small utilities (filters) with Unix pipes (filter chains).

· ☕ 0 分钟
· ☕ 1 分钟

https://istio.cn/t/topic/299

Envoy源码分析之Dispatcher：https://developer.aliyun.com/article/659277

线程相关 Misc：

  • Envoy进程由一个Main Thread和多个Worker Thread 组成
  • 每个Main和Worker包含一个eventloop，所有的处理都是由eventloop触发开始
  • Main负责xDS等功能，Worker负责处理连接和请求
  • 当一个client向Envoy建立连接的时候，因为所有Worker的EventLoop都注册了listening fd(启用SO_PORTREUSE除外)，会由内核决定分配给哪个Worker
  • 当一个下游client连接到了Envoy，在保持连接不断的情况下，会和同一个Worker进行通讯
· ☕ 2 分钟

HTTP/1.1 Header Casing

https://www.envoyproxy.io/docs/envoy/latest/configuration/http/http_conn_man/header_casing#config-http-conn-man-header-casing

When handling HTTP/1.1, Envoy will normalize the header keys to be all lowercase. While this is compliant with the HTTP/1.1 spec, in practice this can result in issues when migrating existing systems that might rely on specific header casing.

To support these use cases, Envoy allows configuring a formatting scheme for the headers, which will have Envoy transform the header keys during serialization.

  • To configure this formatting on response headers, specify the format in the http_protocol_options.
  • To configure this for upstream request headers, specify the formatting in http_protocol_options in the cluster’s extension_protocol_options.

Currently Envoy supports two mutually exclusive types of header key formatters: