From 891882ce89e37e1bd24fb357bdaa724b9115dc6a Mon Sep 17 00:00:00 2001 From: Hao Lee Date: Tue, 27 Dec 2016 20:10:16 +0800 Subject: [PATCH] =?UTF-8?q?=E4=B8=AD=E6=96=87=E7=BF=BB=E8=AF=91=E5=AE=9A?= =?UTF-8?q?=E7=A8=BF=EF=BC=8C=E7=A7=BB=E9=99=A4=E8=8B=B1=E6=96=87=E5=AF=B9?= =?UTF-8?q?=E7=85=A7?= MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit --- Misc/contribute.md | 113 +++++---------------------------------------- 1 file changed, 12 insertions(+), 101 deletions(-) diff --git a/Misc/contribute.md b/Misc/contribute.md index 432892e..1c6d45a 100644 --- a/Misc/contribute.md +++ b/Misc/contribute.md @@ -1,49 +1,35 @@ -Linux kernel development Linux 内核开发 ================================================================================ -Introduction 简介 -------------------------------------------------------------------------------- -As you already may know, I've started a series of [blog posts](http://0xax.github.io/categories/assembly/) about assembler programming for `x86_64` architecture in the last year. I have never written a line of low-level code before this moment, except for a couple of toy `Hello World` examples in university. It was a long time ago and, as I already said, I didn't write low-level code at all. Some time ago I became interested in such things. I understood that I can write programs, but didn't actually understand how my program is arranged. 如你所知，我从去年开始写了一系列关于 `x86_64` 架构汇编语言程序设计的[博文](http://xinqiu.gitbooks.io/categories/assembly/)。除了大学期间写过一些 `Hello World` 这样的玩具例程之外，我从来没写过哪怕一行的底层代码。那些例程也是很久以前的事情了，就像我刚才说的，我几乎完全没有写过底层代码。直到不久前，我才开始对这些事情感兴趣，因为我意识到我虽然可以写出程序，但是我却不知道我的程序是怎样被组织运行的。 -After writing some assembler code I began to understand how my program looks after compilation, **approximately**. But anyway, I didn't understand many other things. For example: what occurs when the `syscall` instruction is executed in my assembler, what occurs when the `printf` function starts to work or how can my program talk with other computers via network. [Assembler](https://en.wikipedia.org/wiki/Assembly_language#Assembler) programming language didn't give me answers to my questions and I decided to go deeper in my research. I started to learn from the source code of the Linux kernel and tried to understand the things that I'm interested in. The source code of the Linux kernel didn't give me the answers to **all** of my questions, but now my knowledge about the Linux kernel and the processes around it is much better. 在写了一些汇编代码之后，我开始**大致**了解了程序在编译之后会变成什么样子。尽管如此，还是有很多其他的东西我不能够理解。例如：当 `syscall` 指令在我的汇编程序内执行时究竟发生了什么，当 `printf` 函数开始工作时又发生了什么，还有，我的程序是如何通过网络与其他计算机进行通信的。[汇编](https://en.wikipedia.org/wiki/Assembly_language#Assembler)语言并没有为这些问题带来答案，于是我决定做一番深入研究。我开始学习 Linux 内核的源代码，并且尝试着理解那些让我感兴趣的东西。然而 Linux 内核源代码也没有解答我**所有的**问题，不过我自身关于 Linux 内核及其外围流程的知识确实掌握的更好了。 -I'm writing this part nine and a half months after I've started to learn from the source code of the Linux kernel and published the first [part](https://0xax.gitbooks.io/linux-insides/content/Booting/linux-bootstrap-1.html) of this book. Now it contains forty parts and it is not the end. I decided to write this series about the Linux kernel mostly for myself. As you know the Linux kernel is very huge piece of code and it is easy to forget what does this or that part of the Linux kernel mean and how does it implement something. But soon the [linux-insides](https://github.com/0xAX/linux-insides) repo became popular and after nine months it has `9096` stars: -在我开始学习 Linux 内核的九个半月之后，我写了这部分内容，并且发布了本书的[第一部分](https://0xax.gitbooks.io/linux-insides/content/Booting/linux-bootstrap-1.html)。到现在为止，本书共包括了四个部分，而这并不是终点。我之所以写这一系列关于 Linux 内核的文章其实更多的是为了我自己。你也知道，Linux 内核的代码量极其巨大，另外还非常容易忘记这一块或那一块内核代码做了什么，或者忘记某些东西是怎么实现的。出乎意料的是 [linux-insides](https://github.com/0xAX/linux-insides) 很快就火了，并且在九个月后积攒了 `9096` 个星星。 +在我开始学习 Linux 内核的九个半月之后，我写了这部分内容，并且发布了本书的[第一部分](https://0xax.gitbooks.io/linux-insides/content/Booting/linux-bootstrap-1.html)。到现在为止，本书共包括了四个部分，而这并不是终点。我之所以写这一系列关于 Linux 内核的文章其实更多的是为了我自己。你也知道，Linux 内核的代码量极其巨大，另外还非常容易忘记这一块或那一块内核代码做了什么，或者忘记某些东西是怎么实现的。出乎意料的是 [linux-insides](https://github.com/0xAX/linux-insides) 很快就火了，并且在九个月后积攒了 `9096` 个星星： ![github](http://s2.postimg.org/jjb3s4frt/stars.png) -It seems that people are interested in the insides of the Linux kernel. Besides this, in all the time that I have been writing `linux-insides`, I have received many questions from different people about how to begin contributing to the Linux kernel. Generally people are interested in contributing to open source projects and the Linux kernel is not an exception: -看起来人们对 Linux 内核的内在机制非常的感兴趣。除此之外，在我写 `linux-insides` 的这段时间里，我收到了很多人发来的问题，这些问题大都是关于如何开始向 Linux 内核贡献代码。通常来说，人们是很有兴趣为开源项目做贡献的，Linux 内核也不例外。 +看起来人们对 Linux 内核的内在机制非常的感兴趣。除此之外，在我写 `linux-insides` 的这段时间里，我收到了很多人发来的问题，这些问题大都是关于如何开始向 Linux 内核贡献代码。通常来说，人们是很有兴趣为开源项目做贡献的，Linux 内核也不例外： ![google-linux](http://s4.postimg.org/yg9z5zx0d/google_linux.png) -So, it seems that people are interested in the Linux kernel development process. I thought it would be strange if a book about the Linux kernel would not contain a part describing how to take a part in the Linux kernel development and that's why I decided to write it. You will not find information about why you should be interested in contributing to the Linux kernel in this part. But if you are interested how to start with Linux kernel development, this part is for you. 这么看起来大家对 Linux 内核的开发流程非常感兴趣。我认为如果这么一本关于 Linux 内核的书却不包括一部分来讲讲如何参与 Linux 内核开发的话，那就非常奇怪了。这就是我决定写这篇文章的原因。在本文中，你不会看到为什么你应该对贡献 Linux 内核感兴趣，但是如果你想参与 Linux 内核开发的话，那这部分就是为你而作。 -Let's start. 让我们开始吧。 -How to start with Linux kernel 如何入门 Linux 内核 --------------------------------------------------------------------------------- -First of all, let's see how to get, build, and run the Linux kernel. You can run your custom build of the Linux kernel in two ways: -首先，让我们看看如何获取、构建并运行 Linux 内核。你可以通过两种方式来运行你自己定制的内核。 +首先，让我们看看如何获取、构建并运行 Linux 内核。你可以通过两种方式来运行你自己定制的内核： -* Run the Linux kernel on a virtual machine; -* Run the Linux kernel on real hardware. * 在虚拟机里运行 Linux 内核； * 在真实的硬件上运行 Linux 内核。 -I'll provide descriptions for both methods. Before we start doing anything with the Linux kernel, we need to get it. There are a couple of ways to do this depending on your purpose. If you just want to update the current version of the Linux kernel on your computer, you can use the instructions specific to your Linux [distro](https://en.wikipedia.org/wiki/Linux_distribution). 我会对这两种方式都展开描述。在我们开始对 Linux 内核做些什么之前，我们首先需要先获取它。根据你目的的不同，有两种方式可以做到这一点。如果你只是想更新一下你电脑上的 Linux 内核版本，那么你可以使用特定于你 [Linux 发行版](https://en.wikipedia.org/wiki/Linux_distribution)的命令。 -In the first case you just need to download new version of the Linux kernel with the [package manager](https://en.wikipedia.org/wiki/Package_manager). For example, to upgrade the version of the Linux kernel to `4.1` for [Ubuntu (Vivid Vervet)](http://releases.ubuntu.com/15.04/), you will just need to execute the following commands: 在这种情况下，你只需要使用[软件包管理器](https://en.wikipedia.org/wiki/Package_manager)下载新版本的 Linux 内核。例如，为了将 [Ubuntu (Vivid Vervet)](http://releases.ubuntu.com/15.04/) 系统的 Linux 内核更新至 `4.1` 版本，你只需要执行以下命令： ``` @@ -51,38 +37,32 @@ $ sudo add-apt-repository ppa:kernel-ppa/ppa $ sudo apt-get update ``` -After this execute this command: 在这之后，再执行下面的命令： ``` $ apt-cache showpkg linux-headers ``` -and choose the version of the Linux kernel in which you are interested. In the end execute the next command and replace `${version}` with the version that you chose in the output of the previous command: 然后选择你感兴趣的 Linux 内核的版本。最后，执行下面的命令并且将 `${version}` 替换为你从上一条命令的输出中选择的版本号。 ``` $ sudo apt-get install linux-headers-${version} linux-headers-${version}-generic linux-image-${version}-generic --fix-missing ``` -and reboot your system. After the reboot you will see the new kernel in the [grub](https://en.wikipedia.org/wiki/GNU_GRUB) menu. 最后重启你的系统。重启完成后，你将在 [grub](https://en.wikipedia.org/wiki/GNU_GRUB) 菜单中看到新的内核。 -In the other way if you are interested in the Linux kernel development, you will need to get the source code of the Linux kernel. You can find it on the [kernel.org](https://kernel.org/) website and download an archive with the Linux kernel source code. Actually the Linux kernel development process is fully built around `git` [version control system](https://en.wikipedia.org/wiki/Version_control). So you can get it with `git` from the `kernel.org`: 另一方面，如果你对 Linux 内核开发感兴趣，那么你就需要获得 Linux 内核的源代码。你可以在 [kernel.org](https://kernel.org/) 网站上找到它并且下载一个包含了 Linux 内核源代码的归档文件。实际上，Linux 内核的开发流程完全建立在 `git` [版本控制系统](https://en.wikipedia.org/wiki/Version_control)之上，所以你需要通过 `git` 来从 `kernel.org` 上获取内核源代码： ``` $ git clone git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git ``` -I don't know how about you, but I prefer `github`. There is a [mirror](https://github.com/torvalds/linux) of the Linux kernel mainline repository, so you can clone it with: 我不知道你怎么看，但是我本身是非常喜欢 `github` 的。它上面有一个 Linux 内核主线仓库的[镜像](https://github.com/torvalds/linux)，你可以通过以下命令克隆它： ``` $ git clone git@github.com:torvalds/linux.git ``` -I use my own [fork](https://github.com/0xAX/linux) for development and when I want to pull updates from the main repository I just execute the following command: 我是用我自己 [fork](https://github.com/0xAX/linux) 的仓库来进行开发的，等到我想从主线仓库拉取更新的时候，我只需要执行下方的命令即可： ``` @@ -90,14 +70,12 @@ $ git checkout master $ git pull upstream master ``` -Note that the remote name of the main repository is `upstream`. To add a new remote with the main Linux repository you can execute: 注意这个主线仓库的远程主机名叫做 `upstream`。为了将主线 Linux 仓库添加为一个新的远程主机，你可以执行： ``` git remote add upstream git@github.com:torvalds/linux.git ``` -After this you will have two remotes: 在此之后，你将有两个远程主机： ``` @@ -108,44 +86,36 @@ upstream https://github.com/torvalds/linux.git (fetch) upstream https://github.com/torvalds/linux.git (push) ``` -One is of your fork (`origin`) and the second is for the main repository (`upstream`). 其中一个远程主机是你的 fork 仓库 (`origin`)，另一个是主线仓库 (`upstream`)。 -Now that we have a local copy of the Linux kernel source code, we need to configure and build it. The Linux kernel can be configured in different ways. The simplest way is to just copy the configuration file of the already installed kernel that is located in the `/boot` directory: -现在，我们已经有了一份 Linux 内核源代码的本地副本，我们需要配置并编译内核。Linux 内核的配置有很多不同的方式，最简单的方式就是直接拷贝 `/boot` 目录下已安装内核的配置文件。 +现在，我们已经有了一份 Linux 内核源代码的本地副本，我们需要配置并编译内核。Linux 内核的配置有很多不同的方式，最简单的方式就是直接拷贝 `/boot` 目录下已安装内核的配置文件： ``` $ sudo cp /boot/config-$(uname -r) ~/dev/linux/.config ``` -If your current Linux kernel was built with the support for access to the `/proc/config.gz` file, you can copy your actual kernel configuration file with this command: 如果你当前的内核被编译为支持访问 `/proc/config.gz` 文件，你也可以使用以下命令复制当前内核的配置文件： ``` $ cat /proc/config.gz | gunzip > ~/dev/linux/.config ``` -If you are not satisfied with the standard kernel configuration that is provided by the maintainers of your distro, you can configure the Linux kernel manually. There are a couple of ways to do it. The Linux kernel root [Makefile](https://github.com/torvalds/linux/blob/master/Makefile) provides a set of targets that allows you to configure it. For example `menuconfig` provides a menu-driven interface for the kernel configuration: -如果你对发行版维护者提供的标准内核配置文件并不满意，你也可以手动配置 Linux 内核，有两种方式可以做到这一点。Linux 内核的根 [Makefile](https://github.com/torvalds/linux/blob/master/Makefile) 文件提供了一系列可配置的目标选项。例如 `menuconfig` 为内核配置提供了一个菜单界面。 +如果你对发行版维护者提供的标准内核配置文件并不满意，你也可以手动配置 Linux 内核，有两种方式可以做到这一点。Linux 内核的根 [Makefile](https://github.com/torvalds/linux/blob/master/Makefile) 文件提供了一系列可配置的目标选项。例如 `menuconfig` 为内核配置提供了一个菜单界面： ![menuconfig](http://s21.postimg.org/zcz48p7yf/menucnonfig.png) -The `defconfig` argument generates the default kernel configuration file for the current architecture, for example [x86_64 defconfig](https://github.com/torvalds/linux/blob/master/arch/x86/configs/x86_64_defconfig). You can pass the `ARCH` command line argument to `make` to build `defconfig` for the given architecture: - `defconfig` 参数会为当前的架构生成默认的内核配置文件，例如 [x86_64 defconfig](https://github.com/torvalds/linux/blob/master/arch/x86/configs/x86_64_defconfig)。你可以将 `ARCH` 命令行参数传递给 `make`，以此来为给定架构创建 `defconfig` 配置文件。 + `defconfig` 参数会为当前的架构生成默认的内核配置文件，例如 [x86_64 defconfig](https://github.com/torvalds/linux/blob/master/arch/x86/configs/x86_64_defconfig)。你可以将 `ARCH` 命令行参数传递给 `make`，以此来为给定架构创建 `defconfig` 配置文件： ``` $ make ARCH=arm64 defconfig ``` -The `allnoconfig`, `allyesconfig` and `allmodconfig` arguments allow you to generate a new configuration file where all options will be disabled, enabled, and enabled as modules respectively. The `nconfig` command line arguments that provides `ncurses` based program with menu to configure Linux kernel: `allnoconfig`、 `allyesconfig` 以及 `allmodconfig` 参数也允许你生成新的配置文件，其效果分别为尽可能多的选项都关闭、尽可能多的选项都启用或尽可能多的选项都作为模块启用。`nconfig` 命令行参数提供了基于 `ncurses` 的菜单程序来配置 Linux 内核： ![nconfig](http://s29.postimg.org/hpghikp4n/nconfig.png) -And even `randconfig` to generate random Linux kernel configuration file. I will not write about how to configure the Linux kernel or which options to enable because it makes no sense to do so for two reasons: First of all I do not know your hardware and second, if you know your hardware, the only remaining task is to find out how to use programs for kernel configuration, and all of them are pretty simple to use. `randconfig` 参数甚至可以随机地生成 Linux 内核配置文件。我不会讨论如何去配置 Linux 内核或启用哪个选项，因为没有必要这么做：首先，我不知道你的硬件配置；其次，如果我知道了你的硬件配置，那么剩下的问题就是搞清楚如何使用程序生成内核配置，而这些程序的使用都是非常容易的。 -OK, we now have the source code of the Linux kernel and configured it. The next step is the compilation of the Linux kernel. The simplest way to compile Linux kernel is to just execute: 好了，我们现在有了 Linux 内核的源代码并且完成了配置。下一步就是编译 Linux 内核了。最简单的编译 Linux 内核的方式就是执行以下命令： ``` @@ -172,20 +142,17 @@ CRC 82703414 Kernel: arch/x86/boot/bzImage is ready (#73) ``` -To increase the speed of kernel compilation you can pass `-jN` command line argument to `make`, where `N` specifies the number of commands to run simultaneously: 为了增加内核的编译速度，你可以给 `make` 传递命令行参数 `-jN`，这里的 `N` 指定了并发执行的命令数目： ``` $ make -j8 ``` -If you want to build Linux kernel for an architecture that differs from your current, the simplest way to do it pass two arguments: 如果你想为一个架构构建一个与当前内核不同的内核，那么最简单的方式就是传递下面两个参数： -* `ARCH` command line argument and the name of the target architecture; -* `CROSS_COMPILER` command line argument and the cross-compiler tool prefix; +* `ARCH` 命令行参数是目标架构名； +* `CROSS_COMPILER` 命令行参数是交叉编译工具的前缀； -For example if we want to compile the Linux kernel for the [arm64](https://en.wikipedia.org/wiki/ARM_architecture#AArch64_features) with default kernel configuration file, we need to execute following command: 例如，如果我们想使用默认内核配置文件为 [arm64 架构](https://en.wikipedia.org/wiki/ARM_architecture#AArch64_features)编译 Linux 内核，我们需要执行以下命令： ``` @@ -193,15 +160,12 @@ $ make -j4 ARCH=arm64 CROSS_COMPILER=aarch64-linux-gnu- defconfig $ make -j4 ARCH=arm64 CROSS_COMPILER=aarch64-linux-gnu- ``` -As result of compilation we can see the compressed kernel - `arch/x86/boot/bzImage`. Now that we have compiled the kernel, we can either install it on our computer or just run it in an emulator. 编译的结果就是你会看到压缩后的内核文件 - `arch/x86/boot/bzImage`。既然我们已经编译好了内核，那么就可以把它安装到我们的电脑上或者只是将它运行在模拟器里。 -Installing Linux kernel 安装 Linux 内核 -------------------------------------------------------------------------------- -As I already wrote we will consider two ways how to launch new kernel: In the first case we can install and run the new version of the Linux kernel on the real hardware and the second is launch the Linux kernel on a virtual machine. In the previous paragraph we saw how to build the Linux kernel from source code and as a result we have got compressed image: -就像我之前写的，我们将考察两种用来运行新内核的方法：第一种情况，我们可以在真实的硬件上安装并运行新版本的 Linux 内核，第二种情况就是在虚拟机上运行 Linux 内核。在前面的段落中我们看到了如何从源代码来构建 Linux 内核，并且我们现在已经得到了内核的压缩镜像。 +就像我之前写的，我们将考察两种用来运行新内核的方法：第一种情况，我们可以在真实的硬件上安装并运行新版本的 Linux 内核，第二种情况就是在虚拟机上运行 Linux 内核。在前面的段落中我们看到了如何从源代码来构建 Linux 内核，并且我们现在已经得到了内核的压缩镜像： ``` ... @@ -210,22 +174,19 @@ As I already wrote we will consider two ways how to launch new kernel: In the fi Kernel: arch/x86/boot/bzImage is ready (#73) ``` -After we have got the [bzImage](https://en.wikipedia.org/wiki/Vmlinux#bzImage) we need to install `headers`, `modules` of the new Linux kernel with the: -在我们获得了 [bzImage](https://en.wikipedia.org/wiki/Vmlinux#bzImage) 之后，我们需要使用以下命令来为新的 Linux 内核安装 `headers` 和 `modules` +在我们获得了 [bzImage](https://en.wikipedia.org/wiki/Vmlinux#bzImage) 之后，我们需要使用以下命令来为新的 Linux 内核安装 `headers` 和 `modules`： ``` $ sudo make headers_install $ sudo make modules_install ``` -and directly the kernel itself: 以及内核自身： ``` $ sudo make install ``` -From this moment we have installed new version of the Linux kernel and now we must tell the `bootloader` about it. Of course we can add it manually by the editing of the `/boot/grub2/grub.cfg` configuration file, but I prefer to use a script for this purpose. I'm using two different Linux distros: Fedora and Ubuntu. There are two different ways to update the [grub](https://en.wikipedia.org/wiki/GNU_GRUB) configuration file. I'm using following script for this purpose: 从这时起，我们已经安装好了新版本的 Linux 内核，现在我们需要通知 `bootloader` 新内核已经安装完成。我们当然可以手动编辑 `/boot/grub2/grub.cfg` 配置文件并将新内核添加进去，但是我更推荐使用脚本来完成这件事。我现在在使用两种不同的 Linux 发行版：Fedora 和 Ubuntu，有两种方式可以用来更新 [grub](https://en.wikipedia.org/wiki/GNU_GRUB) 配置文件，我目前正在使用下面的脚本来达到这一目的： ```shell @@ -246,13 +207,10 @@ fi echo "${Green}Done.${Color_Off}" ``` -This is the last step of the new Linux kernel installation and after this you can reboot your computer and select new version of the kernel during boot. 这是新 Linux 内核安装过程中的最后一步，在这之后你可以重启你的电脑，然后在启动过程中选择新版本的内核。 -The second case is to launch new Linux kernel in the virtual machine. I prefer [qemu](https://en.wikipedia.org/wiki/QEMU). First of all we need to build initial ramdisk - [initrd](https://en.wikipedia.org/wiki/Initrd) for this. The `initrd` is a temporary root file system that is used by the Linux kernel during initialization process while other filesystems are not mounted. We can build `initrd` with the following commands: 第二种情况就是在虚拟机内运行新的 Linux 内核，我更倾向于使用 [qemu](https://en.wikipedia.org/wiki/QEMU)。首先我们需要为此构建初始的虚拟内存盘 - [initrd](https://en.wikipedia.org/wiki/Initrd)。`initrd` 是一个临时的根文件系统，它在初始化期间被 Linux 内核使用，而那时其他的文件系统尚未被挂载。我们可以使用以下命令构建 `initrd`： -First of all we need to download [busybox](https://en.wikipedia.org/wiki/BusyBox) and run `menuconfig` for its configuration: 首先我们需要下载 [busybox](https://en.wikipedia.org/wiki/BusyBox)，然后运行 `menuconfig` 命令配置它： ```shell @@ -264,12 +222,10 @@ $ make menuconfig $ make -j4 ``` -`busybox` is an executable file - `/bin/busybox` that contains a set of standard tools like [coreutils](https://en.wikipedia.org/wiki/GNU_Core_Utilities). In the `busysbox` menu we need to enable: `Build BusyBox as a static binary (no shared libs)` option: `busybox` 是一个可执行文件 - `/bin/busybox`，它包括了一系列类似于 [coreutils](https://en.wikipedia.org/wiki/GNU_Core_Utilities) 的标准工具。在 `busysbox` 菜单界面上我们需要启用：`Build BusyBox as a static binary (no shared libs)` 选项： ![busysbox menu](http://s18.postimg.org/sj92uoweh/busybox.png) -We can find this menu in the: 我们可以按照下方的路径找到这个菜单项： ``` @@ -277,7 +233,6 @@ Busybox Settings --> Build Options ``` -After this we exit from the `busysbox` configuration menu and execute following commands for building and installation of it: 之后，我们从 `busysbox` 的配置菜单退出去，然后执行下面的命令来构建并安装它： ``` @@ -285,7 +240,6 @@ $ make -j4 $ sudo make install ``` -Now that `busybox` is installed, we can begin building our `initrd`. To do this, we go to the previous `initrd` directory and: 既然 `busybox` 已经安装完了，那么我们就可以开始构建 `initrd` 了。为了完成构建过程，我们需要返回到之前的 `initrd` 目录并且运行命令： ``` @@ -296,7 +250,6 @@ $ mkdir -pv {bin,sbin,etc,proc,sys,usr/{bin,sbin}} $ cp -av ../busybox-1.23.2/_install/* . ``` -copy `busybox` fields to the `bin`, `sbin` and other directories. Now we need to create executable `init` file that will be executed as a first process in the system. My `init` file just mounts [procfs](https://en.wikipedia.org/wiki/Procfs) and [sysfs](https://en.wikipedia.org/wiki/Sysfs) filesystems and executed shell: 这会把 `busybox` 复制到 `bin` 目录、`sbin` 目录以及其他相关目录内。现在我们需要创建可执行的 `init` 文件，该文件将会在系统内作为第一个进程执行。我的 `init` 文件仅仅挂载了 [procfs](https://en.wikipedia.org/wiki/Procfs) 和 [sysfs](https://en.wikipedia.org/wiki/Sysfs) 文件系统并且执行了 shell 程序： ```shell @@ -308,14 +261,12 @@ mount -t sysfs none /sys exec /bin/sh ``` -Now we can create an archive that will be our `initrd`: 最后，我们创建一个归档文件，这就是我们的 `initrd` 了： ``` $ find . -print0 | cpio --null -ov --format=newc | gzip -9 > ~/dev/initrd_x86_64.gz ``` -We can now run our kernel in the virtual machine. As I already wrote I prefer [qemu](https://en.wikipedia.org/wiki/QEMU) for this. We can run our kernel with the following command: 我们现在可以在虚拟机里运行内核了。就像我之前写过的，我偏向于使用 [qemu](https://en.wikipedia.org/wiki/QEMU) 来完成这些工作，下面的命令可以用来运行我们的 Linux 内核： ``` @@ -324,20 +275,15 @@ $ qemu-system-x86_64 -snapshot -m 8GB -serial stdio -kernel ~/dev/linux/arch/x86 ![qemu](http://s22.postimg.org/b8ttyigup/qemu.png) -From now we can run the Linux kernel in the virtual machine and this means that we can begin to change and test the kernel. 从现在起，我们就可以在虚拟机内运行 Linux 内核了，这意味着我们可以开始对内核进行修改和测试了。 -Consider using [ivandaviov/minimal](https://github.com/ivandavidov/minimal) to automate the process of generating initrd. 除了上面的手动过程之外，还可以考虑使用 [ivandaviov/minimal](https://github.com/ivandavidov/minimal) 来自动生成 `initrd`。 -Getting started with the Linux Kernel Development Linux 内核开发入门 --------------------------------------------------------------------------------- -The main point of this paragraph is to answer two questions: What to do and what not to do before sending your first patch to the Linux kernel. Please, do not confuse this `to do` with `todo`. I have no answer what you can fix in the Linux kernel. I just want to tell you my workflow during experimenting with the Linux kernel source code. 这部分的核心内容主要回答了两个问题：在你发送第一个 Linux 内核补丁之前你应该做什么 (`to do`) 和不能做什么 (`not to do`)。请千万不要把应该做的事 (`to do`) 和待办事项 (`todo`) 搞混了。我无法回答你能为 Linux 内核修复什么问题，我只是想告诉你我拿 Linux 内核源代码做实验的过程。 -First of all I pull the latest updates from Linus's repo with the following commands: 首先，我需要使用以下命令从 Linus 的仓库中拉取最新的更新： ``` @@ -345,10 +291,8 @@ $ git checkout master $ git pull upstream master ``` -After this my local repository with the Linux kernel source code is synced with the [mainline](https://github.com/torvalds/linux) repository. Now we can make some changes in the source code. As I already wrote, I have no advice for you where you can start and what `TODO` in the Linux kernel. But the best place for newbies is `staging` tree. In other words the set of drivers from the [drivers/staging](https://github.com/torvalds/linux/tree/master/drivers/staging). The maintainer of the `staging` tree is [Greg Kroah-Hartman](https://en.wikipedia.org/wiki/Greg_Kroah-Hartman) and the `staging` tree is that place where your trivial patch can be accepted. Let's look on a simple example that describes how to generate patch, check it and send to the [Linux kernel mail listing](https://lkml.org/). 在这之后，我的本地 Linux 内核源代码仓库已经和[主线](https://github.com/torvalds/linux)仓库同步了。现在我们可以在源代码上做些修改了。就像我之前写的，关于从哪开始修改或者可以做些什么，我并不能给你太多建议。不过，对于新手来说最好的地方就是 `staging` 源码树，也就是 [drivers/staging](https://github.com/torvalds/linux/tree/master/drivers/staging) 上的驱动集合。`staging` 源码树的主要维护者是 [Greg Kroah-Hartman](https://en.wikipedia.org/wiki/Greg_Kroah-Hartman)，该源码树正是你的琐碎补丁可以被接受的地方。让我们看一个简单的例子，该例子描述了如何生成补丁、检查补丁以及如何将补丁发送到 [Linux 内核邮件列表](https://lkml.org/)。 -If we look in the driver for the [Digi International EPCA PCI](https://github.com/torvalds/linux/tree/master/drivers/staging/dgap) based devices, we will see the `dgap_sindex` function on line 295: 如果我们查看一下为 [Digi International EPCA PCI](https://github.com/torvalds/linux/tree/master/drivers/staging/dgap) 基础设备所写的驱动程序，在295行我们将会看到 `dgap_sindex` 函数： ```C @@ -370,17 +314,14 @@ static char *dgap_sindex(char *string, char *group) } ``` -This function looks for a match of any character in the group and returns that position. During research of source code of the Linux kernel, I have noted that the [lib/string.c](https://github.com/torvalds/linux/blob/master/lib/string.c#L473) source code file contains the implementation of the `strpbrk` function that does the same thing as `dgap_sinidex`. It is not a good idea to use a custom implementation of a function that already exists, so we can remove the `dgap_sindex` function from the [drivers/staging/dgap/dgap.c](https://github.com/torvalds/linux/blob/master/drivers/staging/dgap/dgap.c) source code file and use the `strpbrk` instead. 这个函数查找 `group` 和 `string` 共有的字符并返回其位置。在研究 Linux 内核源代码期间，我注意到 [lib/string.c](https://github.com/torvalds/linux/blob/master/lib/string.c#L473) 文件里实现了一个 `strpbrk` 函数，该函数和 `dgap_sinidex` 函数做了同样的事。使用现存函数的另一种自定义实现并不是一个好主意，所以我们可以从 [drivers/staging/dgap/dgap.c](https://github.com/torvalds/linux/blob/master/drivers/staging/dgap/dgap.c) 源码文件中移除 `dgap_sindex` 函数并使用 `strpbrk` 替换它。 -First of all let's create new `git` branch based on the current master that synced with the Linux kernel mainline repo: -首先，让我们基于当前主分支创建一个新的 `git` 分支，该分支与 Linux 内核主仓库同步。 +首先，让我们基于当前主分支创建一个新的 `git` 分支，该分支与 Linux 内核主仓库同步： ``` $ git checkout -b "dgap-remove-dgap_sindex" ``` -And now we can replace the `dgap_sindex` with the `strpbrk`. After we did all changes we need to recompile the Linux kernel or just [dgap](https://github.com/torvalds/linux/tree/master/drivers/staging/dgap) directory. Do not forget to enable this driver in the kernel configuration. You can find it in the: 然后，我们可以将 `dgap_sindex` 函数替换为 `strpbrk`。做完这些修改之后，我们需要重新编译 Linux 内核或者只重编译 [dgap](https://github.com/torvalds/linux/tree/master/drivers/staging/dgap) 目录。不要忘了在内核配置文件中启用这个驱动，你可以在如下位置找到该驱动： ``` @@ -391,7 +332,6 @@ Device Drivers ![dgap menu](http://s4.postimg.org/d3pozpge5/digi.png) -Now is time to make commit. I'm using following combination for this: 现在是时候提交修改了，我使用下面的命令组合来完成这件事： ``` @@ -399,17 +339,14 @@ $ git add . $ git commit -s -v ``` -After the last command an editor will be opened that will be chosen from `$GIT_EDITOR` or `$EDITOR` environment variable. The `-s` command line argument will add `Signed-off-by` line by the committer at the end of the commit log message. You can find this line in the end of each commit message, for example - [00cc1633](https://github.com/torvalds/linux/commit/00cc1633816de8c95f337608a1ea64e228faf771). The main point of this line is the tracking of who did a change. The `-v` option show unified diff between the HEAD commit and what would be committed at the bottom of the commit message. It is not necessary, but very useful sometimes. A couple of words about commit message. Actually a commit message consists from two parts: 最后一条命令运行后将会打开一个编辑器，该编辑器会从 `$GIT_EDITOR` 或 `$EDITOR` 环境变量中进行选择。 `-s` 命令行参数会在提交信息的末尾按照提交者名字加上一行 `Signed-off-by`。你在每一条提交信息的最后都能看到这一行，例如 - [00cc1633](https://github.com/torvalds/linux/commit/00cc1633816de8c95f337608a1ea64e228faf771)。这一行的主要目的是追踪谁做的修改。`-v` 选项按照合并格式显示 `HEAD` 提交和即将进行的最新提交之间的差异。这样做不是并必须的，但有时候却很有用。再来说下提交信息，实际上，一条提交信息由两部分组成： -The first part is on the first line and contains short description of changes. It starts from the `[PATCH]` prefix followed by a subsystem, driver or architecture name and after `:` symbol short description. In our case it will be something like this: 第一部分放在第一行，它包括了一句对所做修改的简短描述。这一行以 `[PATCH]` 做前缀，后面跟上子系统、驱动或架构的名字，以及在 `:` 之后的简述信息。在我们这个例子中，这一行信息如下所示： ``` [PATCH] staging/dgap: Use strpbrk() instead of dgap_sindex() ``` -After short description usually we have an empty line and full description of the commit. In our case it will be: 在简述信息之后，我们通常空一行再加上对本次提交的详尽描述。在我们的这个例子中，这些信息如下所示： ``` @@ -417,10 +354,8 @@ The provides strpbrk() function that does the same that the dgap_sindex(). Let's use already defined function instead of writing custom. ``` -And the `Sign-off-by` line in the end of the commit message. Note that each line of a commit message must no be longer than `80` symbols and commit message must describe your changes in details. Do not just write a commit message like: `Custom function removed`, you need to describe what you did and why. The patch reviewers must know what they review. Besides this commit messages in this view are very helpful. Each time when we can't understand something, we can use [git blame](http://git-scm.com/docs/git-blame) to read description of changes. 在提交信息的最后是 `Sign-off-by` 这一行。注意，提交信息的每一行不能超过 `80` 个字符并且提交信息必须详细地描述你所做的修改。千万不要只写一条类似于 `Custom function removed` 这样的信息，你需要描述你做了什么以及为什么这样做。补丁的审核者必须据此知道他们正在审核什么内容，除此之外，这里的提交信息本身也非常有用。每当你不能理解一些东西的时候，我们都可以使用 [git blame](http://git-scm.com/docs/git-blame) 命令来阅读关于修改的描述。 -After we have committed changes time to generate patch. We can do it with the `format-patch` command: 提交修改之后，是时候生成补丁文件了。我们可以使用 `format-patch` 命令来完成： ``` @@ -428,14 +363,12 @@ $ git format-patch master 0001-staging-dgap-Use-strpbrk-instead-of-dgap_sindex.patch ``` -We've passed name of the branch (`master` in this case) to the `format-patch` command that will generate a patch with the last changes that are in the `dgap-remove-dgap_sindex` branch and not are in the `master` branch. As you can note, the `format-patch` command generates file that contains last changes and has name that is based on the commit short description. If you want to generate a patch with the custom name, you can use `--stdout` option: 我们把分支名字 (这里是`master`) 传递给 `format-patch` 命令，该命令会根据那些包括在 `dgap-remove-dgap_sindex` 分支但不在 `master` 分支的最新改动来生成补丁。你会发现， `format-patch` 命令生成的文件包含了最新所做的修改，该文件的名字是基于提交信息的简述来生成的。如果你想按照自定义的文件名来生成补丁，你可以使用 `--stdout` 选项： ``` $ git format-patch master --stdout > dgap-patch-1.patch ``` -The last step after we have generated our patch is to send it to the Linux kernel mailing list. Of course, you can use any email client, `git` provides a special command for this: `git send-email`. Before you send your patch, you need to know where to send it. Yes, you can just send it to the Linux kernel mailing list address which is `linux-kernel@vger.kernel.org`, but it is very likely that the patch will be ignored, because of the large flow of messages. The better choice would be to send the patch to the maintainers of the subsystem where you have made changes. To find the names of these maintainers use the `get_maintainer.pl` script. All you need to do is pass the file or directory where you wrote code. 最后一步就是在我们生成补丁之后将之发送到 Linux 内核邮件列表。当然，你可以使用任意的邮件客户端，不过 `git` 为此提供了一个专门的命令：`git send-email`。在发送补丁之前，你需要知道发到哪里。虽然你可以直接把它发送到 `linux-kernel@vger.kernel.org` 这个邮件列表，但这很可能让你的补丁因为巨大的消息流而被忽略掉。最好的选择是将补丁发送到你的修改所属子系统的维护者那里。你可以使用 `get_maintainer.pl` 这个脚本来找到这些维护者的名字。你所需要做的就是将你代码所在的文件或目录作为参数传递给脚本。 ``` @@ -449,7 +382,6 @@ devel@driverdev.osuosl.org (open list:STAGING SUBSYSTEM) linux-kernel@vger.kernel.org (open list) ``` -You will see the set of the names and related emails. Now we can send our patch with: 你将会看到一组姓名和与之相关的邮件地址。现在你可以通过下面的命令发送补丁了： ``` @@ -462,26 +394,19 @@ $ git send-email --to "Lidza Louina " \ --cc "linux-kernel@vger.kernel.org" ``` -That's all. The patch is sent and now you only have to wait for feedback from the Linux kernel developers. After you send a patch and a maintainer accepts it, you will find it in the maintainer's repository (for example [patch](https://git.kernel.org/cgit/linux/kernel/git/gregkh/staging.git/commit/?h=staging-testing&id=b9f7f1d0846f15585b8af64435b6b706b25a5c0b) that you saw in this part) and after some time the maintainer will send a pull request to Linus and you will see your patch in the mainline repository. 这就是全部的过程。补丁被发出去了，现在你所需要做的就是等待 Linux 内核开发者的反馈。在你发送完补丁并且维护者接受它之后，你将在维护者的仓库中看到它 (例如前文你看到的[补丁](https://git.kernel.org/cgit/linux/kernel/git/gregkh/staging.git/commit/?h=staging-testing&id=b9f7f1d0846f15585b8af64435b6b706b25a5c0b))。一段时间后，维护者将会向 Linus 发送一个拉取请求，之后你就会在主线仓库里看到你的补丁了。 -That's all. 这就是全部内容。 -Some advice 一些建议 -------------------------------------------------------------------------------- -In the end of this part I want to give you some advice that will describe what to do and what not to do during development of the Linux kernel: -在该部分的最后，我想给你一些建议，这些建议大都是关于在 Linux 内核的开发过程中需要做什么以及不能做什么的。 +在该部分的最后，我想给你一些建议，这些建议大都是关于在 Linux 内核的开发过程中需要做什么以及不能做什么的： -* Think, Think, Think. And think again before you decide to send a patch. * 考虑，考虑，再考虑。在你决定发送补丁之前再三考虑。 -* Each time when you have changed something in the Linux kernel source code - compile it. After any changes. Again and again. Nobody likes changes that don't even compile. * 在你每次改完 Linux 内核源代码之后 - 试着编译它，我指的是任何修改之后，都要不断的编译。没有人喜欢那些连编译都不通过修改。 -* The Linux kernel has a coding style [guide](https://github.com/torvalds/linux/blob/master/Documentation/CodingStyle) and you need to comply with it. There is great script which can help to check your changes. This script is - [scripts/checkpatch.pl](https://github.com/torvalds/linux/blob/master/scripts/checkpatch.pl). Just pass source code file with changes to it and you will see: * Linux 内核有一套代码规范[指南](https://github.com/torvalds/linux/blob/master/Documentation/CodingStyle)，你需要遵守它。有一个很棒的脚本可以帮你检查所做的修改。这个脚本就是 - [scripts/checkpatch.pl](https://github.com/torvalds/linux/blob/master/scripts/checkpatch.pl)。只需要将被改动的源码文件传递给它即可，然后你就会看到如下输出： ``` @@ -497,7 +422,6 @@ CHECK: spaces preferred around that '|' (ctx:VxV) ``` -Also you can see problematic places with the help of the `git diff`: 在 `git diff` 命令的帮助下，你也会看到一些有问题的地方： ![git diff](http://oi60.tinypic.com/2u91rgn.jpg) @@ -505,7 +429,6 @@ Also you can see problematic places with the help of the `git diff`: * [Linus doesn't accept github pull requests](https://github.com/torvalds/linux/pull/17#issuecomment-5654674) * [Linus 不接受 github pull requests](https://github.com/torvalds/linux/pull/17#issuecomment-5654674) -* If your change consists from some different and unrelated changes, you need to split the changes via separate commits. The `git format-patch` command will generate patches for each commit and the subject of each patch will contain a `vN` prefix where the `N` is the number of the patch. If you are planning to send a series of patches it will be helpful to pass the `--cover-letter` option to the `git format-patch` command. This will generate an additional file that will contain the cover letter that you can use to describe what your patchset changes. It is also a good idea to use the `--in-reply-to` option in the `git send-email` command. This option allows you to send your patch series in reply to your cover message. The structure of the your patch will look like this for a maintainer: * 如果你的修改是由一些不同的且不相关的改动所组成的，你需要通过分离提交来切分修改。`git format-patch` 命令将会为每个提交生成一个补丁，每个补丁的标题会包含一个 `vN` 前缀，其中 `N` 是补丁的编号。如果你打算发送一系列补丁，也许给 `git format-patch` 命令传递 `--cover-letter` 选项会对此很有帮助。这会生成一个附加文件，该文件包括的附函可以用来描述你的补丁集所做的改动。在 `git send-email` 命令中使用 `--in-reply-to` 选项也是一个好主意，该选项允许你将补丁集作为对附函的回复发送出去。对于维护者来说，你补丁集的结构看起来就像下面这样： ``` @@ -514,46 +437,34 @@ Also you can see problematic places with the help of the `git diff`: |----> patch_2 ``` -You need to pass `message-id` as an argument of the `--in-reply-to` option that you can find in the output of the `git send-email`: 你可以将 `message-id` 参数传递给 `--in-reply-to` 选项，该选项可以在 `git send-email` 命令的输出中找到。 -It's important that your email be in the [plain text](https://en.wikipedia.org/wiki/Plain_text) format. Generally, `send-email` and `format-patch` are very useful during development, so look at the documentation for the commands and you'll find some useful options such as: [git send-email](http://git-scm.com/docs/git-send-email) and [git format-patch](http://git-scm.com/docs/git-format-patch). 有一件非常重要的事，那就是你的邮件必须是[纯文本](https://en.wikipedia.org/wiki/Plain_text)格式。通常来说，`send-email` 和 `format-patch` 这两个命令在内核开发中都是非常有用的，所以请查阅这些命令的的相关文档，你会发现很多有用的选项，例如：[git send-email](http://git-scm.com/docs/git-send-email) 和 [git format-patch](http://git-scm.com/docs/git-format-patch)。 -* Do not be surprised if you do not get an immediate answer after you send your patch. Maintainers can be very busy. * 如果你发完补丁之后没有得到立即答复，请不要惊讶，因为维护者们都是很忙的。 -* The [scripts](https://github.com/torvalds/linux/tree/master/scripts) directory contains many different useful scripts that are related to Linux kernel development. We already saw two scripts from this directory: the `checkpatch.pl` and the `get_maintainer.pl` scripts. Outside of those scripts, you can find the [stackusage](https://github.com/torvalds/linux/blob/master/scripts/stackusage) script that will print usage of the stack, [extract-vmlinux](https://github.com/torvalds/linux/blob/master/scripts/extract-vmlinux) for extracting an uncompressed kernel image, and many others. Outside of the `scripts` directory you can find some very useful [scripts](https://github.com/lorenzo-stoakes/kernel-scripts) by [Lorenzo Stoakes](https://twitter.com/ljsloz) for kernel development. * [scripts](https://github.com/torvalds/linux/tree/master/scripts) 目录包含了很多对 Linux 内核开发有用的脚本。我们已经看过此目录中的两个脚本了：`checkpatch.pl` 和 `get_maintainer.pl`。除此之外，你还可以找到 [stackusage](https://github.com/torvalds/linux/blob/master/scripts/stackusage) 脚本，它可以打印栈的使用情况，[extract-vmlinux](https://github.com/torvalds/linux/blob/master/scripts/extract-vmlinux) 脚本可以提取出未经压缩的内镜镜像，还有很多其他的脚本。在 `scripts` 目录之外，你也会发现很多有用的[脚本](https://github.com/lorenzo-stoakes/kernel-scripts)，这些脚本是 [Lorenzo Stoakes](https://twitter.com/ljsloz) 为内核开发而编写的。 -* Subscribe to the Linux kernel mailing list. There are a large number of letters every day on `lkml`, but it is very useful to read them and understand things such as the current state of the Linux kernel. Other than `lkml` there are [set](http://vger.kernel.org/vger-lists.html) mailing listings which are related to the different Linux kernel subsystems. * 订阅 Linux 内核邮件列表。`lkml` 列表中每天都会有大量的信件，但是阅读它们并了解一些类似于 Linux 内核目前开发状态的内容是很有帮助的。除了 `lkml` 之外，还有[一些](http://vger.kernel.org/vger-lists.html)其他的邮件列表，它们分别对应于不同的 Linux 内核子系统。 -* If your patch is not accepted the first time and you receive feedback from Linux kernel developers, make your changes and resend the patch with the `[PATCH vN]` prefix (where `N` is the number of patch version). For example: * 如果你发的补丁第一次没有被接受，你就会收到 Linux 内核开发者的反馈。请做一些修改然后以 `[PATCH vN]`(`N` 是补丁版本号) 为前缀重新发送补丁，例如： ``` [PATCH v2] staging/dgap: Use strpbrk() instead of dgap_sindex() ``` -Also it must contain a changelog that describes all changes from previous patch versions. Of course, this is not an exhaustive list of requirements for Linux kernel development, but some of the most important items were addressed. 同样的，这次的补丁也必须包括更新日志以便描述自上一次的补丁以来所做的修改。当然，本文并不是对 Linux 内核开发详尽无遗的指导清单，但是一些最重要的事项已经都被阐明了。 Happy Hacking! -Conclusion 总结 -------------------------------------------------------------------------------- -I hope this will help others join the Linux kernel community! -If you have any questions or suggestions, write me at [email](kuleshovmail@gmail.com) or ping [me](https://twitter.com/0xAX) on twitter. 我希望这篇文章能够帮助其他人加入 Linux 内核社区！ 如果你有其他问题或建议，可以给我写[邮件](kuleshovmail@gmail.com)或者在 Twitter 上联系[我](https://twitter.com/0xAX)。 -Please note that English is not my first language, and I am really sorry for any inconvenience. If you find any mistakes please let me know via email or send a PR. 请注意，英语并不是我的母语，对此带来的不便我感到很抱歉。如果你发现了错误，请通过邮件或发 PR 来通知我。 -Links 相关链接 --------------------------------------------------------------------------------