From 0094f3f87275b9f5eb9fb5bbf07efcd7b599174d Mon Sep 17 00:00:00 2001
From: Xingyu Wang <xingyu.wang@gmail.com>
Date: Sat, 15 Jul 2023 11:43:42 +0800
Subject: [PATCH] ATRP

@wxy
https://linux.cn/article-16002-1.html
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+[#]: subject: "A 10-minute guide to the Linux ABI"
+[#]: via: "https://opensource.com/article/22/12/linux-abi"
+[#]: author: "Alison Chaiken https://opensource.com/users/chaiken"
+[#]: collector: "lkxed"
+[#]: translator: "ChatGPT"
+[#]: reviewer: "wxy"
+[#]: publisher: "wxy"
+[#]: url: "https://linux.cn/article-16002-1.html"
+
+10 分钟让你了解 Linux ABI
+======
+
+![][0]
+
+> 熟悉 ABI 的概念�ABI 稳定性的��性以� Linux 稳定 ABI 中包�的内容。
+
+> LCTT 译注：昨天，AlmaLinux 称将 [放弃](https://linux.cn/article-16000-1.html) 对 RHEL 的 1:1 兼容性，但将��对 RHEL 的 ABI 兼容，以便在 RHEL 上�行的软件�以无�地�行在 AlmaLinux 上。�能有的�学对 ABI 的概念还�是很清楚，因此翻译此文供大家了解。
+
+许多 Linux 爱好者都熟悉 Linus Torvalds 的 [著�告诫][1]：“我们�破�用户空间�，但�能并��个�到这��的人都清楚其�义。
+
+这个“第一规则��醒开�人员关于应用程�的二进制接�（ABI）的稳定性，该接�用于应用程�与内核之间的通信和�置。接下�的内容旨在使读者熟悉 ABI 的概念，�述为什么 ABI 的稳定性很��，并讨论 Linux 稳定 ABI 中包�了哪些内容。Linux 的�续增长和演进需�对 ABI 进行�更，其中一些�更引起了争议。
+
+### 什么是 ABI？
+
+ABI 表示 <ruby>应用程�二进制接�<rt>Applications Binary Interface</rt></ruby>。�解 ABI 概念的一�方�是考虑它与其他概念的区别。对于许多开�人员�说，<ruby>应用程�编程接�<rt>Applications Programming Interface</rt></ruby>（API）更为熟悉。通常，库的头文件和文档被认为是其 API，以�还有� [HTML5][2] 这样的标准文档。调用库或交�字符串格�数�的程�必须�守 API 中所�述的约定，�则�能得到�外的结果。
+
+ABI 类似于 API，因为它们规定了命令的解释和二进制数�的交�方�。对于 C 程�，ABI 通常包括函数的返回类型和�数列表�结构体的布局，以�枚举类型的�义�顺�和范围。截至 2022 年，Linux 内核�然几乎完全是 C 程�，因此必须�守这些规范。
+
+“[内核系统调用接�][3]� 的�述�以在《[Linux 手册第 2 节][4]》中找到，并包括了�从中间件应用程�调用的类似 `mount` 和 `sync` 的 C 版本函数。这些函数的二进制布局是 Linux ABI 的第一个��组�部分。对于问题 “Linux 的稳定 ABI 包括哪些内容？�，许多用户和开�人员的回答是 “sysfs（`/sys`）和 procfs（`/proc`）的内容�。而实际上，[官方 Linux ABI 文档][5] 确实主�集中在这些 [虚拟文件系统][6] 上。
+
+����介�了 Linux ABI 在程�中的应用方�，但未涵盖�等��的人为因素。正如下图所示，ABI 的功能需�内核社区�C 编译器（如 [GCC][7] 或 [clang][8]）�创建用户空间 C 库（通常是 [glibc][9]）的开�人员，以�按照 [�执行与链接格�（ELF）][10] 布局的二进制应用程�之间的�作努力。
+
+![开�社区内的�作][11]
+
+### 为什么我们关注 ABI？
+
+�自 Torvalds 本人的 Linux ABI 的稳定性��，使得 Linux �行版和个人用户能够独立更新内核，而���作系统的影�。
+
+如果 Linux 没有稳定的 ABI，那么�次内核需�修补以解决安全问题时，�作系统的大部分甚至全部内容都需��新安装。显然，二进制接�的稳定性是 Linux 的�用性和广泛采用的��因素之一。
+
+![Terminal output][12]
+
+如上图所示，内核（在 `linux-libc-dev` 中）和 Glibc（在 `libc6-dev` 中）都�供了定义文件��的�掩�。显然，这两个定义集必须一致�`apt` 软件包管�器会识别软件包�供�个文件。Glibc ABI 的潜在�稳定部分�于 `bits/` 目录中。
+
+在大部分情况下，Linux ABI 的稳定性���作良好。按照 <ruby>[康韦定律][13]<rt>Conway's Law</rt></ruby>，在开�过程中出现的烦人技术问题往往是由于��软件开�社区之间的误解或分歧所致，而这些社区都为 Linux �出了贡献。��社区之间的接��以通过 Linux 包管�器的元数�轻�地进行想象，如上图所示。
+
+### Y2038：一个 ABI 破�的例�
+
+通过考虑当�正在进行的�[缓慢�生][14] 的 “Y2038� ABI 破�的例�，�以更好地�解 Linux ABI。在 2038 年 1 月，32 �时间计数器将回滚到全零，就�较旧车辆的里程表一样。2038 年 1 月�起�还很�远，但�以肯定的是，如今销售的许多物�网设备�将处于�行状�。�今年安装的 [智能电表][15] 和 [智能�车系统][16] 这样的普通产��能采用的是 32 �处�器架构，而且也�能�支�软件更新。
+
+Linux 内核已�在内部转�使用 64 �的 `time_t` ��明数�类型�表示更晚的时间点。这�味�� `time()` 这样的系统调用在 64 �系统上已��更了它们的函数签�。这些努力的艰难程度�以在内核头文件中（例如 [time_types.h][17]）清楚地看到，在那里放�新的和 `_old` 版本的数�结构。
+
+![里程表翻转][18]
+
+Glibc 项目也 [支� 64 �时间][19]，那么就大功告�了，对�？�幸的是，根� [Debian 邮件列表中的讨论][20] �看，情况并�如此。�行版�临难以选择的问题，�么为 32 �系统�供所有二进制软件包的两个版本，�么为安装介质�供两个版本。在�一�情况下，32 �时间的用户将�得��新编译其应用程�并�新安装。正如往常一样，专有应用程��是一个真正的头疼问题。
+
+### Linux 稳定 ABI 里到底包括什么内容？
+
+�解稳定 ABI 有些微妙。需�考虑的是，尽管大部分 sysfs 是稳定 ABI，但调试接�肯定是�稳定的，因为它们将内核内部暴露给用户空间。Linus Torvalds 曾表示，“��破�用户空间�，通常情况下，他是指�护那些 “�想它能工作� 的普通用户，而�是系统程�员和内核工程师，�者应该能够阅读内核文档和�代�，以了解��版本之间�生了什么�化。下图展示了这个区别。
+
+![稳定性��][21]
+
+普通用户�太�能与 Linux ABI 的�稳定部分进行交互，但系统程�员�能无�中这样�。除了 `/sys/kernel/debug` 以外，sysfs（`/sys`）和 procfs（`/proc`）的所有部分都是稳定的。
+
+那么其他对用户空间��的二进制接�如何呢，包括 `/dev` 中的设备文件�内核日志文件（�通过 `dmesg` 命令读�）�文件系统元数�或在内核的 “命令行� 中�供的 “引导�数�（在引导加载程�如 GRUB 或 u-boot 中��）呢？当然，“这�视情况而定�。
+
+### 挂载旧文件系统
+
+除了 Linux 系统在引导过程中出现挂起之外，文件系统无法挂载是最令人失望的事情。如果文件系统�于付费客户的固�硬盘上，那么问题确实�分严�。当内核�级时，一个能够在旧内核版本下挂载的 Linux 文件系统应该�然能够挂载，对�？实际上，“这�视情况而定�。
+
+在 2020 年，一��到伤害的 Linux 开�人员在内核的邮件列表上 [抱怨�][23]：
+
+> 内核已�接�这个作为一个有效的�挂载文件系统格�，没有任何错误或任何类型的警告，而且已�这样稳定地工作了多年……我一直普�地以为，挂载现有的根文件系统属于内核<->用户空间或内核<->现有系统边界的范围，由内核接�并被现有用户空间�功使用的内容所定义，�级内核应该与现有用户空间和系统兼容。
+
+但是有一个问题：这些无法挂载的文件系统是使用一��赖于内核定义，但并未被内核使用的标志的专有工具创建的。该标志未出现在 Linux 的 API 头文件或 procfs/sysfs 中，而是一� [实现细节][24]。因此，在用户空间代�中解释该标志�味��赖于“[未定义行为][25]�，这是个几乎会让�个软件开�人员都感到战栗的短语。当内核社区改进其内部测试并开始进行新的一致性检查时，“[man 2 mount][26]� 系统调用�然开始拒�具有专有格�的文件系统。由于该格�的创建者明确是一�软件开�人员，因此他未能得到内核文件系统维护者的�情。
+
+![施工标志上写�工作人员在树上进行工作][27]
+
+### 线程化内核的 dmesg 日志
+
+`/dev` 目录中的文件格�是���稳定或�稳定？[dmesg 命令][28] 会从文件 `/dev/kmsg` 中读�内容。2018 年，一�开�人员 [为 dmesg 输出实现了线程化][29]，使内核能够“在打�一系列 `printk()` 消�到控制�时，�会被中断和/或被其他线程的并� `printk()` 干扰�。�起�很棒�通过在 `/dev/kmsg` 输出的�一行添加线程 ID，实现了线程化。密切关注的读者将�识到这个改动改�了 `/dev/kmsg` 的 ABI，这�味�解�该文件的应用程�也需�进行相应的修改。由于许多�行版没有编译�用新功能的内核，大多数使用 `/bin/dmesg` 的用户�能没有注�到这件事，但这个改动破�了 [GDB 调试器][30] 读�内核日志的能力。
+
+确实，��的读者会认为 GDB 的用户�气�佳，因为调试器是开�人员工具。实际上并�如此，因为需�更新以支�新的 `/dev/kmsg` 格�的代��于内核自己的 Git �代�库的 “树内� 部分。对于一个正常的项目�说，�个代�库内的程�无法��工作就是一个明显的错误，因此已��并了一份 [使 GDB 能够与线程化的 /dev/kmsg 一起工作的补�][32]。
+
+### 那么 BPF 程�呢？
+
+[BPF][33] 是一�强大的工具，�以在�行的内核中监控甚至实时进行�置。BPF 最�的目的是通过�许系统管�员�时从命令行修改数�包过滤器，从而支�实时网络�置。[Alexei Starovoitov 和其他人�大地扩展了 BPF][34]，使其能够跟踪任�内核函数。跟踪明显是开�人员的领域，而�是普通用户，因此它显然��任何 ABI ��的约�（尽管 [bpf() 系统调用][35] 具有与其他系统调用相�的稳定性承诺）。�一方�，创建新功能的 BPF 程�为“[�代内核模��为扩展内核的事实标准手段][36]��供了�能性。内核模�使设备�文件系统�加密�网络等工作正常，因此明显是“�希望它工作�的普通用户所�赖的设施。问题是，与大多数开�内核模���，BPF 程�传统上�在内核�代�中。
+
+2022 年春季，[一个�案][37] �为了焦点，该�案�议使用微型 BPF 程�而�是设备驱动程�补�，对广泛的人机接�设备（如鼠标和键盘）�供支�。
+
+��进行了一场激烈的讨论，但这个问题显然在 [Torvalds 在开�峰会上的评论][38] 中得到解决：
+
+> 他指出，如果你破�了“普通（�内核开�人员）用户使用的真实用户空间工具�，那么你需�修�它，无论是�使用了 eBPF。
+
+一致��似乎正在形�，�希望其 BPF 程�在内核更新��能正常工作的开�人员 [将需�将其�交到内核�代�库中一个尚未指定的�置][39]。敬请关注�继�展，以了解内核社区对于 BPF 和 ABI 稳定性将采�什么样的政策。
+
+### 结论
+
+内核的 ABI 稳定性��适用于 procfs�sysfs 和系统调用接�，但也存在��的例外情况。当内核�更破�了“树内�代�或用户空间应用程�时，通常会迅速回滚有问题的补�。对于�赖内核实现细节的专有代�，尽管这些细节�以从用户空间访问，但它并没有�到�护，并且在出现问题时得到的�情有�。当� Y2038 这样的问题无法�� ABI 破�时，会以尽�能慎�和系统化的方�进行过渡。而� BPF 程�这样的新功能�出了关于 ABI 稳定性边界的尚未解答的问题。
+
+### 致谢
+
+感谢 [Akkana Peck][40]�[Sarah R. Newman][41] 和 [Luke S. Crawford][42] 对早期版本�料的有益评论。
+
+*（题图：MJ/da788385-ca24-4be5-bc27-ad7e7ef75973）*
+
+--------------------------------------------------------------------------------
+
+via: https://opensource.com/article/22/12/linux-abi
+
+作者：[Alison Chaiken][a]
+选题：[lkxed][b]
+译者：ChatGPT
+校对：[wxy](https://github.com/wxy)
+
+本文由 [LCTT](https://github.com/LCTT/TranslateProject) 原创编译，[Linux中国](https://linux.cn/) �誉推出
+
+[a]: https://opensource.com/users/chaiken
+[b]: https://github.com/lkxed
+[1]: https://lkml.org/lkml/2018/12/22/232
+[2]: https://www.w3.org/TR/2014/REC-html5-20141028/
+[3]: https://www.kernel.org/doc/html/v6.0/admin-guide/abi-stable.html#the-kernel-syscall-interface
+[4]: https://www.man7.org/linux/man-pages/dir_section_2.html
+[5]: https://www.kernel.org/doc/html/v6.0/admin-guide/abi.html
+[6]: https://opensource.com/article/19/3/virtual-filesystems-linux
+[7]: https://gcc.gnu.org/
+[8]: https://clang.llvm.org/get_started.html
+[9]: https://www.gnu.org/software/libc/
+[10]: https://www.man7.org/linux/man-pages/man5/elf.5.html
+[11]: https://opensource.com/sites/default/files/2022-11/1cooperation.png
+[12]: https://opensource.com/sites/default/files/2022-12/better_apt-file-find_ABI-boundary.png
+[13]: https://en.wikipedia.org/wiki/Conway's_law
+[14]: https://www.phoronix.com/news/MTc2Mjg
+[15]: https://www.lfenergy.org/projects/super-advanced-meter-sam/
+[16]: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7506899/
+[17]: https://github.com/torvalds/linux/blob/master/include/uapi/linux/time_types.h
+[18]: https://opensource.com/sites/default/files/2022-11/3speedometerrollingover_0.jpg
+[19]: https://www.phoronix.com/scan.php?page=news_item&px=Glibc-More-Y2038-Work
+[20]: https://groups.google.com/g/linux.debian.ports.arm/c/_KBFSz4YRZs
+[21]: https://opensource.com/sites/default/files/2022-11/4stability.png
+[22]: https://lwn.net/Articles/833696/
+[23]: https://lwn.net/ml/linux-kernel/20201006050306.GA8098@localhost/
+[24]: https://en.wikipedia.org/wiki/Encapsulation_(computer_programming)
+[25]: https://en.wikipedia.org/wiki/Undefined_behavior
+[26]: https://www.man7.org/linux/man-pages/man2/mount.2.html
+[27]: https://opensource.com/sites/default/files/2022-11/5crewworkingintrees.jpg
+[28]: https://www.man7.org/linux/man-pages/man1/dmesg.1.html
+[29]: https://lkml.org/lkml/2018/11/24/180
+[30]: https://sourceware.org/gdb/current/onlinedocs/gdb/
+[31]: https://unix.stackexchange.com/questions/208638/linux-kernel-meaning-of-source-tree-in-tree-and-out-of-tree
+[32]: https://lore.kernel.org/all/20191011142500.2339-1-joel.colledge@linbit.com/
+[33]: https://opensource.com/article/19/8/introduction-bpftrace
+[34]: https://lwn.net/Articles/740157/
+[35]: https://www.man7.org/linux/man-pages/man2/bpf.2.html
+[36]: https://lwn.net/Articles/909095/
+[37]: https://lwn.net/ml/ksummit-discuss/CAO-hwJJxCteD_BHZTeqQ1f7gWOHoj+05qP8bmFsRYVfMc_3FxQ@mail.gmail.com/
+[38]: https://lwn.net/ml/ksummit-discuss/20220621110514.6ef174d0@rorschach.local.home/
+[39]: https://lwn.net/ml/ksummit-discuss/20220616125128.68151432@gandalf.local.home/
+[40]: https://shallowsky.com/blog/
+[41]: https://www.socallinuxexpo.org/scale/19x/presentations/live-patching-down-trenches-view
+[42]: https://www.amazon.com/Book-Xen-Practical-System-Administrator/dp/1593271867
+[0]: https://img.linux.net.cn/data/attachment/album/202307/15/114240eo7her2zbdqqp448.jpg
\ No newline at end of file
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-[#]: subject: "A 10-minute guide to the Linux ABI"
-[#]: via: "https://opensource.com/article/22/12/linux-abi"
-[#]: author: "Alison Chaiken https://opensource.com/users/chaiken"
-[#]: collector: "lkxed"
-[#]: translator: " "
-[#]: reviewer: " "
-[#]: publisher: " "
-[#]: url: " "
-
-A 10-minute guide to the Linux ABI
-======
-
-Many Linux enthusiasts are familiar with Linus Torvalds' [famous admonition][1], "we don't break user space," but perhaps not everyone who recognizes the phrase is certain about what it means.
-
-The "#1 rule" reminds developers about the stability of the applications' binary interface via which applications communicate with and configure the kernel. What follows is intended to familiarize readers with the concept of an ABI, describe why ABI stability matters, and discuss precisely what is included in Linux's stable ABI. The ongoing growth and evolution of Linux necessitate changes to the ABI, some of which have been controversial.
-
-### What is an ABI?
-
-ABI stands for Applications Binary Interface. One way to understand the concept of an ABI is to consider what it is not. Applications Programming Interfaces (APIs) are more familiar to many developers. Generally, the headers and documentation of libraries are considered to be their API, as are standards documents like those for [HTML5][2], for example. Programs that call into libraries or exchange string-formatted data must comply with the conventions described in the API or expect unwanted results.
-
-ABIs are similar to APIs in that they govern the interpretation of commands and exchange of binary data. For C programs, the ABI generally comprises the return types and parameter lists of functions, the layout of structs, and the meaning, ordering, and range of enumerated types. The Linux kernel remains, as of 2022, almost entirely a C program, so it must adhere to these specifications.
-
-"[The kernel syscall interface][3]" is described by [Section 2 of the Linux man pages][4] and includes the C versions of familiar functions like "mount" and "sync" that are callable from middleware applications. The binary layout of these functions is the first major part of Linux's ABI. In answer to the question, "What is in Linux's stable ABI?" many users and developers will respond with "the contents of sysfs (/sys) and procfs (/proc)." In fact, the [official Linux ABI documentation][5] concentrates mostly on these [virtual filesystems][6].
-
-The preceding text focuses on how the Linux ABI is exercised by programs but fails to capture the equally important human aspect. As the figure below illustrates, the functionality of the ABI requires a joint, ongoing effort by the kernel community, C compilers (such as [GCC][7] or [clang][8]), the developers who create the userspace C library (most commonly [glibc][9]) that implements system calls, and binary applications, which much be laid out in accordance with the Executable and Linking Format ([ELF][10]).
-
-![Cooperation within the development community][11]
-
-### Why do we care about the ABI?
-
-The Linux ABI stability guarantee that comes from Torvalds himself enables Linux distros and individual users to update the kernel independently of the operating system.
-
-If Linux did not have a stable ABI, then every time the kernel needed patching to address a security problem, a large part of the operating system, if not the entirety, would need to be reinstalled. Obviously, the stability of the binary interface is a major contributing factor to Linux's usability and wide adoption.
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-![Terminal output][12]
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-As the second figure illustrates, both the kernel (in linux-libc-dev) and Glibc (in `libc6-dev`) provide bitmasks that define file permissions. Obviously the two sets of definitions must agree! The `apt` package manager identifies which software project provided each file. The potentially unstable part of Glibc's ABI is found in the `bits/` directory.
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-For the most part, the Linux ABI stability guarantee works just fine. In keeping with [Conway's Law][13], vexing technical issues that arise in the course of development most frequently occur due to misunderstandings or disagreements between different software development communities that contribute to Linux. The interface between communities is easy to envision via Linux package-manager metadata, as shown in the image above.
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-### Y2038: An example of an ABI break
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-The Linux ABI is best understood by considering the example of the ongoing, [slow-motion][14] "Y2038" ABI break. In January 2038, 32-bit time counters will roll over to all zeroes, just like the odometer of an older vehicle. January 2038 sounds far away, but assuredly many IoT devices sold in 2022 will still be operational. Mundane products like [smart electrical meters][15] and [smart parking systems][16] installed this year may or may not have 32-bit processor architectures and may or may not support software updates.
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-The Linux kernel has already moved to a 64-bit `time_t` opaque data type internally to represent later timepoints. The implication is that system calls like `time()` have already changed their function signature on 64-bit systems. The arduousness of these efforts is on ready display in kernel headers like [time_types.h][17], which includes new and "_old" versions of data structures.
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-![Odometer rolling over][18]
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-The Glibc project also [supports 64-bit time][19], so yay, we're done, right? Unfortunately, no, as a [discussion on the Debian mailing list][20] makes clear. Distros are faced with the unenviable choice of either providing two versions of all binary packages for 32-bit systems or two versions of installation media. In the latter case, users of 32-bit time will have to recompile their applications and reinstall. As always, proprietary applications will be a real headache.
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-### What precisely is in the Linux stable ABI anyway?
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-Understanding the stable ABI is a bit subtle. Consider that, while most of sysfs is stable ABI, the debug interfaces are guaranteed to be _un_stable since they expose kernel internals to userspace. In general, Linus Torvalds has pronounced that by "don't break userspace," he means to protect ordinary users who "just want it to work" rather than system programmers and kernel engineers, who should be able to read the kernel documentation and source code to figure out what has changed between releases. The distinction is illustrated in the figure below.
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-![Stability guarantee][21]
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-Ordinary users are unlikely to interact with unstable parts of the Linux ABI, but system programmers may do so inadvertently. All of sysfs (`/sys`) and procfs (`/proc`) are guaranteed stable except for `/sys/kernel/debug`.
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-But what about other binary interfaces that are userspace-visible, including miscellaneous ABI bits like device files in `/dev`, the kernel log file (readable with the `dmesg` command), filesystem metadata, or "bootargs" provided on the kernel "command line" that are visible in a bootloader like GRUB or u-boot? Naturally, "it depends."
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-### Mounting old filesystems
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-Next to observing a Linux system hang during the boot sequence, having a filesystem fail to mount is the greatest disappointment. If the filesystem resides on an SSD belonging to a paying customer, the matter is grave indeed. Surely a Linux filesystem that mounts with an old kernel version will still mount when the kernel is upgraded, right? Actually, "[it depends][22]."
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-In 2020 an aggrieved Linux developer [complained on the kernel's mailing list][23]:
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-> The kernel already accepted this as a valid mountable filesystem format, without a single error or warning of any kind, and has done so stably for years. . . . I was generally under the impression that mounting existing root filesystems fell under the scope of the kernel<->userspace or kernel<->existing-system boundary, as defined by what the kernel accepts and existing userspace has used successfully, and that upgrading the kernel should work with existing userspace and systems.
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-But there was a catch: The filesystems that failed to mount were created with a proprietary tool that relied on a flag that was defined but not used by the kernel. The flag did not appear in Linux's API header files or procfs/sysfs but was instead an [implementation detail][24]. Therefore, interpreting the flag in userspace code meant relying on "[undefined behavior][25]," a phrase that will make software developers almost universally shudder. When the kernel community improved its internal testing and started making new consistency checks, the "[man 2 mount][26]" system call suddenly began rejecting filesystems with the proprietary format. Since the format creator was decidedly a software developer, he got little sympathy from kernel filesystem maintainers.
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-![Construction sign reading crews working in trees][27]
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-### Threading the kernel dmesg log
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-Is the format of files in `/dev` guaranteed stable or not? The [command dmesg][28] reads from the file `/dev/kmsg`. In 2018, a developer [made output to dmesg threaded][29], enabling the kernel "to print a series of printk() messages to consoles without being disturbed by concurrent printk() from interrupts and/or other threads." Sounds excellent! Threading was made possible by adding a thread ID to each line of the `/dev/kmsg` output. Readers following closely will realize that the addition changed the ABI of `/dev/kmsg`, meaning that applications that parse that file needed to change too. Since many distros didn't compile their kernels with the new feature enabled, most users of `/bin/dmesg` won't have noticed, but the change broke the [GDB debugger][30]'s ability to read the kernel log.
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-Assuredly, astute readers will think users of GDB are out of luck because debuggers are developer tools. Actually, no, since the code that needed to be updated to support the new `/dev/kmsg` format was "[in-tree][31]," meaning part of the kernel's own Git source repository. The failure of programs within a single repo to work together is just an out-and-out bug for any sane project, and a [patch that made GDB work with threaded /dev/kmsg][32] was merged.
-
-### What about BPF programs?
-
-[BPF][33] is a powerful tool to monitor and even configure the running kernel dynamically. BPF's original purpose was to support on-the-fly network configuration by allowing sysadmins to modify packet filters from the command line instantly. [Alexei Starovoitov and others greatly extended BPF][34], giving it the power to trace arbitrary kernel functions. Tracing is clearly the domain of developers rather than ordinary users, so it is certainly not subject to any ABI guarantee (although the [bpf() system call][35] has the same stability promise as any other). On the other hand, BPF programs that create new functionality present the possibility of "[replacing kernel modules as the de-facto means of extending the kernel][36]." Kernel modules make devices, filesystems, crypto, networks, and the like work, and therefore clearly are a facility on which the "just want it to work" user relies. The problem arises that BFP programs have not traditionally been "in-tree" as most open-source kernel modules are. A proposal in spring 2022 to [provide support to the vast array of human interface devices (HIDs) like mice and keyboards via tiny BPF programs][37] rather than patches to device drivers brought the issue into sharp focus.
-
-A rather heated discussion followed, but the issue was apparently settled by [Torvalds' comments at Open Source Summit][38]:
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-> He specified if you break 'real user space tools, that normal (non-kernel developers) users use,' then you need to fix it, regardless of whether it is using eBPF or not.
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-A consensus appears to be forming that developers who expect their BPF programs to withstand kernel updates [will need to submit them to an as-yet unspecified place in the kernel source repository][39]. Stay tuned to find out what policy the kernel community adopts regarding BPF and ABI stability.
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-### Conclusion
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-The kernel ABI stability guarantee applies to procfs, sysfs, and the system call interface, with important exceptions. When "in-tree" code or userspace applications are "broken" by kernel changes, the offending patches are typically quickly reverted. When proprietary code relies on kernel implementation details that are incidentally accessible from userspace, it is not protected and garners little sympathy when it breaks. When, as with Y2038, there is no way to avoid an ABI break, the transition is made as thoughtfully and methodically as possible. Newer features like BPF programs present as-yet-unanswered questions about where exactly the ABI-stability border lies.
-
-##### Acknowledgments
-
-Thanks to [Akkana Peck][40], [Sarah R. Newman][41], and [Luke S. Crawford][42] for their helpful comments on early versions of this material.
-
---------------------------------------------------------------------------------
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-via: https://opensource.com/article/22/12/linux-abi
-
-作者：[Alison Chaiken][a]
-选题：[lkxed][b]
-译者：[译者ID](https://github.com/译者ID)
-校对：[校对者ID](https://github.com/校对者ID)
-
-本文由 [LCTT](https://github.com/LCTT/TranslateProject) 原创编译，[Linux中国](https://linux.cn/) �誉推出
-
-[a]: https://opensource.com/users/chaiken
-[b]: https://github.com/lkxed
-[1]: https://lkml.org/lkml/2018/12/22/232
-[2]: https://www.w3.org/TR/2014/REC-html5-20141028/
-[3]: https://www.kernel.org/doc/html/v6.0/admin-guide/abi-stable.html#the-kernel-syscall-interface
-[4]: https://www.man7.org/linux/man-pages/dir_section_2.html
-[5]: https://www.kernel.org/doc/html/v6.0/admin-guide/abi.html
-[6]: https://opensource.com/article/19/3/virtual-filesystems-linux
-[7]: https://gcc.gnu.org/
-[8]: https://clang.llvm.org/get_started.html
-[9]: https://www.gnu.org/software/libc/
-[10]: https://www.man7.org/linux/man-pages/man5/elf.5.html
-[11]: https://opensource.com/sites/default/files/2022-11/1cooperation.png
-[12]: https://opensource.com/sites/default/files/2022-12/better_apt-file-find_ABI-boundary.png
-[13]: https://en.wikipedia.org/wiki/Conway's_law
-[14]: https://www.phoronix.com/news/MTc2Mjg
-[15]: https://www.lfenergy.org/projects/super-advanced-meter-sam/
-[16]: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7506899/
-[17]: https://github.com/torvalds/linux/blob/master/include/uapi/linux/time_types.h
-[18]: https://opensource.com/sites/default/files/2022-11/3speedometerrollingover_0.jpg
-[19]: https://www.phoronix.com/scan.php?page=news_item&px=Glibc-More-Y2038-Work
-[20]: https://groups.google.com/g/linux.debian.ports.arm/c/_KBFSz4YRZs
-[21]: https://opensource.com/sites/default/files/2022-11/4stability.png
-[22]: https://lwn.net/Articles/833696/
-[23]: https://lwn.net/ml/linux-kernel/20201006050306.GA8098@localhost/
-[24]: https://en.wikipedia.org/wiki/Encapsulation_(computer_programming)
-[25]: https://en.wikipedia.org/wiki/Undefined_behavior
-[26]: https://www.man7.org/linux/man-pages/man2/mount.2.html
-[27]: https://opensource.com/sites/default/files/2022-11/5crewworkingintrees.jpg
-[28]: https://www.man7.org/linux/man-pages/man1/dmesg.1.html
-[29]: https://lkml.org/lkml/2018/11/24/180
-[30]: https://sourceware.org/gdb/current/onlinedocs/gdb/
-[31]: https://unix.stackexchange.com/questions/208638/linux-kernel-meaning-of-source-tree-in-tree-and-out-of-tree
-[32]: https://lore.kernel.org/all/20191011142500.2339-1-joel.colledge@linbit.com/
-[33]: https://opensource.com/article/19/8/introduction-bpftrace
-[34]: https://lwn.net/Articles/740157/
-[35]: https://www.man7.org/linux/man-pages/man2/bpf.2.html
-[36]: https://lwn.net/Articles/909095/
-[37]: https://lwn.net/ml/ksummit-discuss/CAO-hwJJxCteD_BHZTeqQ1f7gWOHoj+05qP8bmFsRYVfMc_3FxQ@mail.gmail.com/
-[38]: https://lwn.net/ml/ksummit-discuss/20220621110514.6ef174d0@rorschach.local.home/
-[39]: https://lwn.net/ml/ksummit-discuss/20220616125128.68151432@gandalf.local.home/
-[40]: https://shallowsky.com/blog/
-[41]: https://www.socallinuxexpo.org/scale/19x/presentations/live-patching-down-trenches-view
-[42]: https://www.amazon.com/Book-Xen-Practical-System-Administrator/dp/1593271867