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【翻译完成】20141125 Four ways Linux is headed for no-downtime kernel patching.md
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翻译中 by coloka
Four ways Linux is headed for no-downtime kernel patching
================================================================================
![Credit: Shutterstock](http://images.techhive.com/images/article/2014/10/patch_f-100526950-primary.idge.jpeg)
Credit: Shutterstock
These technologies are competing to provide the best way to patch the Linux kernel without reboots or downtime
Nobody loves a reboot, especially not if it involves a late-breaking patch for a kernel-level issue that has to be applied stat.
To that end, three projects are in the works to provide a mechanism for upgrading the kernel in a running Linux instance without having to reboot anything.
### Ksplice ###
The first and original contender is Ksplice, courtesy of a company of the same name founded in 2008. The kernel being replaced does not have to be pre-modified; all it needs is a diff file listing the changes to be made to the kernel source. Ksplice, Inc. offered support for the (free) software as a paid service and supported most common Linux distributions used in production.
All that changed in 2011, when [Oracle purchased the company][1], rolled the feature into its own Linux distribution, and kept updates for the technology to itself. As a result, other intrepid kernel hackers have been looking for ways to pick up where Ksplice left off, without having to pay the associated Oracle tax.
### Kgraft ###
In February 2014, Suse provided the exact solution needed: [Kgraft][2], its kernel-update technology released under a mixed GPLv2/GPLv3 license and not kept close as a proprietary creation. It's since been [submitted][3] as a possible inclusion to the mainline Linux kernel, although Suse has rolled a version of the technology into [Suse Linux Enterprise Server 12][4].
Kgraft works roughly like Ksplice by using a set of diffs to figure out what parts of the kernel to replace. But unlike Ksplice, Kgraft doesn't need to stop the kernel entirely to replace it. Any running functions can be directed to their old or new kernel-level counterparts until the patching process is finished.
### Kpatch ###
Red Hat came up with its own no-reboot kernel-patch mechanism, too. Also introduced earlier this year -- right after Suse's work in that vein, no less -- [Kpatch][5] works in roughly the same manner as Kgraft.
The main difference, [as outlined][6] by Josh Poimboeuf of Red Hat, is that Kpatch doesn't redirect calls to old kernel functions. Rather, it waits until all function calls have stopped, then swaps in the new kernel. Red Hat's engineers consider this approach safer, with less code to maintain, albeit at the cost of more latency during the patch process.
Like Kgraft, Kpatch has been submitted for consideration as a possible kernel inclusion and can be used with Linux kernels other than Red Hat's. The bad news is that Kpatch isn't yet considered production-ready by Red Hat. It's included as part of Red Hat Enterprise Linux 7, but only in the form of a technology preview.
### ...or Kgraft + Kpatch? ###
A fourth solution [proposed by Red Hat developer Seth Jennings][7] early in November 2014 is a mix of both the Kgraft and Kpatch approaches, using patches built for either one of those solutions. This new approach, Jennings explained, "consists of a live patching 'core' that provides an interface for other 'patch' kernel modules to register patches with the core." This way, the patching process -- specifically, how to deal with any running kernel functions -- can be handled in a more orderly fashion.
The sheer newness of these proposals means it'll be a while before any of them are officially part of the Linux kernel, although Suse's chosen to move fast and made it a part of its latest enterprise offering. Let's see if Red Hat and Canonical choose to follow suit in the short run as well.
--------------------------------------------------------------------------------
via: http://www.infoworld.com/article/2851028/linux/four-ways-linux-is-headed-for-no-downtime-kernel-patching.html
作者：[Serdar Yegulalp][a]
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) 原创翻译，[Linux中国](http://linux.cn/) 荣誉推出
[a]:http://www.infoworld.com/author/Serdar-Yegulalp/
[1]:http://www.infoworld.com/article/2622437/open-source-software/oracle-buys-ksplice-for-linux--zero-downtime--tech.html
[2]:http://www.infoworld.com/article/2610749/linux/suse-open-sources-live-updater-for-linux-kernel.html
[3]:https://lwn.net/Articles/596854/
[4]:http://www.infoworld.com/article/2838421/linux/suse-linux-enterprise-12-goes-light-on-docker-heavy-on-reliability.html
[5]:https://github.com/dynup/kpatch
[6]:https://lwn.net/Articles/597123/
[7]:http://lkml.iu.edu/hypermail/linux/kernel/1411.0/04020.html

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四招搞定Linux内核热补丁
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![Credit: Shutterstock](http://images.techhive.com/images/article/2014/10/patch_f-100526950-primary.idge.jpeg)
Credit: Shutterstock
多种技术在竞争成为实现inux内核热补丁的最优方案。
没人喜欢重启机器，尤其是涉及到一个内核问题的最新补丁程序。
为达到不重启的目的，目前有3个项目在朝这方面努力，将为大家提供对内核进行运行时打热补丁的机制，这样就可以做到完全不重启机器。
### Ksplice项目 ###
首先要介绍的项目是Ksplice，它是热补丁技术的创始者，并于2008年建立了与项目同名的公司。Ksplice在替换新内核时，不需要预先修改；只需要一个diff文件，将内核的修改点列全即可。Ksplice公司免费提供软件，但技术支持是需要收费的，目前能够支持大部分常用的Linux发行版本。
但在2011年[Oracle收购了这家公司][1]后，情况发生了变化。 这项功能被合入到Oracle的Linux发行版本中，且只对Oralcle的版本提供技术更新。 这就导致，其他内核hacker们开始寻找替代Ksplice的方法，以避免缴纳Oracle税。
### Kgraft项目 ###
2014年2月，Suse提供了一个很好的解决方案：[Kgraft][2]，该技术以GPLv2/GPLv3混合许可证发布，且Suse不会将其作为一个专有的实现。Kgraft被[提交][3]到Linux内核主线，很有可能被内核主线采用。目前Suse已经把此技术集成到[Suse Linux Enterprise Server 12][4]。
Kgraft和Ksplice在工作原理上很相似，都是使用一组diff文件来计算内核中需要修改的部分。但与Ksplice不同的是，Kgraft在做替换时，不需要完全停止内核。 在打补丁时，正在运行的函数可以先使用老版本中对应的部分，当补丁打完后就可以切换新的版本。
### Kpatch项目 ###
Red Hat也提出了他们的内核热补丁技术。同样是在今年年初 -- 与Suse在这方面的工作差不多 -- [Kpatch][5]的工作原理也和Kgraft相似。
主要的区别点在于，正如Red Hat的Josh Poimboeuf[总结][6]的那样，Kpatch不能将内核调用重定向到老版本。相反，它会等待所有函数调用都停止时，再切换到新内核。Red Hat的工程师认为这种方法更为安全，且更容易维护，缺点就是在打补丁的过程中会带来更大的延迟。
和Kgraft一样，Kpatch不仅仅能在Red Hat的发行版本上可以使用，同时也被提交到了内核主线，作为一个可能的候选。 坏消息是Red Hat还未将此技术集成到产品中。 它只是被合入到了Red Hat Enterprise Linux 7的技术预览版中。
### ...也许 Kgraft + Kpatch更合适? ###
Red Hat的工程师Seth Jennings在2014年11月初，提出了[第四种解决方案][7]。将Kgraft和Kpatch结合起来, 补丁包用这两种方式都可以。在新的方法中，Jennings提出，“热补丁核心为其他内核模块提供了热补丁的注册机制”， 通过这种方法，打补丁的过程 -- 更准确的说，如何处理运行时内核调用 --可以被更加有序的进行。
这项新建议也意味着两个方案都还需要更长的时间，才能被linux内核正式采纳。尽管Suse步子迈得更快，并把Kgraft应用到了最新的enterprise版本中。让我们也关注一下Red Hat和Linux官方近期的动态。
--------------------------------------------------------------------------------
via: http://www.infoworld.com/article/2851028/linux/four-ways-linux-is-headed-for-no-downtime-kernel-patching.html
作者：[Serdar Yegulalp][a]
译者：[coloka](https://github.com/coloka)
校对：[校对者ID](https://github.com/校对者ID)
本文由 [LCTT](https://github.com/LCTT/TranslateProject) 原创翻译，[Linux中国](http://linux.cn/) 荣誉推出
[a]:http://www.infoworld.com/author/Serdar-Yegulalp/
[1]:http://www.infoworld.com/article/2622437/open-source-software/oracle-buys-ksplice-for-linux--zero-downtime--tech.html
[2]:http://www.infoworld.com/article/2610749/linux/suse-open-sources-live-updater-for-linux-kernel.html
[3]:https://lwn.net/Articles/596854/
[4]:http://www.infoworld.com/article/2838421/linux/suse-linux-enterprise-12-goes-light-on-docker-heavy-on-reliability.html
[5]:https://github.com/dynup/kpatch
[6]:https://lwn.net/Articles/597123/
[7]:http://lkml.iu.edu/hypermail/linux/kernel/1411.0/04020.html