Click here to close now.




















Welcome!

Linux Containers Authors: Samuel Scott, Mike Kavis, Tim Hinds, Elizabeth White, Liz McMillan

Related Topics: Linux Containers

Linux Containers: Article

Kernel source merging 101

How to play Linus Torvalds and update the Linux kernel yourself

(LinuxWorld) -- If you're not familiar with the kernel patch and development process, here it is in a nutshell. People modify source files to fix bugs, add or remove features, or adapt to changes in the way the kernel handles certain tasks. They produce patch files by using a utility called diff. diff compares the old source file to the new one and produces a text file from the differences. You can then distribute this text file to others, who can use it to patch their source code with the utility called (what else?) patch.

Incidentally, the tradition for using patch to produce kernel patch files is to add the command line switches -urN, which tells diff to use the unified output format (which is what everyone on the kernel development team uses), recurse through directories, and keep track of new files that appear in one branch but not another. The full command would be diff -Nru.

Until recently, kernel developers submitted their patch files by including them within the body of an email message. Then they sent the message to one or more kernel maintainers and/or the kernel development mailing list. I'm not quite sure how the patch submission process will change now that Linus Torvalds and others are using the Bitkeeper Web-based source management system, but it looks like they'll still rely largely on the diff

Linus or one of the other kernel maintainers merge the various patches into the kernel source tree, make other changes, and then release a collection of patches in one large text file, which is compressed for faster downloads. If you want to apply the patches, you download the file and apply it to the correct version of the kernel source code.

I don't know how others do this, but I keep kernel versions in directories like /usr/src/linux-2.4.18-pre8 to identify the kernel version for that source tree. Then I download the latest patches to the /usr/src directory. For example, I downloaded the Michael Cohen patch file patch-2.4.18-pre8-mjc.bz2 and put it in /usr/src. If I wanted to apply the Michael Cohen patch as is, I would then change to the /usr/src/linux-2.4.18-pre8 directory and run the command:

# bzcat ../patch-2.4.18-pre8-mjc.bz2 | patch -p1 -E --dry-run

Don't type the pound sign (#) - it's the part of the prompt that usually tells you you're logged in as the root user.

The -p1 switch tells patch to ignore the first level of directories in the patch file. This can be important, because the maintainers all seem to use their own conventions for the root directory for the kernel source tree, and that directory name gets included in the patch file. For example, if someone keeps the old kernel source in /usr/src/oldkernel and the modified source in /usr/src/newkernel, then the patch file will contain the two directory names oldkernel and newkernel. If you use the switch -p0, patch will expect to find the newkernel directory name on your system as part of the full path name (for example, newkernel/drivers/ide/ide-dma.c). If, like me, you named the top directory of the kernel tree something like linux-2.4.18-pre8, patch will fail. The -p1 switch tells it to ignore that top level and go straight to drivers/ide/ide-dma.c.

The -E switch tells patch to go ahead and delete any files that shouldn't exist after the patch. These are generally files that the maintainer moved to another location or deleted because they were no longer needed.

The --dry-run portion of the command tells patch to pretend to apply the patches without actually changing anything. I do this out of habit because it prevents me from making stupid mistakes like changing to the wrong kernel tree before applying the patch. If the patch process produces many error messages, I know I've probably done something wrong. If it looks like everything patched ok, then I run the command again, only for real. That "for real" command is just the same command without the --dry-run:

# bzcat ../patch-2.4.18-pre8-mjc.bz2 | patch -p1 -E

The challenge

The 2.5 branch is still in too transitory a state to tackle with any confidence, so I started with linux-2.4.18-pre8. I figured I'd better take it slow. I've led a rather sedentary lifestyle when it comes to examining the kernel source, so I didn't want to break into a sprint on the first go and risk a heart attack. In other words, I wanted to merge only a handful of changes, not 50 at a shot the way Linus and others do.

I noticed that Michael Cohen had released a large patch against 2.4.18-pre8 that included many interesting features. It merges the code to handle hardware health sensors (so you can view things like the fan speed on your motherboard). It also adds code to make the kernel preemptive. It has other performance enhancing modifications to the kernel and includes several fixes that weren't in the 2.4 branch at the time Cohen posted his patch, such as fixes to the Reiserfs file system.

Thibaut Laurent posted on the kernel development mailing list that there was a minor problem with the file timer.c in Cohen's patch. Thomas Hood pointed out that Cohen's updates to the plug-and-play BIOS code were out of date. Paul P Komkoff Jr posted a set of patches that adds new capabilities for IP net filtering. Finally, I like to add a line to drivers/acpi/hardware/hwsleep.c to force the kernel to shut off the machine. This is not a patch for general use. I only include it because the funky ACPI BIOS tables in ASUS motherboards keep me from being able to shut off my system with the halt command.

I figured it would be a good lesson in patch management if I could apply all of the above fixes and additions to Michael Cohen's patch and produce my own patch from the result.

I downloaded the latest PnP BIOS code for 2.4.18-pre8 by Thomas Hood and began the grunt work of replacing the PnP portions of Cohen's patch with the latest code. The job was tedious, but it was easy because both Cohen's patch and Hood's patch are applied against the same kernel version (2.4.18-pre8). So all I really had to do was find all the sections of Cohen's patch that corresponded to Hood's and make the swap. It was even easier to apply the net filter additions, timer.c fix, and my shutdown kludge.

The result is patch-2.4.18-pre8-np.gz, which you can find at the download section of www.varlinux.org. I'm using that kernel right now, but things are moving so quickly it will probably be well out of date by the time you read this. There's already a linux-2.4.18-pre9 available as I write this and pre9 includes some of the same fixes you'll find in my patch. (It lacks all the added features, however, such as the net filter code, preemptive kernel, etc.)

What's the big deal about merging patches? It was only easy for me because I chose to work with a stable branch of the kernel and patches that were supposed to be applied against the same kernel version.

I tackled the 2.5.4-pre3 kernel source just to see what the differences would be like if I used an unstable branch. I didn't even have to look for patches to apply. It wouldn't compile on my system as is. It broke on ide-dma.c, ide-scsi.c, sg.c, and in other places. I couldn't find any fixes for these problems so I started scanning the code to see if I could fix it myself.

That's when I realized what this kernel development process really needs -- an editor with an integrated cross-reference and source code analysis system.

Perhaps people like Linus Torvalds doesn't need such a program because he knows where every instance of a variable appears in the source tree (I doubt it, since so many of his patches lately leave many files with legacy variables and structures unpatched to work with updates to other parts of the kernel source tree). Alternatively, perhaps he and others have some neat command-line utilities that do the job. I'm not an emacs user, so for all I know emacs has these capabilities (I have no idea if Linus uses emacs anyway).

However, I would want something more powerful than a multi-file editor for a job like this. So I searched Freshmeat and found a few snazzy products that analyze source code, cross reference the source, and let you perform recursive updates in ways that help prevent disaster. Some run on Linux, so I plan to play with one or two.

I'll get back to you on them when I've had time to learn how well they work. In the meantime, unless you're a kernel guru, stay away from the 2.5 branch. Stick to the easy stuff, like I do. Your heart will thank you for it.

More Stories By Nicholas Petreley

Nicholas Petreley is a computer consultant and author in Asheville, NC.

Comments (0)

Share your thoughts on this story.

Add your comment
You must be signed in to add a comment. Sign-in | Register

In accordance with our Comment Policy, we encourage comments that are on topic, relevant and to-the-point. We will remove comments that include profanity, personal attacks, racial slurs, threats of violence, or other inappropriate material that violates our Terms and Conditions, and will block users who make repeated violations. We ask all readers to expect diversity of opinion and to treat one another with dignity and respect.


@ThingsExpo Stories
While many app developers are comfortable building apps for the smartphone, there is a whole new world out there. In his session at @ThingsExpo, Narayan Sainaney, Co-founder and CTO of Mojio, will discuss how the business case for connected car apps is growing and, with open platform companies having already done the heavy lifting, there really is no barrier to entry.
As more intelligent IoT applications shift into gear, they’re merging into the ever-increasing traffic flow of the Internet. It won’t be long before we experience bottlenecks, as IoT traffic peaks during rush hours. Organizations that are unprepared will find themselves by the side of the road unable to cross back into the fast lane. As billions of new devices begin to communicate and exchange data – will your infrastructure be scalable enough to handle this new interconnected world?
SYS-CON Events announced today that Micron Technology, Inc., a global leader in advanced semiconductor systems, will exhibit at the 17th International Cloud Expo®, which will take place on November 3–5, 2015, at the Santa Clara Convention Center in Santa Clara, CA. Micron’s broad portfolio of high-performance memory technologies – including DRAM, NAND and NOR Flash – is the basis for solid state drives, modules, multichip packages and other system solutions. Backed by more than 35 years of technology leadership, Micron's memory solutions enable the world's most innovative computing, consumer,...
SYS-CON Events announced today that Pythian, a global IT services company specializing in helping companies leverage disruptive technologies to optimize revenue-generating systems, has been named “Bronze Sponsor” of SYS-CON's 17th Cloud Expo, which will take place on November 3–5, 2015, at the Santa Clara Convention Center in Santa Clara, CA. Founded in 1997, Pythian is a global IT services company that helps companies compete by adopting disruptive technologies such as cloud, Big Data, advanced analytics, and DevOps to advance innovation and increase agility. Specializing in designing, imple...
SYS-CON Events announced today that HPM Networks will exhibit at the 17th International Cloud Expo®, which will take place on November 3–5, 2015, at the Santa Clara Convention Center in Santa Clara, CA. For 20 years, HPM Networks has been integrating technology solutions that solve complex business challenges. HPM Networks has designed solutions for both SMB and enterprise customers throughout the San Francisco Bay Area.
Consumer IoT applications provide data about the user that just doesn’t exist in traditional PC or mobile web applications. This rich data, or “context,” enables the highly personalized consumer experiences that characterize many consumer IoT apps. This same data is also providing brands with unprecedented insight into how their connected products are being used, while, at the same time, powering highly targeted engagement and marketing opportunities. In his session at @ThingsExpo, Nathan Treloar, President and COO of Bebaio, will explore examples of brands transforming their businesses by t...
Through WebRTC, audio and video communications are being embedded more easily than ever into applications, helping carriers, enterprises and independent software vendors deliver greater functionality to their end users. With today’s business world increasingly focused on outcomes, users’ growing calls for ease of use, and businesses craving smarter, tighter integration, what’s the next step in delivering a richer, more immersive experience? That richer, more fully integrated experience comes about through a Communications Platform as a Service which allows for messaging, screen sharing, video...
With the proliferation of connected devices underpinning new Internet of Things systems, Brandon Schulz, Director of Luxoft IoT – Retail, will be looking at the transformation of the retail customer experience in brick and mortar stores in his session at @ThingsExpo. Questions he will address include: Will beacons drop to the wayside like QR codes, or be a proximity-based profit driver? How will the customer experience change in stores of all types when everything can be instrumented and analyzed? As an area of investment, how might a retail company move towards an innovation methodolo...
The Internet of Things (IoT) is about the digitization of physical assets including sensors, devices, machines, gateways, and the network. It creates possibilities for significant value creation and new revenue generating business models via data democratization and ubiquitous analytics across IoT networks. The explosion of data in all forms in IoT requires a more robust and broader lens in order to enable smarter timely actions and better outcomes. Business operations become the key driver of IoT applications and projects. Business operations, IT, and data scientists need advanced analytics t...
A producer of the first smartphones and tablets, presenter Lee M. Williams will talk about how he is now applying his experience in mobile technology to the design and development of the next generation of Environmental and Sustainability Services at ETwater. In his session at @ThingsExpo, Lee Williams, COO of ETwater, will talk about how he is now applying his experience in mobile technology to the design and development of the next generation of Environmental and Sustainability Services at ETwater.
WebRTC has had a real tough three or four years, and so have those working with it. Only a few short years ago, the development world were excited about WebRTC and proclaiming how awesome it was. You might have played with the technology a couple of years ago, only to find the extra infrastructure requirements were painful to implement and poorly documented. This probably left a bitter taste in your mouth, especially when things went wrong.
SYS-CON Events announced today that IceWarp will exhibit at the 17th International Cloud Expo®, which will take place on November 3–5, 2015, at the Santa Clara Convention Center in Santa Clara, CA. IceWarp, the leader of cloud and on-premise messaging, delivers secured email, chat, documents, conferencing and collaboration to today's mobile workforce, all in one unified interface
As more and more data is generated from a variety of connected devices, the need to get insights from this data and predict future behavior and trends is increasingly essential for businesses. Real-time stream processing is needed in a variety of different industries such as Manufacturing, Oil and Gas, Automobile, Finance, Online Retail, Smart Grids, and Healthcare. Azure Stream Analytics is a fully managed distributed stream computation service that provides low latency, scalable processing of streaming data in the cloud with an enterprise grade SLA. It features built-in integration with Azur...
Too often with compelling new technologies market participants become overly enamored with that attractiveness of the technology and neglect underlying business drivers. This tendency, what some call the “newest shiny object syndrome,” is understandable given that virtually all of us are heavily engaged in technology. But it is also mistaken. Without concrete business cases driving its deployment, IoT, like many other technologies before it, will fade into obscurity.
Akana has announced the availability of the new Akana Healthcare Solution. The API-driven solution helps healthcare organizations accelerate their transition to being secure, digitally interoperable businesses. It leverages the Health Level Seven International Fast Healthcare Interoperability Resources (HL7 FHIR) standard to enable broader business use of medical data. Akana developed the Healthcare Solution in response to healthcare businesses that want to increase electronic, multi-device access to health records while reducing operating costs and complying with government regulations.
For IoT to grow as quickly as analyst firms’ project, a lot is going to fall on developers to quickly bring applications to market. But the lack of a standard development platform threatens to slow growth and make application development more time consuming and costly, much like we’ve seen in the mobile space. In his session at @ThingsExpo, Mike Weiner, Product Manager of the Omega DevCloud with KORE Telematics Inc., discussed the evolving requirements for developers as IoT matures and conducted a live demonstration of how quickly application development can happen when the need to comply wit...
The Internet of Everything (IoE) brings together people, process, data and things to make networked connections more relevant and valuable than ever before – transforming information into knowledge and knowledge into wisdom. IoE creates new capabilities, richer experiences, and unprecedented opportunities to improve business and government operations, decision making and mission support capabilities.
Explosive growth in connected devices. Enormous amounts of data for collection and analysis. Critical use of data for split-second decision making and actionable information. All three are factors in making the Internet of Things a reality. Yet, any one factor would have an IT organization pondering its infrastructure strategy. How should your organization enhance its IT framework to enable an Internet of Things implementation? In his session at @ThingsExpo, James Kirkland, Red Hat's Chief Architect for the Internet of Things and Intelligent Systems, described how to revolutionize your archit...
MuleSoft has announced the findings of its 2015 Connectivity Benchmark Report on the adoption and business impact of APIs. The findings suggest traditional businesses are quickly evolving into "composable enterprises" built out of hundreds of connected software services, applications and devices. Most are embracing the Internet of Things (IoT) and microservices technologies like Docker. A majority are integrating wearables, like smart watches, and more than half plan to generate revenue with APIs within the next year.
Growth hacking is common for startups to make unheard-of progress in building their business. Career Hacks can help Geek Girls and those who support them (yes, that's you too, Dad!) to excel in this typically male-dominated world. Get ready to learn the facts: Is there a bias against women in the tech / developer communities? Why are women 50% of the workforce, but hold only 24% of the STEM or IT positions? Some beginnings of what to do about it! In her Opening Keynote at 16th Cloud Expo, Sandy Carter, IBM General Manager Cloud Ecosystem and Developers, and a Social Business Evangelist, d...