The Linux kernel developers realize that users do not wish to download the entire source code to the kernel for every update. That would be a waste of bandwidth and time. Because of this, they offer a patch that can upgrade an older kernel release to a newer one.[*]
[*] It is called patch because the program patch takes the file and applies it to the original tree, creating the new tree. The patch file contains a representation of the changes that are necessary to reconstruct the new files, based on the old ones. Patch files are readable, and contain a list of the lines that are to be removed and the lines that are to be added, with some context within the file showing where the changes should be made.
On the main kernel.org web site, you will remember that it contained a list of the current kernel versions that are available for download, as shown in Figure 6-1.
Figure 6-1. The main kernel.org web site
Previously, you used the link pointed to you by the F to download the entire source code for the kernel. However, if you click on the name of the kernel release, it will download a patch file instead, as shown in Figure 6-2.
Figure 6-2. Downloading a patch from kernel.org
This is what we want to do when upgrading. But we need to figure out what patch to download.
6.1.1. Which Patch Applies to Which Release?
A kernel patch file will upgrade the source code from only one specific release to another specific release. Here is how the different patch files can be applied:
Stable kernel patches apply to the base kernel version. This means that the 2.6.17.10 patch will only apply to the 2.6.17 kernel release. The 2.6.17.10 kernel patch will not apply to the 2.6.17.9 kernel or any other release.
Base kernel release patches only apply to the previous base kernel version. This means that the 2.6.18 patch will only apply to the 2.6.17 kernel release. It will not apply to the last 2.6.17.y kernel release, or any other release.
Incremental patches upgrade from a specific release to the next release. This allows developers to not have to downgrade their kernel and then upgrade it, just to switch from the latest stable release to the next stable release (remember that the stable release patches are only against the base kernel, not the previous stable release). Whenever possible, it is recommended that you use the incremental patches to make your life easier.
6.1.2. Finding the Patch
As we want to go from the 2.6.17.9 kernel release, to the 2.6.17.11 release, we will need to download two different patches. We will need a patch from the 2.6.17.9 release to the 2.6.17.10 release, and then from the 2.6.17.10 release to the 2.6.17.11 release.[*]
[*] If you need to upgrade more than two versions, it is recommended as a way to save steps, to go backward and then upgrade forward. In this case, we could go backward from 2.6.17.9 to 2.6.17 and then forward from 2.6.17 to 2.6.17.11.
The stable and base kernel patches are located in the same directory structure as the main source trees. All incremental patches can be found one level lower, in the incr subdirectory. So, to find the patch that goes from 2.6.17.9 to 2.6.17.10, we look in the /pub/linux/kernel/v2.6/incr directory to find the files we need:[]
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