# kernel-wedge, an industrial strength kernel splitting tool kernel-wedge is used to generate kernel module udebs for the debian installer. kernel-wedge is now used as part of the build process of the linux and kfreebsd-* source packages, but can also be used separately. ## Configuration directory layout The default-configuration directory contains the following files: modules/*
package-list The environment variable `$KW_DEFCONFIG_DIR` must be set, naming the default-configuration directory. Each configuration directory contains the following files: kernel-versions
modules/*arch*/\*
exclude-packages (optional)
package-list The environment variable `$KW_CONFIG_DIR` may be set, naming the configuration directory; otherwise the default value is "`.`". Typically there is a separate configuration directory per architecture, but this is not required. The configuration directory may be the same as the default-configuration directory. ## Use in a kernel source package ### Configuration files The kernel-versions file lists the kernel flavours to produce packages for. There are 6 whitespace separated fields per line, and it looks something like this: # arch version flavour installedname suffix build-depends i386 - 686 - - - i386 - 686-pae - - - The arch column must be set to the target Debian architecture and the flavour to the kernel flavour name that appears in the package and file names. The version, installedname and build-depends columns must all be set to "`-`" in this case. The suffix column is either `y`, `-` or `-`*suffix*; if it is `y` then the kernel image inside the udeb will include the version and flavour in its name, if it is `-`*suffix* then it will include this. (So will the System.map). The udebs are named with the version of the kernel in their package name, since that can be useful during kernel transitions. The string `-di` is appended to prevent any posible collisions in names with real debs. The package-list and (optional) exclude-packages configuration files are used by `gen-control`, as explained in its online help. Finally, you need a modules/*arch* directory, or directories. These are used to list the modules that go in a package. For example, for i386, we want to have some nic drivers, so we create a modules/i386/nic-modules listing them: # My short list of nic modules. 8139too e100 natsemi ne2k-pci tulip winbond-840 3c59x But for Linux, drivers are organised into subdirectories by type, and we can instead include (most) Ethernet drivers using a wildcard: drivers/net/ethernet/** Suppose we want a different set of modules in the 686 flavour kernel. Then create a `modules/`*arch*-*flavour*`/nic-modules` instead, and it will be used by preference. One udeb will be created for each modules list file, containing the listed modules. The names of the files should match the names of the various modules listed in the package-list file in the default-configuration directory. You will also want a special modules list file for the kernel-image udeb. If you need to include no modules with your kernel, it can be an empty file. but you should have a modules/*arch*/kernel-image. `kernel-wedge` will copy the listed modules into each package. If a listed module does not exist, it will fail by default. Sometimes you might want to make a module be included but it's not fatal for it not to be available. To indicate this, follow the module with a space and a "`?`". Module list files can also include other module lists by reference. This works similar to cpp includes, and can be used to include module lists distributed as part of kernel-wedge, or others. For example: # kernel-wedge's standard set of cdrom modules #include # my own list #include "../../includes/cdrom-modules" The `` syntax includes a file from the modules subdirectory of the default-configuration directory. A final capability of the module list files is the ability to include a module list and then override parts of it. Follow a module name with " `-`" to remove it from the list if it was previously listed, as by an include: # kernel-wedge's standard set of cdrom modules #include # but not this one sr_mod - ### Debian directory To add the udeb packages to the control file, run for each architecture: `kernel-wedge gen-control `*version*` >> debian/control` Where *version* is the kernel ABI/version that appears in package names. In case you use the same kernel flavour name on multiple architectures, you will need to merge the output from multiple invocations of `kernel-wedge gen-control`. ## Use in a separate source package ### Configuration files The kernel-versions file looks something like this: # arch version flavour installedname suffix build-depends i386 2.4.25-1 386 2.4.25-1-386 - kernel-image-2.4.25-1-386, kernel-pcmcia-modules-2.4.25-1-386 i386 2.4.24 speakup 2.4.24-speakup - kernel-image-2.4.24-speakup In this case we are building two different flavours of i386 kernels. We could just as easily be building kernels for different architectures. The arch, flavour and suffix columns are set as above. The version is the kernel version, or can be "`-`", in which case a version must be specified when running the `gen-control` and `install-files` commands. The installedname column gives the directory/filename that the kernel and modules are installed using in the kernel `.deb`. If it is "`-`", it's generated from the version and flavor. The build-depends are the package that is split up by kernel-wedge. The other configuration files are set in the same way as normal. ### Debian directory Your source package will be very simple, looking something like this: debian/copyright
debian/changelog
debian/rules
debian/control.stub Let's get the easy files out of the way. The changelog is a changelog, like any other, as is the copyright. The debian/rules can be something as simple as this: #!/usr/bin/make -f include /usr/share/kernel-wedge/generic-rules Or you can use the `kernel-wedge` command directly in your own rules file. Run it for some semblance of usage help. `debian/control.stub` is the top of a control file. Something like this: Source: linux-kernel-di-i386 Section: debian-installer Priority: optional Maintainer: Debian Install System Team Build-Depends: kernel-wedge The rest of the control file will be generated for you. Once you have your source package set up, run: kernel-wedge gen-control > debian/control You only need to do this once. Then build it like any other package. Note that you will have to have the kernels listed as build dependencies installed normally; but see "`kernel-wedge help build-all`" for an alternative. ## Misc other info The "`kernel-wedge copy-modules`" command does the actual copying of modules to the temp dirs that are used to build the package. It is complicated by the need to make sure that all of a module's dependencies are included in its package, or in a package on which it depends. If necessary, extra modules will be added to a package to make sure the dependencies are satisfied. The dependency information from modules.dep is compared with the output of the "`kernel-wedge gen-deps`" command, which extracts dependency information from package-lists, and formats it in a form used by tsort. If any additional modules are needed to meet dependencies of modules in the udebs, they will automatically be added. Since that might result in modules being copied to multiple udebs, the "`kernel-wedge find-dups`" command is used to scan for duplicates of modules. When you have duplicates, you need to find (or make) a package that both packages depend on, and move the duplicate modules to it. Alternatively, as a quick hack you can just touch a file named ignore-dups in the root of your package and duplicate modules will stop being a fatal error. `SOURCEDIR` can be set to a directory containing a tree of kernel modules and kernel image, and it will be used instead of the usual tree. That directory will need to have a modules.dep file already generated for this to work though -- but the modules.dep can even be copied from another system and it'll work. This can be useful if you cannot install the required kernel-image package, or are cross-compiling.