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docs: Update kernel documentation

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Signed-off-by: Rolf Neugebauer <rolf.neugebauer@docker.com>
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Rolf Neugebauer 2017-04-26 17:54:30 +01:00
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50
docs/kernels.md
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# Working with Linux kernel patches for LinuxKit
# LinuxKit kernels
Currently, LinuxKit supports a number of kernels. These kernels are
typically based on the latest stable releases and are updated
frequently to include bug and security fixes. For some kernels we do
carry some additional patches, which are mostly back-ported fixes from
newer kernels. The full kernel source with patches is on
[github](https://github.com/linuxkit/linux).
The kernel images are stored on Hub under
[linuxkit/kernel](https://hub.docker.com/r/linuxkit/kernel/). Each
kernel image is tagged with the full kernel version plus the hash of
the files it was created from (git tree hash of the `./kernel`
directory). For convenience, the latest kernel of each stable series
is also available under the a shorthand tag,
e.g. `linuxkit/kernel:4.9.x` for the latest `4.9` kernel.
## Working with Linux kernel patches for LinuxKit
We may apply patches to the Linux kernel used in LinuxKit, primarily to
cherry-pick some upstream patches or to add some additional
@ -12,10 +30,13 @@ Patches are located in `kernel/patches-<kernel version>` and should follow these
which they are applied.
- If patches are cherry-picked, they *must* be cherry-picked with `-x`
to contain the original commit ID.
- If patches are from a different git tree (other than the stable
tree), or from a mailing list posting they should contain an
`Origin:` line with a link to the source.
This document outlines the recommended procedure to handle
patches. The general process is to apply them to a branch of the
[Linux stable tree](https://kernel.googlesource.com/pub/scm/linux/kernel/git/stable/linux-stable/)
[Linux stable tree](https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux-stable.git/)
and then export them with `git format-patch`.
If you want to add or remove patches currently used, please also ping
@ -24,12 +45,13 @@ ensure that patches are carried forward if we update the kernel in the
future.
# Preparation
### Preparation
Patches are applied to point releases of the linux stable tree. You need an up-to-date copy of that tree:
```sh
git clone git://git.kernel.org/pub/scm/linux/kernel/git/stable/linux-stable.git
```
Add it as a remote to a clone of the [LinuxKit clone](https://github.com/linuxkit/linux).
We use the following variables:
- `KITSRC`: Base directory of LinuxKit repository
@ -42,7 +64,7 @@ LINUXSRC=~/src/linuxkit/linux
to refer to the location of the LinuxKit and Linux kernel trees.
# Updating the patches to a new kernel version
### Updating the patches to a new kernel version
There are different ways to do this, but we recommend applying the patches to the current version and then rebase to the new version. We define the following variables to refer to the current base tag and the new tag you want to rebase the patches to:
```sh
@ -53,24 +75,24 @@ NEWTAG=v4.9.15
If you don't already have a branch, it's best to import the current patch set and then rebase:
```sh
cd $LINUXSRC
git checkout -b ${NEWTAG}-moby ${CURTAG}
git checkout -b ${NEWTAG}-linuxkit ${CURTAG}
git am ${KITSRC}/kernel/patches/*.patch
git rebase ${NEWTAG}-moby ${NEWTAG}
git rebase ${NEWTAG}-linuxkit ${NEWTAG}
```
The `git am` should not have any conflicts and if the rebase has conflicts resolve them, then `git add <files>` and `git rebase --continue`.
If you already have linux tree with a `${CURTAG}-moby` branch, you can rebase by creating a new branch from the current branch and then rebase:
If you already have linux tree with a `${CURTAG}-linuxkit` branch, you can rebase by creating a new branch from the current branch and then rebase:
```sh
cd $LINUXSRC
git checkout ${CURTAG}-moby
git branch ${NEWTAG}-moby ${CURTAG}-moby
git rebase --onto ${NEWTAG} ${NEWTAG} ${NEWTAG}-moby
git checkout ${CURTAG}-linuxkit
git branch ${NEWTAG}-linuxkit ${CURTAG}-linuxkit
git rebase --onto ${NEWTAG} ${NEWTAG} ${NEWTAG}-linuxkit
```
Again, resolve any conflicts as described above.
# Adding/Removing patches
### Adding/Removing patches
If you want to add or remove patches make sure you have an up-to-date branch with the currently applied patches (see above). Then either any normal means (`git cherry-pick -x`, `git am`, or `git commit`, etc) to add new patches. For cherry-picked patches also please add a `Origin:` line after the DCO lines with a reference the git tree the patch was cherry-picked from.
@ -82,13 +104,13 @@ DCO lines, e.g.:
Origin: https://patchwork.ozlabs.org/patch/622404/
```
# Export patches to LinuxKit
### Export patches to LinuxKit
To export patches to LinuxKit, you should use `git format-patch` from the Linux tree, e.g., something along these lines:
```sh
cd $LINUXSRC
rm $KITSRC/kernel/patches-4.9/*
git format-patch -o $KITSRC/kernel/patches-4.9 v4.9.15..HEAD
rm $KITSRC/kernel/patches-4.9.x/*
git format-patch -o $KITSRC/kernel/patches-4.9.x v4.9.15..HEAD
```
The, create a PR for LinuxKit.

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kernel/README.md
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Linux kernel builds, based on mostly-vanilla upstream Linux kernels.
See [../docs/kernel-patches.md](../docs/kernel-patches.md) for how the local patches in `patches-*`
are maintained.
The build is mostly silent. A local build can be run via `make`. To view
the output use `docker log -f <containerid>`. The build creates multiple
containers, so multiple invocations may be necessary. To view the full build
output one may also invoke `docker build .` and then copy the build artefacts
from the image afterwards.
See [../docs/kernel-patches.md](../docs/kernels.md) for more
information on kernel builds.
To build with various debug options enabled, build the kernel with
`make DEBUG=1`. The options enabled are listed in `kernel_config.debug`.