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:penguin: Kernels on Scaleway

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# Kernel Config
[![Build Status](https://travis-ci.org/scaleway/kernel-tools.svg?branch=master)](https://travis-ci.org/scaleway/kernel-tools)

https://community.cloud.online.net/t/official-linux-kernel-new-modules-optimizations-hacks/226

The kernel is built with the official mainline kernel, here are the .config files used.

The list of Scaleway's bootscripts is available at http://devhub.scaleway.com/#/bootscripts.

## Modifications

We added kernel module to simulate some virtualization features:
- serial console activation
- remote soft reset trigger

---

## How to build a custom kernel module

You'll need the usual toolchain for kernel compilation, which on Ubuntu is generally fulfilled by `apt-get install build-essential libssl-dev`. Then, the following script can be run.

```bash
# Determine versions
arch="$(uname -m)"
release="$(uname -r)"
upstream="${release%%-*}"
local="${release#*-}"

# Get kernel sources
mkdir -p /usr/src
wget -O "/usr/src/linux-${upstream}.tar.xz" "https://cdn.kernel.org/pub/linux/kernel/v4.x/linux-${upstream}.tar.xz"
tar xf "/usr/src/linux-${upstream}.tar.xz" -C /usr/src/
ln -fns "/usr/src/linux-${upstream}" /usr/src/linux
ln -fns "/usr/src/linux-${upstream}" "/lib/modules/${release}/build"

# Prepare kernel
zcat /proc/config.gz > /usr/src/linux/.config
printf 'CONFIG_LOCALVERSION="%s"\nCONFIG_CROSS_COMPILE=""\n' "${local:+-$local}" >> /usr/src/linux/.config
wget -O /usr/src/linux/Module.symvers "http://mirror.scaleway.com/kernel/${arch}/${release}/Module.symvers"
apt-get install -y libssl-dev # adapt to your package manager
make -C /usr/src/linux prepare modules_prepare
```

Then you can make your module as usual by configuring `KDIR=/lib/modules/$(uname -r)/build/`

Alternatively, you can now build a DKMS-based kernel module, for instance: `apt-get install zfsutils-linux`

## Kernels

Name              | Maintainer      | Sources | Target | Links
------------------|-----------------|---------|--------|-------
3.2.34            | Marvell         | Closed  | C1     | n/a
3.18.20           | Linux community | Open    | C1     | [Sources](https://git.kernel.org/cgit/linux/kernel/git/stable/linux-stable.git/tree/?id=v3.18.20)
3.19.8            | Linux community | Open    | C1     | [Sources](https://git.kernel.org/cgit/linux/kernel/git/stable/linux-stable.git/tree/?id=v3.19.8)
4.1.6             | Linux community | Open    | C1     | [Sources](https://git.kernel.org/cgit/linux/kernel/git/stable/linux-stable.git/tree/?id=v4.1.6)
4.2               | Linux community | Open    | C1     | [Sources](https://git.kernel.org/cgit/linux/kernel/git/stable/linux-stable.git/tree/?id=v4.2)

---

## Build a custom kernel using Docker

Run a `make menuconfig` for `3-18-std/.config`

make menuconfig KERNEL=3.18-std

Build a kernel with `3.17-std/.config` file

make build KERNEL=3.17-std

## Advanced options

Create a new `3.10-new/.config` file from scratch for kernel `3.10`

make create defconfig KERNEL=3.10-new

Make oldconfig a `3.18-std` kernel

make oldconfig KERNEL=3.18-std

Run a shell in the container for easy debugging and run custom commands

make shell KERNEL=3.17-std

## Test a kernel with QEMU

You should use a config file made for `versatile`.

Build a `3.18` kernel for `versatile`:

make build KERNEL=3.18-defconfig_versatile

Run the kernel in qemu

make qemu KERNEL=3.18-defconfig_versatile

## How to upgrade a kernel

**An example with 4.0.8-docker**

You should move the directory

git mv 4.0.8-docker 4.0.9-docker

Run a `make oldconfig` with the newest version

make oldconfig KERNEL=4.0.9-docker

---

## Build a custom kernel from scratch (without Docker)

### Prerequisites:

- An arm(hf) compiler:
  - a cross-compiler on non-armhf host, ie `gcc-arm-linux-gnueabihf`
  - a standard compiler from an armhf host (you can build a kernel from your C1)
- Theses packages: git, wget, make

### Steps:

- Configure environment
  ```bash
export VERSION=3.17
export ARCH=arm
export ARTIFACTS=artifacts
```

- Download archive via web
  ```bash
wget https://kernel.org/pub/linux/kernel/v3.x/linux-$VERSION.tar.xz && tar xf linux-$VERSION.tar.xz
  ```
  or via git
  ```bash
git clone -b v$VERSION --single-branch git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git linux-$VERSION
```

- Generate a base `.config` file by building it
  ```
make ARCH=arm mvebu_v7_defconfig
```
  or by fetching our one
  ```
wget -O .config https://raw.githubusercontent.com/scaleway/kernel-tools/master/$VERSION/.config
```

- Tune the .config
  ```bash
make ARCH=arm menuconfig
# ... configure using console interface
```

- Building kernel and modules
  ```bash
make -j $(echo `nproc` ' * 2' | bc) uImage modules LOADADDR=0x8000
```

- Export the artifacts (kernel, header, modules) to `$ARTIFACTS` directory
  ```bash
mkdir -p $ARTIFACTS
cp arch/arm/boot/uImage $ARTIFACTS/
cp System.map $ARTIFACTS/
cp .config $ARTIFACTS/
make headers_install INSTALL_HDR_PATH=$ARTIFACTS/ > /dev/null
find $ARTIFACTS/include -name ".install" -or -name "..install.cmd" -delete
make modules_install INSTALL_MOD_PATH=$ARTIFACTS/ > /dev/null
rm -rf $ARTIFACTS/modules && \
   mv $ARTIFACTS/lib/modules $ARTIFACTS && \
   rmdir $ARTIFACTS/lib && \
   rm $ARTIFACTS/modules/*/source $ARTIFACTS/modules/*/build
```

### Minimal configuration for C1 servers

```gherkin
- Networking support
  - Networking options
    - 802.1Q/802.1ad VLAN Support -> **YES**
    - Packet socket -> **YES**
    - Unix domain sockets -> **YES**
- Device Drivers
  - Network device support
    - PHY Device support and infrastructure
      - Driver for MDIO Bus/PHY emulation with fixed speed/link PHYs -> **YES**
  - Block devices
    - Network block device support -> **YES**
- Kernel hacking
  - Kernel low-level debugging functions -> **YES**
  - Early prink -> **YES**
- File systems
  - The Extended 4 (ext4) filesystem -> **YES**
```

### How to bump multiple kernels at once

```bash
# It's an example to bump the kernels from 4.5.7 to 4.6.4
git mv x86_64/4.{5.7,6.4}-std
git mv x86_64/4.{5.7,6.4}-docker
git mv x86_64/4.{5.7,6.4}-apparmor
git mv x86_64/4.{5.7,6.4}-coreos
git mv x86_64/4.{5.7,6.4}-fedora
git mv x86_64/4.{5.7,6.4}-rancher
git mv armv7l/4.{5.7,6.4}-std
git mv armv7l/4.{5.7,6.4}-apparmor
git mv armv7l/4.{5.7,6.4}-debug
git mv armv7l/4.{5.7,6.4}-docker
git mv armv7l/4.{5.7,6.4}-fedora
for kernel in `find x86_64 -name "4.6.4-*"`; do make oldconfig KERNEL=$kernel; done
for kernel in `find armv7l -name "4.6.4-*"`; do make oldconfig KERNEL=$kernel; done
```

### How to bump a kernel

```bash
git mv x86_64/4.{5.7,6.4}-std
make oldconfig KERNEL=x86_64/4.6.4-std
```

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