In Buildroot, the kernel is built and installed *before* the root
filesystems are built. This allows the root filesystem to correctly
contain the kernel modules that have been installed.
However, in the initramfs case, the root filesystem is part of the
kernel. Therefore, the kernel should be built *after* the root
filesystem (which, in the initramfs case simply builds a text file
listing all files/directories/devices/symlinks that should be part of
the initramfs). However, this isn't possible as the initramfs text
file would lack all kernel modules.
So, the solution choosen here is to keep the normal order: kernel is
built before the root filesystem is generated, and to add a little
quirk to retrigger a kernel compilation after the root filesystem
generation.
To do so, we add a ROOTFS_$(FSTYPE)_POST_TARGETS variable to the
fs/common.mk infrastructure. This allows individual filesystems to set
a target name that we should depend on *after* generating the root
filesystem itself (contrary to normal ROOTFS_$(FSTYPE)_DEPENDENCIES,
on which we depend *before* generating the root filesystem).
The initramfs code in fs/initramfs/initramfs.mk uses this to add a
dependency on 'linux26-rebuild-with-initramfs'.
In linux/linux.mk, we do various things :
* If BR2_TARGET_ROOTFS_INITRAMFS is enabled (i.e if initramfs is
enabled as a root filesystem type), then we create an empty
rootfs.initramfs file (remember that at this point, the root
filesystem hasn't been generated) and we adjust the kernel
configuration to include an initramfs. Of course, in the initial
kernel build, this initramfs will be empty.
* In the linux26-rebuild-with-initramfs target, we retrigger a
compilation of the kernel image, after removing the initramfs in
the kernel sources to make sure it gets properly rebuilt (we've
experienced cases were modifying the rootfs.initramfs file wouldn't
retrigger the generation of the initramfs at the kernel level).
This is fairly quirky, but initramfs really is a special case, so in
one way or another, we need a little quirk to solve its specialness.
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
These targets allow the user to customize the configuration of the
Linux kernel. After changing the kernel configuration, the next time
the user runs "make", the kernel is rebuilt to take into account the
new configuration (not rebuilt from scratch).
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
We only adjust the configuration or ARM EABI and IPv6. The (more
complicated) initramfs case is handled in a separate commit. The user
is expected to take care of all other configuration details (like
having Netfilter enabled to make iptables work, etc.)
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
In order to not depend on module init tools being installed on the
development environment of the Buildroot user, let's build module init
tools for the host.
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
This patch introduces a single, simple, infrastructure to build the
Linux kernel. The configuration is limited to :
* Kernel version: a fixed recent stable version, same as kernel
headers version (for internal toolchains only), custom stable
version, or custom tarball URL
* Kernel patch: either a local file, directory or an URL
* Kernel configuration: either the name of a defconfig or the
location of a custom configuration file
* Kernel image: either uImage, bzImage, zImage or vmlinux.
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
