path: root/linux
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authorGravatar Thomas Petazzoni <thomas.petazzoni@free-electrons.com>2010-06-13 19:19:38 +0200
committerGravatar Thomas Petazzoni <thomas.petazzoni@free-electrons.com>2010-06-22 21:20:28 +0200
commitf507921d391bb2578261a9e45c003e72302dc67a (patch)
treeae071e5efda5cd4c1e5f69f375d79ac2d9a482e4 /linux
parent4944e8c883efd0e11cc9e7585905e89941eb825b (diff)
linux: add support for initramfs
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>
Diffstat (limited to 'linux')
1 files changed, 30 insertions, 0 deletions
diff --git a/linux/linux.mk b/linux/linux.mk
index d1f1842f71..593a1b40a9 100644
--- a/linux/linux.mk
+++ b/linux/linux.mk
@@ -95,6 +95,19 @@ ifeq ($(BR2_INET_IPV6),y)
+ # As the kernel gets compiled before root filesystems are
+ # built, we create a fake initramfs file list. It'll be
+ # replaced later by the real list, and the kernel will be
+ # rebuilt using the linux26-rebuild-with-initramfs target.
+ touch $(BINARIES_DIR)/rootfs.initramfs
+ $(call KCONFIG_SET_OPT,CONFIG_INITRAMFS_SOURCE,\"$(BINARIES_DIR)/rootfs.initramfs\",$(@D)/.config)
$(TARGET_MAKE_ENV) $(MAKE) $(LINUX26_MAKE_FLAGS) -C $(@D) oldconfig
$(Q)touch $@
@@ -127,6 +140,23 @@ linux26: host-module-init-tools $(LINUX26_DEPENDENCIES) $(LINUX26_DIR)/.stamp_in
linux26-menuconfig linux26-xconfig linux26-gconfig: $(LINUX26_DIR)/.stamp_configured
$(MAKE) $(LINUX26_MAKE_FLAGS) -C $(LINUX26_DIR) $(subst linux26-,,$@)
+# Support for rebuilding the kernel after the initramfs file list has
+# been generated in $(BINARIES_DIR)/rootfs.initramfs.
+$(LINUX26_DIR)/.stamp_initramfs_rebuilt: $(LINUX26_DIR)/.stamp_installed $(BINARIES_DIR)/rootfs.initramfs
+ @$(call MESSAGE,"Rebuilding kernel with initramfs")
+ # Remove the previously generated initramfs which was empty,
+ # to make sure the kernel will actually regenerate it.
+ $(RM) -f $(@D)/usr/initramfs_data.cpio.*
+ # Build the kernel.
+ # Copy the kernel image to its final destination
+ $(Q)touch $@
+# The initramfs building code must make sure this target gets called
+# after it generated the initramfs list of files.
+linux26-rebuild-with-initramfs: $(LINUX26_DIR)/.stamp_initramfs_rebuilt
ifeq ($(BR2_LINUX_KERNEL),y)