[v2] Add support for custom initramfs contents

Message ID 20180825195152.25669-1-richard.kunze@web.de
State New
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Series
  • [v2] Add support for custom initramfs contents
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Commit Message

Richard Kunze Aug. 25, 2018, 7:51 p.m.
This adds an option to build an initramfs image with different content
than the rootfs within a single defconig. The intended use case is to
provide a minimal early userland for systems that cannot mount their
root file system directly from the kernel (e.g. because that rootfs
resides in an image file on a FAT formatted SD card, which has to be
mounted first before the rootfs can be set up).

The rationale for implementing this as an option for initramfs instead
of using two different configurations is ease of use: One configuration
is easier to maintain and builds faster than two.

Signed-off-by: Richard Kunze <richard.kunze@web.de>
---
 fs/initramfs/Config.in    | 34 +++++++++++++++++++++++++++++++++-
 fs/initramfs/initramfs.mk | 18 +++++++++++++++++-
 linux/linux.mk            |  8 ++++----
 3 files changed, 54 insertions(+), 6 deletions(-)

Patch

diff --git a/fs/initramfs/Config.in b/fs/initramfs/Config.in
index 9d5a3f92e6..9b7ac9475e 100644
--- a/fs/initramfs/Config.in
+++ b/fs/initramfs/Config.in
@@ -1,6 +1,22 @@ 
 config BR2_TARGET_ROOTFS_INITRAMFS
 	bool "initial RAM filesystem linked into linux kernel"
 	depends on BR2_LINUX_KERNEL
+	help
+	  Integrate an initramfs inside the kernel image.
+	  This integration will take place automatically.
+
+	  The initramfs contents can either be the full root filesystem
+	  generated by buildroot, or an image built from a custom list
+	  of files specified via the BR2_TARGET_ROOTFS_INITRAMFS_CUSTOM_CONTENTS
+	  config option.
+
+choice
+	prompt "initial RAM filesystem contents"
+	depends on BR2_TARGET_ROOTFS_INITRAMFS
+
+config BR2_TARGET_ROOTFS_INITRAMFS_ROOTFS
+	bool "rootfs.cpio"
+	depends on BR2_TARGET_ROOTFS_INITRAMFS
 	select BR2_TARGET_ROOTFS_CPIO
 	help
 	  Integrate the root filesystem generated by Buildroot as an
@@ -13,10 +29,26 @@  config BR2_TARGET_ROOTFS_INITRAMFS
 	  is used, regardless of how buildroot's cpio archive is
 	  configured.
 
-	  Note that enabling initramfs together with another filesystem
+	  Note that enabling this option together with another filesystem
 	  formats doesn't make sense: you would end up having two
 	  identical root filesystems, one embedded inside the kernel
 	  image, and one separately.
+config BR2_TARGET_ROOTFS_INITRAMFS_CUSTOM
+	bool "custom initramfs contents"
+	depends on BR2_TARGET_ROOTFS_INITRAMFS
+	help
+	  Use the contents of BR2_TARGET_ROOTFS_INITRAMFS_CUSTOM_CONTENTS
+	  as the linux kernel configuration variable CONFIG_INITRAMFS_SOURCE
+
+endchoice
+
+config BR2_TARGET_ROOTFS_INITRAMFS_CUSTOM_CONTENTS
+	string "custom initramfs contents"
+	depends on BR2_TARGET_ROOTFS_INITRAMFS_CUSTOM
+	help
+	  Custom value to use as CONFIG_INITRAMFS_SOURCE linux kernel configuration
+	  variable. See Documentation/filesystems/ramfs-rootfs-initramfs.txt in the
+	  linux kernel sources for details.
 
 comment "initramfs needs a Linux kernel to be built"
 	depends on !BR2_LINUX_KERNEL
diff --git a/fs/initramfs/initramfs.mk b/fs/initramfs/initramfs.mk
index c751093214..ef3fdc6d3d 100644
--- a/fs/initramfs/initramfs.mk
+++ b/fs/initramfs/initramfs.mk
@@ -4,6 +4,12 @@ 
 #
 ################################################################################
 
+ifeq ($(BR2_TARGET_ROOTFS_INITRAMFS_ROOTFS),y)
+ROOTFS_INITRAMFS_DEPENDENCIES += rootfs-cpio
+endif
+
+ROOTFS_INITRAMFS_DEPENDENCIES += $(BINARIES_DIR)/initramfs.cpio
+
 # The generic fs infrastructure isn't very useful here.
 #
 # The initramfs image does not actually build an image; its only purpose is:
@@ -19,13 +25,23 @@ 
 # advertise that our dependency is on the rootfs-cpio rule, which is
 # cleaner in the dependency graph.
 
-rootfs-initramfs: linux-rebuild-with-initramfs
+rootfs-initramfs: $(ROOTFS_INITRAMFS_DEPENDENCIES) linux-rebuild-with-initramfs
 
 rootfs-initramfs-show-depends:
 	@echo rootfs-cpio
 
 .PHONY: rootfs-initramfs rootfs-initramfs-show-depends
 
+ifeq ($(BR2_TARGET_ROOTFS_INITRAMFS_ROOTFS),y)
+$(BINARIES_DIR)/initramfs.cpio: rootfs-cpio
+	ln -sf rootfs.cpio $(BINARIES_DIR)/initramfs.cpio
+endif
+
+ifeq ($(BR2_TARGET_ROOTFS_INITRAMFS_CUSTOM),y)
+$(BINARIES_DIR)/initramfs.cpio: target-finalize $(call qstrip,$(BR2_TARGET_ROOTFS_INITRAMFS_CUSTOM_CONTENTS))
+	$(LINUX_DIR)/usr/gen_init_cpio $(BR2_TARGET_ROOTFS_INITRAMFS_CUSTOM_CONTENTS) > $(BINARIES_DIR)/initramfs.cpio
+endif
+
 ifeq ($(BR2_TARGET_ROOTFS_INITRAMFS),y)
 TARGETS_ROOTFS += rootfs-initramfs
 endif
diff --git a/linux/linux.mk b/linux/linux.mk
index 675e7906a8..5f4ddbb316 100644
--- a/linux/linux.mk
+++ b/linux/linux.mk
@@ -300,8 +300,8 @@  define LINUX_KCONFIG_FIXUP_CMDS
 	# replaced later by the real cpio archive, and the kernel will be
 	# rebuilt using the linux-rebuild-with-initramfs target.
 	$(if $(BR2_TARGET_ROOTFS_INITRAMFS),
-		touch $(BINARIES_DIR)/rootfs.cpio
-		$(call KCONFIG_SET_OPT,CONFIG_INITRAMFS_SOURCE,"$${BR_BINARIES_DIR}/rootfs.cpio",$(@D)/.config)
+		touch $(BINARIES_DIR)/initramfs.cpio
+		$(call KCONFIG_SET_OPT,CONFIG_INITRAMFS_SOURCE,"$${BR_BINARIES_DIR}/initramfs.cpio",$(@D)/.config)
 		$(call KCONFIG_SET_OPT,CONFIG_INITRAMFS_ROOT_UID,0,$(@D)/.config)
 		$(call KCONFIG_SET_OPT,CONFIG_INITRAMFS_ROOT_GID,0,$(@D)/.config))
 	$(if $(BR2_ROOTFS_DEVICE_CREATION_STATIC),,
@@ -528,11 +528,11 @@  endif # BR_BUILDING
 $(eval $(kconfig-package))
 
 # Support for rebuilding the kernel after the cpio archive has
-# been generated.
+# been generated in $(BINARIES_DIR)/initramfs.cpio.
 .PHONY: linux-rebuild-with-initramfs
 linux-rebuild-with-initramfs: $(LINUX_DIR)/.stamp_target_installed
 linux-rebuild-with-initramfs: $(LINUX_DIR)/.stamp_images_installed
-linux-rebuild-with-initramfs: rootfs-cpio
+linux-rebuild-with-initramfs: $(BINARIES_DIR)/initramfs.cpio
 linux-rebuild-with-initramfs:
 	@$(call MESSAGE,"Rebuilding kernel with initramfs")
 	# Build the kernel.