[Buildroot] [PATCH v2] Add support for custom initramfs contents

[Yann E. MORIN <yann.morin.1998@free.fr>]

Richard, All,

On 2018-08-25 21:51 +0200, Richard Kunze spake thusly:
> 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.

We discussed this change during the developpers meeting, and we all
concluded that we did not want this, as I explaiend in my previous
review.

Regards,
Yann E. MORIN.

> 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(-)
> 
> 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.
> -- 
> 2.18.0
> 
> 
> _______________________________________________
> buildroot mailing list
> buildroot at busybox.net
> http://lists.busybox.net/mailman/listinfo/buildroot

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