[Buildroot] [PATCH 1/1] fs/cpio: add option to manually specify file list

[Seamus Connor <sconnor@lynx.com>]

For some systems it may be desireable to have an initramfs that is
smaller than the full root filesystem. This commit adds support for
creating an initramfs based on a manually specified set of files. It is
up to the user to define a sensible set of files. This file list could
either be statically created, or it could be created as the result of a
pre-fs hook script.

Signed-off-by: Seamus Connor <sconnor@lynx.com>
---
 fs/cpio/Config.in | 30 ++++++++++++++++++++++++++++++
 fs/cpio/cpio.mk   | 10 ++++++++++
 2 files changed, 40 insertions(+)

diff --git a/fs/cpio/Config.in b/fs/cpio/Config.in
index 206baca677..21aa2c6fb8 100644
--- a/fs/cpio/Config.in
+++ b/fs/cpio/Config.in
@@ -7,6 +7,36 @@ config BR2_TARGET_ROOTFS_CPIO
 
 if BR2_TARGET_ROOTFS_CPIO
 
+choice
+	prompt "Seleted Fileset"
+	default BR2_TARGET_ROOTFS_CPIO_INCLUDE_ALL
+	help
+	  Select the set of files to include in the cpio of the root filesystem.
+	  This may either be all files installed to the target, or it may be a
+	  subset defined in the custom file list.
+
+config BR2_TARGET_ROOTFS_CPIO_INCLUDE_ALL
+	bool "Include all files from target"
+	help
+	  Include all files from the target directory in the root filesystem.
+
+config BR2_TARGET_ROOTFS_CPIO_INCLUDE_CUSTOM
+	bool "Include a subset of files from target"
+	help
+	  Include a subset of the files from the target directory in the root filesystem.
+	  This requires a custom file list to be defined.  The actual file list may be
+	  generated by a user script defined as part of the pre-fs hook.
+
+endchoice
+
+config BR2_TARGET_ROOTFS_CPIO_CUSTOM_FILELIST
+	string "path to a custom file list"
+	depends on BR2_TARGET_ROOTFS_CPIO && BR2_TARGET_ROOTFS_CPIO_INCLUDE_CUSTOM
+	help
+	  This file defines the contents of the rootfilesystem.  All files and folders
+	  created in the rootfilesystem must be defined here.  This file can be statically
+	  defined, or created as part of the pre-fs hook.
+
 choice
 	prompt "Compression method"
 	default BR2_TARGET_ROOTFS_CPIO_NONE
diff --git a/fs/cpio/cpio.mk b/fs/cpio/cpio.mk
index e82167e512..984ff37895 100644
--- a/fs/cpio/cpio.mk
+++ b/fs/cpio/cpio.mk
@@ -27,10 +27,20 @@ endif # BR2_ROOTFS_DEVICE_CREATION_STATIC
 
 ROOTFS_CPIO_PRE_GEN_HOOKS += ROOTFS_CPIO_ADD_INIT
 
+ifeq ($(BR2_TARGET_ROOTFS_CPIO_INCLUDE_ALL),y)
+
 define ROOTFS_CPIO_CMD
 	cd $(TARGET_DIR) && find . | cpio --quiet -o -H newc > $@
 endef
 
+else
+
+define ROOTFS_CPIO_CMD
+	cd $(TARGET_DIR) && cpio --quiet -o -H newc < $(BR2_TARGET_ROOTFS_CPIO_CUSTOM_FILELIST) > $@
+endef
+
+endif
+
 $(BINARIES_DIR)/rootfs.cpio.uboot: $(BINARIES_DIR)/rootfs.cpio host-uboot-tools
 	$(MKIMAGE) -A $(MKIMAGE_ARCH) -T ramdisk \
 		-C none -d $<$(ROOTFS_CPIO_COMPRESS_EXT) $@
-- 
2.14.2