initial buildroot for linux 5.15

fs/cpio/Config.in

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+config BR2_TARGET_ROOTFS_CPIO
+	bool "cpio the root filesystem (for use as an initial RAM filesystem)"
+	help
+	  Build a cpio archive of the root filesystem. This is typically
+	  used for an initial RAM filesystem that is passed to the
+	  kernel by the bootloader.
+
+if BR2_TARGET_ROOTFS_CPIO
+
+choice
+	prompt "Compression method"
+	default BR2_TARGET_ROOTFS_CPIO_NONE
+	help
+	  Select compressor for cpio filesystem of the root filesystem.
+	  If you use the cpio archive as an initial RAM filesystem, make
+	  sure the kernel contains the decompression algorithm selected
+	  here.
+
+config BR2_TARGET_ROOTFS_CPIO_NONE
+	bool "no compression"
+	help
+	  Do not compress the cpio filesystem.
+
+config BR2_TARGET_ROOTFS_CPIO_GZIP
+	bool "gzip"
+	help
+	  Do compress the cpio filesystem with gzip.
+
+config BR2_TARGET_ROOTFS_CPIO_BZIP2
+	bool "bzip2"
+	help
+	  Do compress the cpio filesystem with bzip2.
+
+config BR2_TARGET_ROOTFS_CPIO_LZ4
+	bool "lz4"
+	help
+	  Do compress the cpio filesystem with lz4.
+
+config BR2_TARGET_ROOTFS_CPIO_LZMA
+	bool "lzma"
+	help
+	  Do compress the cpio filesystem with lzma.
+
+config BR2_TARGET_ROOTFS_CPIO_LZO
+	bool "lzo"
+	help
+	  Do compress the cpio filesystem with lzop.
+
+config BR2_TARGET_ROOTFS_CPIO_XZ
+	bool "xz"
+	help
+	  Do compress the cpio filesystem with xz.
+
+config BR2_TARGET_ROOTFS_CPIO_ZSTD
+	bool "zstd"
+	help
+	  Do compress the cpio filesystem with zstd.
+
+endchoice
+
+config BR2_TARGET_ROOTFS_CPIO_UIMAGE
+	bool "Create U-Boot image of the root filesystem"
+	select BR2_PACKAGE_HOST_UBOOT_TOOLS
+	help
+	  Add a U-Boot header to the cpio root filesystem. This allows
+	  the initramfs to be loaded with the bootm command in U-Boot.
+
+	  The U-Boot image will be called rootfs.cpio.uboot
+
+endif # BR2_TARGET_ROOTFS_CPIO

fs/cpio/cpio.mk

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+################################################################################
+#
+# cpio to archive target filesystem
+#
+################################################################################
+
+ifeq ($(BR2_ROOTFS_DEVICE_CREATION_STATIC),y)
+
+define ROOTFS_CPIO_ADD_INIT
+	if [ ! -e $(TARGET_DIR)/init ]; then \
+		ln -sf sbin/init $(TARGET_DIR)/init; \
+	fi
+endef
+
+else
+# devtmpfs does not get automounted when initramfs is used.
+# Add a pre-init script to mount it before running init
+# We must have /dev/console very early, even before /init runs,
+# for stdin/stdout/stderr
+define ROOTFS_CPIO_ADD_INIT
+	if [ ! -e $(TARGET_DIR)/init ]; then \
+		$(INSTALL) -m 0755 fs/cpio/init $(TARGET_DIR)/init; \
+	fi
+	mkdir -p $(TARGET_DIR)/dev
+	mknod -m 0622 $(TARGET_DIR)/dev/console c 5 1
+endef
+
+endif # BR2_ROOTFS_DEVICE_CREATION_STATIC
+
+ROOTFS_CPIO_PRE_GEN_HOOKS += ROOTFS_CPIO_ADD_INIT
+
+# --reproducible option was introduced in cpio v2.12, which may not be
+# available in some old distributions, so we build host-cpio
+ifeq ($(BR2_REPRODUCIBLE),y)
+ROOTFS_CPIO_DEPENDENCIES += host-cpio
+ROOTFS_CPIO_OPTS += --reproducible
+endif
+
+define ROOTFS_CPIO_CMD
+	cd $(TARGET_DIR) && \
+	find . \
+	| LC_ALL=C sort \
+	| cpio $(ROOTFS_CPIO_OPTS) --quiet -o -H newc \
+	> $@
+endef
+
+ifeq ($(BR2_TARGET_ROOTFS_CPIO_UIMAGE),y)
+ROOTFS_CPIO_DEPENDENCIES += host-uboot-tools
+define ROOTFS_CPIO_UBOOT_MKIMAGE
+	$(MKIMAGE) -A $(MKIMAGE_ARCH) -T ramdisk \
+		-C none -d $@$(ROOTFS_CPIO_COMPRESS_EXT) $@.uboot
+endef
+ROOTFS_CPIO_POST_GEN_HOOKS += ROOTFS_CPIO_UBOOT_MKIMAGE
+endif
+
+$(eval $(rootfs))

fs/cpio/init

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+#!/bin/sh
+# devtmpfs does not get automounted for initramfs
+/bin/mount -t devtmpfs devtmpfs /dev
+
+# use the /dev/console device node from devtmpfs if possible to not
+# confuse glibc's ttyname_r().
+# This may fail (E.G. booted with console=), and errors from exec will
+# terminate the shell, so use a subshell for the test
+if (exec 0</dev/console) 2>/dev/null; then
+    exec 0</dev/console
+    exec 1>/dev/console
+    exec 2>/dev/console
+fi
+
+exec /sbin/init "$@"