initial buildroot for linux 5.15

fs/tar/Config.in

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+config BR2_TARGET_ROOTFS_TAR
+	bool "tar the root filesystem"
+	default y
+	help
+	  Build a tar archive of the root filesystem
+
+choice
+	prompt "Compression method"
+	default BR2_TARGET_ROOTFS_TAR_NONE
+	depends on BR2_TARGET_ROOTFS_TAR
+	help
+	  Select compressor for tar archive of the root filesystem
+
+config BR2_TARGET_ROOTFS_TAR_NONE
+	bool "no compression"
+	help
+	  Do not compress the tarball.
+
+config BR2_TARGET_ROOTFS_TAR_GZIP
+	bool "gzip"
+	help
+	  Do compress the tarball with gzip.
+
+config BR2_TARGET_ROOTFS_TAR_BZIP2
+	bool "bzip2"
+	help
+	  Do compress the tarball with bzip2.
+
+config BR2_TARGET_ROOTFS_TAR_LZ4
+	bool "lz4"
+	help
+	  Do compress the tarball with lz4.
+
+config BR2_TARGET_ROOTFS_TAR_LZMA
+	bool "lzma"
+	help
+	  Do compress the tarball with lzma.
+
+config BR2_TARGET_ROOTFS_TAR_LZO
+	bool "lzo"
+	help
+	  Do compress the tarball with lzop.
+
+config BR2_TARGET_ROOTFS_TAR_XZ
+	bool "xz"
+	help
+	  Do compress the tarball with xz.
+
+endchoice
+
+config BR2_TARGET_ROOTFS_TAR_OPTIONS
+	string "other random options to pass to tar"
+	default ""
+	depends on BR2_TARGET_ROOTFS_TAR
+	help
+	  Any other flags you want to pass to tar
+	  Refer to tar --help for details

fs/tar/tar.mk

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+################################################################################
+#
+# tar to archive target filesystem
+#
+################################################################################
+
+TAR_OPTS = $(call qstrip,$(BR2_TARGET_ROOTFS_TAR_OPTIONS))
+
+ROOTFS_TAR_DEPENDENCIES = $(BR2_TAR_HOST_DEPENDENCY)
+
+# do not store atime/ctime in PaxHeaders to ensure reproducbility
+TAR_OPTS += --pax-option=exthdr.name=%d/PaxHeaders/%f,atime:=0,ctime:=0
+
+define ROOTFS_TAR_CMD
+	(cd $(TARGET_DIR); find -print0 | LC_ALL=C sort -z | \
+		tar $(TAR_OPTS) -cf $@ --null --xattrs-include='*' --no-recursion -T - --numeric-owner)
+endef
+
+$(eval $(rootfs))