image_types.bbclass: allow replacing tar command

Usually, the host's tar command is sufficient. However, special cases
like archiving xattrs depend on a modern GNU tar version. The new
IMAGE_CMD_TAR makes that possible, with xattrs given as example.

Signed-off-by: Patrick Ohly <patrick.ohly@intel.com>
Signed-off-by: Ross Burton <ross.burton@intel.com>

diff --git a/meta/classes/image_types.bbclass b/meta/classes/image_types.bbclass
index 35ceb7beafcc6a21537454f49af177570e8dc10e..8547574a1ddb52bf5acfba2f6aea0d0ef6ed9af6 100644 (file)
--- a/meta/classes/image_types.bbclass
+++ b/meta/classes/image_types.bbclass
@@ -71,7 +71,19 @@ IMAGE_CMD_btrfs () {
 IMAGE_CMD_squashfs = "mksquashfs ${IMAGE_ROOTFS} ${DEPLOY_DIR_IMAGE}/${IMAGE_NAME}.rootfs.squashfs ${EXTRA_IMAGECMD} -noappend"
 IMAGE_CMD_squashfs-xz = "mksquashfs ${IMAGE_ROOTFS} ${DEPLOY_DIR_IMAGE}/${IMAGE_NAME}.rootfs.squashfs-xz ${EXTRA_IMAGECMD} -noappend -comp xz"
 IMAGE_CMD_squashfs-lzo = "mksquashfs ${IMAGE_ROOTFS} ${DEPLOY_DIR_IMAGE}/${IMAGE_NAME}.rootfs.squashfs-lzo ${EXTRA_IMAGECMD} -noappend -comp lzo"
-IMAGE_CMD_tar = "tar -cvf ${DEPLOY_DIR_IMAGE}/${IMAGE_NAME}.rootfs.tar -C ${IMAGE_ROOTFS} ."
+
+# By default, tar from the host is used, which can be quite old. If
+# you need special parameters (like --xattrs) which are only supported
+# by GNU tar upstream >= 1.27, then override that default:
+# IMAGE_CMD_TAR = "tar --xattrs --xattrs-include=*"
+# IMAGE_DEPENDS_tar_append = " tar-replacement-native"
+# EXTRANATIVEPATH += "tar-native"
+#
+# The GNU documentation does not specify whether --xattrs-include is necessary.
+# In practice, it turned out to be not needed when creating archives and
+# required when extracting, but it seems prudent to use it in both cases.
+IMAGE_CMD_TAR ?= "tar"
+IMAGE_CMD_tar = "${IMAGE_CMD_TAR} -cvf ${DEPLOY_DIR_IMAGE}/${IMAGE_NAME}.rootfs.tar -C ${IMAGE_ROOTFS} ."
 
 do_rootfs[cleandirs] += "${WORKDIR}/cpio_append"
 IMAGE_CMD_cpio () {