busybox: add initrd variant

Add a busybox variant that inherits almost all of its support from
the core busybox recipe, but adds configuration values that are
appropriate to be used in an initrd.

In particular:

  - we build busybox statically
  - we enable runlevel and init functionality
  - mdev is always enabled
  - applet install support is enabled

Signed-off-by: Bruce Ashfield <bruce.ashfield@xilinx.com>
Signed-off-by: Bruce Ashfield <bruce.ashfield@gmail.com>

recipes-core/busybox/busybox-initrd/initrd.cfg

@@ -0,0 +1,14 @@
+CONFIG_INIT=y
+CNOFIG_FEATURE_UTMP=y
+CONFIG_RUNLEVEL=y
+CONFIG_FEATURE_USE_INITTAB=y
+CONFIG_HALT=y
+CONFIG_POWEROFF=y
+CONFIG_FEATURE_KILL_DELAY=0
+CONFIG_TELINIT_PATH=""
+CONFIG_INIT_TERMINAL_TYPE=""
+
+# CONFIG_FEATURE_SHADOWPASSWDS is not set
+CONFIG_USE_BB_PWD_GRP=y
+
+CONFIG_STATIC=y

recipes-core/busybox/busybox-initrd/runx.cfg

@@ -0,0 +1 @@
+CONFIG_FEATURE_INSTALLER=y

recipes-core/busybox/busybox-initrd_1.32.0.bb

@@ -0,0 +1,20 @@
+FILESEXTRAPATHS_prepend := "${THISDIR}/busybox-initrd:${COREBASE}/meta/recipes-core/busybox/busybox:${COREBASE}/meta/recipes-core/busybox/files:"
+
+require recipes-core/busybox/busybox_${PV}.bb
+
+SRC_URI += "file://init.cfg \
+            file://mdev.cfg \
+            file://runx.cfg \
+            file://initrd.cfg"
+
+S = "${WORKDIR}/busybox-${PV}"
+
+# override security-flags settings, we have some warnings to ignore
+SECURITY_STRINGFORMAT = ""
+
+# we do this to get the target binary available to recipes that
+# depend on busybox
+SYSROOT_DIRS += "/bin"
+BUSYBOX_SPLIT_SUID = "0"
+
+FILES_${PN} += "${sysconfdir}/init.d/*"