resize rootfs partition during first boot

diff --git a/modules/autoresize.mk b/modules/autoresize.mk
new file mode 100644 (file)
index 0000000..fba31eb
--- /dev/null
+++ b/modules/autoresize.mk
@@ -0,0 +1,51 @@
+export autoresize autoresize_unit
+
+define autoresize :=
+#!/bin/sh
+
+rootfs="$$(mount |grep -w / |cut -d' ' -f1)"
+
+case $$rootfs in
+  /dev/mmcblk?p2) rootdev="$${rootfs%p2}";;
+  /dev/[sh]d?2) rootdev="$${rootfs%2}";;
+  *) exit 0;;
+esac
+
+before="$$(sfdisk --dump "$$rootdev")"
+
+sfdisk --dump "$$rootdev" |sed '$$s;, size=.*,;,;;' \
+| sfdisk --force "$$rootdev"
+
+after="$$(sfdisk --dump "$$rootdev")"
+
+if [ "$$before" = "$$after" ]; then
+  # second stage
+  resize2fs "$$rootfs"
+  systemctl disable autoresize
+else
+  # finish first stage
+  shutdown -r now
+fi
+
+endef
+
+define autoresize_unit :=
+[Unit]
+Description=Resize root filesystem at boot
+
+[Service]
+ExecStart=/opt/autoresize.sh
+
+[Install]
+WantedBy=multi-user.target
+endef
+
+.PHONY: _autoresize
+_config: _autoresize
+
+_autoresize: ${CFGROOT}
+       mkdir -p "$${CFGROOT}/etc/systemd/system/"
+       printf '%s\n' "$$autoresize" >"$${CFGROOT}/opt/autoresize.sh"
+       chmod 755 "$${CFGROOT}/opt/autoresize.sh"
+       printf '%s\n' "$$autoresize_unit" >"$${CFGROOT}/etc/systemd/system/autoresize.service"
+       chroot "$${CFGROOT}" systemctl enable autoresize