--- /dev/null
+#!/bin/sh
+
+ROOT=${1:-/dev/root}
+
+fail() { echo "growroot: FAIL:" "$@" 1>&2; exit 1; }
+msg() { echo "$@"; }
+
+# figure out what disk ROOT is on
+{ [ ! -L "${ROOT}" ] && rootdev=${ROOT} || rootdev=$(readlink -f "${ROOT}") ; } ||
+ fail "failed to get target of link for ${ROOT}"
+
+case "${rootdev}" in
+ *[0-9]) : ;;
+ # the root is a disk, not a partition (does not end in a digit)
+ # no need to do anything in this case, kernel already knows the full size.
+ *) exit 0;;
+esac
+
+# remove all consective numbers from the end of rootdev to get 'rootdisk'
+rootdisk=${rootdev}
+while [ "${rootdisk%[0-9]}" != "${rootdisk}" ]; do
+ rootdisk=${rootdisk%[0-9]};
+done
+partnum=${rootdev#${rootdisk}}
+
+# if the basename of the root device (ie 'xvda1' or 'sda1') exists
+# in /sys/block/ then it is a block device, not a partition
+# (xen xvda1 is an example of such a funny named block device)
+[ -e "/sys/block/${rootdev##*/}" ] && exit 0
+
+# if growpart fails, exit. its failure messages should go
+# to stderr, so they'll get to the console
+out=$(growpart "${rootdisk}" "${partnum}")
+ret=$?
+
+# if growpart output starts with 'CHANGED:' then it did something.
+# anything else, exit
+case "$ret" in
+ 0|1) echo "GROWROOT: $out";;
+ *)
+ echo "$out";
+ exit $ret;;
+esac
+
+# write to /etc/grownroot-grown.
+{ date --utc > "${rootmnt}/etc/growroot-grown" ; } >/dev/null 2>&1 || :
+
+# vi: ts=4 noexpandtab