trim.sh: Work-in-progress container reduction script

Dump everything except @world and it's runtime dependencies (and dump
the Docker history too) to get a container down to a reasonable size.

diff --git a/trim.sh b/trim.sh
new file mode 100755 (executable)
index 0000000..1091a69
--- /dev/null
+++ b/trim.sh
@@ -0,0 +1,71 @@
+#!/bin/sh
+#
+# Copyright (C) 2013-2014 W. Trevor King <wking@tremily.us>
+#
+# Redistribution and use in source and binary forms, with or without
+# modification, are permitted provided that the following conditions are met:
+#
+# * Redistributions of source code must retain the above copyright notice, this
+# list of conditions and the following disclaimer.
+#
+# * Redistributions in binary form must reproduce the above copyright notice,
+# this list of conditions and the following disclaimer in the documentation
+# and/or other materials provided with the distribution.
+#
+# THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+# AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+# IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+# ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE
+# LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
+# CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
+# SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+# INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
+# CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+# ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+# POSSIBILITY OF SUCH DAMAGE.
+
+die()
+{
+       echo "$1"
+       exit 1
+}
+
+trim()
+{
+       IMAGE="$1"
+       NAMESPACE_REPOSITORY="${IMAGE%:*}"
+       TAG="${IMAGE#*:}"
+       if [ "${TAG}" = "${NAMESPACE_REPOSITORY}" ]
+       then
+               TAG=""
+       fi
+       REPOSITORY="${NAMESPACE_REPOSITORY#*/}"
+       CONTAINER="${REPOSITORY}-trimmed-container"
+       IMG="${NAMESPACE_REPOSITORY}-trimmed"
+       if [ -n "${TAG}" ]
+       then
+               IMG="${IMG}:${TAG}"
+       fi
+       #sys-apps/openrc     (/sbin/rc)
+       #sys-apps/net-tools  (/bin/hostname)
+       #sys-devel/gettext   (/usr/bin/envsubst)
+       # unmerge GCC to break the GCC <-> libc dependency loop
+       docker run -t --name "${CONTAINER}" \
+               -v "${PWD}/empty-system.py:/tmp/empty-system.py" \
+               "${IMAGE}" /bin/bash -c "
+                       /tmp/empty-system.py &&
+                       emerge --noreplace app-shells/bash sys-apps/net-tools sys-apps/openrc sys-devel/gettext &&
+                       emerge --unmerge sys-devel/gcc &&
+                       emerge -v --depclean &&
+                       rm -rf /usr/portage" ||
+               die "failed to create ${CONTAINER}"
+       docker export "${CONTAINER}" | docker import - "${IMG}" ||
+               die "failed to export/import ${IMG}"
+       docker rm "${CONTAINER}" ||
+               die "failed to remove ${CONTAINER}"
+}
+
+for IMAGE in "$@"
+do
+       trim "${IMAGE}"
+done