Add a mkimage package

This will replace the tools/mkimage-* Docker images.

Signed-off-by: Justin Cormack <justin.cormack@docker.com>

pkg/mkimage/Dockerfile

@@ -0,0 +1,23 @@
+FROM linuxkit/alpine:6336329f15b4166514782eaa555cf0ffd35c519c@sha256:f6c2ce92910b1d6e4e5557850a554f4a3ae9f66c1e89ad86a24d6c6e550f165e AS mirror
+
+RUN mkdir -p /out/etc/apk && cp -r /etc/apk/* /out/etc/apk/
+RUN apk add --no-cache --initdb -p /out \
+    alpine-baselayout \
+    busybox \
+    e2fsprogs \
+    e2fsprogs-extra \
+    musl \
+    sfdisk \
+    syslinux \
+    xfsprogs \
+    && true
+RUN rm -rf /out/etc/apk /out/lib/apk /out/var/cache
+
+FROM scratch
+ENTRYPOINT []
+CMD []
+WORKDIR /
+COPY --from=mirror /out/ /
+COPY mkimage.sh /usr/bin/
+CMD ["mkimage.sh"]
+LABEL org.mobyproject.config='{"readonly": true, "capabilities": ["CAP_SYS_ADMIN", "CAP_MKNOD"], "binds": ["/dev:/dev", "/data:/data"]}'

pkg/mkimage/Makefile

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+.PHONY: tag push
+default: push
+
+ORG?=linuxkit
+IMAGE=mkimage
+DEPS=Dockerfile mkimage.sh
+
+HASH?=$(shell git ls-tree HEAD -- ../$(notdir $(CURDIR)) | awk '{print $$3}')
+
+tag: $(DEPS)
+	docker build --no-cache --network=none -t $(ORG)/$(IMAGE):$(HASH) .
+
+push: tag
+	docker pull $(ORG)/$(IMAGE):$(HASH) || \
+	docker push $(ORG)/$(IMAGE):$(HASH)

pkg/mkimage/mkimage.sh

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+#!/bin/sh
+
+# currently only supports ext4 disks; will extend for other filesystems, ISO, ...
+
+do_mkfs()
+{
+	diskdev="$1"
+
+	# new disks does not have an DOS signature in sector 0
+	# this makes sfdisk complain. We can workaround this by letting
+	# fdisk create that DOS signature, by just do a "w", a write.
+	# http://bugs.alpinelinux.org/issues/145
+	echo "w" | fdisk $diskdev >/dev/null
+
+	# format one large partition
+	echo ";" | sfdisk --quiet $diskdev
+
+	# update status
+	blockdev --rereadpt $diskdev 2> /dev/null
+
+	# wait for device
+	for i in $(seq 1 50); do test -b "$DATA" && break || sleep .1; mdev -s; done
+
+	FSOPTS="-O resize_inode,has_journal,extent,huge_file,flex_bg,uninit_bg,64bit,dir_nlink,extra_isize"
+
+	mkfs.ext4 -q -F $FSOPTS ${diskdev}1
+}
+
+DEV="$(find /dev -maxdepth 1 -type b ! -name 'loop*' | grep -v '[0-9]$' | sed 's@.*/dev/@@' | sort | head -1 )"
+
+[ -z "${DEV}" ] && exit 1
+
+DRIVE="/dev/${DEV}"
+
+# format
+do_mkfs "$DRIVE"
+
+PARTITION="${DRIVE}1"
+
+# mount
+mount "$PARTITION" /mnt
+
+# copy kernel, initrd
+cp -a /data/kernel /data/initrd.img /mnt/
+
+# create syslinux.cfg
+CMDLINE="$(cat /data/cmdline)"
+
+CFG="DEFAULT linux
+LABEL linux
+    KERNEL /kernel
+    INITRD /initrd.img
+    APPEND ${CMDLINE}
+"
+
+printf "$CFG" > /mnt/syslinux.cfg
+
+# install syslinux
+extlinux --install /mnt
+
+# unmount
+umount /mnt
+
+# install mbr
+dd if=usr/share/syslinux/mbr.bin of="$DRIVE" bs=440 count=1
+
+# make bootable
+sfdisk -A "$DRIVE" 1