tests: add an new composefs-setup-root test

This script can be run under `unshare -Umr` to test that
composefs-setup-root is working properly, without building a VM image.

This helped a lot with manual testing during the original development of
composefs-setup-root and will be expanded in the future to include more
scenarios (different types of /etc and /var mounting, transient
overlays, and so on).

Signed-off-by: Allison Karlitskaya <[email protected]>

Author: allisonkarlitskaya

tests/test.sh

@@ -0,0 +1,84 @@
+#!/bin/sh
+
+set -eux
+
+if [ "$(id -u)" != '0' -o -z "${1:-}" ]; then
+    echo "*** run as: unshare -Umr $0 /path/to/tmpdir"
+    false
+fi
+
+top="$1"
+test -d "${top}"
+test -w "${top}"
+
+mkd() {
+    mkdir -p "$1"
+    echo "$1"
+}
+
+assert_fail() {
+    if "$@"; then
+        echo "*** unexpectedly passed: $*"
+        false
+    fi
+}
+
+imageid='0123456789abcdef0123456789abcdef0123456789abcdef0123456789abcdef'
+null=''
+
+# this is present in the initramfs itself
+config="${top}/config"
+tee "${config}" <<EOF
+EOF
+
+# this is the filesystem directly on the block device
+blkdev="$(mkd "${top}/blkdev")"
+repo="$(mkd "${blkdev}/composefs")"
+state="$(mkd "${blkdev}/state")"
+deployment="$(mkd "${state}/${imageid}")"
+dply_etc="$(mkd "${deployment}/etc")"
+dply_etc_u="$(mkd "${dply_etc}/upper")"
+dply_etc_w="$(mkd "${dply_etc}/work")"
+dply_var="$(mkd "${deployment}/var")"
+
+# fake composefs content (because we can't mount erofs)
+root="$(mkd "${top}/root-fs")"
+root_etc="$(mkd "${root}/etc")"
+root_var="$(mkd "${root}/var")"
+root_sysroot="$(mkd "${root}/sysroot")"
+mount -o bind,ro "${root}" "${root}"  # see open_root_fs()
+
+# this emulates the initramfs initially mounting the block device on /sysroot
+sysroot="$(mkd "${top}/sysroot")"
+mount -o bind "${blkdev}" "${sysroot}"
+
+composefs-setup-root \
+    --config "${config}" \
+    --cmdline "composefs=${imageid}" \
+    --root-fs "${root}" \
+    --sysroot "${sysroot}" \
+    ${null}
+
+grep "${top}" /proc/mounts
+
+# these are in the newly mounted root filesystem now
+var="${sysroot}/var"
+etc="${sysroot}/etc"
+
+assert_fail touch "${sysroot}/a"  # read-only
+touch "${etc}/file.conf"
+touch "${var}/db"
+
+# make sure those went into the expected places
+test -f "${dply_etc}/upper/file.conf"
+test -f "${dply_var}/db"
+
+find "${top}"
+
+umount -R "${sysroot}"  # this should entirely reverse the impact of the pivot
+umount -R "${root}"  # reverse the ro-bindmount above
+assert_fail grep "${top}" /proc/mounts  # make sure nothing else is mounted
+
+find "${top}"
+
+# from here we can inspect the after-effects