Add "cross-emulation" support

docs/1-installing.md

@@ -35,7 +35,7 @@ To also set up crun-vm for use with Docker:
 1. Install crun-vm's runtime dependencies:
 
    ```console
-   $ dnf install bash coreutils crun genisoimage grep libselinux-devel libvirt-client libvirt-daemon-driver-qemu libvirt-daemon-log openssh-clients qemu-img qemu-system-x86-core shadow-utils util-linux virtiofsd
+   $ dnf install bash coreutils crun crun-krun genisoimage grep libselinux-devel libvirt-client libvirt-daemon-driver-qemu libvirt-daemon-log openssh-clients qemu-img qemu-system-x86-core sed shadow-utils util-linux virtiofsd
    ```
 
 2. Install Rust and Cargo if you do not already have Rust tooling available:

docs/2-podman-docker.md

@@ -96,6 +96,25 @@ in a container image.
 Note that flag `--persistent` has no effect when running VMs from container
 images.
 
+### From bootable container images
+
+crun-vm can also work with [bootable container images], which are containers
+that package a full operating system:
+
+```console
+$ podman run \
+    --runtime crun-vm \
+    -it --rm \
+    quay.io/fedora/fedora-bootc:40
+```
+
+Internally, crun-vm generates a VM image from the bootable container and then
+boots it.
+
+By default, the VM image is given a disk size roughly double the size of the
+bootc container image. To change this, use the `--bootc-disk-size <size>[KMGT]`
+option.
+
 ## First-boot customization
 
 ### cloud-init
@@ -317,8 +336,12 @@ $ podman run \
 ### System emulation
 
 To use system emulation instead of hardware-assisted virtualization, specify the
-`--emulated` flag. Without this flag, attempting to create a VM on a host tbat
-doesn't support KVM will fail.
+`--emulated` flag. Without this flag, attempting to create a VM from a guest
+with a different architecture from the host's or on a host that doesn't support
+KVM will fail.
+
+It's not currently possible to use this flag when the container image is a bootc
+bootable container.
 
 ### Inspecting and customizing the libvirt domain XML
 
@@ -340,6 +363,7 @@ be merged with it using the non-standard option `--merge-libvirt-xml <file>`.
 > Before using this flag, consider if you would be better served using libvirt
 > directly to manage your VM.
 
+[bootable container images]: https://containers.github.io/bootable/
 [cloud-init]: https://cloud-init.io/
 [domain XML definition]: https://libvirt.org/formatdomain.html
 [Ignition]: https://coreos.github.io/ignition/

embed/bootc/config.json

@@ -0,0 +1,88 @@
+{
+    "ociVersion": "1.0.0",
+    "process": {
+        "terminal": true,
+        "user": { "uid": 0, "gid": 0 },
+        "args": ["/output/entrypoint.sh", "<IMAGE_NAME>"],
+        "env": [
+            "PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin",
+            "TERM=xterm"
+        ],
+        "cwd": "/",
+        "capabilities": {
+            "bounding": [],
+            "effective": [],
+            "inheritable": [],
+            "permitted": [],
+            "ambient": []
+        },
+        "rlimits": [
+            {
+                "type": "RLIMIT_NOFILE",
+                "hard": 262144,
+                "soft": 262144
+            }
+        ],
+        "noNewPrivileges": true
+    },
+    "root": {
+        "path": "<ORIGINAL_ROOT>",
+        "readonly": false
+    },
+    "hostname": "bootc-install",
+    "mounts": [
+        {
+            "type": "bind",
+            "source": "<PRIV_DIR>/root/crun-vm/bootc",
+            "destination": "/output",
+            "options": ["bind", "rprivate", "rw"]
+        },
+        {
+            "destination": "/proc",
+            "type": "proc",
+            "source": "proc"
+        },
+        {
+            "destination": "/dev/pts",
+            "type": "devpts",
+            "source": "devpts",
+            "options": [
+                "nosuid",
+                "noexec",
+                "newinstance",
+                "ptmxmode=0666",
+                "mode=0620",
+                "gid=5"
+            ]
+        }
+    ],
+    "linux": {
+        "namespaces": [
+            { "type": "pid" },
+            { "type": "network" },
+            { "type": "ipc" },
+            { "type": "uts" },
+            { "type": "cgroup" },
+            { "type": "mount" }
+        ],
+        "maskedPaths": [
+            "/proc/acpi",
+            "/proc/asound",
+            "/proc/kcore",
+            "/proc/keys",
+            "/proc/latency_stats",
+            "/proc/timer_list",
+            "/proc/timer_stats",
+            "/proc/sched_debug",
+            "/sys/firmware",
+            "/proc/scsi"
+        ],
+        "readonlyPaths": [
+            "/proc/bus",
+            "/proc/fs",
+            "/proc/irq",
+            "/proc/sys",
+            "/proc/sysrq-trigger"
+        ]
+    }
+}

embed/bootc/entrypoint.sh

@@ -0,0 +1,51 @@
+#!/bin/sh
+# SPDX-License-Identifier: GPL-2.0-or-later
+
+set -e
+
+image_name=$1
+
+# monkey-patch loopdev partition detection, given we're not running systemd
+# (bootc runs `udevadm settle` as a way to wait until loopdev partitions are
+# detected; we hijack that call and use partx to set up the partition devices)
+
+original_udevadm=$( which udevadm )
+
+mkdir -p /output/bin
+
+cat >/output/bin/udevadm <<EOF
+#!/bin/sh
+${original_udevadm@Q} "\$@" && partx --add /dev/loop0
+EOF
+
+chmod +x /output/bin/udevadm
+
+# default to an xfs root file system if there is no bootc config (some images
+# don't currently provide any, for instance quay.io/fedora/fedora-bootc:40)
+
+if ! find /usr/lib/bootc/install -mindepth 1 -maxdepth 1 | read; then
+    # /usr/lib/bootc/install is empty
+
+    cat >/usr/lib/bootc/install/00-crun-vm.toml <<EOF
+    [install.filesystem.root]
+    type = "xfs"
+EOF
+
+fi
+
+# build disk image using bootc-install
+
+PATH=/output/bin:$PATH bootc install to-disk \
+    --source-imgref docker-archive:/output/image.docker-archive \
+    --target-imgref "$image_name" \
+    --skip-fetch-check \
+    --generic-image \
+    --via-loopback \
+    --karg console=tty0 \
+    --karg console=ttyS0 \
+    --karg selinux=0 \
+    /output/image.raw
+
+# communicate success by creating a file, since krun always exits successfully
+
+touch /output/bootc-install-success

embed/bootc/prepare.sh

@@ -0,0 +1,127 @@
+#!/bin/bash
+# SPDX-License-Identifier: GPL-2.0-or-later
+
+set -o errexit -o pipefail -o nounset
+
+engine=$1
+container_id=$2
+original_root=$3
+priv_dir=$4
+disk_size=$5
+
+__step() {
+    printf "\033[36m%s\033[0m\n" "$*"
+}
+
+bootc_dir=$priv_dir/root/crun-vm/bootc
+
+mkfifo "$bootc_dir/progress"
+exec > "$bootc_dir/progress" 2>&1
+
+# this blocks here until the named pipe above is opened by entrypoint.sh
+
+# get info about the container *image*
+
+image_info=$(
+    "$engine" container inspect \
+        --format '{{.Config.Image}}'$'\t''{{.Image}}' \
+        "$container_id"
+    )
+
+image_name=$( cut -f1 <<< "$image_info" )
+# image_name=${image_name#sha256:}
+
+image_id=$( cut -f2 <<< "$image_info" )
+
+# check if VM image is cached
+
+container_name=crun-vm-$container_id
+
+cache_image_label=containers.crun-vm.from=$image_id
+cache_image_id=$( "$engine" images --filter "label=$cache_image_label" --format '{{.Id}}' )
+
+if [[ -n "$cache_image_id" ]]; then
+
+    # retrieve VM image from cached containerdisk
+
+    __step "Retrieving cached VM image..."
+
+    trap '"$engine" rm --force "$container_name" >/dev/null 2>&1 || true' EXIT
+
+    "$engine" create --quiet --name "$container_name" "$cache_image_id" >/dev/null
+    "$engine" export "$container_name" | tar -C "$bootc_dir" -x image.qcow2
+    "$engine" rm "$container_name" >/dev/null 2>&1
+
+    trap '' EXIT
+
+else
+
+    __step "Converting $image_name into a VM image..."
+
+    # save container *image* as an archive
+
+    echo -n 'Preparing container image...'
+
+    "$engine" save --output "$bootc_dir/image.docker-archive" "$image_id" 2>&1 \
+        | sed -u 's/.*/./' \
+        | stdbuf -o0 tr -d '\n'
+
+    echo
+
+    # adjust krun config
+
+    __sed() {
+        sed -i "s|$1|$2|" "$bootc_dir/config.json"
+    }
+
+    __sed "<IMAGE_NAME>"    "$image_name"
+    __sed "<ORIGINAL_ROOT>" "$original_root"
+    __sed "<PRIV_DIR>"      "$priv_dir"
+
+    # run bootc-install under krun
+
+    if [[ -z "$disk_size" ]]; then
+        container_image_size=$(
+            "$engine" image inspect --format '{{.VirtualSize}}' "$image_id"
+            )
+
+        # use double the container image size to allow for in-place updates
+        disk_size=$(( container_image_size * 2 ))
+
+        # round up to 1 MiB
+        alignment=$(( 2**20 ))
+        disk_size=$(( (disk_size + alignment - 1) / alignment * alignment ))
+    fi
+
+    truncate --size "$disk_size" "$bootc_dir/image.raw"
+
+    trap 'krun delete --force "$container_name" >/dev/null 2>&1 || true' EXIT
+    krun run --config "$bootc_dir/config.json" "$container_name" </dev/ptmx
+    trap '' EXIT
+
+    [[ -e "$bootc_dir/bootc-install-success" ]]
+
+    # convert image to qcow2 to get a lower file length
+
+    qemu-img convert -f raw -O qcow2 "$bootc_dir/image.raw" "$bootc_dir/image.qcow2"
+    rm "$bootc_dir/image.raw"
+
+    # cache VM image file as containerdisk
+
+    __step "Caching VM image as a containerdisk..."
+
+    id=$(
+        "$engine" build --quiet --file - --label "$cache_image_label" "$bootc_dir" <<-'EOF'
+        FROM scratch
+        COPY image.qcow2 /
+        ENTRYPOINT ["no-entrypoint"]
+EOF
+    )
+
+    echo "Stored as untagged container image with ID $id"
+
+fi
+
+__step "Booting VM..."
+
+touch "$bootc_dir/success"

scripts/entrypoint.sh → embed/entrypoint.sh

@@ -5,6 +5,8 @@ trap 'exit 143' SIGTERM
 
 set -o errexit -o pipefail -o nounset
 
+is_bootc_container=$1
+
 # clean up locks that may have been left around from the container being killed
 rm -fr /var/lock
 
@@ -53,6 +55,22 @@ virsh --connect "qemu+unix:///session?socket=$socket" "\$@"
 EOF
 chmod +x /crun-vm/virsh
 
+# wait until VM image is generated from bootable container (if applicable)
+
+if (( is_bootc_container == 1 )) && [[ ! -e /crun-vm/image/image ]]; then
+
+    fifo=/crun-vm/bootc/progress
+    while [[ ! -e "$fifo" ]]; do sleep 0.2; done
+    cat "$fifo"
+    rm "$fifo"
+
+    [[ -e /crun-vm/bootc/success ]]
+
+    mkdir -p /crun-vm/image
+    mv /crun-vm/bootc/image.qcow2 /crun-vm/image/image
+
+fi
+
 # launch VM
 
 function __bg_ensure_tty() {

plans/tests.fmf

@@ -11,6 +11,7 @@ prepare:
       - cargo
       - coreutils
       - crun
+      - crun-krun
       - docker
       - genisoimage
       - grep