Add --bootc-disk-size option

It allows settings the disk size of the VM image that is generated from
a bootc container image.

Also improve the default disk size by basing it on the container image
size.

Signed-off-by: Alberto Faria <[email protected]>

docs/2-podman-docker.md

@@ -111,6 +111,10 @@ $ podman run \
 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

embed/bootc/prepare.sh

@@ -7,6 +7,7 @@ engine=$1
 container_id=$2
 original_root=$3
 priv_dir=$4
+disk_size=$5
 
 __step() {
     printf "\033[36m%s\033[0m\n" "$*"
@@ -79,7 +80,20 @@ else
 
     # run bootc-install under krun
 
-    truncate --size 10G "$bootc_dir/image.raw"  # TODO: allow adjusting disk size
+    if [[ -z "$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

src/commands/create/custom_opts.rs

@@ -55,6 +55,9 @@ pub struct CustomOptions {
     #[clap(long, help = "Use system emulation rather than KVM")]
     pub emulated: bool,
 
+    #[clap(long)]
+    pub bootc_disk_size: Option<String>,
+
     #[clap(long)]
     pub cloud_init: Option<Utf8PathBuf>,
 

src/commands/create/mod.rs

@@ -14,7 +14,9 @@ use std::process::{Command, Stdio};
 
 use anyhow::{anyhow, bail, ensure, Context, Result};
 use camino::{Utf8Path, Utf8PathBuf};
+use lazy_static::lazy_static;
 use nix::sys::stat::{major, makedev, minor, mknod, Mode, SFlag};
+use regex::Regex;
 use rust_embed::RustEmbed;
 
 use crate::commands::create::custom_opts::CustomOptions;
@@ -38,12 +40,7 @@ pub fn create(args: &liboci_cli::Create, raw_args: &[impl AsRef<OsStr>]) -> Resu
 
     let engine = Engine::detect(&args.container_id, bundle_path, &spec, &original_root_path)?;
     let custom_options = CustomOptions::from_spec(&spec, engine)?;
-    let is_bootc_container = is_bootc_container(&original_root_path, engine)?;
-
-    ensure!(
-        !is_bootc_container || !custom_options.emulated,
-        "--emulated is incompatible with bootable containers"
-    );
+    let is_bootc_container = is_bootc_container(&original_root_path, &custom_options, engine)?;
 
     // We include container_id in our paths to ensure no overlap with the user container's contents.
     let priv_dir_path = original_root_path.join(format!("crun-vm-{}", args.container_id));
@@ -121,6 +118,7 @@ pub fn create(args: &liboci_cli::Create, raw_args: &[impl AsRef<OsStr>]) -> Resu
             .arg(&args.container_id)
             .arg(&original_root_path)
             .arg(&priv_dir_path)
+            .arg(custom_options.bootc_disk_size.unwrap_or_default())
             .stdin(Stdio::null())
             .stdout(Stdio::null())
             .stderr(Stdio::null())
@@ -152,14 +150,43 @@ fn ensure_unprivileged(spec: &oci_spec::runtime::Spec) -> Result<()> {
     Ok(())
 }
 
-fn is_bootc_container(original_root_path: &Utf8Path, engine: Engine) -> Result<bool> {
+fn is_bootc_container(
+    original_root_path: &Utf8Path,
+    custom_options: &CustomOptions,
+    engine: Engine,
+) -> Result<bool> {
     let is_bootc_container = original_root_path.join("usr/lib/bootc/install").is_dir();
 
     ensure!(
         !is_bootc_container || engine == Engine::Podman || engine == Engine::Docker,
         "bootc containers are only supported with Podman and Docker"
     );
 
+    ensure!(
+        !is_bootc_container || !custom_options.emulated,
+        "--emulated is incompatible with bootable containers"
+    );
+
+    if let Some(size) = &custom_options.bootc_disk_size {
+        lazy_static! {
+            static ref SIZE_PATTERN: Regex = Regex::new(r"^[0-9]+[KMGT]?$").unwrap();
+        }
+
+        ensure!(
+            SIZE_PATTERN.is_match(size),
+            concat!(
+                "--bootc-disk-size value must be a number followed by an optional suffix K",
+                " (kilobyte, 1024), M (megabyte, 1024k), G (gigabyte, 1024M), or T (terabyte,",
+                " 1024G)",
+            )
+        );
+
+        ensure!(
+            is_bootc_container,
+            "--bootc-disk-size only applies to bootable containers"
+        );
+    }
+
     Ok(is_bootc_container)
 }
 

tests/t/bootc-disk-size.sh

@@ -0,0 +1,23 @@
+# SPDX-License-Identifier: GPL-2.0-or-later
+
+image="${TEST_IMAGES[fedora-bootc]}"
+user="${TEST_IMAGES_DEFAULT_USER[fedora-bootc]}"
+
+__run() {
+    __engine run --detach --name bootc-disk-size "$image" --bootc-disk-size "$1"
+}
+
+! RUST_LIB_BACKTRACE=0 __run 0
+__engine rm bootc-disk-size
+
+for size in 1K 1M; do
+    __run "$size"
+    ! __engine exec bootc-disk-size --as "$user"
+    __engine rm --force bootc-disk-size
+done
+
+for size in 1G 1T 1024T; do
+    __run "$size"
+    __engine exec bootc-disk-size --as "$user"
+    __engine rm --force bootc-disk-size
+done