WIP: install: Add --no-bootloader to skip bootloader setup

crates/lib/src/bootc_composefs/boot.rs

@@ -1231,7 +1231,12 @@ pub(crate) async fn setup_composefs_boot(
         .or(root_setup.rootfs_uuid.as_deref())
         .ok_or_else(|| anyhow!("No uuid for boot/root"))?;
 
-    if cfg!(target_arch = "s390x") {
+    // If bootloader is disabled, we skip the installer calls
+    let skip_bootloader = state.config_opts.no_bootloader;
+
+    if skip_bootloader {
+        tracing::info!("Skipping bootloader installation (--no-bootloader requested)");
+    } else if cfg!(target_arch = "s390x") {
         // TODO: Integrate s390x support into install_via_bootupd
         crate::bootloader::install_via_zipl(&root_setup.device_info, boot_uuid)?;
     } else if postfetch.detected_bootloader == Bootloader::Grub {
@@ -1257,20 +1262,26 @@ pub(crate) async fn setup_composefs_boot(
 
     let boot_type = BootType::from(entry);
 
-    let boot_digest = match boot_type {
-        BootType::Bls => setup_composefs_bls_boot(
-            BootSetupType::Setup((&root_setup, &state, &postfetch, &fs)),
-            repo,
-            &id,
-            entry,
-            &mounted_fs,
-        )?,
-        BootType::Uki => setup_composefs_uki_boot(
-            BootSetupType::Setup((&root_setup, &state, &postfetch, &fs)),
-            repo,
-            &id,
-            entries,
-        )?,
+    // We calculate the digest only if we are actually setting up the boot files.
+    // If we skip, we use a placeholder digest for the state file.
+    let boot_digest = if skip_bootloader {
+        "skipped".to_string()
+    } else {
+        match boot_type {
+            BootType::Bls => setup_composefs_bls_boot(
+                BootSetupType::Setup((&root_setup, &state, &postfetch, &fs)),
+                repo,
+                &id,
+                entry,
+                &mounted_fs,
+            )?,
+            BootType::Uki => setup_composefs_uki_boot(
+                BootSetupType::Setup((&root_setup, &state, &postfetch, &fs)),
+                repo,
+                &id,
+                entries,
+            )?,
+        }
     };
 
     write_composefs_state(

crates/lib/src/install.rs

@@ -373,6 +373,12 @@ pub(crate) struct InstallConfigOpts {
     #[clap(long)]
     #[serde(default)]
     pub(crate) bootupd_skip_boot_uuid: bool,
+
+    /// Disable all bootloader integration and requirements
+    // This allows installing to a filesystem without boot and ESP partitions.
+    #[clap(long)]
+    #[serde(default)]
+    pub(crate) no_bootloader: bool,
 }
 
 #[derive(Debug, Default, Clone, clap::Parser, Serialize, Deserialize, PartialEq, Eq)]
@@ -1737,30 +1743,35 @@ async fn install_with_sysroot(
         .physical_root
         .open_dir(&deployment_path)
         .context("Opening deployment dir")?;
-    let postfetch = PostFetchState::new(state, &deployment_dir)?;
 
-    if cfg!(target_arch = "s390x") {
-        // TODO: Integrate s390x support into install_via_bootupd
-        crate::bootloader::install_via_zipl(&rootfs.device_info, boot_uuid)?;
+    if state.config_opts.no_bootloader {
+        tracing::debug!("Skipping bootloader installation (--no-bootloader requested)");
     } else {
-        match postfetch.detected_bootloader {
-            Bootloader::Grub => {
-                crate::bootloader::install_via_bootupd(
-                    &rootfs.device_info,
-                    &rootfs
-                        .target_root_path
-                        .clone()
-                        .unwrap_or(rootfs.physical_root_path.clone()),
-                    &state.config_opts,
-                    Some(&deployment_path.as_str()),
-                )?;
-            }
-            Bootloader::Systemd => {
-                anyhow::bail!("bootupd is required for ostree-based installs");
+        let postfetch = PostFetchState::new(state, &deployment_dir)?;
+
+        if cfg!(target_arch = "s390x") {
+            // TODO: Integrate s390x support into install_via_bootupd
+            crate::bootloader::install_via_zipl(&rootfs.device_info, boot_uuid)?;
+        } else {
+            match postfetch.detected_bootloader {
+                Bootloader::Grub => {
+                    crate::bootloader::install_via_bootupd(
+                        &rootfs.device_info,
+                        &rootfs
+                            .target_root_path
+                            .clone()
+                            .unwrap_or(rootfs.physical_root_path.clone()),
+                        &state.config_opts,
+                        Some(&deployment_path.as_str()),
+                    )?;
+                }
+                Bootloader::Systemd => {
+                    anyhow::bail!("bootupd is required for ostree-based installs");
+                }
             }
         }
+        tracing::debug!("Installed bootloader");
     }
-    tracing::debug!("Installed bootloader");
 
     tracing::debug!("Performing post-deployment operations");
 
@@ -1890,7 +1901,11 @@ async fn install_to_filesystem_impl(
         let (id, verity) = initialize_composefs_repository(state, rootfs).await?;
         tracing::info!("id: {id}, verity: {}", verity.to_hex());
 
-        setup_composefs_boot(rootfs, state, &id).await?;
+        if state.config_opts.no_bootloader {
+            tracing::debug!("Skipping setup composefs boot (--no-bootloader requested)");
+        } else {
+            setup_composefs_boot(rootfs, state, &id).await?;
+        }
     } else {
         ostree_install(state, rootfs, cleanup).await?;
     }
@@ -2138,7 +2153,16 @@ fn remove_all_except_loader_dirs(bootdir: &Dir, is_ostree: bool) -> Result<()> {
 }
 
 #[context("Removing boot directory content")]
-fn clean_boot_directories(rootfs: &Dir, rootfs_path: &Utf8Path, is_ostree: bool) -> Result<()> {
+fn clean_boot_directories(
+    rootfs: &Dir,
+    rootfs_path: &Utf8Path,
+    is_ostree: bool,
+    skip: bool,
+) -> Result<()> {
+    if skip {
+        return Ok(());
+    }
+
     let bootdir =
         crate::utils::open_dir_remount_rw(rootfs, BOOT.into()).context("Opening /boot")?;
 
@@ -2359,7 +2383,13 @@ pub(crate) async fn install_to_filesystem(
                 .await??;
         }
         Some(ReplaceMode::Alongside) => {
-            clean_boot_directories(&target_rootfs_fd, &target_root_path, is_already_ostree)?
+            let skip_cleaning = state.config_opts.no_bootloader;
+            clean_boot_directories(
+                &target_rootfs_fd,
+                &target_root_path,
+                is_already_ostree,
+                skip_cleaning,
+            )?
         }
         None => require_empty_rootdir(&rootfs_fd)?,
     }
@@ -2410,14 +2440,14 @@ pub(crate) async fn install_to_filesystem(
 
     let boot_is_mount = {
         let root_dev = rootfs_fd.dir_metadata()?.dev();
-        let boot_dev = target_rootfs_fd
-            .symlink_metadata_optional(BOOT)?
-            .ok_or_else(|| {
-                anyhow!("No /{BOOT} directory found in root; this is is currently required")
-            })?
-            .dev();
-        tracing::debug!("root_dev={root_dev} boot_dev={boot_dev}");
-        root_dev != boot_dev
+        if let Some(boot_metadata) = target_rootfs_fd.symlink_metadata_optional(BOOT)? {
+            let boot_dev = boot_metadata.dev();
+            tracing::debug!("root_dev={root_dev} boot_dev={boot_dev}");
+            root_dev != boot_dev
+        } else {
+            tracing::debug!("No /{BOOT} directory found");
+            false
+        }
     };
     // Find the UUID of /boot because we need it for GRUB.
     let boot_uuid = if boot_is_mount {
@@ -2461,7 +2491,10 @@ pub(crate) async fn install_to_filesystem(
         .install_config
         .as_ref()
         .and_then(|c| c.boot_mount_spec.as_ref());
-    let mut boot = if let Some(spec) = fsopts.boot_mount_spec.as_ref().or(config_boot_mount_spec) {
+
+    let mut boot = if state.config_opts.no_bootloader {
+        None
+    } else if let Some(spec) = fsopts.boot_mount_spec.as_ref().or(config_boot_mount_spec) {
         // An empty boot mount spec signals to omit the mountspec kargs
         // See https://github.com/bootc-dev/bootc/issues/1441
         if spec.is_empty() {
@@ -2963,4 +2996,14 @@ UUID=boot-uuid /boot ext4 defaults 0 0
 
         Ok(())
     }
+
+    #[test]
+    fn test_clean_boot_directories_explicit_skip() -> Result<()> {
+        let td = cap_std_ext::cap_tempfile::TempDir::new(cap_std::ambient_authority())?;
+        let root_path = Utf8Path::new("/target");
+        // Case: Explicit Skip should succeed even if /boot doesn't exist
+        let res = clean_boot_directories(&td, root_path, false, true);
+        assert!(res.is_ok());
+        Ok(())
+    }
 }

docs/src/man/bootc-install-to-filesystem.8.md

@@ -49,6 +49,11 @@ is currently expected to be empty by default.
 
     The default mode is to "finalize" the target filesystem by invoking `fstrim` and similar operations, and finally mounting it readonly.  This option skips those operations.  It is then the responsibility of the invoking code to perform those operations
 
+**--no-bootloader**
+
+    Disable all bootloader integration and requirements. This allows installing to a
+    filesystem without boot and ESP partitions
+
 **--source-imgref**=*SOURCE_IMGREF*
 
     Install the system from an explicitly given source