install: Enable installing to multi device parents

When the root filesystem spans multiple backing devices (e.g., LVM
across multiple disks), discover all parent devices and find ESP
partitions on each. For bootupd/GRUB, install the bootloader to all
devices with an ESP partition, enabling boot from any disk in a
multi-disk setup. systemd-boot and zipl only support single-device
configurations.

This adds a new integration test validating both single-ESP and dual-ESP
multi-device scenarios.

Fixes: #481

Assisted-by: Claude Code (Opus 4.5)
Signed-off-by: ckyrouac <ckyrouac@redhat.com>

Author: ckyrouac

crates/lib/src/bootc_composefs/boot.rs

@@ -520,8 +520,23 @@ pub(crate) fn setup_composefs_bls_boot(
 
             cmdline_options.extend(&Cmdline::from(&composefs_cmdline));
 
-            // Locate ESP partition device
-            let esp_part = esp_in(&root_setup.device_info)?;
+            // Find all ESP partitions across all backing devices.
+            // For composefs with systemd-boot, we only support a single ESP.
+            let mut esp_parts: Vec<&bootc_blockdev::Partition> = Vec::new();
+            for device in &root_setup.device_info {
+                if let Some(esp) = device.find_partition_of_esp()? {
+                    esp_parts.push(esp);
+                }
+            }
+            let esp_part = match esp_parts.len() {
+                0 => {
+                    anyhow::bail!("Cannot locate ESP: no ESP partition found on any backing device")
+                }
+                1 => esp_parts.into_iter().next().unwrap(),
+                n => anyhow::bail!(
+                    "Found {n} ESP partitions across backing devices; only a single ESP is supported for composefs boot"
+                ),
+            };
 
             (
                 root_setup.physical_root_path.clone(),
@@ -1063,7 +1078,12 @@ pub(crate) fn setup_composefs_uki_boot(
         BootSetupType::Setup((root_setup, state, postfetch, ..)) => {
             state.require_no_kargs_for_uki()?;
 
-            let esp_part = esp_in(&root_setup.device_info)?;
+            //TODO: Handle multiple devices (RAID, LVM, etc)
+            let device_info = root_setup
+                .device_info
+                .first()
+                .ok_or_else(|| anyhow!("Cannot locate ESP: no backing device found"))?;
+            let esp_part = esp_in(device_info)?;
 
             (
                 root_setup.physical_root_path.clone(),
@@ -1233,7 +1253,8 @@ pub(crate) async fn setup_composefs_boot(
 
     if cfg!(target_arch = "s390x") {
         // TODO: Integrate s390x support into install_via_bootupd
-        crate::bootloader::install_via_zipl(&root_setup.device_info, boot_uuid)?;
+        // zipl only supports single device
+        crate::bootloader::install_via_zipl(root_setup.device_info.first(), boot_uuid)?;
     } else if postfetch.detected_bootloader == Bootloader::Grub {
         crate::bootloader::install_via_bootupd(
             &root_setup.device_info,
@@ -1242,8 +1263,9 @@ pub(crate) async fn setup_composefs_boot(
             None,
         )?;
     } else {
+        // systemd-boot only supports single device
         crate::bootloader::install_systemd_boot(
-            &root_setup.device_info,
+            root_setup.device_info.first(),
             &root_setup.physical_root_path,
             &state.config_opts,
             None,

crates/lib/src/bootloader.rs

@@ -82,7 +82,7 @@ pub(crate) fn supports_bootupd(root: &Dir) -> Result<bool> {
 
 #[context("Installing bootloader")]
 pub(crate) fn install_via_bootupd(
-    device: &PartitionTable,
+    devices: &[PartitionTable],
     rootfs: &Utf8Path,
     configopts: &crate::install::InstallConfigOpts,
     deployment_path: Option<&str>,
@@ -97,26 +97,61 @@ pub(crate) fn install_via_bootupd(
     } else {
         vec![]
     };
-    let devpath = device.path();
-    println!("Installing bootloader via bootupd");
-    Command::new("bootupctl")
-        .args(["backend", "install", "--write-uuid"])
-        .args(verbose)
-        .args(bootupd_opts.iter().copied().flatten())
-        .args(src_root_arg)
-        .args(["--device", devpath.as_str(), rootfs.as_str()])
-        .log_debug()
-        .run_inherited_with_cmd_context()
+
+    // No backing devices with ESP found. Run bootupd without --device and let it
+    // try to auto-detect. This works for:
+    // - BIOS boot (uses MBR, not ESP)
+    // - Systems where bootupd can find ESP via mounted /boot/efi
+    // UEFI boot will fail if bootupd cannot locate the ESP.
+    if devices.is_empty() {
+        tracing::warn!(
+            "No backing device with ESP found; UEFI boot may fail if ESP cannot be auto-detected"
+        );
+        println!("Installing bootloader via bootupd (no target device specified)");
+        return Command::new("bootupctl")
+            .args(["backend", "install", "--write-uuid"])
+            .args(verbose)
+            .args(bootupd_opts.iter().copied().flatten())
+            .args(&src_root_arg)
+            .arg(rootfs.as_str())
+            .log_debug()
+            .run_inherited_with_cmd_context();
+    }
+
+    // Install bootloader to each device
+    for dev in devices {
+        let devpath = dev.path();
+        println!("Installing bootloader via bootupd to {devpath}");
+        Command::new("bootupctl")
+            .args(["backend", "install", "--write-uuid"])
+            .args(verbose)
+            .args(bootupd_opts.iter().copied().flatten())
+            .args(&src_root_arg)
+            .args(["--device", devpath.as_str()])
+            .arg(rootfs.as_str())
+            .log_debug()
+            .run_inherited_with_cmd_context()?;
+    }
+
+    Ok(())
 }
 
 #[context("Installing bootloader")]
 pub(crate) fn install_systemd_boot(
-    device: &PartitionTable,
+    device: Option<&PartitionTable>,
     _rootfs: &Utf8Path,
     _configopts: &crate::install::InstallConfigOpts,
     _deployment_path: Option<&str>,
     autoenroll: Option<SecurebootKeys>,
 ) -> Result<()> {
+    // systemd-boot requires the backing device to locate the ESP partition
+    let device = device.ok_or_else(|| {
+        anyhow!(
+            "Cannot install systemd-boot: no single backing device found \
+             (root may span multiple devices such as LVM across multiple disks)"
+        )
+    })?;
+
     let esp_part = device
         .find_partition_of_type(discoverable_partition_specification::ESP)
         .ok_or_else(|| anyhow::anyhow!("ESP partition not found"))?;
@@ -161,7 +196,15 @@ pub(crate) fn install_systemd_boot(
 }
 
 #[context("Installing bootloader using zipl")]
-pub(crate) fn install_via_zipl(device: &PartitionTable, boot_uuid: &str) -> Result<()> {
+pub(crate) fn install_via_zipl(device: Option<&PartitionTable>, boot_uuid: &str) -> Result<()> {
+    // zipl requires the backing device information to install the bootloader
+    let device = device.ok_or_else(|| {
+        anyhow!(
+            "Cannot install zipl bootloader: no single backing device found \
+             (root may span multiple devices such as LVM across multiple disks)"
+        )
+    })?;
+
     // Identify the target boot partition from UUID
     let fs = mount::inspect_filesystem_by_uuid(boot_uuid)?;
     let boot_dir = Utf8Path::new(&fs.target);

crates/lib/src/install.rs

@@ -1141,7 +1141,10 @@ pub(crate) fn exec_in_host_mountns(args: &[std::ffi::OsString]) -> Result<()> {
 pub(crate) struct RootSetup {
     #[cfg(feature = "install-to-disk")]
     luks_device: Option<String>,
-    pub(crate) device_info: bootc_blockdev::PartitionTable,
+    /// Information about the backing block device partition tables.
+    /// Contains all devices that have an ESP partition when the root filesystem
+    /// spans multiple backing devices (e.g., LVM across multiple disks).
+    pub(crate) device_info: Vec<bootc_blockdev::PartitionTable>,
     /// Absolute path to the location where we've mounted the physical
     /// root filesystem for the system we're installing.
     pub(crate) physical_root_path: Utf8PathBuf,
@@ -1602,7 +1605,9 @@ async fn install_with_sysroot(
 
     if cfg!(target_arch = "s390x") {
         // TODO: Integrate s390x support into install_via_bootupd
-        crate::bootloader::install_via_zipl(&rootfs.device_info, boot_uuid)?;
+        // zipl only supports single device
+        let device = rootfs.device_info.first();
+        crate::bootloader::install_via_zipl(device, boot_uuid)?;
     } else {
         match postfetch.detected_bootloader {
             Bootloader::Grub => {
@@ -1733,15 +1738,21 @@ async fn install_to_filesystem_impl(
     // Drop exclusive ownership since we're done with mutation
     let rootfs = &*rootfs;
 
-    match &rootfs.device_info.label {
-        bootc_blockdev::PartitionType::Dos => crate::utils::medium_visibility_warning(
-            "Installing to `dos` format partitions is not recommended",
-        ),
-        bootc_blockdev::PartitionType::Gpt => {
-            // The only thing we should be using in general
-        }
-        bootc_blockdev::PartitionType::Unknown(o) => {
-            crate::utils::medium_visibility_warning(&format!("Unknown partition label {o}"))
+    // Check partition type of all backing devices
+    for device_info in &rootfs.device_info {
+        match &device_info.label {
+            bootc_blockdev::PartitionType::Dos => {
+                crate::utils::medium_visibility_warning(&format!(
+                    "Installing to `dos` format partitions is not recommended: {}",
+                    device_info.path()
+                ))
+            }
+            bootc_blockdev::PartitionType::Gpt => {
+                // The only thing we should be using in general
+            }
+            bootc_blockdev::PartitionType::Unknown(o) => crate::utils::medium_visibility_warning(
+                &format!("Unknown partition label {o}: {}", device_info.path()),
+            ),
         }
     }
 
@@ -2291,27 +2302,69 @@ pub(crate) async fn install_to_filesystem(
     };
     tracing::debug!("boot UUID: {boot_uuid:?}");
 
-    // Find the real underlying backing device for the root.  This is currently just required
-    // for GRUB (BIOS) and in the future zipl (I think).
-    let backing_device = {
+    // Walk up the block device hierarchy to find physical backing device(s).
+    // Examples:
+    //   /dev/sda3 -> /dev/sda (single disk)
+    //   /dev/mapper/vg-lv -> /dev/sda2, /dev/sdb2 (LVM across two disks)
+    let backing_devices: Vec<String> = {
         let mut dev = inspect.source;
         loop {
             tracing::debug!("Finding parents for {dev}");
-            let mut parents = bootc_blockdev::find_parent_devices(&dev)?.into_iter();
-            let Some(parent) = parents.next() else {
-                break;
-            };
-            if let Some(next) = parents.next() {
-                anyhow::bail!(
-                    "Found multiple parent devices {parent} and {next}; not currently supported"
+            let parents = bootc_blockdev::find_parent_devices(&dev)?;
+            if parents.is_empty() {
+                // Reached a physical disk
+                break vec![dev];
+            }
+            if parents.len() > 1 {
+                // Multi-device (e.g., LVM across disks) - return all
+                tracing::debug!(
+                    "Found multiple parent devices: {:?}; will search for ESP",
+                    parents
                 );
+                break parents;
+            }
+            // Single parent (e.g. LVM LV -> VG -> PV) - keep walking up
+            dev = parents.into_iter().next().unwrap();
+        }
+    };
+    tracing::debug!("Backing devices: {backing_devices:?}");
+
+    // Determine the device and partition info to use for bootloader installation.
+    // If there are multiple backing devices, we search for all that contain an ESP.
+    let device_info: Vec<bootc_blockdev::PartitionTable> = if backing_devices.len() == 1 {
+        // Single backing device - use it directly
+        let dev = &backing_devices[0];
+        vec![bootc_blockdev::partitions_of(Utf8Path::new(dev))?]
+    } else {
+        // Multiple backing devices - find all with ESP
+        let mut esp_devices = Vec::new();
+        for dev in &backing_devices {
+            match bootc_blockdev::partitions_of(Utf8Path::new(dev)) {
+                Ok(table) => {
+                    if table.find_partition_of_esp()?.is_some() {
+                        tracing::info!("Found ESP on device {dev}");
+                        esp_devices.push(table);
+                    }
+                }
+                Err(e) => {
+                    // Some backing devices may not have partition tables (e.g., raw LVM PVs
+                    // or whole-disk filesystems). These can't have an ESP, so skip them.
+                    tracing::debug!("Failed to read partition table from {dev}: {e}");
+                }
             }
-            dev = parent;
         }
-        dev
+        if esp_devices.is_empty() {
+            // No ESP found on any backing device. This is not fatal because:
+            // - BIOS boot uses MBR, not ESP
+            // - bootupd may auto-detect ESP via mounted /boot/efi
+            // However, UEFI boot without a detectable ESP will fail.
+            tracing::warn!(
+                "No ESP found on any backing device ({:?}); UEFI boot may fail",
+                backing_devices
+            );
+        }
+        esp_devices
     };
-    tracing::debug!("Backing device: {backing_device}");
-    let device_info = bootc_blockdev::partitions_of(Utf8Path::new(&backing_device))?;
 
     let rootarg = format!("root={}", root_info.mount_spec);
     let mut boot = if let Some(spec) = fsopts.boot_mount_spec {

crates/lib/src/install/baseline.rs

@@ -485,7 +485,7 @@ pub(crate) fn install_create_rootfs(
         BlockSetup::Direct => None,
         BlockSetup::Tpm2Luks => Some(luks_name.to_string()),
     };
-    let device_info = bootc_blockdev::partitions_of(&devpath)?;
+    let device_info = vec![bootc_blockdev::partitions_of(&devpath)?];
     Ok(RootSetup {
         luks_device,
         device_info,

tmt/plans/integration.fmf

@@ -166,4 +166,10 @@ execute:
     how: fmf
     test:
       - /tmt/tests/tests/test-33-bib-build
+/plan-34-multi-device-esp:
+  summary: Test multi-device ESP detection for to-existing-root
+  discover:
+    how: fmf
+    test:
+      - /tmt/tests/test-32-multi-device-esp
 # END GENERATED PLANS