lib: Fallback to partition table for ESP

Currently, the installation requires the ESP to be explicitly mounted.
This change allows the bootloader logic to locate the ESP by scanning
the partition table if the mount check fails.

The baseline installation path is updated to allow this fallback,
improving robustness when the filesystem is not fully mounted.

Signed-off-by: Daniele Guarascio <guarascio.daniele@gmail.com>

Author: Guara92

crates/lib/src/bootc_composefs/boot.rs

@@ -1291,6 +1291,7 @@ pub(crate) async fn setup_composefs_boot(
             &state.config_opts,
             None,
             get_secureboot_keys(&mounted_fs, BOOTC_AUTOENROLL_PATH)?,
+            root_setup.require_esp_mount,
         )?;
     }
 

crates/lib/src/bootloader.rs

@@ -72,6 +72,28 @@ pub(crate) fn require_boot_efi_mount(root: &Dir) -> Result<String> {
     Ok(source)
 }
 
+/// Helper to find the ESP device, either via mount or partition table scan
+pub(crate) fn get_esp_device(
+    root: &Dir,
+    device_info: &PartitionTable,
+    require_mount: bool,
+) -> Result<String> {
+    if require_mount {
+        require_boot_efi_mount(root)
+    } else {
+        match require_boot_efi_mount(root) {
+            Ok(p) => Ok(p),
+            Err(e) => {
+                tracing::debug!(
+                    "ESP mount check failed in permissive mode: {e}; falling back to partition table scan"
+                );
+                let esp = esp_in(device_info)?;
+                Ok(esp.node.clone())
+            }
+        }
+    }
+}
+
 /// Determine if the invoking environment contains bootupd, and if there are bootupd-based
 /// updates in the target root.
 #[context("Querying for bootupd")]
@@ -180,13 +202,14 @@ pub(crate) fn install_via_bootupd(
 #[context("Installing bootloader")]
 pub(crate) fn install_systemd_boot(
     root: &Dir,
-    _device: &PartitionTable,
+    device: &PartitionTable,
     _rootfs: &Utf8Path,
     _configopts: &crate::install::InstallConfigOpts,
     _deployment_path: Option<&str>,
     autoenroll: Option<SecurebootKeys>,
+    require_mount: bool,
 ) -> Result<()> {
-    let esp_device = require_boot_efi_mount(root)?;
+    let esp_device = get_esp_device(root, device, require_mount)?;
 
     let esp_mount = mount_esp(&esp_device).context("Mounting ESP")?;
     let esp_path = Utf8Path::from_path(esp_mount.dir.path())

crates/lib/src/install/baseline.rs

@@ -496,6 +496,6 @@ pub(crate) fn install_create_rootfs(
         boot,
         kargs,
         skip_finalize: false,
-        require_esp_mount: true,
+        require_esp_mount: false,
     })
 }