feat(bls): read the extended boot loader partition in the BLS generator

Add an xbootldr option to the BLS generator. When it is enabled, the
partition with the XBOOTLDR type on the same disk as Sprout's partition
is read as well, and its entries and unified kernel images are sorted
with the others. As their files are on that partition, every entry has
an entry-root value, which is the device of the partition or nothing for
Sprout's own, to use in a path like $entry-root\$chainload. It is off
by default, as existing actions would look for the files on the wrong
partition.

crates/boot/src/autoconfigure/bls.rs

@@ -102,6 +102,9 @@ pub fn scan(
         },
         path: format!("{}\\loader", root),
         uki_path: None,
+        // Every filesystem is scanned, including the Extended Boot Loader Partition, which
+        // gets a generator of its own.
+        xbootldr: false,
         pin_names: true,
     };
 

crates/boot/src/generators/bls.rs

@@ -66,6 +66,7 @@ fn bootable_entry(
     name: &str,
     entry: &BlsEntry,
     initrds: &[String],
+    entry_root: &str,
 ) -> BootableEntry {
     // Produce a new sprout context for the entry with the extracted values.
     let mut context = context.fork();
@@ -84,6 +85,9 @@ fn bootable_entry(
         title_base.clone()
     };
 
+    // The device that the files of the entry are on, for a path like "$entry-root\\$chainload".
+    // It is empty for the partition that Sprout was loaded from.
+    context.set("entry-root", entry_root.to_string());
     context.set("title-base", title_base);
     context.set("title", title_full);
     context.set("chainload", chainload);
@@ -132,6 +136,7 @@ fn generate_type1(
     context: &Rc<SproutContext>,
     bls: &BlsConfiguration,
     path: &str,
+    entry_root: &str,
 ) -> Result<Vec<(BlsEntry, BootableEntry)>> {
     let mut entries = Vec::new();
 
@@ -259,7 +264,7 @@ fn generate_type1(
             continue;
         }
 
-        let mut boot = bootable_entry(context, bls, &name, &entry, &initrds);
+        let mut boot = bootable_entry(context, bls, &name, &entry, &initrds, entry_root);
         boot.set_id_suffix(&extension);
 
         // Record where the boot counter lives so a try can be consumed when this entry boots.
@@ -287,6 +292,7 @@ fn generate_type2(
     context: &Rc<SproutContext>,
     bls: &BlsConfiguration,
     uki_path: &str,
+    entry_root: &str,
     entries: &[(BlsEntry, BootableEntry)],
 ) -> Result<Vec<(BlsEntry, BootableEntry)>> {
     let resolved = eficore::path::resolve_path(Some(context.root().loaded_image_path()?), uki_path)
@@ -356,7 +362,7 @@ fn generate_type2(
             let mut entry = profile.entry;
             entry.boot_counter = boot_counter;
 
-            let mut boot = bootable_entry(context, bls, &name, &entry, &[]);
+            let mut boot = bootable_entry(context, bls, &name, &entry, &[], entry_root);
             boot.set_id_suffix(&extension);
             if let Some(ref suffix) = suffix {
                 boot.set_id_profile(suffix);
@@ -392,18 +398,19 @@ fn generate_type2(
     Ok(found)
 }
 
-/// Generates entries from the BLS entries directory and the unified kernel image directory
-/// using the specified `bls` configuration and `context`. The BLS conversion is best-effort
-/// and will ignore any unsupported entries.
-pub fn generate(context: Rc<SproutContext>, bls: &BlsConfiguration) -> Result<Vec<BootableEntry>> {
-    // Stamp the path to the BLS directory.
-    let path = context.stamp(&bls.path);
-
-    let uki_path = bls.uki_path_for(&path);
-
+/// Generates the entries of one partition, from the BLS entries directory at `bls_path` and the
+/// unified kernel image directory at `uki_path`, if there is one. The files of the entries are on
+/// the device `entry_root`.
+fn generate_partition(
+    context: &Rc<SproutContext>,
+    bls: &BlsConfiguration,
+    bls_path: &str,
+    uki_path: Option<&str>,
+    entry_root: &str,
+) -> Result<Vec<(BlsEntry, BootableEntry)>> {
     // A problem reading the Type #1 entries only stops the unified kernel images when there
     // are none to add, so that either kind of entry can still boot.
-    let mut entries = match generate_type1(&context, bls, &path) {
+    let mut entries = match generate_type1(context, bls, bls_path, entry_root) {
         Ok(entries) => entries,
         Err(error) if uki_path.is_some() => {
             warn!("unable to generate bls entries: {:#}", error);
@@ -415,8 +422,8 @@ pub fn generate(context: Rc<SproutContext>, bls: &BlsConfiguration) -> Result<Ve
     // Add the unified kernel images, unless that is disabled. A problem scanning them
     // should not prevent booting the other entries.
     if let Some(uki_path) = uki_path {
-        let uki_path = context.stamp(&uki_path);
-        match generate_type2(&context, bls, &uki_path, &entries) {
+        let uki_path = context.stamp(uki_path);
+        match generate_type2(context, bls, &uki_path, entry_root, &entries) {
             Ok(found) => entries.extend(found),
             Err(error) => warn!(
                 "unable to generate unified kernel image entries: {:#}",
@@ -424,6 +431,74 @@ pub fn generate(context: Rc<SproutContext>, bls: &BlsConfiguration) -> Result<Ve
             ),
         }
     }
+    Ok(entries)
+}
+
+/// Finds the root of the Extended Boot Loader Partition on the disk that Sprout was loaded from,
+/// as the text of the device with a trailing slash. None if there is no such partition.
+fn xbootldr_root(context: &Rc<SproutContext>) -> Result<Option<String>> {
+    let Some(path) = eficore::xbootldr::find_xbootldr(context.root().loaded_image_path()?)? else {
+        return Ok(None);
+    };
+    let mut root = path
+        .to_string16(DisplayOnly(false), AllowShortcuts(false))
+        .context("unable to convert the xbootldr device path to a string")?
+        .to_string();
+    // Add a trailing forward-slash to the root to ensure the device root is completed.
+    root.push('/');
+    Ok(Some(root))
+}
+
+/// Generates entries from the BLS entries directory and the unified kernel image directory
+/// using the specified `bls` configuration and `context`, and from the Extended Boot Loader
+/// Partition if that is enabled. The BLS conversion is best-effort and will ignore any
+/// unsupported entries.
+pub fn generate(context: Rc<SproutContext>, bls: &BlsConfiguration) -> Result<Vec<BootableEntry>> {
+    // Stamp the path to the BLS directory.
+    let path = context.stamp(&bls.path);
+
+    let uki_path = bls.uki_path_for(&path);
+    let mut entries = generate_partition(
+        &context,
+        bls,
+        &path,
+        uki_path.as_deref(),
+        BlsConfiguration::root_of(&path),
+    )?;
+
+    // Add the entries of the Extended Boot Loader Partition, which are sorted together with the
+    // others. A problem with it should not prevent booting from the entries that are found.
+    if bls.xbootldr {
+        match xbootldr_root(&context) {
+            Ok(Some(root)) => {
+                let xbootldr_uki = uki_path.as_ref().map(|_| format!("{}\\EFI\\Linux", root));
+                match generate_partition(
+                    &context,
+                    bls,
+                    &format!("{}\\loader", root),
+                    xbootldr_uki.as_deref(),
+                    &root,
+                ) {
+                    Ok(found) => {
+                        for (entry, boot) in found {
+                            // An entry that is on both partitions would be ambiguous.
+                            if entries.iter().any(|(_, other)| other.id() == boot.id()) {
+                                warn!(
+                                    "xbootldr entry {} has the same id as another entry, skipping",
+                                    boot.id()
+                                );
+                            } else {
+                                entries.push((entry, boot));
+                            }
+                        }
+                    }
+                    Err(error) => warn!("unable to generate xbootldr entries: {:#}", error),
+                }
+            }
+            Ok(None) => info!("no xbootldr partition was found"),
+            Err(error) => warn!("unable to find the xbootldr partition: {:#}", error),
+        }
+    }
 
     // Sort all the entries according to the BLS sort system.
     entries.sort_by(sort_entries);