feat(initrd): support chaining multiple initrds (#101)

Add linux-initrd-chain to the chainload action and initrd-chain to the
edera action. Each file in the list is read in order and concatenated
into a single initrd. The chain can't be combined with the single
initrd option on the same action.

BLS entries with multiple initrds, either as repeated initrd lines or
as multiple paths on one line, previously only loaded the last one.
Parse all of them and set them in the initrd-0 through initrd-7 slots,
which the autoconfigured BLS action now chains. Unused slots stamp to
the filesystem root and are skipped. Entries with more than 8 initrds
are skipped with a warning.

crates/boot/src/generators/bls.rs

@@ -18,11 +18,18 @@ use uefi::{
     proto::media::fs::SimpleFileSystem,
 };
 
+/// The number of initrd slots set on each BLS entry.
+/// Entries set `initrd-0` through `initrd-7`, and slots without an initrd are empty.
+pub const BLS_INITRD_SLOTS: usize = 8;
+
 // TODO(azenla): remove this once variable substitution is implemented.
-/// This function is used to remove the `tuned_initrd` variable from entry values.
+/// This function is used to remove the `tuned_initrd` variable from the initrd paths.
 /// Fedora uses tuned which adds an initrd that shouldn't be used.
-fn quirk_initrd_remove_tuned(input: String) -> String {
-    input.replace("$tuned_initrd", "").trim().to_string()
+fn quirk_initrd_remove_tuned(paths: Vec<String>) -> Vec<String> {
+    paths
+        .into_iter()
+        .filter(|path| path != "$tuned_initrd")
+        .collect()
 }
 
 /// Sorts two entries according to the BLS sort system.
@@ -139,6 +146,18 @@ pub fn generate(context: Rc<SproutContext>, bls: &BlsConfiguration) -> Result<Ve
             continue;
         }
 
+        // Put the initrds through a quirk modifier to support Fedora.
+        let initrds = quirk_initrd_remove_tuned(entry.initrd_paths());
+
+        // Skip entries with more initrds than there are slots, as they can't be fully loaded.
+        if initrds.len() > BLS_INITRD_SLOTS {
+            warn!(
+                "bls entry {} has more than {} initrds, skipping",
+                name, BLS_INITRD_SLOTS
+            );
+            continue;
+        }
+
         // Produce a new sprout context for the entry with the extracted values.
         let mut context = context.fork();
 
@@ -148,9 +167,6 @@ pub fn generate(context: Rc<SproutContext>, bls: &BlsConfiguration) -> Result<Ve
         let version = entry.version().unwrap_or_default();
         let machine_id = entry.machine_id().unwrap_or_default();
 
-        // Put the initrd through a quirk modifier to support Fedora.
-        let initrd = quirk_initrd_remove_tuned(entry.initrd_path().unwrap_or_default());
-
         // Combine the title with the version if a version is present, except if it already contains it.
         // Sometimes BLS will have a version in the title already, and this makes it unique.
         let title_full = if !version.is_empty() && !title_base.contains(&version) {
@@ -163,7 +179,19 @@ pub fn generate(context: Rc<SproutContext>, bls: &BlsConfiguration) -> Result<Ve
         context.set("title", title_full);
         context.set("chainload", chainload);
         context.set("options", options);
-        context.set("initrd", initrd);
+        // The initrd value keeps the last initrd, which is what it held before
+        // multiple initrds were supported.
+        context.set("initrd", initrds.last().cloned().unwrap_or_default());
+
+        // Set every initrd slot, even the unused ones. An unset slot would let "$initrd-1"
+        // match "$initrd" instead, producing the initrd value followed by "-1".
+        for slot in 0..BLS_INITRD_SLOTS {
+            context.set(
+                format!("initrd-{}", slot),
+                initrds.get(slot).cloned().unwrap_or_default(),
+            );
+        }
+
         context.set("version", version);
         context.set("machine-id", machine_id);