Allow passing absolute paths to initrd and vmlinuz

Grub needs absolute paths to initrd and vmlinuz if we do not have
`/boot` in a boot partition, which we do not in bootc.

Add param `boot_subdir` which acts like a subdirectory in the boot
directory in case the boot partition is mounted in another directory.

Signed-off-by: Pragyan Poudyal <[email protected]>

Author: Johan-Liebert1

crates/cfsctl/src/main.rs

@@ -279,6 +279,7 @@ async fn main() -> Result<()> {
                     entry,
                     &id,
                     bootdir,
+                    None,
                     entry_id.as_deref(),
                     &cmdline_refs,
                 )?;

crates/composefs-boot/src/bootloader.rs

@@ -144,7 +144,7 @@ impl<ObjectID: FsVerityHashValue> Type1Entry<ObjectID> {
     // This is a bit of a strange operation: for each file mentioned in the bootloader entry, move
     // the file into the given 'entry_id' pathname and rename the entry file itself to
     // "{entry_id}.conf".
-    pub fn relocate(&mut self, entry_id: &str) {
+    pub fn relocate(&mut self, boot_subdir: Option<&str>, entry_id: &str) {
         self.filename = Box::from(format!("{entry_id}.conf").as_ref());
         for line in &mut self.entry.lines {
             for key in ["linux", "initrd", "efi"] {
@@ -159,7 +159,14 @@ impl<ObjectID: FsVerityHashValue> Type1Entry<ObjectID> {
 
                 let new = format!("/{entry_id}/{basename}");
                 let range = substr_range(line, value).unwrap();
-                line.replace_range(range, &new);
+
+                let final_entry_path = if let Some(boot_subdir) = boot_subdir {
+                    format!("/{boot_subdir}{new}")
+                } else {
+                    new.clone()
+                };
+
+                line.replace_range(range, &final_entry_path);
 
                 if let Some(file) = file {
                     self.files.insert(new.into_boxed_str(), file);

crates/composefs-boot/src/write_boot.rs

@@ -16,10 +16,18 @@ use crate::{
 pub fn write_t1_simple<ObjectID: FsVerityHashValue>(
     mut t1: Type1Entry<ObjectID>,
     bootdir: &Path,
+    boot_subdir: Option<&str>,
     root_id: &ObjectID,
     cmdline_extra: &[&str],
     repo: &Repository<ObjectID>,
 ) -> Result<()> {
+    let bootdir = if let Some(subdir) = boot_subdir {
+        let subdir_path = Path::new(subdir);
+        bootdir.join(subdir_path.strip_prefix("/").unwrap_or(subdir_path))
+    } else {
+        bootdir.to_path_buf()
+    };
+
     t1.entry
         .adjust_cmdline(Some(&root_id.to_hex()), cmdline_extra);
 
@@ -63,35 +71,78 @@ pub fn write_t2_simple<ObjectID: FsVerityHashValue>(
     Ok(())
 }
 
+/// Writes boot entry to the boot partition
+///
+/// # Arguments
+///
+/// * repo           - The composefs repository
+/// * entry          - Boot entry variant to be written
+/// * root_id        - The content hash of the generated EROFS image id
+/// * boot_partition - Path to the boot partition/directory
+/// * boot_subdir    - If `Some(path)`, the path is prepended to `initrd` and `linux` keys in the BLS entry
+///
+/// For example, if `boot_partition = "/boot"` and `boot_subdir = Some("1")` ,
+/// the BLS entry will contain
+///
+/// ```text
+/// linux /boot/1/<entry_id>/linux
+/// initrd /boot/1/<entry_id>/initrd
+/// ```
+///
+/// If `boot_partition = "/boot"` and `boot_subdir = None` , the BLS entry will contain
+///
+/// ```text
+/// linux /<entry_id>/linux
+/// initrd /<entry_id>/initrd
+/// ```
+///
+/// * entry_id       - In case of a BLS entry, the name of file to be generated in `loader/entries`
+/// * cmdline_extra  - Extra kernel command line arguments
+///
 pub fn write_boot_simple<ObjectID: FsVerityHashValue>(
     repo: &Repository<ObjectID>,
     entry: BootEntry<ObjectID>,
     root_id: &ObjectID,
-    bootdir: &Path,
+    boot_partition: &Path,
+    boot_subdir: Option<&str>,
     entry_id: Option<&str>,
     cmdline_extra: &[&str],
 ) -> Result<()> {
     match entry {
         BootEntry::Type1(mut t1) => {
             if let Some(name) = entry_id {
-                t1.relocate(name);
+                t1.relocate(boot_subdir, name);
             }
-            write_t1_simple(t1, bootdir, root_id, cmdline_extra, repo)?;
+            write_t1_simple(
+                t1,
+                boot_partition,
+                boot_subdir,
+                root_id,
+                cmdline_extra,
+                repo,
+            )?;
         }
         BootEntry::Type2(mut t2) => {
             if let Some(name) = entry_id {
                 t2.rename(name);
             }
             ensure!(cmdline_extra.is_empty(), "Can't add --cmdline args to UKIs");
-            write_t2_simple(t2, bootdir, root_id, repo)?;
+            write_t2_simple(t2, boot_partition, root_id, repo)?;
         }
         BootEntry::UsrLibModulesUki(_entry) => todo!(),
         BootEntry::UsrLibModulesVmLinuz(entry) => {
             let mut t1 = entry.into_type1(entry_id);
             if let Some(name) = entry_id {
-                t1.relocate(name)?;
+                t1.relocate(boot_subdir, name);
             }
-            write_t1_simple(t1, bootdir, root_id, cmdline_extra, repo)?;
+            write_t1_simple(
+                t1,
+                boot_partition,
+                boot_subdir,
+                root_id,
+                cmdline_extra,
+                repo,
+            )?;
         }
     };