composefs/boot: Fix sd-boot order on update

Grub sorts its BLS config in descending order, while sd-boot sorts the
configs in ascending order. While upgrading we were always setting the
new sort key to be `1` which would work for Grub but not for sd-boot.

Fixes: #1777

Signed-off-by: Pragyan Poudyal <pragyanpoudyal41999@gmail.com>

Author: Johan-Liebert1

crates/lib/src/bootc_composefs/boot.rs

@@ -474,7 +474,8 @@ pub(crate) fn setup_composefs_bls_boot(
             let boot_digest = compute_boot_digest(usr_lib_modules_vmlinuz, &repo)
                 .context("Computing boot digest")?;
 
-            let default_sort_key = "1";
+            let default_sort_key = bootloader.default_sort_key();
+
             let default_title_version = (id.to_hex(), default_sort_key.to_string());
 
             let osrel_res = osrel_title_and_version(fs, &repo)?;
@@ -540,7 +541,7 @@ pub(crate) fn setup_composefs_bls_boot(
         let boot_dir = Dir::open_ambient_dir(&entry_paths.config_path, ambient_authority())?;
 
         let mut booted_bls = get_booted_bls(&boot_dir)?;
-        booted_bls.sort_key = Some("0".into()); // entries are sorted by their filename in reverse order
+        booted_bls.sort_key = Some(bootloader.secondary_sort_key().into());
 
         // This will be atomically renamed to 'loader/entries' on shutdown/reboot
         (
@@ -788,7 +789,7 @@ fn write_systemd_uki_config(
     boot_label: UKILabels,
     id: &Sha512HashValue,
 ) -> Result<()> {
-    let default_sort_key = "0";
+    let default_sort_key = Bootloader::SYSTEMD_PRIMARY_SORT_KEY;
 
     let mut bls_conf = BLSConfig::default();
     bls_conf

crates/lib/src/spec.rs

@@ -197,6 +197,31 @@ impl FromStr for Bootloader {
     }
 }
 
+impl Bootloader {
+    pub(crate) const SYSTEMD_PRIMARY_SORT_KEY: &str = "0";
+    // Grub entries are sorted by their filename in reverse order
+    pub(crate) const GRUB_PRIMARY_SORT_KEY: &str = "1";
+
+    pub(crate) const SYSTEMD_SECONDARY_SORT_KEY: &str = "1";
+    pub(crate) const GRUB_SECONDARY_SORT_KEY: &str = "0";
+
+    /// Sort key for the primary BLS entry
+    pub(crate) fn default_sort_key(&self) -> &str {
+        match self {
+            Bootloader::Grub => Self::GRUB_PRIMARY_SORT_KEY,
+            Bootloader::Systemd => Self::SYSTEMD_PRIMARY_SORT_KEY,
+        }
+    }
+
+    /// Sort key for the secondary BLS entry
+    pub(crate) fn secondary_sort_key(&self) -> &str {
+        match self {
+            Bootloader::Grub => Self::GRUB_SECONDARY_SORT_KEY,
+            Bootloader::Systemd => Self::SYSTEMD_SECONDARY_SORT_KEY,
+        }
+    }
+}
+
 /// A bootable entry
 #[derive(Debug, Clone, Serialize, Deserialize, PartialEq, Eq, JsonSchema)]
 #[serde(rename_all = "camelCase")]