cfs/rollback: Update the way we get rollback

Instead of blindly selecting the "second" one in a list of sorted boot
entries as the rollback and failing if there are more than one rollback
candidate, sort the rollback candidates in the same order as the boot
entries and take the first one as rollback.

All the remaining deployments become `other_deployments`. This is
especially useful if and when we implement pinned deployments for
composefs

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

Author: Johan-Liebert1

crates/lib/src/bootc_composefs/status.rs

@@ -1,4 +1,4 @@
-use std::{collections::HashSet, io::Read, sync::OnceLock};
+use std::{io::Read, sync::OnceLock};
 
 use anyhow::{Context, Result};
 use bootc_kernel_cmdline::utf8::Cmdline;
@@ -831,7 +831,6 @@ async fn composefs_deployment_status_from(
         Err(e) => Err(e),
     }?;
 
-    // NOTE: This cannot work if we support both BLS and UKI at the same time
     let mut boot_type: Option<BootType> = None;
 
     // Boot entries from deployments that are neither booted nor staged deployments
@@ -966,6 +965,8 @@ async fn composefs_deployment_status_from(
 
     // Determine rollback deployment by matching extra deployment boot entries against entires read from /boot
     // This collects verity digest across bls and grub enties, we should just have one of them, but still works
+    //
+    // We want this ordered, so we have a vector here
     let bootloader_configured_verity = sorted_bls_config
         .iter()
         .flatten()
@@ -976,9 +977,9 @@ async fn composefs_deployment_status_from(
                 .flatten()
                 .map(|menu| menu.get_verity()),
         )
-        .collect::<Result<HashSet<_>>>()?;
+        .collect::<Result<Vec<_>>>()?;
 
-    let rollback_candidates: Vec<_> = extra_deployment_boot_entries
+    let mut rollback_candidates: Vec<_> = extra_deployment_boot_entries
         .into_iter()
         .filter(|entry| {
             let verity = &entry
@@ -990,10 +991,22 @@ async fn composefs_deployment_status_from(
         })
         .collect();
 
-    if rollback_candidates.len() > 1 {
-        anyhow::bail!("Multiple extra entries in /boot, could not determine rollback entry");
-    } else if let Some(rollback_entry) = rollback_candidates.into_iter().next() {
-        host.status.rollback = Some(rollback_entry);
+    // We get sorted bootloader entries, so here we re-sort the rollback candidates
+    // wrt their positions in the sorted bootloader entries as that's what determines
+    // what's shown on the bootloader menu. The very next boot entry, that's not the
+    // default should be the rollback
+    rollback_candidates.sort_by_key(|ent| {
+        bootloader_configured_verity
+            .iter()
+            // SAFETY: ent.composefs will definitely exist
+            .position(|v| ent.composefs.as_ref().unwrap().verity == *v)
+    });
+
+    if !rollback_candidates.is_empty() {
+        let mut iter = rollback_candidates.into_iter();
+
+        host.status.rollback = iter.next();
+        host.status.other_deployments = iter.collect();
     }
 
     host.status.rollback_queued = is_rollback_queued;