fix import/discovery panic (openzfs#523)

When starting the agent and discovering zettacaches, if there's an old zettacache (with an older on-disk format) present, the agent crashes. We should instead ignore this old cache. Bonus cleanup: document recommended relationship between tunables.
pcd1193182 · Jul 26, 2022 · 0dea6d8 · 0dea6d8
1 parent 48a470b
commit 0dea6d8
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Showing 3 changed files with 11 additions and 10 deletions.
diff --git a/cmd/zfs_object_agent/zettacache/src/open.rs b/cmd/zfs_object_agent/zettacache/src/open.rs
@@ -183,15 +183,14 @@ fn is_valid_cache(
 
     match primary {
         Some(disk) => {
-            let disks_from_primary = disk
-                .superblock
-                .primary
-                .as_ref()
-                .unwrap()
-                .disks
-                .iter()
-                .map(|(k, v)| (*k, v.guid))
-                .collect::<HashMap<_, _>>();
+            let disks_from_primary = match &disk.superblock.primary {
+                Some(primary) => primary
+                    .disks
+                    .iter()
+                    .map(|(k, v)| (*k, v.guid))
+                    .collect::<HashMap<_, _>>(),
+                None => return false,
+            };
 
             // Only retain disks with IDs that are part of the primary block
             disks.retain(

diff --git a/cmd/zfs_object_agent/zettacache/src/slab_allocator.rs b/cmd/zfs_object_agent/zettacache/src/slab_allocator.rs
@@ -53,6 +53,7 @@ tunable! {
 
     // Try to keep this amount of slabs available for normal (i.e. BlockAllocator) use.  Ideally
     // this will be enough space to absorb all the writes that can occur between index merges.
+    // This should be less than TARGET_FREE_BLOCKS_PCT.
     static ref TARGET_AVAILABLE_SLABS_PCT: Percent = Percent::new(2.0);
 }
 

diff --git a/cmd/zfs_object_agent/zettacache/src/zettacache/mod.rs b/cmd/zfs_object_agent/zettacache/src/zettacache/mod.rs
@@ -113,7 +113,8 @@ tunable! {
     // keep at least 5% of the cache "free".  We need to have slop for the rebalance code to be
     // able to consolidate slabs (to create empty slabs) to accomodate block size changes in the
     // workload.  This target includes both free blocks within the BlockAllocator, and free slabs
-    // within the SlabAllocator which are available to the BlockAllocator.
+    // within the SlabAllocator which are available to the BlockAllocator.  This should be more
+    // than TARGET_AVAILABLE_SLABS_PCT.
     static ref TARGET_FREE_BLOCKS_PCT: Percent = Percent::new(5.0);
 
     // Keep the total footprint for the pending changes and index cache data at about 12% of