[PATCH proxmox-backup] chunk store: s3: mute warning on overwrite empty chunk in local cache

[Christian Ebner <c.ebner@proxmox.com>]

For regular datastores overwriting chunks which have 0 size is
unexpected and cannot happen under regular operation. For datastores
backed by an S3 object storage, this is however expected as regular
operation if the cache reaches its capacity, since chunks get evicted
from the cache by leaving an empty file as chunk marker behind.

While the warning is benign, it causes false alerts in the task logs.
Therefore, silence the warning if the chunk insert overwriting the
file happens via the local datastore cache.

Fixes: https://forum.proxmox.com/threads/181330/
Signed-off-by: Christian Ebner <c.ebner@proxmox.com>
---
 pbs-datastore/src/chunk_store.rs               | 7 +++++--
 pbs-datastore/src/local_datastore_lru_cache.rs | 2 +-
 2 files changed, 6 insertions(+), 3 deletions(-)

diff --git a/pbs-datastore/src/chunk_store.rs b/pbs-datastore/src/chunk_store.rs
index bd1dc353b..773167a6d 100644
--- a/pbs-datastore/src/chunk_store.rs
+++ b/pbs-datastore/src/chunk_store.rs
@@ -667,7 +667,7 @@ impl ChunkStore {
         let _lock = self.mutex.lock();
 
         // Safety: lock acquired above
-        unsafe { self.insert_chunk_nolock(chunk, digest) }
+        unsafe { self.insert_chunk_nolock(chunk, digest, true) }
     }
 
     /// Safety: requires holding the chunk store mutex!
@@ -675,6 +675,7 @@ impl ChunkStore {
         &self,
         chunk: &DataBlob,
         digest: &[u8; 32],
+        warn_on_overwrite_empty: bool,
     ) -> Result<(bool, u64), Error> {
         // unwrap: only `None` in unit tests
         assert!(self.locker.is_some());
@@ -695,7 +696,9 @@ impl ChunkStore {
                 self.touch_chunk_no_lock(digest)?;
                 return Ok((true, old_size));
             } else if old_size == 0 {
-                log::warn!("found empty chunk '{digest_str}' in store {name}, overwriting");
+                if warn_on_overwrite_empty {
+                    log::warn!("found empty chunk '{digest_str}' in store {name}, overwriting");
+                }
             } else if chunk.is_encrypted() {
                 // incoming chunk is encrypted, possible attack or hash collision!
                 let mut existing_file = std::fs::File::open(&chunk_path)?;
diff --git a/pbs-datastore/src/local_datastore_lru_cache.rs b/pbs-datastore/src/local_datastore_lru_cache.rs
index f39b26ebb..ac27d4637 100644
--- a/pbs-datastore/src/local_datastore_lru_cache.rs
+++ b/pbs-datastore/src/local_datastore_lru_cache.rs
@@ -38,7 +38,7 @@ impl LocalDatastoreLruCache {
 
         // Safety: lock acquire above
         unsafe {
-            self.store.insert_chunk_nolock(chunk, digest)?;
+            self.store.insert_chunk_nolock(chunk, digest, false)?;
         }
         self.cache.insert(*digest, (), |digest| {
             // Safety: lock acquired above, this is executed inline!
-- 
2.47.3