mount: let filer handle chunk deletion decision (#7900)

* mount: let filer handle chunk deletion decision

Remove chunk deletion decision from FUSE mount's Unlink operation.
Previously, the mount decided whether to delete chunks based on
its locally cached entry's HardLinkCounter, which could be stale.

Now always pass isDeleteData=true and let the filer make the
authoritative decision based on its own data. This prevents
potential inconsistencies when:
- The FUSE mount's cached entry is stale
- Race conditions occur between multiple mounts
- Direct filer operations change hard link counts

* filer: check hard link counter before deleting chunks

When deleting an entry, only delete the underlying chunks if:
1. It is not a hard link
2. OR it is the last hard link (counter <= 1)

This protects against data loss when a client (like FUSE mount)
requests chunk deletion for a file that has multiple hard links.

weed/filer/filer_delete_entry.go

@@ -53,7 +53,11 @@ func (f *Filer) DeleteEntryMetaAndData(ctx context.Context, p util.FullPath, isR
 	}
 
 	if shouldDeleteChunks && !isDeleteCollection {
-		f.DeleteChunks(ctx, p, entry.GetChunks())
+		if len(entry.HardLinkId) != 0 && entry.HardLinkCounter > 1 {
+			// if the file is a hard link and there are other hard links, do not delete the chunks
+		} else {
+			f.DeleteChunks(ctx, p, entry.GetChunks())
+		}
 	}
 
 	if isDeleteCollection {

weed/mount/weedfs_file_mkrm.go

@@ -140,8 +140,9 @@ func (wfs *WFS) Unlink(cancel <-chan struct{}, header *fuse.InHeader, name strin
 
 	// first, ensure the filer store can correctly delete
 	glog.V(3).Infof("remove file: %v", entryFullPath)
-	isDeleteData := entry != nil && entry.HardLinkCounter <= 1
-	err := filer_pb.Remove(context.Background(), wfs, string(dirFullPath), name, isDeleteData, false, false, false, []int32{wfs.signature})
+	// Always let the filer decide whether to delete chunks based on its authoritative data.
+	// The filer has the correct hard link count and will only delete chunks when appropriate.
+	err := filer_pb.Remove(context.Background(), wfs, string(dirFullPath), name, true, false, false, false, []int32{wfs.signature})
 	if err != nil {
 		glog.V(0).Infof("remove %s: %v", entryFullPath, err)
 		return fuse.OK