btrfstree: Don't let (most) validation errors prevent parsing

1 files changed, 18 insertions, 7 deletions

diff --git a/lib/btrfs/btrfstree/types_node.go b/lib/btrfs/btrfstree/types_node.go
index 48a065d..58dc8e5 100644
--- a/lib/btrfs/btrfstree/types_node.go
+++ b/lib/btrfs/btrfstree/types_node.go
@@ -408,7 +408,7 @@ func ReadNode[Addr ~int64](fs diskio.File[Addr], sb Superblock, addr Addr, exp N
 		return nodeRef, fmt.Errorf("btrfs.ReadNode: node@%v: %w", addr, err)
 	}
 
-	// sanity checking
+	// sanity checking (that prevents the main parse)
 
 	if nodeRef.Data.Head.MetadataUUID != sb.EffectiveMetadataUUID() {
 		return nodeRef, fmt.Errorf("btrfs.ReadNode: node@%v: %w", addr, ErrNotANode)
@@ -424,6 +424,23 @@ func ReadNode[Addr ~int64](fs diskio.File[Addr], sb Superblock, addr Addr, exp N
 			addr, stored, calced)
 	}
 
+	// parse (main)
+	//
+	// If the above sanity checks passed, then this is at least
+	// node data *that got written by the filesystem*.  If it's
+	// invalid (the remaining sanity checks don't pass), it's
+	// because of something the running filesystem code did; the
+	// bits are probably useful to poke at, so parse them.
+	// Whereas if the above check didn't pass, then this is just
+	// garbage data that is was never a valid node, so parsing it
+	// isn't useful.
+
+	if _, err := binstruct.Unmarshal(nodeBuf, &nodeRef.Data); err != nil {
+		return nodeRef, fmt.Errorf("btrfs.ReadNode: node@%v: %w", addr, err)
+	}
+
+	// sanity checking (that doesn't prevent parsing)
+
 	if exp.LAddr.OK && nodeRef.Data.Head.Addr != exp.LAddr.Val {
 		return nodeRef, fmt.Errorf("btrfs.ReadNode: node@%v: read from laddr=%v but claims to be at laddr=%v",
 			addr, exp.LAddr.Val, nodeRef.Data.Head.Addr)
@@ -442,12 +459,6 @@ func ReadNode[Addr ~int64](fs diskio.File[Addr], sb Superblock, addr Addr, exp N
 		}
 	}
 
-	// parse (main)
-
-	if _, err := binstruct.Unmarshal(nodeBuf, &nodeRef.Data); err != nil {
-		return nodeRef, fmt.Errorf("btrfs.ReadNode: node@%v: %w", addr, err)
-	}
-
 	// return
 
 	return nodeRef, nil